Structures Congress 2008: Crossing Borders

The experimental and the analytical studies demonstrated that the enhancement in fatigue resistance of the treated details was dependent on both S_r and S_min,. The extent of improvement was more at a lower level of S_min, i.e., at low R, and was more pronounced at a lower S_r particularly in the infinite life regime. The beneficial effect of the treatment was reduced when subjected to high S_min after treatment. At high values of nominal S_min, substantial enhancement can be achieved when the surface treatment is applied under sustained gravity load. Fatigue cracking of the treated details originated from the slag inclusion discontinuities that could not be suppressed through surface erosion and/or by plastic deformation. UIT improved the weld toe geometry by introducing a finite radius in place of a sharp notch like condition at the as-welded toe, and consequently reduced the stress concentration. The treatment introduced compressive residual stresses in the treated zone, which had a beneficial "clamping" effect on the micro discontinuities at the weld toe, requiring the applied tensile stresses to overcome the compressive stresses first, before causing any fatigue damage. Thus, under lower levels of S_min, higher S_r was required to open up the crack-like tip of the discontinuities, and to cause fatigue crack growth. On the contrary, at higher levels of S_min this condition was reached at a lower S_r, causing an apparent reduction in the extent of enhancement at a higher level of R. The cumulative effects of the treatment enhanced the fatigue strength of the treated details by elevating the fatigue crack growth threshold. This coupled with stage I growth of shallow cracks at small values of effective stress ratio contributed to the increase in fatigue life of the treated details.

Regarding the analyses presented herein, the following comments can be made: 1 Both models show a decrease in the treatment benefit (fatigue life improvement) with an increase in the stress range under constant amplitude loading for all stress ratios. 2 Under constant amplitude loading, the strain-based model predicts higher fatigue lives for the untreated weld and a lower treatment benefit, regardless of the stress range/ratio. 3 Despite the lower benefit predicted by the strain-based model, significant fatigue life improvements are still seen. For example, at stress ranges less than ∼450 MPa at R = –1 or ∼250 MPa at R = 0, a fatigue life improvement of 100% or greater is still predicted. 4 Both models predict that the effect of the periodic compressive overloads on the fatigue life of the untreated weld will generally be less significant than for the treated weld. 5 For the treated weld, the fatigue life can be seen to decrease as the magnitude of the overload stress increases. This is also reflected in the calculated treatment benefit at the various stress ranges. Interestingly, the drop in the treatment benefit (in terms of the fatigue life improvement) is most pronounced in the results obtained using the LEFM model. When comparing the results obtained using the two models, it may be noted that the largest differences can be seen at the lower stress ranges, even though the influence of the non-linear material behaviour is the lowest at these stress ranges. The reason for this trend is that the stress intensity factor (SIF) calculated using (10) considers the effect of the non-uniform stress distribution along the crack edges, whereas the SIF calculated using (3) does not. As the crack grows out of a weld toe notch, this effect becomes more significant and the influence of the non-linear material behaviour diminishes. The reason that (3) has been used successfully in [11–13] to model the behaviour of small cracks emanating from notches may be that the non-uniform stress distribution plays a much less significant role in this case, in particular when the level of yielding is significant. One possible way to account for this observation would be to use a hybrid model that uses (3) for the smaller crack depths and then switches to (10) when the influence of the nonlinear material behaviour is seen to become negligible. Despite the apparent limitations of the models employed herein, the following conclusions can be drawn from this work: 1 Under constant amplitude loading conditions, although considering the nonlinear material behaviour appears to reduce the predicted treatment effectiveness, substantial benefits are still seen — even at relatively high applied stress range levels. 2 Both the LEFM and strain-based fracture mechanics models predict a significant decrease in the treatment effectiveness for load histories that include periodic compressive overloads. The reduction in fatigue life due to the compressive overloads is generally greater for the treated welds than for the corresponding untreated welds. 3 On this basis, it is concluded that, although residual stress-based post-weld treatments have shown strong potential as a means for improving or rehabilitating the welds in existing steel structures such as bridges, it is important that the influence of the true load history be considered when exploiting the benefits of these treatments.

Low strength-to-weight ratios and crack-growth-inhibiting natures of fiber reinforced polymers (FRPs) make them ideal materials to repair and strengthen fatigue-critical details in steel bridges. FRP materials can have distinct strength advantages over steel when loaded in their optimal orientation, and fiber composite materials such as graphite (carbon)-epoxy and Kevlar-epoxy can outperform steel when subjected to uniform tension. External layers of composite material can be attached to a fatigue-critical detail with the goal of providing an alternate load path, and consequently reducing the stress demand. If the reduction in the stress range is significant, it can lead to a substantial increase in the fatigue life of fatigue-prone details in steel bridge members. This technique has been studied in riveted joints with limited success in recent years. However, use of CFRP materials as a fatigue enhancement technique has proven challenging in past investigations due to localized delamination failures experienced at the bond between the steel and composite materials. Recent research at the University of Kansas has investigated the use of CFRP materials to stiffen fatigue details in steel bridge girders. In the study external layers of CFRP material were bonded to a fatigue-critical detail to provide an alternate load path and reduce the stress demand. To prove the viability of this concept as a repair and strengthening technique, a composite overlay, or doubler element, was bonded over a fatigue-critical weld (AASHTO category E') in a steel test specimen with the goal of reducing the peak stress at the weld. The test specimen was subjected to fatigue cycles in bending until the composite delaminated from the steel and/or the steel substrate experienced a fully propagated fatigue crack. This paper describes the development of this composite doubler element.

1 Three post-weld treatemnt methods (UIT, Air Hammer Peening, Shot Peening) are discussed in this study. Fatigue tests carried out on AL-6XN stainless steel specimens treated by these techniques showed that fatigue resistance has been significantly enhanced compared with the as-welded conditions. The enhancement is comparably effective for these three treatment methods in circumstance of this study. 2 Residual stress measurements were carried out using X-ray and neutron diffraction techniques to characterize the magnitude and subsurface distribution of the compressive stresses induced by UIT and shot peening treatments. Both treatments induced very high compressive stresses near the treatment location and the material was plastically deformed. 3 The compressive strength region by UIT alone (base metal) was 1.5–1.7mm in depth and ∼±15mm in width. For the welded specimen, this compressive layer could be reduced to 1mm deep due to existence of tensile weld residual stress. 4 The magnitude of compressive stress induced by shot peening was comparable to UIT, but the compressive layer was about half the depth (0.8mm) of that for UIT.

Tests were conducted on twelve interstate highway bridges in Illinois over a two-year period. The bridges were instrumented on their beam webs with strain gage rosettes installed on each beam to measure shear stresses caused by loads. Long-term test data were collected for approximately 6 months at each bridge to determine the loading trends for these bridges. The project required extensive fieldwork and logistics to install the approximately 400 strain gages at locations up to 125 miles from the university. Hardware needed to complete the extensive data acquisition requirements of the project was chosen to meet the technical and anticipated environmental conditions. This paper addresses the planning, hardware design, fabrication and installation, software design, routine maintenance and decommissioning phases of the project.

A deck truss bridge consists of two simple spans of 218 feet each. The lower lateral bracing system was found to exhibit excessive vibration under truck crossings. Fatigue cracks were found at the gusset plate connecting the lower lateral bracing diagonal to the truss bottom chord. In-service monitoring was performed to measure the vibration properties of the truss and the lateral bracing members. The measurement results were correlated with the calculated natural frequencies of the structural system and the excitation frequency of crossing vehicles. It was determined that the vehicle passages between floor beams correspond to observed vibration frequency of the lower lateral members. Based on results of in-service monitoring and finite element analysis, a retrofit was developed to increase the natural frequency of the lower lateral system to avoid resonance with the excitation frequency.

The typical biennial bridge inspection is more qualitative than quantitative in nature, and as a result, sufficiency ratings will vary depending on the inspector. It is clear that to better manage our bridges, more quantitative data about the bridge behavior under site specific traffic needs to be gathered as part of the inspection process. A project is currently underway at the University of Delaware Center for Innovative Bridge Engineering (CIBrE) to gather in-service strain data from a sample of twelve typical slab-on-steel girder bridges, in conjunction with the bridge's biennial inspection. The bridges to be monitored have been selected from those in the state that are due for inspection, and where access is relatively easy. On the day of the inspection, a single strain transducer and battery powered monitoring system are installed on a key location on the bridge (typically at mid-span of a girder). Strains are then continuously monitored for a period of two weeks. After that time the data and monitoring system are retrieved. The data recorded includes just peak strain recordings that exceeded a specified threshold, as well as the date and time at which they occur (the quantity of actual data is limited). The collected data is to become part of the permanent inspection record of the bridge. Future records can be compared to the original records to see if there is any difference in the response, which might suggest possible damage or deterioration, or changes in the traffic. The data is also used to estimate a two-year load rating factor for the bridge that should be more reflective of the actual condition of the bridge. Presented in the paper is a description of the sample of twelve bridges that have been monitored. Sample data from two bridges is presented and the updated load rating factors are presented.

Motion detecting instruments have been used to record seismic motions of the ground, buildings, and bridges for many years. More recently, interest has grown in using this instrumentation for monitoring the state of health of a structure without the need of a "triggering seismic event." Structural damage will result in permanent changes in structural stiffness. These changes may be detected through structural monitoring. The use of vibrational monitoring is a field of structural analysis that is capable of assisting in both detecting and locating structural damage. The work presented in this paper is aimed at better understanding the variability in dynamic properties so that structural changes can be correctly interpreted if outlying data is recorded.

The seismic performance of RC bridge piers is a significant issue because the interaction of flexural ductility and shear capacity of such piers with varied amounts of lateral reinforcement is not well established. Several relationships between flexural ductility and shear capacity have been proposed by various researchers in the past. In this paper a parametric study on RC bridge piers is conducted using a nonlinear finite element program, "Simulation of Reinforced Concrete Structures (SRCS)," developed at the University of Houston. SRCS has been previously used to predict the seismic behavior of such piers. The predicted results were compared with the test results obtained from experiments available in literature. Based on the results of the parametric study performed in this paper, a set of new relationships between flexural ductility and shear capacity of high strength RC columns is proposed.

Wide reinforced concrete beams are frequently used as primary structural members in buildings or bridges, to support floor loads and to transfer forces from discontinuous walls or columns above. In these roles, these critical members may in turn be supported on walls extending across the full width of the beam, or on narrower columns. While punching shear capacity on a perimeter around the column must be checked in the latter case, design code provisions require that one-way shear capacity be assessed for a cross-section encompassing the full width of the beam for both the wall and column support configurations. There was concern that this full-width shear area approach may lead to poor predictions of one-way shear strength, due to local geometry influences at the wide-beam-to-narrow-column connection. An experimental program on 8 large-scale shear-critical reinforced concrete beams is presented, where the support or load width, relative to the member width, was a primary test variable. The results show that the one-way shear strength was moderately reduced as the support width to beam width ratio decreased. This influence occurred for members without shear reinforcement and for members with a moderate shear reinforcement ratio. A capacity reduction function was developed to account for this influence on one-way shear strength, and its application demonstrated with a design example.

Based on the results of the foregoing studies the AASHTO LRFD Specifications for the 4^th Edition were revised as follows: 1 The limit of 10 ksi on the concrete compressive strength that could be used for shear design in the LRFD Specifications through the 3^rd Edition was raised to 18 ksi. 2 The limit on the maximum shear stress for shear design was reduced from 0.25f'_c plus the effect of the vertical contribution of the prestress force to 0.18f'_c plus the effect of the vertical contribution of the prestress force. However, the value of 0.25f'_c can continue to be used if the beam is built integrally into its support at the end so that it is fully supported over its depth at the end, or if the end region is designed by strut and tie modeling. 3 Provisions were introduced for checking for shear cracking since shear stresses in excess of 0.15f'_c can result in shear cracking and localized stirrup yield under service load levels. 4 The option for the use of the staggered shear design method away from the support region has been removed. 5 Simplified provisions were introduced for the design of beams, prestressed and non-prestressed, that contain at least the minimum required amount of shear reinforcement.

Several changes relating to timber bridges have been incorporated into the AASHTO-LRFD Bridge Design Specifications recently. In addition, the Federal Highway Administration is strongly encouraging an LRFD-based design approach for all new bridges in the United States. The Bridge Design Code in Canada was one of the first to adopt the limit states design philosophy, doing so many years ago. This paper presents an overview of the United States and Canadian bridge design codes, highlighting similarities and differences that relate to the design of timber bridges.

Many timber trestle railroad bridges in Wisconsin have experienced deterioration and are in need of rehabilitation. In addition, the railroad industry is increasing the weights of cars. The combined effect of heavier loads and deterioration threatens to cut short the service life of timber bridges. One of the most critical problems that has been identified was the overloading of timber piles in bridges, which can be remedied by creating a stiffer pile cap. The goal of this investigation was to show that fiber reinforced polymer (FRP) strips fastened to timber with screws can be used to create composite action between two beams in flexure or truss action between two deep beams. Ultimately this may help redistribute the loads to piles when FRP strips are used as struts on cap beams over short spans. Several test series were conducted with beams in flexure, deep beams over short spans, and full scale specimens to determine the manner in which FRP strips improved the members' performance. Mechanically fastened FRP strips were effective in developing composite action in slender beams in flexure and truss action in short deep beams.

The Transportation Equity Act for the 21st Century (TEA-21) as amended by the TEA-21 Restoration Act established the National Historic Covered Bridge Preservation Program (NHCBPP). This program includes preservation of covered bridges that are listed, or are eligible for listing, on the National Register of Historic Places. Beyond its primary funding focus on actual construction work on historic covered bridges, the program also includes funding of research for better means of restoring and protecting covered bridges. Technology transfer is encouraged to disseminate information on covered bridges as a means of preserving our cultural heritage. The development of the Covered Bridge Manual (hereinafter referred to as the manual) is one of the research projects funded through NHCBPP — Contract No. DTFH61-00-C-001161 that culminated in Report No. FHWA-HRT-04-098. The author of this paper was the Principal Investigator and primary author of the manual. The broad objectives of the NHCBPP research program are to find means and methods to restore and rehabilitate historic covered bridges to preserve our heritage using advanced technologies, and to assist in rehabilitating and restoring these bridges. The specific objectives of this research project are to provide comprehensive support to those readers involved with maintaining, assessing, strengthening, or rehabilitating any covered bridge. The manual is intended primarily for engineers and historic bridge preservationists to provide technical and historical information on preservation of covered bridges. It will also be of interest to others involved with these bridges—including lay people, owners, and contractors. The manual is separated into several sections with a number of chapters devoted to the specifics of each. The sections include background, description of bridge components, technical engineering issues, existing bridges, and references. The appendices include multiple case studies of existing bridge rehabilitation and construction of new authentic covered bridges. This paper and the corresponding presentation to be made at the 2008 ASCE Structures Congress in Vancouver, BC, will provide: 1 a summary of the manual, 2 discussion of the special challenges confronting engineers when working on covered bridges, 3 an update on research related to covered bridges, and 4 highlights of rehabilitation of a number of covered bridges.

The Sioux Narrows Bridge in Northern Ontario was a 64m long timber truss structure originally constructed in the 1930's. It was located across a narrows on Lake of the Woods in the picturesque, historic community of Sioux Narrows in Northern Ontario and is owned by the Province of Ontario, Ministry of Transportation (MTO). It had been heralded as one of the longest single span timber bridges in the world. In light of its age and uniqueness the Province of Ontario listed the structure on the Ontario Heritage Bridge List [MofC 1983]. In 2002 the bridge was discovered to be in a state of progressive collapse and a decision was ultimately made to replace it. From a planning and engineering perspective the heritage designation required the project team to consider heritage and aesthetic issues as an integral component when examining alternatives to address the structural deficiencies. The final solution was one where the original heritage features of the bridge were preserved while at the same time providing a new, durable and highly functional bridge.

A wireless sensor integrates a radio to facilitate the exchange of data by wireless communications. In recent years, wireless sensors have rapidly matured with current platforms offering performance levels on par with traditional tethered sensors. The elimination of extensive wiring typical of tethered monitoring systems keeps the cost of wireless monitoring systems low. In addition to the inclusion of a radio, most wireless sensors include low-power microcontrollers in their hardware design. The inclusion of computational resources allows the sensor to autonomously process data, a revolutionary concept not previously seen in tethered structural monitoring systems. In this paper, the distributed computing resources inherent to a wireless structural monitoring system are leveraged to conduct model updating. A parallelized version of simulated annealing model updating procedures is embedded in a network of wireless sensors for autonomous execution. Automated model updating by a wireless monitoring system allows the system to keep analytical models current for long-term health monitoring of the structure.

This paper explores the inter-relationship and differences between NDT and SHCE/SHM using some commonly used NDT methods to explore the reasons for under-utilization of NDT methods. This showed that use of NDT methods has been successful in SHCE/SHM when hazard-centric needs of SHCE/SHM and physical demands of these hazards are recognized.

Engineers have always been challenged when it comes to developing an economical, efficient, and safe demolition approach for an existing long span truss bridge spanning over a major navigational channel. The technical reasons are simply a large number of site specific and structural specific parameters. This paper outlines the issues encountered during demolition process and adopted methods of dismantling 2-miles long two bridges over Cooper River, named "Grace Memorial (built in the year 1929) and Silas N. Pearman Bridge (built in the year 1966)". The demolition process was started in the middle of the year 2005 and was completed in April 2007. Both the bridges were consisted of various types of superstructure systems such as (i) Multi span steel truss (ii) Concrete deck on steel girder framing and (iii) Concrete deck on prestressed and precast concrete girders system. Since they were spanning over water and land, therefore, it was very important to maintain the stability of the remaining portions of the bridges during demolition process. One of the major challenges was the structural modeling of the section under demolition consideration, based on existing condition as well as adjacent span's behavior. At every demolition stage various dismantling options were studied, including imploding steel truss by blast, lowering down portions of a span with hydraulic machines, dropping the deck framing members on the ground, and removal of members piece by piece. Structural vibration and its propagation was the main concern and therefore, every span of the bridges was analyzed. Temporary support systems like shoring towers, temporary trestle etc., were designed wherever needed. Superstructure and substructure were checked for construction loads from the equipments e.g. excavator and cranes. The elements, unable to support these construction loads, were strengthened before using the equipments. The coordination and discussion between design and construction engineering teams was very important for overall cost-effectiveness.

This case study describes the design of a new bridge superstructure and modifications to an existing bridge substructure that carries a heavily traveled urban arterial just south of Boston, Massachusetts; an area with little tolerance for increased travel delays and almost no tolerance for construction. The Massachusetts Highway Department (MHD) required a rapid replacement design that did not involve experimental techniques or materials. What the MHD wanted was a new structure designed and built with known materials and techniques (in other words, "off the shelf technology"). The design consisted of using new steel stringers made composite with pre-cast concrete and steel gird deck panels, reconfiguring the existing 5 simple span arrangement into simple end spans and 3 span continuous middle spans, and using a two stage construction sequence. The design also included several time and cost saving ideas to live up to the FHWA's rapid replacement slogan "Get in, Get out and Stay out". This case study demonstrates how a little extra design time and cost can reduce construction time and cost. Considering the number of highway bridges that will need to be replaced in the near future, any opportunities to save time, money and reduce public inconvenience should be exploited.

The Bonner Bridge spans the Oregon Inlet from Bodie Island at the north end to Pea Island at the south end, along the Cape Hatteras National Seashore in Dare County, North Carolina (Figure 1). The structure is 12,865± feet long with one lane in each direction. The original contract for construction of the Bonner Bridge was awarded by the North Carolina Department of Transportation (NCDOT) to McLean Contracting Company, Baltimore, MD on February 15, 1962. Construction of the bridge was completed on April 7, 1964. The bridge is now nearing the end of its useful life and is scheduled for replacement within the next 10 years. Currently, there are two replacement options under consideration — a new 2.7 mile long bridge parallel to the existing bridge (short bridge option) and a 17.5 mile long bridge around the Pea Island National Wildlife Refuge (long bridge option). Cost estimates, including beach nourishment, NC 12 bridge alternates, new intersections, etc. are 260 to 347 million dollars for the short bridge and 930 million to 1.4 billion dollars for the long bridge. Cost estimates do not include future operation and maintenance costs.

This paper describes a new system for construction of bridge decks using longitudinally post-tensioned precast deck panels. Deck panels, either full or partial depth units, are rolled into position, leveled and post-tensioned while suspended on wheeled forming bogies which ride on the bottom flanges of precast girders. After post-tensioning, final adjustments to the profile grade are made using leveling bolts, then grout is pumped into the void between girders and panels to yield a composite structural system.

Recent earthquakes have illustrated the vulnerability of bridges to damage and collapse. One of the emerging tools for protecting bridges from the damaging effects of earthquakes is the use of isolation systems. However, to date, few adequate models exist to evaluate the comparative viability of the two main isolator types: sliding and elastomeric. This paper compares sliding versus elastomeric seismic isolation of a typical Multi-Span bridge to enhance the understanding of their unique impacts on bridge response. The Friction Pendulum System (FPS) and the Lead Rubber Bearing (LRB) are selected as representative examples of sliding and elastomeric isolators, respectively. Detailed isolator models that can account for the in-plane and vertical coupling of the response are developed in OpenSees. Particular emphasis is given to the distinct vertical load dependency modeling of the two isolators. A seismic evaluation of the bridge, isolated in one case with the LRB and in another case with the FPS, is performed for a hazard level of 7% in 75 years using a nonlinear three-dimensional (3-D) analytical model. Maximum isolator forces and displacements, and column drifts are selected as response quantities. The results show that despite attaining similar structural periods, there are notable differences among the two seismic isolation scenarios for the bridge. The FPS placed larger demands on the columns however acquired smaller deformations compared to the LRB. The LRB response is influenced less from the vertical components of ground motions compared to the FPS but susceptible from a stability point of view.

Deteriorated deck joints and cracks in girders pose a persistent performance and maintenance problem for our bridges. Using jointless bridge decks reduces direct and indirect costs associated with bridge maintenance and repair. Also, using FRP in girders' flexure strengthening proved to be effective. In this research, an experimental testing was conducted on five girders to study the effect of CFRP bonded to the tension fibers in flexure and sides in shear. This paper also presents an approach to investigate the behavior of jointless bridge deck systems using a nonlinear finite element analysis for bridges subjected to instantaneous and time-dependent effects. The study covers key parameters such as support configurations, time-dependent effects, link slab stiffness, and debonded length. Analytical results of mode of deformation, strains, and deflections were compared with experimental testing. The study suggested that the use of debonded link slab and CFRP laminate's in girder repair can be effective in extending the service life of new or repaired bridges.

Fiber reinforced polymer composites provide the advantages of a higher strength/weight ratio, higher stiffness/weight ratio, and better corrosion resistance than traditional civil structural materials such as steel, concrete, and wood. Bridge engineers hope to benefit from these qualities in the form of glass fiber reinforced polymer (GFRP) bridge decks. By minimizing bridge dead load, larger live loads can be handled in the case of retrofits and smaller sections can be used for the design of new structures. Shorter construction time due to preassembled GFRP deck components and increased service life of the superstructure due to smaller fatigue stress ranges have also been suggested. This may translate to reduced life cycle costs, especially if increased demand initiates increased production and competition among manufacturers. The Federal Highway Administration initiated research on GFRP bridge decks in the early 1980s to transfer FRP composite technology to the design and construction of bridge decks. This has lead to the design, installation, and testing of numerous GFRP decks. A survey of bridge and county engineers showed GFRP bridge deck panels were most commonly used in low-volume rural areas and bituminous was the preferred wearing surface material, although it was noted that an insufficient amount of performance data existed to determine which wearing surface was more efficient and productive. In field and laboratory testing of GFRP decks subjected to seven million cycles of truck loading, Zhou reported no significant loss of strength or stiffness and safety factors above four. However, he observed cracking of unsupported GFRP deck components at the pavement approach/GFRP panel joint. Other reported performance problems with GFRP decks include delamination of GFRP deck components and delamination and cracking of the wearing surface. Resolution of these durability issues were suggested for future applicability of FRP materials in bridge deck applications. This paper describes laboratory testing for two GFRP decks being considered for the retrofit of the Granite Falls Bridge. This bridge is located in Snohomish County, WA and is an example of a retrofit project where a GFRP bridge deck is being designed to replace a heavier concrete deck, thus allowing widening of the roadway. A GFRP deck will reduce the weight of the structure, thereby reducing the supporting member forces and providing savings in the retrofit of the steel truss arch superstructure. A comparison of the two GFRP decks, discussion of the testing setup and testing sequence, and results from laboratory fatigue and ultimate testing are presented, followed by a summary and conclusions.

Despite their magnificent load-carrying properties, some orthotropic steel plates in steel bridge decks are showing signs of reduced fatigue resistance. This has led to much costly repair and maintenance work that in turn restricts traffic flow, an issue of particular concern within the heavily occupied German highway system. Drawing upon the experience of the ship-building industry, which has encountered the same problem of fatigue-induced damage with roll-on/roll-off ferries, the viability of transferring Sandwich-Plate-System (SPS) technology to steel road bridges was considered. On behalf of the German Federal Ministry of Transportation, the Northrhine-Westfalia Department of Transportation and the state-owned company Strassen.NRW decided, therefore, to undergo a pilot project aimed at a permanent reconstruction and rehabilitation of orthotropic steel deck plates in a road bridge for the first time. This paper reports on the reasons for such rehabilitation measures and the fundamental design issues of the project, and illustrates the repair work that has been done.

The steel suspension Waldo-Hancock Bridge carried U.S. Route 1 travelers over the Penobscot River, near the town of Bucksport, Maine for 74 years. This vitally important transportation link provided safe passage for carloads of tourists through the years, in addition to significant commercial traffic related to regional paper-making, granite-quarrying, boat building, manufactured housing production and a host of freight items, such as delivery of home heating oil. In 2002, a scheduled renovation began and in the summer of 2003, the main suspension cables were unwrapped to prepare for a visual inspection of the individual wires in the 37 cables in each main cable. Deterioration of the main cable on the south side of the bridge was much more advanced than expected, leading the bridge owner, Maine Department of Transportation, to simultaneously undertake a strengthening project on the Waldo-Hancock Bridge and the design of the Penobscot Narrows Bridge & Observatory on a parallel alignment to the existing bridge.

This paper outlined the theoretical background of the necessary steps of wind design of long span bridges. To this end the overall process was spitted into the characterisation of the air flow and corresponding aerodynamic coefficients by means of the DVM. The second step was to evaluate the different design checks with the previously calculated coefficients. Several tests for the steady state coefficients predicted a good applicability for the full scale model. Comparisons of the flutter prognosis with wind tunnel test as well as numerical simulations showed a good agreement. The overall analysis was performed within one software package. The advantage of this approach was that the same cross sections can be used as basis for the structural analysis and the CFD calculation. Moreover, the data exchange between different analysis tasks was simplified and accelerated. Thus the application of such an all-in-one solution significantly improves the efficiency of design tools for long span bridges.

The design for the new Golden Ears Bridge in British Columbia, Canada is an efficient, low profile, multi-span hybrid cable-stayed bridge. The structure offers an interesting solution to the particular span constraints, seismic conditions and foundation conditions encountered at the 1 km long crossing of the Fraser River near Vancouver, Canada. The bridge design utilizes a unique combination of new and existing composite cable-stayed technologies to provide an aesthetically, pleasing, functional, low maintenance solution.

The new Veterans' Glass City Skyway in Toledo, Ohio incorporates many unique structural and aesthetic features. It was constructed completely from the "top-down" by cantilevering in one direction from the main pylon over the main shipping channel of the Maumee River. All precast segments were delivered over the completed back spans, allowing uninterrupted shipping to the busy Port of Toledo. The stays are the largest of any known cable-stayed bridge in the world, with up to 156 strands. The bridge is the first in the United States to use low maintenance stainless steel stay sheathing and the first to be designed with the new cradle system for passing the stay cables through the pylon. The stay cradle provides an efficient means of transferring cable forces to the pylon concrete, eliminating the need for anchorages in the pylon and the associated additional rebar, post-tensioning, or steel anchorage box. The highly efficient force transfer also allowed the cross-sectional shape of the pylon to incorporate, for the first time in any cable-stayed bridge in the world, glass panels and multicolored LED lighting for the upper 196 ft of the pylon above deck level. The glass panels and LED aesthetic lighting represent less than 1% of the total project cost and are expected to require only minimal maintenance during the bridge's service life. However, the aesthetic impact of these first-of-a-kind features is extremely high, and the bridge is expected to become a new landmark not only for Toledo but for the United States.

Infrastructure, in particular transportation sector in developing nations are facing increasing difficulty in introducing Flyovers/Bridges over the existing network of roads, as they have to be constructed without disturbing or blocking the existing traffic. Such problems can be tackled by introducing new technologies like segmental construction of larger spans so that the ground below is disturbed to very minimum. Long span structures definitely require huge investments which may seem uneconomical, but if structural performance is greater than normal structures, this itself is a good return. This was brought into sharp focus when in Amman, the Capital city of Hashemite Kingdom of Jordan, a signature bridge was to be constructed over an existing and a busy highway without disturbing and blocking the existing traffic. Adding to this was stringent quality requirement for trouble free life of the bridge for over 100 years. This aesthetic bridge designed as a cable stayed structure forms part of inner ring road being developed by the Municipality of Greater Amman to avoid traffic congestion in the city.

The Super T bridge beam system has become the standard system for bridges in the 20 to 35m span range in use in Australasia totally replacing the previously popular precast I girder bridging system. The Super T system has proved to provide a versatile and economic solution to structures in this range offering speedy construction and the versatility to be able to accomodate the complex geometry demanded in modern motorway and interchange configurations and maximising the off site labour component of the work.

It is important to be able to accurately predict the effective prestressing force because a poor prediction can lead to an increased potential for cracking. If the force is lower than predicted, there is a chance that cracking may occur on the bottom of the section. If the force is higher than predicted, there is the chance that cracking may occur at the top of the section. Recently, studies have indicated that the high temperatures used during steam curing may cause the prestressing force at release to be lower than predicted. The field study presented in this paper was done in order to monitor the influence of steam curing temperatures on the force in the prestressing strands up to the time of release. This field study was designed to monitor the temperature and strains in six full-depth Precast Concrete Bulb Tee (PCBT) sections each 15 ft – 4 in. (4.7 m) long during the curing phase. The changes in the strains and the modulus of the elasticity of the concrete were also measured at release. In addition to the six PCBT test specimens, three full length (70 ft (21.3 m)) beams were cast in the same bed. Due to bad weather and other circumstances, the six PCBT specimens were cast one day and the three full-size specimens were cast the following day.

