Structures 2004: Building on the Past, Securing the Future

The existing MTA-New York City Transit's (MTA-NYCT) No. 7 Subway was built in the early 1900's and currently terminates at Times Square near 41^st Street and Seventh Avenue. As part of the City's redevelopment of the west side of Manhattan, the MTA-NYCT's No. 7 Subway extension project will add approximately 1.5-miles of twin tunnel alignment to the current line. The proposed alignment will extend from the existing Times Square Station west beneath 41^st Street then turn south under 11^th Avenue and terminate between 24^th and 25^th Streets. The project will include two new stations, a two-track line station and a three-track terminal. The project includes two major construction contracts: the running tunnels which would include TBM launching shaft (Shaft A) and retrieval shaft (Shaft L), and (2) the follow-on contract, which would include drill-and-blast mined cavern enlargements of the two stations and the drill-and-blast excavation for tunnels connecting the end of the TBM running tunnels to the existing No. 7 Subway Line at Times Square Station. This paper will focus on how Shaft A will be designed and constructed to mitigate impact on adjacent properties and utilities. A stiff support system will be adopted to minimize deflections to the shaft walls. Instrumentation will be utilized to monitor the performance of the support system and to verify the design and predicted effects of construction. The instrumentation will be designed to monitor actual loads and deflections within the shaft as well as the associated ground movements and settlements.

Structures including buildings and bridges deteriorate and may not function in a satisfactory way as expected with time. Increasing number of cases of lack of satisfactory performances prompted the profession to consider developing performance-based design guidelines replacing or at least providing alternatives to the current specification (code) based practices. However, before developing such guidelines, the civil engineering profession should reach consensus on the definition of performance and establish quantitative, measurable indices that will permit the measurement of current or the projection of expected future performances. Performance-based design concept depends on many inter-connected issues including areas of applications, definition of performance, tools for measuring performance, quantitative indices that need to be satisfied, and performance under uncertainty. It is also important to note that since all major building codes on concrete, steel, wood, and masonry are now based on the Load and Resistance Factor Design (LRFD) concept; the future performance-based design guidelines should reflect the thinking behind this same concept. It is also known that the performance-based design concept is relatively new for civil engineers, the area is evolving, and comprehensive basic research is in its infancy. The paper will outline some of the recent thoughts on developing performance-based design guidelines.

In order to establish a rational maintenance program for bridge structures, it is necessary to evaluate the structural performance of existing bridges in a quantitative manner. In this paper, an attempt is made to discuss the relationships among several performance measures and provide rational balances of these measures by using the multi-objective genetic algorithm.

This paper summarizes some of the recent accomplishments and delineates the future challenges in life-cycle cost analysis for highways bridges. The study is intended to provide the necessary background in order to evaluate alternative bridge investment options based on life-cycle cost.

Analytical equations are developed to estimate maximum length of integral bridges based on the lateral displacement capacity of steel-H piles under the effect of cyclic thermal variations. For this purpose, a low-cycle fatigue damage model is employed to determine the maximum cyclic curvatures such piles can sustain. The determined cyclic curvature limits are used in static pushover analyses of two steel H-piles driven in soil to obtain the maximum thermal-induced cyclic lateral displacements such piles can accommodate. Using the pushover analyses results, the maximum length limits for integral bridges subjected to cyclic thermal variations are formulated as a function of pile's properties, soil type and stiffness.

In this study, the concept of the hybrid FRP-concrete design was exploited in a new type of bridge superstructure. The proposed bridge consists of glass fiber reinforced polymer (GFRP) box sections with a thin layer of concrete. This paper presents results from the experimental study on a scale bridge model as well as the finite element analyses. In the experiment, the scale model was subjected to quasi-static and fatigue loadings. The test results showed that the proposed bridge meets the stiffness requirement and has significant reserve strength. Stiffness degradation after 2 x 10⁶ load cycles was found to be insignificant. The finite element analyses were able to accurately predict responses of the scale model under quasi-static loadings very well.

The cast-in-place post-tensioned box girder bridge has been a popular bridge type in the western United States, particularly in the state of California. This type of construction allows for an efficient and cost-effective alternative, while being a very aesthetically pleasing structure. While post-tensioning provides the required service strength, the monolithic pier construction enhances the seismic performance of the bridge. Due to the relatively high torsional rigidity, these bridges have typically been designed as a unit, rather than individual girders. The LRFD specifications have introduced several changes that affect the design of this type of bridge. These include live load application, live load distribution factors, live load reduction due to skew, loss of prestress and post-tension, partial prestressing, and revised load factors and load combination Limit States. As the implementation of the LRFD continues for this type of bridge, the effect of the new specifications needs to be understood. This paper will present some of the key issues affecting the CIP box girder bridges. Analytical results comparing the AASHTO Standard and LRFD specifications will be presented to highlight their differences.

Several cable-stayed bridges have shown signs of damages mostly induced by susceptibility of stay cables to wind-induced vibrations and corrosion. This has caused some concerns among bridge owners and initiated a series of inspection and health monitoring programs. This paper reviews existing methods for inspection and monitoring of cable-stayed bridges and summarizes the findings of several projects conducted to date. A unified approach for health monitoring and problem solving for stay cables of cable-stayed bridges is described. This approach has been developed based on information gathered from evaluation of the strength and reliability of stay-cable systems for nearly 30 long-span bridges worldwide and instrumentation, health monitoring, and inspection of more than 8 cable-stayed bridges. An ongoing project for inspection and damage detection of the Luling Bridge in Louisiana, an all-steel cable-stayed bridge, is described in detail. The approach follows the new unified methodology for addressing problems directed toward stay cables and their boundaries, and includes analysis, field measurements, and inspection procedures. Global and local damage detection methods have been used to complement each other, the former for rapid identification of damage and its location and the latter for in-depth inspection and potential damage detection of suspect locations. A summary of the findings is presented, and mitigation measures are recommended in this paper.

Slocum/Wood Street is an east—west roadway that crosses over the mouth of the Acushnet River on the border between the Town of Acushnet (Slocum Street) and the City of New Bedford (Wood Street) in southeastern Massachusetts. Area surrounding the bridge is an urban mix of single family homes, stores and manufacturing. Notable, is the Acushnet division of Titliest Company located at the southeast corner of the bridge. Titliest is one of the largest employers in southeastern Massachusetts. The existing bridge was built in 1914 and consists of three spandrel filled reinforced concrete arches. Each arch spans 17.678 meters, is elliptical, and provides a clear opening of 15.240 meters wide by 1.981 meters high above mean sea level. Originally, the bridge did not carry any utilities. Over time, utilities were attached to the structure as the communities grew.

The life-cycle philosophy has recently garnered favor in the realm of bridges and other public transportation infrastructure, where maintenance is already acknowledged as a major element of cost of operation, and where the federal mandate for a comprehensive bridge maintenance policy has led to the development of Bridge and Pontis. Application of life-cycle concepts to buildings invokes additional considerations that must be addressed before the concept will be widely adopted, such as the fact that maintenance of the structure itself is usually a much smaller cost factor than in bridges, and most buildings are constructed with private sector funding, in which the advantage of lower life-cycle costs as a tradeoff to initial cost is not clear. An additional factor arises because the public takes building performance for granted, spending more time in buildings than on bridges and associating them with the vitality of their community. Therefore, issues of risk and risk perception, sustainability of individual buildings and its implication for community economic well-being, and non-economic issues such as ecology, beauty and pride become important.

This study provides a probabilistic life-cycle analysis of deteriorating structures under multiple performance constraints. For these structures, a probabilistic model is used to predict the evolution in time of three performance indicators, namely condition, reliability and cost. The uncertainties associated with these performance indicators and their time-dependent interactions are considered.

This paper discusses the authors' recent experiences with two large-scale rainscreen recladdings of two existing high-rise buildings. Both structures leaked extensively and both were repaired using large aluminum rainscreen panels. This paper presents some of the more significant design and quality control issues that engineers and architects should consider to achieve a successful project.

Vibration damping is becoming increasingly important for improved vibration and noise control, dynamic stability, and fatigue and impact resistance in advanced engineering systems. There is a particularly strong need for information on methods for improvement of damping in lightweight structural composite material so that they may be more effectively used in the design of high performance structures and machines. This paper discusses some experimental results regarding the improvement and optimization of damping in polymer composite materials at micromechanical levels.

High strength concrete has experienced an increased use by engineers over the last decade due to its large ratio of compressive strength to unit cost, unit weight, and unit volume. However, the gain in strength is achieved at the cost of a loss in ductility of the material. The requirements for transverse steel reinforcement in HSC columns under high shear forces result in high volumetric ratios, which cause reinforcement congestion within the column cross section. An experimental investigation involving the testing of fourteen full-size (355 mm by 355 mm by 1520 mm), high-strength concrete columns in axial compression was undertaken to determine the effectiveness of using Welded Wire Fabric (WWF) as transverse reinforcement in the columns. The performance of columns laterally reinforced with WWF was compared with that of columns laterally reinforced with conventional ties, as well as with unconfined concrete. Axial stress-strain diagrams of the concrete core from the experimental tests showed that substantial gains in strength and ductility of columns laterally reinforced with WWF can be achieved if the volumetric ratio of transverse steel was above 3.5 percent. Strength increases of at least 15 percent were observed, while ductility increases of 250 percent and more were recorded in the specimens with WWF when compared with the corresponding specimens with conventional ties.

This paper summarizes a theoretical model to predict the monotonic load-deformation behavior of diagonally reinforced coupling beams. The model assumes all load is resisted by diagonal tension and compression. The diagonal compression is carried by the diagonal reinforcement and the concrete core surrounded by the diagonal bars in that direction, while the diagonal tension is carried only by the diagonal reinforcement. Either rupture of the diagonal reinforcement or crushing of the concrete core defines the end point of the behavior (failure) of the coupling beam. The strain hardening of the reinforcing steel is considered in this study, which is an important source of strength at high deformation. The model is automated in a computer program that can be easily used by design engineers to predict the monotonic load-deformation response of such elements. The model is applied and compared to experimental tests that were done by several investigators (total of 13 specimens). The specimens vary in terms of dimensions, reinforcement and material properties. The model gave good results compared to the test results.

An analytical approach is presented for predicting the shear load-deformation behavior of concrete filled circular FRP composite tubes with full- and non-composite interaction. The procedure integrates an iterative algorithm following the modified compression field theory in combination with a smeared shear modulus for cracked concrete and inclusion of extension/shear coupling effects of anisotropic FRP laminates. The analytical response was found to be in satisfactory agreement when compared with experimental data from large- and small-scale tests. The analytical method and results provide useful information and insight on the shear behavior of FRP/concrete members particularly on the contribution of the concrete core.

The Seismic Infill Wall Isolator Subframe (SIWIS) system is developed for use in building frames with masonry infill walls in order to prevent damage to columns or infill walls and minimize life-safety hazards during potentially damaging earthquakes. The SIWIS system, which consists of two vertical and one horizontal sandwiched light-gauge steel plates with "rigid-brittle" elements in the vertical members, is designed to allow infill wall-frame interaction under wind loading and minor to moderate earthquakes for reduced building drift but to disengage them under damaging events. The SIWIS system acts as a "sacrificial" element just like a "fuse" to save the infill wall and frame from failure. This paper introduces the concept and presents some analytical results for the behavior of a finite element model of an infill wall with SIWIS elements.

This paper presents the summary of a literature survey on the design of concrete structures for blast, impact and progressive collapse. A brief review of some documents including the publicly available material from the Department of Defense, the General Services Agency, etc is presented. The paper also discusses the inadequacy of current codes such as the IBC, UBC, BOCA, SBC and ACI in loading and design and detailing provisions for blast/impact and progressive collapse design of civilian structures. Based on this study, some recommendations are provided and areas of further research identified.

Certainly the events of September 2001 have heightened awareness regarding the potential devastating damage to civil infrastructure due to impact loading. Perhaps the most vulnerable are old, brittle masonry structures, which may not be capable of remaining stable during large blast (impact) loading, particularly in the out-of-plane direction. Although design guidelines are in place for developing load-resistance functions under these extreme-loading conditions, use of modern materials and novel installation solutions can assist in expanding our database of available, practical solutions. To this end, an exploratory experimental program was conducted to investigate the feasibility of retrofitting masonry walls with different Polyurethane and Polyurethane -fiber combinations. A series of masonry wall segments, each coated with a different Polyurethane or Polyurethane-fiber combination, were subjected to simultaneous axial compression and monotonic out-of-plane loading. Two different types of Polyurethane coating, of thickness ranging from 6.4 to 22.2 mm, and two different types of carbon fiber fabric layers were considered. This paper will describe the testing program, summarize the experimental load-displacement resistance functions obtained, and describe the damage characteristics observed for the masonry wall segments. Test results indicate that the addition of even a single thin layer of Polyurethane can greatly enhance the out-of-plane performance and stability of the wall system. However, in select cases, undesirable brittle failures were observed as well as debonding at masonry joints and delamination between the masonry and Polyurethane coating.

Engineering research efforts aiming at the development of blast-resistant and blast-retrofit designs is a priority for many government and state agencies. The success and advancement of structural designs to resist loads due to explosions depends on the ability to develop prediction methodologies and engineering design tools. This paper will present the analytical modeling and experimental evaluation of a steel-stud wall system with window opening under blast loads. The analytical and static experimental results were used to develop the static resistance function for the wall system, which was incorporated into a single degree of freedom (SDOF) dynamic model. The results of the static component tests were used to predict the structural performance and provide recommendations for the design of the blast-resistant wall system. The paper will discuss the performance of a blast-resistant wall system under static and dynamic field tests using live explosives.

This paper presents a simplified methodology for estimating impact loads for the preliminary design of fixed vehicle barriers. Adjustments for vehicle type (car or truck/SUV) and impact mode (rigid wall or rigid pole) are included.

It is well known that thermal and time-dependent effects induce volumetric changes in bridge superstructures. Resulting movements have historically been accommodated through the use of expansion joints and bearings. Transportation departments have encountered problems with such systems in long-term service and maintenance. Elevation changes associated with successive paving must be eventually addressed by repositioning of joints. Corrosion of girder ends, bearings, and substructure members, is accelerated by leaking through deck joints of water, which can be laden with deicing chemicals. This leaking is an aesthetic concern as well. Loose materials that find their way into expansion joints from the roadway reduce the ability of the superstructure to expand, and can cause further deterioration of the joint. Joints are susceptible to wear from traffic, especially that of snowplows. With this issue come undesirable driving surface conditions associated with roadway discontinuity at the joint. High costs of expansion bearings are not justified, considering their potential for failure that is brought on by increased friction due to corrosion or loss of lubrication. Moreover, high costs are associated with manufacturing, installation, and repair and maintenance of expansion joints and bearings.

