Structures Congress 2010

As noted in the "Durability Survey of Segmental Concrete Bridges"¹, third Edition published September 2007, the state of Florida has built and cataloged over 76 concrete segmental bridges since 1981. As one of the first states to fully embrace this technology Florida has also experienced several durability issues related to inadequate design detail, pour construction practices, and insufficient material specifications. Despite these issues all concrete segmental bridges in the state of Florida have an average superstructure rating of 7.4 which correlates between very good condition (8) to good condition (7). Florida first response was through design bulletins and DCE memorandums to address the immediate needs. This process included inspection of all existing structures for problems followed by implementing design changes that include fundamental change to design philosophy as well as improvements to the design and construction details for new structures. This effort was not limited to design only but also included the training of Engineers and technicians implementing grouting certifications, post-tensioning certification and the implementation of new material standards for post-tensioning systems and ducts. This effort led the State of Florida to take a very aggressive five part strategy to improve the durability of these structures.

I-4/Lee Roy Selmon Expressway Interchange at Tampa, Florida is a multilevel Freeway-to-freeway interchange project will facilitate traffic movement between I-4 and Lee Roy Selmon Expressway. It includes 23 bridges, mostly elevated Interchange ramps, with a total approximate length of 12 miles and approximately 1.5 million SF of bridge deck. The project stakeholders are Florida Department of Transportation, Tampa Hillsborough Expressway Authority and Florida's Turnpike. The project was awarded for construction in September 2009, and it is expected that the bridge will be open to the traffic in Spring 2013. The construction capital cost of this interchange is $389 million dollars.

The Memorial Causeway Bridge connects Clearwater and Clearwater Beach, Florida by spanning across the Intracoastal Waterway. The structure is composed of two parallel, elevated, cast-in-place, post-tensioned, trapezoidal box girders. The approach spans were placed on falsework while the channel spans were placed using the balanced cantilever method. During construction of the bridge, two separate falsework collapses occurred and the causes of those collapses were investigated.

Due to the severe curvature and narrow box girder width, along with small ratios of the anchor span to the main span at many locations of the I-4 Connector, the use of two bearings per box resulted in a significant uplift. PBS&J investigated several alternatives including outriggers and modifications to the erection sequence to eliminate the uplifting. Most of the options investigated were expensive, not practical or aesthetically not pleasing. With the cooperation of the FDOT central office, a single pot bearing support was introduced at the end of the anchor span for certain units. This paper will discuss the approach of the design, several implemented details, and the limitation of the proposed method.

This intersection is one of the most highly traveled and congested intersections in Central Florida. The improvements include the widening of SR 50 and the construction of a bridge over SR 436. The resulting bridge contains a varied span arrangement due to a skewed approach of SR 436. Several superstructure and substructure alternatives were studied. Special aesthetics requirements, Traffic control restrictions, and the construction sequencing also impacted the evaluation of structure types. The use of simple spans reduced the complexity during construction by minimizing the impact on the traveling public. The bents for the bridge were placed normal to the roadway in order to simplify construction. The intermediate bents consist of an inverted T-cap section. This article will discuss the implementation of both the superstructure and substructure design types for this unique project. This includes the use of simply supported box-girders, post-tensioned post-tensioned inverted T-caps, simplified construction sequences, girder shipping lengths, and accelerated erection times.

Prestressed concrete tub girders curved in plan (hereinafter abbreviated CPPCG) have seen increasing use in Colorado as a substitute for steel I/tub girders or cast-in-place, post-tensioned concrete box girder systems. This presentation will cover design, fabrication, and shipping/erection issues as well as owner-related considerations. Multiple metrics will be used to compare this system to more traditional structure types. Examples from projects built or in the construction stage will be given.

Bridge load testing is one of the options increasingly becoming popular among bridge owners to extend service life of in-service bridges by obtaining better estimates of the actual load capacity and as a periodic monitoring tool to evaluate new materials and designs. This paper provides the details of a generalized model suggested recently by the authors for evaluating the value of load testing.

The flame shortening procedure often used to adjust tensions in the eyebar members of steel railroad trusses relies upon observed vibrations of the eyebars to predict dead load stresses in these members. The method is based on a model that assumes pinned-end conditions, but for vibrations about the minor axis of an eyebar, the potential exists for a significant degree of rotational end restraint. This paper develops the analytical model for fixed-end conditions and demonstrates that when such conditions exist, the use of the conventional pinned-end model can result in significant error, particularly for eyebars of relatively low slenderness. Field test results are discussed that show eyebar behavior to be consistent with fixed-end conditions when pin joints are tight. Charts are presented that enable the accurate determination of dead load stresses for fixed-end eyebars; these tools may have additional utility for bridge inspection and rating.

In today's economic climate - of making every infrastructure dollar count — it is critically important to properly inspect and maintain our older long span bridges. Routine bridge inspections and maintenance not only provide the user with a safer structure, but also provides the owner with a bridge that will stand the test of time. Bridge inspection/maintenance procedures, however, can be costly to the owner and a major inconvenience to the user when access to the underside of the structure can only be achieved from inspection vehicles parked on the bridge deck. Travel lane closures to complete the required work can cause significant safety and traffic problems, especially on narrow bridges. To address these concerns, the Burlington County Bridge Commission made the decision to install a motorized rolling traveler platform beneath its Burlington-Bristol Bridge. The Burlington-Bristol Bridge is a long span moveable toll structure that crosses the Delaware River, connecting southeastern Pennsylvania with New Jersey. The bridge carries two 10' travel lanes and a 4' sidewalk, thus requiring a night time bridge closure when inspection or construction access vehicles, such as snoopers, are required. The traveler system was installed on the Burlington-Bristol Bridge during the summer of 2009. When suspended from the underside of the bridge, the traveler platform will be guided by motorized carriages that will travel along steel track beams. The total travel range of the platform is 940' and includes access to the 540' moveable vertical lift main span and the two adjacent 200' tower spans. When needed, the traveler platform will be lifted in place from a small boat along the river, eliminating traffic disruptions on the bridge, and used for bridge inspection, maintenance and repairs. It will only occupy the underside of the bridge when being used; once work is complete it will be removed. The traveler platform will greatly benefit the owner as well as the user by providing a more economical, safer and non-disruptive underside inspection and repair alternative when compared to past procedures that required travel lane closures.

During a review of the test results and toughness calculations for cracked wires found in samples removed from the Severn Bridge in the UK, it came to our attention that, although the tensile strength (breaking load divided by the original area of the wire) of the wires was reduced, recalculating the tensile stress on the remaining area of the wires resulted in the same stress as the tensile strength of the wires that were not cracked. Wires that were found broken in the cable, however, broke at the working stress in the cable. Since many broken wires are estimated to be present in the cable, it would be expected that some tested wires would have broken at a stress lower than the wire's tensile strength, but greater than the stress in the cable. The fact that no such cracked wires were found leads to the possibility that even low stress range fatigue contributes greatly to the rate at which cracked wires deteriorate once the crack depth reaches a critical value and the time to failure becomes so short that very few of these wires will be found during an inspection. This suggests the need for fatigue tests on already cracked wires to determine whether there is an effect.

This study examines the structural behavior of bridge timber piles under eccentric compression loading. A collapsed rural concrete bridge supported on timber piles was used as a prototype in this study. Samples of the collapsed piles were retrieved and experimentally tested under compression and combined compression and flexure. The experimental timber pile response was used to calibrate an numerical model of the full timber piles of the prototype bridge, including material and geometric nonlinearity as well as soil-structure interaction. The numerical results illustrated that the pile strength was significantly reduced under eccentric load compared to concentric load. It was concluded that the effect of compression-flexure interaction on bridge timber piles must be checked during design, especially in the case of simply-supported superstructures where loading on one span may lead to eccentric loading on a timber pile group.

Buckling of piles may become a severe issue for bridges when scour increasingly erodes away soils around the pile foundation, exposing unsupported lengths above the ground surface. A p-y based approach for buckling analysis was developed to consider buckling behavior of piles due to scour. The procedure utilized multilinear spring stiffnesses to approximately representp-y curves at different depths. The approximated spring stiffnesses were incorporated into the structural analysis model, and buckling analyses were conducted. The p-y based approach for buckling analysis was verified by laboratory tests presented in the literature. Buckling of axially loaded piles due to scour was investigated based on the p-y based approach. The results showed that multilinear soil stiffness may be successfully used to represent the p-y curve as a result of considerable agreement of deflections of piles calculated based on the multilinear springs and p-y curves. The calculated buckling load based on p-y approach generally compared well with the measured results. Scour significantly reduced the buckling capacity of piles. Effects of sand density and fixity of pile head were also considered for buckling analysis of piles at different scour depth.

The Indian River Inlet Bridge (IRIB) is a steel I-girder bridge where strong tidal flows have caused significant scour holes to form. Because of this, a monitoring system consisting of tilt sensors placed at the top of each of two in-water piers has been installed. Two structural analysis techniques were then devised for evaluating the field data from these sensors. These consist of a pushover capacity analysis of the pier to evaluate stability of the substructure and finite element analysis to determine stress conditions in the superstructure as a result of pier movements. These analyses suggest that, when evaluating the subject bridge under scour conditions, the strength of the superstructure may govern over the stability of the substructure. The applicability of these results to other steel bridges is also considered.

The design of deep foundations must consider soil-structure interaction in order to properly model the side and tip resistance components. A soil-structure interaction model such as the t-z model method allows for the settlement analysis of a deep foundation over a range of applied vertical loads. The developed load-settlement curve can be analyzed using performance-based design criteria, such as a limiting tolerable settlement and a serviceability settlement. The limiting tolerable settlement can be selected to correspond to a movement that will either cause excessive stresses in the structure or render a structure inoperable while a serviceability settlement would correspond to a movement that would cause adverse performance or excessive maintenance issues with the structure. In this paper, a performance-based soil-structure interaction design approach for axial design of deep foundations under the AASHTO Strength and Service Limit States is presented. The design approach can be integrated within the Load and Resistance Factor Design (LRFD) framework to develop an efficient methodology for satisfying these limit state criteria.

A large number of movable bridges exist in Florida. These movable bridges are at critical intersection points of highway and marine traffic. Since these structures are composed of structural, mechanical and electrical components, encountered maintenance problems are different in nature and are observed more frequently. Therefore, movable bridge rehabilitation and maintenance costs are considerably higher than those of fixed bridges. The main issues are the deterioration due to their proximity to waterways, mechanical system failures, and fatigue due to the stress fluctuations during the operation. To improve their maintenance and predict possible problems ahead of time, continuous monitoring of these structures can be considered as a promising approach. In this study, the authors first discuss the problems and monitoring needs of such bridges. In the second part, design of the sensor network, data acquisition setup and data analysis methodologies are reviewed. Then, the field implementation and related challenges are described for a particular bridge. Finally, preliminary sample results from the analysis of the field data are discussed from safety, operation and maintenance point of view.

Movable bridges present a unique opportunity and challenge for their owners. By utilizing an engineered maintenance approach, clients can extend the useful life of these costly structures while improving reliability and reducing operating costs. This paper will discuss a predictive maintenance (asset management) approach which has resulted in positive results. The current NBIS inspection program provides a knowledge base which can be leveraged into routine maintenance actions or a predictive approach. By investigating and resolving the reason for as found deficiencies, the maintenance staff is more effectively utilized and the structures life is extended. This approach is particularly valuable for the mechanical and electrical systems on movable bridges. These M&E systems need to be constantly maintained and adjusted. We have identified simple approaches which can assist the maintenance staff into more effective results. The paper will discuss how to build a predictive maintenance program using NBIS inspection data, and implementing a routine minor repair program. We will also present simple tips for bridge owners to immediately reduce operating costs. The financial payback for the program is also discussed.

Fatigue performance of high-mast lighting poles was evaluated by experimental and analytical studies. The existing AASHTO specification for these structures, which is based on nominal stress and derived from the guidelines that are valid for predominantly in-plane stresses or membrane stresses, is often inadequate in designing these structures against service limit state of fatigue. Fatigue performance of the connections in the thin walled tubular structures are controlled by localized secondary bending stress, the magnitude of which depends on the relative stiffness of the connecting elements. Thirty three full size specimens with stiffened and un-stiffened socket and un-stiffened groove welded pole-to-base plate connections were fatigue tested to determine the fatigue performance of the connections in finite and infinite life regime. The research results demonstrated that with suitable combination of the geometric parameters, the constant amplitude fatigue threshold of these connections can exceed that of AASHTO fatigue category D for sections widely used in highway high level lighting structures.

Wind-induced fatigue failure of traffic and light poles has not been sufficiently studied neither has it been used as a design criteria by many pole manufactures. This paper presents the results of experimental testing of a new steel-concrete composite pole. The new pole features a thin-walled hollow steel tube partially filled with concrete near the base. The experimental work aimed to evaluate the natural frequencies of the poles and find the optimal concrete filling length for the best dynamic performance. Experimental results showed that for the tested poles, the optimal length of concrete filling ranged between 37% and 43% of the total length, and yielded 18% to 26% increase in the first natural frequency of the pole. The experimental results were within 10% difference when compared to predicted values using a finite element-based modal analysis. The new optimized composite poles, with natural frequencies higher than the inherited frequencies of typical wind loads, would better endure wind-induced vibrations.

The South Park Bascule Bridge crosses the Duwamish Waterway near downtown Seattle in Washington State. The new bridge will be a double-leaf trunnion bascule bridge and will be constructed on an alignment approximately parallel to the existing bridge. The existing bridge has suffered significant deterioration over the past 79 years and damage from the Nisqually Earthquake in February of 2001. The project corridor is generally underlain by soft or loose soils extending to a considerable depth. Drilled shafts and sunken caissons were both considered for the foundations of the bascule piers. Based on the site condition, seismic requirements, constructability, environmental impact, and construction cost, caisson foundations were selected for the bascule piers of the South Park Bridge. This paper will focus on the merits of caisson foundations for the bridge under seismic loading. The results of non-linear time history analysis incorporating soil-structure interaction will be presented. Other measures that were incorporated in the design of the bascule bridge will also be discussed.