The Influence line (IL) is an important concept in bridge design and load-capacity evaluation and can be used to calculate live load effects and to position loads to have their maximum effect. Generally, ILs serve two purposes: (1) ILs can be used qualitatively to determine the position of the live loads that will lead to maximum effects, and (2) they can be used quantitatively to calculate the maximum response value directly by making use of ILs. A theoretical IL can be derived using equilibrium equations or the virtual work method and are available for common structures in the literature. However, theoretical IL's do not account for the in-situ performance of bridges, which is important for the calculation of the true load carrying capacity. So it is necessary to obtain an experimental IL. The usefulness of ILs in determining the load capacity of the bridge has long been realized by engineers. Previous studies on experimental IL studies have focused mainly on strain (or stress) experimental Ils. This can be attributed to the difficulty in measuring small displacements of a bridge using conventional displacement sensors. However, with the development of innovative methods for measuring displacement, such as GPS and laser, the limitations of conventional displacement measurement techniques have been, or will soon be, largely overcome. The displacement measurement by using these new technologies in field test is becoming more and more convenient, fast, and easy. In order to utilize the benefits of these new displacement instruments, one way is through the experimental displacement ILs. In this paper, one methodology, which is referred as the Continuous Experimental Displacement Influence Line (CDIL) method, has been developed to experimentally determine a displacement influence line of a bridge from a semi-static diagnostic load test. The procedure to determine the experimental displacement influence line is presented and verified on one bridge.

A detailed instrumentation system has been developed to examine the behavior of different components of a bridge structure under the effect of temperature variations. A 3-span steel girder continuous girder bridge with integral abutment at the ends was selected for this study. The bridge is located in Evansville, West Virginia and the construction was completed in June 2003. The instrumentation plan is based on continuous monitoring of the triaxial state of strain, temperature gradient, crack opening, and relative movement between the substructure elements. The relative motion between the abutment and the pier at the edge span and between the two piers at the middle span its effect on the thermal strains and stresses induced in the steel girders as well as concrete bridge deck has been examined. The results indicates that motion of the substructure due to the expansion or contraction of the bridge superstructures is partially restrained, which generates thermal stresses in the girders and the deck that are not currently accounted for in the design. Additionally, the instrumentation approach used in this study has shown that it could be used as an alert system for the deterioration of bridge structures.

The west coast of BC lies in Canada's highest seismic zone under threat of three different types of large, highly destructive earthquakes. The British Columbia Ministry of Transportation (BCMoT) is responsible for 400 km of provincial Disaster Response Routes. The loss of any portion of one of these routes could significantly impact emergency response efforts and negatively affect public well being. The Ministry maintains 900 structures in the highest seismic zones, many of which are vulnerable to extensive damage in even a moderate quake and potential collapse in a major earthquake. The loss of the use of several structures would not only have immediate impact on public well being and the ability of emergency vehicles to respond effectively, but would also cripple the economic recovery of the region. The effects would be felt across the nation and for many years into the future. The better the information on which areas, structures and facilities are most vulnerable, the better planning and preparation can be done. By identifying those structures and facilities most susceptible to seismic forces, decision-makers can do effective risk management. Fast, accurate field intelligence immediately following an earthquake can ensure the most effective deployment of vital services and mitigate damage to the built environment. Preparation and mitigation will both aid economic recovery. Earthquakes hazards are very complex and each event unique. Most of the significant advances in identifying and understanding seismic hazards over the past 50 years have been aided by the availability of seismic monitoring data. The BCMoT has in the past had few bridges instrumented. Five structures have between two and six accelerometers and two structures have limited strain gauges. Only one structure uploads data to an internet site. The data from all the other structures must be collected at the site. This has proven most inefficient. The BCMoT has embarked on a program to instrument key structures to provide confirmation of seismic capacity, assist in focussing retrofit efforts, detect damage from any cause and provide rapid damage assessment of those structures following a seismic event. The data from this instrumentation will be capable of remote configuration and will automatically upload via the internet. The Ministry is working with the University of British Columbia to develop effective damage detection algorithms that will provide reliable intelligence close to real time. The purpose of this paper is to evaluate the status and effectiveness of the implementation.

This presentation discusses the possibilities associated between the existing available applied research in wireless sensors and the always increasing need to identify/address existing railroad bridges performance under actual traffic. In one hand, universities and research centers today are developing the advance theory and framework for the use of wireless sensors in structures health monitoring. To implement wireless sensors in the areas where quantitative / objective data is required. Timber trestle bridges are carrying most of the main line traffic in the US, especially in the South Regions, and a significant number of those are in need of maintenance and or replacement. The maintenance and/or replacement of timber bridges is based on visual/direct and individual inspections, which can not assess objective/quantitative data of the bridge performance under loading. Different bridge inspectors will not be able to determine objective parameters for different bridges, and even more, different loading conditions. The dynamic response of the timber trestle bridge continues to be an isolated parameter that can not be compared with the existing maintenance/inspection program. The authors gathered data obtained by connecting wireless sensors to existing timber trestle bridges which were identified to show excessive longitudinal and transversal displacement under regular traffic loading. The paper includes the description on the implementation process of wireless sensors under real on-site conditions, critique to the results and their validity, and proposed improvements in the entire data acquisition, comprised in concrete proposals. It finally summarizes recommendations for future/potential use in the railroad timber trestle railroad bridge maintenance, inspection and assessment.

The bridge model is quite sensitive to the change in stiffness as governed by the bearing stiffness. The analytical bridge model shows the stiffness of the bearings to be the most flexible (smaller stiffness value) element within the system, thereby controlling the response of the system. From the analyses of the Northridge ground motion, the rocker bearings reveal larger displacements for which toppling is probably occurring in the model and actually occurred on some bridges as a result of the earthquake. The friction pendulums tend to increase the stiffness of the system, thereby allowing the model to not be as susceptible to lateral displacements. Recommendations addressing inadequate seat widths due to large displacement demands are determined from the analyses. The toppling of the rocker bearings may occur when longitudinal movement exceeds the seat width, where an increase of the bearing stiffness should be applied using restrainers or other types of retrofit measures or the seat width should be increased to prevent toppling.

A continuous post-tensioned bridge over seven spans, 27m each, was recently designed and is currently under construction in Quito, Ecuador. Located in one of the most active seismic/volcanic regions of South America, several challenges were faced during the bridge design. In addition to the limits on the deck horizontal displacement because of the adjacent buildings, a substructure system of circular columns without pier-caps or framing connections into the deck was adopted to satisfy the required vertical clearance. Consequently, the post-yield behaviour of pier reinforcement could not be allowed as a hysteretic energy dissipation system since the formation of plastic hinges at such piers impairs not only the control over deck displacement but also the stability of the bridge deck. A response spectrum analysis was first conducted on a three dimensional finite element model (3D-FEM) in order to study the relationship between superstructure, bearings, substructure and foundations as well as to obtain a preliminary design of bridge components. Thereafter, a non-linear time history analysis accompanied by a parametric study was carried out considering different types of base isolation bearings. The study emphasized that the interaction between the superstructure and substructure through the bearings is a major key to achieve the target level of energy dissipation, base shear, and deformations. Herein, the FEM, seismic analysis, as well as the part of the conducted parametric study for a flat sliding friction/spring type of bearings are presented.

The current codes provide information for general approach but limited information's related to requirement for performance based seismic analysis and design for movable bridges and hence requires experience and engineering judgment in developing project specific performance criteria's. Still, further work is needed to define explicitly the requirements for performance based seismic analysis and design for movable bridges. 3-D numerical model and site-specific time history method is recommended for seismic analysis of movable bridges. It can provide engineers better understanding the performance of the structure.

This analytical work focuses on enhancing the seismic performance of reinforced concrete (RC) bridge columns by using innovative active confinement technique. Although the passive confinement approach has been widely accepted and used, research has shown that better results could be obtained by applying external confining pressure on the concrete element; a technique that has been widely known as active confinement. The approach proposed in this paper focuses on exploring the concept of using rings made of Shape Memory Alloys (SMAs) in providing active confinement The shape recovery phenomenon of SMAs is utilized to apply the external confining pressure without the need for excessive hardware or labor. An analytical model of a bridge column is developed and analyzed. A comparison is conducted between the cyclic behavior of the column when retrofitted using the proposed technique and the passive confinement approach using carbon fiber composite wraps. Two constitutive models are used to describe the stress-strain behavior of the confined concrete using the two techniques. The results show a significant improvement in the ductility capacity associated with less level of damage in the columns retrofitted using the proposed SMA rings compared to the fiber composite wraps.

Probabilistic seismic demand analyses are central to performance-based evaluation of structures and seismic risk assessments. The anticipated structural response and demand under earthquake loading is often characterized using a tool known as a probabilistic seismic demand model (PSDM). However, the degree of uncertainty in the model is dependent on the ground motion intensity measure (IM) used for conditioning the response (e.g. peak ground acceleration, spectral acceleration). Vulnerability assessments of general classes; or portfolios of structures, are becoming more essential because of their use in risk assessment packages such as HAZUS-MH, and hence the need for identification of optimal IMs increases. Appropriate intensity measures for general classes of bridges are evaluated as a part of this study, and the conditions under which various conclusions are valid. The influence of characteristics of the demand analysis on selecting an IM is assessed, such as the use of synthetic or recorded ground motions. The results are intended to offer guidance for appropriate intensity measure selection for probabilistic seismic demand models of bridge portfolios, which will considerably enhance future structural performance evaluations and regional risk assessments for transportation networks.

Kohl's Department Stores headquartered in Menomonee Falls, Wisconsin, has operated 929 department stores nationwide since 1962. Since 1994, over 650 new stores, including thirty-five two-story stores and four structural slabs, one distribution center, and three phases of their corporate headquarters were constructed utilizing composite steel joists.

A significant amount of data has been accumulated from testing that has been performed on composite steel joists over the past 40 years. The results of these experimental and analytical research projects have been reviewed by the Steel Joist Institute's Composite Joist Committee and the committee determined that it is possible to accurately predict the load-carrying capacities and deflection behavior of composite steel joists. The committee also found that the ultimate strength models that were originally developed for composite wide flange beams are applicable to composite steel joists. Based on all the available information to date on the behavior of composite steel joists, the committee was able to develop the new Standard Specifications for Composite Steel Joists, CJ-Series that has been published by SJI in the First Edition 2007 Composite Steel Joist Catalog.

Composite Steel Joists may be used to provide an economical shallow floor system with reduced floor-to-floor heights, increased flexibility in laying out floor plans uninterrupted by closely spaced columns, and allow the routing of HVAC ducts, plumbing, electrical conduits, and telecommunications through the open-web system of the joists. The Steel Joist Institute has recently published the First Edition Catalog for the CJ-Series that contains the Standard Specifications for Composite Joists, Weight Tables, Bridging Tables, and Code of Standard Practice to assist Specifying Professionals with the design and selection of Composite Steel Joists. A copy of this catalog can be obtained from the Steel Joist Institute's website at http://www.steeljoist.org/publications or by contacting the SJI office.

The determination of loads and displacement demands for seismic design of reinforced concrete walls is typically accomplished in practice using elastic shell-element models and response-spectrum analysis methods. Here, the results of a series of shake-table tests of reinforced concrete wall specimens are used to evaluate commonly used and newly proposed methods for determining the effective stiffness used in these analyses. These methods are evaluated on the basis of how accurately the initial period, building displacements, story accelerations and load distribution are simulated. The results of this study include recommended methods for application of elastic, response-spectrum analysis for seismic design of concrete walls.

A macromodel-based approach to simulate the flexural and shear sliding behavior of shear walls resulting from partial damage was investigated in this study. A modified MVLE model is utilized to simulate local effects of the damaged wall, for example plane sections of the wall at lower story levels do not remain plane after deformation. Based on the limited analytical simulations reported here and additional simulations (not included because of space constraints), it is concluded that simplified macromodeling approaches are a viable alternative to detailed finite element analysis for simulating partial damage in reinforced concrete shear walls. However, careful calibration of the model (in this case, the spring parameters) plays an important role in enabling such simulations. The lack of corresponding experimental data makes the calibration task more challenging.

This paper presents an overview of a recommended methodology developed by a project (ATC-63) of the Applied Technology Council (ATC) to reliably quantify building system performance and response parameters for use in seismic design. The Methodology provides a basis for establishing Seismic Performance Factors (SPF's), including the Structural Response Modification Factor (R Factor), of new seismic-force-resisting systems proposed for inclusion in model building codes. The Methodology also provides a more rational basis for re-evaluation of the SPF's of existing seismic-force-resisting systems of model building codes and resource documents.

This is one of four companion papers describing the Applied Technology Council project (ATC-63) to develop a methodology to assess seismic design provisions for building systems. This paper describes the underlying approach to evaluate the collapse safety of a set of archetype buildings, whose designs reflect the key features of the seismic design requirements. The companion papers provide a broader overview of the ATC 63 project and two application studies to reinforced concrete moment frames and wood-frame buildings. Following an overview of the assessment methodology, this paper reviews specific aspects related to (a) modeling collapse assessment of buildings by nonlinear time-history analysis, (b) development of collapse fragility curves, including variability due to design, construction, and modeling uncertainties, (c) ground motion characteristics with adjustment for spectral shape effects for collapse assessment, (d) evaluation and acceptance criteria for archetype building models.

The Applied Technology Council, under the direction of the Federal Emergency Management Agency, has recently completed the ATC-63 document which contains a codified assessment methodology for quantifying structural collapse safety under seismic loading. This methodology is described in related companion papers. This paper illustrates how the ATC-63 performance assessment methodology can be applied to the class of reinforced concrete (RC) special moment frames (SMFs). The purpose of this example is two-fold: (a) to illustrate an application of the methodology; and (b) to "benchmark" the methodology by showing that it concludes that code-conforming RC SMF buildings, designed by recent code provisions, pass the method and are deemed to have acceptable collapse safety. This finding has one caveat; this work found that use of the ASCE 7-05 provisions result in unacceptable collapse safety for some tall buildings. To remedy this, the minimum base shear requirement of ASCE 7-02 is reinstated so that acceptable collapse safety can be achieved.

This paper presents a full example of the application of the ATC-63 methodology to assess the seismic performance of the class of wood light-frame buildings. The system design requirements of ASCE 7-05 are used as the framework, and then the seismic performance factors, SPFs, are determined by iteration until the acceptance criteria of the ATC-63 methodology are met.

Rounded Dovetail Connections (RDC) are a relatively new method for connecting structural members. The use of RDC in timber construction has significantly increased in Europe, with the most common application being the connection of a joist to a beam or a beam to a girder. A number of experimental studies on RDC provided valuable insight into the structural performance of this versatile connection [Kreuzinger and Spengler, 1999; Blass and Saal, 1999; Hochstrate, 2000; Bobacz, 2002; Tannert and Lam, 2006; Tannert et al., 2007]. The load transfer mechanism of RDC is governed by its geometric features. A revival of interest in timber frame buildings in the United States occurred during the 1970s and since that time, has led to growth in the timber framing industry to keep up with demand for timber frame structures [O'Connell and Smith, 1999] and carpentry connections are being used in a growing number of timber buildings [Schmidt and Scholl, 2000]. But the acceptance of carpentry connections in the North American structural engineering and architectural community is affected by a lack of design values and provisions in building codes [Bamford, 2003]. Engineers and architects indicate that there is a diverse demand and need for guidance in designing connections in wood construction throughout North America, and existing design codes need to be expanded and updated to reflect the acceptance and use of modern wood connections [Snow et al., 2006]. Nevertheless, the Rounded Dovetail Connection is increasingly being used, driving the demand and need for guidance in designing such connections in timber construction throughout North America.

The Masonry Standards Joint Committee (MSJC) Building Code Requirements for Masonry Structures currently requires a W1.7 gauge continuous, single-wire joint reinforcement at a maximum spacing of 18 in. (450 mm) O.C. vertically be provided in Seismic Design Categories (SDC) E and F. The purpose of this paper is to investigate the justification for this requirement and to determine its necessity. Previous research and testing have been studied, and in-plane and out-of-plane analyses have been completed. Finally an experimental program was designed to determine the effects of joint reinforcement on the brick veneer wall system.

Current shear design guidelines propose that the nominal shear capacity of concrete beams reinforced with fibre-reinforced polymer (FRP) can be calculated using existing shear design equations for steel-reinforced concrete beams provided that the axial rigidity of FRP longitudinal bars and the capacity of FRP stirrups at the bent portions are accounted for. However, they noticeably vary in the manner they account for concrete contribution to shear as well as the shear capacity of FRP stirrups. This paper presents a simple yet more accurate equation to determine the shear capacity of FRP stirrups in FRP-reinforced concrete beams based on genetic algorithms approach. The shear capacity of FRP stirrups calculated using the proposed equation is compared to those obtained using equations provided by four commonly used shear design guidelines for FRP reinforced concrete beams, namely the ACI 440, CSA S806, JSCE, and ISIS Canada. Results show that current guidelines overestimate the capacity of FRP stirrups and that such capacity is best represented by a square root function of the stirrups ultimate capacity rather than a linear function as proposed by the guidelines. The shear capacity of FRP stirrups calculated using the proposed equation are in better agreement with available experimental data than those calculated using shear equations recommended by current guidelines.

Wood beam-columns are mostly subjected to three-dimensional load effects, such as combined compressive load and biaxial bending moment. Without appropriate provision of lateral bracings, they are susceptible to buckling in weak axis. Many research activities have been conducted to investigate the stability capacity of wood beam-columns under eccentric compression load. However, most of these research were restricted to two-dimensional problems due to the modeling or experimental difficulties. Song presented a numerical analysis procedure based on Column Deflection Curve (CDC) method and considered the biaxial bending moment. However, the CDC method can not trace the post-buckling behavior. This paper presents a Finite Element Method (FEM) based three-dimensional analysis to study the stability capacity of wood beam column subjected to compressive load and biaxial bending moments. The model considers the material nonlinearity, geometrical changes and variation of wood mechanical properties applicable to wood beam-columns with various boundary conditions. The Arc-length and Newton Raphson methods are incorporated to trace the post-buckling behavior. Parallel-to-grain wood compression and tension test and biaxial eccentric compression test of wood beam-columns were conducted to provide input data and verification for the FEM model from the perspective of stability performance.

This paper is on the behavior and design of anchorages for unbonded post-tensioning (PT) strands in seismic regions. While current design guidelines for unbonded post-tensioned structures require that the strands remain essentially linear-elastic under the "Design Basis Earthquake," significant post-yield strand stresses can develop under the "Maximum Considered Earthquake." Thus, the use of unbonded post-tensioning for seismic resistance can put the anchorage regions under extreme demands where premature strand wire fractures can occur. This paper describes an experimental study on the behavior of single strand/anchorage systems under monotonic tension loading, considering various design and construction parameters that can affect the performance of a strand inside an anchor. The parameters investigated include: (1) strand size (0.5-inch and 0.6-inch nominal strand diameters); (2) anchor type (cast type and barrel type anchors); (3) number of anchor wedges (2-piece and 3-piece wedges); and (4) presence of a binding ring around the wedges. The test results are used to evaluate strand/anchor configurations that may provide better probability of reaching higher strand ductility.

The issuance and widespread adoption of the current suite of U.S. codes and standards (2006 IBC, ASCE 7-05, ACI 318-05) addressing the anchorage of nonstructural components for earthquake forces raises several questions regarding requirements and expectations for the ductility of the anchorage. This presentation explores the implications of the current code requirements and offers a realistic assessment of what is achievable in the context of structural practice and anchor design.

Developed by Steel Cast Connections, Lehigh University, and IFC Kaiser Engineers, the Kaiser bolted bracket (KBB) is a proprietary steel beam-to-column moment-resisting connection. The connection consists of cast high-strength steel haunch brackets that are fastened to the flanges of a beam and then bolted to a column. The brackets can be either fillet welded or bolted to a beam. At high levels of inelastic drift, connection yielding and plastic hinge formation occur primarily in the beam near the tip of the bracket, thereby directing deformation away from the column face and outside the connected region. The connection is designed to eliminate field welding, facilitate erection, and reduce installation costs. The brackets are manufactured in a variety of sizes and are proportioned to develop the probable maximum moment capacity of the connecting beam. The connection has been tested for a number of beam and column sizes with specimens exceeding the interstory drift angle requirements without significant strength degradation. This paper summarizes the results of the inelastic cyclic tests and their relation with the requirements of AISC 341, Seismic Provisions for Structural Steel Buildings hereafter referred to as the AISC Seismic Provisions. The paper also includes historical background on the development of the connection.

The effect of fire induced restraint and fire scenario on the fire response of reinforced concrete beams is addressed in this paper. A macroscopic finite element model, capable of tracing the behavior of restrained reinforced concrete beams from prefire stage to collapse in fire is used in the analysis. The model is applied to investigate the effect of three parameters; namely, fire scenario, axial restraint effect, and failures criteria on the fire response of reinforced concrete beams. The predicted fire resistance of reinforced concrete beams is compared to those computed as specified in ACI 216.1 and Eurocode 2. Results from the analysis indicate that the fire scenario has significant influence on fire resistance of reinforced concrete beams. The fire resistance of reinforced concrete beams generally increases with the degree of axial restraint. Also, the limiting criteria used to define failure can have significant influence on the resulting fire resistance. These factors, which are not taken into account in conventional prescriptive based approaches, should be given due consideration for realistic assessment of fire resistance of reinforced concrete beams under performance based codes.

This study evaluates some modeling parameters that affect the use of FE models to predict the behavior and capacity of a high-rise steel moment frame under fire. In particular, the study focuses on the perimeter columns and the girders that frame into them perpendicular to the building's exterior. The parameters examined in this paper are: (1) 3-D frame model versus a 2-D plane frame model; and (2) the representation of the slab in the 2-D plane-frame model. Results from a prototype building frame show that the 3-D and 2-D models experience similar structural behavior and reach the element limit states. The 3-D models, however, require significantly more run time and computational effort. The 2-D models can therefore be used to reasonably and efficiently model the fire-exposed performance of a plane frame. Results also indicate that in the 2-D models, the slab should be considered in the thermal analysis of the girder, but it can be neglected in the structural analysis since it has a negligible effect.

This paper presents the development of a fiber based beam-column finite element for modeling the structural behavior of columns and other members under elevated temperatures from fire loading. Several such elements can be combined to: (i) model structural members and frames, and (ii) analyze them for fire loading conditions. The finite element is programmed within the context of an indigenous finite element analysis program that uses the modified Newton-Raphson (NR) iterative solution algorithm to conduct nonlinear analysis. The paper also presents a limited validation of the finite element (and program) for simple benchmark problems and steel column fire tests conducted in the recent past. The validated finite element was used to conduct parametric analyses to investigate the effects of structural loading and restraint parameters on the fire behavior and strength of steel columns.

Wood frame house construction is very common in North America. These structures are vulnerable to fire hazard, fire following an earthquake event is not uncommon. After an earthquake the structure may sustain a considerable damage and the fire resistance of the system will be significantly impaired. Current building codes do not take this into account adequately. This article presents a framework for carrying out a systematic study for post-earthquke fire performance of buildings structures. In addition, a simulation of fire performance of a stud wall system has been carried out. The wall system was a part of an earlier experimental study. The validated simulation model would be used from futher analysis of post-earthquake fire response as envisioned in the framework presented here.

Cyclic tests on nine full-scale beam-column subassemblages were carried out in support of the development of a new lateral load-resisting system recently introduced in AISI-S110: Standard for Seismic Design of Cold-Formed Steel Structural Systems—Special Bolted Moment Frames. With double channel beams and HSS columns interconnected by bearing-type high-strength bolts, all specimens showed an story drift capacity significantly larger than 0.04 radian. Typical response is characterized by a linear response, a slip range, followed by a significant hardening region due to bolt bearing. Three failure modes were identified. Confining in the connection region, inelastic action through bolt slippage and bearing is ductile and desirable. Such inelastic action always occurs first, but either column or beam may also experience buckling. Beam buckling is most undesirable due to significant post-buckling strength degradation. Extending the concept of instantaneous center of rotation of an eccentrically loaded bolt group, a model that can reliably simulate the cyclic behavior of the bolted moment connection is presented.

Design provisions of the Cold-Formed Steel—Special Bolted Moment Frame (CFS—SBMF) system in the proposed AISI Seismic Standard (AISI S110) are developed such that energy dissipation in the form of bolt slippage and bearing in the bolted beam-to-column moment connections would occur during a major seismic event. Beams and columns are then designed following the capacity design principles to remain elastic. Based on the instantaneous center of rotation concept, this paper presents background information for the design provisions in the AISI standard for calculating the expected maximum seismic force in the beams and columns at the design story drift. This requires that the resistance from both the bolt slippage and bearing actions in the moment connection be computed. Design tables are provided to facilitate the design. The recommended seismic design procedure is also provided.

Cold-formed steel has been widely used for components and main force resisting systems in commercial, industrial, and residential buildings. Cold-formed steel structural members are designed using AISI S100, North American Specification for the Design of Cold-Formed structures Members. For applications in high seismic regions, additional requirements may be needed. In fact, cold-formed steel design standards have been developed for applications in high seismic regions for both rack structures and cold-formed steel light frame construction. In 2003, the American Iron and Steel Institute (AISI) established a seismic design committee. Composed of suppliers, manufacturers, engineers, researchers and professors, the committee is responsible for developing design standards applicable to cold-formed steel structural systems located in seismic regions. The first edition of the Standard for Seismic Design of Cold-Formed Steel Structural Systems — Special Bolted Moment Frames (hereinafter referred as the Standard) was finished in 2007. As the title indicates, this edition of the Standard focuses on the design of the seismic force resisting system for special bolted moment frames, which consist of tubular columns, cold-formed channel beams and bolted moment connections. A typical connection of a cold-formed steel special bolted moment frame (CFS-SBMF) is illustrated in Figure 1. This type of special bolted moment frame is widely used in industrial platform mezzanines such as the one shown in Figure 2. The 2007 edition of the Standard is based on the 2005 edition of the ANSI/AISC 341, Seismic Provisions for Structural Steel Buildings, and research work on cold-formed steel special bolted moment frame systems as a seismic force resisting system. This paper will briefly review the design provisions included in the Standard.

A soon to be published American Institute of Steel Construction (AISC) Design Guide is reviewed. A consistent design approach to bracing connections, based on the Lower Bound Theorem of Limit Analysis and analytical and experimental testing, is presented. Corner connections, central connections, and truss connections are discussed, and the corner connection case is generalized to non-orthogonal configurations. While there are many methods to design connections, emphasis is on the Uniform Force Method, which was developed by the first author and generalized by the second. A number of worked examples are presented in the Design Guide. This paper extracts parts of this Design Guide for presentation here.

The geometry of a single-plate connection is really quite simple — a rectangular plate is fillet welded to a support, and field-bolted to a beam. But the simple elegance of this connection can often be overshadowed by the complexity of the structural model. The force distribution on this connection is indeterminate, and the connection itself, being relatively stiff, has inelastic features that are important to its performance. Unlike many of the other types of connections, shear tabs rely upon inelastic deformation of the plate to achieve the level of rotation that allows it to be considered a simple connection by the definitions presented in the AISC Specification. The complexity of the inelastic performance of shear tab connections prompted the AISC Committee on Manuals and Textbooks to develop the new, largely prescriptive design procedure now found in the Steel Construction Manual, 13^th Edition. The Manual presents two newly developed design procedures — one that is a refinement of older procedures for the design of the classic shear tab connection, now called "conventional" single-plate connections, and an entirely new design procedure for other applications, termed "extended" single-plate connections in the Manual. Like all simple shear connections, single-plate shear connections have some level of restraint and a corresponding eccentricity on the connection. This restraint is largely relieved before the connection reaches its ultimate strength through both elastic deformations, such as flexing of the plate and bending of the supporting member, and inelastic deformations associated with the movement of the bolts as they shift in the holes. As the ultimate load is approached, the bolt holes deform in the plate, providing relief to much of the eccentricity of load.

Reduced beam section (RBS) moment resisting connections are among the most economical and practical rigid steel connections for high rise buildings that developed after the 1994 Northridge, earthquake. Section weakening concept in the plastic hinge region of beam cause to reduction of beam plastic section modulus in this region, and force plastic hinge to occur within the reduced section. In the ordinary RBS connection mostly portions of the beam flanges are selectively trimmed in the region adjacent to the beam-to-column connection that causes the plastic hinge to form in weakening section. This paper presents a new RBS connection that has been used aforesaid weakening concept in it, with this difference that corrugated plate webs instead of beam flange cutting were used in limited specific length near the column face. Corrugated plates because of their accordion effect don't have bending rigidity. Then using of these plates in plastic hinge region reduces the beam plastic section modulus and plastic hinge is formed in corrugated region. For investigating the seismic behavior and performance of new RBS moment connection, finite element analyses were executed. All of the analytical results of new RBS connection were compared with ordinary RBS connection results. This comparison shows that the corrugated webs will improve the plastic stability and provide capability of large plastic rotation at the plastic hinge location without any appreciable buckling and brittle fractures in this region. Comparison of the seismic performance of new RBS connection with ordinary reduced beam section connection (dogbone connection) led to the conclusion that new RBS connection allows for the most stable motonic response at large story drift levels.

The Reduced Beam Section (RBS) moment-resistant connection was introduced to the structural engineering community shortly after the 1994 Northridge Earthquake. Since its introduction this connection has been incorporated into many moment frames throughout the world. Research related to the analysis of frames incorporating beams with RBS connections ("RBS frame elements", Figure 1) lagged behind the physical testing of RBS connections, which assessed their ductility and robustness. However, in 1997 theses and research papers began immerging that provided technical insight into the stiffness matrix of RBS frame elements. Knowledge of the stiffness matrix of a two-dimensional RBS frame element is fundamental to the quantification of both the elastic and inelastic performance of structures that incorporate RBS connections. This paper discusses the mathematical problem formulation that is needed to determine the stiffness matrix of a two dimensional RBS frame element, proposed solutions to the problem, and approaches to accommodate the stiffness of the element when structural analysis software does not accept user-defined stiffness matrices.

Since the terrorist attacks of September 11, 2001 and the collapse of three very tall buildings at New York's World Trade Center, some members of the public, building officials, legislators and engineers have stated a belief that present design standards do not provide sufficient safeguards to ensure that buildings will be able to withstand collapse in the event of reasonably foreseeable attacks and incidents. The issue at question, however, is what constitutes a reasonably foreseeable event. In fact our present building codes and standards do require design to provide collapse prevention for reasonably foreseeable events including snow storms, wind storms, fires and earthquakes. Indeed, this is one of the primary purposes of these codes and standards. However, the magnitude of the event for which collapse protection is provided is not intended to cover the worst occurrence of such events that could ever occur. Rather, the intensity of design events are generally selected for these hazards in a manner that balances the cost of providing protection against collapse and the probability of experiencing the initiating event. Thus, in typical buildings, we design for wind loads with a 50-year mean recurrence interval; in hurricane-prone regions we design for 100-year storms; and for most of the nation, we design to withstand collapse 2,500-year earthquakes. While we can reasonably foresee that a tornado may strike a building in the mid-west; or that a meteor may land on a building at any location in the U.S., we design for neither of these events, as well as many other foreseeable events because for any one building, the likelihood is so low that the cost of providing the protection would far outweigh the benefits of having such protection. Recognizing the difficulty of identifying specific design scenarios beyond those already covered by the building codes and standards that should be included in design, in their report on the World Trade Center Collapse, the National Institute of Standards and Technology (NIST) recommended a series of improvements to current design practice to reduce the potential for disproportionate collapse of structures. The concept behind designing to prevent disproportionate collapse is that it does not matter what the initiating event is, an airplane impact, a meteorite, or terrorist bomb, relatively small initiating events should not result in large-scale failure and collapse. NIST and other organization introduced proposals to the International Code Council that required specific disproportionate collapse analyses of many types of structures. In response, the National Council of Structural Engineering Associations, in cooperation with industry associations representing the concrete, masonry, steel and timber construction industries developed a series of alternative proposals to place supplemental structural integrity criteria into the International Building Code. This paper provides an overview of these proposed requirements.