Joints in bridges have historically led to various in-service problems, the presence of which led bridge design engineers in some states to design bridges of relatively short lengths to be jointless. Successful design of these bridges led to the design of jointless bridges of longer lengths. While not a pioneer in the use of jointless bridges, the Tennessee Department of Transportation (TDOT) has in recent years extended the limiting boundaries for jointless bridges to unprecedented lengths. A series of field tests on prestressed concrete piles supporting integral abutments was sponsored by TDOT and performed by personnel from The University of Tennessee, Knoxville. Lateral load was applied to the simulated abutment to produce a horizontal deflection at the top of the pile. Rotation of the pile was restrained by the hold-down beams to simulate the restraint provided by the bridge deck system in an integral abutment bridge. The loading was applied in most of the tests at a rate of 25.4 mm (1 in.) in 4 hours to simulate the expansion and contraction in a bridge due to temperature change. The primary objectives of this paper are (a) to describe the tests performed on the four prestressed piles, (2) to present some typical results, and (3) to discuss the feasibility of using prestressed concrete piles in integral abutment bridges designed according to TDOT's criteria.

Steel H-piles are commonly used to support integral abutments. In the absence of expansion joints that allow the superstructure to expand and contract freely, piles supporting integral abutments are subjected to lateral displacement, horizontal shear, and bending moment. Calculating the true structural capacity of a horizontally displaced pile can be a daunting task. Engineers often design these piles according to AASHTO or AISC beam-column equations and neglect lateral support provided by surrounding soil. Results obtained from typical beam-column equations can be extremely conservative when applied to laterally displaced piles. Piles supporting integral abutments are not laterally loaded, but laterally displaced. The lateral displacement is a result of thermal expansion or contraction of the superstructure and all resulting forces are a function of pile stiffness, rotational restraint of the pile head, pile embedment depth, lateral displacement, and soil stiffness. Superstructure expansion and contraction are typically assumed to occur without significant resistance from the supporting piles. The piles are not capable of resisting the magnitude of force required to restrain the superstructure's massive cross-sectional area from longitudinal movement. Therefore, the magnitude of lateral displacement is assumed to be a function of the superstructure's coefficient of thermal expansion, length, and temperature range, but not a function of pile or soil stiffness.

Jointless bridges, which have been constructed by several states, promote reduced maintenance costs, improved riding quality, lower impact loads, reduced snowplow damage to decks and approaches, and improved seismic resistance. In spite of many of these recognized benefits, the behavior of such structures is not yet fully understood, and nationally adopted criteria for their design are still lacking. This paper presents the results of an experimental and analytical research program, funded by the Federal Highway Administration, on the behavior of jointless and integral abutment bridges. The experimental work included testing and monitoring of bridge models and a bridge structure under construction, tests of bridge components; and a field survey of fifteen jointless bridges. Experimental results have resolved many questions regarding environmental effects, long-term and time dependent loading in combination with live and dead load effects. Results indicated that the live load continuity of the bridge can be reduced significantly with long-term and time dependent loading effects. In the analytical phase, the response of a jointless bridge was evaluated with respect to various design parameters. The research indicated that analysis procedures can be used to adequately quantify the structural response if accurate material and environmental parameters are known. However, in lieu of complex analyses, simplified design procedures are recommended.

The Applied Technology Council (ATC), in a joint venture with the Multidisciplinary Center for Earthquake Engineering Research (MCEER), has recently developed Comprehensive Specifications for the Seismic Design of Highway Bridges (National Cooperative Highway Research Program, NCHRP Project 12-49). The American Association of State Highway and Transportation Officials (AASHTO) is considering these recommended specifications for possible incorporation into the future AASHTO Load and Resistance Factor Design Specifications. The primary objective of NCHRP Project 12-49 was to develop seismic design provisions that reflect the latest research findings, design philosophies, and design approaches. In this study, the substructures of two existing Missouri bridges with Seismic Performance Category of "C" and "D" were redesigned according to the proposed NCHRP provisions. These bridges have different resisting systems; in one bridge abutments contribute in lateral resisting system and in the second bridge, only the intermediate bent resist against earthquake forces. The design results were compared for these bridges.

The impact of seismic retrofitting of typical Illinois bridges, via response modification using friction pendulum bearings (FPB), on the state economy is studied. For this purpose, two typical bridges with distinct characteristics were selected by Illinois Department of Transportation (IDOT). The seismic analyses of the bridges revealed that the bearings, wingwalls and substructures are vulnerable and need to be retrofitted. Conventional retrofitting strategies are developed for the bridges and the retrofitting costs are estimated. The same bridges are further studied to develop appropriate techniques for upgrading their seismic capacity using FPB and the seismic analyses are repeated. It is observed that the FPB effectively mitigated the seismic forces and eliminated the need for retrofitting of the substructures of the bridges. This resulted in a considerable reduction in the seismic retrofitting costs of the bridges.

This paper presents the results of full-scale static and dynamic load testing of a curved box girder bridge. Two Florida Department of Transportation (FDOT) test trucks with a total weight of up to 117 tons provided the static loading. One FDOT test truck with a total weight of 52.7 tons applied the dynamic loading. Two different theoretical mechanical models were developed to evaluate the test results. The agreement between test and analytical results supports the expectation that actual bridge responses can be well predicted through theoretical analysis with limited experimental data. The influence of barriers, effective width of concrete slabs and impact factors are discussed. The research results are instructive and applicable to bridge design and bridge load-rating activities.

The study concluded that the bridge could be rehabilitated, but that extensive work was needed. The concrete in both the superstructure and substructure had always been a problem; so long term solutions were necessary so as not to impose excessive maintenance costs on the city. The work would have to be carefully done to respect the historic integrity of the bridge. The important elements such as the piers and trusses would have to incorporate details that were acceptable to the State Historic Preservation Officer.

Engineers who work on historic truss rehabilitation encounter projects for conversion of former vehicular bridges to pedestrian usage. The engineer finds today's design vertical live loads to be on the same order as those used by the designer from a century ago. Material allowable stresses are also similar (or better). But design wind load is significantly higher. This paper examines non-traditional load paths as an alternative to conventional "skeleton" approach to analysis. The authors' conclude that alternate load paths do exist and could be utilized by designers using commonly available computer software.

On April 12, 2003 at approximately 4:00 pm EST a fire ignited underneath an important bridge in the City of Manchester, New Hampshire. In the year and a half since the fire, the investigation into fire has determined the official cause as arson. Although the fire was intentionally set and caused major interruptions to traffic telephone lines, and some city fire department communications there is no evidence that this was an act of terrorism. Since the terrorist attacks on our country great emphasis has been placed on protecting our infrastructure. Although there are emergency plans in place and we take great precautions to prevent additional threats, disasters (natural and man-made) are still going to occur.

The Municipality of Anchorage Department of Project Management and Engineering chose to rehabilitate the Eklutna River Bridge, a historic three-span structure comprised of two multiple I-beam approaches and a unique arched deck truss main span. The geometry of the main span is complicated with three truss lines, canted exterior trusses, and an arched bottom chord. The bridge is located north of Anchorage, Alaska, in an area of high seismicity. This paper discusses the finite element modeling and structural analysis performed, and presents the main rehabilitation tasks undertaken. The rehabilitation includes repairing the existing deterioration, widening the deck with new bridge rail for combination vehicle and bicycle traffic, increasing the live load capacity to HS20, and upgrading the structure for seismic loads. All rehabilitation was designed while preserving this historic structure for its intrinsic value.

The Rainbow Bridge, an arch-shaped truss bridge originally engineered by the Chinese in or before the 12^th Century, is of unique curve configuration, piecing together a few unstable trusses into one stable truss assembly which is not only cost-efficient but more structurally sound in terms of lighter dead load than the traditional arch bridge and simple details of member connection. The Rainbow Bridge is revolutionary in its design, it behaves neither like a beam nor like a truss, but a combination of both, and it would better suit today's bridge and other structure design than many existing configurations. This paper aims to briefly examine the structural configuration and behavior of the bridge. A scaled-down physical model of the Rainbow Bridge was constructed to test for deflection, and it compared well the finite element models. A parametric study indicated that the design of the Rainbow Truss with flat curves and long members causes it to induce less bending moment and deflection.

This paper summarizes the field performance of three stress-laminated deck timber bridges located in Wisconsin, New York, and Arizona. The deck superstructures of these single-span highway bridges is comprised of full-span glued laminated timber (glulam) beam laminations manufactured with southern pine, hem fir/red maple combination, and/or Douglas fir lumber species. These bridge structures were evaluated as part of a National Timber Bridge Monitoring Program for 2–3 years following construction. Field data collection for these single-span bridges included moisture content, prestressing force, and static load tests. Based upon these collected field data and comprehensive visual inspections, the bridges have performed satisfactorily with no structural or serviceability deficiencies.

Overhead sign support structures number in the tens of thousands throughout the trunk-line roadways in the U.S. A recent two-phase study sponsored by the National Cooperative Highway Research Program resulted in the most significant changes to the AASHTO design specifications for sign support structures to date. The driving factor for these substantial changes was fatigue related cracks and some recent failures. This paper presents the results of a subsequent study sponsored by the Michigan Department of Transportation (MDOT) to develop a performance-based procedure to rank overhead sign support structures around the country based on their expected fatigue life and an approximate measure of cost. This was accomplished by combining a random vibrations approach with six degree-of-freedom linear dynamic models for fatigue life estimation. Then, expert opinion of a panel formed especially for this project was used to determine the importance, i.e. weighting, of cost and an optimization function was developed. The optimization function was used to rank selected sign support structures from around the country with the goal of maximizing the optimization function, thus selecting the structures most likely to meet the new AASHTO design criteria. Sixteen possible candidates were considered from around the country.

Current bridge design provisions specify the use of an equivalent static load approach to represent barge impact loading conditions. This paper presents two dynamic analysis techniques as alternative procedures for quantifying barge impact loads on bridge piers. A variety of impact analyses are conducted using the two techniques and the results are then compared. Comparisons are also made between the equivalent static load method prescribed by current bridge design specifications and the proposed dynamic analysis techniques.

The City of Nashville, Tennessee contracted with HNTB Corporation to complete environmental documents, preliminary design and final design for the new Gateway Boulevard Bridge over the Cumberland River in downtown Nashville. The primary criterion for the bridge was to create a "signature bridge" that would become a trademark of Nashville. HNTB developed several alternatives for this bridge including haunched plate girders, thru arch, tied arch and cable-stayed alternatives. The City chose the thru arch as the structure type to be advanced to final design and construction. The total bridge length is 495 meters (1624 feet) with a navigation span of 180 meters (591 feet). The cross section of the bridge includes six traffic lanes with a bike lane and 3 meter (10 foot) sidewalks on each side giving an overall bridge width of 31 meters (102 feet). This project includes roadway design, geotechnical investigation and evaluation, aesthetic lighting and drainage design. It is anticipated that the construction will be completed near the end of 2003. This paper will look at the design, fabrication and erection of the steel box arch rib and roadway, including very different foundation conditions on the east and west banks of the Cumberland River.

In design and analysis of steel-concrete composite girders, values of maximum deflection, stress and strength are typically obtained from simple beam theory by utilizing the effective slab width concept. Shear-lag effects are indirectly accounted for, by replacing the actual slab width by an appropriate reduced "effective" width. In this research, a new effective slab width definition is introduced. A three-dimensional non-linear finite element analysis is employed to evaluate and determine the actual effective slab width of steel-composite composite bridge girders. The resulting effective width is believed to be larger than the ones provided by many design specifications, both nationally and internationally. The revised effective slab width criteria based on the proposed effective slab width definition is compared with other design specifications, specifically AASHTO LRFD, British, Canadian, Japanese, and Eurocode design specifications. The comparative studies include the comparisons of service limit state, positive versus negative moment regions, and interior versus exterior girders of a multiple span continuous configuration.

Finite Segment-Finite String method for the pushover analysis of multiple-column bridge bents is presented in this paper. The advantage of using this method is that the distributed plasticity of a column element and second order P - δ effect is automatically taken into account in the element stiffness formulation. In addition, the interaction between biaxial moments and axial load is also included in the element stiffness formulation. The results from the analyses were verified with available experimental test results. It shows that the numerical results are in favorable agreement with the test results.

Long span concrete box girder bridges first appeared in the 1950's. From the beginning, this bridge type was built segmentally using the balanced cantilever method of construction with form travelers and cast-in-place segments. After half a century of developments, concrete box girder bridges have a positive track record, are widely used, and have reached spans of up to 988 ft. These bridges present specific challenges to the designer that have to be addressed in the context of design codes, available materials, prevailing construction methods and project constraints. This paper describes current design trends for cross-section design, post tensioning layout and superstructure articulation. It also discusses the opportunities provided by high strength and lightweight concrete, and the impact of the new AASHTO LRFD code. The design of the Kanawha River Bridge in West Virginia is used to illustrate these topics. This river crossing, recently designed by T.Y. Lin International, will have a 760-foot main span, the longest concrete box girder span in the United States, and a total length of 2,975 ft.

The provisions of Article 6.10 of the 2004 AASHTO LRFD Specifications for Bridge Design, pertaining to the design of steel I-sections in flexure, have been revised in their entirety relative to the previous Specifications to simplify their logic, organization and application while also improving their accuracy and generality. This paper provides a brief overview of the new Article 6.10 provisions.

An impact assessment methodology is being developed for measuring and improving the performance of bridge infrastructure to extend their useful service life. The performance of bridge infrastructure is assessed from life-cycle perspective by compiling the relevant input information, and interpreting the output results from inventory analysis and impact assessment in relation to the infrastructure performance. Life-cycle assessment is a process applied in the present study to evaluate the impact on performance associated with physical condition, functional capacity, and cost. Using the design approach to long-term investment of transportation infrastructure has the potential to maximize benefits and to minimize the combined costs incurred by the service provider and the users that are affected by the operation of infrastructure facilities.

The paper presents an analytical model for estimating the composite action of prismatic reinforced concrete (r.c.) members repaired/strengthened by r.c. jacketing. The model considers the slip at the interface between the existing member and the jacket and establishes the mechanisms mobilized to resist this action thereby supporting composite behavior. An algorithm has been developed for calculating the response taking into account the shear phenomena that appear due to sliding at the interfaces as well as the spacing and penetration of flexure-shear cracks. Results calculated using the analytical model are corroborated with selected experiments from the international literature.