Choosing the direction of applied earthquake forces has always been an important issue in earthquake engineering, especially as it refers to nonlinear analysis. Determination of the response to all possible incident angles is too time consuming and not practical. Fortunately, in recent years, some studies have been conducted on the response spectrum method of analysis of structures subjected to multicomponent earthquake excitation that enables the designer to find the most critical angle of excitation. However, the results from these studies are only valid for the response spectrum method for a linear elastic analysis. As such, there is no method to find the critical angle of excitation for a nonlinear time history analysis. This paper investigates the orthogonal effects in nonlinear analysis of candidate single-span bridges subjected to multicomponent earthquake excitations, and evaluates the effects of nonlinearities in candidate bridges affected by varying angles of excitation to determine the most critical angle. Also a comparison will be made between the results of the multicomponent earthquake excitations and AASHTO combination rule for combining the effects of separate unidirectional excitations. Although seismic analysis is not necessary for single-span bridges based on AASHTO, this paper applies AASHTO procedure on single-span bridges to compare the procedure to the results of nonlinear time history analyses (NTHA) at various excitation angles. Results show that the critical excitation angle is not the same in linear and nonlinear models and nonlinear models are more sensitive to the angle of excitation. It is also concluded that AASHTO procedure may underestimate the maximum probable response.

This paper discusses the seismic behavior of a bridge bent systems that consist of round HSS piles welded to a steel HP section cap beam. Past practice has typically utilized a simple fillet weld with no backer ring to complete the connection between the pile and cap beam. The results of the research indicate that the overall ductility capacity of this system is controlled by the configuration of the welded connection between the piles and cap beam. Due to the lack of prior knowledge concerning this type of connection, six full scale bridge bent tests have been conducted at North Carolina State University's Constructed Facilities Laboratory to evaluate the performance of the system when subjected to incremental simulated seismic loading. The two main goals of the research were to first evaluate the behavior of the system with a fillet weld which mimics the current typical design practice, and secondly to improve performance by investigating alternative weld configurations and connection details. The results indicate that the use of a simple fillet weld led to connection failure at a low ductility level rendering the detail inadequate for even moderate seismic regions. Subsequent tests showed that the use of other weld configurations, such as full joint penetration welds, improved the capabilities of the system but were still inadequate for higher seismic regions. However, promising results were obtained from a connection in which the flexural hinge region was relocated away from the pile to cap beam connection weld. This connection system remained essentially elastic at the pile to cap beam interface, which allowed for a more ductile base metal failure away from the connection.

The design and construction of bridge systems with long-term durability and low maintenance requirements is a significant challenge for bridge engineers. A possible solution to this challenge might exist through the use of new materials, i.e. fiber reinforced polymer (FRP) composites, combined with traditional materials that are arranged as an innovative hybrid structural system. An experimental investigation was conducted to gain an improved understanding of the long-term structural behavior and viability of a hybrid FRP-concrete (HFRPC) bridge deck system. This paper presents the results of fatigue and ultimate strength testing performed on a 3/4 scale bridge model consisting of a hybrid FRP-concrete bridge deck connected to supporting steel girders through shear stud clusters. The results of the fatigue and destructive testing suggest the hybrid FRP-concrete bridge deck might be a viable alternative to traditional cast-in-place reinforced concrete deck from a structural performance perspective. The specimen showed no degradation in stiffness or composite action between the deck and steel girders after 2 million cycles of dynamic loading with a peak load of 1.26 times the scaled tandem load and an ultimate capacity of 6 times the scaled tandem load.

The Nichols Bridgeway is a 620' long steel pedestrian bridge that spans from the centre of Chicago's Millennium Park, over a city street, and onto the top floor of the New Modern Wing of the Art Institute. Both the bridge and Art Institute are designed by renowned architect Renzo Piano. The structural engineer for the bridge superstructure is Ove Arup and Partners Ltd (Arup), and for the substructure Wiss, Janney, Elstner Associates (WJE). Conceived by Piano as a fine blade, the bridge is extremely slender in elevation. The structural depth varies from 2'–2" to 4'–6". For the primary span of 200ft the span-to-depth ratio is 44. The superstructure comprises a one-of-a-kind lightweight steel box-girder. The bottom flange of the girder is a 10-ft wide curved plate that is exposed to public view, making the structural and architectural design inseparable. The south end of the bridge is supported by the new Art Institute structure, using cantilever beams that support the deck so avoiding the need for columns immediately below. The bridge piers to the north are founded upon the roof of the existing Millennium Park parking garage and rail yard structure that was completed several years before the bridge project was envisioned. The existing structure was designed to support several feet of soil, but not the sizeable forces imparted by the new bridge. To accommodate the bridge loads, existing soil surcharge was strategically removed or replaced with lightweight fill, and some garage roof framing members were strengthened by constructing supplemental concrete members atop the garage roof. The bridge crosses several expansion joints in the existing structure, requiring the bridge structure to accommodate thermal movement of the underlying structural framing. The performance of the bridge is defined by footfall induced vertical and lateral vibration criteria, which were key factors in the design and steered the development of the concept. Providing high lateral stiffness together with relatively low mass ensures that the frequencies of the natural modes preclude resonant lateral response. Vertical vibration response is limited by balancing the mass and stiffness in the relevant modes of vibration, eliminating the requirement for added damping.

The 1378-ft-long, 10-span continuous Kootenai River Bridge in Bonner's Ferry, Idaho is a rare example of composite design utilizing a prestressed concrete deck and steel plate girders. Through the use of transverse and longitudinal post-tensioning in the cast-in-place deck, a minimum girder spacing of 18 ft was achieved. Additionally, this structure was constructed in the early 1980's without any interior expansion joints, accommodating all longitudinal movement at the bridge ends via finger plate expansion joints. The functionality of the expansion joints and the condition of the bridge's pot bearings were investigated in 2004. Although the bridge superstructure and substructure were in satisfactory condition, some of the bearings required replacement as a result of deterioration due to exposure to the elements and leakage through the expansion joint. In order to facilitate removal and replacement of the deteriorated bearings, the superstructure required raising. It was infeasible to raise the entire bridge, requiring that the bridge be raised partially (i.e. differentially) which led to distortion of the bridge cross section. A series of finite element analyses were performed to investigate the stress changes and total stresses due to various bridge partial raising scenarios. Strengthening plans were subsequently developed for structural elements that would be subject to higher demands than their capacities. Where members could not be practically strengthened, analyses could be used as a tool to determine the allowable differential jacking heights. The finite element analyses also provided reactions at various supports, which were then used to develop requirements for jacks and jacking stiffeners. Construction was completed in 2008. This paper presents the analytical technique used to investigate the impact of partial raising on the composite post-tensioned concrete deck, steel plate girder bridge and discusses lessons learned during the course of design and construction.

Pedestrian bridges are special structures. Distinct from street or railway bridges, they should be functional as well as visually interesting. Footbridge designers are often asked to create a contextualized, unique, beautiful structure considering the human scale of the users. It must have its own identity, fashioned from its locale, materials, lighting design, structural approach and form. The environs surrounding footbridges, like adjacent parks or, conversely, restricted urban spaces for the approaches, have prompted layouts which use the curvature in plan as the defining characteristic of their overall design and architecture. To keep curved pedestrian bridge designs competitive, it is essential to fully understand how the design principles of bridge engineering for straightforward layouts can be transformed and altered for curved geometries; even more important is to use the benefits of the curvature and arrange the structural elements accordingly, particularly now, when computers are ever more capable of calculating almost every type of structure. The paper focuses primarily on the design of cable supported curved footbridges, the principles behind that design, formfinding of the cable geometry and potential advantages of the curved layout. These aspects will be illustrated using examples of finished curved bridge projects with main spans of up to 200m from the offices of Schlaich Bergermann and Partner. Schlaich Bergermann and Partner - with offices in Stuttgart, Berlin and New York City - have designed major bridges around the world and unique footbridges in Europe and North America. Many projects received awards for outstanding bridge design like the 2006 OCEA for the (curved) Liberty Bridge in Greenville, South Carolina by the ASCE.

A Fiber Reinforced Polymer Honeycomb (FRPH) bridge was installed in Huron County, Ohio in August, 2008. The bridge has a span of approximately 17 ft (5.2 m) and is located on a low traffic volume rural road. This case study describes the design, fabrication, testing of a full-scale prototype bridge section, and commissioning testing of the bridge. A fiber reinforced polymer honeycomb (FRPH) sandwich panel was chosen for this superstructure replacement because it was strong and lightweight and the cost was defrayed by the FHWA Innovative Bridge Program. The bridge design incorporated AASHTO loads. The FRPH has a relatively low modulus of elasticity so deflection governed the design. Because each FRPH is unique, a full-scale prototype bridge panel was constructed alongside the actual bridge panels. The prototype panel was tested to destruction. The prototype results were used to establish panel behavior and modify the bridge panels. After installation of the bridge was completed, instrumentation was installed and truck tests were conducted to verify the stiffness.

This paper studies the uncertainties associated with design of reinforced concrete highway bridges under combined effects of scouring and earthquake. The extent of scouring effects on a bridge spanning a waterway is usually characterized by the scour depth. The models suggested for the estimation of scour depth are reviewed in the current study and the uncertainties inherent in their parameters are discussed. To obtain a realistic prediction of scour depth, two rivers located in the Southern and Northern California are selected. Considering the flow discharge rates of rivers in addition to the other sources of uncertainty, risk curves are developed to indicate the probability of exceeding any specific level of scour depth at the bridge location. A group of case-study bridges are modeled to evaluate the structural capacity and seismic response of bridges after degradation due to the various scour scenarios. The developed seismic fragility curves show that the probability of exceeding a damage state may significantly change by assuming scour depths with different occurrence probabilities and this variation should be considered during the bridge design process.

Combining theoretical analysis and field tests can greatly enhance the understanding of the performance of the bridges for engineers, which can be applied to evaluate the load carrying capacity of bridges without plans. Researchers at the University of Delaware previously developed a methodology, the steel area method (SAM), to rate concrete bridges without plans, which uses strain or displacement measurements from field testing in conjunction with basic mechanics principles to estimate the unknown area of reinforcing steel in a concrete bridge. The estimated reinforcing steel area can then be used with traditional rating techniques. In this paper, the SAM procedure has been extended and improved to accommodate more realistic general load configurations used in a typical load test. A procedure for load rating bridges without plans incorporating the results of a diagnostic load test is proposed based on the improved SAM approach. A concrete slab bridge with original structural drawings is used to validate the proposed procedures. Conclusions of the proposed methodology are drawn based on the test verifications.

Fatigue design provisions for stud shear connectors in the current AASHTO LRFD Bridge Design Specifications are based on the research conducted in the mid 1960s by Slutter and Fisher, who tested 44 push-out specimens to determine the fatigue life of the shear connector. An analysis of test data produced by Slutter and Fisher and an examination of the current AASHTO design provisions in comparison with their European and Japanese counterparts suggest that the AASHTO may significantly underestimate the fatigue life of stud shear connectors, especially in the range of fatigue behavior where most bridges are designed. A design example is presented that demonstrates that the required number of studs according to the AASHTO can be more than twice the number required by other design codes in Europe and Japan. A possible reason for this discrepancy is discussed.

Until recently, (sub)contractors have been relied on rules of thumb on L/b ratios to check girder stability under erection, where "L" is the unbraced length and "b" is the compressive flange width. Certain limits on L/b ratios were developed, which dictate if a specific girder will remain stable, needs stability check, or requires temporary support during erection. Although the rules of thumb are very convenient to use on site, it is necessary to check these rules through the latest AASHTO LRFD code. Parametric studies were conducted to (1) determine the effects of girder cross-sectional configuration and material strength on stability during erection; and (2) check the rules of thumb on L/b ratios. From the study, it was concluded that (1) flange width and web depth have the most effects on girder stability during erection; (2) the combined effects of gravity and wind load control in most cases; (3) rules of thumb on L/b ratios were too conservative for cantilevers and unsafe for simply supported girders, and were therefore modified.

The Seattle Department of Transportation (SDOT) is constructing a new two-lane eastbound off-ramp from the South Spokane Street Viaduct (SSSV) to 4th Avenue South near downtown Seattle. The ramp project encompasses a length of six (6) city blocks and includes surface street improvements. This paper presents the parameters and methodology used in an Alternatives Selection Worship for this 9-span tapering cast-in-place concrete t-beam and 5-span continuous post-tensioned cast-in-place concrete box girder ramp. Although the project originally required complete separation between the existing viaduct (circa 1941) and new ramp structure, also included herein is an overview of the seismic analysis performed to determine impacts of a closure slab. The post-tensioned concrete box girder portion of the bridge has an unbalanced span arrangement governed by cross-street geometry. The box girder is on a tight 56 meter minimum radius horizontal curve requiring special design methodologies that are also included. The engineer's estimate was $19.5M.

Loop anchorages were incorporated in the post-tensioning system for three single-span post-tensioned concrete slab bridges that were part of the I-35W St. Anthony Falls Bridge Design-Build Project in Minneapolis, Minnesota. Constraints on the available structure depth and owner-specified modifications to the AASHTO Load and Resistance Factor Design specifications required a very close spacing of the post-tensioning tendons. Several post-tensioning options were considered. A typical post-tensioning system with two accessible anchorages would have produced interference problems in the anchorage zones. The use of non-accessible dead-end anchorages was eliminated due to the great difficulties associated with replacing tendons in case a tendon should fail during the stressing operations. Such problems would have delayed the project schedule and would have adversely affected the life expectancy of the slab. The use of loop anchorages effectively doubled the distance between the stressing anchorages, eliminated the concerns surrounding embedded dead-end anchorages, and helped provide the required levels of the prestressing force.

The I-405 SB Bridge over I-90 is a part of the WSDOT South Bellevue Widening Project to help relieve congestion at one of the worst choke points along the I-405 corridor. Atkinson was awarded the Design/Build project on March 2007. Jacobs Engineering provided the design. Construction of the bridge began in September 2007 and opened on December 15, 2008. The bridge length is 272 meters, of six spans using WSDOT WF74G girders up to 50 meters long. The roadway width is 17 meters. All interior piers have two 1.8 meter diameter columns on 2.4 meter diameter drilled shafts. The abutments are cantilever "L" type spread footings on MSE walls up to 15 meters tall. The paper will provide an overview of the bridge and include both design and construction challenges. It will conclude with a discussion of how project issues were satisfactorily resolved between WSDOT, Atkinson and Jacobs Engineering.