The primary author has investigated a wide variety of curtain walls exhibiting many types of distress. As part of these investigations, original and remedial designs were reviewed to assess the structural adequacy of the existing or supplemental anchorages. The designs often included curtain wall components attached by multiple anchorages. In an effort to simplify the structural analyses of these anchorages, the relative stiffness between fastened curtain wall components was occasionally neglected so that the applied wind load could be distributed uniformly to the anchors. As a result of this design simplification, some existing or supplemental anchorages would be relatively dormant under applied loads, while others would be overstressed. To illustrate the consequence of neglecting relative stiffness in the analyses of curtain wall anchorages, the authors will present three short case histories involving a variety of curtain wall types in different areas and territories of the United States. The case histories include a typhoon-damaged hotel with an exterior insulation and finish system (EIFS) located on a Pacific island, a high-rise office structure with failed granite panel anchors located in the Midwest, and a high-rise office structure with a planned aluminum spandrel overcladding program located in the West.

The design process for stone veneers typically involves a series of iterations that are focused primarily in the selection of the color, shape and texture of a particular stone type. In addition to aesthetics of the façade, another very important condition that, in the author's opinion, is frequently overlooked in many projects is the evaluation of the long-term durability characteristics of stone material as well as strength characteristics. Moreover, the use of thin stone veneers in exterior wall cladding resulted in types of failures in the stone cladding that did not take place in the thicker stone walls. This condition occurred because the use of thin stone cladding places greater reliance on design and on the physical long-term properties of the stone than it did previously for the successful performance of the veneers, and failures often occur whenever the design, the construction, and/or the stone material of the veneer system is inadequate. The importance of this problem involving the durability of building stones is becoming widely recognized by building owners. The restoration of stone veneers involves an additional appreciable financial burden to owners and in many situations the façade deterioration conditions can endanger public safety. This paper presents typical problems that have arisen from the use of natural stone veneers.

The most documented reason for the height restriction on wood backing appears to be the vertical differential movement caused by expansion of the brick veneer and shrinkage of the wood framing. Thermal expansion and shrinkage can occur in steel stud backing, but to a much smaller degree. In the current US masonry standard, height restrictions still exist for brick veneers supported by steel stud backing, but they are larger than those for wood. Concrete and masonry backing will experience similar moisture and thermal expansion as the brick veneer, and there is no height restriction for these backing systems. A solution to this problem would be to use engineered lumber. As the calculations will show, the expected shrinkage when using engineered lumber is much smaller than that of sawn lumber. The expected differential movement when using sawn lumber is 1.70 in. (4.32 cm) for a 30 ft. (9.1 m) exterior wall. If the floor joists are switched to LVL spruce-pine I-joists, similar differential movement (1.59 in., 4.04 cm) can be obtained by going up to a 50 ft. (15.2 m) wall. By switching the entire framing system to engineered lumber, the wall height can go up to 120 ft. (36.6 m) before getting similar differential movement (1.58 in., 4.01 cm). Masonry standards should include an allowance for a height increase for brick veneer supported by engineered wood construction. Another possible reason for these restrictions has to do with seismic concerns. It could be related to the horizontal differential movement between the brick veneer and the wood framing. If this is a concern, the wood framing could be stiffened with additional sheathing in order to reduce the amount of movement during a seismic event and increase the wall height. In this case, the standard should include an allowable horizontal movement due to seismic loading for wood framing supporting brick veneer. Finally, to get a small increase in allowable height, a standard mean roof height could be maintained. The code currently restricts the height at the plate to 30 ft. (9.1 m) and at the gable to 38 ft. (11.6 m), giving a mean roof height of 34 ft. (10.4 m). If this mean roof height is maintained, the height of the wall could be increased slightly to allow for larger story heights.

This study focused on the impact damage causing or exacerbating water penetration through the exterior cladding material and through additional elements in typical light frame wall systems. The exterior cladding materials tested were brick veneer, vinyl siding, fiber-cement siding, concrete stucco and synthetic stucco. All wall segments were built according to the industry standards or the materials supplier's recommendations. Wall segments were eight feet in height by four feet in width. After any standard dwell period (as for curing of masonry), they were tested according to guidelines developed from the E 514 method of water penetration using driving pressures of two, six, and ten pounds per square foot. After the initial series of E 514 tests of the as-constructed wall, the wall was subjected to a missile impact, followed by another series of E 514 tests. Both four and nine pound missiles were used in the testing program. The missile impact velocity was 15.2 m/s (50 ft/s). The results of this study show the relative performance of wall systems in geographic areas where wind-borne objects may be expected. In particular, this simulated "storm damage" shows that water penetration can be appreciable, even in the absence of visible damage, suggesting damage to framing and accumulation of water within wall elements.

The author describes the development of the feature glass structures that have been the focus of the architectural design of the high profile Apple Computer stores in the USA, UK and Japan between 2001 and 2006, culminating in the design and construction of an all glass cube on 5th Avenue, New York City. The authors have been the principle designers for these structures throughout the world and this paper briefly summarizes the innovations in glass stair design developed through the retail store roll-out over the last five years. The paper then gives a detailed account of the design of the glass cube along with the challenges it faced through its development and construction including the design of the feature glass stair and elevator within the glass cube.

The architectural space formed by the load bearing glass wall is visually remarkable and psychologically very intriguing. The large area of roof which cantilevers out past the glass wall is very dramatic in the way it both frames the landscape and pulls the viewer out towards it. The hovering roof plane provides an unusual sense of shelter because there is clearly no visible means of support. Once the viewer is made aware that the pure glass wall is holding up the roof the perception changes again to one of surprise and curiosity. Glass bearing walls represent an important step in the quest for truly transparent structure that allows a seamless flow between interior and exterior. The use of glass bearing walls is an exciting opportunity to blur the distinction between engineering and aesthetics and thereby expand the vocabulary of architecture.

Safety is a major issue in structural engineering. Structures have in general a good record and failures are mainly due to natural disasters or human errors or a combination of both. Safety is a property of the structure that can be achieved or assured and is quantified usually by the probability of failure or the associated reliability index. A more complete parameter to approach safety is risk which is a combination of the likelihood and the consequences of structural failure, viewed in a context. Thereby it is important to distinguish between various types of consequences, i.e. human losses, environmental damage and economic losses. Structural codes traditionally have been concerned foremost with public safety preventing loss of life or injury. The context aspect of risk refers to the environment in which the risk based decision is made and in practice is linked to the decision. Structural codes aim at delivering structures with acceptable risks, i.e. with risks that are acceptable to the public. Procedures and current codified criteria for safety acceptance of new and existing structures are reviewed in this contribution. General approaches for selecting target and acceptable reliability levels such as 1 Human safety approach, 2 Calibration to previous codes, 3 Optimization (cost-benefit) are discussed first. Then the current risk acceptance criteria inherent in the codes and standards are reviewed. Thereby the difference in setting risk acceptance criteria for new and existing structures is highlighted. A "discount" in the safety requirements for existing structures is namely unavoidable due to economical and legal constraints. The need for periodic review of risk acceptance criteria is emphasized. Suggestions for future recommendations regarding the harmonization of safety criteria for new and existing structures are provided.

In 1994, the American Association of State Highway Transportation Officials (AASHTO) introduced the Load and Resistance Factor Design (LRFD) Bridge Specifications. The LRFD, based on a probabilistic design philosophy, was calibrated based only on the ultimate strength limit state (ULS). Other limit sates such as serviceability and fatigue were determined according to the performance of existing bridges designed using previous design codes. Live load deflection limits, historically carried over from previous code editions dating back to the 1930s, are now made optional (except for orthotropic decks). Such limits were first introduced in response to complaints of objectionable vibration of some bridges. In an investigation by the Bureau of Public Roads, bridges with objectionable vibrations, subjectively determined by human tolerance levels, were linked with deflections in excess of Span/800. Although not strictly enforced by the LRFD, many state highway departments specify their own deflection limits based on a rather arbitrary criteria. Wisconsin, for example, has a relatively low legal limit of 80 kips (356 kN) yet enforces one of the strictest deflection limits of Span/1600 whereas Michigan with the highest legal load tolerance of 164 kips (730 kN) has a deflection limit of Span/800. In addition, the live load used in the calculation of girder displacement varies considerably from one state to another. For example, Idaho uses the HS20 truck with dynamic load allowance, whereas California uses the HS20 truck plus lane load plus the dynamic load allowance. The use of load factors is another source of variation among state design practices; Arkansas uses factored live loads while Colorado does not for the same live load type. These variations among states can ultimately lead to non-uniformity in design and result in a wide range of girder stiffness for the same load demand. The objective of this study is to present results of a reliability-based analysis of live load deflections in steel girder bridges. The analysis uses actual truck traffic load data to calculate maximum deflections. Girder displacement values are forecast for different return periods (i.e. 1-, 2- ... 75-years) using extreme value theory (EVT). Results presented herein provide an alternate approach for developing a deflection limit state.

The basic problem of structural reliability is to ascertain that the strength R will be larger than the load (or load effects) S throughout the useful life of the structure. Due to uncertainties in the determination of strength and loads, reliability can only be established in probabilistic terms, i.e., P(R > S). For real structures this is a complex issue, and as in every complex issue, guidance is needed in the design process which is provided through technical standards and codes. Current design codes and standards (e.g. ASCE-SEI 7, ACI 318) are based on semi-probabilistic approaches. While it is agreed that the ideal would be to design a structure or structural element for a given probability of failure, the appeal of the semi-probabilistic approach stems from the coupling of design simplicity and the implicit incorporation of probabilistic concepts. While some practitioners understand the advantages in evolving towards semi-probabilistic code formats, a large number of structural engineers still see Structural Reliability as an unnecessary burden. It is believed that for many engineers, much of their reluctance in accepting Structural Reliability and Reliability-Based Design comes from the lack of formal education in this subject of those professionals. As such, in this paper, Structural Reliability basics will be reviewed. Here, the major goal is to introduce this subject in a language that can be easily understood by the practitioner. Initially, the presence of uncertainties in almost all variables pertaining to the structural response (materials properties, geometries, predictive models, loads, etc.) will be discussed. In the sequence, methods for Reliability Analysis, — FOSM, FORM, SORM and also Monte Carlo simulation-, will be briefly presented. A number of attendant concepts (reliability index, probability of failure, performance function, design point, etc.) will be introduced. Levels of reliability methods and their relationships with current design codes will be examined. The importance of Structural Reliability concepts and methods in providing rational tools for design code development will be demonstrated from problems of current Structural Engineering practice.

This paper discusses the use of simulation methods in structural reliability. The main objective is to highlight the utility of simulation in reliability problems that are otherwise difficult or practically impossible to solve. To this aim, Monte Carlo simulation is used as a general tool for reliability analysis of structural systems with respect to the collapse. The structural problem is investigated by means of limit analysis. The usefulness and effectiveness of simulation are shown through the application to the reliability analysis of an existing arch bridge.

High rise building with general pyramid geometry have been increasing used in new development zones. It is seen that even in high prone areas, there are many high rise building under design and construction. On the other hand, in relevant seismic codes there are no specific criteria for such type of structural systems. The structural systems in these buildings are moment resisting frames with or without bracing frames or shear walls. The structural elements are usually composed of beams and vertical columns in middle part and inclined columns in side faces of buildings. The inclined column element in this type of structure makes the structural behavior in different manner. Nevertheless, there are some special structural aspects of these building, especially due to earthquake events; one of the most important obscurity manners is extremely torsional effects structures of asymmetric pyramid building especially in lower stories. In this paper the results of numerous analytical studies performed for asymmetric, symmetric pyramid structures compared with regular structure and compare to codes requirement are shown.

Coupled core wall (CCW) systems resist lateral loads through a combination of the frame-action of the coupling effect, and the flexural action of the individual wall piers. Often, in a two-wall coupled system, the proportion of total overturning forces resisted by frame action, referred to as the "degree of coupling", results in one wall pier experiencing near-zero axial load or net tension, while the other wall pier experiences relatively large axial compressive loads. The adopted terminology in this case is to refer to the wall pier experiencing tensile forces due to the frame action as the tension wall, and the other wall as the compression wall. This is analogous to the windward and leeward walls, respectively, when the system is subject to wind loads. To take advantage of the coupling effect, designers permit the tension wall in two-wall systems to experience net tension only under design seismic load combinations. In such a case, wall pier design is driven by the axial tensile loads. Consequently, such wall piers will typically have a large reserve axial compressive capacity relative to the compressive demands. Common guidance with respect to compression wall capacity is that walls having compressive forces exceeding 35% of the wall pier axial capacity (P₀) should not be considered to contribute to the calculated strength of the structure for resisting earthquake-induced forces. This was first adopted in the 1997 Uniform Building Code (ICBO 1997) in Section 1921.6.6.3. Commentary in the 1999 SEAOC (Structural Engineers Association of California) Blue Book (SEAOC 1999) indicates that this axial force limit is based on the assumption that 0.35P₀ corresponds to the balanced point of a wall pier's axial force-moment (P-M) interaction diagram below which the tensile steel strains reach yield prior to the concrete compressive strains exceeding 0.003. This limit implies that wall piers used as part of a lateral-force-resisting system must designed so as to be tension-controlled. This guideline is somewhat arbitrary and does not apparently consider CCW systems. Similarly, requirements of ACI 318 Chapter 21 with respect to wall pier compressive behavior are not based on CCW systems. This paper examines limits to compression wall behavior in CCWs, recognizing the unique nature of their tension-dominated design and provides some discussion of design recommendations. Results from multiple CCW designs conducted using both conventional strength-based and performance-based design philosophies are used to evaluate the compression wall design guidance.

Constructing a new building on top of existing structure can sometimes feel like trying to fit a square peg into a round hole. Several years after construction had stalled on a prominent development, Thornton Tomasetti was asked to re-engineer the unfinished plans for a mid-rise building near Chicago's Magnificent Mile. A new development team purchased the property and commissioned an architectural design that varied greatly from the original plans. The key change was from a 13-story square donut shaped tower to a 25-story tower with an elliptical floor plan. The new tower would be centered above a previously designed light core. This loaded the interior columns and foundations beyond their designed capacity. A 6'-0" deep transfer mat and a 16'-0" deep transfer girder were required to spread the load to columns with adequate capacity. Overcoming these challenges also influenced many other aspects of the building's design. The construction team likewise faced challenges with the site. A parking garage and grocery store were located in the existing podium. The need to keep these facilities open during construction greatly affected construction sequencing. This paper will explore the design and construction processes that facilitated the development of a 25-story composite tower on top of an existing 8-story concrete garage. Project milestones, creative design solutions, and construction challenges will be outlined in an attempt to present a set of best practices for similar projects.

The Plaza 66 Tower 2, recently completed in Shanghai, China, balances the demands of structural engineering, architectural vision and construction constraints. This is a 46-story concrete moment frame and core wall structure. The unique design by architect KPF posed many engineering challenges to be resolved. Although modern computer technology allows for precise analyses and design of various systems for high-rise buildings, it does not readily provide insight for choosing among the alternative systems to arrive at the best overall design. This paper presents our design and analysis process, from the conceptual phase to detailed design, during which we resolved the following engineering challenges: (1) Determining and mitigating effects of pile mat foundation differential settlement, addressed through multiple stages of finite element analysis models. (2) Determining a cost-effective structural system by developing multiple options, using approximate analysis, and a cost comparison database. (3) Designing a curved 65 m (215 ft) long span steel bridge between two towers, an important architectural and functional feature. (4) Designing and detailing another important architectural feature, a two-way sloped steel cantilever thin steel lantern, using a three-dimensional structural information model to help both analysis and accuracy in connection details to benefit all members of the project team.

The energy dissipation characteristics of diagonally reinforced concrete coupling beams in coupled core wall lateral force resisting systems is investigated through finite element analysis where the axial restraint due to the wall piers and/or the presence of a floor slab is included. A mesh density analysis is performed to ensure acceptable accuracy of the finite element solution. Furthermore, the modeling technique is validated using experimental results obtained through previous research on reinforced concrete beams with complex geometry. Finally, a finite element model is created based on experimental research on diagonally reinforced concrete coupling beams carried out at the University of Cincinnati. The finite element model is analyzed first with no axial restraint, then with full axial restraint in order to draw conclusions as to the influence of axial restraint on the energy dissipation characteristics of the diagonally reinforced concrete coupling beam lateral force resisting system. It is expected that the restrained structure will offer larger compressive strength and better post-peak behavior than the unrestrained one.

This paper summarizes the analysis and design as well as special component testing performed for the Millennium Tower project located at 301 Mission Street in San Francisco. When completed in 2008, at 645 feet, this project will be the tallest reinforced concrete structure situated in a seismic zone 4 region, the 4th tallest structure in the City of San Francisco, and the tallest residential building in the U.S. west of Chicago. The tower has 58 occupied floors and combines with an adjacent 12-story tower and surrounding podium to provide over 1,150,000 sf of luxury condominiums and recreational amenities. The tower's immense height posed many challenges and required the creative use of technologies and cutting edge innovations. The tower's dual lateral system is comprised of a 36-inch-thick concrete shear wall core and partial perimeter Special Moment Resisting Frames (SMRF). The heaviest building ever constructed in San Francisco on a psf basis, the tower is supported by a mat foundation resting on 950 130-ton piles, each approximately 80 feet in length. Outrigger trusses connect the interior core with robust perimeter super-columns at three intermediate levels to control lateral deflections. In order to reduce the required floor-to-floor heights, shallow steel link beams are used within the shear wall core as coupling beams, in lieu of deeper diagonally reinforced concrete beams. Closely spaced ties in columns and walls posed a challenge to the placement of the high strength 10 ksi concrete needed for this project. To alleviate some of this congestion, DeSimone specified a system of Welded Reinforcement Grid (WRG) that eliminated all hooks, significantly reduced the volume of rebar, and decreased overall labor costs. A successful laboratory test program was implemented, in conjunction with supporting calculations, to demonstrate the adequacy of this product for use on the project.

Tall buildings become increasingly sensitive to wind as they go higher and for super-tall towers, which are going up at an increasing rate, wind becomes the dominant factor in the structural design, not only for strength but also for keeping the building motions within a comfort range for the occupants. Along wind forces are important but even more important are the crosswind forces. While stiffening the structure, increasing its mass, or adding supplementary damping systems are all ways of reducing the response, it must be remembered that the source of the wind excitation is interaction of the wind with the building's shape. The dominant form of excitation of building motions is often vortex shedding. Various shaping strategies such as tapering, varying the cross-section with height, softening the corners, using spoilers, and inserting openings in the building have been used to mitigate or even completely suppress vortex excitation. The alignment of the tower with strong wind directions or even with other towers nearby can also be important. Substantial cost savings are possible if the effect of shape is taken into account early in the design.

Atop one of San Francisco's famous seven hills, One Rincon Hill stands as a beacon for the emerging Rincon Hill neighborhood and as a sentry landmark for visitors entering the city by the Bay Bridge. The San Francisco skyline has forever changed. In addition to providing a significant visual impact, One Rincon Hill establishes a new benchmark for architectural and structural design of tall buildings in regions of high seismicity. Some of the most notable attributes of the building include the following: 1 Tallest residential structure on the west coast of the United States, 2 Tallest cast-in-place concrete building on the west coast of the United States, 3 Tallest performance-based design building in the United States, 4 First use of buckling restrained braces as outriggers in a high-rise building, 5 First use of a tuned liquid mass damper for occupant comfort in the United States. Developing and incorporating these new technologies into the design required close collaboration between the project's owner, architect, engineers, and contractor. The primary goal of the design team was to develop a safe, reliable, economical, and attractive building that would be well-received by the residential marketplace and the San Francisco community as a whole. The result of these efforts is a stunning building that has reshaped the San Francisco skyline with underlying design technology that is reshaping the way tall buildings are designed.

When completed in 2009, Trump International Hotel and Tower, Chicago will rise to a height of 1134 ft (345.6 m) (1362 ft [415.1 m] including the spire). Designed by Skidmore, Owings & Merrill LLP (SOM) the 92 story Trump Tower will be the tallest concrete building in the United States, and the tallest building built in North America since the completion of Sears Tower in 1974. New ground is being broken through a series of high performance concrete mixes designed by Prairie Material Sales, Inc. and employed by SOM on the project. It is believed to be the first application of 16,000 psi (110 MPa) self-consolidating concrete pumped and placed to an elevation up to 650' (200 metres) above grade. Dense limestone ½" (12 mm) topsize aggregate from the Material Service Corporation. Thornton quarry in northern Illinois has been specified for the high strength concrete on the project. The paper presents detailed structural engineering aspects of the tower design including a description of the reinforced concrete systems chosen for the project, design for occupant perception of motion due to wind, design challenges and the creative use of high strength concrete for this landmark tower.

The main vertical and lateral structural elements used in Waterview Tower, a 90-Story hotel/condominium currently under construction in downtown Chicago, have concrete strengths ranging from 6 ksi to 14 ksi. The assignment of specific concrete mixes to specific structural elements was a very interesting balancing act between cost, constructability, strength, and stiffness. This paper will discuss some of the key structural elements of Waterview Tower and the analyses performed to find the desired balance. Also discussed is the creep and shrinkage analysis completed as part of the design and the resulting adjustments for both horizontal and vertical deformations.

During and after any extreme event of natural or man-made origin, getting people out of harm's way and to an area of safety are primary objectives. Orderly and efficient evacuations are the key to saving lives. This was clearly demonstrated during the attacks on the Pentagon and World Trade Center towers on September 11, 2001. One of the major recommendations from the US Government's Draft Final Report on the World Trade Center Towers collapse was that building evacuation modeling and procedures should be improved to facilitate safe and rapid egress and support better occupant preparedness for evacuation during emergencies. Performing actual physical evacuations of large occupied facilities is expensive and disruptive to occupants and visitors. Accurately evaluating the affects of various events such as loss of power, smoke, fire, explosions, chemical contamination and structural collapse on human movements is not feasible in real world evacuation exercises. This paper examines a new technology, computer-aided, intelligent agent-based evacuation modeling, that can model and help plan emergency evacuations; run numerous, accurate event-driven evacuation scenarios; support the design of egress for new facilities or facility modernizations; support research in the areas of human behavior in disaster sociology; and model the movement of first responders and security personnel.

While the threat of terrorist attacks against buildings and other important structures has increased over the last several years, so has the ability of the design community to mitigate the damage associated with these events in more cost effective ways. By learning from past experiences, taking advantage of advancing engineering capabilities, and using state of the art materials and construction techniques, architects and engineers are increasing their ability to respond to the increased need for security and safety. With the increased focus on protecting the public from terrorist attacks, new materials are being introduced into the construction industry at a phenomenal rate. Several of these materials have shown promise in their ability to resist high explosive loadings while being thinner, lighter, more cost effective and potentially more environmentally friendly than conventional construction. This paper will focus on the possible applications of several of these materials while also discussing additional testing and analysis that the authors believe may need to be done in order to fully understand their capabilities.

Retrofitting masonry walls to enhance their blast resistance may be accomplished in a variety of ways, including the use of FRP, reinforced and unreinforced polymer coatings, shotcrete and dowels, and sheet metal. This paper will describe the manner and benefits of deploying each of these. Also, the actual and predicted behavior of masonry walls subjected blast are described in an attempt to address a common assessment problem, namely predicting failures when none are likely to occur, which seems to be associated with a misunderstanding of the basic behaviors related to blast for this class of walls.

Design of Blast Resistant Buildings due to Vapor Cloud Explosion (VCE) is one of the measures to minimize the risk to personnel lives and facilities in petrochemical and/or refinery complexes. This article introduces a new approach to design front wall of Blast Resistant Reinforced Concrete Buildings (the wall facing the blast wave) to reduce induced forces. In this method, there are two independent vertical and horizontal resisting systems: Simple Steel Frames to carry gravitational loads and Concrete Shear Walls to carry lateral blast loads. Utilizing this design approach as well as ductile design of structure, forming wide plastic region due to flexural deformation in front wall is achievable without collapse in structure. It causes large energy dissipation and also increases in the wall out-of-plane vibration natural period which consequently results in reducing dynamic reactions. In other words, front wall of a Blast Resistant Building can be treated as a fuse of energy. By using this technique, despite a large plastic deflection in the front wall, the stability of the structure as a whole can be preserved. Accuracy of performed analysis is verified using three finite element computer programs and also an approximate hand calculation method to eliminate modeling errors and provide a calibrated mathematical modeling system able to compute effects of Cracking, Damping, Dynamic Strength Increase and Nonlinear Behavior of Concrete and Reinforcing Bars. As a conclusion, by separating load bearing systems, eliminating brittle modes of failure and satisfying particular ductility conditions, larger plastic deflections in the front wall will be achievable. This enables us to have large dissipation of energy, a lower base shear and hence a reduction in costs. This new approach leads us to a safer and more economical design.

The alternate path method (APM) is a popular analysis technique that is used to ensure that structural systems have adequate resistance to progressive collapse. The APM, however, does not give an indication of residual capacity in cases where the structure under consideration is deemed to be able to survive loss of critical members. This information is necessary to gage if a damaged structure is near an incipient collapse state. In this paper we present a new analysis technique which we refer to as "pushdown analysis" that can be used to determine the collapse modes and ultimate load carrying capacity of a structure with lost or damaged critical members. Two-dimensional 10-story steel moment frames are used as prototype systems to demonstrate the method.

Structural engineers are often called upon to evaluate a structure after a failure or collapse. The evaluation may range from simply a qualitative judgment call to an advanced analysis of the structure. The various types of assessment required by a building could not be more evident than those conducted following the events of September 11, 2001. In the hours, days, weeks, and months that followed, structural engineers were called upon to evaluate the safety of several damaged buildings. One such building, which suffered significant structural damage, was the 39-story 130 Liberty Street, Manhattan or The Bankers Trust Building, also known as Deutsche Bank. The first assessment was provided only hours after debris scarred a large portion of the building and was based on superficial and partial information. Over the following weeks and months more additional evaluations were performed which included simple two-dimensional frame models and, finally, a complete three-dimensional push-over analysis. This paper illustrates the process undertaken to evaluate the safety of the Bankers Trust Building after the events of September, 2001.

The design of new buildings using Progressive Collapse criteria has become better understood since the nation's largest landlord, the General Services Administration (GSA), incorporated progressive collapse design criteria into their standard design requirements. Other institutions, such as the Department of Defense (DoD), also have incorporated progressive collapse design criteria into their design requirements for both new and existing structures. The DoD presents their progressive collapse requirements in the Unified Facilities Criteria (UFC) document UFC 4-023-03 (25 January 2005), "Design of Buildings to Resist Progressive Collapse". While there are numerous similarities between the UFC progressive collapse criteria and the GSA Progressive Collapse Guidelines, there are several key differences which can increase the time and cost of the design process, as well as the final construction cost of the project.

This study is on progressive collapse analysis of a sample steel building using various procedures suggested by the General Service Administration (GSA) and the Department of Defense (DoD). The progressive collapse was accommodated by removing columns as per above guidelines. The analysis methods considered are linear static, linear dynamic and non linear static using SAP2000 structural simulation program. The analysis model is a 3D nine story steel moment resisting building. For linear analysis rigid moment connections were used while for nonlinear analysis pre-Northridge connections were used. The effect of an extreme event is incorporated by removing a column in the analysis model. The static analysis was performed on the model with a column removed subjected to static gravity loadings. To simulate the dynamic effect of the removal of a column, a ramp function was used to apply the gravity loadings. For nonlinear analysis, material nonlinearity was incorporated using strength degrading nonlinear hinges of pre-Northridge connections as per FEMA 356. The paper documents the results of this analysis with comparison among methods. The potential of collapse and performance levels of the buildings were determined using the Demand Capacity Ratio (DCR) and the rotational limit obtained through the analysis.

As demonstrated in this paper, the updated UFC 4-023-03 has been significantly revised and improved relative to the initial version, to satisfy both DoD and GSA requirements. The modifications address shortcomings in the Tie Force and Alternate Path methods and result in a document that is more technically sound and rigorous, based on analysis and experimental data. The use of Occupancy Categories to determine applicability and level of design requirements should open the combined GSA and DoD progressive collapse design requirements to a wider audience. Procedures outlined in the updated UFC 4-023-03 will also provide a substantial basis for prescriptive methods planned as a part of progressive collapse mitigation approaches being developed for consensus-based, civilian building design codes.

Steel Plate Shear Walls (SPSW) consist of unstiffened infill steel panels surrounded by columns, called Vertical Boundary Elements (VBE), on both sides, and beams, called Horizontal Boundary Elements (HBE), above and below. These infill steel panels are allowed to buckle in shear and subsequently form a diagonal tension field. SPSW are progressively being used as the primary lateral force resisting systems in buildings. Past monotonic, cyclic and shaking table tests on SPSW in the United States, Canada, Japan, Taiwan and other countries have shown that this type of structural system can exhibit high initial stiffness, behave in a ductile manner and dissipate significant amounts of hysteretic energy, which make it a suitable option for the design of new buildings as well as for the retrofit of existing constructions. Analytical research on SPSW has also validated useful models for design and analysis of this lateral load resisting system. Recent design procedures for SPSW are provided by the CSA Limit States Design of Steel Structures and the AISC Seismic Provision for Structural Steel Buildings. Innovative SPSW designs have also been proposed and experimentally validated to expand the range of applicability of SPSW. However, some impediments still exist that may limit the widespread acceptance of SPSW. For example, little experimental information exists on the behavior of intermediate HBE in SPSW as well as the performance of such HBE having reduced beam section (RBS) connections and composite behavior. Note that intermediate HBE are those to which are welded infill steel panels above and below, by opposition to anchor HBE that have steel panels only below or above. To further address the pressing concerns regarding behavior and design of intermediate HBE, a two-phase experimental program was developed to test a two-story SPSW specimen having an intermediate composite beam with RBS connections under the collaboration of the Multidisciplinary Center for Earthquake Engineering Research (MCEER) in the U.S. and the National Center for Research on Earthquake Engineering (NCREE) in Taipei, Taiwan. In this paper, following a brief review of the experimental observations from the MCEER/NCREE testing, the design recommendations will be presented, followed by examinations and explanations on the observed failure of the intermediate HBE.

Research on conventional steel plate shear walls has developed recently to the point where their behaviour is reasonably well understood. However, the potential exists to design steel plate shear walls to take advantage of the benefits of composite columns and in this regard, considerably less information is available to designers. In addition to increasing the axial capacity of the columns, the presence of the concrete increases their flexural stiffness, thereby providing good anchorage for the development of the post-buckling capacity of the infill plate without requiring overly deep members. This research program was initiated with the aim of making partially encased composite columns a viable option available to steel plate shear wall designers. The research program involves the design and testing of three steel plate shear walls with partially encased composite columns as the vertical boundary elements. Gravity loads are applied to the columns and the steel plate shear walls are then loaded laterally under gradually increasing cyclic loads to failure. The paper describes some preliminary results of the completed first test, as well as plans for a test on a modular wall, fabricated primarily with erection economy in mind, and a test with reduced beam sections incorporated into the horizontal boundary elements.