Fatigue cracks initiated from various connection details are common problems in steel bridge structures. Extensive research has been performed in the past few decades and design/evaluation guidelines have been developed for bridge engineers. Nevertheless, various fatigue problems are still occurring on a frequent basis with the aging of our infrastructure systems. This paper discusses a few types of fatigue cracks in highway steel bridges based on recent experience. The emphasis is on the subjects where technical guidelines are not available from the current specifications. Several cases are discussed for lessons learned from repairing fatigue cracks in bridge connections.

Variable Message Sign (VMS) panels are becoming increasingly popular. Wind loading on these signs sometimes results in significant cyclic loading of the support structure. The wind loading can result from gusts from the passing of trucks or from natural wind. An analytical and experimental investigation of the cyclic loading and resulting fatigue stress ranges produced by wind in a VMS sign structure are discussed in this paper. Comparisons of analytical and experimental results are presented. A summary of the relative effects of wind gusts due to passing trucks and due to natural wind are presented. Comparisons of fatigue stress ranges and fatigue limits are presented.

This paper describes an evaluation of a brittle fracture that was discovered in one of the welded plate girder members of the I-64 Blue River Bridge in Harrison County of southern Indiana. The study conducted to evaluate the fracture involved a number of different aspects, including a review of previous case histories of cracking at web connection plates, a material testing program to evaluate the strength and notch toughness of the steel, and an analysis of the fracture susceptibility of the detail used in the bridge member. It was found that a number of factors were responsible for the brittle fracture: a small lateral gap between weld toes in the region between the vertical connection plate and a horizontal gusset plate, a sustained period of very low temperatures, and a poor welding detail that initiated a prior fracture in the horizontal attachment plate that resulted in a loss of positive attachment.

A major trend in bridge engineering has been the replacement of aging urban interchanges due to a combination of physical deterioration of the structures and the need to expand the capacity of the interchange. The Kansas City "Triangle" in Kansas City, Missouri is one such high-profile interchange that is currently being replaced at an estimated cost of $230 million and scheduled over an eight-year construction period. Because of the deteriorating physical condition of the structures and the large increase in traffic through this urban interchange, there were numerous traffic accidents and severe congestion that prompted the Missouri Department of Transportation to select HNTB to entirely redesign this complex interchange. The "Triangle" interchange contains over 900,000 square feet of bridges and provides for the intersection of I-435, I-470, and U.S. 71 highways while crossing two creeks and two local streets. This paper will focus on the three items that define the standard for all future urban interchange replacements: construction phasing, creative and innovative engineering solutions; and aesthetic considerations.

Recent research into improving glued laminated (glulam) beam performance has focused on the use of fiber-reinforced polymer (FRP) reinforcement bonded to the glulam tension face to increase flexural capacity. However, to date the fatigue resistance of FRP-reinforced glulams has not been quantified. This is a serious concern given that such beams are increasingly used as bridge girders, which see large numbers of load cycles during their design life. In this study, nine Douglas fir glulam beams with 1.9% by volume FRP tension reinforcing are tested in load-controlled flexural fatigue and their residual strengths are then determined from static bending tests. Three of the specimens had reinforcing running the full length of the tension face, and the remaining six specimens had partial-length reinforcing to study the effect of this important detail. The loadings and number of fatigue cycles used in the testing program are consistent with accepted bridge design practices. The results of the tests indicate that girders with full-length or properly confined partial-length reinforcing have sufficient fatigue resistance for use as bridge girders. However, beams with unconfined partial-length reinforcing exhibited markedly poorer performance, and may not be suitable for use when fatigue is a design consideration.

Large buildings greatly alter the microclimate in their vicinity. In particular the wind flows around their base are often accelerated, with the potential to cause uncomfortable or dangerous conditions. As a result, many cities have required that the impact of any new tall building be evaluated during its design. In order to bring more uniformity into the methods and criteria used in these assessments, an ASCE task committee on Outdoor Human Comfort was formed by the Aerodynamics Committee of the Aerospace Division. This paper provides an overview of the report and describes criteria (including thermal as well as wind force effects), assessment methods, and the use of building design features as control measures. The criteria that are proposed are based on the extensive experience of the committee members and other contributors on many projects. In selecting the format for the criteria, it has been born in mind that frequently they will be used in situations where lay persons, not versed in wind effects or statistics will need to understand the results. Therefore they have been couched in terms that have been found by experience to be readily understood by the non specialist. A relatively new development has been the inclusion of thermal effects in criteria.

A windy environment around the base of a building, particularly near a main entrance or plaza area, will detract from the appeal of the site and perhaps discourage clients and shoppers from visiting the area. Many examples exist of unsuccessful outdoor restaurants and cafes in a windy environment at the base of tall buildings. Similarly, an outdoor pedestrian space, such as a recreational pool area of a residential condominium, should be protected from strong, mean winds. Thus, there is a direct financial motivation to ameliorate the wind environment if it is going to adversely influence the appeal of a building to the owners and customers of that building. In the extreme case a site may be dangerous, particularly to the infirm. Penwarden and Wise discuss the case of two elderly women who were killed when a gust of wind at the base of a tall building blew them over. Whilst this is not a common event, potential litigation is a design parameter that should be considered.

Computational Fluid Dynamics (CFD) methods have been used for calculating wind flow around buildings and predicting pedestrian wind conditions. Compared to the traditional wind tunnel testing, CFD has the potential to be more efficient and its graphic presentation of wind flow fields is particularly attractive to architects and planners. Attempts have been made by various researchers to advance the CFD technique in wind engineering, with the hope that it will eventually replace the wind tunnel testing. However, difficulties in turbulence simulation and other areas have limited CFD's applications. The paper will examine the state of the art and review some recent progresses in using CFD for predicting pedestrian wind conditions. Discussions will focus on the areas where CFD is capable of making immediate application impacts and on topics where more research efforts are needed. With the advances in computing power and methods, CFD is expected to play a more important role in predicting pedestrian wind conditions.

Since 1960's, pedestrian wind conditions around buildings have been studied extensively through wind-tunnel testing, full-scale measurements, numerical simulation and other approaches. These studies have created a broad knowledge base for pedestrian wind conditions around different building configurations. In many situations, the knowledge base allows for a reliable desk-top estimation of pedestrian wind conditions around new developments without wind-tunnel testing. A typical desk-top analysis may require a direct or indirect use of information from wind-tunnel measurements. The paper describes several effective methods of desk-top analysis currently used in the field of pedestrian wind studies. The focus of this paper, however, is on an innovative computer program developed as a time and cost-efficient alternative to the traditional approaches. The computer program has been updated through consulting practice and has proved to be reliable, consistent and efficient. A desk-top analysis is particularly useful at the preliminary stage of building design, when different building dimensions, orientations and configurations can be evaluated for improving pedestrian wind conditions.

A method for determining design snow loads on roofs using a combination of wind tunnel testing and analysis is described. Physical model tests are used to determine the snow deposition characteristics on a roof during snowfall at wind directions where snowfall in the presence of wind is common. Wind interaction with the building and drifting of snow on the roof during the snowfall affect the snow deposition patterns. An hour-by-hour simulation by computer of 30 to 40 years of past meteorological events is used to determine the times and amounts of application of snow to the roof, and the subsequent addition of new snow, melting by heat transfer from the air, heat transfer from solar radiation, and heat transfer from the underlying roof. From the resulting record of snow accumulations on the roof, design-level snow loads can be predicted.

An analytical procedure for evaluating roof snow drift loads is described herein. The procedure is based upon the physics of drift formation. Specifically the transport rate quantifies the snow flux from the snow source area and the trapping efficiency quantifies the percentage of transported snow from the source area which is captured in the aerodynamic shade of the drift formation area. The procedure is used to evaluate the annual maximum drift for a given snow source area. It is shown that current leeward roof step drift provisions in ASCE 7-02, yield loads with something close to a 50-year mean recurrence interval, while the gable roof drift provisions are arguably overly conservative.

Building codes and standards often indicate that unbalanced loading of arched roofs need not be considered if the roof is flat enough. They typically provide a threshold value for arch height as the criterion. However, real snow doesn't behave differently slightly above the threshold than slightly below. Recent building collapses have brought this issue into discussion since buildings designed below the threshold still produced significant unbalanced loads. The purpose of this research project was to investigate the lower bound of arched roof geometry and to compare the results with provisions of the 1995 National Building Code of Canada (NBCC) and the American Society of Civil Engineers Standard (ASCE 7-02). Parametric Finite Area Element (FAE) snow loading simulations were performed on a range of arched roof geometries using a range of meteorological data sets. The results indicated that, in certain situations, significant unbalanced loading could be expected for roofs that would otherwise be treated as flat, warranting special consideration in the appropriate codes and standards. The study also indicated that the azimuthal orientation of the roof relative to the prevailing winds plays a major role in some cases.

This paper presents selected results from a study to assess the reliability of wood members designed in accordance by current LRFD procedures. This study was part of a larger project to evaluate reliability levels associated with current LRFD design procedures in light of evolutionary changes to load and resistance factors as well as assumptions underlying resistance statistics for wood-based materials. The present paper examines the range of computed reliability indices for simple flexural members considering the flexural limit state only. The results show that the range of computed reliability indices can be significantly influenced by regional variations in load statistics.

As part of a project partially funded by the ASCE Structural Engineering Institute, several facets of reliability estimates are being reassessed using the latest available data for both loads and resistances. This brief paper describes the basis for updated judgments regarding representative coefficients of variation and separation factors for several types of wood-based products. The authors have consulted with members of the Subcommittee on Structural Design of the American Wood Council, who concur that these values are reasonable estimates upon which the analyses can be based. The distribution parameters in this paper are proposed as reasonable benchmarks for structural wood products for use in reliability analyses. Users are cautioned that these distribution parameters do not reflect species-wide full-distribution estimates such as those generated by broad-based in-grade testing. However, they are believed to provide reasonable benchmarks for analyses such as reliability calculations and system factor assessments.

Reliability analyses were performed for nailed and bolted wood connections designed to ASCE 16. The reliability analyses were performed using the European yield model to determine the connection capacity. Using reasonable statistics for the random variables in the yield equations, a reliability index was determined for each of the possible failure modes for both single and double-shear connections. Ditlevsen bounds were then determined for the reliability index of the series system consisting of multiple failure modes. These reliability indices show that designs to the present ASCE 16 do not always exhibit consistent reliability across the range of possible designs. One way to increase consistency for nailed connections is to use the full set of yield equations rather than the simplified set of design equations now present in ASCE 16 for most of the connectors. Other modifications may also be desirable since there are somewhat inconsistent reliablity levels even for those connectors designed to the full set of equations, e.g., bolted connections, but these modifications are beyond the scope of this study.

In the United States the vast majority of single and multi-family homes are designed and built using light-frame wood construction. These structures resist lateral loads, i.e. wind or earthquake induced, primarily through a system of wood shearwalls. The LRFD design standard for the construction of wood shearwalls is AF&PA/ASCE 16. The purpose of this paper is to present the results of a preliminary analysis to assess the reliability of wood shearwalls subjected to wind and earthquake forces, one task of an ASCE/SEI Special Project entitled "Re-evaluation of LRFD for Engineered Wood Products: Keeping Pace with Changes in ASCE 7". This was accomplished by examining the performance of a portfolio of twelve different wood shearwalls, each designed to AF&PA/ASCE 16. An ultimate strength limit state was used and was treated as deterministic within the analyses, that is to say material uncertainty was neglected. These results are expected to provide some insight into the inherent reliability level of wood shearwalls in the current LRFD design standard.

This paper introduces the 2004 version of the wind load provisions of the AIJ Recommendations for Loads on Buildings. One of the largest revisions is the introduction of wind directionality factor. If the building orientation is engineered, an economic design becomes possible that considers wind directionality. However, in this case, the combination of the along-wind force, crosswind force and torsional forces should be taken into account in the structural design not only for high-rise buildings but also for low- and medium-rise buildings. These are also introduced clearly in the provisions. The gust loading factor currently based on the tip displacement has been replaced by one based on the base bending moment. Other major revisions have been made on topographic effects, calculation formula for roof wind load, calculation formula for wind load on components and cladding, and aerodynamic shape factors.

The European Union has developed structural codes for civil engineering works which will be authoritative in the 16 member states, and will as well be adopted by new members. The wind loading code is part of the series on load specifications. A Technical Committee has developed the wind loading code in an attempt to incorporate the modern state of approved technical knowledge, the differing wind climates in Europe, and the individual building traditions in the member states. Being an international code, it might be useful as a template to other countries.

This paper introduces, and presents a progress report on the Revision of ISO 4354, Wind Actions on Structures. The objectives of the Revision and the proposals to make this an Internationally usable Standard are outlined. In particular the range of wind data acceptance and output format to meet the requirements of all countries is set out.

Most buildings are designed using wind loading codes rather than wind tunnel testing. This paper discusses some of the experiences of using a range of international codes in an international design practice. A comparison of wind loads predicted by a range of wind loading codes for two building types, a city centre tall building and an isolated low-rise building with a long-span roof, are then presented.

This study investigates the use of Near Infrared (NIR) spectroscopy as a nondestructive means of determining wood properties. The parallel to the grain modulus of elasticity was predicted from the near infrared spectra and compared to the modulus of elasticity obtained from tensile tests. Analysis was also performed to determine if NIR spectroscopy is a viable means to determine in situ properties of wood using hand-held spectrometers that have a smaller spectra range. The hand-held spectrometers were modeled by using reduced NIR spectra in order to determine the modulus of elasticity. The results demonstrated that NIR spectroscopy has excellent correlation (r = 0.93) to the modulus of elasticity. The reduced NIR spectra also had a good correlation (r = 0.90) thus making Near Infrared spectroscopy a feasible, nondestructive technique to determine wood properties.

Timber piles support thousands of bridges throughout the United States. Many of these timber piles have experienced significant deterioration due to fungal decay of the wood. Decayed piles mainly consist of a hollow center with an outer shell. As a result of decay many bridges with timber piles are in need of repair. Conventional repair methods typically involve expensive processes. These include providing support for the bridge in the form of falsework jacking, then extracting and replacing decayed timber piles. A cost effective timber pile repair technique was experimentally evaluated and developed. The repair method involved three basic steps. First, severely decayed material was removed and remaining wood material was treated to prevent future decay. Second, the removed wood material was replaced with aggregate and epoxy to provide compression strength. Third, the timbers were wrapped in glass fiber to provide material confinement. Actual field repaired specimens were evaluated. The repair technique provides for substantial recovery of original strength.