It is well realized that difficulties in quality control of casting concrete on site and incapability of delivery of long precast girders are the principal problems of medium-scale bridge construction in a far rural area. To get rid of these impedances, the precast segmental approach was adopted to construct a bridge with 20-meter span length in Sakhonnakorn Province, Thailand. Not only girders, but also piers and cap beams were separated into segments. Each segment was manufactured in a well quality-controlled casting yard and transported to construction site by trucks so that they would be assembled and installed. This paper will describe construction procedure with the precast segmental approach. It can be found, from the construction, that the precast segmental technique can reduce the construction period significantly. Moreover, the quality of construction was provided well.

Post-tensioning tendons in segmental bridge construction are often only anchored within the deviator and pier segments. The effectiveness of the post-tensioning (PT) system is therefore dependent on proper functioning of the anchorages. On August 28, 2000 a routine inspection of the Mid-Bay Bridge (Okaloosa County, Florida) revealed corrosion in numerous PT tendons. Moreover, one of the 19-strand tendons was completely slacked, with later inspection revealing a corrosion-induced failure at the pier anchor location. Anchorage failure caused all PT force to transfer to the steel duct located within the pier segment that in turn slipped and caused the tendon to go completely slack. After the application of PT force, the anchorage assembly and steel pipes that house the tendon are filled with grout. These short grouted regions could, in the event of anchorage failure, provide a secondary anchorage mechanism preventing the scenario mentioned above from occurring. This paper presents the results of a full-scale experimental investigation on anchorage tendon pull-out. The study focuses on the length required to develop the in-service PT force within the pier segment grouted steel tube assembly. Seven, twelve, and nineteen 0.6" diameter strand tendons with various development lengths were considered. Recommendations for pier section pipe detailing and design will be discussed.

This paper presents a method to evaluate the blast pressures due to conventional blast loads on a two span continuous composite steel girder bridge system. The bridge design is based on AASHTO LRFD method. Resistance capacities of bridge deck and composite steel girder are calculated according to AASHTO specifications. Five different blast load cases are considered that affects i) the deck slab and girders, ii) deck slab, girders and substructure pier cap, and iii) substructure pier, deck slab, and girders. The blast loads on a composite steel bridge system are estimated based on the principles of blast wave propagation. Peak blast pressures on the bridge deck resulting from the blast at any given location vary with different arrival times. The peak pressures decay with increases in time duration (t_d), as the blast wave traverses along the bridge deck.

Structural health monitoring (SHM) of civil infrastructures is becoming more feasible with the help of recent developments in sensing and computing technologies being more available and affordable. The SHM system may contain various types of measurements including, but not limited to, vibration, strain and image data. In this paper, the authors provide a general discussion of the two critical aspects of SHM: assessment of the current condition and future performance prediction from their recent studies at the University of Central Florida. First, SHM data can be used to track and evaluate the current condition of the structure with the help of statistical pattern recognition algorithms and computer vision techniques. Statistical analysis of these types of data can provide rapid extraction of information about the changes in structural behavior whereas the use of the computer vision technologies in a monitoring system offers to detect events visually. Subsequently, the available information obtained can be used for decision-making about the future performance of the structure. Prediction of the future performance is a very crucial step in better managing the life cycle safety, serviceability and costs.

Florida has the largest stock of moveable bridges in the United States. More than half of these bridges are located along the inter-coastal waterways in Miami and Ft Lauderdale. Most of the moveable bridges use open grid steel decks. These open grid decks have several disadvantages, including poor skid resistance, high maintenance costs, high noise levels, and susceptibility to vibrations. It is therefore desirable to find alternative deck systems with better performance. Three potential deck systems: a lightweight aluminum bridge deck system made by SAPA Group (Sweden), a waffle shape reinforced ultra-high performance concrete (UHPC) deck system, and a fiber-reinforced polymer tube-UHPC composite deck system were selected for further development and experimental testing. The first system is currently commercially available while the latter two systems are newly proposed composite systems. The component-level tests on all three systems and system-level tests on the first two systems are presented in this paper. Results confirm that the first system is a feasible alternative (already available) to the open grid steel decks from a strength and serviceability point of view. The proposed UHPC composite systems are promising alternatives based on preliminary results.

In this study, we present an algorithm for estimating the parameters of a hysteretic model of a single-story torsional-shear building. We adopt the Bouc-Wen model to parameterize the nonlinear force-displacement loops of the structure. Using an Extended Kalman filtering approach, and data gathered during a damaging event, we aim to localize hysteresis at the level of individual elements that comprise the lateral load-resisting system.

Static and dynamic response of reinforced concrete (RC) bridge elements depends on the material characteristics and possibly introduced damage. While initial material variability can be introduced during construction, the dominant changes are a result of deterioration processes in RC elements. The most commonly found problem in bridge decks is corrosion induced concrete deterioration, which is initiated by rebar corrosion and afterwards extends into concrete cracking, delamination and ultimately concrete spalling. The effects of deterioration can be effectively detected and characterized using several complementary nondestructive evaluation (NDE) technologies. The presented approach relies on the use of five NDE technologies namely: impact echo, ultrasonic surface waves, ground penetrating radar, half-cell potential and electrical resistivity. The application of listed technologies is illustrated on material characterization and defect/deterioration detection of RC bridge decks. Incorporation of the NDE results in an enhanced structural identification analysis is illustrated.

Structural Identification (St-Id) has been widely applied to civil infrastructure systems similar based on the developments in System Identification (Sys-Id), which is very simply establishing relationships between inputs and outputs to a system. Sys-Id started in electrical engineering by taking advantage of control theory. Recently, Sys-Id has been implemented in almost all engineering disciplines, mathematics, physics as well as social sciences. Taking advantage of previous work in Sys-Id, St-Id of civil infrastructure systems has experienced major research and developments since the 70s especially with the advances in computational power and sensing technologies. Due to the multidisciplinary and broad nature of St-Id, a wide variety of theory and applications such as ranging from geometric modeling to parameter identification to model updating can be found in the literature. Consequently, parts and pieces of these developments in St-Id have been employed for research studies or for real life problems with advanced engineering requirements. By recognizing the importance of St-Id, ASCE-SEI Performance of Structures Track established a technical committee on "Structural Identification (St-Id) of Constructed Systems" in 2005. One of the objectives of the committee is to develop guidelines for reliable field-calibrated analytical modeling and characterization of existing constructed systems to fill the gap between theory and practice by utilizing various methods and technologies for St-Id. The committee established six critical steps for conducting a complete and successful St-ID for constructed facilities. These steps are: 1) Establishing the drivers for St-ID, 2) A-Priori Modeling, 3) Experimentation, 4) Processing data for parameter ID and interpretation, 5) Evaluation of model errors and 6) Utilization for decision making. This paper summarizes these steps, the fundamental knowledge areas and their relation to concepts presented in the Committee Report. As a result, this paper provides detailed information about the collective efforts of the committee for developing St-ID guidelines for constructed facilities.

Recently, a suit of data-driven localized damage detection techniques, which do not require a direct comparison with the previously obtained baseline data, has been developed specifically for field applications. We call them as reference-free techniques. The main advantage of the reference-free techniques is that they can provide robust diagnosis even when the system being monitored is exposed to ambient variations such as traffic and temperature variations. Since the reference-free techniques do not rely on comparison with previously obtained baseline data, they could be less sensitive to these undesirable changes. This study leverages a unique opportunity to conduct destructive testing on field bridges. Representative defects have been introduced to a decommissioned bridge, and the performance of the proposed techniques is examined by applying these techniques to the data obtained from the decommissioned bridge. To our best knowledge, this is one of the few studies where local online damage detection techniques are tested under field bridge structures.

Starting early 1990s, fatigue cracks were found to have developed at many floorbeam to girder connections of the I-345 Bridges. The bridges were designed with a special framing and support system, which caused cracks to develop at various welded details. Part of the bridges was previously repaired, but cracks continued to grow, and in some cases occurred again at the repaired details. A new retrofit plan was therefore developed recently by the Texas Department of Transportation, Bridge Division, through a combined research effort with the University of Texas at Austin, Ferguson Structural Engineering Laboratory. This paper discusses the authors' experience obtained through the repair of the I-345 Bridges, including lessons learned from the previous repairs, development of the new repair strategy, findings obtained from the field test and finite element analysis, and recommendations for future work. The repair construction is current underway and scheduled to be completed by June 2010.

Distortion-induced fatigue in steel bridges is a continuing problem for bridge engineers. Accordingly, a cumulative review and discussion of scholarly literature on this topic as well as focused analytical research aimed at studying bridge system performance when various retrofit techniques are applied to connection details are described herein. Driving forces behind distortion-induced fatigue are presented, including the effects of bridge system geometry and specific detail geometries. Retrofit techniques including positive attachement, back-up transverse stiffeners, slotted connection stiffeners, and removal of lateral brace elements were studied analytically to determine effectiveness. Results from finite element analyses are presented showing relative success of various retrofit techniques. Appropriateness of retrofit techniques under various conditions is disseminated.

Distortion-induced fatigue cracks are common occurrences in older bridges where details were used that are now known to be fatigue prone. These details generally consist of transverse stiffeners cut short of the girder flange to which a diaphragm or cross bracing is connected. The issues related to the assessment of existing bridge with this poor fatigue detail include the evaluation of the remaining fatigue life, the susceptibility of the damaged girders to brittle fracture as the fatigue crack grows, and the repair of these fatigue cracks. A study that included both experimental work and numerical analysis was conducted to assess an existing railway bridge in which over 300 cracks had been detected before it was replaced. The experimental work, which included both field measurements on the bridge before it was taken down and controlled laboratory fatigue tests, was conducted to assess the behavior of the bridge in-situ and the behavior of the web gap. The results of the field work were used to design the laboratory experiment to replicate the field conditions. Finite element analyses provided useful information for the design of the laboratory test program and to evaluate the fatigue susceptibility of web gaps in steel plate girders. Extensive analysis of web gap areas was used to validate simple procedures for the calculation of web gap stresses. This paper presents the results of this analysis and presents an assessment of commonly used web gap stress calculation method.

Delaware County, NY owns approximately 270 bridges and 130 major culverts (greater than 1.5 m (5 ft) long) and performs bridge design, maintenance and replacement with an experienced Department of Public Works' staff. The County is located in rural upstate New York and is larger in area than Rhode Island. Many of its bridges have relatively low traffic counts, yet are subject to heavy truck loading due to it agricultural, logging, and mining industries. The most common type of superstructure in the County is comprised of longitudinal steel beams (nearly 50% of the total). Deck types include traditional reinforced concrete, transverse corrugated steel pans with asphalt fill, open metal grid decks, and timber (about 15% of the total). Over the past 25 years, the use of timber at DCDPW as a deck material has evolved from nail laminated 50 mm (2 in) nominal thick boards on edge to transverse glu-laminated deck panels to heavy timbers (150 mm x 200 mm (6 in x 8 in) ). Many variations have been tried and details have evolved for construction, connections, and protection. This presentation will include highlights of the evolution of preferences based on engineering, availability, constructability, construction duration, durability, maintenance experience and costs.

Covered wooden bridges proliferated in the United States in the mid-nineteenth century. Today an estimated 800 covered bridge structures remain, but they are nevertheless cherished links to the technological heritage of the United States. The through-truss designs vary from the Kingpost trusses built in the craft tradition to the engineered Burr arch and Paddleford trusses. Covered bridges are our links to the past and the pioneering bridge-building efforts, and as such, are considered important early American transportation structures to preserve for posterity. This paper provides an update on the National Historic Covered Bridge Preservation (NHCBP) Research Program sponsored by the Federal Highway Administration (FHWA). An overview of the National Program is included along with an update of the latest research activities funded by the recent SAFETEA-LU legislation over the past 3 years. The NHCBP program provides funds to support preservation/restoration efforts for covered bridges that are listed, or are eligible for listing, on the National Register of Historic Places. Program funds also support research and technology transfer activities for restoring, preserving, and protecting covered bridges, including an educational component to disseminate information as a means of preserving our cultural heritage.

Wearing surface performance has been problematic in the past for timber bridges with transverse panel glued-laminated deck systems. This paper will describe the laboratory testing and field demonstration of a new glued-laminated timber girder bridge. Laboratory work addressed the problematic asphalt cracking common in transverse glued-laminated panel decks. The field demonstration project showcases the retrofit detail which was determined to provide the best field performance. The project was a cooperative effort between the Bridge Engineering Center (BEC) at Iowa State University (ISU) and the USDA Forest Service-Forest Products Laboratory (FPL).

Specially formulated Polysulfide Epoxy Polymer Concrete Bridge Deck Overlays were developed almost twenty years ago. These thin overlays offer reduced dead load as compared to asphalt overlays, and will not heave in high temperature locations. Unlike other epoxy systems Polysulfide Epoxy is formulated to resist the long term effects of ultra violet rays, which can lead to oxygenation, overlay material hardening, and premature material failure. Successful application and overlay performance is based on proper project specifications. Surface preparation, environmental conditions, material mixing, application methods, wearing surface aggregate broadcast and proper inspection will be discussed along with the importance of each of these factors. There are several methods of application that are currently in use. Each of the application methods has benefits and the paper will discuss these benefits as well as a direct comparison of the long term performance of each.