This paper describes the seismic design procedures of steel plate shear wall (SPSW) systems, including the capacity design of the boundary beams and columns adjacent to the steel plates. Cyclic loading tests of four 2-story narrow SPSW have been conducted in Taiwan National Center for Research on Earthquake Engineering. The main objectives of the tests include the verification of the capacity design method suggested in this research and investigation on the seismic performance of the SPSW systems constructed with horizontal buckling restrainers (Restrained SPSW). The key test results are introduced in this paper.

Steel plate shear walls (SPSWs) are one of the most economical and under-utilized lateral load resisting systems currently available to structural engineers. In comparison with traditional lateral load systems, such as steel braced frames, reinforced concrete walls and moment resisting frames, SPSWs have fewer costly detailing requirements, require less stringent construction tolerances, allow for rapid construction, and result in fewer bays of lateral load resisting framing. Past studies have also shown that SPSWs can exhibit exemplary seismic performance. Despite these advantages, SPSWs are not widely used because: i) traditional SPSW configurations result in large column dimensions and prohibit the use of narrow walls, thereby reducing the system's economy, ii) numerical models used to analyze SPSW systems are cumbersome and overly time consuming for engineers, iii) SPSW system behavior is not well understood, leading to conservative design requirements and further reduction in economy, and iv) SPSWs have a lower flexural stiffness relative to concrete walls, making their use in taller buildings more challenging. Further, SPSW systems must be studied in the context of performance-based design as this will result in reliable and robust systems. This paper will discusses the issues above, with specific examples and propose solutions for developing the next-generation of steel plate shear walls. These solutions will allow SPSWs to be economically implemented by providing new configurations, new modeling techniques, and a more complete understanding of system behavior. Development of these solutions and performance-based criteria for their design will require a significant, coordinated research initiative. As such, research needs are identified and discussed.

The 1994 Northridge Earthquake caused significant damage to steel momenet resisting frame buildings throughout the epicentral region. This damage surprised many in the seismic structural engineering community because this system was believed to provide superior ductility based on previous laboratory testing. As the damage was discovered following the earthquake, various means of seismic retrofit techniques were investigated and employed to strengthen existing buildings. The SAC Joint Venture initiative concentrated its repair research and recommendations, provided first in FEMA-273 and later FEMA-352, on methods "to restore damaged elements...to their original configuration, strength, stiffness, and deformation capacity." While these recommendations provide some marginal improvement to the original structure, they do not provide significant improvement. Therefore, an alternative to the recommendations of FEMA-273 and FEMA-352 are desirable where a higher seismic performance is necessary, such as hospital acute care buildings. Hospital acute care buildings constructed in California following the 1971 San Fernando Earthquake must be reasonably capable of providing healthcare services to the publice after a disaster. These structurres are essential facilities that provide critical post-earthquake services. The California Building Code (CBC) requires repair of structural elements where damage has reduced the lateral load capacity by more than 10% at any story. The repair must be performed in accordance with the Code at the time of repair to meet the seismic performance requirements for new hospitals. Strengthening an acute care building to restore the building to its original strength is not sufficient to meet the 2001 CBC. Therefore, a Steel Plate Shear Wall (SPSW) retrofit approach was used to stiffen and strengthen a damaged hospital building to meet these higher standards of the CBC.

The steel plate shear wall is a very efficient system for reinforcing existing buildings. The system is analogous to a vertical cantilever beam, with columns acting as flanges, the plate as a web and the floor as stiffeners. This is an economical system, as well as having good performance. A steel plate shear wall within the concrete structures shall provide sufficient rigidity to reinforce the concrete structure so as to withstand earthquake loads. This system proved to be cost effective by minimizing construction time and disruption to the tenants. In the rehabilitation of existing concrete buildings, the strategy is to limit drifts so that the concrete elements would remain essentially elastic. The main concern is to provide good transferring forces at the interface of the steel and concrete, plus considering that concrete is less ductile than the steel infill panel. In this project we used both, anchor bolts going through the structural elements and epoxy glue between the steel and the concrete elements over and above the security factor. We can add that our calculations showed that infill plates can be very thin in order to yield and dissipate energy, but from a fabrication point of view, it is difficult for the plates to be less than 3/16" (4.8 mm) thick. We were pleasantly surprised from our analysis and design, that the SPSW system has such a high initial stiffness and remains very ductile for better energy dissipation. It is our understanding that the system is becoming more and more popular because of its excellent rigidity and easy installation.

Steel plate shear walls were introduced into US codes as "Special Plate Shear Walls" (SPSW) in the 2005 edition of the AISC Seismic Provisions for Structural Steel Buildings, also referred to as AISC 341; the provisions were derived from those in Canadian Standards Association (CSA) standard CAN/CSA-S16-01. Limit States Design of Steel Structures Steel plate shear wall provisions originally appeared in the 1994 edition of Canadian standard S16 as a non-mandatory appendix. Since this introduction, the system's use in the US and elsewhere, as well as design studies, has led to a refinement of several aspects of the design requirements, which are being considered for the 2010 AISC editions. Simultaneously, AISC 341 is being revised to clarify the desired behavior and basis of design for each system. These developments have resulted in the following changes for SPSW: explicit definition of the capacity-design mechanism; identification of expected regions of inelastic strain; simplification of the calculation of web-tension angle; clarification of strong-column/weak-beam design procedures; and inclusion of methodologies for perforated web plates and walls with reinforced corner cut-outs. Additionally, changes to AISC 341 that would permit design of columns considering expected forces below those corresponding to the sum of all member capacities are being considered. This paper presents some of the anticipated changes to the SPSW provisions in the context of the broader changes to AISC 341. Since their original introduction into CSA standard S16, steel plate shear wall design provisions have evolved as new research into their behavior has become available and field experience has been gained. In the upcoming 2009 edition of the standard, changes to the provisions are expected to be largely consistent with those being considered for incorporation into the new AISC seismic provisions, including such issues as improved capacity design guidance and the introduction of a means of design for steel plate shear walls with perforated infill plates. Some of the anticipated changes to S16 are also discussed below.

This paper concentrates on the experimental studies of an innovative steel shear wall system used in buildings in USA, presents a summary of test results and discussion on post-test data-analyses, and compares the experimental results to FEA analyses. The innovative steel plate shear wall system, originally developed by the Magnusson Klemencic Associates of Seattle, consists of steel plate shear walls welded inside a steel boundary moment frame in two bays. The two bays are connected through wide flange (WF) coupling beams. The steel moment frame consists of exterior concrete filled steel tubes (CFT), interior WF columns, and horizontal WF beams. Cyclic quasi-static tests were conducted on two half-scale specimens representing this system with two different wall span-to-height- ratios of one-to-one and one-to-one and half. Both specimens showed high ductility and stable inelastic behavior with inter-story drift values exceeding 0.03 radians. Data analyses were conducted after the test to validate test observations and summarize general seismic behavior of the system. FEM model of the test specimen were constructed and the analytical results were compared with test results.

Lateral stiffness is an essential design parameter for steel shear wall systems. The research presented in this paper consisted of conducting nonlinear finite element analyses of steel shear wall systems to investigate lateral load resisting strength as well as lateral stiffness of this type of structural systems. Detailed parametric studies were carried out to provide a better understanding of initial buckling behavior, lateral stiffness during the pre- and post-buckling region as well as during the post-yielding region. The studies indicated that initial buckling generally occurs under relatively small drift in the order of 0.0002 radians and after buckling the stiffness of the wall is reduced to less than 70% of its initial stiffness. When the steel shear wall yields, the stiffness rapidly decreases to the level of stiffness provided by the frame alone, which in general was about 20% of the total stiffness. In the parametric studies, the effects of wall thickness, strength and stiffness of the boundary elements as well as aspect ratio of the wall were varied and their effects on the lateral stiffness studied.

Recent research has demonstrated that Steel Plate Shear Wall (SPSW) structures can act as an effective and economical lateral bracing system. In this paper, simplified and detailed analytical models of a 4-storey specimen tested at the University of British Columbia (UBC) were generated to assess the ability of current analysis techniques to reasonably describe the behaviour observed during the experiment. The yield and ultimate strength as well as post-buckling behaviour of the specimen were reasonably well predicted by the simplified models. The orthotropic model representation of a SPSW system produced stresses in the beams, columns and infill plates consistent with the results obtained from a detailed explicit finite element formulation.

Two three-story unstiffened ductile steel plate shear walls were tested under cyclic loading. The shear walls had two types of beam-to-column connections consisting of rigid (SPSW-R) and simple (SPSW-S). Low and high strengths steel were used in the plates of panels and boundary frames, respectively. Both specimens endured many cycles of loading most of which were in the inelastic range. They showed excellent ductility and energy dissipation characteristics and exhibited stable behavior at very large deformations.

This paper will summarize the Steel Joist Institute and OSHA requirements for steel joist and Joist Girder bridging, and will categorized those requirements by the three functional purposes of bridging. As a complement to what is in the Specifications, some of the underlying theory, equations, and references for bridging have been provided. Future research with regard to joist bridging is likely to include a review of the construction stress levels, a unification of the K-Series and LH- and DLH-Series bridging requirements, and a better understanding of the accumulation of bridging forces due to net uplift.

Light gage metal sheeting is commonly used in the building and bridge industries for concrete formwork. In addition to supporting the concrete, the metal forms also improve the lateral-torsional buckling capacity of the beam or girder they are fastened to since they behave as a shear diaphragm and restrain the warping deformation of the top flange. However, the stability bracing requirements for shear diaphragms are not well established. This paper discusses the strength and stiffness requirements of diaphragm bracing of beams. The bracing behavior was investigated by conducting parametrical finite element investigations. The diaphragms in the study were connected along two edges to the top flanges of adjacent girders. Design expressions are presented for the stiffness and strength requirements of the diaphragm.

There are a host of methods available which can be used to provide stability to floor beams in a structure. Often the flooring is in the form of a concrete deck which provides continuous stability of the compression flange of a flexural member. In Heavy Industrial Structures, the "floor" is little more than a collection of walkways and equipment supports. This lack of continuity requires the need to seek stability from other sources, with the primary means being diagonal horizontal braces or torsional braces. Each of these concepts has a benefit and an impact. When and where to use them and the point at which one system starts to become impractical is important to understand. How a beam is going to be braced, connected, fabricated, and erected all play an important part in the decision making process.

Current ACI and CSA code provisions recommend large amount of shear reinforcement for concrete frame joints in the form of closed hoops and cross ties to ensure confinement of the joint core. This reinforcement, along with the bends required for anchoring the beam bars, lead to significant congestion within the joint. Double-headed studs are proposed as shear reinforcement in lieu of conventional closed hoops and cross ties. Five full-scale frame joint specimens were tested under cyclic loading. One control specimen was designed without shear reinforcement within the joint. Another control specimen was reinforced with closed hoops and cross ties in the joint according to the Canadian Code provisions. The joints of the remaining three specimens were reinforced with two different arrangements and amounts of double-headed studs. In comparison with the joint without shear reinforcement, the specimens reinforced with headed studs exhibited considerable enhancement in the behavior, in terms of strength, ductility, and energy dissipation.

The results of an experimental investigation into the application of steel-reinforced polymer (SRP) composites for strengthening shear-deficient exterior beam-column joints in reinforced concrete frames subjected to seismic loads are presented. Four frac12;-scale beam-column joint specimens were tested under a quasi-static cyclic load applied at the beam tip to simulate high levels of inelastic deformations similar to those experienced during a severe earthquake. The first specimen was tested without strengthening and used as control specimen for comparison purposes. The remaining three specimens were strengthened before testing using SRP sheets bonded externally to the joint region in three different arrangements. The SRP sheets selected for this investigation consist of unidirectional twisted high strength steel cords impregnated with polymeric resin. The strengthening technique proved to be efficient in upgrading the capacity and enhancing the ductility and energy dissipation ability of shear-deficient beam-column joints.

A significant portion of the existing building stock constructed prior to the enactment of modern seismic design provisions consists of Gravity-Load-Designed Reinforced Concrete (GLDRC) frames and unreinforced masonry infill walls which were used as partition walls in those buildings. Common construction practice before modern seismic design codes appeared, allowed the use of columns lap splices above the slab in each floor or above the foundation. The splices were typically 20 to 24 longitudinal bar diameters in length. Shear reinforcement was in the form of stirrups with 90-degree bends and spaced at half the depth of the frame member. As a result, the section at the base of these columns is unconfined and susceptible to shear failure or to a premature failure of the lap splices before yielding of the longitudinal bars, under reversed cyclic loadings in the event of an earthquake. The masonry infill walls used as partitions were often ignored by design engineers since such walls were considered as non resistant architectural elements. However, lessons learned from past earthquakes and from several tests performed have shown that those walls tend to interact with the bounding frame when the structural system is subjected to moderate or severe earthquake ground motions and that such interaction may not be beneficial to the performance of the structure. This paper presents the results of a series of tests, one monotonic and several shake table tests, conducted on two similar 1/2 scale gravity-load-designed reinforced concrete frames containing an unreinforced masonry infill wall built using hollow concrete blocks. One specimen was subjected to a static monotonic lateral loading and the other to prescribed simulated ground motions at different intensities to identify the interaction between the reinforced concrete frame and the masonry infill wall, the degradation in stiffness, and failure mechanism. The tests were conducted at the Earthquake Engineering Research Facility at the University of British Columbia in Vancouver, Canada.

This paper presents the results of a series of vibration tests conducted on tall reinforced concrete shear-wall buildings located in Downtown Vancouver, British Columbia, Canada. The buildings tested were the Sheraton Wall Centre, The City Tower building, The Heritage Court Tower and The Melville. Ambient vibration tests were performed on each building to obtain its dynamic characteristics. Overall vibration levels, mode shapes, modal frequencies and modal damping were determined. In addition, detailed ground measurements were taken on the Melville and the City Tower buildings to examine potential rocking behaviour and soil-structure interaction effects of the raft foundation. Interesting results of the study show that some lateral modes of vibration of the buildings include base rocking, even at low levels of vibration, and that modal coupling between the lower modes of vibration is significant. These findings indicate that the seismic response of these buildings during severe shaking may be different than that predicted during the design process.

In 2004, the Province of British Columbia, on the West Coast of Canada, announced a 10–15 year, $1.5 billion seismic retrofit program for the province's 750 at-risk public schools. The purpose of this earthquake preparedness initiative is to accelerate the upgrading of school public safety in the moderate and high seismicity regions of the province. Given the magnitude of the mitigation program, the province's Ministry of Education and the federal agency Western Economic Diversification Canada made a commitment to support the development of state-of-the-art performance-based seismic engineering technology for achieving optimum safety within a cost-effective mitigation framework, which could not be achieved based on current practice. This paper gives an overview of the formulation of performance-based structural assessment and retrofit design guidelines, which are currently being used by engineers to determine retrofit strategies for schools in British Columbia.

This paper provides a summary of the ice force monitoring program and the results that have been obtained since Confederation Bridge opened in 1997. The paper summarizes the rationale for an ice force monitoring system, the objectives of the system, and describes the instrumentation and associated data acquisition system. Summaries of the results are then presented in the form of the observations related to the behaviour of the ice against the instrumented piers, the ice data that has been observed/measured and summarizes the statistics associated with these ice observations. These observations include information on the effectiveness of the conical piers in clearing ice and the forms of ice failure that have been observed. The paper describes the process by which ice loads are determined from the instrumentation data, and summarizes the results related to ice forces and pressures. Finally, the paper describes an extreme ice loading event.

The Confederation Bridge SHM slow speed data management system was developed to collect and manage the slow-speed sensor data and fibre optic sensor (FOS) data from the bridge, and to provide tools to aid in the assessment of the real-time long-term continuous monitoring of the structural behavior of the Confederation Bridge using the data collected. A generic design of the SHM data management system was proposed and its implementation on the Confederation Bridge projected has proven to meet the system requirements. Several computationally-inexpensive and model-free data analysis tools have also been developed and tested with the data collected from the Confederation Bridge. The experience gained during the development of this system is also valuable for the development of other future systems. The system is now ready to be used as a tool by structural engineers and researchers in the analysis of the data and related behaviour of the bridge.

Examination of the critical observed temperature profiles will lead to the following conclusions: 1 Thick bottom slabs in deep sections (Sections 1 and 2) lead to lower than predicted temperatures and significant tensile stresses in these slabs. 2 The difference in temperature between the two webs of box girders are the source of a horizontal thermal gradient in deep box girder sections (Sections 1 and 2). For shallower section (Section 3), this was not observed. 3 The effect of horizontal temperature gradient cannot be ignored for deep sections when calculating continuity stresses. For shallow section this can be ignored. 4 The maximum seasonal displacement the bridge experienced during the 3-year period was found to be 226 mm. The Canadian standard CSA-S6-00 gives a good estimate for maximum temperature but seriously underestimates minimum temperature and differential temperature, for deep sections. Also, the code lacks guidance regarding design values for horizontal differential temperature.

The Confederation Bridge was the subject of extensive wind tunnel studies to define the response characteristics and the wind loads for design. The wind climate at the site was studied to better define the wind speeds for design of the completed structure as well as loads during construction. Both section model and full aeroelastic model techniques were employed. In addition, the questions of snow accumulation on the deck and the overturning of vehicles were examined. The principal results of these studies are presented. Validation of wind tunnel model tests of long span bridges is an important component of the wind engineering of these structures. Full-scale monitoring permits a corroboration of the predicted wind-induced responses and loads and also a confirmation of the dynamic properties of the structure. Few bridges have been monitored over an extended period of time, permitting the collection of significant wind "events" in comparison with design return periods; therefore extrapolation well beyond the annual extreme is necessary. The Confederation Bridge has an extensive array of instrumentation which has been in service since the construction of the bridge in 1997. The aims of the monitoring program at the outset were focused on the ice and traffic loads on the bridge as well as an assessment of the structural properties post-construction. However, an opportunity to assess the performance of the bridge under extreme winds and hence compare to the design loads was presented during several winter storms of exceptional severity. The paper focuses on the performance of this bridge to strong wind and compares the observed behaviour to the wind tunnel tests of a full aeroelastic model in addition to the development of wind loads used for the design.

The bridges presented in this paper illustrate an open view of bridge engineering design. The design process of bridges should be open, flexible and sometimes sympathetic to the parameters and circumstances that escape from the objective world. This can be done through an exhaustive knowledge of the resistance language and the exploration of plastic forms. The exploration and use of new/advanced materials in structural engineering constitutes a metaphor to the innovation and a vindication of the enormous value of engineering as an impelling element of the development and progress of the society.

Advances in seismic design technology today enable structural engineers to design buildings with a variety of seismic safety levels corresponding to different demands of the society. However, target of design is basically limited to secure life safety level within relatively short time span, i.e., serviceable life of each building. Aspects of constructing sustainable cities, which consists of buildings with long life, are not taken into account in general. Strong earthquakes occur at intervals that are longer than life of individual building or people. On the other hand, as life of cities is obviously much longer, the corresponding seismic action is stronger than the design action and may cause serious damage in buildings designed for their life only. Taking these into account, we have to design each building for earthquakes considering the life of cities in order to secure continuity of urban activities over disastrous earthquakes. However, there are problems to be solved in order to implement such seismic design. In this paper, factors in seismic engineering that hinder to realize long life city are identified and discussions on future steps of structural engineers to contribute in constructing sustainable society are indicated.

The structure has brought together world class standards of design, engineering and construction to produce a singular structure which was an alternative design procured by competitive Build-Operate-Transfer. Holistic design of all elements viaduct and main span resulted in no cost-premium for the single deck cable-stayed structure over more traditional twin parallel box girder bridges for the approaches and the river span. It was part of the Designer's Award of the Milne Medal by the British Group of IABSE in 2003, and the ICE International Medal in 2007. It also was a significant element in the second author's Award of the fib Diploma for Younger Engineers in 2007.

Wood, timber and engineered timber products offer considerable opportunities in the construction of schools and houses, offices, concert halls and longspan public buildings in the context of a world of finite resources. Variations of grain density and moisture, the need for preservation and fire resistance profoundly affect its success in architecture. Computer aided design and 3D virtual prototyping offer great opportunity for manipulation of a light, strong material that is inherently capable of `distortion' into a wide range of architectural forms. Engineering design is discussed for a range of timber buildings that have used roundwood, laminated timber frames and arches, green oak frames and American white oak, a range of gridshells using hemlock, oak, larch laths and LVL.

Engineering in Canada frequently is carried out under extreme environmental conditions, extreme loading, and in rugged terrain. Based on this experience, Associated Engineering has tackled bridge engineering in other parts of the world under similar challenging conditions. Projects are described where several types of extreme conditions were encountered.

Fire resistance of steel framed structures has traditionally been ensured by attaching insulating materials around the steelwork. These include concrete, masonry, and plaster but lightweight specialist systems are now largely used including sprays, boards, blankets, and intumescent coatings. These can be expensive and evidence from real fires suggests that reduced levels of protection may be sufficient.

From the team behind the iconic London Eye project, the Brighton i360 Viewing Tower is a futuristic visitor attraction sited directly on the beach at Brighton, a South Coast resort in the UK. The London Eye is the one of the world's most popular viewing attraction and stands over 135 m above the River Thames. The Brighton i360 tower stands almost 180 metres high and is formed from a single structural tube, 3.90 metres diameter, fabricated in sections ("cans") with bolted joints. It is erected without the use of high-reach mobile or tower cranes. Internally there is access by ladders and platforms, and externally there are tracks on which the "pod" ascends the tower, using a novel counterweight drive system adapted from cable-car technology. The structural design of the tower has been dominated by wind engineering considerations. The design includes a number of features aimed at mitigating vortex shedding and other dynamic wind effects, both in relation to structural performance and passenger comfort. These include a perforated metal rainscreen cladding, and damping systems for the lowest three modes of natural vibration. The passenger pod, 19 metres diameter, holds up to 200 persons and provides a 360 degree view through curved glass. The pod is entered at ground level and it rises to a height of 150 metres above sea level.

Numerous older buildings are frequently preserved, rejuvenated, or simply re-used for a new occupancy. These processes often include significant modifications to the structural systems, or, as a minimum, a contemporary assessment of the strength of the existing structural system to verify its suitability for the new purpose. For buildings that are in excess of 80 years old, structural elements may include cast iron columns, wrought iron beams, and structural clay tile arches. These structural systems and their materials are unknown entities to the contemporary structural engineer — and also unknown to contemporary structural design codes. As an example, old structural steel manufactured during the 1880s through the 1930s is sufficiently different from contemporary structural steel that it too should be considered obsolete and therefore not fully represented by contemporary materials specifications. This paper reviews selected properties of antiquated and obsolete structural materials in the context of contemporary structural design codes. This includes a contemporary assessment in terms of reliability. The reviews and comparisons are accomplished through the use of case studies, concentrating on buildings from Chicago in the period of the 1880s to the 1910s. Recommendations are made on how to work with antiquated systems and now-obsolete materials while using contemporary structural design codes.

Two relatively new standards, ASCE-31, Seismic Evaluation of Existing Buildings, and ASCE-41, Seismic Rehabilitation of Existing Buildings, are being touted as great developments in earthquake engineering — the next wave of performance-based engineering. However, belying the polished appearance of these standards, is the reality that standards like these will constrict the application of engineering first-principles in the existing buildings evaluations — even by engineers who have significant performance-based experience in earthquake engineering — and will result in condemnation or strengthening of elements of structures or structures in their entirety that ought not be condemned or upgraded. In parallel, use of these standards by engineers who are inexperienced in earthquake engineering may result both in a false sense of security and in buildings that will not perform as expected. In our opinion, ASCE-31 and ASCE-41 represent significant dangers to bur profession, simultaneously squelching appropriately creative performance-based methodologies, promoting the expenditures of large sums of money on inappropriate engineering analysis and strengthening, and encouraging inexperienced practitioners to leap unprepared into performance-based seismic evaluation and design.

The International Existing Building Code (IEBC) sets forth specific loss-of-capacity-based "triggers" for partial and full structural upgrades of existing damaged or deteriorated structures. These controversial triggers fly in the face of decades of experience with prior codes that encouraged maintenance of existing building stock without mandating widespread or wholesale structural upgrades as a result of repairs. The paper describes the evolution of the IEBC through the 2006 edition. In the paper, we discuss problematic language and logical inconsistencies in the code. We also discuss the new "Disaster Repair and Reconstruction Model Ordinance", which is being promoted by the California Building Officials (CALBO) as a way to ensure funding for upgrades from the Federal Emergency Management Agency after a disaster. This paper presents a discussion of history of the IEBC and addresses whether the CALBO repair ordinance and the triggers in the IEBC are morally defensible.

Failure of roof-to-wall top plate connections is a major cause of damage in light frame wooden structures subjected to high wind loads. Numerous post-storm investigations revealed that these connections fail below design wind loads [FEMA 2005; FEMA 2006; Kareem 1985]. This damage history highlights the need for understanding their resistance and behavior under such extreme loads. Earlier research studies replicated roof-to-wall top plate connections in the laboratory to study their ultimate capacity, but failed to capture the actual capacity of the connections in their "as built" in-situ condition. Furthermore, little effort has been made in the past to identify the probability distributions that describe the response and the ultimate capacity of these connections. This knowledge is needed to set the appropriate structural resistance criteria for the structural members and develop risk-consistent and reliable structural design methodologies for low-rise, wood-framed buildings. In this study, the uplift capacities of existing roof-to-wall toe nailed connections are determined and their associated probability distributions are presented. About 81 existing roof-to-wall top plate connections in light-framed wood residential structures built between 50 and 60 years ago were tested in accordance with ASTM D1761-2000 to determine their uplift performance. The results provided a robust statistical sample to assess the uplift capacity and probability distributions for typical toe-nailed roof-to-wall top plate connections in these residential structures. Results show that connections using 2-16d toenails have a mean ultimate capacity of 1.52 kN (342 lbs) and a coefficient of variation (COV) of 0.35. This COV value is found to be approximately twice that found from previous laboratory based studies lending motivation for conducting in-situ tests. Furthermore, cyclic testing of these connections also provided load-displacement relationships from which stiffness values were approximated. Results show that capacity and stiffness can plausibly be modeled as jointly lognormal.

An impediment to the development of performance-based seismic design for woodframe buildings is the lack of understanding of the factors that affect the seismic behavior of woodframe structural systems. Few numerical seismic analysis models capable of considering all the factors influencing the seismic behavior for three-dimensional woodframe structures currently exist. Furthermore, only limited experimental data have been generated at the system level and never on a structure with realistic dimensions. This paper discusses the results of a shake table testing program on a full-scale woodframe structure conducted within the NSF-funded NEES Wood Project. The test structure considered was a full-scale two-story townhouse, having approximately 1800 ft2 of living space with an attached two-car garage. It was assumed to be located on a level lot with a slab-on-grade and spread foundations and to have been built as a "production house" in either the 1980's or 1990's, located in either Northern or Southern California. The design was based on engineered construction. The size and weight of the test structure required the simultaneous use of the two three-dimensional shake tables at the Structural Engineering and Earthquake Simulation Laboratory (SEESL) at the University at Buffalo. The testing program focused on the various construction elements that have significant influence on the seismic response of woodframe buildings. Five different testing phases were conducted to investigate the influence of the following elements on the seismic behavior: Phase 1 - Engineered wood structural (shear) walls alone; Phase 2 - Wood structural walls incorporating viscous fluid dampers; Phase 3 - Installation of gypsum wallboards to engineered wood structural walls; Phase 4 - Installation of gypsum wallboards to interior partition walls and ceilings; and Phase 5 - Installation of stucco as exterior wall finish.

Damage to gypsum wallboard can be an indicator of the level of lateral movement experienced during an earthquake. A series of 17 experiments conducted at San Jose State University recorded common failure modes of gypsum wallboard typical of construction in woodframe structures. These experimental tests showed the relationship between lateral movement of the ceiling and floor and the type and extent of the resulting damage. This knowledge can be used to make field judgments about the level of movement that may have resulted during an earthquake or other severe lateral loading. This paper will review the damage thresholds observed during the experimental testing and the fragility curves developed for each damage threshold.

A wealth of data has become available since 2001 about the performance of drywall shear walls under cyclic loading. Drywalls and stucco are the only earthquake lateral force resisting system in many existing residential buildings, especially single-family homes built in 1970's and earlier. This paper takes a closer look at the actual laboratory cycle by cycle data from two test programs (CoLA-UCI and CUREE W-25 Reports) and uses them to clarify the meaning of significant damage in regards to gypsum sheathed shear walls. This paper can be viewed as an extension of the valuable information in the reports by the original authors with a focus on the interpretation and use of the test data for the evaluation of damage to existing wood-frame buildings. Analysis of the data considers the strength loss observed between the initial and later cycles when the wall is loaded to a certain displacement and shows that a loss of strength does occur. In this regard the paper can also be valuable to others working on performance based design development.

The 1994 Northridge Earthquake provided the impetus for much research in the field of seismic performance of woodframe residential buildings, resulting, in part, in specialized analytical software and an array of laboratory test data. Utilization of these new tools and data permit detailed analysis of the response of woodframe buildings to any arbitrary ground motion. While the software has been, and continues to be, benchmarked against laboratory studies of particular damage mechanisms (by virtue of design and construction details of the specimens), these tools have not, as yet, been benchmarked against the seismic performance of real woodframe buildings subjected to actual earthquake ground shaking. This paper presents the results of a series of analyses utilizing the new software (SAWS and SAPWood) and laboratory test data (COLA, CUREE-CalTech, CUREE-EDA) to hind cast the performance of two real woodframe buildings with documented damage due to the Northridge Earthquake. Comparison of predicted wall finish damage based on calculated drift estimates to field observations demonstrates that good correlation can be attained if the data and software are used judiciously. Using the analytical software benchmarked to the actual performance of these buildings, the paper also presents results of an analytical evaluation wherein one of the buildings is subjected to suites of ground motions that, on average, represent 10% and 2% probability of exceedance in 50 years for Los Angeles.

The system identification (Sys-Id) concept, defined as the estimation of a system based on the correlation of inputs and outputs, originated in electrical engineering in relation to circuit and control theory. Paralleling the advances in technology over the past several decades, the Sys-Id concept has flourished as numerous engineering disciplines have recognized its value. Today, Sys-Id serves as a fundamental prerequisite for addressing systems problems in mathematics, physics, economics, social sciences, and throughout engineering. Structural identification (St-Id) is a transformation and application of Sys-Id to mechanical (manufactured) and civil (constructed) structural systems. The paradigm was first introduced to engineering mechanics researchers by Hart and Yao and to civil-structural engineering researchers by Liu and Yao. These seminal papers gradually inspired many researchers to investigate various aspects of St-Id, and nearly 30 years later St-Id remains an active research area in both engineering mechanics and civil-structural engineering. During the last 30 years, there has been considerable research on St-Id. There have also been a number of reported applications to constructed systems. However, relative to manufactured systems such as airplanes, cars and space structures, the applications to constructed systems remains in its infancy and has enjoyed only sparse implementation in practice. Several researchers have argued that this is primarily due to a lack of practical sensing and networking technology, however recent advances in these areas have not yet been accompanied by increasing implementations of St-Id. Rather, it is becoming increasingly clear that the lack of implementation and the skepticism towards St-Id expressed by many owners/stewards of constructed systems also stems from an observation that there have not been sufficient demonstrations of an ability to reliably design and implement St-Id to real constructed systems followed by leveraging of the results to influence management decisions. This is compounded by the reality that in many cases irrelevant and unreliable data, especially erroneous identification of a lack of structural reliability as well as deterioration or damage, become a liability for managers. The purpose of this paper and the recent efforts summarized in this paper are for leveraging the promise of St-Id as a foundation for advancing the practice of civil engineering design and construction.