This discusses the strategy, method and progress of an integrated series of studies aimed at rectifying major deficiencies in design of low-rise light-frame timber buildings. An industrial shed with an open interior is already being monitored to determine environmental forces applied to it, and how those forces flow from surfaces over which they are applied to the foundation. Two single story houses are being specially constructed for the research and will yield information about loads on, and flow of forces within, what are relatively complex structural arrangements. Experimentation is linked to full-scale laboratory studies and whole-building finite element modeling. Expected outcomes include improved design code provisions for wind load, and development and validation of practical methods for sizing components in superstructures.

Conventional wood frame shear walls are designed by prescriptive guidelines. They are typically constructed of dimension lumber framework connected together with nails and then sheathed with structural panels. An engineered wood frame shear wall panel system was investigated using conventional materials except the dimension lumber framework was connected with toothed metal plate connectors instead of nails. These moment resistant connections transform the framework into moment resistant frames that increase resistance to lateral loads. The lateral load behavior of unsheathed and sheathed frames connected with metal plate connectors is discussed.

In this paper, a conceptual design, fabrication, and testing of the advanced Polymer Matrix Composite (PMC) infill system are addressed as a seismic retrofit strategy. Such a system is designed to have PMC multi-infill panels with passive energy mechanism. The basic configuration of this system is composed of two separate components - namely, an inner PMC sandwich panel and outer damping panels. The inner PMC sandwich infill consists of two fiber-reinforced polymer (FRP) laminates with an infill of Divincell H core, and outer damping panels are made of FRP laminate plates and passive energy constrained damping layers—combining polymer honeycomb and 3M viscoelastic solid materials — at the interface between the laminates. The interaction of these two components may produce considerable stiffness and enhanced damping properties in the structure following different drift level. As lateral drift increases, the FRP outer damping panels are designed to produce the damping through the cyclic shear straining of the combined interface damping layers. Otherwise, after the specified lateral drift of the contact, a PMC sandwich infill is designed conceptually to provide considerable lateral stiffness to resist severe earthquake excitation and avoid excessive relative floor displacements that causes both structural and non-structural damage. As part of this research, analytical and experimental studies were performed to investigate the effectiveness of the proposed multi-infill panel concept. The prefabricated multi-panel PMC infill holds a great promise for enhanced damping performance, the simplification of the construction process, and the reduction of time and cost when used for seismic retrofitting applications.

Numerous seismic deficiencies were identified during the study of a historic, 11-story office building in downtown Seattle, Washington. This paper discusses the thought processes and engineering techniques used in the seismic evaluation and upgrade design for this building and can be used as a model for seismic upgrades of other buildings throughout the country, including those in eastern states.

The Steel Buckling-Restrained Braced Frame (BRBF) is a new element in the Structural Engineer's toolkit. It provides the familiar stiffness and strength of a steel brace, without the problem of compression buckling. In addition, yielding limits the maximum force in connections and collecting elements, simplifying design. Lastly, the Steel Buckling-Restrained Braced Frame can also be used to dissipate energy through stable hysteretic behavior. Steel Buckling-Restrained Braced Frames were chosen for the retrofit of the Marin County Hall of Justice, originally designed by Frank Lloyd Wright. The investigation showed many lateral structural deficiencies including non-continuous columns, inadequate number of lateral resisting elements, inadequate diaphragm strength, inadequate transfer mechanisms between resisting elements, and incompatible building segments. Steel Buckling-Restrained Braced Frame elements were chosen as part of the retrofit scheme for their ability to limit the load on the weak diaphragm, to reduce the interstory drift of the building during a seismic event, as well as their ability to dissipate energy during high level earthquakes. The seismic retrofit scheme was constrained by the architecturally sensitive public spaces and maintaining the building's functionality throughout construction.

The code provisions for determining the design seismic drift for exterior elements of buildings have been substantially revised over the past 40 years. This paper presents a brief history of design drift requirements, technical background for the requirements, and the reasoning behind the changes, starting with the 1967 Uniform Building Code (UBC) through present day. Five building envelope designs from existing buildings are then compared with the code-prescribed requirements.

A curtain wall system must be designed for multiple performance functions including aesthetic, thermal insulation, sound insulation, water tightness, tolerance for inter-floor deflection, and structural safety against various loads including thermal, wind, and seismic. The recent trend in the building frame design against seismic force calls for a much larger amount of story drift. This trend causes extreme difficulty for maintaining the various curtain wall functions in the conventional curtain wall design approaches. The purpose of this paper is to analyze the cause and effect of seismic force on the curtain wall performances leading to a new set of design principles and approaches.

Since 1896, NFPA's mission has been to reduce the worldwide burden of fire and other hazards on the quality of life by providing and advocating scientifically based consensus codes and standards, research, training and education. Many of NFPA's activities involve the development, publication, and dissemination of more than 300 codes and standards under a process accredited by the American National Standards Institute (ANSI). To effectively deal with the built environment, the C3 code set addresses both new construction and, in some instances, existing buildings. However, in any given year, only about 2% of the building stock can be considered `new', which leaves a sizable portion in the category of `existing.' This paper explores how the C3 code set deals with the issues surrounding the rehabilitation of existing buildings.

In the fall of 1999 the International Code Council (ICC) Board of Directors appointed the International Existing Building Code (IEBC) Drafting Committee. The drafting committee was assigned the task of developing state-of-the-art code provisions for existing structures. After nearly two years of study, discussion, and deliberation, the International Existing Building Code Drafting Committee completed its task of drafting the International Existing Building Code (IEBC). The IEBC Final Draft was published in August of 2001 and after going through the 2002 ICC Code Development Cycle, the first edition of the IEBC was published in February of 2003.

ASCE 31-03: Seismic Evaluation of Existing Buildings is the next step in a very successful series of evaluation tools used by structural engineers nationwide to evaluate the seismic adequacy of existing buildings. This document has evolved from the tradition of visiting sites damaged by earthquakes and observing what works and what does not work in structural systems. It also embodies the latest efforts in the development of performance-based analysis techniques and reflects the most recent earthquake hazard demand criteria. This document is the last step in the development of a standard for seismic evaluation of existing buildings applicable across the entire nation. The previous version of this document, FEMA 310: Handbook for the Seismic Evaluation of Buildings — A Prestandard, was developed jointly by the Federal Emergency Management Agency (FEMA) and the American Society of Civil Engineers (ASCE). ASCE has since taken this document through a consensus process to turn it into a national standard. Major changes to this document include a reorganization of the nonstructural checklists and a rewrite of the unreinforced masonry (URM) special procedure. With the publication of ASCE 31-03, the first national seismic evaluation standard reflecting the most current thinking and applying a consistent methodology to the seismic evaluation of existing buildings is now available to the structural engineering community.

The objective of this investigation is to evaluate the FEMA-356 Nonlinear Static Procedure (NSP) and a recently developed Modal Pushover Analysis (MPA) procedure using recorded motions of two steel buildings that were damaged during the 1994 Northridge earthquake. It is found that the FEMA-356 NSP typically underestimates the drifts in upper stories. Among the four FEMA-356 distributions considered, the "Uniform" distribution led to the most excessive underestimation indicating that this distribution may be unnecessary. The MPA procedure, in general, provides much-improved estimates of the response compared to the FEMA-356 NSP.

Nonlinear static analysis using pushover procedures are becoming increasingly common in engineering practice for seismic evaluation of building structures. Various invariant distributions of lateral forces are recommended in FEMA-356 (2000) to perform a pushover analysis. However, the use of these invariant force distributions does not adequately represent the effects of varying dynamic characteristics during the inelastic response or the influence of higher modes. More recently, new approaches to combining lateral load distributions have been proposed to overcome some of the drawbacks in FEMA procedures. In this paper the validity and applicability of several lateral load configurations are assessed by comparison of the pushover response of eight and twelve story steel moment frame buildings with benchmark solutions based on nonlinear time history analyses. The study reveals the suitability of using unique modal combinations to determine lateral load configurations that best approximate the inter-story demands in multistory frame buildings subjected to seismic loads.

A preliminary version of a new seismic analysis procedure is presented. The Scaled Nonlinear Dynamic Procedure (NDP) overcomes inaccuracies associated with other methods of analysis and can readily be used in conjunction with the Nonlinear Static Procedure (NSP) for performance-based seismic design and evaluation.

Building code provisions for the design of buildings to resist earthquake ground motion are prescribed requirements originally intended to provide designers with minimum, simple-to-apply design methods to improve the resistance of buildings to earthquake ground shaking. Over the decades, these provisions have been expanded and made more complicated, ostensibly to correct deficiencies in the performance of buildings and building components observed during earthquakes and in laboratory tests. The code is now so voluminous and so convoluted that it is rapidly reaching a point where understanding the code is more burdensome than understanding how a particular building will actually respond during a major earthquake. Over the years, there has been a movement toward developing performance-based seismic engineering (PBSE) procedures that would give the engineer better tools to satisfy design goals. True PBSE is not a new concept; it has been practiced for decades by experienced engineering firms. As PBSE has become more popular and attempts have been made to codify it, some controversy and disagreement have arisen regarding the attributes of the various available methodologies. In some cases, controversy arises due to the gap between practicing engineers and academic researchers. In other cases, controversy arises from the fact that the PBSE procedures themselves are becoming prescriptive rather than performance-based and thus weakened in the process.

A previously proposed semi-active control algorithm was employed to drive a prototype piezoelectric friction damper, which was installed on the first story of a ¼-scale, 3-story building model. The performance of the damper and the simple semi-active control strategy were evaluated both numerically and experimentally under four modified earthquake ground motion records of various amplitudes. The seismic effectiveness and adaptability of the algorithm as well as the effect of damper saturation on structural responses were investigated. Numerical simulations agree well with the experimental results. The proposed control strategy not only effectively suppresses the structural vibration but also is adaptive to varying excitations from weak to strong earthquakes. Experimental results indicate that a piezoelectric friction damper with slight saturation could be advantageous to the seismic mitigation of buildings. However, significant saturation will degrade the performance of the semi-active control strategy.

Shape memory alloys (SMAs) in martensitic form and austenitic form are studied to evaluate their damping potential for applications in earthquake engineering. Shape memory alloy wires and bars are subjected to cyclical loadings similar to that expected during a seismic event. The damping properties of the shape memory alloys in both the martensitic form and austenitic form are compared with respect to bar size, loading rate, and maximum strain cycle. The results show that in the superelastic form, the damping properties of shape memory alloys are generally low, ranging from 2%–7% equivalent viscous damping. The damping properties generally peak at 4%–5% strain and begin to degrade at larger strains. In the martensitic form, shape memory alloys have significant energy dissipation with equivalent viscous damping ratios ranging from 15%–25%. Strain rate effects are evaluated by loading the bars at rates up to 2Hz (maximum strain rate of 7.90% per second). The results show that increased strain rates lead to a reduction in the energy dissipation capabilities of shape memory alloys in both forms. The effectiveness of using shape memory alloys for damping applications is evaluated through a comparison with current passive energy dissipation technology in the field of earthquake engineering showing the viability of using shape memory alloys for passive damping applications.

In recent years, smart damper technologies have been under development for application to base-isolated buildings. Research has shown that such dampers are capable of improving the performance of base-isolated structures, particularly when consideration is given to the disparate nature of earthquake ground motions (near-field vs. far-field). The type of near-field ground motion that is of particular concern is a long period, pulse-type motion that occurs near the point of fault rupture in the fault-perpendicular direction in the forward-directivity region. A direct result of this pulse-type motion is large displacement and velocity demands at the isolation level. The results of this study show that supervisory fuzzy logic controllers have the potential to improve the performance of smart seismic isolation systems by reducing isolation system demands as compared to smart isolation systems that employ a single fuzzy controller.

This paper proposes an innovative hybrid control system consisting of a passive fluid viscous damper installed in parallel to a semi-active friction damper for applications to structures subject to near-field earthquakes. The hybrid control system combines the best features of both control devices and possesses the great advantage that it is capable of quickly responding to external excitations. A nonlinear semi-active controller for the hybrid control system is further developed based on the high order optimal polynomial control algorithm, in which the linear part of control force is assumed to be achieved by the passive damper, and the nonlinear part is implemented by the semi-active damper. The near-field ground motion is modeled by a new velocity pulse model. To illustrate the adaptability of the proposed hybrid control system to various ground motions, 53 typical recorded near-field and long duration ground motions as well as the analytical velocity pulse model are employed in the numerical simulation of a SDOF structure. Results show the proposed hybrid control system is very effective in reducing the responses of structures due to near-filed earthquake excitations. The performance of the proposed passive/semi-active hybrid control system is very similar to that of an ideal passive/active hybrid control system, and significantly surpasses the performance of the passive control system.

This paper will describe a procedure for evaluating the contributions of nonstructural finish materials (such as stucco and gypsum wallboard) to the seismic performance of woodframe shearwalls and incorporating that information into a performance-based shearwall selection procedure. The paper will also examine selected construction quality issues and describe possible procedures for including their effects in a performance-based selection procedure for woodframe shearwalls. An analysis of peak displacements under seismic loading (characterized by a suite of ordinary ground motion records) is used to assess shearwall performance considering different combinations of performance level and seismic hazard. This is done using a nonlinear dynamic time-history analysis with either fastener-level hysteretic parameters or, in the case of walls with nonstructural finish materials, global assembly hysteretic parameters obtained from fitting to actual wall test data.

Single plate shear connections are commonly used in many types of structural frames. Currently these connections are designed to resist gravity loads and little consideration is given during the design process to their performance under seismic loading. The lateral displacements experienced by structures responding to seismic loads place significant local deformation demands at these "pinned end" shear connections. In certain instances these demands exceed the ability of the connection to respond and maintain structure continuity. This paper investigates the nature of the deformation demand placed on single plate shear connections, develops an analysis method, and recommends a deformation limit state for the connections to be used during their design and evaluation.

Conventional column design in multi-story, braced frames is typically based on the assumption that the effective column length equals the story height, that is, K=1. This implies simultaneous, anti-symmetric buckling of the column at all floors, and ignores the buckling resistance provided by underutilized columns above and below as well as the stiffness contribution from the floor framing. This paper reviews the safety factors inherent in the K=1 assumption. The inherent safety factors are shown to be significant, particularly when using a moment magnifier method. Also, investigations into building performance of steel frame buildings after the Northridge earthquake suggests that the rotational stiffness provided by "simple" connections can be substantial.