Many of the world's signature long-span steel bridge structures utilize the orthotropic steel plate as one of the basic building blocks in the structural system, for distribution of traffic loads in decks and for the stiffening of slender girder plate elements in compression. Orthotropic bridge behavior is complicated since the deck plate distributes wheel loads in two directions, with different structural rigidity in the longitudinal and transverse directions; and involves integral behavior of the deck with the floorbeams and girders. U.S. engineers are often unfamiliar with these types of structures and existing published manuals are limited in their ability to guide complete engineering design. One of the primary reasons for advancement of orthotropic deck details in recent years is from application of modern, refined techniques for engineering analysis and design. Emphasis is now placed on the fact that the design of these structures is mostly controlled by fatigue limit states. Complex details necessary to make these structures work require advanced fatigue evaluation techniques which must rest on accurate stress range calculations with the use of refined Finite Element Analysis (FEA) or prototype testing. Such an approach to design verification has broad implications to bridge engineering practice in the U.S. and special application of the AASHTO Specifications. This paper provides a summary of a recommended approach to fatigue evaluation of an orthotropic steel bridge for design based on the current state of the practice.

Tall buildings are one of the few constructed facilities whose design relies solely upon analytical and scaled models, which, though based upon fundamental mechanics and years of research and experience, lack thorough full-scale validation. In response to this deficiency, the Chicago Full-Scale Monitoring Program was instituted and has been continuously monitoring the responses of three tall buildings in Chicago since 2002, expanding recently to additional buildings internationally. Observations made through this program, while showing general agreement between measured and predicted behaviors, have also highlighted some discrepancies between the projected periods of vibration using finite element models and the in-situ periods drawn from full-scale data. The implications with respect to predicted accelerations are presented in this study, various techniques for modeling elements of the lateral systems of these buildings are explored, and sensitivity analyses are conducted to direct the physically-meaningful calibrations of these finite element models to the full-scale observations.

In the last 15 years, Structural Health Monitoring has become a useful and increasingly widely used tool for the construction, management and lifetime extension of bridges and other civil structures. A lot of attention has been devoted to dynamic monitoring of structures in the aim of performing system identification and damage detections. The monitoring of static parameters such as strains, deformations, tilts and displacements is another useful and complementary tool to asses the long term performance and to identify changes in behavior that are often difficult to spot with dynamic monitoring. This paper is based on the experience gathered in monitoring more than 40 bridge monitoring projects carried out over the last 15 years using advanced sensing systems including fiber optics, GPS and corrosion sensing. In particular we concentrate on the analysis of the different types of bridges that were monitored, their situation (new construction, existing structure, refurbishment...) and the main purpose of the installed monitoring system. Two main categories emerge form this analysis: new bridges with innovative aspects or particular relevance and existing bridges with known deficiencies. A methodology to design an integrated monitoring system capable of monitoring the whole structure with a limited number of sensors, of the right type and placed at the right locations will be introduced. Finally, an application example of Structural Health Monitoring system design and implementations for the I35W will be briefly presented.

Dynamic testing of civil infrastructure is required for reasons ranging from, for example, checking performance of new or retrofitted structures, evaluating and predicting vibration serviceability, calibrating structural models and establishing baseline performance for structural health monitoring. There are also, in limited cases, possibilities to identify, characterise and diagnose structural defects. For the above reasons and with increased interests in performance of constructed facilities, challenging new applications for dynamic testing are found and met with improving technology. Together with advances in instrumentation capabilities, there have been in the last decade great advances in techniques for system identification, allowing for effective dynamic testing of practically any kind of structure. Among dynamic testing technologies, forced or artificial excitation of civil structures and system identification procedures borrowed from mechanical/aerospace disciplines have proven ability to identify true mode shapes in the most demanding conditions (strong noise, large scale and having closely spaced, complex and even nonlinear modes). At the other end of the spectrum, operational modal analysis (OMA) now has proven capabilities for structures where forces cannot be applied or used effectively, to the extent that OMA now appears to be the preferred choice. We find that in some cases both procedures may be required for full identification, and a hybrid form that uses a mix of artificial and ambient excitation has been developed in order to extract the missing mode scaling (mass) parameter for OMA. The paper presents a sample of techniques in different applications to bridges, illustrating strengths and weaknesses, to provide engineers with information to understand the process of dynamic testing and appreciate the validity of the results.

The objective of this paper is to discuss some relevant aspects of how experimental data (through the process of structural identification (St-Id)) may be used to make rational decisions regarding infrastructure systems. The discussion presented is part of the recently completed state-of-the-art report on St-Id assembled by the ASCE SEI Structural Identification of Constructed Systems Committee.

Structural identification programs executed without appropriate methods for data interpretation usually fail to provide meaningful information to support engineering decisions. Identifying and implementing appropriate data interpretation methods represent fundamental scientific challenges in the field of structural identification. Given the many recent developments in and diversity of available sensor technologies, and the impressive gains in computing capacity, data interpretation challenges often remain as the final "bottleneck" restricting the potential of structural identification through static and quasi-static measurements. High quality data interpretation leads to a significantly increased understanding of the real structural behavior. Analytical quality and measurement data quality both need to be evaluated to establish the degree of correlation between predictive structural analysis-based responses and the collected measurements; however, an exact correlation should rarely be the objective. This paper will discuss the issues related to quality of measurements and interpretation of this data using structural analysis and structural identification algorithms. It should be noted that data interpretation methods must always respect the physical reality associated with structures, and no single approach is best for all cases.

Nanotechnology has become very much the buzz-word of the 21^st century. While tangible benefits are being realized in industries ranging from medical to consumer products, the conservative construction sector has been slow to embrace the new technology. Despite the availability of various construction products that claim nanotechnology-based improvements the question still remains whether these developments are true breakthroughs in themselves — or is it that we can now see structures and interactions under the "nano-scope" for the first time? Identifying step-change developments in concrete materials and systems due to nanotechnology is a challenge for practicing engineers. However, this will become more visible as more breakthroughs are made, so the sector may benefit from intelligent, cost effective, safer, durable and environmentally friendly materials and structures. This paper sets out some of the challenges facing the civil engineering industry and looks at possible developments in nanotechnology that may help address the challenges over the coming decade.

An array of weldable and rosette strain gages were placed on the Wolf Creek Bridge, a multi-span curved girder bridge. Strains were measured under both static and dynamic loads applied by a truck that is similar to the HS20 truck. The measured strains were compared with strains computed using a finite element model of the bridge. Dynamic amplification factors and distribution factors under the truck loading were estimated from both the field measurements and the FE model.

Four full-scale prestressed concrete (PC) I-beams were tested to study the effects of steel fibers on the increase in shear strength and ductility of beams. Beams were cast with no traditional transverse steel reinforcement. To study the effect of steel fibers on shear behavior, all four beams were cast using different amounts of steel fibers. The beams were subjected to concentrated vertical loads up to their maximum shear or moment capacity using four MTS actuators in load and displacement control mode. During the load tests, Linear Voltage Displacement Transducers (LVDTs) were used to measure displacements at several critical points on the web in the end zone of the beams. Several LVDTs were also placed under the beams at the points of loading to measure the actual total and net displacements of the beams. From the load tests, it was observed that the shear capacities of the beams increased significantly due to the addition of steel fibers in concrete. Complete replacement of shear reinforcement with steel fibers also increased the ductility and energy dissipation capacity of the PC I-beams.

The estimation of life cycle cost of a reinforced concrete bridge is critical in choosing an optimized inspection and maintenance program. This estimation becomes more important when the bridge is located in chloride contaminated environments under the chloride-induced corrosion. The present paper studies the total life cycle cost of typical bridges under different corrosion scenarios. The uncertainties associated with the estimation of corrosion initiation time are discussed and their effects on the calculation of bridge life cycle cost are evaluated through a probabilistic approach. Furthermore, the influences of decision-making parameters, such as inflation rate and expected life cycle, are considered to provide a broader view of budget allocation requirements. The total life cycle cost of bridge is calculated from the present value of construction cost, inspection and maintenance costs, serviceability failure costs, and associated user costs. The mentioned costs are reviewed in detail and their relevant assumptions are examined to obtain a more realistic estimation of total cost considering various inspection and maintenance strategies.

For any suspension bridge, the wind-induced vibrations are mostly studied due to some historical failure events. For a proper prediction of the wind-induced vibrations of a suspension bridge, it is necessary to use a representative wind velocity profile at the bridge site. Measurement of wind velocity at the bridge site thus plays an important role in a realistic prediction of the wind-induced response. In an effort to assess the buffeting response of the Vincent Thomas suspension bridge, which connects the city of San Pedro and Terminal Island of Los Angeles Port, recently, three anemometers have been installed at three different strategic locations on this bridge. Two of them are located on the deck level while the third one is located at the top of the east tower. These locations are chosen so that the velocity profiles can be simulated at the deck level as well as along the height of the towers. A new technique of non-Gaussian conditional simulation is proposed to conditionally simulate the wind velocity profiles by utilizing the measured wind velocities. Buffeting responses of the bridge are then evaluated by using the conditionally simulated wind velocity profiles as obtained from the proposed algorithm and a critical comparison is made with the other cases of wind velocity profile simulation.

This paper presents a summary of a project where post-installed shear connectors were used to strengthen an older non-composite steel girder bridge located near the town of Hondo, Texas. The use of post-installed shear connectors permits the development of composite action between the existing steel girders and the existing reinforced concrete deck, thereby increasing the flexural strength of the girders. The very good fatigue strength of these post-installed shear connectors enabled the use of partial composite design. As a result, far fewer post-installed shear connectors were needed than if conventional welded studs were used. For this bridge, the addition of post-installed shear connectors resulted in approximately a 65-percent increase in the Inventory and Operating level load ratings. Also presented in this paper are load test results which were conducted to verify composite action at the steel-concrete interface after the retrofit and compare the structural behavior of the bridge before and after the retrofit.

The Sunshine Skyway Bridge is one of the most recognized structures in the United States. With its signature bright yellow stay cables, the bridge resembles a sailboat, with its towers holding up the triangular sails across Tampa Bay in Florida. The Sunshine Skyway Bridge is comprised of the main span, the high level approach, and the low level trestle spans. A total of 650 precast concrete girders support the northbound trestle spans and another 650 girders support the southbound trestle spans. AASHTO Type IV girders were used for a majority of the 100 ft. long trestle spans. Shear cracking was observed during routine inspections of the bridge. The Sunshine Skyway Bridge was designed for a 75-year life span and the presence of shear cracks in the concrete girders less than 20 years after the bridge opened was a cause for concern. Any cracks in the concrete girders could provide a direct access for chlorides and moisture to the prestressed strands. In order to restore the shear deficiencies at the end of the AASHTO girders, a bidirectional carbon fiber fabric was used to wrap the members. Most of the repairs for this project took place from a barge under the bridge thereby eliminating any traffic concerns on the bridge. The bridge was successfully strengthened with CFRP to meet the Florida DOT requirements at a cost approximately $1.6 million and took approximately 8 months to complete.

Retrofitting of structures has become a major issue worldwide due to increases in the applied loads, human error in initial construction, legal requirement to comply with updated versions of existing codes, or the loss of strength due to deterioration over time. In this regard, fiber reinforced polymer `FRP' retrofitting systems are enjoying a great deal of popularity as a result of the unique properties of FRPs. Retrofitting with epoxy bonded FRP composites is suitable for environments where the temperature is well below the glass transition temperature T_g of the epoxy adhesive. T_g is normally in the range of 55–60 °C. It would be very beneficial if it is replaced with cementious (mineral) based bonding agents in order to produce fire resistant strengthening system. Pilot testing conducted by the authors have shown that excellent bonding properties can be achieved using the cement based adhesives. Tests include the investigation of bond strength of FRP fabrics to the concrete substrate by single-lap shear test and flexural behavior of FRP strengthened reinforced concrete beam using cement based adhesives. The bond-slip response has been developed for the strengthening system. It is concluded that using cement based bonding materials is a promising technique in FRP application for structures located in hot regions or in danger of fire.

This experimental study focuses on investigating the cyclic behavior of reinforced concrete (RC) circular columns retrofitted with an innovative active confinement technique. Most of the attempts for applying active confinement using conventional materials have yielded little success due to practical difficulties associated with applying the external pressure on site. This paper investigates the feasibility of using shape memory alloy (SMA) spirals to enhance the flexural ductility and shear capacity of reinforced concrete columns under lateral cyclic loading. Four 1:3 scale RC columns are prepared and tested under quasi-static cyclic loading. Two of the tested columns are retrofitted with SMA spirals. One of these two columns is wrapped with glass FRP (GFRP) sheets in addition to the SMA spirals. For comparison, a column is confined passively with GFRP sheets and another column is tested in its as-built condition. The experimental results show that the actively confined columns exhibit superior performance to passively confined and unconfined columns. This superior behavior is primarily attributed to the increase in concrete strength and ultimate strain associated with active confinement. Also, SMA spirals show an outstanding ability to mitigate the damage sustained by the columns.

There continues to be a need for the accurate determination of the effective prestress force in precast, prestressed concrete bridge girders. In general, design codes lead to conservative estimations of in-service prestress forces which in turn can lead to permit and load posting requirements. The focus of this research is on the development of a nondestructive method to more accurately determine this effective prestress force. The research results are based on the testing of eight AASHTO Type II bridge girders that were in service for approximately 40 years. On average, the non-destructive tests results were within 94% of the results based on cracking tests; a technique that has more traditionally been used to directly determining residual prestress force. The residual prestress force was also compared with values obtained according to current code procedures. On average, the AASHTO LRFD-04 and 07 detailed methods overestimated the measured prestress force, by 12% by way of the cracking tests and 17% by way of the non-destructive tests. On average, the AASHTO Lump Sum Method agreed with measured residual prestress force obtained with the cracking tests and overestimated the measured values by 6% in comparison to the non-destructive tests. The details of the testing and proposed methodology are presented in this paper.

Instrumentation, structural modeling, and model updating are incorporated into the design and construction process of a multi-span bridge to change the paradigm of traditional bridge design to a long-term bridge design. A continuous three span composite steel stringer bridge in Barre, Massachusetts was used as a pilot bridge. A monitoring system was installed in order to capture structural behavior during construction and into the service life of the bridge. Strain data from the steel girders was collected during the concrete deck pour. Two finite element models were created using shell/solid elements and frame/shell elements. Both computer model responses are compared with field strain measurements of the full scale bridge during the concrete deck pour. Both the shell/solid and frame/shell FEMs produced close estimates of the measured strain data. Modeling assumptions for boundary conditions and temperature effects play a major role in magnitudes of the analytical responses. In the future, truck load tests will be used for baseline model updating of the completed bridge. The structural model that reflects the actual bridge 3D system behavior can be used for load rating and overload permitting.