When measurements are taken from complex structures, structural identification methodologies cannot reveal unique values for parameters with satisfactory reliability. This weakness is due in part to inaccurate analytical models of structures. For example, many modeling assumptions may not correspond to reality. Furthermore, errors in measurement create additional conditions where errors can compensate so that exact matches between measurements and predictions are provided by wrong models. This paper reviews recent developments on parameter identification approaches and presents recent proposals that accommodate assumptions and measurement error more explicitly. Simultaneous consideration of a set of candidate models (each containing unique combinations of values of parameters) provides opportunities for quantifying identification reliability and for selecting the best sensor location for subsequent measurements. When many tens of models are possible, data mining methods add to the knowledge of the population of model candidates.

Structural identification, the process for determining `how a structure works', begins with experimental measurement of the in-situ structure, to obtain data on the loading and response at various timescales. By timescales is meant not only the data rate (dynamic or static) but the duration (ranging from hours to years), so that both short term dynamic testing and long term performance monitoring are included. In the armory of the experimental engineer there exists a huge range of testing technology, a range constantly expanding as technological advances lead to new sensors types and new analysis procedures. This paper is a precursor to a more comprehensive study on the range of technology available and in use. It provides sufficient information, including an extensive reference list, for a busy engineer considering the commission of an experimental investigation to have an overview of the technology available, and in the presentation is accompanied with case studies highlighting specific applications.

The motivation, success and prevalence of full-scale monitoring of constructed buildings vary considerably across the hazard of concern (earthquakes, strong winds, etc.), due in part to various fiscal and life safety motivators. Yet while the challenges of successful deployment and operation of large-scale monitoring initiatives are significant, they are perhaps dwarfed by the challenges of data management, interrogation and ultimately system identification. Practical constraints on everything from sensor density to the availability of measured input has driven the development of a wide array of system identification and damage detection techniques, which in many cases become hazard-specific. In this study, the authors share their experiences in full-scale monitoring of buildings across hazards and the associated challenges of system identification. The study will conclude with a brief agenda for next generation research in the area of system identification of constructed facilities.

There were many great things about this course that helped students not only to increase their knowledge of wood as a structural and architectural material, but also provided an opportunity to experience the Swedish culture. They also had the chance to interact with students, faculty and professionals within the Swedish timber and construction industry. Most of the students who have gone on these trips have said that they probably would not have taken a full year or even a semester to study abroad. This course, therefore, accomplished one of its purposes of providing an international experience to students who otherwise would have not taken advantage of other available opportunities. While not being taught in the summer of 2008, this course is planned to be offered again in the summer of 2009 and then possibly at two year intervals after that. For structural engineering students, this course has been found to provide many different opportunities, not only to learn about the timber industry but also provide a chance to interact with a different culture at the same time.

The benefits of interdisciplinary learning - having students from diverse academic backgrounds work together in one class - are becoming well accepted in today's institutions of higher learning. The design, build and engineering professions have much to gain from this teaching philosophy as budding architects, engineers and builders interact in these classes often for the first time — giving them invaluable experience and skills for their future careers. According to employers, these critical thinking and communication skills are missing from today's civil engineering graduates. Management and successful implementation of an interdisciplinary course, however, can often be challenging because the diverse student backgrounds impose very different viewpoints preconceptions and attitudes; Architecture students often align with Art and Engineering students with Science. This paper discusses state-of-the-art pedagogical strategies as applied to an existing interdisciplinary courses in wood engineering at the University of Massachusetts, Amherst. The paper further elucidates how incorporation of interdisciplinary methodologies in engineering curriculum may tie in well with the goals and objectives of the proposed civil engineering Body of Knowledge (BOK) necessary for entry into the practice of civil engineering which supported by the American Society of Civil Engineers (ASCE) policy statement 465.

Engineering educators in the U.S. have witnessed changes both in their students and in their universities. Students' interests, career goals, perspectives, and study habits have changed. As well, universities at all tier levels have put increasing pressures on faculty research productivity; and they, under the pressure of increasing tuition and fees, have often sacrificed some scientific and technical detail to the point of alarm. This suggests that old pedagogies and traditional teaching approaches may not sustain, through the next decade and beyond, some engineering areas; and especially one often viewed as so minor as timber engineering education. These changes, as well as the restricted budget environment and the emphasis on research, present challenges to timber engineering education; but also the opportunity to choose a different path. Reflecting on more than 50 years of university in-the-classroom teaching experience, short course experience to both the consulting world and government agencies, the authors examine the role of universities, industry, and government agencies in seeing that the structural engineering community maintains the professional knowledge base for continued successful design of wood structures and an understanding of their behavior. Several ideas are proposed as well as new educational strategies for all stakeholders.

The number of civil engineering departments that offer one timber design course to their students has changed little since 1986. The specific departments that offer a course has changed, but the losses and gains in courses has been about equal. The number of departments that have two courses available to their students appears to have slightly increased. The future of wood engineering education is unclear due to the limits on wood research leading to Ph.D.s. I suspect that we in the wood engineering community will find it a challenge to keep the number of courses offered in civil engineering departments at the same level as it is today.

BIM is the natural evolution of CAD as Construction professionals, and more specifically designers, have started to recognize the value of information technology, using computational power of what is available rather than transforming the computer to an perform in digital format what was analog drafting in the past. The process can be accelerated through the accumulation of information and the generation of methods of assessment and decision to be taken. BIM is still in a stage where users give input and it is simply recorded into a file that can be viewed in virtual 3D space. The computation power of IT in conjunction with the information that can be accumulated should allow the computer to act as an autonomous decision making agent that implements resolutions into designed forms and generate reports on process for the users to review. Two small processes of multiplicity of data were presented. One was the process of generating a Tensegrity roof structure, the other was the arrangement of interior spaces and openings for optimum lighting conditions and passive energy control. These two examples are indications of how data can be assessed and choices can be made. At an early stage it can be anticipated that a series of smaller tasks like, the above mentioned can be performed, slowly leading to an expanded environment where the users will feed the information to an open computational network. This will allow the computer to perform assessments and process a design from the stage of Pre Project Planning to the Construction Documents, and even in robotics control according to schedule produced and adjusted throughout the whole operation.

Structural engineers often lament that architects just do not understand the structural consequences of their designs. At the same time, most engineers are reluctant to engage in a campaign to teach others about the principles of their profession. In some circles, it is conceded that the educational divide is too great — that neither side would understand the first thing about the other. The education of architects and engineers appears to proceed on diverging tracks. Beginning in 2006, a group of practicing structural engineers in Chicago was presented with the opportunity to change that trend. The School of the Art Institute of Chicago had established a new Master of Architecture degree program and wanted practicing engineers to provide a new experience for their students. This agreement would prove to be challenging for both the instructors and the students. However, through the use of special software, hands-on projects, and traditional instruction, the goal was to give the students a solid background for understanding engineering. This paper presents the history of that program to date (it seems likely to continue for the foreseeable future). Each course in the three-part series is described, and the syllabi are included. The teaching methods employed and the lessons learned by the instructors are explained. It is the intent of the instructors that this material may provide guidance to other practicing engineers considering the opportunity to teach their trade.

This paper investigates how the `collaborative architecture' of Building Information Modeling (BIM) facilitates team learning environments for engineering students. The National BIM Standard Project Committee defines BIM as `a digital representation of physical and functional characteristics of a facility. A BIM is a shared knowledge resource for information about a facility forming a reliable basis for decisions during its life-cycle'. Current research illustrates that the intervention of BIM facilitates a more efficient means of providing design services over traditional methods. Therefore, the faculty was responsive to the constituents' future needs of having students obtain the ability to understand and function in the BIM domain by introducing BIM into the architectural design studios in the Architectural Engineering baccalaureate degree program at the University of Wyoming. The authors conducted a qualitative study in the participant observation tradition and evaluated unobtrusive artifacts such as drawings, informal interviews, surveys, participant journaling and dialogues, and raw field notes. The results indicate that BIM promotes clearly defined roles in the group-based classroom management approach of team learning. This encourages the students to pursue deeper explorations into their areas of interest, or to pursue more rigorous investigations of design alternatives. The authors provide best practices strategies for team learning and recommendations for refining the accreditation criteria.

In the field of structural engineering, the Master of Science (MS) degree or equivalent is becoming the entry-level academic qualification. This has already taken place in the hiring practice of firms that perform leading edge engineering on complex structural systems and is in the process of being mandated through the implementation of ASCE 465. It is expected that a large majority of the students seeking the MS will not be interested in using the degree as a step to the doctorate and will not have a deep interest in research. Many graduate programs however are designed as preparation for Ph.D. students and coincide with the interests of faculty members who are highly research oriented and may have minimal interest in practice. The authors see a need for professionally oriented courses in masters programs that can add value to the entry-level structural engineer and one such course is described here as an example.

Loss of a column can cause catastrophic collapse of a building. In air-blast analysis, consideration of column design is critical, particularly for ground floor columns as they are often subjected to substantial axial loads and high blast pressures due to their proximity to unsecured public streets. While there are extensive studies of columns subjected to static out-of-plane loads, relatively little information is available regarding the dynamic behaviour of such elements. As a result, column response is evaluated using simplified dynamic methods and conservative flexural deformation performance limits are set in order to account for column behaviour not explicitly included in the analysis, such as the possibility of buckling. Structural behaviour of columns subjected to air-blast load can be analyzed using advanced dynamic methods, such as explicit and implicit finite element methods. These methods take into account the complexity of the beam-column behaviour including buckling and axial-bending-shear interaction. Additionally, non-uniform loading and arrival time effects can be considered. Although these methods provide enhanced modeling of column behaviour, existing failure criterion is still based on conservative flexural deformation performance limits developed for more simplified analysis methods. In this paper, the authors examine available criteria for columns. Column response to air-blast loads using explicit finite element methods is determined and compared with results determined using single-degree-of-freedom (SDoF) analyses. Column performance is evaluated based on current design ductility and rotation limits and failure criterion is examined.

Snow loading on building roofs is an important consideration in the design process in many regions across the United States. It is especially important for buildings that have roof geometries that promote drifting of snow. When snow is transported across the roof of a building to a drift accumulation area, it causes a large concentrated load. Building roofs are more likely to suffer structural damage, or failure, from this large concentrated load rather than from a uniform load acting over the entire roof. Current building code provisions for roof snow drifts have typically been based on reviews of insurance case histories. This methodology considers a drift on a particular building, during the particular year of the insurance claim. As a result, there is no easily determined return period associated with the case history. Hence, the return period for the relationship developed from the case histories is unknown. By using a mathematical procedure to simulate roofsnow drift loads, the maximum annual drift load can be computed for each year over a period of years. From these annual maximums, the return period for a design drift can be estimated. The mathematical procedure is based on the physics of drift formation which involves a transport rate and trapping efficiency. The procedure used to simulate the maximum annual drift for a particular roof during a particular winter involves: (1) determining the amount of "driftable" snow in the roofs snow source area, (2) determining the amount of snow transported from the roof's snow source area based on the winter's wind speed record and transport rate, (3) and finally applying the trapping efficiency to determine the amount of transported snow that is in the drift. The procedure outlined above is applied to each winter's weather data for a period of 19 years at each of 46 weather stations across the United States. The maximum annual drifts from each station are then fit with a Gumbel Distribution to determine the 50- year drift load from each station for both a gable and lee-step roof geometry. These 50- year drift loads are than used to find the 50- year drift ratios, which are compared with the drift ratios for a leeward step and gable roof geometry using the methodology in the ASCE- 7 Load Standard. From this comparison conclusions are made on the accuracy of the current method for calculating drift loads.

It has been suggested that building designed for strong ground motions will also have improved resistance to blast loads. As an initial attempt to qualify this improvement, the response of a three story steel building, designed for the 1994 building code, with lateral resistance provided by perimeter moment frames, is considered. An analytical model of the building is developed and the magnitude and distribution of blast loads on the structure are estimated using available computer software based on empirical methods. To obtain the relationship between pressure, time duration, and standoff distance, these programs are used to obtain an accurate model of the air blast loading. A hemispherical surface burst for various explosive weights and standoff distances are considered for generating the air blast loading. Linear and nonlinear analyses are conducted for these loadings. Air blast demands on the structure are compared to current seismic guidelines. These studies present the displacement responses, story drifts, stress distributions and inelastic demands.

Anti-Ram Barrier systems require foundations that are able to develop sufficient stiffness and strength in order to resist the specified vehicle impact. Although the performance of these systems is traditionally evaluated using tested assemblies and equivalent static force and energy methods, the limited test data and simplified engineering methods result in uncertainty and uneconomical design. Furthermore, these simplified methods do not take into account atypical site conditions, which may require modifications to standard details in order to avoid existing utilities and subsurface structures. However, dynamic inelastic analyses may also be used to determine the performance of these anti-ram systems in response to impact loading. These dynamic inelastic finite element analyses, which consider the interaction of the attack vehicle and the barrier system, accurately represents the potential failure mechanisms and provide the most accurate and economical design for anti-ram bollard systems. This paper will discuss the various subgrade conditions that limit the effectiveness of anti-ram barriers and the modifications to foundation designs that address these atypical conditions. This paper will describe the analytical methods that may be used to evaluate the performance of barrier systems in response to vehicle impact, including the advanced analytical methods that more accurately evaluate the system response.

Traditionally limited to high-security military and diplomatic facilities, the market for blast resistant windows and curtain walls has greatly expanded in the last decade to include courthouses, government office buildings, military housing, commercial buildings and research institutions. These buildings often have architectural, operational and budgetary requirements which are a challenge to satisfy when combined with the need to achieve high levels of protection. Single degree of freedom (SDOF) analytical methods typically used in the design of blast resistant glazed facade systems have been repeatedly shown to produce conservative designs when compared to results from explosive testing. The development of advanced analysis software has allowed engineers to more closely calculate the actual performance of glazed facade systems, achieving more cost efficient and aesthetically pleasing designs without compromising protection. In particular, non-linear, explicit, dynamic, finite element software that has the capability to model coupled behavior between the glass and framing members has been developed and validated through explosive testing. This paper examines recent advances in analytical tools used to predict the behavior of windows and curtain walls when subjected to blast loadings. Comparisons of designs developed using SDOF methodologies and advanced analytical approaches are presented.

Objectives of the Environmental Wind Engineering Committee The objectives of the committee are to promote the application of current knowledge in environmental wind engineering to the planning and design of urban and other environments, their buildings and structures, to encourage research and publication in the field, and to interact with other appropriate ASCE Divisions and Committees.

The Technical Council on Wind Engineering (TCWE) was created in January 2007 with the approval of TAC. It combines the Aerodynamics Committee within the Aerospace Division with the Wind Effects Committee within the Structural Engineering Institute. This process was initiated by members of these wind-engineering committees during informal discussions within ASCE two years earlier, and was confirmed as a desire of both committees in a vote of all the committee members at the Structures Congress held at Saint Louis in May 2006.

Wind engineering as a discipline was previously addressed within ASCE in three primary committees. The Wind Effects Committee, which was part of the Dynamics Technical Activities Committee structure in the Structural Engineering Institute, concentrating on wind effects on structures. This was an active committee, which met regularly at the Structures Congress and supported technical sessions at Structures Congresses; another primary responsibility was the review of articles for the Journal of Structural Engineering. The Aerodynamics Committee in the Aerospace Division focused more generally on wind (atmospheric) flows, sometimes considering fluid structure interaction. This was also an active committee, in fact one of the more active committees in the Aerospace Division. It also had traditionally met at the Structures Congress. Unfortunately, its connection to the missions of the Aerospace Division and other committees within the Division had been rather weak. The ASCE-7 Wind Loads Committee, which has overlap in membership with the above two committees, is also an active and important committee within the SEI.

Canada and the US have been leaders in developing the field of wind engineering. In the US one can go back to the collapse of Tacoma Narrows Bridge in 1940 as a triggering event for much of the early research by F.B Farquharson, von-Karman and others during the 1940's and 1950's into bridge aerodynamics. Later, in the 1960's J. Cermak and his co-workers at Colorado State University undertook pioneering work in developing accurate simulations of the natural wind within the planetary boundary layer. Almost in parallel, in Canada, at the University of Western Ontario techniques were being developed by A.G. Davenport and co-workers for measuring the complex wind loading patterns on buildings, and for studying the dynamic response of large structures such as tall buildings (e.g. the original World Trade Centre towers of New York) and bridges. Cermak was very instrumental in having wind runnel testing methods recognized in wind codes and standards and in developing wind loading provisions in the US. In Canada Davenport was equally active in developing the wind provisions for the National Building Code of Canada. As the 1970's progressed the knowledge of wind effects on buildings was greatly advanced by both Cermak's and Davenport's teams. Also other institutes in Canada such as the National Research Council of Canada, the University of British Columbia, the University of Toronto and Concordia in Montreal became active in the field of wind engineering research and consultation as well as several others such as MIT, Texas Tech and Johns Hopkins in the US. R. Scanlan pioneered advanced methods for analyzing bridge flutter in the US at Princeton and Johns Hopkins Universities. In the early 1970's the first purely private consulting firm in wind engineering was formed in Guelph, Ontario, Canada. It built its own wind tunnels and eventually became known as RWDI (short for Rowan Williams Davies and Irwin Inc.). Also in the US in the early 1980's the private firm of CCP, short for Cermak Peterka Peterson Inc., was formed by members of the group at Colorado State University to provide wind engineering services similar to RWDI's. By the 1990's the field of wind engineering had grown substantially and besides the major research programs going on at Universities such as Texas Tech, Colorado State, Western Ontario, and Concordia, wind tunnel testing of large buildings, stadiums and bridges had become routine at the private wind tunnel testing houses such as RWDI and CPP. All of this activity meant that there was considerable world leading expertise present on both sides of the border and the competition between the various test houses led to an acceleration in the range of wind engineering services provided and techniques used. It also led to numerous collaborative efforts in the development of various wind codes and standards, which this paper will now briefly summarise.

Canadian researchers in the area of wind engineering have been members of the ASCE 7 Task Committee on Wind Loads since its inception. This close collaboration among engineers across the border has helped establishing strongly shared research knowledge apparent in its application to the development and evolution of wind load provisions in ASCE 7, one of the most comprehensive wind standards in the world with 100 pages in its current version. The Task Committee is presently working towards the development of ASCE 7-10 updating the provisions of ASCE 7-05. The work of the Committee has been extremely important since ASCE 7, although a standard on its own, seems to have evolved to a "unified" code since other codes in the U.S. explicitly refer to and follow its provisions. The paper will glance at a number of issues the Committee is working at present and will concentrate on some issues that will eventually be addressed by the Committee. Research work relevant to current wind provisions and difficulties with the interpretation of others are the main forces motivating these changes. However, since this paper refers only to work in progress, a strong disclaimer regarding the final outcome of deliberations and voted decisions about changes in the wind load provisions of Chapter 6 is in order.

This paper addresses wind driven rain (WDR) forces that are additional forces on buildings and structures above wind loads as defined in ASCE 07. WDR is described as raindrops falling into a wind field at an angle from vertical under the effects of gravity and wind drag forces. A WDR force computational model is developed to include the influence of wind, building geometry and rainfall intensity. The magnitude of these additional forces may be significant in designing buildings and structures to withstand tropical storm and hurricane force winds along with heavy rainfall. In addition, WDR causes hygrothermal damages to the building envelope.

From the observed damage and the building specific failures noted in the report, there appears to be good agreement between at least a few of the EF Scale DOD determinations and the associated wind speeds. The mapping of the approximate wind speeds can illustrate wide fluctuations for tornados because of the severity of and rapidly changing wind speeds within the storm. Wind designs to building code wind speeds in hurricane prone areas (for most of the country this is a Category 3 hurricane on the Saffir-Simpson scale) would provide protection for nearly all tornadoes classified EF3 and lower. In tornado-prone areas, the high wind design needs to be accompanied with windborne debris protection because of the numerous high speed missiles generated by a tornado event. This would provide protection for most tornado events in the country. The primary protection from tornado events however, should be a shelter — either in the residence or a nearby community shelter. Buildings built specifically to withstand the extreme winds of violent tornadoes and provide protection from wind-borne missiles will provide the most protection. While the examples of failures from this event only provide a few specific data points for calibrating the new EF Scale, these types of studies should continue when possible to build evidence of real and specific failures for the various points of POD on the new EF Scale. It is recommended that consideration be given to adding two additional building types to the EF scale. One would be old load bearing masonry buildings (of the type built in the early part of the 20^th century). The scale should also include timber frame buildings similar to the First United Methodist Church sanctuary. Timber stresses are very different than other materials and are subject to wide variability in response to extreme loads due to the condition and age of the timber. It was obvious from this event that the tornado debris field is filled with many types of missiles (wood studs, steel stairs, pieces of steel tanks, bricks, tree limbs, automobiles, farm equipment, etc). The current shelter test missile is a 15-lb 2 x 4 wood stud. Additional study work is recommended on how debris fields in this suburban-like environment affect building performance since multiple missiles in the momentum range of the current test missile could strike a building, causing a breach in the envelope and thus potentially injuring or killing building occupants. Testing of the methodology used in this study is encouraged. There are many ways building failures could occur and the failure modes selected and studied from this event for the four specific cases could be only one of several ways the failures could have occurred.

This paper will show: 1 Given the significant contribution of WDR to building damage and the fact that other environmental loads are already considered by engineers involved in building envelope design, consideration of WDR by the engineer may be a reasonable expectation. 2 The use of WDR as a design parameter could help in the construction of buildings that have greater resistance to water intrusion and long-term deterioration from exposure to moisture. The computed pressures and associated WDR values could help designers select appropriately rated window and wall systems. 3 WDR intensity on the various elevations of a building can be reasonably approximated using publicly available weather data and the semi-empirical methodology presented herein. 4 AS shown by examples of WDR and pressure calculations for 4 California cities, WDR intensity varies considerably by location and by building elevation. This fact could lead to the development of WDR index maps similar to those generated for freeze-thaw or for wind and snow loads. 5 Based on limitations of the currently available weather data, the methodology presented herein is appropriate for providing relative assessments of WDR exposures between various geographic areas and building elevations.

Structurally used tubular glass provides stunning possibilities for architectural applications, which have hardly been explored yet. Over the last decade, only a handful of experimental structures have been presented, such as a 3D lattice structure by the University of Stuttgart [1], a tensigrity structure [2] and columns in a pavilion by the TU Delft [3]. Just one project of significant size has been realized in practice: the hanging glass atrium facade of the Tower Place office building in London, UK, is horizontally supported by a field of glass tubes [4]. All these examples make use of geometrically relatively simple shapes, i.e. tubes. However, welding and hot shaping techniques for glass make it possible to produce much more complex shapes. The possibilities this offers on small scale design of mechanical joints have been explored in a case-study design for facade struts by Bos [5]. However, a glance in an average chemistry laboratory will give you a better impression of what could be possible. Little is known about glass welding for the building industry. Especially the bond strength is an important unknown as is the reliability. Other constraints such as which types of glass can be used and what shapes can be forged are also unknown. The existing projects have already shown the use of glass tubes introduces specific engineering problems compared to ordinary flat glass. They are normally only available in limited size, up to 1.5 m. Force transfer into a glass tube is also complicated as the geometry prohibits drilling holes and complicates adhesive joints. The potential of welding for structural applications of glass tubes has been explored by graduate student C. Giezen, by producing a case-study design alternative for the (existing) façade structure of a curtain facade of the Faculty of Architecture building. This paper is largely based on the results of that study. Theory on welding is reviewed and the practical possibilities of shaping by existing commercial firms explored. Experimental research, carried out on different welded specimens to investigate welded joint strength, is presented. Finally, a facade structure design based on 3D cross-shaped welded glass components, is presented. This study shows welding provides ample design possibilities without significantly compromising the component strength.

This paper discusses the historical evolution of reinforcement detailing in RC structures as stipulated in the ACI Code since 1956. The provisions for the required development length, splice length, hooks and bend diameters are compared for the 1956 ACI code, 1963 code, 1971 code, 1989 code and the current code. It is shown that the development lengths and splice lengths have increased significantly since 1956. At the same time, the bend diameters have been significantly relaxed to eliminate concerns of potential cracking of concrete due to tight bend radii. The detailing changes have been even more dramatic for structures expected to perform in moderate to high seismic regions (Chapter 21 of ACI 318). FEMA 356 and ATC-40 provide guidance for estimating the effect of insufficient development/splice length for seismic evaluation of structures designed for pre-70 codes. However, no guidance seems to exist for evaluation of the effect of tight bend diameters of standard hooks and tie hooks specified in the pre-70 codes. Note that evaluation of detailing is an integral part of strength evaluation of existing structures. Currently, there does not seem to be a uniform approach for detailing evaluation of pre-70 structures. Therefore, some guidelines are required in order to bring consistency to structural evaluation for general industry use.

Numerous historical structures were built with structural walls of stone masonry and mortar. Many have not survived the test of time. Some have had obvious signs of distress such as bowing, bulging, and cracking. Others have had catastrophic failures occur without warning. As part of a research project sponsored by the National Center of Preservation Technology and Training Ryan-Biggs Associates, P.C., as a consultant to Fort Ticonderoga, investigated using acoustic emission technology as a means of monitoring historical stone structures, detecting damage, and predicting impending failure. This paper presents some of the findings of the research project. Acoustic emission technology has been successful in structural health monitoring in materials such as composites, steel, and concrete and has the potential to be an effective economical tool to monitor the structural integrity of stone-masonry walls.

The use of the expression Structural Elegance should be used more often to describe excellence in Structural Engineering. Only Structural Engineers are qualified to decide which structures possess the quality of Structural Elegance: The attributes which define the expression are herein discussed. Structural aesthetics are a part but only a part of Structural Elegance. It is possible to have structural elegance without aesthetics. Many structures today are built on whimsical structural decisions rather than on classical methods. Structural Elegance also includes a clear sense of purpose, efficiency of materials and construction methods and lastly daring. The best way of illustrating these qualities is by comparing examples of structures which posses structural elegance with those which do not. The author begins with the bridges of Maillart and the shells of Felix Candela as examples of Structural Elegance. Other well known examples are shown with comments. The paper suggests that structural engineers should routinely discuss their peer's success or failure in achieving Structural Elegance. This would clarify their understanding of Structural Elegance. The possibility, in the future, of achieving some of the properties of Structural Elegance by use of Computational Morphogenesis is briefly discussed.

Eero Saarinen, noted American architect, was born in Finland but practiced exclusively in the United States. He was educated at Yale University and traveled extensively in Europe and Scandinavia before joining his father's practice at the Cranbrook Academy of Art, near Detroit, Michigan. He opened his own office in 1948 upon winning the competition for the Jefferson Memorial Arch in St. Louis, Missouri. He designed many significant and often controversial buildings, including the General Motors Technical Center in Michigan, TWA Terminal at JFK Airport, Ingalls Hockey Rink for Yale, North Christian Church in Indiana, Kresge Auditorium and Chapel for MIT, John Deere Headquarters in Illinois, and the Dulles Airport in Virginia. Incredibly energetic, Eero Saarinen produced over 90 structures in his 13-year practice and won numerous awards. He died at age 51 from a sudden brain tumor.

Bio-based structural building products have several characteristics that are radically different from non-bio-based products. Some of these characteristics are so different that it is difficult to develop useful measuring sticks when discussing the topic of sustainability. This paper explores the sustainability attributes of products made from wood or agricultural fibers. It answers the following questions: 1 What measuring sticks should standards development organizations use to weigh the sustainability advantages of one product attribute versus another? 2 How does an engineer know if a bio-based building product comes from a sustainable source? 3 What are the advantages and disadvantages of using products made from short rotation agricultural crop fibers versus long-rotation forest fiber? 4 A What are some of the sustainability attribute differences between various types of wood-based building products (i.e., solid sawn lumber versus engineered wood)? The paper addresses these questions, where possible, in the context of life-cycle assessment studies that measure the attributes of embodied energy, global warming potential, air emissions, water emissions, and solid waste for bio-based products.

Sustainable buildings are achieved through integrated building design—an approach to design and construction that involves the participation of owners, contractors, suppliers, building users, and design professionals during the initial design phase and at other key points in the design process. The goal of integrated design is to achieve high performance and synergistic benefits that minimize a building's environmental impacts throughout its life cycle. For example, in an integrated design approach, the mechanical engineer will calculate energy use and cost very early in the design process, and inform designers of the energy-use implications of building orientation, configuration, fenestration, mechanical systems, and lighting options. Similarly, the participation of structural engineers in the integrated design process can create opportunities for green design strategies. For example, the choice of structural system, whether steel, wood, or concrete, during the initial design phase can affect the amount of energy needed for heating and cooling, as well as the ability to incorporate local and recycled-content materials into the building project. This paper describes the aspects of concrete construction that contribute to sustainable buildings. The discussion will refer to the point system of the Leadership in Energy and Environmental Design Green Building Rating System for New Construction and Major Renovation (LEED-NC) LEED-NC is a voluntary rating system for designing, building, and certifying green buildings. It is widely used to determine if a new building meets the behavior requirements for the level of LEED rating required by the owner. Sustainable aspects of green buildings are often grouped into categories so that members of the design team have a structure around which to integrate green design strategies into a sustainable design. LEED-NC uses the following five categories: 1 Sustainable site planning and use 2 Safeguarding water and water conservation 3 Energy conservation and protection of the atmosphere 4 Efficient use of materials and resource conservation 5 Protection of indoor environmental quality.

This paper will touch upon some of the considerations a structural engineer will need to consider when designing with steel, or in many cases, with any other building material. The key is integration with other design professionals, and integration as early as possible in the design process. Current trends in several building sectors seem to be moving in the opposite direction: tight time constraints, lowest bidder practices, reduced time for design and bid, and the flooding of the market with structural and other materials all claiming high levels of "green" have not made the job easier for the structural engineer. However, with some construction types, with design-build, and with the increasing amounts and types of pre-engineered components, the structural engineer on these types of projects are seeing the opportunity for integration of their design with others in the design team, to develop synergies and symbiotic relationships between systems and materials. Several sources exist for the engineer to consider, including the soon to be published "Report on Sustainability" from the ASCE SEI Committee on Sustainability. Several of the concepts briefly touched upon in this paper will be covered in-depth in the committee's report, this will be an excellent resource: for structural engineers, and for those that have the opportunity to have structural engineers on their design team.