Analytical models are developed for beam column elements, panel zones and RBS connections to enable realistic modeling of a RBS structural system. To investigate the behavior of RBS moment frames, 3 buildings that are 4, 8, and 16 stories tall are designed following the latest seismic design provisions. A series of nonlinear static (pushover) and dynamic analysis are performed according to provisions in FEMA-273 and FEMA-350. Both material and geometry nonlinearities are considered in the analyses, which are conducted for seismic hazard levels corresponding to 2% and 50% probabilities of exceedance in 50 years. A variety of parameters are investigated including: P-delta effect, level of damping, column axial force, panel zone distortion, and interstory drift.

Modular connections have been developed for use in seismic-resistant steel moment frames. The connections are configured specifically for optimal seismic response through the use of a steel casting process. The impetus for developing these connections is the recently discovered susceptibility of steel special moment frames during earthquakes. Major features of the modular connections are the minimization of stress/strain and the removal of the field weld from the critical cross-section. To date, two prototypes had been fully developed: (1) a panel zone dissipator modular node (PZ-MN); and (2) a bolted modular connector (MC). The PZ-MN dissipates energy through stable panel zone yielding without column kinking and weld distress; the MC dissipates energy in a variable-arm connector that minimizes plastic strain demand and eliminates prying forces. The prototypes were developed through a comprehensive analytical program using nonlinear finite element (FE) analysis. Full-scale prototypes were cast and tested under the FEMA-350 protocol. These connections exhibited stable energy dissipation and remarkable ductility.

Four double channel built-up members were tested to failure to investigate their behavior under reversed cyclic bending. The main experimental parameters investigated were channel size, location of lateral support, and the spacing of stitches in the built-up members. The response of the test specimens is described in terms of moment versus drift and total plastic hinge rotation. Test results indicate that the stitch spacing and lateral support requirements in the current LRFD provisions do not ensure adequate ductility under large displacement reversals. Proper lateral support at the location of the first stitch is essential to mitigate lateral-torsional deformation in the plastic hinge region. Specimens with adequate stitch spacing and lateral support exhibited excellent load vs. displacement response with total plastic hinge rotations exceeding 5.0%.

A rational procedure is developed for applying equivalent nonstructural static force design requirements to generate a dynamic qualification test method for seismic validation of equipment for commercial service. The equipment qualification required response spectrum (RRS) is derived based on the National Earthquake Hazard Reduction Program's (NEHRP) lateral force procedure in conjunction with the building design earthquake response spectrum. This generic approach accounts for above grade elevation equipment installations, with or without knowing the building dynamic characteristics. Provisions are included to extend the qualification methodology to families of products by employing type-testing rationalization techniques. A well-defined pass/fail acceptance criterion is established that utilizes the equipment importance factor to define post-test acceptability.

Since 1997, the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures (NEHRP Provisions) has served as the primary resource document for all recently developed seismic codes and standards in the United States including American Society of Civil Engineers Standard 7 (ASCE 7). Also since 1997, the NEHRP Provisions have contained a separate chapter devoted to nonbuilding structures. Nonbuilding structures are generally defined as all self-supported structures other than buildings that have the capacity to carry gravity loads and to resist the effects of earthquakes. In this paper, the role of the NEHRP Provisions and ASCE 7 in the seismic code and development process is described. Also described are current and most recently adopted NEHRP Provisions for nonbuilding structures.

Preliminary performance and outage results obtained for an urban utility distribution system located in the Pacific Northwest subject to the Nisqually earthquake of 2001 are presented. The details of statistical and GIS-based investigations are provided. Correlations of outage data with instrumental Modified Mercalli Intensity, peak ground velocity and peak ground acceleration data are given. Through GIS-based comparisons, utility damage is estimated through a damage intensity factor. Implications of this factor are discussed.

Structures are generally regarded as having many attributes, including: 1) are self-supporting, 2) have the capacity to support gravity loads, and 3) have the capacity to resist seismic forces imposed at their base. Building codes historically are most interested in life safety and have historically concentrated on prescribing requirements for buildings occupied by the general public. Over time, the existence of nonbuilding structures has been acknowledged by building codes, with prescription requirements gradually being incorporated based on the performance of building structures. They have also recognized that some nonbuilding structures have building like systems (industrial frame structures, pipe racks) and some don't (tanks, vessels, silos, chimneys, cooling towers, etc.). This paper will show how nonbuilding structures similar to buildings have been handled in past building codes and summarize proposed changes for future building codes.

This paper examines an innovative project delivery system for structural steel buildings in the context of several case studies of actual projects. On each of the projects, the structural engineer provided complete structural design services for the entire building on a conventional contractor-led design-build team. In addition to those services, the structural engineer — under a separate contract to the general contractor — provided steel shop drawings, fabrication, and erection of the structural steel. The pros and cons of this delivery system are discussed in the context of the experiences related in the case studies.

This paper introduces ThinkTank a web-based asynchronous collaboration tool developed at the Project Based Learning Lab at Stanford University that provides many of the advantages of face-to-face team meetings combined with the utility of e-mail and the organization of database technology. An overview of the ThinkTank is presented. Three scenarios of use in the context of an industry pilot illustrate how ThinkTank can support key corporate activities. The experience gained and lessons learned during the industry pilot project in a structural engineering design office examine the impact of this collaboration technology on the design process as it relates to team dynamics and communications.

This paper presents an innovative use of web technologies to store and retrieve standard details over the Internet while capturing and presenting the rich knowledge behind the details in a way that facilitates retrieval and learning. With the implementation, the web becomes a virtual mentor. A feedback feature provides an interface with a web-based Discussion Forums that facilitates continuous feedback and refinement of the details that is transparent to all users, further increasing the educational value of the tool, as well as leveraging new experiences across projects and engineers in the firm.

As in any industry, trade practices have developed among those that are involved in the design, purchase, fabrication and erection of structural steel. AISC, through a consensus committee comprised of structural engineers, architects, fabricators, general contractor, steel detailers and erectors, completely revised the "Code of Standard Practice" dated March 7, 2000. This fifth revision of the code, first published in 1924, provides a useful framework for a common understanding of acceptable standards when contracting for structural steel. As such, it is useful for owners, architects, engineers, general contractors, construction managers, fabricators, steel detailers, erectors and others that are associated with structural steel construction. The intent of this presentation is to assist the SER and, in fact, the entire design and construction team in their understanding of the Code and to point out specific provisions that may warrant special attention. The SER, on the basis of his/her review of the Code and of this presentation, may wish to include specific specifications requirements in their bid or construction documents that would modify or enhance the application of the Code.

For the first time, AISC brought together representatives from the entire steel design and construction team to revise the Code of Standard Practice for Steel Buildings and Bridges. The new document, the fifth revision since it was first published in 1924, also features another first: It can be downloaded at no charge from AISC's website.

SDNF and CIS/2 were developed with different purposes in mind. SDNF supports the exchange of a steel structure design between two applications. CIS/2 was developed as a comprehensive exchange mechanism for multiple applications over the lifecycle of steel design, analysis, detailing, fabrication and erection. CIS/2 supports bi-directional file exchange, as well as direct linking between applications and neutral database implementations, with incremental updates. It was designed to also serve as a project repository.

The use of 3D modeling by fabricators has been common for more than a decade. The use of this technology within the design community to increase steel supply chain collaboration is explored in this paper. The primary case study was the recent project for the Adaptive Reuse of Soldier Field in Chicago, where the design team modeled the steelwork. The adoption of a model-based approach for steelwork has led to other relevant initiatives that will be discussed, including Concrete, Cladding and data standards such as CIMsteel Integration Standards (CIS/2) and IAI IFC's.

The primary constraint to realizing the full potential of data exchange and interoperability of three-dimensional structural models is not technology. Developing new business practices that support the generating, storing, revising, and accessing structural data are critical to successfully making the transition from executing projects using two-dimensional information (drawings), to working effectively within a three-dimensional environment. The structural steel industry is leading the way in making this transition. The steel industry is in a unique position to capitalize on the use 3D models rather than 2D drawings to control structural data. Historically the design and analysis of steel structures using computers has been a common practice for more than thirty years. This level of familiarity with electronically performing stress checks and member selection is not found in any other building component. Since the first inception of plant modeling, software that places steel beams, columns, and bracing has been a standard practice. This has provided easy access to structural data such as total steel weight, number of pieces, etc. The American Institute of Steel Construction (AISC) recognized the potential benefits of controlling structural data in a 3D model in the late 1990's. By promoting the use of the CIM Steel Integration Standard (CIS/2) as a worldwide electronic data exchange protocol for structural steel, the AISC provided important leadership in defining the technology necessary for multiple software applications to work together. The selection of a single data exchange protocol coupled with a long history of use of electronic data has led to a structural steel industry that is technically equipped to realize significant cost and schedule benefits for the use of 3D model data. However, realization of these benefits requires redefining business practices.

Recently, several organizations have issued position statements and guidelines recommending that the Structural Engineer of Record (SER) serve as the Special Inspector (SI) whenever possible and practical. The stated purpose for this recommendation is to assure that the SER is present on-site during construction of principal structural components thereby reducing the chance of structural failures due to unnoticed and uncorrected flaws or on-site changes. The key document cited in support of this recommendation is the Committee on Science and Technology's report titled Structural Failures in Public Facilities, House Report 98-621 that was presented to the 98^th Congress.

Just as an author of a book is communicating ideas when a book is written, so to is the structural engineer who is showing the contractor what to construct to comply with the engineer's intent. The tools of the engineer to communicate these instructions are the drawings and specifications comprising the construction documents. This information must be clear and concise and in sufficient detail to afford the contractor every opportunity to properly interpret the designer's intent. The type and amount of information that is required to properly specify the connection design for a structural steel project can be quite complex depending on the type of structure being built. This paper will describe how to properly convey the information needed by the steel fabricator and erector to connect the steel frame together.

Transfer forces are loads that are transmitted across joints in a structure. The determination transfer forces can be time consuming, but is an essential step in the design of safe and economical structures. This paper describes why the connection configuration must be determined before the transfer forces can be calculated. An example is presented that shows how to calculate the transfer forces for a simple structure.

The communication of connection design requirements between the Engineer of Record and the Connection Design Engineer is of the utmost importance to ensure both the safety and economy of structural steel projects. This paper explores and recommends some ways in which this information can be communicated.

The paper discusses the usefulness of business training for engineers in the A/E industry. The challenges of culture, industry practice and change are discussed. Given the current pace of advancements in technology and business, it is argued that a business training is necessary for engineers and companies alike to stay ahead of the curve.

For over thirty years, before becoming a professor of Civil Engineering at the Georgia Institute of Technology (GT), teaching students in 3 cities from his location in Savannah, Georgia, the writer was founder and president of his own consulting structural engineering firm. During this time, he had multiple contacts with universities through teaching, consulting, committee work, etc. However, these contacts did not prepare him for the tremendous change in how classes can now be taught and managed. Distance Education (DE) concepts were entirely new to the writer. After spending about two semesters "learning the ropes", it became clear that many of the DE techniques had tremendous application in the business world. Although there are many firms that are beginning to employ some techniques used by DE, there are many other DE techniques that that have enormous potential for business applications. Three of the most promising are the subject of this paper.

Large highly cored extruded day units with multiple cores and numerous thin webs offer the advantage of quick construction and excellent thermal properties. The units have been used in European construction, but are new to the United States. Testing included unit compressive tests, bond wrench flexural testing, and prism compressive tests. A modified bond wrench was constructed which allowed the testing of the large units. The modified bond wrench consists of a cable and pulley system that applies a pure couple to the specimen. The average flexural strength was 448 kPa (65 psi). The average unit compressive strength was 19995 kPa (2900 psi), with the average prism compressive strength being 6205 kPa (900 psi). The geometry of the highly cored units makes analysis for unreinforced masonry difficult. Therefore, an approximation was developed for determining the net moment of inertia for unreinforced masonry design.

Masonry is one of mankind's oldest building materials serving admirably in construction of shelters, buildings, and monuments for centuries. We marvel at the structures that stand after thousands of years. A testament to that system is the continued use of conventional brick, block and stone in all type and sizes of construction facilities in the USA. The last few years has seen an emergence in the USA of a new addition to the masonry system — Autoclaved Aerated Concrete Masonry. Autoclaved aerated concrete masonry units are manufactured from Portland cement, quartz sand, water, lime, gypsum and a gas forming agent. The units are steam cured under pressure in an autoclave transforming the material into a hard calcium silicate. The units are large, solid, rectangular prisms which are laid into masonry assemblages using thin-bed mortar. This paper covers all aspects of this masonry product from production to construction to applications to rational design provisions.

Fire ratings of wall assemblies can be determined by three different methods. The first and most used is by testing the actual assembly at a fire testing laboratory using ASTM E-119 standards. The second is where empirical calculations are used to determine the assembly's fire rating and lastly is performance based where the assembly is tested under actual conditions. This paper focus on approved performance based design and relation to ASTM E-119 test. Methods to improve the fire resistance of masonry walls are also discussed.

Current AISC ponding provisions are derived from simply-supported primary framing systems. When applied to framing systems where the primary framing is cantilevered over the supports (cantilever framing), the existing equations are overly conservative and take away much of the potential economy presented by cantilever framing. This paper provides a proposed modification to the current provisions, by deriving a modification to the flexibility constant, C_p, of the primary framing. This proposed modification is equally applicable to Load and Resistance Factor Design and Allowable Stress Design methods.

The uplift resistance of K-series open web steel joist seats was determined by physical testing of twenty-eight specimens to failure. The experimental data obtained from the physical testing was evaluated along with the mechanical properties of the steel material used in fabricating the joist seat test specimens. A simple analytical model was developed based on the experimental results using yield-line theory, which adequately predicts the ultimate uplift capacity of the joist seat. This ultimate strength model was modified to create simple AISC-ASD and AISC-LRFD design equations to be used in the analysis of K-series joist seats for uplift. Both the AISC-ASD and the AISC-LRFD design equations consider the following variables: Joist seat yield strength (nominally 50 ksi), anchorage weld length, seat length, and seat angle thickness.

The Metal Building Manufacturers Association (MBMA) has sponsored the development of a comprehensive manual for the practical seismic design of metal building systems. The manual, entitled the "Seismic Design Guide for Metal Building Systems", provides design approaches and procedures that are intended to be compliant with the seismic requirements of the 2000 International Building Code (IBC). The Guide, which is expected to be published and available in the second quarter of 2004, uses an example problem format and thereby provides interpretations about common design and analysis situations, which are common to metal buildings.