This paper describes analytical structural models created for various components of the Tobin Memorial Bridge, and a program of instrumentation and non-destructive testing for the Little Mystic Span. A detailed global finite element model of the Little Mystic Span, one of the two truss spans, was developed along with supporting special studies of continuity and boundary conditions. Special studies include modeling the rotational stiffness of the truss connections and consideration of the piers and bridge shoes. An instrumentation plan was developed and deployed for the Little Mystic Span to capture structural responses of key truss members. Nondestructive testing using loaded trucks was carried out for the purpose of model verification and calibration. Preliminary comparisons between experimental and analytical strains for key truss members show reasonable agreement. Special study results will be used to fine-tune the global finite element model. The verified models may be used as a condition assessment program and structural health monitoring system for the management of the Tobin Memorial Bridge.

This paper addresses delamination detection and location in reinforced concrete decks from dynamic characteristics. To investigate the effects of delamination on the modal parameters, the appropriate finite-element models are established for concrete decks. The delaminations with different sizes and locations are introduced into several models as damage scenario. The modal analyses demonstrate that the delaminated models' natural frequencies are reduced and mode shapes are irregular compared to those of non-delaminated decks. The changes in modal properties depend on the delamination sizes, locations and mode orders, consequently they can indicate the degree of damage and location. The transient analyses are carried out and three distinct excitations are applied. The modal frequencies extracted from the responses are capable of showing the delamination occurrence. The method followed in this research provides a feasible way for delamination detection in bridge decks using vibration data. This is cost-effective and real time contrasted to conventional techniques which require field tests and bridge closure.

Applications of high performance materials in structures results in smaller cross sections and much more economical designs. Smaller cross section also leads to more flexible bridges that may not satisfy the existing serviceability deflection criteria. Deflection limits were employed to avoid "undesirable structural and psychological effects due to their deformations." Results of prior studies indicate that deflection and L/D limits do not necessarily address these objectives. Existing limits do not prevent damages in structures because they check global deflection while the damages are mostly the consequence of local deformations. Furthermore, human comfort can be achieved directly by limiting the more relevant vibration characteristics such as acceleration. Thus, there is a need for additional work on understanding bridge vibrational characteristics and to provide simple methods to estimate bridge dynamic response parameters that can be use in design, which are the objectives of this study and some of the results are presented in this paper.

Between 1875 and 1877, G. Eiffel & Cie designed and built the Maria Pia Bridge in Porto, Portugal. Original analyses included dead load and three positions of static live loads. The dynamic effects of a train crossing the bridge were not considered. This paper will discuss the original calculations and present a dynamic analysis of a train crossing. We used Structural Analysis Program to perform finite element analyses and to calculate the mode shapes and frequencies. DynamAssist calculates the dynamic impact factors and force-time histories. This study found low dynamic impact factors for train velocities less than 200kph (124mph). Stresses in the arch under the highest speed train are negligibly different from a quasi-static case. Stresses from superimposed dead and impact loads do not exceed the allowable stress and a comparison with original static live loadings shows the original calculations captured the behavior of a train crossing.

In the United States, barge impact resistant bridge design typically involves static application of code-prescribed impact loads. However, recently conducted full-scale experimental collision tests led to the discovery of significant inertial effects not accounted for in existing design provisions. Subsequent to the experiments, a numerically efficient dynamic (time history) analysis procedure was developed to quantify transient impact loads and load effects. While this technique is capable of accurately predicting member design forces, a time-domain dynamic analysis may not be warranted for the design of certain structures, or during preliminary design iterations when detailed structural parameters cannot be adequately estimated. In this paper, common modes of dynamic pier response arising during barge impact loading are characterized for a wide range of bridge configurations. Dynamic amplifications of pier member design forces are quantified by comparing forces obtained from time-history dynamic simulations to those obtained from static analyses. As a means of capturing dynamic amplification effects, an equivalent static analysis procedure is developed that mimics pier response during dynamic barge impact events. The proposed static method is shown to produce conservative predictions of both pier and substructure design forces, relative to dynamic analysis.

Most aged existing barrel type rigid-frame bridges were designed and constructed in the early 20^th century to overcome the grade separations and expensive excavation of arch bridges. The rehabilitation and conservation of these bridges has shown the urgent need for reliable methods and practical instructions for load ratings. Although elastic frame method has been adopted on strength assessment of arch bridges, the application of this method without any modifications on rigid-frame bridges is still cautious and some detailed calculations deserve special attention. This work investigated each critical aspect related to the load rating of rigid frame bridge using the elastic frame method based on Snuff Mill Road Bridge in New York, a barrel-type rigid frame bridge. Geometric and material properties are obtained from its as-built plan and site inspections. And the results were found to be consistent with the bridge's existing physical condition. Some practical instructions were proposed regarding the load rating of rigid-frame bridges using the elastic frame method.

Safety considerations and alignment issues dominate the design of highways and highway bridges and, as a result, skewed girder alignments relative to the abutments and piers are common for highway bridges. It has been reported in the past that approximately 40% of all bridge deck area in North America is on skewed alignments. While number of skewed structures continues to increase, limited research has been performed investigating their behavior. This paper will summarize research conducted at the Pennsylvania State University that examined the level of deformations and stresses generated in a skewed, prestressed, I-girder bridge constructed in central Pennsylvania. Models were created that studied levels of lateral bending and torsion experienced by the girders during deck placement, the effects of deck stiffness development during deck placement, and the effect of support conditions on the constructed bridge. A discussion of the models that were created along with limited findings, focusing on lateral deformations and bending stresses induced during the deck pour, will be given.

Recent changes in the American Concrete Institute's Building Code Requirements for Structural Concrete (ACI 318) significantly reduce the design capacity of near-edge concrete anchors. Because of this change, the conventional practice of using 2 x 4 sole plates with 1/2-inch bolts spaced at 4 feet or 6 feet on center in residential construction has come into question. The purpose of this study is to evaluate the performance of cast-in-place foundation anchor bolt connections in shear parallel to the concrete edge and help improve accuracy of design methods for residential anchors. This is done by capturing representative failure modes, response variability, and applicable safety margins. Single and multiple anchor bolt configurations, as well as full-scale shear configurations were tested. Test results showed that sole plate to concrete connections exhibited significant displacement capacity (i.e., ductile behavior) and were relatively tolerant to cracked concrete conditions. Comparison to the ACI-318 design values suggests that the penalties for cracked concrete and non-ductile behavior are overly conservative for wood sole plate anchors.

The NEESWood project was a four-year five-university project whose objective was to provide the technical support to safely increase the height of light-frame wood buildings to six stories through the development of a performance-based design philosophy. The project culminated with a series of tests called the Capstone tests. The Capstone test program has two major objectives: (1) To help validate the performance-based seismic design philosophy developed during the project; and (2) To provide a better understanding of the seismic behavior of existing four and five story light-frame wood buildings in the western United States. This paper focuses on objective (1) by comparing the response and overall performance of the building during tri-axial shake table tests on the worlds' largest shake table to the performance expectations set out during the design process. The Capstone building has several configurations, with the focus in the paper on the 12.5-m x 18-m x 18-m tall six-story apartment building with 23 one- and two-bedroom living units for a total of 36 bedrooms and a total of 1350 sq meters (14000 sq ft) of living space. The building was subjected to various scaling of the Northridge Canoga Park tri-axial earthquake record with the largest being an MCE level event. The six-story building includes a continuous rod hold down system throughout its six levels of stacked wood shear walls.

This paper presents the development and validation of a new two-dimensional (2D) numerical framework, suitable for nonlinear inelastic static and dynamic analysis of light-frame wood buildings that incorporate sheathed woodframe shear walls as a lateral-load-resisting system. The 2D building model is based on a sub-structuring approach that considers each floor diaphragm as a rigid body with three kinematic degrees-of-freedom (DOF). A sub-structure model is developed for each individual single-story wall assembly that interacts with the adjacent diaphragms and generates the resisting internal forces. The 2D shear wall model takes explicit consideration of all sheathing-to-framing connections while offers the capability to optionally simulate deformations in the framing members and contact/separation phenomena between framing members and diaphragms, as well as any anchoring equipment (i.e. anchor bolts, holdown devices) typically installed in light-frame shear walls to develop a vertical load path that resists overturning moments. Corotational descriptions are used to solve for displacement fields that satisfy the equilibrium equations in the deformed configuration, accounting for geometric nonlinearity and P-Δ effects. To validate the proposed numerical framework, a number of simulation examples are presented, based on experimental results from pseudo-static cyclic tests of single- and two-story full-scale shear wall specimens. These examples demonstrate the capability of the model to simulate accurate load paths in the structure and successfully predict variations in strength, stiffness and energy dissipation characteristics of the lateral-load-resisting system.

This paper presents a simplified direct displacement design (DDD) procedure which was used in the design of the shear walls for a six-story wood frame test building for a Network for Earthquake Engineering Simulation project (NEESWood). The test building was designed to meet four performance expectations (damage limitation, life-safety, far-field collapse prevention, and near-fault collapse prevention). The NEESWood Capstone Building was recently tested in-full-scale on the E-defense (Miki) shake table in July 2009. As part of the pre-test performance assessment process, a series of nonlinear time-history analyses were performed to verify that the inter-story drift requirements were met. Additionally, collapse analysis in accordance with the methodology presented in the ATC-63 90% draft report was also carried out. The results of incremental dynamic analyses confirmed that the Capstone Building designed using the DDD procedure has adequate capacity or margin against collapse.

In recent years, seismic damping systems have been employed in numerous steel and concrete framed buildings. Such systems dissipate a significant portion of the seismic input energy, thereby relieving the energy dissipation demand on the structural framing system and thus reducing damage. As part of a NEESR project to develop a performance-based approach to seismic design of multi-story light-framed wood structures, the application of damping systems to such structures has been evaluated via seismic shaking table tests and numerical simulations. This paper focuses on the results from shaking table tests of wood shear walls employing toggle-braced fluid dampers. Within the context of performance-based seismic design, the effect of the fluid dampers on the deformation demand and hysteretic energy dissipation demand is emphasized. The results demonstrate that toggle-braced fluid dampers provide a significant increase in the seismic resistance of the walls, allowing them to achieve high levels of performance when subjected to strong ground motions.

Recent earthquakes have demonstrated the weakness of light-frame construction buildings that rely on gypsum drywall sheathing as shear walls. Seismic design codes now limit the use of gypsum sheathing as a shear resisting elements creating a large inventory of seismically suspect buildings — including many two-three- and four-story residential apartment buildings constructed between 1950 and 1980. Potential earthquake damage could be devastating, heavy enough to require the displacement many residents, greatly impacting the surrounding communities. The conventional method to seismically upgrade these buildings has been to remove existing gypsum sheathing, install new structural plywood, upgrade sill bolts and hold-downs, and then re-apply gypsum and finish. This approach, although effective, is expensive and intrusive, resulting in the retrofit of only a few buildings. A test program at the University Of California Irvine (UCI) was developed to investigate the performance of gypsum sheathed shear walls reinforced with glass fiber-wrap material. The glass fiber wrap material would provide an alternative load path from the wall's top plates to the foundation that would more effectively mitigate the shear forces developed in the structure during a seismic event. The test specimens utilized both 1/2-inch and 5/8-inch gypsum wallboard sheathing, with framing and nailing simulating typical light-frame construction from the 1950s to the 1980s. The test program encompassed 9 half-scale (4 ft x 4 ft) and 8 full-scale (8 ft by 8 ft) wall specimens loaded cyclically to obtain the force/displacement relationships and strength parameters to be used in retrofit design. All testing was conducted using computer-controlled, cyclical test protocols [ASTM E 2126-07]. The Half-scale tests validated the capacity of the glass-fiber anchors through the use of a force-controlled protocol, while full-scale tests examined the overall panel strength. This paper presents experimental results including: (a) composite anchor strength results and failure modes; (b) control and retrofitted panel strength results, force-displacement relationships and failure modes; and (c) preliminary concepts and recommendations for application in seismic retrofit design.

This paper presents a portion of extensive experimental and analytical studies on two joist supported laboratory footbridges to determine the effect of bottom chord extensions on their static and dynamic properties. Finite element computer models were created to simulate and compare the results of stiffness and vibrations tests for different bottom chord extension configurations. The philosophy was to test the footbridges and update the finite element model, trying to minimize the discrepancies between the test results and the FE model for better response prediction. The stiffness test results indicate that bottom chord extensions help reduce deflections; placing them before the concrete placement is observed to be a better solution than reinstalling them to a joist supported system with a cured concrete slab. The vibration test results indicate that bottom chord extensions increase the natural frequencies, but they do not necessarily decrease the peak acceleration levels.

Floors whose dynamic response to human traffic is dominated by transient response to individual footfalls rather that by resonant build up are known as `High frequency floors' (HFFs). While there is often a duality in performance with lightweight floors in offices and residences sometimes having elements of HFF performance, floors in industrial facilities such as chip plants and multi-level factories are deliberately designed to be both stiff and massive so that resonance is a practical impossibility. Their design is traditionally carried out using simplistic formulae that are frequently shown to be inappropriate. This paper reports on a study on the characteristics of these floors, comparing the simplified methods with finite element analysis. The inadequacies of the current popular design guides are exposed and sound principles for their design are proposed.

Vibration serviceability of building floors is becoming a governing design criterion for many open plan building floors. To make correct decisions about floor vibration performance, calculating only the highest vibration response of the floor is not sufficient anymore. Because of the considerable complexity of the problem and shortcomings of practically all codified procedures for checking floor vibration serviceability, it is prudent to use not one but several assessment strategies while making sure that application of the first principles in structural dynamics is preserved. Also, rather than focusing on a single highest response value, calculating distribution of the highest responses at each floor point is the way forward to obtain a more informed vibration serviceability check. Finally, easy link to commercial structural analysis packages and dynamic testing results, comprehensive but quick dynamic response calculation and effective visualisation of the measured and calculated vibration responses are of paramount importance in modern floor vibration serviceability design (for new structures) and assessment (for existing structures). To address all these issues, this paper presents Vibration Serviceability Assessment Tools (VSATs), a MATLAB-based software package, developed to aid not only assessment of vibration serviceability of floors, but also development of new floor designs and research into their vibration behaviour. Its operation and application of a number of procedures useful for vibration serviceability assessment together with pertinent visualisation tools is presented to increase awareness of various state-of-the-art procedures available nowadays.