One of the desirable attributes of sustainable design in residential construction is to have high thermal mass (HTM) walls. Such wall systems would have large thermal storage capacity and ideally function to absorb direct solar radiation during the day and release the stored heat to the interior during the night. Because conventional residential exterior wall systems generally consist of thin and light screen walls (e.g., exterior light-frame walls with brick veneer or other types of siding), which rely heavily on batt or rigid insulation for thermal purposes, they cannot function as ideal HTM exterior walls. As a result, there is renewed interest in the use masonry walls, which are known to have HTM property. Although the use of masonry as the load-bearing exterior walls is common for low-rise buildings, today's use of load-bearing masonry walls in residential construction may stem from energy efficiency and sustainability considerations rather than the need for a gravity load-bearing system. Nonetheless, the structural behavior of the types of masonry walls that may be considered suitable for sustainable design is a primary concern, given the emerging new masonry materials and in some cases, the use of indigenous materials. In particular, because HTM walls are usually thick and architectural features of sustainable design such as wall setbacks with respect to the roof or re-entrant corners for shading introduce more complicated structural response under lateral loads, additional experimental studies seem to be necessary. In an effort to develop a basic understanding of the structural behavior of HTM walls, a pilot study was undertaken at Penn State University to evaluate the in-plane and out-of-plane capacity of three types of masonry walls some architects use in sustainable designs. The masonry types were chosen to span from the indigenous materials to modern types. For this reason, concrete masonry unit (CMU) was chosen to represent the currently popular masonry type, adobe was chosen to represent the traditionally oldest masonry type used for thousands of years (to be rediscovered today for some sustainable designs), and autoclaved aerated concrete (AAC) was chosen as a relatively modern material. In subsequent sections, a brief background and literature review, the experimental program, and the test results are discussed.

Structural engineers are now expected to consider the environmental impacts of their designs, alongside the more traditional performance measures of strength, safety, serviceability and cost. Life cycle assessment (LCA) is a tool to analyze the environmental impacts of a building, from construction to end-of-life; thereby identifying ways to reduce those impacts. The application of LCA to the complex, inter-related nature of buildings represents a significant challenge and the field continues to develop rapidly. Nevertheless, LCA is becoming an important tool in the building design industry, and structural engineers need to be conversant in the basics of LCA. This paper will introduce fundamental concepts of LCA of buildings allowing structural engineers to become more involved in the sustainable building design process.

This article describes the development of "design by analysis" methods for innovative navigation structures. The modeling approach is designed to facilitate the development of a complex three-dimensional finite element mesh and efficiently analyze the structure. Techniques to automatically generate a detailed model of the structure and perform required analysis and design calculations for the individual concrete slabs under all applied loads are illustrated, along with methods for identifying and reporting details of the design for each slab under the worst-case loading. This article begins with a description of assumptions made concerning in-the-wet construction techniques and how these assumptions are accounted for in this development. Then the methods used to replicate typical details of the float-in segments are illustrated. The finite element formulation for the two element types is then presented. Shell elements are used to model the individual concrete slabs. These are connected with superelements derived to provide an accurate solid model of the joint details, including tapers between slabs. An innovative approach to efficiently calculate the stiffness matrix and the slave-master transformation matrix for an arbitrary joint geometry is introduced. The two-way slab design approach (based on American Concrete Institute requirements, ACI 318-02) is summarized, along with a description of methods to calculate shear, moment, and thrust throughout the shell elements and at selected cross sections of the superelements. The design section includes the approach used to modify design parameters based on analysis results. Finally, guidelines are provided for modeling the response of soil and piles used in the foundation.

In a petrochemical plant, there are several buildings that require blast-resistant design such as operator service building, control room, electrical and mechanical buildings, warehouse, administration building, medical and fire stations. These buildings normally have multiple openings and un-symmetric layout. The current approach of blast resistant building design is typically based on a highly simplified dynamic model of a Single Degree of Freedom (SDOF) system. This approach may be appropriate for regular building shapes without openings. For a complex structure with openings, the SDOF system may not be applicable due to closely spaced frequencies between connecting components and difficulty in evaluating the equivalent inertia and stiffness. In addition, the explosions in the petrochemical plants are mostly vapor cloud explosions. For proper design of the buildings, the blast pressure loads need to be applied to the front, side, rear and roof surfaces simultaneously for dynamic response evaluation. In SDOF analysis method, it is a tedious process to transfer pressure load from front wall to roof and then to side walls. Consequently, Finite Element Analysis (FEA) approach becomes a preferred or even required method to evaluate the dynamic response of the complex structure. The main purpose of this study is to demonstrate that the dynamic nonlinear FEA of a concrete structure is a practical approach for blast loadings. During the course of this study, comparisons between FEA and SDOF were made; these comparisons are included in this paper. This paper will also present the effects of openings on the dynamic responses.

Analysis methods described in the ASCE guideline "Design of Blast Resistant Buildings in Petrochemical Facilities" published in 1997 focused on simplified methods for blast load prediction and structural response. While these methods are still widely used, advances in modeling techniques and tools as well as increased computing capability have made use of advanced analysis techniques more feasible for analysis and design of structures subjected to vapor cloud explosion, vessel bursts and other explosion hazards in chemical plants and refineries. This paper reviews techniques for advanced blast load prediction, including computational fluid dynamics. A comparison of the capabilities and level of effort required for advanced blast analysis methods and more conventional simplified methods is provided. A discussion of situations where advanced analysis is advisable or required is also covered. Advanced dynamic structural analysis techniques, including non-linear finite element analysis (FEA) will be reviewed for petrochemical facility applications.

This paper presents actual cases for evaluating existing buildings within petrochemical facilities subjected to postulated vapor cloud explosion blast scenarios. An evaluation will estimate the expected damage (i.e., Light, Moderate, Severe, Failure) to each building component that makes up the exterior building envelope. If an unacceptable cumulative overall building damage is assigned and a decision is made not to de-occupy the building then upgrades to the building to significantly enhance its current blast capacity are required. Based on operational, construction, and existing cable and control panel configurations, a cost effective retrofit option is selected. The paper will describe several upgrade techniques such as building a new building around the existing building and adding reinforcement bars or steel posts to exterior concrete masonry walls and framing a new steel frame roof over the existing roof. The discussed retrofits are based on analytical dynamic non-linear models that were used in their design. Some of these analytical models have been validated with test data produced using the BakerRisk shock tube.

An Office Container was tested for 1250+ lbs ANFO charge (1000 lbs of TNT equivalent charge) at 110 ft standoff distance. The damage observed in the container during the test was in the "Low Response Range". The damage of non-structural components (e.g. conduit pipes, light fixtures, HVAC units and interior wall sheating) was minor. No damage was observed for the inside occupant. The test and analyses showed that the container will experience less damage for the design load (5 psi, 150 ms free field). Blast load design specifications of 5 psi refer to long duration (150 msec) free-field pressures and this does not mean that container could not withstand higher reflected pressures. Front and end-walls were exposed to peak reflected pressures of approximately 20 psi (short duration blast) with minimal or no damage. Doors opened at the time of maximum negative net pressures, that is, between 87-90 milliseconds. Net peak pressures of +3.8 and –2 psi were seen at the back wall exposing door latches to an approximate net suction peak force in excess of 3100 pounds. Blast load estimations proved to match reasonably well with measured pressures. Estimated permanent sliding displacement of the container compared well with actual acceleration-derived displacements and passive-measured displacements, that is, between 0.6 – 0.75 inches. Tipping was found to be negligible.

Blast-resistant modular (BRM) steel-framed buildings have been utilized in petrochemical facilities and are becoming more common — both for turnaround situations and as alternatives to conventional in-place construction. These modular buildings utilize steel structural frame members (usually HSS members that are `seismically' compact per AISC 341) with crimped steel plate walls. The method of attaching the plate walls to the frame members typically does not utilize mechanical fasteners; rather, continuous welded construction is usually used. Roof joists and floor joists (usually seismically compact steel sections) typically support flat plate roofs and floors. BRM buildings can be designed for blast loading conditions that are on par with other blast resistant construction. BRM buildings may be anchored or unanchored. If unanchored, they may slide which can result in additional risks. Typical `building blocks' are 10 to 14 ft (3.0 to 4.3 m) wide by 20 to 50 ft (6.1 to 15.2 m) long. BRM buildings can range from single module structures to multi-module and multi-story, integrally-connected structures, with floor areas over 10,000 ft² (929 m²) (see Figures 1 and 2). Refer to for further details related to construction. This paper examines design issues for modular blast-resistant steel-framed buildings, as presented in the upcoming 2008 edition of the ASCE guideline "Design of Blast Resistant Buildings in Petrochemical Facilities".

In response to input from individuals and companies in the petrochemical industry, in 1995 the ASCE Petrochemical Committee established several task committees for the purpose of developing and publishing design information on current practice. Five specific subjects were deemed to be of the greatest interest to the petrochemical community; anchor bolt embedment, secondary containment, seismic design, wind loading, and blast resistant design. The task committee on blast resistant design was then formed with membership representing design engineers, blast design specialists, owner companies, and product manufacturers. The task committee spent two years preparing a state-of-the-practice report that was published in 1997. The report was prepared based on the expressed need for more uniform design information to protect against the effects of accidental industrial explosions. Since its publication, the report has been widely accepted throughout the petrochemical structural engineering community, and is considered a significant reference for the blast resistant design community in general. In 2005, the Petrochemical Committee felt that an update to several of the 1997 reports was needed in order to address recent technical advances. The reports selected for update were anchor bolt embedment, wind loading, seismic design, and blast resistant design. Thus the task committee on blast resistant design was reformed. The previous representative mix of design engineers, blast design specialists, owner companies, and product manufacturers was again pursued and obtained. Several members from the original committee also served on the new committee and provided a degree of continuity. The task committee first met in January 2006 and completed its work in January 2008. The basis of the updated report, to promote the use of uniform design information in order to protect against the effects of accidental industrial explosions, was retained. Significant elements of the original report, such as the basic procedure (Figure 1), use of simplified design methods including empirical load determination, response charts, numerical integration, and SDOF equivalent response calculations, were retained. Much original information from TM 5-1300 (Structures to Resist the Effects of Accidental Explosions) was also retained. The report continues to emphasize the use of design examples to illustrate the proper implementation of design methods. The updated report incorporates errata discovered from the previous report. A number of sections were edited for greater clarity and understanding. Updated design standards were incorporated such as ACI 318-05, Building Code Requirements for Structural Concrete, and AISC 360-05, Specification for Structural Steel Buildings. Updated blast design references were also considered including PDC-TR 06-08, Single Degree of Freedom Structural Response Limits for Antiterrorism Design, the ASCE blast standard currently in progress, and API RP 753, Management of Hazards Associated with Location of Process Plant Portable Buildings.

The Task Committee on Blast Resistant Design of the Petrochemical Committee of the Energy Division of ASCE will publish a new edition of the manual Design of Blast Resistant Buildings in Petrochemical Facilities. This edition will have updated response criteria defining three levels of component response to blast loads; High response, Medium response, and Low response, in terms of maximum ductility ratio and/or support rotation criteria for each response level. Separate criteria are defined for different component types (i.e., steel beams, concrete slabs, etc.), where the number of component types have been expanded to include prestressed concrete. The criteria address primary and secondary components and frame components with and without significant axial load.

The object of this paper is the analysis of the effects of crack sizes and orientations in a concrete dam resting on a rock foundation using the finite element method. The stress intensity factor at the crack tip is chosen as fracture criterion. The effects of hydrostatic and up lift pressures are highlighted. The obtained results show that the geometrical properties of the structures, the applied loading and the difference between the mechanical properties of concrete and rock lead to a mixed mode behaviour of the crack. The mode I stress intensity factor increases significantly when the crack length reaches 40% of the dam width. The mode II stress intensity factor becomes sensitive to the increase of the crack length when this one reaches 70% of the dam width. The hydrostatic pressure has an important effect on the SIF variation. However, the uplift pressure effect is more sensitive as the crack length increases.

The renewable fuels industry is growing rapidly as alternatives to fossil fuels become more and more desirable. One such renewable fuel is ethanol. The expansion of the ethanol production industry over the last seven years has been dramatic. A total of 80 biorefineries have been built and put into production since 2000. An additional 77 new or expanded facilities are coming on line in the near future. U.S. ethanol production has grown from 1,750 million gallons per year (mgy) in 2000 to 7,230 mgy today. The new and expanded facilities will add an additional 6,220 mgy, pushing the total ethanol production capacity to over 13,450 mgy. This paper will discuss the evaluation and remediation of a large mat foundation supporting two 150 feet tall concrete grain silos at a new 100 million gallon ethanol facility in the Midwest. The mat foundation and associated tunnel structures began exhibiting significant distress shortly after being put into service. Investigation methods and findings will be discussed as will remediation options and methodologies. American Engineering Testing, Inc. (AET) was retained by the owner of the facility following initiation of the distress to review the activities of the design and construction teams, perform our own investigations and advise them on the proposed remediation program. AET was not involved in the preconstruction or construction activities on the site.

Southern California Edison has begun an extensive rehabilitation program of their Kern River hydroelectric facilities. Most of these hydroelectric systems were built nearly one hundred years ago, and have been in nearly continuous operation ever since. Located in the Kern Canyon, 16 miles east of Bakersfield, California the Kern River #1 forebay is located over 900 vertical feet from the valley bottom, and with the only access to the site via a gondola or through tunnel adits, rehabilitation of the penstock required an innovative design and construction approach. To meet the design standards of the California Building Code, as well as ACI 350 — Environmental Engineering Concrete Structures, a composite wall section system was finally selected as the most viable design alternative. In consideration of the stringent specification requirements coupled with the concrete transportation constraints, quality control measures were implemented and enforced during construction. Completed in early 2006, the forebay rehabilitation was a successful project incorporating new gates and control systems, and is designed to resist the expected hydrodynamic and seismic loads. The paper also covers the original design with photos of its first years in service.

Codes and standards have generally provided conservative guidelines for design of tall reinforced concrete chimneys because of their inherent brittle nature and low redundancy. This paper reviews the state-of-the-practice for seismic design of concrete chimneys. The codes and standards reviewed in this paper are the American Concrete Institute's Committee for Design and Construction of Reinforced Concrete Chimneys (ACI 307-98 and the proposed ACI 307-XX), International Conference of Building Officials (UBC 1997), the International Building Code (IBC 2006), the International Committee on Industrial Chimneys (CICIND 2001) and Eurocode 8-6 (2005). The paper discusses the provisions presented in the above codes and standards and compares them from the point of view of design philosophies, expected chimney behavior, required detailing, economy of design and design rationality. Based on this review, some concluding remarks are presented for design of RC chimneys in the United States.

Our proposal that some of the parameters of the two-mass model for a not-flat-bottom tank may be approximated with sufficient accuracy for use in design by an equivalent cylindrical tank with a flat bottom with the same volume and free surface area as the not-flat-bottom tank is supported by its application to the determination of 1. the sloshing mass and frequency of liquids in spherical tanks, 2. the impulsive mass and its location above the bottom (for calculating moment exclusive of base pressure) of four large tanks with not-flat bottoms.

There are numerous parameters and assumptions that relate to seismic design of liquid-containing structures. Many of these parameters and assumptions require a mixture of science and engineering judgment to arrive at reasonable results. However, there are often differing opinions regarding the appropriate assumptions and appropriate design parameters to apply. This paper summarizes some topics that continue to generate a variety of opinions as to validity of approach. The intent of this paper is not to provide all of the answers, but rather to generate further discussion of these topics. Much of the discussion in this paper is related to seismic design of concrete liquid-containing structures, as defined in ACI 350.3-06. However, many of the topics will also apply to seismic design of other types of liquid-containing structures.

When the time came to fill the Twin Oaks II Reservoir with water, there was virtually no detectable loss of water. After passing the watertighness test, the reservoir was backfilled and placed online. It is expected to serve with no regular maintenance for decades. The success of a large prestressed concrete reservoir can be summarized as follows: 1 The larger the tank is, the greater volume (water capacity) to surface area (structure) ratio. For example, one 40 million gallon tank has less material than two 20 million gallon tanks or four 10 million gallon tanks would. This translates to a significant savings to the owner by a shorter construction duration, less material and equipment usage. 2 Prestressing can be used to balance virtually any hydrostatic or hydrodynamic load. Without prestressing, water-induced hoop-stress would go into the reinforced concrete as tensile stress. Filling and draining a reservoir without prestressing will cycle the structure through different degrees of tensile stress, which are problematic in liquid-containing reinforced concrete structures. As a prestressed concrete reservoir is filled and drained the concrete will always remain in compression, which ensures long-term durability. 3 High water pressure near the base of the wall of an anchored-flexible base will neither transfer moment into the footing nor retain these stresses by a restrained connection. Large water pressures can simply be balanced by providing an appropriate quantity of prestressing. 4 The design and construction of a large prestressed concrete reservoir parallels that of a smaller one in many ways. However, special attention to certain details and the ability to manage the logistics of such projects will assure success. Having an experienced designer and contractor would be an essential part of a successful team.

Environmental engineering structures are designed for strength but crack control to prevent leakage and other long-term durability problems remain important serviceability requirements. The service design requirement is accomplished by using the environmental durability factor (EDF) on top of the applicable load factors to limit the stresses/strains in reinforcement at the service load level. The use of EDF increases the factor of safety and reduces the strain in tension steel at nominal strength. This is not consistent with the concept of Unified Design Approach (UDA) adopted in the 2006 edition of the ACI 350 code. The UDA requires that for flexural tension controlled sections, strain in the tension reinforcement should reach at least 0.005 at nominal strength. This paper proposes a more rational design method for environmental structures based on limiting strain and crack width at service level and ensuring strength at the ultimate loads. Design procedure is streamlined and the use of EDF eliminated. An example is included to illustrate the problems with the current design approach and the applicability of the proposed method.

Relatively massive concrete walls have been used for over a 100 years in a variety of environmental engineering concrete structures. Even with over a century of experience in design and construction of concrete liquid-containing structures (LCS), we still see new tanks leak. This may happen on the first filling or after a couple of seasonal cycles. Why after all the decades of experience do many of our concrete tanks still leak? We will look at the impact of many factors in design, material selection and construction of concrete liquid-containing tanks on the cracking and resulting leakage. We also identify pertinent design aspects of the ACI 350-06 Code Requirements for Environmental Engineering Concrete Structures. Also, we use decades of design, construction and evaluation experience in liquid-containing structures to identify common problems with specifications, materials and construction techniques that can cause excessive cracking and leakage.

Hurricanes have caused severe damage to the electric power distribution system in the U.S., leading to widespread, prolonged power outages. Electric power is critical to post-hurricane disaster response as well as to long-term recovery for impacted areas, and power restoration depends on effective pre-storm planning and resource allocation. Power outage estimates form the basis of pre-storm decisions that utility companies must make about the number of crews to request through mutual aid agreements and the locations where crews and materials should be staged in preparation for a recovery effort. Managing power outage risk and properly preparing for post-storm recovery efforts requires rigorous methods for estimating the number and location of power outages before a storm makes landfall. These estimates must be geographically detailed and accurate while also accounting for the complicated relationships between a number of possible explanatory variables and power outages. Previous research in estimating power outages during hurricanes has relied on negative binomial generalized linear models (GLMs) that use the standard linear relationship between the log of the expectation of the response variable Y (i.e., the number of power outages in a geographic area) and a set of explanatory variables given in the matrix X. However, these models have been shown to substantially overestimate the number of power outages in urban areas in some cases (Han et al. 2007a), and they do not provide insight into the possibility of non-linear relationships between the elements of X and the response variable. This paper shows how generalized additive models (GAMs), a class of semi-parametric regression models, can be used to more accurately estimate power outages during hurricanes. This is done through an analysis of a data set consisting of power outages in 6,681 3.66 km (12,000 foot) by 2.44 km (8,000 foot) grid cells during five hurricanes in the service area of a large, investor-owned utility company serving a large portion of a Gulf Coast state that has been impacted by a number of hurricanes in the past. The results show that GAMs can provide more accurate predictions of the number of power outages in each geographic area of a utility company's service area and a better understanding of the response of the system than GLMs do. The explanatory variables used in the regression model include information about (1) the winds experienced in each grid cell during each hurricane, (2) the long-term precipitation and the soil moisture levels in each grid cell at the time of the hurricane, (3) the power system components in each grid cell, and (4) land use and land cover in each grid cell. The underlying goal in developing an outage count prediction model is to provide a basis for choosing how many crews and materials to request from other utility companies as a hurricane is approaching and where to position these crews and materials in order to restore electric power as quickly as possible without incurring unnecessary expense.

The high intensity winds (HIW) associated with thunderstorm outflows (downbursts, tornados) have profile shapes that differ greatly from the straight line winds in conventional atmospheric boundary layers that form the basis of the design wind loads for electricity transmission line systems. Evidence from line failures, such as Manitoba Hydro's (MH) on 5^th September 1996, that caused failure of 19 towers and a 5-day line outage, suggests that many are the result of HIW, due to a combination of extreme wind speed and an off-design wind load distribution. Whilst the complete upgrading of any given line system to withstand the severest storms is not feasible, some critical locations (e.g. major river / road / rail crossings) could benefit from remediation based on a thorough understanding of HIW loads. The authors have completed the first phase of a comprehensive research program aimed at quantifying these HIW wind fields, their loading on transmission line tower and line components and the resultant response of the transmission line system. The main outcomes from that phase were 1 Formulation of a computational fluid dynamics (CFD) model of downburst and tornado wind fields validated by small-scale laboratory experiments and a theoretical / analytical model 2 Derivation of a loading model for downburst winds and application of this model to fully non-linear finite element (FE) models of a MH Type A guyed tower / line system. Identification of some of the critical members and failure mechanisms. A second phase of work is currently in progress that is concerned with the validation and implementation of the previously developed concepts, encompassing 1 Design and construction of a large scale downburst simulator (based on a 2-D wall jet concept) 2 Testing of tower/line physical models in the large-scale downburst simulator, with comparison to loads derived from atmospheric boundary layer wind profile model testing. 3 Improving the downburst and the tornado numerical models by introducing atmospheric parameters and comparison with Doppler radar atmospheric data.

Winter storm damage can be severe. Most of the damage is to the interdependent lifelines such as the power delivery system, the transportation grid and the wastewater system. Evidence of the closed-loop interdependencies as described for hurricanes between power delivery and transportation was apparent for the Hanukkah Eve Storm. Power outages can create difficulties in the winter due to low temperatures. Air quality suffers during periods of extended outages due to smoke from fireplaces. Unfortunately, the few deaths that occurred were primarily attributed to carbon monoxide poisoning or smoke inhalation. Investigations of the infrastructure damage are ongoing at the University of Washington.

In many regions of the world not exposed to atmospheric icing, localized High Intensity Winds pose the greatest risk to failure of overhead lines. However, only a few countries have put in place codified procedures that provide a level of mitigation of the effects and provide increased security of overhead lines. In other regions where localized HIW events now appear to be more frequent than previously anticipated, utilities are looking at simple ways of reducing the risk of catastrophic failures. For existing lines, it is feasible to increase significantly the survival of supports to localized HIW storms with relatively simple improvements to the structures such as higher diagonal bracing capacity in self-supporting towers and higher flexural mast rigidity in guyed structures. For new supports, appropriate design loadings applicable to the predominant wind storm type of the region will necessarily influence the detailed design. Some simplified design loading cases are proposed here to account for the effects of localized HIW on overhead line supports. They are recommended for use by utilities without codified procedures in place. When the hazard is real and its mitigation on existing lines is impractical, security measures should be implemented to reduce the probability of cascading failures.

The effectiveness of numerical prediction of structural dynamic response is assessed for a wind mast support structure typical of wind turbines, but without the turbine itself. This effectiveness is assessed by comparison of predicted mechanical strain below the waterline of the structure with measured field data. Particular attention is paid to the effects of wave directional spreading. In the model, wave loads are generated from a series of simulated irregular time-histories associated a single significant wave height and period, but two distinct spreading parameters. Load predictions are based the Morrison equation and the structural response is computed by solving a finite element model of the structure in the time domain. Comparisons are based on the variances of the response process.

Design standards for wind turbines such as the guidelines from the International Electrotechnical Commission (IEC) require, for at least one design load case, statistical extrapolation of loads from limited simulation analyses. Extrapolation refers to prediction of a rare load fractile. Several statistical extrapolation techniques are possible; one includes the use of the peak-over-threshold method in which load maxima between successive upcrossings of a selected threshold are defined as the extremes for random variables. With such "extremes" models, it is common to fit parametric distributions to the loads data and to then attempt to predict load levels associated with rare occurrence rates (in ten minutes), generally on the order of one in 1 million or even rarer. Structural reliability principles can be employed to improve the efficiency in such computations. In this study, ultimate limit states will be evaluated for a 5MW offshore wind turbine by first studying short-term load statistics (conditional on wind speed and wave height); then, upon integration of these short-term distributions with site-specific environmental climate descriptions, long-term turbine loads will be derived.

The investigation reported in this paper examined the possibility of using displacement ductility capacity, instead of strain limits, as the acceptance criteria for reinforced-concrete piles used in marine oild terminals. It is shown that the displacement ductility capacity is a robust parameter: it is essentially independent of the pile length, cross sectional properties (i.e., pile cross sectional dimensions, longitudinal reinforcement, and transverse reinforcement), and axial load. It only depends on the acceptable strain limits. Based on theoretical analysis and parametric simulations, lower bound values of acceptable displacement ductility of reinforced-concrete piles are proposed.

Inaugurated in June 2003, a part of the Roissy Terminal 2E in France collapsed. The accident was produced by the failure and the drop of the horizontal beam out of its supports and the punching of the concrete vault by the stays used to support it. So we have studied this problem from the available data in our possession in order to examine the real reasons of the incident and to see if it were possible to predict the structure deficiency from the beginning. That's why some deterministic analyses and a mechanical reliability assessment were performed. At the end, some recommendations have been mentioned in order to avoid such incidents in the future, showing the importance of reliability assessment and long term strains of materials, especially for public constructions where the human and economic repercussions are heavy to bear.

Low rise reinforced concrete (RC) moment frame buildings are designed for dead, live, non coastal wind loads and moderate seismic zones according to 2006 IBC and ACI 318-05 provisions. Pressure-Impulse curves for typical columns in these buildings are generated using a modified TM 5-1300 procedure that uses a fiber hinge model. The curves are used to map damage from scenario blast pressures applied to building faces. Geometric and design parameters influencing redistribution of forces under external blast scenarios are investigated using nonlinear static finite element models.

Recent incidents of scaffolding collapses in the construction industry prompt the need for forensic investigations to help engineers have a better understanding of failures, their causes, and mitigation procedures. This paper presents a case study involving the investigation of a bridge scaffolding collapse; where interdisciplinary expertise of professional divers, underwater investigators, and structural engineers was employed. The study presents the process of forensic investigation; including assessment protocol, accurate data collection, evidence collection under water, and preservation of physical evidence. The gathered information describe the incident, type of collapsed scaffolding, underwater photos of the failed scaffolding, side-scan sonar survey of the accident site, scaffolding orientation under water, visible damage, weather, water visibility and conditions, probable mechanism of events, and summary of the incident. The study also presents the used tools/technologies for the identification, collection, preservation, and/or analysis of forensic evidence. The case study underscores the value of forensic engineering techniques to identify design/construction problems and to elevate the understanding of professionals engaged in forensic engineering.

The purpose of this paper is to present straightforward statistical methods that may be used in performing structural evaluations. A structural evaluation can be necessitated by several situations including: proposed change in structure use; damage to a structure due to an event, including failure (i.e. forensic evaluation); noticeable deterioration or poor performance; the need to verify as-built conditions, during or after construction; the desire to ascertain a specific material property; and the desire or need to assess overall condition. It is important to note that an evaluation should be entered into with clearly defined objectives. To the extent possible, these objectives should be ageed upon by all responsible parties prior to starting the evaluation. Frequently, however, the true scope of services to accomplish the objectives cannot be readily defined at the outset fo the evaluation. Therefore, subsequent tasks may be recommended following completion of the initial scope of work. In order to define the initial and/or final scope, it may be necessary to determine how many samples will be evaluated to determine the desired variable. Organizing structural elements in preparation for sampling is presented in the context of an evaluation hierarchy. Additionally, examples are presented to illustrate the application of the evaluation hierarchy and procedure. It should be noted, however, that sampling may not be necessary for all types or categories of evaluation and it is important to assess each structure on a case-by-case basis.

In this paper, a total strain-based hysteretic material model is proposed for nonlinear finite element analysis of 2D planar reinforced concrete structures. Although many concrete models have been proposed for simulating behavior of structures under cyclic loading conditions, accurate simulations remain challenging due to limited understanding of failure mechanisms. The proposed model is equipped with a fully generalized hysteresis rule and is formulated for ID plane stress nonlinear finite element analysis. The proposed model has been verified with a series of experimental results of 2D RC panels.

Buckling-restrained braces (BRBs) have recently become popular for use in the primary lateral-force-resisting systems of structures located in high seismic regions of the United States. A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression. Concentrically-braced frames (CBFs) incorporating BRBs are known as buckling-restrained braced frames (BRBF). Since BRBFs are a relatively new structural system in the U.S., current design provisions require qualification tests to demonstrate acceptable BRB performance. Numerous isolated BRB tests have been conducted in support of building projects, and several large-scale BRBFs have also been tested. In general, these experiments have shown that BRBs exhibit robust cyclic performance and possess large ductility capacity. Although procedures for predicting BRB maximum ductility demands have been developed [19], no generally accepted method exists for predicting the cumulative plastic ductility (CPD) capacity of BRBs, where CPD capacity is defined by the cumulative plastic deformation sustained before fracture of the steel core. In addition, CPD capacity has been shown to be dependent on loading history; Carden [9] and Fahnestock have observed that braces which undergo large maximum deformations exhibit lower CPD capacity than those braces which undergo relatively smaller maximum deformations. Furthermore, other important parameters affecting capacity have not been clearly identified yet. As an effort to answer these needs, this paper develops ductility capacity models for BRBs using a Bayesian methodology. As one of the few CPD capacity models available, Takeuchi developed a deterministic fatigue model. This model can account for the effect of loading history on BRB CPD capacity by dividing the imposed brace deformations into skeleton and Bauschinger parts as described by Benavent-Climent. By contrast to the deterministic approach by Takeuchi, this research effort employs a Bayesian methodology, which is probabilistic in nature. Through this method, test observations are used to update the capacity model parameters based on the probabilities that the observed results would be predicted by the model. The result is a model that relates CPD capacity to selective predictive parameters. Although subjective information to select a distribution prior to the updating is not available, a Bayesian methodology is selected because the method (1) produces unbiased models, (2) is flexible in regards to model form, (3) can accommodate both failure and non-failure test specimens, (4) quantifies the model error probabilistically, and (5) provides the ability to identify important parameters affecting capacity.

In the last decades of the XXth century the development of new technologies such as the thin monolithic meniscus mirrors with active optics, the segmented mirrors and the adaptive optics broke the limitations in the feasible diameter for the primary mirror and caused the origin of the 8–10m class telescopes. Considering the successful operation of 8–10m class telescopes in operation as the KECKs and the VLTs, both the American Community and the European Community began to prepare the next generation of telescopes, the Extremely Large Telescopes. Within the American-Australian Community two projects are currently being developed: the TMT (Thirty Meters Telescope), a 30m segmented mirror telescope developed by USA and Canada, and the GMT (Giant Magellan Telescope), a 24.5 meter aperture multi mirror telescope developed by USA and Australia. In Europe, the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) launched in December 2006 the Detailed Study of the European Extremely Large Telescope (E-ELT). The E-ELT is a 42m segmented primary mirror telescope with a five mirrors optical configuration. With respect to its enclosure, after some preliminary studies of different alternatives, a non co-rotating spherical dome configuration was selected.