This paper summarizes a state-of-the-art (SOTA) study that reviews a suite of special issues encountered in the design of reinforced concrete structural members subjected to torsion, namely: (1) compatibility torsion and torsion redistribution; (2) limit design; (3) open sections subjected to torsion; and (4) behavior of steel-concrete composite sections. The intent of the detailed SOTA study is to review the available literature and consequently identify code's gaps and areas of needed research. This paper provides a summary of the surveyed literature and highlights the main findings of the detailed study.

Research is being conducted by ORNL for the USNRC to address aging of nuclear power plant (NPP) containment structures in light-water reactor plants. The importance and operating experience of nuclear power plant containments is reviewed. Factors that can lead to age-related degradation of containment metallic pressure boundaries (i.e., steel containments and liners of reinforced concrete containments) and reinforced concrete structures are identified and their manifestations described. Background information and data to develop methods to assess the effects of age-related degradation on structural performance are provided. Techniques for detection of degradation are reviewed and related research is presented. A probabilistic methodology for condition assessment and reliability-based life prediction is provided.

The paper will present a model for improving the durability and doubling the life of highway bridges. Data from a detailed characterization of highway bridges and new concrete mixture designs is presented to show the potential for simulation based reliability assessment (SBRA) for predicting chloride intrusion into bridge decks exposed to deicing salts. The paper presents performance based guidelines that can improve the long-term durability of bridges through the design and control of concrete constituents and construction practices.

Underground concrete vaults have been proposed to serve as secondary containment to prevent the release of low-level radioactive contaminants. The integrity of the concrete vault is crucial to isolate the saltstone (cement-grouted nuclear waste) from direct contact with the exterior environment. The concrete vault will most likely degrade through a combination of coupled multiple physical, chemical and mechanical degradation processes. The objective of this study is to develop a risk assessment methodology for evaluating the long-term durability of the concrete vault. Several significant physical and chemical degradation mechanisms, such as thermal expansion/contraction, drying shrinkage, and carbonation etc., are considered in this paper, under varying environmental conditions such as humidity and temperature. A finite element-based computational methodology is developed to compute the effect of multiple coupled degradation processes on the mechanical stress distribution and crack propagation in concrete vaults. The methodology is demonstrated using finite element software ANSYS.

This paper presents a reliability-based methodology for the evaluation of stiffness degradation of automotive spot-welded joints under high mileage. A global-local finite element analysis is used, with the loads on the detailed three-dimensional joint model coming from finite element analysis of the entire car model with proving ground loads. Probabilistic fatigue crack propagation analysis is developed for multi-axial variable amplitude loading history on the joint. Multiple spot welds contribute to the stiffness of the joint. Hence the problem is addressed through system reliability techniques. The effect of spot-weld separation on joint stiffness, and on global vehicle stiffness, is incorporated. This results in the computation of the statistics of vehicle stiffness degradation with mileage.

The probabilistic response (fragility) of light-frame wood construction exposed to extreme winds and earthquakes is assessed. Performance goals and specific limit states are identified from a review of building performance during recent hurricanes and earthquakes in the United States. Computational structural models provide platforms for risk analysis of light-frame wood structural systems, and model-based simulation is required to assess performance metrics. The reliability and risk analysis is demonstrated for selected common building configurations and construction (defined, e.g., by roof sheathing, truss spacing, and roof or shear wall nailing patterns). Limit state probabilities of structural systems for the performance levels identified above are developed as a function of 3-s gust wind speed (hurricanes) and spectral acceleration (earthquakes), establishing a connection with wind and earthquake hazards stipulated in ASCE Standard 7-02.

In order to demonstrate the application of a probabilistic simulation-based reliability assessment method SBRA in case of stability assessment of a simple system, a steel frame containing leaning columns is analyzed and its reliability is expressed by comparing the calculated probability of failure and the target probability defined in codes. The input variables are expressed by non-parametric distributions. An analytical transformation model is used and the reference function is defined by the onset of yielding.

The lack of ductility of plain high-strength concrete (HSC) has put some strong concerns on the adequacy of HSC columns when a higher ductility of the structural member is required, as in zones of high seismicity. In this study, the numerical simulation of the ductility of HSC columns is presented. Two mathematical models representing confined concrete behavior are discussed: the Razvi and Saatcioglu and the modified Fafitis and Shah models. Monte Carlo simulation is used to generate curvature ductility statistics for different concrete compressive strengths, amount of longitunal and transversal steel, and axial load levels acting on the column. It is shown that ductility may be largely increased if adequate amounts of confining and longitudinal steel are used.

The objective of this paper is to present the development of live load model using field measurement of truck load and live load effect in bridge components. The major truck parameters include gross vehicle weight (GVW), axle weights, and axle configuration (spacing). These parameters can be measured using weigh-in-motion technique, invisible to the drivers (to avoid bias).

The various issues of fire resistance design is outlined and the importance of performance-based design is emphasized. Systems approach to fire resistance design and evaluation is considered and a scheme for fire protection design is presented.

This paper outlines some of the main results in an ongoing project aimed at developing high-temperature models for the behaviour of the main components of steel end-plate beam-to-column connections in fire. In this particular phase of the work the emphasis is on the compression zone in the column web, when transverse compression acts concurrently with axial compression due to superstructure loading. The ultimate objective is to be able to construct component-based models of end-plate connections within global numerical modelling of steel and composite building structures in fire conditions. This is the only feasible analytical approach to connection modelling under the simultaneous effects of loading, thermal degradation of materials and forces due to restraint to thermal expansion. A simplified semi-empirical model has been validated against ANSYS modelling and isothermal high-temperature experiments.

An analytical approach consisting of three sequential analytical steps, namely, fire analysis, heat transfer analysis, and stress analysis was developed for predicting the behavior of CFT columns under fire loading. Analytical models were developed for each of these analysis steps. These included 3D finite element models for nonlinear heat transfer and stress analysis. The analytical approach and models were validated by comparing predictions with experimental results for CFT columns subjected to the standard ASTM fire test. The developed models and analytical approach are recommended for predicting the behavior of CFT columns under fire loading.

Reinforced high-strength concrete structures exposed to intensive fire have been found to be prone to explosive spalling. The objective of this study is to identify and quantify, using the numerical methodology presented, the development of thermal stress states that account for the occurrence of moisture induced spalling under rapid heating conditions. By use of the theory of stress superposition, pore pressures and concrete temperatures predicted by the model are included in a stress analysis that considers thermal dilatation and boundary constraint. The modeling techniques presented in the paper will be of interest to researchers involved in assessing the fire performance of high strength concrete.

To better understand how concrete behaves under fire conditions, an experimental program coupled with numerical modeling (using theories of heat and mass transfer) was implemented to measure and predict pore pressures in concrete under extreme temperatures. In an intense fire condition, the low permeability of concrete will inhibit the internal flow of steam (generated by the fire) and thus cause an increase in pore pressure that may then lead to spalling. Therefore, an experimental program of five concrete mixtures with various levels of permeability and porosity were subjected to conditions similar to those of a fire (time-temperature curves similar to those in the ASTM E119 and E1529 specifications) to evaluate the pore pressure buildup and spalling behavior. The pore pressures were then compared to those predicted by a finite difference numerical program for solving heat and mass flow problems.

A full-scale three-story, three-bay composite steel-concrete frame was pseudo-dynamically tested under ground motions representing four earthquakes of varying hazard levels, with imposed story drift ratios up to about 5.5%. The frame was then subjected to a quasi-static pushover, which imposed story drifts up to 10%. Overall, the test demonstrates that the composite frame performs as implied by building provisions, exhibiting very little damage under frequent earthquakes, controlled and repairable damage under the design earthquake, and collapse prevention under the maximum considered earthquake. This paper summarizes the planning, design, construction, and execution of the frame test, including a summary of the test results. Comparisons with analytical simulations and design implications are discussed in a second companion paper.

This is the second of two companion papers describing an investigation of a full-scale three-story composite steel-concrete frame that was pseudo-dynamically and quasi-statically tested out to inter-story drift ratios of 10%. This paper summarizes the analytical studies of the test frame, including comparisons with measured response and design implications. Damage indices are investigated to help interpret the analytical results and relate the calculated engineering demand parameters to physical damage in the frame. In terms of peak displacements and overall response, the analytical and measured frame response agree fairly well up to drift ratios of about 3%. Beyond this, discrepancies occur, which are likely due to degradation effects (e.g., local flange buckling) that are not modeled in the analysis. Comparison between calculated damage indices and observed damage suggest the need for further research to improve the performance simulation tools.

Innovative combinations of two or more materials can result in very efficient and high performing structural systems to resist severe forces due to events such as earthquakes. During the past two decades or so, significant gains in the knowledge base regarding the seismic behavior of composite and hybrid structural components and systems have been made. Much of this has been accomplished through international cooperative research programs. This paper presents an overview of two such major programs: The US-Japan Research Program which spanned over a period approximately seven years from 1993–2000, followed by the US-Taiwan Cooperative Research Program which started in 2001 and is currently in progress. While the US-Japan Program was significantly broader in scope and magnitude, greater emphasis was placed on component and sub-assemblage studies and testing of full scale structures could not be undertaken due to time and budget limitations. The US-Taiwan Program was designed to fill this gap, by undertaking testing of two full size three story, three bay frames at the National Center for Research in Earthquake Engineering (NCREE), Taiwan, accompanied by related sub-assemblage tests at participating research institutions in Taiwan and analytical and design implication studies in the US. The two structural systems selected for the US-Taiwan program are: RC column- steel beam (RCS) moment frames, and concrete-filled tubular columns-steel beams-buckling restrained composite braced frames (CFT-BRBF).

A full scale 3-story 3-bay concrete filled steel tube (CFT) column and buckling restrained braced (BRB) composite frame was tested using pseudo dynamic testing procedures and four earthquake accelerations. The key features of the structural system include using three different types of beam-to-CFT column moment connections as well as three different types of BRB. The CFT/BRB frame was designed using the displacement based seismic design procedure with a target inter-story drift limits of 0.02 and 0.025 radians for two hazard levels, 10% and 2% chances of exceedance in 50 years, respectively. The pseudo dynamic and analytical predicted responses of the specimen observed during the application of the earthquake load effects are in good agreement. This experimental program illustrates that the experimental response data and the video images of the specimen can be effectively disseminated through the Internet during and after the tests.

Recently, the authors proposed an analytical model based on decaying sinusoids for near-fault ground motion velocity pulses. This pulse model is used to investigate relations between strength reduction factor and ductility demand of inelastic structures subject to near-fault ground motions. It is shown that pulse ductility demand and pulse strength reduction factors match well with those of actual ground motions for which the pulse approximation has been obtained. It is found that the ratio of the period of structures to that of the velocity pulses, T/T_g, and the decaying factor for ground motion pulses, ζ_g, determine the strength reduction factor for constant ductility demand.

A thirteen span bridge was constructed in 2000 along the I-15 corridor in Salt Lake City, Utah. The S-shaped steel plate girder bridge continuously spans twelve concrete bents over a total length of 670 meters. Testing of this bridge provided an opportunity to analyze the bridge's natural frequencies and mode shapes from both forced and ambient vibration. An eccentric mass-shaking machine placed at the middle bent induced the forced vibration. Frequency sweeps were conducted in the horizontal direction. Local traffic, wind, and other sources produced the ambient vibration. Data was collected using two separate systems. The first was a permanent array of eighteen uni-axial accelerometers wired to two recorders at an adjacent free field site. The second was an array of temporary accelerometers and velocity transducers. The permanent instrumentation provides many opportunities in addition to the ability of recording large ground motion. The bridge can be continuously monitored through the collection of ambient vibration data. This data may be accessed through a dial-up modem. A few selected channels are being monitored using a real time link, which may be utilized for on-going studies and to monitor any changes in dynamic parameters due to normal aging processes.

Evaluation of a cracked hanger plate weld on Route 213 over Rondout Creek bridge, Eddyville, NY, is discussed in this paper. The bridge is a pinned-pinned steel structure consisting of two box arches and pin-and-hanger assemblies transferring deck dead load and live from the floor beams to the arches. Cracks were observed in the welds connecting the hanger plates to the diaphragm plate, at the West support of the second floor beam from the North bridge entrance. The cracks varied in length from 8 to 10 in., and have since been repaired/welded. The investigation was conducted to determine the forces and moments transmitted to the hanger plates through the pin connecting the hanger and link plates and estimate the distribution of stresses along the weld lines due to these forces and moments. The link assembly plates and diaphragm were instrumented to measure live load and thermal strains, and a finite element analysis was performed to determine the stress distribution in the repaired plate assembly. The investigation concluded that the observed cracking was caused by a misalignment in the assembly and that the contribution of thermal stresses was significant.

Case studies for integral abutment bridges with skew and with no skew are presented. Unlike conventional single span bridges where seismic forces are neglected, there is a need to consider seismic behavior in single span bridges with integral abutments to help design the buried abutment piles. Freedom of top of pile movement for thermal and seismic loads is provided by placing the top unsupported 5 M length in a steel pipe. Only a single row of piles is used. For pile design, seismic moments and forces be combined with dead load and partial live load results. Since the pile minor axis is placed perpendicular to the direction of beam, it is important to check the total unsupported pile length of pile, for axial buckling. For bridge stability, efficient details of integral connections between pile cap (with single row of piles) and beam ends are required. Connection details from various state bridge design codes are studied.

Like most of the states of Eastern United States, New York State ignored the potential for seismic damage to its huge population of bridges. There are about 20,000 bridges in New York State and majority of these bridges were designed with no consideration for seismic forces. This paper presents a comprehensive program, which was initiated, immediately after the Loma Prieta earthquake (1989), to evaluate and retrofit the potential seismic vulnerabilities of the existing bridges. As the researchers and seismologists developed advance methodologies and knowledge, the seismic provisions for the design of new structures and retrofitting of existing structures were refined accordingly.