This paper presents the results of experimental and analytical studies conducted in a series of Long Span Deck Floor Systems. In-situ tests in floors of buildings under construction and in a laboratory footbridge were conducted to measure the vibration properties of this type of floor system. Three different analytical methods commonly used to predict the modal properties of floor structures were studied to determine their applicability for assessment of Long Span Deck Floor System dynamic behavior.

The Direct Strength Method is an entirely new design procedure for cold-formed steel member design, and was formally adopted into AISI Standards (AISI-S100-07). The method integrates computational determination of cross-section stability and maps the stability to appropriate limit states for design in a highly compact and efficient format. This new design method does not rely on effective width and is able to provide a consistent design methodology for general cold-formed steel cross-sections. This workshop on the Direct Strength Method provides attendees with (a) background and examples, (b) the latest advances including members with holes, and (c) an industry perspective for a company utilizing the method in new product development.

In typical brace-beam-column connections of concentrically braced frames (CBFs) with tubular braces, a gusset plate is used to connect the brace to the beam and column. The slotted tubular brace is welded to the gusset plate and subsequently the gusset plate is also welded to the beam and column. The beam-to-column connection at the gusset plate is either welded or bolted at the face of the column flange. Even though a bolted connection is provided at the face of the column flange, stiff gusset plates connected to beam and column could still provide a fully restrained beam-to-column connection as in the case of welded connection. Such a fully restrained beam-to-column connections in CBFs are such that plastic hinges will form in the column upon continued lateral deformation under severe shaking: hence, higher drift concentrations can be expected in the bottom storey when the partially restrained or pin-ended column-to-base connections are provided. For these reasons, this study investigates the local and global seismic performances of fully restrained brace-to-beam/column connections through numerical analyses. The global performance is examined using a 4, 8 and 12 storey concentrically braced prototype frames modelled in OpenSees, while the local performances are examined through the detailed finite element model of a single storey single bay frame located at the ground floor of the four storey brace frame using the finite element program MIDAS. Furthermore, this study introduces a partially restrained bolted connection at the corner of the gusset plate rather than providing it at the face of column flange in order to facilitate beam rotation at the bolted connection upon continued lateral deformation; this is expected to prevent the formation of plastic hinges in the columns and to distribute the inelastic drift demand over the full height of the structure. Finally, global performances of partially and fully restrained connections are compared in terms of storey displacement and inter-storey drift, while local performances of two models are compared in terms of strain concentrations in gusset plate, beam and the column.

Structural integrity has been required by ASCE 7 for many years but there has not been a specific criterion as to how this requirement could be met. IBC 2009 now contains a structural integrity requirement that applies to high rise buildings assigned to Occupancy Category III or IV. ASCE 7–10 will also have revised integrity requirements International Overview: The UK standards have specific rules for steel structures that were incorporated decades ago as a response to the Government directive that buildings must be resistant to Disproportionate Collapse. Similar rules have now been incorporated into the Eurocodes. This paper highlights the differences between the European and IBC requirements and also discusses the UFC requirements relative to the IBC and ASCE 7. Design Example: The 2009 IBC, Section 1614.3.2, requires that each beam connection have a minimum horizontal tension capacity and also that each column splice have a minimum vertical tension capacity. These requirements are not specifically intended to prevent disproportionate collapse like the UK standards but rather as the section title states, are minimum integrity requirements. This paper provides a discussion of the intent of this section and identifies the specific IBC and ASCE 7 requirements and their implications to steel structures. Tie-force requirements are new in US building codes and hence there is a need to understand the implications that these requirements have to steel design and detailing. This paper presents the historic background and structural intent of tie-forces—both within the US and internationally—and presents specific examples of how to design steel connections to meet the tie-force requirements and compares these requirements to those used in the UK.

A self-centering moment resisting frame (SC-MRF) is a viable alternative to a conventional MRF with welded beam-column connections for seismic resistant buildings. An SC-MRF is characterized by gap opening and closing at the beam-column interface under earthquake loading. The beams are post-tensioned to columns by high strength post-tensioning (PT) strands oriented horizontally to provide self-centering forces when gap opening occurs. For the SC-MRF investigated in this research, energy dissipation is provided by beam web friction devices (WFDs) attached to the columns at the beam-column interface. The SC-MRF in this study is designed to meet several seismic performance objectives. These include no damage under the Design Basis Earthquake (DBE), leading to immediate occupancy performance following the DBE. In addition, under the Maximum Considered Earthquake (MCE) the structure is designed to have minimal damage and achieve the collapse prevention performance level. A 7-bay, 4-story SC-MRF prototype building located on stiff soil in the Los Angeles area was designed with WFDs using a performance-based design procedure with the above performance objectives. A 0.6-scale model of two bays of the SC-MRF was developed and tested under simulated earthquake loading using the hybrid simulation method to include the remaining parts of the building in the simulation. This paper presents an overview of the moment connections in the SC-MRF, the performance-based design procedure, test results, and an assessment of the design procedure.

Prior to the 1994 Northridge earthquake in California, steel moment frame buildings were thought to perform well under seismic loading conditions. Though none fully collapsed, over 200 buildings with steel moment frames as their primary lateral force resisting system experienced brittle fractures within column to beam connection elements. These fractures were typically initiated at the column-beam flange welds and many propagated into column faces creating an extremely hazardous, weakened condition. Much research has been conducted in order to better understand the behavior of steel moment frames, as well as to develop new connection types that demonstrate adequate structural performance under seismic loading conditions. Prior research suggests that cellular beams may perform well under such conditions due to inelastic deformation developed in the beam web away from the column face; however, no explicit testing has been conducted. The primary goal of this study is to gain an understanding of the behavior of steel moment frame connections using cellular beams. Presented herein is a preliminary finite element analysis demonstrating the adequate performance of a cellular beam connection subjected to cyclic load, as well as a proposed testing program which will be used to verify the analytical results. Both analytical modeling methods and full scale testing of beam to column connection assemblages are to be employed to demonstrate that such beams exhibit sufficient strength, ductility, and stable failure mechanisms under seismic loading. Ultimately, an AISC prequalified connection is desired to enable widespread use of cellular beams in steel moment frame construction in areas of high seismicity.

Hybrid masonry utilizes reinforced masonry, most commonly concrete masonry, in combination with structural steel framing to form a load-sharing structural system. The masonry serves as both wall enclosure and lateral bracing. Options exist for the masonry to participate structurally with the frame to carry both the gravity and lateral loads. The steel framing utilizes simple connections but can also be designed with moment connections. Currently in use primarily for low to mid -rise buildings in seismic design categories A, B, and C, the system is being researched for higher seismic categories. Derived from several historical systems such as confined masonry and transitional building construction, this system offers an efficient use of both the steel framing and masonry. The load-sharing performance of the system is a function of the confinement of the masonry within the steel framing. The load-sharing aspects also offer a design option for progressive collapse. This paper will explain the system and the load-sharing aspects, and describes the three types of hybrid masonry.

A relatively new innovative concept in building construction known as "hybrid masonry" combines conventional steel framing with reinforced concrete masonry structural panels. The system has been used for construction of several low-rise buildings in the eastern and mid-western United States, but has not been implemented in regions of moderate or high seismicity as yet. Unlike a traditional masonry infill-frame system, hybrid masonry panels are explicitly designed as structural elements rather than as an afterthought or non-structural element. The masonry panels can be treated as a surrogate for conventional steel bracing at a far reduced construction cost. As well, masonry panels can be designed to stiffen a bare frame so that performance-based objectives of immediate occupancy can be met for low levels of seismic input, and to provide sufficient lateral strength so that life-safety and collapse-prevention objectives can be met for moderate to high levels of seismic input. Before hybrid masonry can be fully embraced as a seismic structural solution, a simple understanding and confirmation of how it responds to reversed lateral forces is needed. The purpose of this paper is to briefly describe hybrid masonry, its basic governing mechanisms, the impediments to its implementation, and research needs. A new research project is described that will test the concept of hybrid masonry and provide the necessary confirmations for its practical implementation.

Prior to the development of framed structures, the primary building system was loadbearing masonry. With the introduction of structural steel framing in the late 1800s, the logical tendency was to incorporate masonry into the building structures. This resulted in several types of construction starting with caged construction and progressing into transitional building construction. In 1940s, engineers and architects began using veneer construction with steel frames. In each construction type, the structural frame and the masonry interacted differently. This paper will explain the progression of the development of structural steel framing and the interaction of masonry walls. It will also describe how that progression was a necessary step leading to the creation of the new system of hybrid masonry and structural steel framing. Each hybrid type will be described.

During the winter of 2003–2004, a significant number of partial and full fractures were observed in fire retardant treated plate-connected wood roof trusses which spanned over a ten year old elementary school. A test program indicated that the wood strength was still within the parameters of the original design. Review of the fractures indicated that they occurred in both truss members with low calculated stresses as well as those with moderate to high stresses. Close inspection of the members with full fractures revealed that a large percentage of the members contained juvenile wood. Observations, tests and analysis indicated an accelerated frequency of fractures occurring in fire retardant treated members containing juvenile wood. This paper reviews the findings of this investigation and provides a discussion of the contributing factors to the observed distress.

Many nineteenth-century church structures were constructed based on traditional design and construction techniques using native non-stress-graded timbers. Despite the frequent lack of engineering design and quality timbers, many vintage timber-truss structures have performed satisfactorily for more than 100 years. In the past 50 years, some churches have inadvertently and unknowingly increased the live snow loading on their roofs by adding insulation in the attics and causing more snow accumulation on the roofs. Hidden truss failures are often present near the supports, and our modern analysis methods almost always show that some timber-truss components fail to meet the strength requirements of our current design codes. This paper presents a brief review of codes and standards relevant to timber evaluation and repair. Four example projects are presented showing common structural challenges and practical methods of assessment along with repair and strengthening schemes designed to reutilize and extend the service life of existing timber components.

During World War II, a period of history when steel was in short supply, builders resorted to alternative construction techniques to achieve traditional building spaces. Airplane hangars were no exception. The Browning Hangar, named after the Robert Browning family who were early Austin aviators and pioneers in the service of general aviation, was constructed in 1943. The hangar construction consisted of a series of five parallel 3-hinged parabolic arches clear spanning 130 feet to buttressed foundations. The arches were constructed onsite with innovative glued and laminated 1 x 10 pine boards, laminated to variable depths along their lengths. Over time, the arches began to creep and sag. Termites destroyed large amounts of the arch bases. As portions of the roof decking deteriorated, moisture attacked the arches, further deteriorating the wood. Though a limited structural renovation was made in the early 1980s, aggressive deterioration of the hangar continued unabated with the closure of Robert Mueller Municipal Airport in 1999. In 2005, AEC conducted an evaluation and subsequent renovation of the hangar to arrest further degradation. Presently, the hangar stands as one of the only remaining structures of the old airport in a new master-planned mixed-use development of the area fittingly called `Mueller'. This paper will illustrate the various investigation techniques used to evaluate, test, and repair damaged parts of the structure to make the building safe and serviceable for future use.

Thin marble panels (thickness of 5 cm or less), have been a popular cladding material on buildings since the mid 20th century, yet marble panels have continued to fail at an increasing rate despite enhanced knowledge in the technology of marble facades. Design and installation techniques for thin marble facades have evolved from the earliest designs of marble facades to the present. Though a number of deterioration mechanisms exist for a marble façade, hysteresis (irreversible material expansion) tends to be the most damaging. If a marble façade is found to be experiencing hysteresis, an evaluation and repair program should be provided by a licensed professional engineer specialized in the assessment/restoration of façades. The evaluation of a façade experiencing hysteresis may consist of up-close visual observations of 100% of the façade, Non-Destructive Evaluations (NDE), exploratory openings, and destructive testing. Repair of a marble façade typically consists of temporary stabilization, frequent monitoring, and up-close observations. A thin marble façade requires an ongoing maintenance program for the life of the building regardless of age or currently observed deterioration.

Under pressure to maximize structural economy and minimize story heights when designing mid-rise and high-rise buildings, structural engineers often utilize post-tensioned concrete to reduce slab thicknesses. While elevated post-tensioned concrete slabs efficiently use structural material and have a resistance to cracking, they must be designed and constructed with care to control deflections. When unwanted slab deflections do occur, the source of the deflections is often not easily discernible. In this paper, the authors highlight a recent investigation of a structure with cracked and deflecting elevated slabs. A review is presented of the parameters which influence serviceability: slab thickness; concrete quality; quantity, placement, and prestressing force of the post-tensioning reinforcement; and quantity and placement of the mild reinforcement. The means to accurately assess these parameters in the field using common destructive and non-destructive techniques are described in detail. The diagnosis of the slab condition illustrates the importance of recovering the proper quantity and quality of data from the field investigation.

The use of un-bonded post-tensioned (PT) reinforcement in waffle slabs has been popular for many decades in buildings and parking structures. The use of PT reinforcement in waffle slabs greatly reduces the amount of cracking and possible leakage in the structure and also allows economical long-span construction. The boom of the construction of waffle slabs in the United States began in the 1970s. Many of these early PT structures have since been encountered in a deteriorated condition with varying degrees of damage to the PT systems. Unfortunately, not enough information is currently available for practitioners to properly analyze the condition of waffle slabs with corroded/broken PT tendons. This paper illustrates a detailed explanation of the deterioration mechanisms that affect post-tensioned waffle slabs and, more specific, addresses sheathing strand systems. A case study is presented to illustrate the detrimental effects of deterioration mechanisms on post-tensioned structures providing specific repair recommendations in order to mitigate and prevent structural related problems for un-bonded post-tensioned waffle slabs.