Large constructions built using Geosynthetic Reinforced Earth (GRE) have become ever more popular in the last ten years as an alternative to reinforced concrete constructions. The possibility of adding green facing to these constructions has particularly helped to open new areas of application. The first major construction in Germany with a front inclination of 80°, a total height of 19,7m and a total length of 215m was built in 1997 in Iserlohn. Deformation measurement points were installed on the front of the embankment after construction had been completed and the measurements have been recorded for ten years now. In the presented paper the basics of this extremely unusual embankment and the recorded measurement results monitored over long periods of time will be presented and discussed. Bridge abutments represent a particularly demanding technical problem because of the low levels of deformation permitted and the difficult situation in the intersection area between the construction and the adjoining filling soil. In this paper, the first bridge abutment made using Geosynthetic Reinforced Earth in Germany (2000) in Ilsenburg is also presented.

Performance-based methodologies are becoming the norm for seismic design and evaluation of building structures, recognizing that designs based on conventional code methodologies may result in inconsistent seismic performance. However, use of these methodologies is not as widespread for non-building structures, which may pose unique structural problems that can also benefit from a performance-based design and evaluation approach. This paper presents performance-based seismic design of a proprietary self-supporting enclosed industrial storage rack system with a box-type steel structure whose exterior dimensions can be varied to accommodate required storage space and geometric constraints. The lateral load resisting system comprises moment resisting frames with bolted connections in one direction and a combination of moment resisting frames and corrugated panels welded to the columns in the orthogonal direction. Three-dimensional nonlinear finite-element models are developed for structural analysis. Structural adequacy is evaluated through (1) AISC-LRFD criteria using a linear response-spectrum analysis and (2) performance-based provisions of FEMA 356 and FEMA 450 for life safety using a nonlinear pushover analysis. The results of the structural evaluation indicate that for more than half of the configurations, the performance-based criteria control the design and rack content weight capacity. Relying solely on elastic analysis and the LRFD design requirements, while satisfying code requirements, leads to structures that violate performance requirements in terms of excessive beam plastic rotations and column axial forces, indicating potentially poor performance during actual seismic events. Furthermore, P-delta effects, in conjunction with large plastic deformations and column compressive loads, significantly reduce the content weight capacity for taller systems with some configurations being disqualified for high seismic regions.

A recent proposal in Asia called for a ballpark roof that opens like flower pedals with mechanized roof elements having cantilevered spans of two to three hundred feet. The Devil Rays have recently unveiled plans for a new MLB ballpark in St. Petersburg, Florida. This design calls for several acres of fabric to be deployed and tensioned over a cable net structure in the event of rain. When not in use, this fabric roof is collapsed and stored under the inboard edge of the sunscreen structure that covers the seating area. These design challenges call for a variety of new and innovative materials, structural systems, and mechanization methodologies. The keys to the success of integrating large mechanized components into these future stadiums will be much like those of the past. Proven methodologies and technologies should be used when possible. When the design calls for something new and innovative; ample computer modelling/analysis, reduced scale modeling, and full scale prototype testing is imperative in order to validate design concepts and theories as they develop. The limits of this kinetic architecture revolution are bounded only by the vision of the owners, the creativity of their architects, and technical innovativeness of the engineers and constructors that bring these archictectural icons to life.

There are two primary factors that influence the selections of a structural fabricator, cost and schedule. When compared to North American fabricators their Chinese counter parts have significantly lower costs for shop labor. This allows the Chinese to price fabricated steel at 30 to 40 percent less. Heavy industrial projects typically purchase steel directly from the mills rather than from warehouses or service centers. For the past couple of years North American steel mills have been rolling structural shapes at a slower pace than they have previously. In some cases mill orders must be made six months prior to fabrication. This is not the case in China. Our company started focusing on the prospect of using Chinese fabricators in the 90's for a power plant project in Australia. Since then we have investigated means and methods to make the utilization of Chinese Steel possible. To date several industrial projects, including power plants, mining facilities and liquefied natural gas refineries, have been completed using various Chinese fabricators. These projects have been economic success but not without many new challenges and lessons learned. With the cost of structural steel and the lead times for procuring domestic steel increasing, Chinese fabricators have been making inroads into the North American market. The use of off-shore fabricators and locally rolled Chinese steel presents a new set of challenges for the structural engineer. Materials, mills, fabricators, inspection, design, detailing, and transportation must all be considered in order to successfully incorporate Chinese fabrication into a project.

Hurricane Katrina (2005) brought unrivaled destruction to buildings along the Mississippi Coast, generating thousands of property insurance claims. Hurricane Katrina had been a Saffir-Simpson Category 5 storm only 18 hours prior to making landfall at the Category 3 level along the Louisiana/Mississippi state line. At landfall, it still contained enormous potential for storm surge — far greater than the Category 3 landfall designation (based only on sustained windspeed) might indicate. As a result, damage from storm surge tended to be far more severe than damage from wind action, though many buildings sustained some levels of damage from both storm surge and wind. Exclusion of flood damage from standard property insurance policies has resulted in partial or full denial of many Hurricane Katrina-related damage claims, as District Court rulings in Mississippi have considered flood damage to include damage from storm surge. An unparalleled series of legal challenges has followed — pitting homeowners against insurers and requiring resolution of such questions as: 1 Was the residence destroyed by wind or water? 2 How much wind damage, if any, was sustained prior to the eventual destruction of the residence by storm surge? Settlement of these legal challenges has necessitated the separation of probable wind damage and storm-surge damage. The separation of damages is particularly complicated when structures have been completely destroyed or when engineers have been asked to determine wind and water damages long after critical evidence has been removed from the site. However, additional significant data concerning region-wide wind-speed and storm-surge levels (and the timing thereof) may not be available until several months after the hurricane, once detailed analysis of available region-wide observations has concluded. These regional timeline data provide a valuable resource for engineers in the reconstruction of probable wind/surge damage sequences some time after the hurricane damage has been removed.

Hurricane Katrina made landfall near the mouth of the Mississippi River in southeast Louisiana and again at the Pearl River delta on the Louisiana/Mississippi border on the morning of August 29, 2005, as a Category 3 intensity storm on the Saffir-Simpson Scale. Katrina brought high winds and devastating storm surge to locations across southeast Louisiana and coastal Mississippi, destroying many homes and other structures as it passed. FEMA estimated that the total economic losses due to the storm were in excess of $125 billion. The American Red Cross estimated that 275,000 homes were damaged by the storm. In the storm's aftermath, many homeowners and business owners with properties in flooded areas found themselves engaged in disputes with their insurers over the distribution of their flood and wind damage claims. The resolution of these disputes has been complicated by the fact that multiple damage mechanisms contributed to the total damage that property owners were faced with upon their return. Decomposing the resultant damage into its respective components is not always an easy task. It requires an accurate technical knowledge of the environmental conditions and their timing, and an engineering background deep enough to understand the effects that these conditions would have on structures.

Following Hurricane Katrina, engineers from around the country were called upon to evaluate commercial and residential structures along the Louisiana and Mississippi coasts to determine the extent of damage. Of paramount importance to many engineering clients was the separation of wind damage from flooding damage, and the engineer became a focal point for the resolution of many disputes between property owners and their insurance carriers. In these situations, it is essential for the engineering consultant to maintain their independence, objectivity, and adherence to good engineering principles. This requires an understanding of the forces produced by the storm, accurate evaluation of physical evidence available, and the proper interpretation of commonly available storm data. There has been a great deal of research performed regarding the effects of wind and water on structures, and an engineer should be able to rely upon industry-accepted tools like the Enhanced Fujita Scale to determine the relative force level between wind and water, even when the subject structure has been destroyed. Recent advances in computational weather analysis and weather radar can be helpful in some instances; however, the results of these tools should always be verified with real data, and they cannot replace detailed field inspection. When reporting the results of a wind/water analysis, it is important for the engineer to clearly communicate their conclusions and accurately represent the data that is quoted.

Remote-sensing imagery of hurricane-affected areas has proven helpful for rapidly preserving the damage scene soon after a hurricane and for establishing neighborhood damage patterns of both wind and storm surge. Remote-sensing signatures of wind and storm-surge damage have been identified for the primary types of residential construction along the U.S. Gulf Coast. For the three main types of residential construction on the Mississippi Coast, wind damage to buildings has a similar appearance, while remote-sensing signatures of storm-surge actions depend largely on construction type, as described herein. The presence and location of debris relative to visible sources (e.g., roofs) helps to identify storm-surge damage to slab-on-grade and well-anchored pier-and-beam residences. Analysis of remote-sensing imagery also can identify the buoyant transport of intact buildings and intact roof assemblies that have been removed from supporting walls; however, in near-vertical imagery it is difficult to distinguish intact buildings from detached-but-intact roof assemblies. Neighborhood damage patterns derived from remote-sensing imagery have been employed in determining probable wind and storm-surge damage to residences resulting from Hurricane Katrina.

Wood piles are a mainstay of residential construction in certain coastal areas, but some structural engineers have sought improved ways of recognizing that they are not fixed at the ground level—an assumption often made in design—but instead interact with the soil below ground level. This paper is a broad summary of how an analytical study of wood piles may be used to propose a new design procedure. The objective of the study is to propose a new design procedure for wood piles that acknowledges the interaction of the pile and the soil below ground level. Within this objective is the need for the design procedure to be expedient, conservative, and able to be employed without involving finite element or similar software.

Beginning in early 2006, the APA Research Center expanded to include the capability of testing full-scale three-dimensional houses. This paper summarizes results of wall bracing racking tests from a full-scale 25 x 37.5 x 9-ft-tall three-dimensional wood frame house. Monotonic wall racking loads were applied at the corner of the structure in line with a single wall (the 37.5-ft-long wall). The concept of the setup was to investigate the wall behavior as part of a three-dimensional structure i.e. walls and roof are built around it. The roof diaphragm was flat. No finishes (i.e. gypsum, siding, roofing, etc) were installed and the walls were essentially bare with the exception of the applied bracing panels. A total of 23 different tests were conducted. Wall racking was generally limited to 1.5 inches in displacement to minimize damage and repair between tests. Repair was made after each test and the 23rd tests was a repeat of the 1st to compare results after repeated testing of some of the same framing components. The focus of these tests was primarily on the International Residential Code, IRC, wood structural panel type wall bracing. A number of variables were studied, including: 1 Hold-down devices in building corners, 2 Return corners, both 2 feet and 4 feet, 3 Panel placement at corners or away from corners, 4 Single diagonal 1 x 4 bracing, 5 Isolated wood structural panel bracing, 6 Continuous wood structural panel bracing, 7 Continuous wood structural panel bracing cut around openings, 8 Walls braced only by 6:1 aspect ratio portal frames, 9 Wall braced with 50 percent 6:1 aspect ratio portal frames mixed with other continuous wood structural panel bracing. This paper is a summary that discusses the global response of the structure to the applied loads. For more detailed information, including a detailed analysis of local wall responses, please refer to Martin et al.

Wood has been, and will continue to be, a valuable resource for construction. Wood is user-friendly and, properly managed and processed, environmentally friendly. While vulnerable to the environment from which it grew, properly designed, constructed and maintained, wood assemblies can last for decades.

Most wood-frame houses are built without the benefit of structural design. Often, when engineered wood components are called for, the local building official will insist that these elements be designed by a registered professional engineer. In these cases, the resulting design may only be partially engineered. Often, the building official insists only that the engineered piece be sealed. An engineer may be called upon to provide only this service, with no mandate or budget to make a thorough review of the building, or to understand fully the context into which the engineered piece will be placed. The engineering may even be arranged through the local lumber yard. When this happens, the design sheets for wood trusses, joists, and/or girders may be sealed, but the engineering certification does not extend to the entire building, or even to the elements that support the engineered piece. This paper explores the problems that arise from partial engineering, whether it is done by an engineer constrained by budget, opportunity, or experience, or by a lumber yard where pre-packaged software supports engineering the piece, but there is no field investigation to understand the remaining issues.

A principles of mechanics model to predict the strength of wood structural panel portal frames has been developed. The wood structural panel portal frame consists of a wood structural panel overlapping a header to form a moment resisting connection to resist in-plane lateral loads. The advantage of portal frames is that they can resist relatively high lateral loads for a small wall width. The model is based on moment couples and shear strength of the components. Model predictions are compared to test results for a variety of portal frame constructions that have been tested. All portal frame walls were tested with the SEAOSC SPD cyclic load protocol for in-plane shear resistance. Portal frame constructions investigated in this study range from 16 to 24-inch wide, 8 to 10-ft tall, sheathed with OSB or plywood, and with and without hold down devices at the base of the wall segment. Also investigated are portal frames built on raised wood floor assemblies with variable base of wall restraint configurations which are modeled with moment couples. The model is compared to ten unique portal frame constructions that were tested. Comparing the model to the test results shows that the model accurately predicts the strength to within about 5% on average.

The Strut-and-Tie modeling technique is a widely accepted design approach for reinforced concrete deep beams. However, there are significant differences between various design code implementations for this technique with respect to the reinforcement tie influences on the capacity of adjacent concrete struts. Furthermore, each design code specifies different limits on the maximum permitted stress in the ties. Since high-performance reinforcement continues to gain wider acceptance in industry practice, it is necessary to validate existing design approaches, including Strut-and-Tie modeling, for the mechanical properties of these new materials. An experimental campaign was conducted to understand the performance of large-scale reinforced concrete deep beams constructed with high strength longitudinal reinforcement. Test results from six beams are presented, where primary test variables included the shear-span-to-depth aspect ratio and the longitudinal reinforcement ratio. All specimens included a constant quantity of transverse reinforcement. Testing was conducted under a four-point bending configuration, on specimens with cross-section 300 mm wide x 607 mm high. Specimens failed either by shear-compression, or by a flexural mode of longitudinal reinforcement yielding or crushing of the flexural compression zone. The results showed that the member capacity decreased as the shear-span-to-depth ratio increased, and as the longitudinal reinforcement ratio decreased. It was possible to design members to efficiently exploit the high strength reinforcing steel using Strut-and-Tie modeling techniques according to CSA A23.3-04 and ACI 318-05 provisions.

After the 9-11 attack, protection of iconic, strategic and public structures subjected to impact and explosive loadings has been a major topic of research, which also involves with progressive collapse, thermal effects, damage analysis and advanced material technologies. The demand for Light Weight Aggregate Concrete (LWAC) in many recent applications is increasing owing to the fact that lower density of structural material leads to lower gravitational loading of structures and consequently lower earthquake forces. Nevertheless, LWAC usually suffers from low ductility similar to other brittle materials. A remedy is to add fibers to increase the ductility and energy absorption. As these lightweight constructions may be subjected to impact loadings during life time period, investigating the impact behavior of concrete structures is necessary. A few studies were performed on impact behavior of normal fiber reinforced concrete. Nonetheless, there is no report on impact behavior of fiber reinforced lightweight aggregate concrete. In this research, cylindrical fiber lightweight aggregate concrete samples with 150 mm diameter and 60 mm thickness are exposed to low velocity impact load (according to the standard of ACI 544-2R "impact test on fiber reinforced concrete") and compared with plain concrete samples. Coarse pumice aggregates were used in concrete. Also, polypropylene was utilized in mixtures proportion of concrete. In addition to experimental approach, a numerical simulation has been performed to analyze the test specimens under impact loadings using the LS-DYNA finite element software. Comparison of numerical predictions with experimental results illustrates fairly good agreement.

Centrifugal concrete has been quickly developed in prefabricated concrete members, since it was invented by W.R.Hume in 1915. It was reported that hollow centrifugal concrete (HCC in short) filled steel tubular pile was developed in Japan in 1972. In 1994, it was manufactured in Shanghai China. Recently over 6,000 HCC filled steel tubular piles (400,000m in total) have been installed successfully for industry equipment foundation in Shanghai, and it also can be used as frame members in industrial structures. HCC filled steel tubular members can be manufactured in plant and can be transported and installed like other prefabricated steel and concrete members. They have the advantages of cost saving and internal resistance to corrosion. HCC filled square steel tubular members are developed which joints and connections are more convenient than that of HCC filled circular steel tubular members. Load capacity in compression and bending of HCC filled steel tubular member is studied by theoretical analysis and experiments. It is proved that load capacity in compression is influenced by the strength and section area of concrete as well as steel, constraining coefficient, concrete hollow coefficient. As the filled HCC is of C80 strength grade, in order to decrease the thickness of steel tube and improve the constraining coefficient, HCC filled high strength steel tubular member is developed in industrial structure application. In this paper, two important problems of HCC filled steel tubular member used as pile are discussed. The first problem is the reliability degree of axial load capacity, the other is dynamic interaction between HCC and steel tube caused by pile driving pulse and bond strength.

In these two sets of tests, valuable information about the serviceability of bio-based composite structures was obtained. The creep experiments and analysis addressed the performance of the bio-based composite material under sustained load conditions. The thermal bending problem determined a coefficient of thermal expansion for the bio-based composite and analyzed the deflection of a composite sandwich panel roof exposed to a severe thermal gradients. The creep experiments demonstrated that the bio-based composite material shows strong viscoelastic behavior. The behavior can be accurately modeled using a "standard solid" model. The tests also showed that the material properties of the bio-based composite change as the material ages. Although prone to creep deflection throughout the life of the material, the creep rate and the magnitude of creep deflection decrease significantly as the material gets older. Since traditional "post cure" processes would not be feasible for large-scale panels, it may be advisable to allow a curing period during which the composite can gain additional stiffness before being erected as a roof. The CTE experiments and analysis determined a coefficient of thermal expansion for the bio-based composite material. The value of 3.70 x 10^–6 is comparable to those of traditional building materials. The displaced shapes of a hypothetical roof subjected to extreme thermal gradients were calculated. For a worst case 130 °F temperature gradient occurring during the winter, the maximum deflections, occurring at midspan, were well below code serviceability requirements.

Based on past performance during seismic events, masonry veneers can pose a significant hazard to public safety. Because there is a significant inventory of masonry veneers in the built environment, this risk is substantial and must be quantified and systematically mitigated. In addition, current design provisions must be re-evaluated and refined to ensure that new building construction produces masonry wall assemblies with acceptable seismic performance. To address these concerns a number of researchers have investigated this type of wall system under seismic loading. To extend this work further, an effort is being funded under the George E. Brown Network for Earthquake Engineering Simulation to evaluate the response of masonry veneer systems under seismic loading. One of the goals of this investigation is to develop accurate dynamic wall system models for seismic excitation. These models are to be used to support development of performance based design under frameworks such as those proposed by ATC 58. As a part of this multi-institutional investigation, the performance of clay brick veneer walls constructed with wood stud backing walls are being experimentally evaluated. This phase of the testing program subjected full scale brick veneer/wood stud wall specimens constructed to typical code defined residential configurations to quasi-static cyclic in-plane and out-of-plane loadings. A variety of wall specimen configurations are being evaluated, including variables such as the effects of joint reinforcing, the type and spacing of ties, and the effects of openings. The result of these tests will refine the analytical models being developed and support the development of large scale shake table building specimens that will be evaluated at a later date. The results of the quasi-static out-of-plane loading tests are presented in this paper. The following sections describe the details of the testing program.

Light frame low-rise buildings perform relatively well under seismic loads due to their low masses and large energy-dissipation capacity. While safety issues such as loss of life seem to be adequately addressed, the serviceability of these buildings after moderate to severe earthquakes can be compromised. Traditionally, exterior walls in residential buildings (single-family dwellings) have been assigned the lateral load resistance function with partition walls largely neglected. Although extensive studies have been undertaken to develop better understanding of wood-frame construction, few studies have addressed steel stud wall systems. There is an increasing interest in the use of steel stud light-frame systems for residential construction. There is a research void related to information on how structural performance of steel stud walls compare with wood stud systems for interior walls under lateral loading conditions. For interior wall applications, gypsum wall board (GWB) contributes to the lateral load resisting systems, as evidenced by the damage to GWB in past earthquakes. The overall objective of the study reported herein was to develop a better understanding of the differences in behavior of interior GWB sheathed wood stud and steel stud light-frame wall systems under monotonic and cyclic racking loading conditions. It was of interest to also evaluate the effect of finishing GWB joints with tape and joint compound on the lateral load resistance of both construction types.

Nonstructural components comprise an integral part of the buildings. Due to their high inventory cost and effect on loss of operation, they are often critical to a buildings' seismic performance. Suspended ceilings are one of the most widely used nonstructural components. They are a standard feature of modern office building. Past earthquakes have demonstrated the susceptibility of suspended ceilings to failure during seismic events. To address this vulnerability, design codes have developed specific installation criteria for suspended ceilings. However, these units are very difficult to analyze. Thus, there is limited data available to assess the efficacy of such installation. Furthermore, ceiling manufacturers have been investigating and have developed alternate and more time-efficient installation techniques. In lieu of analysis, earthquake simulation testing can be employed to assess the seismic performance of ceilings and to qualify comparatively the alternate perimeter installation.

A unique full-scale study was undertaken to consider the behavior of gypsum board partition walls and typical suspended ceiling systems. Each specimen consisted of four partition walls which created an enclosed space and allowed for the interaction of perpendicular walls framed into each other to be evaluated. The effects of discontinuities in the partition walls were studied through the placement of a large opening in one of the walls and a door frame in the opposite wall. The setup also allowed for the evaluation of interaction between the walls and ceiling system. The specimens were loaded through the use of a shake table such that the behavior and damage could be correlated with particular drift levels. The non-structural walls underwent a rocking behavior as a result of the presence of a perpendicular wall. Significant damage was seen as drift levels reached 1/66 radians with most of this damage concentrated around the door frame and at the corners of the partition walls. Only minimal damage was imparted to the ceiling systems as they performed to design standards. The results of this test were critical in providing preliminary data for the full-scale study of a four-story steel moment frame tested at E-defense in Japan, which incorporated these non-structural systems.

An experimental and analytical investigation was conducted to determine the seismic performance of timber structures with the application of spray-applied infill polyurethane foam (SPF). Full-scale timber shear walls were constructed and tested using the CUREE-Caltech pseudo-static loading protocol and results were used to calibrate a computer based simulation model. Nonlinear time-history analyses of one- and two-story structures over a range of building weights were conducted with ground motion suites of varying hazard levels. It was shown with experimental testing that there is as much as a 30% increase in peak post-yield strength with application of SPF. Computer based simulations suggest that with the application of SPF to standard timber shear walls there is both a reduction in drift demand (up to 40%) as well as ductility demand. However, this benefit is indirectly dependent on number of stories (one or two), building weights, building periods, and ground motion severity.

The seismic resistant characteristics of low yield point (LYP) steel shear wall are examined in this reported research. In the LYP steel plate shear wall system, the LYP steel is selected for steel panel while the boundary frame is constructed by conventional structural steel. A series of experimental studies were carried out to examine the inelastic shear buckling of LYP steel plate panel under monotonic load. The effects of width-to-thickness ratio on the shear buckling of LYP steel plates were examined. Cyclic loading tests were also carried out for multistory LYP steel plate shear wall in order to examine its stiffness, strength, deformation capacity, and energy dissipation capacity. The effect of width-to-thickness ratio of steel plate and the design of beam-to-column connections on the boundary frame were also examined. Excellent deformation capacities and energy dissipation capacities were obtained for all specimens tested. The LYP steel plate shear walls were able to maintain stable even have deformed to 0.06 radium of story drift angle. Based on these studies, suggestions are made for the design of LYP steel plates shear wall system.

A new MBMA/AISC guide for frame design using web-tapered members [Kaehler et al. 2008] is due to be released in the near future. This guide extends the AISC [2005] provisions to the design of web-tapered members. The fundamental concepts employed in this extension are similar to those employed in prior AISC provisions, which are discussed in detail by Lee et al. However, there are a number of important differences that make the new procedures more general and easier to use than the previous provisions. In this paper, the procedures detailed in the new MBMA/AISC design guide are illustrated by showing results for a representative modular metal building frame. The similarities and differences between the new procedures and the previous AISC provisions are discussed.

In the past, most metal building systems were designed using ASD and the effective length method. With the 2005 AISC Specification adoption in IBC 2006, design and analysis methods are changing rapidly. The stability requirements of Chapter C limit the effective length method of analysis to structures with relatively small second order effects. It was known in the past that the effective length method did not always accurately predict the true behavior of all structures. For metal buildings, this can be particularly true of applications with heavier loads from floors or mezzanines. To account for this uncertainty of the analysis and design method, it became common practice to use more conservative load combinations and heavier floor live loading than is required for the floor use. This paper reviews a rigid frame that Chief Buildings designed using ASD per the 9^th Edition of AISC with the effective length method. A comparison is then made with an analysis of this structure with the Direct Analysis Method from Appendix 7 of the 13^th Edition of AISC using both ASD and LRFD load combinations. From the analysis of this rigid frame, it was discovered how various load combinations and methods of applying floor live loads can have very dynamic effects on the amplification of moments due to the P-Δ effects. This physical attribute becomes more apparent when using the Direct Analysis Method. Another finding was that slight variations in the frame configuration and modeling can greatly affect the P-Δ moments. The frame under investigation is a 4 span single slope modular frame that has two floor levels in the right span. The floor is designed with simple span floor beams with pin-pin "leaning" columns in the center. The floor also cantilevers 6.5 feet from the interior column. The exterior columns are tapered; the interior columns are prismatic with fully rigid, fixed connections to the rafter. The rafter has tapered and prismatic segments with variations in flange sizes and web thicknesses. The frame model is shown in Figure 1. The focus of this investigation is placed on the moment at the top of the left interior column. Note that this column does not carry any gravity floor load directly, but it is assisting with resisting lateral sway.

The Metal Building Manufacturers' Association (MBMA) and the American Institute of Steel Construction (AISC) are finalizing a new addition to the AISC Steel Design Guide series entitled "Frame Design Using Web-Tapered Members" (Design Guide). This document presents a comprehensive and up-to-date approach to the design of frames using web-tapered members. The methods provided are applications of, and extensions to, the 2005 AISC Specification for Structural Steel Buildings. The new Specification does not include an appendix with provisions for the design of tapered members, unlike previous AISC Specifications dating back to 1978. The new design guide is intended to fill that gap. The recommendations are based on current and recent research into the behavior of web-tapered members. A significant amount of this research was conducted by the document's coauthors at the Georgia Institute of Technology in the preparation of this document. The major sections of the Design Guide are: 1. Introduction, 2. Web-Tapered Member Behavior, 3. Design Basis, 4. Stability Design and Analysis Requirements, 5. Member Design, 6. Frame Design, 7. Annotated Bibliography, 8. Appendices.

Full-scale testing of a metal building was conducted to develop a seismic design procedure for metal buildings. Testing indicated that the system has high system overstrength and high deformability. A design procedure based on drift considerations is proposed. Drift capacity is calculated from routine design, and drift demand can be calculated from the design spectrum. A case study of 10 metal building frames designed in accordance with the current practice indicates that, for those cases where metal sidewalls were used, a safety factor of 1.4 can be achieved without increasing member sizes. When hard sidewalls are used, however, metal frames designed in accordance with the current design practice can be significantly undersized.

Curved alignments of highway bridges are often necessary for smooth traffic. Furthermore, architects are increasingly opting to more curves in building as aestheticism is being an important element in most designs. Unlike the case of un-curved structural elements, curvature induces complicated stresses and elements behaviour can be quite different from the behaviour of similar but straight elements. This research aims to develop an analytical procedure to predict the behaviour of curved thin-walled curved beams and develop a formulation that helps design against out-of-plane buckling. The analytical approach considers the nonlinear behaviour and large deformation. An extensive theoretical investigation on large displacement behaviour has been carried out using the principle of minimum total potential energy and compatibility equation. The paper presents the nonlinear equations that describe the elastic behaviour of curved thin walled panel. To verify the proposed equations, out of plane displacements are compared with the results of experimental testing. The proposed equations give a good agreement with the test results.

The historical high building density in New York City resulted in narrow structures that are sensitive to both underpinning and demolition operations. Presently these operations are dominated by methods based on empirical approaches. The paper discusses the use of engineering analysis to reduce damage to adjoining brownstones or tenement buildings during demolition and specially underpinning. The author has investigated a number of recent construction failures and has concluded that engineering evaluation, calculations and analysis can improve traditional methods. He presents the broad lines of a methodology to identify the buildings most likely to suffer during underpinning and demolition. The methodology can justify installation of protection measures prior to the start of construction operations.

Structural insulated panels (SIPs), which are structural sandwich panels consisting of a foam plastic insulation core securely bonded between two structural panel facings, such as oriented strand board (OSB), are one of the fastest growing products in the U.S. housing construction industry due in part to its energy and construction efficiencies, and its distinctive structural performance characteristics. These components are used in commercial and residential construction projects worldwide. In the U.S., the design information for SIPs is typically developed and provided by SIP manufacturers through proprietary code reports since the International Building Code (IBC) has not provided coverage for SIPs. In an effort to fill the void in the U.S. building codes and to expand the SIPs market, the Structural Insulated Panel Association (SIPA), APA, and the National Association of Home Builders Research Center (NAHBRC) jointly developed a prescriptive standard for the design and use of SIP walls in residential construction in 2006. Partially funded by the U.S. Department of Housing and Urban Development (HUD), this prescriptive standard specifies material requirements for manufacturing, and provides design and installation recommendations. The basic elements of the prescriptive SIP standard were adopted into the 2007 Supplement to the 2006 the International Residential Code (IRC) in May 2007. While SIPs may be used in roof and floor applications as well, the effort of standardization has been focusing on wall applications up to this point. As a strategic alliance with SIPA, APA worked with its OSB producing members in establishing characteristic performance values for OSB panels suitable for SIPs. Full-scale SIP assembly tests using the characteristic OSB facings and a standard foam core have been conducted at the APA Research Center in Tacoma, WA, on transverse loading, axial loading, and racking shear. In addition, bending capacities of various SIP lintel sizes have also been determined. These results served as the basis for the prescriptive SIP standard and Section R614 of the 2007 Supplement to the 2006 IRC. As an accredited standards developer by the American National Standards Institute (ANSI), APA — The Engineered Wood Association (APA) has also formed a standards committee to develop a consensus-based Standard for Performance-Rated Structural Insulated Panels, PRS-610. This paper describes the development of prescriptive recommendations for SIPs for use in wall applications. The minimum OSB and foam properties required for the prescriptive SIPs are characterized. The performance of prescriptive SIPs, as developed based on the full-scale assembly tests, is also presented.

A new technology in reinforced concrete is seamless large five-sided box modules. The advantages of this type of structural form are discussed in the context of its application to the construction of complete housing units built in a single day. These modules are cast integrally with large window and door frames and MEP systems. They are linked with each other, both horizontally and vertically, to develop complex buildings which may increase the freedom of forms of future buildings. The speed of erection and the high quality finishes result in potentially financing cost reductions and increased safety for workers building tall buildings. This technology is currently being used in schools and multi-family housing in Florida. Finite element analysis of the larger boxes (24 feet wide x 48 feet long x 10 feet high and weighing 60-tons each) shows the highest stresses occurring during the form-releasing and hoisting phases. The paper discusses deformations typical of these large modules and their solutions.