Current Code requirements for bridge design require considerable increased capacity in lateral strength and displacement demand. These requirements for increased lateral capacity is very significant in foundation design and detailing as well as in other portions of the bridge structure. Moreover, rational models for the substructure design and evaluation are needed for the development of a Load and Resistance Factor Design (LRFD) code format. Therefore, modeling of soil and structure as well as the interface between them becomes very important and will have an impact on the design as well as evaluation. In this study, a non-linear finite element program (ABAQUS) is used to model the soil as a continuous medium around the pile. Cohesive and cohesionless soils are investigated using different soil models as well as different support conditions at the top and bottom of the pile. The results of the continuous soil analysis will be used to calibrate the discrete spring model and provide information on the accuracy and the applicability of these models. The results of this investigation will help to better understand the effect of soil stiffness on the structure and the accuracy of soil-spring models. The accuracy and applicability of these models for structural analysis under lateral loads will be verified.

This paper presents the analytical method for predicting the ultimate strength of concrete filled tube (CFT) column section. It is based on the concept that the concrete core develops its ultimate strength as a reference for determining the corresponding steel forces. The steel bar forces for a circular and a rectangular section has already been presented at the ISEC-02 conference. Hence, this paper describes only the method of determining the concrete forces to be added to the steel forces for the ultimate strength of CFT column section. Variables considered are concrete strain, ultimate concrete stress, steel yield strength, dimensions of the concrete core, wall thickness of steel tube and position of the column capacity axis. At ultimate condition of stress/strain, the resulting steel stress volumes on the concrete and on the CFT shell area are thus determined. Comparison of results with published data showed divergent values of the customary methods from this analytical method.

This paper describes the analytical method for predicting the ultimate strength of reinforced concrete columns using the true parabolic stress method of analysis. This methodology precludes the use of the current equivalent rectangular stress block, interaction formula and finite-element procedures to solve the ultimate strength of reinforced concrete section. This analytical method utilizes the concept of column capacity axis for equilibrium of external and internal forces which is a fundamental requirement in any structural analysis. It facilitates the calculation of the ultimate strength capacity of the column section at every depth of concrete section under compression and position of the column capacity axis. Variables considered in this method are the column section dimensions, concrete ultimate strength, f_c', steel yield strength, f_y, number, size, concrete cover, and spacing of reinforcing steel bars, and "θ", the inclination of the column capacity axis with the horizontal or the reference axis. Derived formulas for concrete and bar forces can be easily programmed in Microsoft Excel in customary or SI units.

This paper presents lessons learned from the structural design and construction of the Linear Accelerator Tunnel, the Ring Tunnel, the Ring to Target Beam Transfer (RTBT) Tunnel, and other surface facilities for the Spallation Neutron Source (SNS) Project of the Oak Ridge National Laboratory (ORNL) at Oak Ridge, Tennessee. Stringent design criteria and unique site geologic formation make up the uniqueness of the design and construction of the tunnels for this Project. The unique criteria include the required long service life of these tunnels and facilities in comparison to other general civil infrastructure, the required minimum differential settlement in the tunnels and their connections to other surface facilities, the required consideration of structural material to sustain a specified radiation dosage, and the requirement to survive the seismic event specified. Specific site geology, such as the Karst (sinkhole) formation, and its impact and remedies on the construction of these tunnels are also discussed.

The study addresses the influence of near-source earthquakes and soil-structure interaction on the pounding response of two adjacent bridge frames. In the study the bridge frames and the foundations are described by a finite element method, and the subsoil by a boundary element method. The result reveals that the subsoil together with the long-period pulses in the ground motions can significantly increase the pounding potential of the structure.

Beauty is defined in Webster's Dictionary as qualities that give pleasure to the senses or exalts the mind. In a structural sense, beauty has been defined by Kenner as un-redundant appropriateness, perceived by taste, going on to define taste as comparison performed with the certainty of habit. Mies Van de Rohe put it more succinctly with his words less is more. Most people cannot describe what beauty is but they certainly recognize it when they see it. Achieving that which is considered beautiful is a challenge for all designers.

Engineers lament that their "art" is often buried in concrete or hidden under fire proofing. This is particular so for seismic design where the subtlety of details and the rigour of seismic geometry go unnoticed and the impact of wind loads further masks any seismic innovation. This paper explores the scope for such structural expression in seismic areas in an attempt to get a sense of its potential with examples from New Zealand.

Sample controllers for three dimensional base isolated building benchmark problem with linear and frictional isolation system are presented in this paper. Kalman filter is used to estimate the states based on absolute acceleration measurements. Kanai-Tajimi filters are used to better inform the controller of the spectral content of the earthquake excitations. Reduced order control oriented model of the benchmark problem with linear isolation system is developed. H₂/Linear Quadratic Gaussian controller is presented for the active case; additionally, a clipped optimal controller is presented for the semiactive case. Magneto-Rheological fluid dampers are used for control in the semiactive case and actuators are used for control in the active case. A `skyhook' semiactive controller is also presented for the benchmark problem with nonlinear friction isolation system. Computed results of the passive, semiactive, and active cases are presented. Detailed comparisons of benchmark performance indices for base isolated structures with linear isolation system and nonlinear friction isolation system, with and without control, for a set of strong near field earthquakes are presented. The modeling and sample control designs demonstrated in this paper can be used to form the basis for studying wide variety of active and semiactive control strategies—to be developed by the participants in the benchmark study—for linear and frictional base isolated buildings.

This paper presents a tutorial control design for the base isolated benchmark building with bilinear hysteretic bearings (e.g., lead-rubber bearings) by addressing the coupled problem of finding a good linear model for the controlled nonlinear system and designing a linear optimal controller. First, the dynamics of the benchmark structure are reviewed and developed in a control-oriented manner. Second, an initial linear model, based on small-motion behavior, is developed. This model is then used to determine a reasonable cost function, trading off drifts and absolute accelerations in the structure. Then, an iterative study is described for developing the linearized model and corresponding linear control design. A Kalman filter is used as an estimator, and a Kanai-Tajimi filter is used in the control design to model typical ground motion frequency content. Finally, the responses of the controlled equivalent linear system and the controlled nonlinear system are compared for a specific ground motion data.

This study examines the sensitivity of structural response statistics to the characteristics of both the ground motion and the passive damping components for seismic isolation systems. Conclusions regarding appropriate levels of passive damping to protect an isolated building from ground motions representative of both near-field and far-field motions are based on time domain analysis of a large proto-typical seismically isolated building structure, as described in the Benchmark Problem statement. Results indicate that there are ranges of passive damping for linear isolation systems for which super-structure responses such as floor accelerations and inter-story drifts are minimized and in some cases, these minima are within code requirements.

This paper presents the benchmark problem definition for seismically excited base-isolated buildings. The objective of this benchmark study is to provide a well defined base isolated building with a broad set of carefully chosen parameter sets, performance measures and guidelines to the participants, so that they can evaluate their control algorithms. The control algorithms may be passive, active or semi-active. The benchmark structure considered is an eight story base isolated building similar to existing buildings in Los Angeles, California. The base isolation system includes both linear and nonlinear bearings and control devices. The superstructure is considered to be a linear elastic system with lateral-torsional behavior. A new nonlinear dynamic analysis program has been developed and made available to facilitate direct comparison of results of different control algorithms.

Life cycle cost oriented seismic design of steel moment resisting frame structures is formulated as a multiobjective optimization problem that treats initial material/construction cost, lifetime seismic damage cost, and the number of different standard steel section types as three separate objective functions. The static pushover analysis is used for estimating seismic structural performance in terms of maximum interstory drift ratio demands. In accordance with SAC/FEMA guidelines, the seismic damage cost is computed with percentile probabilities of a spectrum of damage states that are demarcated by respective interstory drift ratio capacities. A multiobjective genetic algorithm is selected for the posed optimal design optimization problem. The present procedure naturally integrates user-specified confidence level on damage cost estimate and produces a wide distribution of alternative designs that exhibits an optimized tradeoff among relevant conflicting objective functions. Therefore, designers have much freedom to determine the final structural design with a preferred balance of initial coat and damage cost, while taking into due account the design complexity issue.

Adaptive Simulated Annealing is used to generate economic cost maps for one-way slabs and beams subject to flexure and shear which are used to establish revised guidelines for economic selection of concrete flexural elements. Using #6 to #11 reinforcing bars produces unnecessarily expensive designs. #3 to #7 bars were present in the overwhelming majority of the optimal designs. For girders, two layers of flexural reinforcing appeared more frequently in optimal designs than did a single layer. The expression bd² = 20 M_u. does not provide a generally accurate means of proportioning the least expensive flexural members. The least expensive members frequently had reinforcement ratios significantly lower than the assumed 1%. For girders, stirrups were very often included in optimal designs. For one-way slabs, small (#3, #4, #5) and medium (#6, #7, #8) bars are used more frequently in optimal designs. When deflection is not calculated, medium bars appear most frequently in optimal slab designs.

One of the great advantages of cold-formed steel is the immense flexibility that the material affords in forming cross-sections. This flexibility would seem to readily lend itself to optimization of member cross-section shapes. However, little research has been conducted to explore this general problem; in part, because most existing optimization attempts have used prescriptive design standards that apply to a very limited set of cross-sections for their objective function evaluation. A newly introduced design procedure, the Direct Strength Method, or DSM, provides a method for evaluating the strength of cold-formed steel sections of arbitrary geometry. However, such an arbitrary problem, with a highly nonlinear objective function, is still difficult to solve by traditional optimization methods. A new technique, known as Knowledge Based Global Optimization, or KBGO, has recently been introduced which appears to hold promise for general optimization problems of this nature. In this paper, KBGO is applied to the member shape optimization of a cold-formed steel column to demonstrate the potential of this new optimization technique when combined with new advanced analysis methods (DSM) for member strength prediction. The results demonstrate that KBGO is indeed effective for such a problem, and can also shed some light on key features that are important for a successful member cross-section.

This paper presents an automated performance-based design methodology of steel moment frames using the reliability methods of FEMA 350. An integrated and flexible computational platform is programmed using Carroll's GA (Carroll) and DRAIN-2DX. It is validated through designing different structural systems for a variety of design optimization objectives. The present paper illustrates the process and discusses the resulting designs of a portal frame subjected to multi-level earthquake scenarios. The automated probabilistic performance-based design (PBD) is implemented using inelastic response history analysis to account for geometric and material non-linearities. The design objective is to minimize the cost of construction constrained by a certain predefined set of confidence levels in meeting multiple structural performance-objectives for multi-level seismic hazard.

The design of steel-concrete composite and non-composite wide-flange beam/girder steel floor systems is considered in this study. A design problem is formulated for least-cost optimization of a floor system panel. Constraints include the latest AISC design specifications, deflections, and vibration due to human activity. User input is limited to loading and overall floor system panel dimensions. A genetic algorithm (GA) is used to generate solutions including the girder shapes, beam shapes, number of "filler beams", number of shear studs on both beams and girders, steel-concrete composite deck profile, and concrete in-fill. Solutions generated by the algorithm are compared to software published by the AISC. The genetic algorithm is then utilized to generate optimal system selection charts for steel floor framing systems for a variety of live loading conditions, consideration of vibrations, and composite versus non-composite beam systems. Discussion of the GA solutions is provided as well as general observations regarding the optimal configuration charts generated.

Concrete Masonry Unit (CMU) wall construction is prevalent throughout the United States and the world. While masonry provides adequate strength for conventional design loads, in many circumstances it is inadequate for meeting the minimum standards mandated for blast protection of new and renovated government construction. Protection of military and civilian occupants of masonry structures has received long needed research, due to increased terrorist threat and government mandates for new construction and renovation of federal buildings. The US Army Engineer Research and Development Center (ERDC) has been involved in blast resistant structures research for decades. In the last ten years analytic approaches developed for hardened structures were adapted to terrorist bombings of conventional construction. In addition, simplified response surface based methods, developed to access damage from accidental explosions, were employed to develop models for terrorist bomb attack. These pressure-impulse (P-I) methods were derived from limited data sets and single-degree-of-freedom analytic models. Retrofits to mitigate blast hazard to occupants of masonry structures have been the focus of recent ERDC research. This research resulted in economical retrofits to reduce debris hazard for occupants rather than to blast-harden the masonry structures. This paper summarizes the development and use of simplified models for the analysis and design of CMU walls and the experimental programs used for model validation.

Reinforced concrete columns and walls in existing buildings can be economically retrofitted to resist blast effects. The blast retrofit of reinforced concrete columns using steel jackets or FRP composites wraps was started after the Oklahoma City bombing. It was shown that, in such events, columns on the first floor can be sheared off and lead to progressive building collapse, but that these columns can be upgraded to resist the blast loads and building collapse can be prevented. Similarly, it was shown that walls can be retrofitted to withstand high loads and protect building occupants. As part of a multiyear anti-terrorist program, under the auspices of the Technical Support Working Group (TSWG) and the Defense Threat Reduction Agency (DTRA), full-scale test series were recently completed to quantify the effects of terrorist explosions on conventional buildings and structural components, and to demonstrate these retrofit methodologies. A retrofit design procedure developed by Karagozian & Case (K&C) using steel jackets and FRP wraps was shown to successfully prevent column damage and building collapse, for circular, square, and rectangular columns. This simple column blast analysis and retrofit design (CBARD) procedure was based on first-principle calculations and has been verified and validated against many full-scale blast tests as well as quasi-static laboratory tests. Similarly, a wall retrofit design procedure was completed. Both procedures were coded to run in a Windows environment. Designs of columns and walls can be completed in minutes by experienced program users.

Recent terrorist bomb attacks on buildings have resulted in increased interest in the protection of key buildings. Various research programs have provided improved design and analysis techniques as well as new mitigation methods. Advanced finite element methods provide the best analytical results because they can take into account the time varying load, dynamic structural response, non-liner material properties, and the non-linear interaction of various response modes (e.g., shear and flexure). These methods require not only time but also specialized expertise to obtain good results. They are therefore generally unpractical for typical blast design problems. Simplified methods can provide reasonable approximations that are adequate for design. A variety of types of simplified models exist. Typical models include single or multi-degree-of-freedom, pressure-impulse (P-I) diagrams, and response surfaces developed from finite element analyses. This paper describes some recently developed simplified models and associated research.

This paper discusses a study performed by the Portland Cement Association (PCA) to examine the application of the progressive collapse analysis and design guidelines included in the U.S. General Services Administration (GSA) publication "Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects" to concrete frame buildings. Three reinforced cast in place concrete moment-resisting frame buildings, each 12 stories high and each with different seismic design categories (SDC), were analyzed and designed using the ETABS Nonlinear version 8.11 structural analyses and design software. The flexural and shear reinforcement for each building was calculated according to the strength requirements of the 2000 International Building Code (2000 IBC). The seismic use group, site class definition, and spectral response accelerations were selected to represent seismic design categories A, C, and D for each building used in the study.