The 2009 L'Aquila, Italy, earthquake highlighted the fact that seismic vulnerability of historic masonry buildings palaces has increased because of "strengthening" retrofit work that has been done in the last 50 years. Italian seismic standard recommended use of traditional reinforcement techniques such as replacing the original wooden roof structure with new reinforced concrete or steel elements, inserting reinforced concrete tie-beams in the masonry and new reinforced concrete floors, and using reinforced concrete jacketing on the shear walls. L'Aquila earthquake has shown numerous limitations of these interventions, because they lead to increased seismic forces (due to greater weight) and to deformations incompatible with the masonry walls. This paper provides a discussion of technical issues pertaining the seismic retrofit of Santa Maria di Collemaggio basilica and in particular the limitations of the last (2000) retrofit intervention. Considerable damage was caused at the church because of questionable actions and incorrect and improper technical choices.

This paper presents a case study on the ExxonMobil office headquarters is a Houston landmark. At the time of its construction in 1964 the 45-story office building held the honor as the tallest building west of the Mississippi. In 2000 and 2001, our team directed exploratory demolition and worked with the Owner, Architect, and Contractor to construct two re-clad mock-ups to assist the owner in determining the desired repair option. Throughout this full-scale re-cladding effort, we provided structural and restoration consulting services on the project. This project is a prime example of large-scale, façade/building type envelope condition assessments.

Prediction or estimation of wind damage to individual structures using analytical techniques is time-consuming, costly, and often limited by unknown loading factors and structural resistances. Detailed analysis of all individual structures affected by hurricanes or large tornadoes is typically not feasible. Alternatively, wind damage functions (WDFs) for structural components and/or overall systems based on the observation of damages distributed spatially across a known wind field can serve as a significant tool for the estimation or prediction of wind-induced damages. The intensity and spatial distribution of maximum wind speeds in severe wind storms have historically been unknown, and the collection of area-wide and comprehensive damage data via ground surveys has generally proved impossible. However, it is now possible to construct improved wind damage functions based on high-resolution post-storm imagery by correlating observed damage levels and known wind speeds established through the merger of significant new technological developments, including: portable ruggedized instruments that measure wind speeds in-situ, numerical modeling techniques that produce regional velocity fields from available multi-platform measurements, remote-sensing platforms that facilitate the rapid capture and preservation of damage data, and interpretation techniques that aid in identifying levels of wind damage depicted in these remote-sensing data.

Despite advances in structural engineering, the damage caused by hurricanes to wood-framed houses continues to increase. The interaction of turbulent winds with houses and the induced structural load paths are not fully understood. Additionally, the small size of typical wind tunnel models limit feasibility to conduct pressure and structural load path studies. As part of an ongoing experiment investigating the interaction of turbulent winds with light-framed wood structures and the resulting structural loads, quantifying the three-dimensional wind flow characteristics around the structure is needed. The experimental study involves subjecting a one-third scale, geometrically accurate model of a light-framed wood gable roof residential building to realistic simulation of design wind speeds and wind flow characteristics, using UF's Hurricane Simulator and concurrently capturing pressure distribution and structural loads on the house model. A four-hole probe called the "Cobra Probe" is been used to characterize the wind field generated for the test. This paper presents preliminary work in validating the Cobra Probe which simultaneously measures wind velocities and turbulence intensities for all three orthogonal directions as well as the static pressure simultaneously. Using two different small wind tunnel facilities, comparisons were made with a hot-wire anemometer. Generally, the results were agreeable with the capabilities of the Cobra Probe far exceeding those of the hot wire anemometer. The test setup for the 1/3-scale model testing is also described.

Structural monitoring of an instrumented experimental single-storey wood building provided important information regarding the behaviour and response of low-rise buildings subjected to wind loads. Foundation wind-induced loads were captured by twenty-seven three-dimensional load cells simultaneously with the envelope pressures and weather characteristics. The distribution of the total wind load to each wall is examined and normalized to the wind speed for each direction. The correlation between loads acting on different wall segments is also quantified in the form of participation factors. In parallel with full-scale findings, a scaled model of the experimental building and its surroundings is tested in a boundary layer wind tunnel. The detailed pressure distribution information for thirty-six wind angles of attack obtained through three different upstream terrain simulations is used to generate expected total uplift wind force. The findings are compared to data acquired directly from the foundation load cells located in the test house. The comparison revealed that in most cases wind tunnel values are within the range of the field results. Discrepancies are somewhat higher for wind tunnel tests conducted using the open/suburban terrain compared to the urban terrain simulation. The results are significant for the improvement of the wind tunnel testing and simulation procedures, for the development of code and standard provisions, as well as for the verification of the finite element numerical model of the test house.

Using the pressure loading actuators (PLA) at the University of Western Ontario, ramp and actual wind loads are applied to toe-nail connections for wood-frame residential construction. The ultimate capacity from the ramp and actual wind load tests are similar to those found in the literature. However, under realistic wind loading, the toe-nail connections are found to fail in increments with only the intermittently occurring peak pressures causing the majority of the damage to the connection. In addition, the effects of construction defects, in this case missing nails, were also examined in order to determine the reduction in capacity caused by these.

The constant natural hazards threat led the engineering community to develop more effective decision making tools, for use by the public and private sectors. An increasing number of stakeholders are no longer only interested in the performance of a single building exposed to deterministic loads but also of a group of buildings subjected to probabilistic demands. This requirement has created a significant challenge for the engineers that face a twofold problem, namely to estimate the performance of heterogeneous groups of structures subjected to uncertain loads. Within this context the Florida Office of Insurance Regulation has sponsored the development of the Florida Public Hurricane Loss Model (FPHLM). This paper presents the vulnerability component of the commercial-residential module of the FPHLM. Its first stage, devised to project insurance losses for single-family residential buildings, was certified by the Florida Commission on Hurricane Loss Projection Methodology. The model was later expanded to deal with commercial-residential low-rise (1–3 stories) and mid-high rise buildings (4+ stories). This paper presents and discusses the methodology to estimate the vulnerability of low and mid/high rise buildings along with selected results.

Two non-iterative finite element formulations for the analysis of ponding are presented. One is based upon the mathematically exact solution of the differential equation, while the other is based upon a virtual work formulation. The virtual work formulation is particularly attractive, as it allows direct ponding analysis to be conducted using many commercial finite element codes. Convergence of the resulting ponding model to the mathematically exact solution is explored for several simple problems as a proof of concept analysis.

A design-oriented model is proposed for computing the load resisting capacity of composite steel-concrete floors subjected to interior column loss. The model is based on the premise that floor collapse is resisted through the development of membrane action in the slab elements and catenary forces in the steel beams. A number of simplifying assumptions are made in the model pertaining to the deformed shape of the system, development of failure resisting mechanisms, and overall system behavior. The proposed model is incremental in nature and tracks the evolution of damage in a floor system loaded up to failure. The model is shown to be able to capture the effect of influential variables on collapse resistance. Key limitations on the model are highlighted and discussed.

Progressive collapse can be defined as a chain reaction of failure initiated by loss of one or a few supporting elements due to manmade or natural hazards. As a result of increasing catastrophic events in recent years, the prevention of progressive collapse is increasingly becoming a requirement in building design and analysis. Many approaches have been proposed to prevent or minimize the risk of progressive collapse in new or existing buildings. Among a number of building codes, standards and design guidelines for progressive collapse, General Services Administration (GSA, [2]) and Department of Defense (DoD, [3]) address progressive collapse mitigation explicitly. They provide quantifiable and enforceable procedures to resist progressive collapse. Over the last decade, extensive studies have been performed to improve the design of buildings against progressive collapse by modifying the design codes, as well as to evaluate the progressive collapse potential of existing or new buildings by computer modelling and experiments. Very limited or no research, however, has been carried out by physically testing an actual full-scale steel building for the progressive collapse analysis. In this study, progressive collapse performance of two existing buildings was investigated through both experimental testing and computational analysis. Each building was tested by physically removing four first story perimeter columns prior to building's scheduled demolition to simulate the sudden column removals that leads to progressive collapse. Progressive collapse resistance of each building was investigated using the commercially available computer program, SAP2000 [4], and following the GSA guidelines. Two different analysis procedures were evaluated for their effectiveness in modeling progressive collapse scenarios; linear static and nonlinear dynamic procedures. Two- and three-dimensional models of steel frame buildings were developed to analyze the progressive collapse response. Differences and implications of each model and analysis are discussed. The strain values recorded in the field were compared with the results from a computer model of each building. It was expected that the field experiments and analytical studies can provide both practical and fundamental information on the collapse response of an existing building with a regular structural configuration.

On June 2, 2004, a partial collapse of the `solar well' curtainwall on the WilTel Building (also referred to as One Technology Center) occurred during a severe storm event in downtown Tulsa, Oklahoma. During the storm, a portion of the structural steel backup frame supporting the solar well collapsed, allowing approximately seventy lites of glass to fall to the street below. The solar well backup frame is comprised of vertical trusses, horizontal tubular girts, and vertical mullions and is laterally braced by the main concrete structure through 4 inch diameter struts that span between pinned connections at the edge of the concrete floor slabs and the ends of the vertical trusses. Based on post-collapse investigations of the structure and its damaged components, two possible failure scenarios were proposed. One scenario identified the bending induced fracture of a threaded stud on an adjusting clevis observed at the connection between a lateral strut and vertical truss as the initiating factor for the collapse. The other identified the disengagement of a clevis pin at the connection between a lateral strut and concrete slab as the initiating factor. In considering the two collapse initiation scenarios, it was determined that the bending induced fracture of the threaded stud on the adjusting clevis could only be fully rationalized if the lateral strut was first released through the disengagement of the pin at the connection of an adjacent strut to the concrete slab. It was concluded that the loss of the strut as a lateral brace for the backup frame permitted increased rotation of the frame during the storm, ultimately resulting in distress to the adjusting clevis and the partial collapse of the curtainwall.

It has been speculated that much of the losses from hurricane damage to single-family wood-framed residential structures is due to design based on faulty understanding of the structural load paths in these buildings. This NSF-supported research presents a new approach to understanding load paths in wood-frame residential structures and establishes a relationship between spatially varying wind loads and structural load paths. A 1/3-scale wood frame gable roof building was constructed with geometrically scaled wood members, sheathing, and nails. The model scaled the flexural stiffness (EI) of the roof sheathing for wind loads applied normal to the surface. A dense grid of point loads were used to develop the influence coefficients (and surfaces) for 20 vertical reactions located at roof-to-wall and wall-to-foundation connections. The linear elastic structural response for roof-to-wall connections was limited on the roof surface to within two trusses of the applied load location. As expected there was a greater spread of load effect at the foundation level (6–8 trusses) because the exterior wood stud walls acted as stiff, vertical diaphragms. The influence functions were combined with wind tunnel pressure data for a similar shaped model from which the dynamic wind loads were estimated using a database-assisted design methodology. There was reasonable agreement between the dynamic reaction load traces with design loads obtained by components and cladding (C&C) design approach of ASCE7. Results also suggest the main wind force resisting system (MWFRS) method underestimates the design wind loads at roof-to-wall connections.

The corner regions of roofs of low-rise buildings are subjected to large fluctuating pressures during windstorms. Damage investigations of metal cladding following hurricanes and cyclones in the US and Australia have shown loss of cladding due to wind induced fatigue cracking. To mitigate for low cycle fatigue failures, cladding systems are required to demonstrate compliance to dynamic wind loading test criteria such as the Low-High-Low (L-H-L) test detailed in the Building Code of Australia. The test criteria's loading sequences are a simplification of the dynamic wind loading environment, where assumptions such as building orientation, cyclone duration, wind direction and cycle range have been made. For example, when applying the Australian test criteria, the L-H-L test, the maximum negative external and maximum positive internal pressures are combined and applied across the load cycles. However, when analysing external and net pressure cycles for various windward and side-wall dominant opening cases, the numbers of cycles vary along with the mean and range, indicating a potentially conservative test criteria. An advanced pressure loading actuator (PLA) developed by UWO, is used to apply the fluctuating pressures of a "design" cyclone to sections of roof cladding. The PLAs permit the application of actual temporally varying wind pressures to a representative test section of the building envelope. The test method is able to replicate cladding failures as observed following severe cyclones and demonstrate conservative aspects of the L-H-L test criteria.

An underground concrete sewage treatment pump station facility located in Bessemer, Alabama had a structural failure in April 2005 soon after it was commissioned. This pump station built into a 100 feet deep excavation in dolomite bedrock is approximately 360 ft long and 230 feet wide. This substructure has three major functional areas; the wet well, the dry well, and the flume. The failure was manifested by the rupture of the mat slab and distress in a significant number of structural elements in the form of wide cracks and spalls. By performing simplistic as well as a detailed analysis using finite element analytical techniques, it was determined that the primary cause of failure was due to the as-designed mat foundation of the structure not having adequate capacity for the hydrostatic forces at the time of failure.

In order for dissimilar materials to act in a composite manner, forces must be transferred between the materials so that they achieve a state of internal equilibrium with one another. Previous editions of the American Institute of Steel Construction (AISC) Specification briefly address load transfer; however, these provisions are quite limited in scope and clarity. The 2010 AISC Specification significantly expands load transfer requirements in a new section. Clear guidance is now provided for the allocation of forces between steel and concrete sections as well as for force transfer mechanisms used for composite members. This paper reviews the new AISC provisions, discusses their application, and provides a brief technical background to the new headed stud anchor provisions as they relate to load transfer.

In recent years much effort has been devoted to the development of reliable analytical tools that model component deterioration and can be used to predict global collapse of structural systems under seismic excitations. This paper focuses on development of a steel component database that can serve as the basis for validation and improvement of analytical models that explicitly model deterioration in structural steel components and can be used in collapse assessment of steel moment resisting frames. Relationships that associate deterioration model parameters with geometric and material properties that control deterioration of steel beams with reduced beam sections (RBS) are proposed. The relationships are based on calibration and evaluation of steel beams with RBS subjected to monotonic and cyclic bending moments. The use and importance of deterioration modeling based on the proposed relationships for collapse prediction is demonstrated on a case study of a 20—story steel building designed based on current seismic provisions and evaluated based on FEMA P695 (ATC-63) performance methodology that requires explicit modeling of structural collapse.