Accidental circumstances must not result in progressive and disproportionate collapse. Strategies for achieving this goal are studied and corresponding design concepts are developed. The focus is on large and slender high-rise buildings with a high degree of significance and exposure. The study is based on an examination, one by one, of five general approaches: non-structural protective measures, specific local resistance, alternative paths, isolation of collapsing sections, and prescriptive design rules. Departing from the specific-local-resistance approach, an arrangement of independent primary and secondary load transfer systems is arrived at where the primary system consists of a compact reinforced-concrete tube forming the building's vertical spine. Based on the isolation approach, a vertical segmentation accomplished by strengthened floor slabs is suggested where a commencing pancake-type collapse is arrested by dissipating energy in shock-absorbing devices. These two design concepts maximize the tolerable accidental circumstances. The alternative-paths approach can be used for secondary systems or when a set of limited accidental actions is agreed upon.

The investigation of structures concerning their susceptibility to progressive disproportionate collapse is attracting increasing attention. At present, there is neither a uniform theory of progressive collapse and collapse resistance nor any agreement on terms and nomenclature. Codes and other relevant literature require a reduction in the susceptibility to progressive collapse. However, mainly qualitative and hardly any quantitative recommendations are provided. Collapse resistance can be influenced in various ways. One possibility is through the structural robustness. In a robust structure, no damage disproportionate to the initial failure will occur. To examine a structure in terms of its robustness, a quantitative description of the robustness by means of a measure would be useful. In this work, basics for the development of measures to quantify structural robustness are formulated. Essential definitions are suggested and the requirements for measures of robustness as well as possible applications are discussed. A selection of publications on the quantification of robustness, or related characteristics such as vulnerability, are presented and discussed regarding the proposed requirements and applications.

The review of the results provided from the performed investigations permit to identify some characteristics in the behavior of the bridge after a damage in the hanger suspension system, that are intrinsic to the structural system (see Fig.7), that are summarized in the following 4 aspects: 1) Minimum number of removed hangers and most sensitive location for the triggering of the progressive collapse: the bridge results to be more sensible to the damage at mid-span, where the removal of just 5 hanger for the symmetrical rupture and 7 hangers for the asymmetrical rupture is needed in order to trigger the collapse propagation. Shifting the initial damage location aside (about at 1/3 of the span) the asymmetrical rupture of 9 hangers is required for the collapse propagation, while moving the initial damage near the tower even the asymmetrical removal of 12 hangers has no global effects on the structure and very 7 hangers must be symmetrically removed on both sides in order to trigger the propagation of the ruptures on the adjoining hangers. 2) Preferential direction for the collapse propagation: to the higher damage sensibility of he bridge central zone counterpoises a lower acceleration of the collapse progression triggered by central ruptures, with respect to that one triggered by lateral ruptures. This effect is due to the particular configuration of the structural system that requires a growing hanger length from the centre to the sides of the bridge: when a chain rupture trigger, the ultimate elongation required to the hangers adjoining the failed ones increases as the collapse propagates (because the unsupported deck length also increases). If the initial damage occurs at mid-span, it involves the shortest hangers and the collapse propagation is partially slowed down from the growing element ductility of sideward hangers. On the contrary, a more intense initial damage is required sideways to trigger chain ruptures, but then the hanger breakdowns speeds up when moving toward the centre, where the hanger length decreases. 3) Qualitative measure that could possibly lead the collapse to an halt: in the case of a central rupture a closer increment in the section of the hangers (that remain instead the same for about 5/6 of the span length) could possibly provide for a collapse standstill. In the case of a chain rupture triggered in a lateral zone the preferential direction showed by the progressive collapse would probably make less effective such a measure. 4) Sensibility to modality of damage (asymmetrical or symmetrical failure): another consideration about the possible collapse standstill concerns the higher susceptibility of the bridge to an unsymmetrical hanger failure than to a symmetrical one: in the last case the symmetrical hinge formations determines a symmetrical moment increment on the deck box-girders, thus possibly allowing for an early deck segment detachment that would arrest the collapse.

The effects of prescribed damage scenario on robustness of structural systems with different degrees of static indeterminacy are investigated. Damage is viewed as a progressive deterioration of the material properties and its amount is specified at the member level by means of a damage index associated with prescribed patterns of cross-sectional deterioration. The variation of meaningful parameters of the structural response with respect to the values associated with the undamaged system are used to formulate dimensionless measures of structural robustness. The differences among robustness, redundancy and static indeterminacy are pointed out. Truss systems are then analyzed to investigate their robustness.

The tensioned fabric canopy roof covering the audience seating at the Toyota Pavilion performing arts center in Montage Mountain, PA failed from snow induced ponding during a snow storm in February 2007. A new fabric membrane was fabricated and installed prior to the opening of the summer season in June of 2007. Tensioned fabric membrane structures are unique in their capability to carry very high loads in relation to their self weight. This is due in part to the large deflection behavior of these structures that renders them relatively insensitive to specific load distributions. This same characteristic causes tensioned membrane roof structures to be uniquely vulnerable to ponding, typically snow induced. The Toyota Pavilion canopy structure had exhibited a vulnerability to ponding in previous winters and was scheduled to undergo modifications to improve its resistance. The paper reviews the ponding phenomena, the replacement of the tensioned fabric membrane, and the changes implemented to mitigate future ponding of the membrane roof.

Most tensioned fabric structures employ membranes that have support geometry resulting in anti-clastic curvature. A lesser number of structures have synclastic forms maintained by air pressure. Fabric membranes with little or no curvature must deflect substantially to resist out of plane loads, and their inefficient load resistance may result in high membrane stresses and heavy loads on the supporting cables and rigid elements. Large deflections may also result in conditions where membrane slope reaches zero under rain or snow loading, with ponding resulting. Uncurved or minimally curved surfaces are therefore generally avoided in design. Architectural, economic, or other reasons create many instances in which uncurved or minimally curved fabric membrane surfaces are desirable. Fabric roofs employing flat membranes can be economical, beautiful, and practical in certain conditions and with appropriate attention to the special design problems that are associated with them. The paper presents case studies of several recently built structures that employ uncurved or minimally curved fabric membranes. It explores the rationale behind the selection of flat forms, and considers how the special risks or costs associated with inefficient load resistance, high deflection, and the threat of ponding were addressed. The structures studied are recently constructed designs engineered by the author.

Urban societies face the challenge of working and living in environments filled with noise and vibration caused by construction, manufacturing, and transportation systems. Due to soaring prices of real estate in modern cities, air-rights developments are becoming more widespread. As residential towers and hotels are built over or adjacent to train stations, subways, and highways, traffic noise and vibration play an ever increasing role in causing discomfort to the occupants. Research laboratories conducting highly sensitive measurements and manufacturing plants for nanotechnology are also prone to disruption by feelable and audible vibrations. In this research, a wave propagation model is developed to predict train-induced vibrations in buildings. The analytical predictions are compared to experimental data obtained using an electrodynamic shaker in a full-scale building. The floor responses to controlled shaking are used to calibrate the wave propagation model by estimating model parameters using optimization techniques. Train-induced vibrations, introduced at the building foundation, are also measured and compared to analytical predictions.

A 4-story scale model building was designed and constructed for the purpose of predicting vibration levels at each floor. Mathematical models of column, beam, and slab elements were developed and combined, forming a system model. Each component of the scale model building was tested in order to validate their corresponding mathematical model. Measured data from the scale model building was then compared to analytical predictions. All analytical models successfully validated their corresponding physical model by accurately predicting resonant amplifications and average vibration levels. Finally, recommendations for the modeling of full-scale structures are presented.

In 2000, the Rollins Road Bridge in Rollinsford, New Hampshire was constructed with partial funding from the Innovative Bridge Research and Construction (IBRC) program administered by the Federal Highway Administration (FHWA). A requirement of the IBRC program is the use of high performance and innovative materials and instrumentation. This paper focuses on use of the collected data, from both strain and temperature sensors, to evaluate thermal performance of a CFRP-reinforced concrete deck. The sensor data will be evaluated based on its value in a long-term structural health monitoring program. The collected data will be compared with the predicted response for a finite element model created in SAP 2000. Also, a statistical analysis of the collected temperature and strain data will be presented for data quality analysis.

This paper illustrates a process for estimating the uncertainty in estimation of collapse capacity of buildings in seismic excitation using Monte Carlo simulation and FOSM method. The structure used in this study is a 4-story steel moment-resisting frame designed based on current seismic provisions whose collapse prediction has been validated through a collapse test of a 1:8 scale model structure at the University of Buffalo's NEES Equipment Site. It is shown that the uncertainty in estimation of collapse capacity due to uncertainty in estimation of deformation parameters of beams and columns that control component nonlinear behavior is moderately dependent on the correlation between these parameters. For the 4-story steel moment-resisting frame used in this study the uncertainty in estimation of collapse capacity due to component modeling uncertainties varies between 0.25 and 0.35 for correlation between these parameters ranging from 0.3 to 1.0. This is due to the fact that for the 4-story structure, the P-Δ effect is the major reason for collapse rather than building component deterioration. Results of this research show that the probability of collapse for the 4-story structure at the 2/50 hazard level can increase from 3% to 18% once a confidence of 90% is sought for the collapse probability.

Seismic performance-based design (PBD) is evolving as the preferred way for engineering of the built environment, especially for rehabilitation of existing buildings. By upgrading to meet specific performance objectives, it provides a critical link between engineering design, risk management, regulation, and policy. Implicit is the notion that probable seismic performance can be predicted. Guidelines such as the ASCE standard [1]: Seismic Rehabilitation of Existing Buildings and the FEMA report [2]: Seismic Evaluation and Upgrade Criteria for Existing Welded Steel Moment-Frame Buildings are now available, and have been accepted by some jurisdictions. These represent state-of-the-art thinking, but incorporate engineering judgment to bridge gaps where research is lacking. Benchmarking PBD against actual building performance is essential to assess its efficacy and to help guide its future development. Since PBD is relatively new, it is not yet possible to judge it via post-earthquake damage surveys. That leaves comparison to shake table tests as one of the best ways currently available to assess PBD. This paper presents a case study on the application of PBD methodology to a full-scale building recently shaken to collapse. The question addressed is: how well do PBD methods characterize an actual collapse?

Design engineers increasingly need to assess the performance of structures responding to extreme loading scenarios. Such scenarios often involve considerable inelastic behavior, and examples include progressive collapse, blast loading, and earthquake response. Concrete slabs can contribute significantly to overall structural performance during such events, and the ability to efficiently include nonlinear slab behavior in structural models would be a valuable addition to both bridge and building design. High fidelity, nonlinear finite element analysis programs do have the ability to predict geometric and material nonlinear behavior of both beam and shell elements, but these programs typically demand heavy personnel commitments and computational resources. Many basic structural analysis programs commonly used in design offices do allow nonlinear behavior in beams, but few currently allow nonlinear behavior in shell elements. The nonlinear shell formulations that are now offered by some commonly used basic structural analysis programs are often insufficient, difficult to use, or computationally intensive. Therefore, design engineers would benefit from a method to compute the inelastic response of slabs using familiar analysis tools. This paper presents the development of a procedure to represent the inelastic response of slab components using a beam element mesh in a structural analysis program frequently employed by design engineers.

In this study, the framework of performance-based earthquake engineering is used to predict the seismic collapse risk of California's older (non-ductile) and modern (ductile) reinforced concrete frame structures. Collapse performance assessments are conducted for two sets of structures, those designed according to an out-dated building code, the 1967 Uniform Building Code (UBC), and those designed according to modern building code provisions, the 2003 International Building Code (IBC). Each set includes 2, 4, 8 and 12 story reinforced concrete frame buildings, designed as space and perimeter frame systems. These preliminary results provide measures of collapse safety of reinforced concrete frame structures and are used to evaluate the level of safety provided by modern building codes, and to quantify differences in safety between older and moden structures, answering questions such as "how safe are code-conforming reinforced concrete frame structures?" and "how much more likely are existing reinforced concrete frames to collapse in an earthquake?"

Building structures are occasionally subjected to extreme events such as fire loading. Significant experimental and analytical research has been conducted on the behavior of building structures under fire loading. However, most of this research has focused on the performance of individual structural components under standard ASTM E119 fire loading. These standard fire tests have been conducted on a wide range of structural components and assemblies with different material, geometric and loading parameters. The standard fire test results are used to compute the design fire resistance rating (FRR) values for the structural components etc. The current building codes emphasize the prescriptive fire resistant design approach, while allowing for performance based design. The prescriptive design approach is more prevalent and commonly used. It specifies the required FRR values for the structural components of the building depending on its size, occupancy, construction materials, importance and other parameters. Fire resistant design is achieved by selecting structural components and assemblies with design FRR values greater than or equal to the required FRR values. It is evident that the prescriptive design approach does not account for the effects of realistic fire loading and thermal and structural interactions between the building components during the fire events. Recent events, for example, the 9/11 WTC Tower collapses, and the following analytical investigations directed by NIST, have highlighted the need for fundamental knowledge of the behavior and stability of building structures under realistic fire loading. The realistic fire behavior of building structures depends on several parameters, the most important of which are: (a) the structural configuration and layout, (b) fire intensity, duration, and spread, (c) structural loading and boundary conditions, and (d) fire protection distribution. This paper presents an analytical approach for simulating the realistic fire behavior of steel building structures. It focuses on the behavior of a hypothetical 10-story office building located in Chicago, and designed according to current U.S. building codes. The structural layout consists of interior gravity frames and perimeter moment resisting frames (MRFs). It is expected that the behavior of other structural configurations will be different from those presented in the paper. However, the paper provides a fundamental primer for simulating and evaluating the realistic fire behavior and stability of steel building structures. This primer will be used to further investigate the behavior of other structural configurations and layouts in this research.

Performance-based structural fire engineering (PB SFE) is internationally a fast growing field of engineering where the design of the fire protection strategy and structural detailing of a building is based on calculating the structure's behaviour under realistic fire scenarios. While current practice in the United States is primarily prescriptive in nature, performance based structural fire engineering is beginning to have an impact on building design particularly as architects conceive more complex designs and engineers have an increased understanding of structural fire response from the WTC collapse and more recently the Windsor tower fire in Madrid. Historically, the determination of structural fire resistance is established in a standard furnace test. These standard tests have existed in the same form for over 100 years. The tests are a necessary part of our regulatory systems because they provide invaluable data on the relative performance of materials and small-scale assemblies in fire. However, the primary concern with prescriptive fire resistance ratings is the reliance on the assumption that a structural system tested at a relatively short span, in a furnace, can robustly translate into a basis for design at the scale required in real buildings where continuity, connections, alternative load paths, and restraint play a significant role in structural performance in fire. The concern with the reliance on these standard fire tests as a basis for design particularly as buildings become larger and more complex, has led to the development of alternative design techniques. Over several decades, various researchers have investigated the phenomenon of real structural fire performance and developed various analytical methods for use in the design domain. Through the use of PB SFE, the structure can be designed to resist a realistic fire with less reliance on passive fire protection. The assessment allows the design engineer to check for any structural design weaknesses/strengths in fire, to identify robust design features, to determine an optimised passive fire protection strategy and if necessary, to provide structural details to enhance the structural performance in fire. This paper presents a case study of performance based structural fire engineering conducted in the U.K. The case study demonstrates how structural fire engineering, using either simple or advanced forms of analysis, can provide a robust and fire safe solution. Note: The advanced finite element analysis presented here is currently being conducted in the U.S. and will be subject of a separate publication.

The conventional wisdom for capital projects such as buildings is to achieve the planned purpose at the lowest possible cost. The easiest and most common way to measure the cost of a capital project is by the initial costs associated with planning, design, and construction. However, future costs are often insufficiently anticipated. The life cycle cost associated with up front decisions or design can be significant and need to be considered when measuring the total project costs. A significant future cost is the potential for damage to a facility from a hurricane. This includes costs associated with physical damage, economic loss, and functional loss of the facility. This is particularly true along the coast of the southeastern United States. While these costs are uncertain, it is possible to quantify them in an approximate and statistical sense. The 2005 hurricane season illustrated the costs associated with hurricane damage. This paper presents an analysis of the damage to a particular building located in Lake Charles, LA. This analysis studied the damage to the facility due to Hurricane Rita as well as the life cycle cost implications. The case study revealed that the costs associated with fortifying the structure against wind damage would have been more than offset by damage from the storm. In order to be able to apply these lessons generically, a method for estimating the losses to a building during its life cycle is presented.

The Florida Public Hurricane Loss Model is one of the first public models entirely accessible for scrutiny to the scientific community. The model incorporates the latest state of the art techniques in hurricane prediction, and vulnerability modeling based on engineering criteria. Although the model was developed for Florida, its methodology is applicable to any hurricane prone region. Version 1.5 of the model was developed before any data from the 2004 hurricane season was available. When data from this intense hurricane season, which produced substantial losses in Florida, became available, it provided the opportunity to validate and recalibrate the loss model against actual claim data. The paper describes the resulting changes in the Model, and how they affected the predicted loss costs in Florida. Scenario analyses illustrate the significance of the model results for the insurance industry and homeowners in the State of Florida.

The Texas Tech Wind Engineering Field Research Laboratory (WERFL) building is equipped with over 200 sensors to measure the pressure on the building. Since its inception, many pressure time histories have been documented. However, a full length thunderstorm record has never been fully studied for its effects on the building and its comparisons with larger scale synoptic winds. On August 24, 2007 a moderate thunderstorm downdraft occurred at the WERFL building with a peak gust approaching 50 mph. An investigation of this thunderstorm is contained within this paper. The large increase in wind speed and air density/pressure accompanied by downburst passage may cause increased pressures on the building. Also, the turbulent and thermodynamic characteristics of thunderstorm winds contribute to large vertical (upward) velocities which may in turn lead to stronger uplift pressures. These pressures on the building may lead to increased damage probabilities on low-rise structures. Comparisons with a non-thunderstorm record at a similar angle of attack are also carried out.

Performance of structures during extreme wind events is an ultimate validation of effectiveness of advances in design and construction practices. These real-world full-scale tests provide information that would be very difficult to duplicate in laboratory experiments and it seems logical to study the damages that take place. From this information and from inferred wind speeds occurring during such events it should be possible to develop countermeasures to eliminate or reduce the levels of damage. Another aspect of collecting perishable damage information is to determine the spatial distribution of damage and to relate it to possible wind fields. Tornadoes pose a particularly difficult problem, as much of the meteorological data is reported from radar observations. Ground level measurements are usually very scarce. Clearly the wind field is quite varied. Even in the most extreme tornadoes, structures located away from the "eye" of the storm will be subjected to a much lower wind velocity and structural loading. For the most intense wind conditions it is possible to provide reinforced shelters that will ride out the storm, although (using present methods of construction) the remainder of the building may be destroyed. Ultimately, the answer will relate to what it will cost to provide more resistant structures versus the cost of shelters and the subsequent costs of disaster response efforts. This paper presents findings of the tornado damage investigation carried out in May 2003 by a team mobilized by the American Association for Wind Engineering (AAWE). A more detailed description of this investigation is presented in the AAWE Report [Bienkiewicz, 2003]. The team visited a total of ten sites in Missouri and Kansas, affected by tornadoes resulting from collision of cold dry air moving from the Rockies with moist air from the Gulf of Mexico, and leading to giant supercell storms and strong tornadoes in up to eight states. First, a description of tornado events of May 2003 in Missouri and Kansas is presented. Two tornado tracks in Missouri and tornado events in Kansas City and in neighboring area are described in detail. Next the observed damage is documented. This description includes: historic structures, manufactured homes, old and new residential homes, emergency facilities, commercial and industrial structures, houses under construction, college dormitory, transmission line, multifamily housing complex, tornado missile hazards and others. Observations resulting from this investigation and recommendations for the future effort in this area are summarized in the concluding section of the paper.

A sensor network used for characterization of the impact from hurricane storms on man made structures is described. The network consists of many sensor units attached to the structure under consideration, a base unit which orchestrates the measurements over a wireless interface and appropriate wireless and wireline backhaul that delivers the data to a central server. At the central server, the measurements are analyzed and presented in a near "real time" fashion. Unlike most of the sensor networks used for wind monitoring which are hardwired, the network described in this paper uses wireless communication interfaces. This allows for a flexible and fast network deployment that is non-intrusive to the monitored structure. The network is designed to collect pressure readings from sensor units, wind speed, wind direction and temperature during the entire period of the hurricane storm. The empirical data collected by the network are used for hurricane characterization and provide a valuable experimental and simulation basis for evaluation of the existing building codes.

A post-tensioned (PT) column base connection for use in a seismic resistant PT frame is presented. The PT column base connection allows for self-centering behavior of columns (i.e., returns to its original position with negligible residual drifts). The PT column base connection consists of PT high strength bars, buckling restrained steel plates, reinforcing plates, keeper plates and shim plates. This paper will discuss design considerations for the PT column base connection based on a performance-based design approach, and evaluate the PT column base connection using validated finite element (FE) models.

In this paper, Predictor-Corrector algorithm for multi-site hybrid simulation has been proposed with AT-modification. The Predictor-Corrector algorithm does not require determination of the initial stiffness values of experimental components and is thus suitable for representing elastic and inelastic systems. Its numerical characteristics are thoroughly investigated comparing with α-Operator Splitting method. Experimental error is inevitably introduced in actual tests. To improve performance of the P-C algorithm under displacement control error in actual testing, the proposed AT-modification uses an algorithmic tangent stiffness calculated using actual feedback values from actuators in the lab. The new correction method shows better performance than I-modification under experimental errors. Error-propagation characteristics of the P-C method are presented under systematic displacement control error. In addition, a multi-site hybrid simulation using P-C method is conducted to show efficacy of the P-C method in a complex structural system.

A number of seismic hazard mitigation devices have been recently developed to enhance the seismic performance of structural systems. Many of these devices are load-rate dependent. The development of performance-based earthquake engineering procedures to effectively design structures with these devices requires that their behavior be well understood, accurate analytical models exist, and the design procedure be verified. These requirements can best be met by performing real-time hybrid tests of structural systems with these devices. The Real-Time Multi-Directional (RTMD) Earthquake Simulation NEES Equipment Site at Lehigh University specializes in real-time hybrid testing. This paper presents the development and application of an explicit integration algorithm for real-time testing at the RTMD facility. The algorithm is unconditionally stable for linear and nonlinear softening structures and developed using an innovative approach based on discrete control theory. This paper includes the development of the integration algorithm, its implementation into the real-time integrated control system at the RTMD facility, and its application to the real-time hybrid testing of passive elastomeric dampers. The integration algorithm is shown to be easy to implement and enable exceptional real-time hybrid test results to be acquired.

Buckling restrained braces were recently developed for seismic design as stiff and ductile structural members. These braces have the advantage of exhibiting symmetric ductile hysteretic behavior in tension and compression making them well suited for resisting reversed or cyclic loading. The compression strength of these members is governed by material yielding rather than global buckling, which is typically achieved by restraining the steel core by encasing in a steel tube filled with mortar. The buckling restrained brace technology has been rapidly adopted, especially in performance based building designs, and is now also part of the AISC Seismic Design Provisions as one of the ductile lateral load resisting systems. This paper outlines the buckling restrained brace concept with the use of fiber reinforced composites and presents results from a pilot cyclic test on a mild steel angle wrapped with glass fiber composite. Eliminating the steel tube and mortar and using fiber reinforced composites significantly reduced the brace weight improving handling during installation. This method can also be used for retrofit of in-place steel braces. In a pilot test, the wrap shifted the mode of failure from global buckling to hinging near the connection, illustrating the potential for this innovative concept while also highlighting the importance of the brace transition and connection details.

Special concentrically braced frames (SCBFs) are economical and provide substantial lateral resistance and stiffness. They are frequently used in seismic design, since recent issues with steel moment resisting frames have increased their cost and raised doubts about their performance. Unfortunately SCBFs are not as well understood as many other structural system, because they rely on inelastic post-buckling of the brace during extreme seismic events. As a result, several research studies have been undertaken to better understand and improve SCBF seismic behavior. A research study has been in progress at the University of Washington (UW) to improve the seismic performance of SCBF gusset plate connections. To date more than 20 large-scale SCBF frames with gusset plate connections have been tested, and extensive analysis has been performed. This work is summarized, and the broad general conclusions from the experimental work are noted and demonstrated. The importance of connection stiffness and gusset plate welding and the relative performance of bolted vs. welded and tapered vs. rectangular gusset plates are shown. The results lead to recommended changes in the current design methods. In particular a modified method for assuring end rotational capacity for brace buckling is proposed. This method provides lighter more compact gusset plates, which develop greater inelastic deformation capacity from the frame and less secondary damage to framing members.

Axial compressive strains that develop in rectangular steel tube braces subjected to cyclic inelastic loading can lead to local buckling and brace fracture. In this study, the influence of the brace effective slenderness on this strain demand is examined as an attempt to assess the effect of brace slenderness on brace fracture. Past test data indicating an impact of brace slenderness on brace fracture is first reviewed. Brace axial deformations at onset of buckling and at first yielding in compression are evaluated using elastic buckling theory. Finite element analysis of bracing members exhibiting different effective slenderness ratios is carried out to evaluate the strain demand after inelastic buckling has occurred and plastic hinging has formed. The strain demand prior to brace buckling and plastic hinging is small and has negligible effect on brace fracture. Compressive strains that develop after brace buckling has occurred and plastic hinging has formed generally decrease as the brace effective slenderness ratio is increased.

A series of nonlinear dynamic analyses are being carried out to improve understanding of the behavior of conventionally braced and buckling restrained braced steel frames, devise loading protocols for experimental assessment of braced frames, and to identify improved performance-based design and analysis procedures. This work extends earlier work by Uriz by updating the edition of the building code used to design the structures being analyzed, and the configuration of the structure is altered from a stacked chevron arrangement to one where the braces are arranged as a double story X. Initial results are presented herein for three-story tall special concentric braced frame (SCBF) structures designed by others in conformance with two recent design guidelines. A variety of results are presented to assess likely behavior for different seismic hazard levels in terms of roof displacement, interstory drifts, residual story displacements, and floor level accelerations.

This paper summarizes the results of a full scale, 2-story braced frame test that was performed at the NCREE Laboratory in Taiwan as part of a small group NEES research project, NSF CMS 0619161, "NEESR-SG International Hybrid Simulation of Tomorrow's Braced Frames," on concentrically braced frames. This is the first in a series of four large-scale tests that will be performed in Taiwan. The first test specimen is a full scale, 2-story, single bay braced frame in a multi-story X-brace configuration. The test has several goals. It will provide a first experimental examination of the multi-story X-brace system and of the midspan gusset plate connections. It will serve as a basis for calibrating nonlinear analytical models of braced frame behavior under development as part of the research. At the same time, it is a confirmation study for past research on corner gusset plate connections performed at the University of Washington. If conditions permit, the frame will be used for a second test with wide flange braces. Details, data and photos of the test frame during construction, preparation and testing are provided on the NCREE website: http://exp.ncree.org/cbf/. This paper was written immediately after completion of the test on December 11, 2007 and includes a summary of the design and analysis of the frame and the initial test results.

Predicting cumulative damage to reinforced concrete (RC) walls from multiple weapon detonations is complicated by the fact that the strength of a wall damaged by a first weapon is less quantifiable than for an undamaged wall. In the past, subscale experiments were conducted to investigate and provide data for predicting RC wall response and damage from a single weapon detonation. ERDC has developed and executed a research program to provide data for predicting RC wall response and damage from multiple weapon detonations. Testing under this effort involved performing a combination of modal and follow-on explosive testing on previously damaged RC walls. High-performance numerical simulations were also performed to support the experiments. The paper will focus on results of one selected cumulative damage experiment.

Management of infrastructure assets has been gaining increased attention recently because of aging infrastructures. Wastewater infrastructures, such as sewers, force mains, etc., maintained by various municipalities across the nation are at increased risk of failure since they are buried underground and are usually scheduled for maintenance/repair only after a breakage. Force mains are vital link in the wastewater infrastructure since they carry wastewater under pressure from a low point in the collection system to water pollution control plant. This paper presents the feasibility of internal inspection of force mains using ultrasonic scanning.

Over the past 5 years, the burgeoning availability and application of remote-sensing technologies integrated with strategically planned field reconnaissance has proven highly effective for resilient post-disaster response, for providing rapid and resourceful information about the location and severity of natural-hazard damage, and for preserving untouched damage scenes for further detailed analysis. Landfall of Hurricane Katrina on August 29, 2005 marked the first opportunity to examine and preserve multi-hazard damage conditions caused by wind, flood, and storm surge via newly available remote-sensing technologies providing unparalleled views of the damage at regional, neighborhood, and per-building levels. Immediately following landfall, MCEER field teams deployed to the Mississippi Coast and New Orleans to perform rapid and widespread assessments of damage at a per-building scale. A subsequent detailed study integrated various remote-sensing platforms with the ground-based survey data to identify the most appropriate roles for these multiple data platforms in rapid understanding of the damages resulting from a hurricane in a multi-tier framework.

Structural Health in Civil Engineering (SHCE) is an emerging field for monitoring the structural condition, at reasonable intervals, for public safety and cost-effective asset management. At the same time, it is desirable and may be essential to sense the structural response remotely during a post-hazard event to assess potential risks, execute appropriate risk-mitigation programs, and coordinate incident responses. Remote structural sensing also is an emerging field and has potential to be used in conjunction with SHCE. This paper presents a review of remote sensing for SHCE.

Wide-ranging participation from the US and Japan is being encouraged in the NEES/E-Defense Collaboration Research Program utilizing the E-Defense shaking table facility. A major research project on steel buildings utilizing the E-Defense three-dimensional shake table facility is underway in Japan. It involves several studies on moment frames, innovative methods for new or existing buildings, protective systems, and nonstructural elements. As one of the studies, a challenging seismic experiment to simulate collapse of a full-scale bulding comprising the moment frame was conducted in September 2007. The term collapse here is defined as the state where the structure loses its ability to sustain gravity loads. This paper presents preliminary reports on the collapse simulation experiments.

The E-Defense shake table facility, which is world's largest earthquake simulator, is being utilized for a major research project on steel buildings in Japan. The project involves several studies on moment frames, innovative methods for new or existing buildings, protective systems, and nonstructural elements [1]. As one of such studies, a challenging full-scale experiment to simulate collapse of a four-story moment frame was carried out in September 2007 [2]. In order to investigate the issues such as modeling techniques, estimation of damping and stiffness of nonstructural components, extensive analytical studies are being conducted by the members of the committee in charge of the test. Among several types of analysis described in Ref. [3], the post-test analysis results by the finite element model is reported in the first part of this study. A blind analysis contest has been conducted in conjunction with the test to stimulate development of computational methods and efficient modeling techniques for collapse analysis of steel frame buildings. The outline of the contest and the types of the analysis methods used by the participants in the contest are reported in the second part of this study.

Wide-ranging participation from the US and Japan is being encouraged in the NEES/E-Defense Collaboration Research Program utilizing the E-Defense shaking table facility. The facility, whose construction was completed in early 2005, is the largest earthquake simulator capable of subjecting full-scale structures to the strongest earthquakes recorded in the worlds. Relatively short term collaboration has already taken place involving geo-structures, wooden buildings, and reinforced concrete buildings. Currently, more emphasis is made on longer term collaboration out to 2010, involving steel buildings and bridges. The steel building project focuses on moment-resisting frames, innovative methods for new or existing buildings, nonstructural elements, and protective systems. Accordingly, the Japan team has four working groups (WG's). This paper discusses the work of Damper and Isolation Systems WG focusing on protective systems, such as passive control systems and base isolation systems for the steel buildings. Three companion papers by Suita et al. Ohsaki et al., and Takeuchi et al. discuss the studies by the other WG's.