The provisions in the applicable building code are almost exclusively oriented toward life safety, with very little if any consideration of protection of property. Similarly, there are no explicit requirements for the consideration of blast and progressive collapse resistance, with the exception of general statements about resiliency, redundancy and robustness. This paper gives guidance for typical buildings, as well as the special cases of prescriptive and performance-based design for blast and progressive collapse resistance. When a building owner chooses or is required to consider defensive design features, the considerations usually fall into one of three general categories.

A design procedure utilizing an ant colony optimization (ACO) technique is developed for discrete optimization of steel frames. The objective function considered is the total weight (or cost) of the structure subjected to serviceability and strength requirements as specified by the American Institute for Steel Construction Load and Resistance Factor Design (AISC-LRFD). The design of steel frames is mapped into a modified traveling salesman problem (TSP) where the configuration of the TSP network reflects the structural topology, and the resulting length of the TSP tour corresponds to the weight of the frame. The resulting system is minimized using an ACO algorithm with a penalty function to enforce strength and serviceability constraints.

Many methods have been developed and are in use for structural sizing optimization, in which the cross-sectional areas, i.e., sizing variables are usually assumed to be continuous. In most practical design problems in structural engineering, however, the design variables are discrete. This paper proposes an efficient optimization method for structures with discrete sizing variables based on the harmony search (HS) heuristic algorithm. The recently developed HS algorithm was conceptualized using the musical process of searching for a perfect state of harmony. It uses a stochastic random search instead of a gradient search, so derivative information is unnecessary. A discrete search strategy using the HS algorithm is presented in detail and its effectiveness and robustness, compared to current discrete optimization methods are demonstrated through a standard truss example. Numerical results reveal that the proposed method is a powerful search and design optimization method for structures with discrete sizing variables and may yield better solutions than those obtained using the current methods.

Particle swarm optimization (PSO) is applied to the low-weight design of trusses. The objective function considered is the total weight (or cost) of the structure subjected to stress and displacement constraints. Traditionally, PSO has been applied to unconstrained problems; in this application, a hybrid PSO procedure incorporates a penalty function to account for stress and displacement constraints. In addition, the hybrid PSO procedure includes a search space reduction strategy that attempts to focus the search in the near-vicinity of the best solution found. The effectiveness of the hybrid PSO design procedure is demonstrated with several examples and compared with other classical optimization methods.

A data classification system is designed by pattern recognition to preprocess data that can be utilized in a genetic algorithm (GA) that performs search and scaling task of finding strong ground motion (SGM) records for seismic design. Tectonic settings, regional consideration of seismology and site characteristics are taken into account as well as nonlinear structural response and performance-based design requirements for selection of input motion records. The objective of this study is twofold. First, a better understanding of SGM characteristics is attained by applying statistical pattern recognition techniques. Second, the classification of records makes it possible for the GA-based search and scaling methodology, developed in an earlier study by the authors, to present more appropriate input motion records in the design bin for the site under consideration. Better seismic hazard representation would result in reduced uncertainty in demand estimation in the probabilistic performance-based context, which in turn will enhance structural performance and cost efficiency of design.

Applications of continuously developing optimization techniques to design and analysis of structures have resulted in very elegant solutions for weight, shape and topology optimization of trusses, frames and other structures. In the algorithms used for this purpose, while the search for the best configuration is performed by the optimization technique chosen, the related structural analysis is carried on by "classical" methods, the most outstanding one being the finite element method. Now it is being shown that the structural analyses themselves can be performed by genetic algorithm, simulated annealing or the like. This new approach, being very practical and standing on very sound simple principles, also have enormous advantages over all other methods including finite element or boundary element methods and present itself as a very efficient structural analysis method, to say the least. The method is successfully applied to trusses with material and geometrical nonlinearities, until and exceeding the loss of stability, giving the deflected shape with very high accuracy. Although the method is applied to trusses in this analysis, it has been explained that it can be generalized for being applied to the analysis of more general types of structures. Besides being an effective tool for structural analysis, the method can be extended to be used as a design tool in finding the optimum shapes taking into account nonlinear behavior.

In this paper, updated evolutionary computation (UEC) is employed in conducting parameter identification (PI) for reinforced concrete (RC) framed structures. In the UEC algorithm a structure of parallelism in genetic learning procedure, exponential-fitness scaling scheme and two methods of mutation (random and uniform) are adopted to improve the numerical efficiency, and finite element method (FEM) is incorporated with evolutionary computation (EC). Based on the site measured displacements and FEM analysis, the algorithm presented uses UEC as a tool to achieve successfully identification for stiffness coefficients and Young's modulus of the RC framed structures. The research work shows that the presented UECalgorithm is efficient and versatile, and its identified results are in a closing agreement with the measured actual data.

This paper presents a new methodology for the solution of simultaneous linear equations. The method bypasses the need for inverting the coefficient matrix or its usual row transformation. The convergence is guaranteed when diagonal of the coefficient matrix is dominant. Any damage assessment of the original structure, even on a percentage basis of damage, can most suitably be made by using this method; such that provisions against any anticipated damage can then be included as a design cycle, right at the outset, in the initial analysis.

Analysis and design optimization of structural systems loaded into nonlinear regimes of behavior is computationally intensive. When stable, implicit modeling techniques are employed, highly nonlinear multi-step problems with millions of degrees of freedom can be encountered. As the size of the model problem n increases the bottleneck operation through which the structural analysis must pass repeatedly is that of solving linear algebraic equations in which the coefficient matrix is semi-sparse and sometimes highly ill-conditioned. Research has been performed on scalable on multi-level solving methods that might require O(n) floating point operations, with optimal bounds on the complexity of the problem so that massively parallel computing architectures can be used efficiently. The performance of multilevel solvers on continuum finite element models of structural mechanics applications is demonstrated and discussed.

This work addresses the time history analysis of structures subjected to dynamic loads using high performance computing environments. Structural mechanics, parallel computing, and object-oriented programming methodologies are integrated to design and implement frameworks for parallel and sequential transient finite element analysis (TFE++ and PTFE++). The object-oriented approach is employed to facilitate extensibility, reusability, maintainability and simplicity of the resulting software. Parallel processing concepts and algorithms are used in the design of PTFE++. An application has been developed to demonstrate the developed frameworks. It has been found that PTFE++ provides an efficient way to analyze large structural systems.

This paper presents a parallel nonlinear finite element program, ParCYCLIC, which is designed for the analysis of cyclic seismically-induced liquefaction problems. Key elements of the computational strategy employed in ParCYCLIC include the deployment of an automatic domain decomposer, the use of the multilevel nested dissection algorithm for the ordering of finite element nodes, and the development of a parallel sparse direct solver. Simulation results of grid models and a centrifuge test model using ParCYCLIC are presented. Performance results show that ParCYCLIC is efficiently scalable to a large number of processors.

In this paper a neural network model is proposed to obtain nonlinear moment rotation curves for semirigid connections. The resulting model is then integrated into a nonlinear frame analysis program to obtain nodal displacements and corresponding frame element forces. A parametric study of two different network topologies is included in which the number of input parameters, neurons, and hidden layers is varied. Results for a two story one bay frame with semi rigid connections are given and compared to previous published results.

The paper describes a numerical study about topography effects on design wind load by using Computational Fluid Dynamics (CFD) techniques. For this purpose a CFD tool was developed using an object oriented approach and C++ programming language. The CFD procedure consisted of solving the Reynolds time-averaged Navier-Stokes equations and the standard k-ε turbulence model using body-fitted nearly orthogonal grids. A robust grid generator tool suitable for producing orthogonal grids over curved and sloping complex surfaces has also been developed. Subsequently, wind load design parameters such as speed-up ratio values were generated for a wide spectrum of terrain geometries that included escarpments, single and multiple hills, and valleys. Ground roughness and geometry approximation effects have been investigated. For validation of the CFD results as well as highlighting advantages and disadvantages of a particular method, results obtained from a variety of sources were compared: the present CFD study, Boundary Layer Wind Tunnel (BLWT) experiments, field measurements, NBCC 1995 provisions, analytical methods, and previous numerical works available in literature. The present CFD results compare well with BLWT data. Speed-up ratio values are produced for both new and covered cases by the 1995 Commentaries of National Building Code of Canada.

Numerical simulations are employed to investigate the scale (Reynolds number) dependency and macro-flow dynamics of impinging jets with applications to downburst simulations. It is found that the flow is Reynolds number dependent most probably due to an unstable separation-reattachment near to the wall. Also, the effect of various axial and radial confinements on the flow is experimentally investigated. While the axial confinements effects are minimal, radial confinements of a radius smaller than approx. eight jet diameters are found to alter the flow dynamics.

In the paper the appropriate use of computational fluid dynamics in wind engineering is discussed. The approach to different application areas is described and discussed. Three application are highlighted through examples: a pedestrian-level wind environment study, flow around a full-scale building and wind effects on bridges.

In this paper, aeroelastical vibration analysis of rectangular cross-sections based on k-ε model is discussed. In the computation of aeroelastic vibrations, two dimensional analysis is advantageous compared with 3D analysis in computational time. In this paper, applicability of the two dimensional k-ε model which incorporates three dimensionality of the flow by its turbulent viscosity on the prediction of aeroelastic vibration is demonstrated through the inspection on its application to various types of phenomena, i.e. the characteristics of the stationary cylinder, vortex-induced vibrations in heaving and torsional mode, torsional flutter and coupled flutter.

In earlier times when computers were neither available nor essential, one objective of the structural design process was to discover a computational method, which was elegant, simple and appropriately accurate. When such a process was identified it was recorded as an expedient approach to solving a recurring structural design problem. Thus, quick "Rules of Thumb" became essential resources for the structural engineer. As computer software has proliferated, become very comprehensive, and been made very user friendly, the importance of "Rules of Thumb" and approximate methods has been diminished. It has been argued that, with the computational speed and ease of application of computer methods, the need for approximations and "Rules of Thumb" no longer exists.

The total cost of construction for a steel building can be classified into four categories: Material costs, Fabrication labor costs, Erection labor costs, and Other costs.

AISC's Steel Solutions Center has spoken with thousands of engineers, architects, general contractors, owners, fabricators and erectors who have questions about anything and everything having to do with steel construction. Often, we are asked the same question a dozen times before it raises a flag. Others are about situations that occurred in the field and we are quick to learn that these only need to be asked once before we have an answer. It is these situations that we want to pass on to the industry as "Lessons Learned from the Field". Hopefully, by learning from others' mistakes, the practicing engineer won't make the same mistake, saving the owner both time and money.

The design of a steel frame structure and its subsequent construction are coupled activities that both derive benefits from regular communication between designer, fabricator, and erector. This presentation describes plans for a software system that fosters this communication by integrating the activities of structural design and construction planning within the framework of a single genetic algorithm. The software is designed to offer incremental improvement suggestions that lower overall cost, considering initial material costs, fabrication and erection costs, and estimated life-time seismic damage costs.

NONLIN is a computer program that has been specifically designed to enhance learning in graduate university classes and continuing education seminars that cover subjects related to structural dynamics and earthquake engineering. The program is highly interactive, graphically intensive, and user friendly. This paper describes the basic features of NONLIN, and provides several suggestions for use in an academic environment. The latest version of NONLIN may be obtained at no cost by sending an e-mail request to the principal author of this paper.

XTRACT started as an academic and research tool at the University of California at Berkeley as a program titled UCFyber. At its infancy, UCFyber was the first interactive Microsoft Windows based program that performed moment curvature analysis for reinforce concrete cross sections. The program had the capability of performing realistic analysis of cross sections incorporating the effects of increased strength and ductility of confined concrete as well as nonlinear steel behavior within a graphical environment. While XTRACT has become an invaluable instrument for concrete research within earthquake engineering, it has also evolved to become a production tool for analysis and design of concrete systems within design offices around the World. XTRACT is an important tool for earthquake engineering analysis when a realistic assessment of moment and curvature capacities of a cross section is required. This paper discusses some of the basic analytical features within XTRACT and introduces some innovative uses of the program for seismic assessment of reinforced concrete columns. During seismic excitation of concrete moment resisting frames axial forces vary due to overturning demands. This, in turn, affects the ultimate curvature capacity and consequentially, the seismic displacement capacity of the concrete columns. By generating a plot of axial force verses ultimate curvature, curvature demands can be checked directly for a concrete column within a seismic force resisting frame. This paper outlines the methodology behind the creation of this type of diagram and includes example diagrams for both unconfined and confined rectangular concrete cross sections.

EQTOOLS is a computer program that has been specifically designed with the objective of providing engineers, researchers, and students with facilitated access to powerful state-of-the-art computational tools in the field of engineering seismology and earthquake engineering within a performance-based design framework. EQTOOLS constitutes an easy and efficient way to process strong-motion data, featuring a user-friendly visual interface and the capability to derive a number of strong-motion parameters often required by structural engineers, seismologists, and geotechnical earthquake engineers. In addition to this, EQTOOLS also provides the necessary means to investigate frequency content of accelerograms, carry out high-pass, low-pass, band-pass, and band-stop filtering using three different digital filter types, generate and scale elastic response spectra, and perform time-domain linear or nonlinear site response analysis. While EQTOOLS may be used for professional practice or academic research, the fundamental purpose behind the development of the software was to make available a classroom/laboratory tool that provides a visual basis for learning the principles behind the selection of ground motion histories and their scaling/modification for input into time domain nonlinear (or linear) analysis of structures. This paper describes the basic features of EQTOOLS, and provides suggestions for its application in a learning environment. The latest version of EQTOOLS may be obtained at no cost by sending an e-mail to the authors of this paper.

The concept of an earthquake design spectrum is an integral part of design codes in the United States and around the world. Such design spectra are idealizations of actual earthquake spectra. The understanding of earthquake spectra and their relationship to the response of a single degree of freedom system is essential to the understanding of the design and performance of structures under earthquakes of any magnitude. As opposed to linear spectra, nonlinear spectra represent the response of structures that undergo yielding and damage during a seismic event, and are hence more representative of actual structural performance under a moderate or significant earthquake event. The computation of nonlinear spectra is complex and involves a significant amount of computation and synthesis of results. Bispec is an interactive computer program that facilitates the process of computing various types of linear and nonlinear spectra. By applying common dynamic analysis algorithms for the computation of the response of one or two degree of freedom systems, and providing access to complex results through a simple user interface, Bispec can be used to analyze simple systems, and to gain a deeper understanding of earthquake ground motions and their effect on structures of various shapes and sizes.