Buckling-restrained braced frame (BRBF) systems exhibit robust performance when subjected to seismic loading. However, the low post-yield stiffness of buckling-restrained braces (BRBs) may cause BRBFs to develop large maximum and residual drifts and allow the formation of soft stories. Thus, reserve strength provided by other elements in the structural system is critical to improving seismic performance of BRBFs. Reserve strength can be provided in two primary ways: (1) moment-resisting connections within the BRBF and (2) a steel special moment-resisting frame (SMRF) in parallel with the BRBF to create a dual system. These two approaches to providing reserve strength can be used together or separately, leading to a variety of potential configurations. In addition, special attention must be given to beam-column connections within the BRBF since moment-resisting connections have been observed experimentally to limit drift capacity due to undesirable connection-related failure modes. This paper presents nonlinear dynamic analysis results and evaluates performance of BRBF and BRBF-SMRF systems using moment-resisting and non-moment-resisting beam-column connections within the BRBF. Reserve strength is shown to play a critical role in seismic behavior and performance of BRBFs.

Conventional special concentrically braced frames (SCBF) have been widely used due to their efficiency in resisting lateral forces. Under severe lateral loading, braces will buckle, laterally and locally, leading to a deterioration of the strength and stiffness of the SCBF and under repeated excursions of cyclic inelastic deformation to fracture of braces. On the other hand, buckling restrained braced frames (BRBF) provide more stable hysteretic behavior. The collapse resistance of SCBF and BRBF systems is examined. A series of 2, 3, 6, 12 and 16 story tall, double story X braced frame archetypes designed using the provisions of ASCE-7/05 for seismic design category D_min and D_max are analyzed using the ATC-63 methodology. The paper examines modeling of steel braced frames, including brace buckling and rupture due to low cycle fatigue, as well as the application of the ATC 63 methodology. Results of representative static pushover and dynamic analyses are presented. For the assumptions in the ATC 63 methodology and the current ability to model braced frame behavior, it was found that, except for low-rise SCBF structures, a high confidence of achieving the collapse prevention limit state was provided. Reasons for the behavior predicted are presented, along with recommendations for improved design and evaluation methods.

This paper summarizes a study focused on evaluating the collapse performance of steel Special Moment Frames (SMFs) by application of the FEMA P695 methodology. In this study, archetypes that comprise 3-bay special SMFs and serve as lateral load resisting system of buildings ranging from 1 to 20 stories are designed using ASCE 7-05 and AISC 341-05 provisions. Nonlinear models are developed using recent advances in structural component modeling, with structural component parameters extracted from a steel component database. These models are analyzed to predict the collapse capacity of each design, and the adjusted collapse margin ratios (ACMR) are evaluated and compared to acceptance criteria. It was found that SMFs designed in accordance with present seismic provisions provide an acceptable margin of safety with the exception of a performance group that contains tall moment resisting frames designed for high seismic zones using the response spectrum analysis procedure.

This paper presents the development of an energy based approach for evaluating equivalent fire resistance of reinforced concrete beams under design fire exposures. The method is based on principle of equivalent energy and estimates equivalent fire resistance by comparing energy transferred under design and standard fire exposures. The validity of the method is established by comparing predictions from the proposed approach with those obtained from other time equivalent methods, empirical formulae and with non-linear finite element (FE) analysis. Based on the results, a correlation is proposed to relate the equivalent fire resistance with maximum temperature of design fire. It is shown through comparison, with existing approaches, that the proposed method is capable of predicting time equivalent with an accuracy that is sufficient for practical purposes.

A simple performance-based test technique was developed for the fire resistance assessment of columns. In this method, the column specimen is tested using a conventional column furnace while it is coupled with a simple analytical model. The simplified model simulates the remainder of the building. The components of interaction between the column specimen and the analytical model are deformations and loads. The new test approach includes the axial load-deformation interaction components. In other words, the axial load of the column specimen is varied according to the structural system response. The simple approach was employed for different building frames and the results were compared and verified with those obtained from an analysis using the SAFIR computer software. This paper provides the theoretical concept and formulation of the simple hybrid test approach. Before putting the model in practice, it will be further verified through a future experimental program.

This paper presents the results of experimental investigations on the structural behavior of composite beam and floor systems subjected to gravity and thermal loading through experimental testing. Two specimens were tested, each 3.96 m by 4.57 m in plan with single plate, beam-to-girder shear connections. Specimens were tested under design and realistic fires and with and without fire-protection on the interior beams. The results show that the removal of fire-proofing caused the composite beam section to: (i) heat more rapidly; (ii) follow the furnace time-temperature curve closely; (iii) have increased deflections at the beam mid-span; and (iv) only nominally affect the temperatures in the girders and connections. The replacement of the design fire conditions with realistic fire conditions caused slower cooling of all elements in the system and increased permanent deformations in the beam and girders.

The performance of steel connections is a crucial, but often overlooked, consideration in the fire protection of steel frame buildings. Traditional methods of fire protection based on limiting the temperature of steel elements below 550°C do not take into account the effects of thermal expansion which can have a significant performance on connection performance in fires. The behavior of a steel seating plate connection in fire is discussed, and it is argued that connections for long span beams need to display adequate ductility, and tolerance of large movements to perform well in fires. This is illustrated by analytical calculations, and nonlinear finite element analysis of a long span steel beam with a simple seating plate connection. Based on these findings, a simple way of estimating beam movements in fire is provided, together with recommendations for required seating plate dimensions for steel beams in fire.

Recent discussions related to the seismic performance of low-ductility steel systems designed for moderate seismic regions have generated new interest in the cost-effective design of ductile systems for such regions. Although eccentrically braced frames (EBFs) have a well-established reputation as high-ductility systems and have the potential to offer cost-effective solutions in moderate seismic regions, their system performance has not been widely discussed. This paper discusses the historical development of EBFs and their provisions, highlighting previous studies on EBF system performance. New performance assessment results for EBFs in moderate seismic regions are compared to previous system studies with the intention of clarifying the nature of EBF system performance including: story drift capacity, response to higher mode effects, and frame overturning forces.

Based on a collection of building peer reviews in moderate seismic regions, this paper discusses the manifold ways that both the spirit and the letter of the building codes and seismic design provisions can be misinterpreted, resulting in designs that are both unsafe and uneconomical. In light of these examples, the paper discusses the challenge of achieving in the building code an appropriate balance between simplicity, sophistication, transparency and prescription. Specific attention is given to design approach, architectural coordination, constructability and cost.

Recent research has demonstrated the importance of reserve capacity for collapse prevention of low-ductility steel concentrically-braced frames (CBFs) commonly used in moderate seismic regions. The beam-column connections within CBFs may be a viable means of providing this reserve capacity, but the cyclic flexural response of these connections is largely unstudied. This research investigates cyclic flexural behavior and performance of various beam-column connection configurations for use in CBFs. A typical connection using double angles provides the baseline and alternate details using end plates, thicker double angles, and supplementary seat angles are studied using full-scale tests. The local behavior of the connection region is characterized by observations related to beam-gusset plate weld failure and principal strain distribution in the gusset plate and beam web.

This paper presents the results of an ongoing research project on the seismic performance of concentrically braced steel frames of the Conventional Construction category designed according to NBCC 2005 and CSA-S16 seismic provisions. These structures are expected to remain essentially elastic during strong ground motions. Linear time history analyses were performed on typical braced steel frames of this category to assess the force demand on brace connections. Different building heights were considered. The structures were assumed to be located in both eastern and western Canada to reflect two different seismic conditions. Two local soil conditions were also examined: site classes C and E. The computed force demand varied with the building height, the location and the site class. In several cases, it exceeded the predictions from multi-modal response spectrum analysis, which is mainly attributed to the assumptions made on damping and higher mode response. Recommendations on design forces are given to prevent brittle failure of brace connections.

As building envelopes become tighter, conditions that compromise the performance of the thermal building envelope become more significant obstacles to the energy efficiency of buildings. Steel, with its high rate of heat conductivity, should be kept out of the building envelope's insulation plane as much as possible. Images from thermal cameras validate the energy loss from steel thermal bridging details. Since energy codes in the U.S. typically don't set limits for thermal steel bridging (as other countries do), it's important to relate this to a building envelope system's R-value. A straightforward way to quantify the reduction in insulation R-value due to the presence of steel elements bridging across the envelope insulation material is presented. Several conditions where thermal bridging can occur are discussed, with suggestions for alternatives to common details that can result in a significant improvement in a building's energy performance. Systems discussed include: cold formed steel stud walls, roof edge conditions, relieving angles, masonry lintels, brick ties, and projecting steel elements.

The connections of the superstructure to the foundation, slab, or the exterior systems of walls and roofs represent a transmissive bridge through the building's thermal and environmental protection system, because of the prevalent use of carbon steel ties, support and fasteners. However this common condition provides structural engineers' with opportunities to enhance the facility's energy use performance by advancing detailing to create thermal breaks. The use of lower conductance foams, wood framing, stainless steels, masonry products, etc. in the connections will be illustrated, in lieu of conventional concrete and steel juxtapositions. Design methods and case study details and specifications will be shown. Potential issues with life-safety and code interpretations or the material behavior will be discussed. With a growing understanding of building energy performance problems in the industry, the paper will attempt to encourage designers to advocate and develop a wider, varied employment of thermal breaks on each project.

The National Renewable Energy Laboratory (NREL) project in Golden, Colorado used an integrated design process in an effort to achieve a LEED Platinum rating. To support the sustainability goals of the project, the structural engineers incorporated the reuse of oil and gas piping as structural columns. LEED, however, does not address specific issues related to the greening of the structural steel design, fabrication, and erection processes. This study focused on the role of the structural steel industry and is divided into two parts: (1) individual and group interviews to identify potential environmental improvements for the structural steel delivery process and (2) a preliminary environmental life cycle assessment of the reused gas piping. Environmental improvements in the steel delivery process could be achieved through the use of an integrated steel delivery process. In addition, the salvaged gas piping used for columns was environmentally superior to standard structural columns.

Although rice straw and other grains have been used in building since prehistory, in the past two decades, there has been a move to utilize this rapidly renewable, locally available, agricultural byproduct. Stak Block, invented by Oryzatech, Inc., is a modular, interlocking block made of a composite of rice straw and binding agent that serves as an evolution in straw bale construction. This study investigates the feasibility of using these Stak Blocks as a structural system. Constitutive properties of the composite straw material such as yield strength and elastic stiffness were determined and then compared to conventional straw bale. Various construction detailing iterations were evaluated during full-scale shear wall testing using a pseudo-static cyclic loading protocol. Finally, the available ductility of the prestressed Stak Block walls in a lateral force resisting application is quantified along with an approximation of potential design shear forces. It was determined that the Stak Block material performed satisfactorily in gravity and lateral force resisting applications, in some respects better than conventional wood-framed construction, and has great potential as a seismically-resistant building material.

This paper evaluates the hysteretic behavior of an innovative compressed elastomer structural damper and its applicability to seismic resistant design of steel moment resisting frames (MRFs). The damper is constructed by pre-compressing a high damping elastomeric material into steel tubes. This innovative construction results in viscous-like damping under small strains and friction-like damping under large strains. A hysteretic model for the damper is presented and calibrated using test data obtained under sinusoidal loading. A simplified design procedure is used to design seven different systems of steel MRFs combined with compressed elastomer dampers in which the properties of the MRFs and dampers were varied. The combined systems are designed to achieve performance which is similar to or better than the performance of conventional steel MRFs designed according to current seismic codes. Based on the results of nonlinear time history analyses, target properties for a new generation of compressed elastomer dampers are defined.

An advanced concept for design of steel moment framed structures, sizing steel members per code guidelines for strength and adding viscous dampers to limit story drifts, this results in robust structures with superior performance to that of conventional designs at the design and maximum considered earthquakes. However, the efficacy of such design at extreme events has not been well documented due to the lack of a comprehensive database detailing their responses and data on the structures with dampers subjected to very large earthquakes. The current research addresses the physical limit states of the dampers, and development of mathematical model of the viscous dampers incorporating such limit states. The adequacy of the model is then verified by correlating it with laboratory data. Next, nonlinear simulations of structures with viscous dampers are conducted to probabilistically determine the collapse performance of the buildings and draw conclusions about key factors affecting the response

Improved seismic performance objectives (Immediate Occupancy and Continued Operation) set by owners of high-tech manufacturing facilities have resulted in increased use of supplemental damping and base isolation designs. This article reviews the design and construction process of industrial base isolated buildings with focus on code requirements, design and analytical methodologies, and constructability challenges. Due to velocity/displacement dependent behavior of base isolation systems, the building code (IBC/ASCE-7) requires performing a Non-Linear Time History (NLTH) analysis to determine the seismic loading on the base isolated structure. However, due to the complexity of NLTH and because the superstructure must be essentially elastic, the code also permits performing a staged analysis. The staged analysis consists of: 1) performing a linear (modal) analysis of the superstructure to determine the lumped-mass dynamic characteristics of the building, 2) performing a NLTH analysis of the isolation system and superstructure to determine system forces, displacements, and base shears, 3) performing superstructure design using a linear (modal) analysis with scaled base shear forces, and 4) designing the base isolator footings and support framing to resist the system design displacements and resulting forces. The required series of time history analyses are performed for a suite of time history records, each scaled to the Design Earthquake (DE) and the Maximum Considered Earthquake (MCE), variations of upper bound and lower bound isolator properties, and position of center of mass at each floor. A case study of a multi-stage analysis, design, and construction of three concrete industrial buildings built on a single base isolation slab is presented to discuss details and challenges related to design and construction of isolator selection, mounting, and support, as well as the design criteria for utility displacement compatibility at the isolator moat, and reduced equipment and contents anchorage requirements.

An important consideration for the design of seismic isolation systems composed of elastomeric bearings is the safety of individual bearings for maximum considered earthquake shaking. One assessment of bearing safety requires the bearing be stable at the maximum displacement. Although there exists no codified procedure for assessing stability in the laterally deformed configuration most engineers use the overlapping area method whereby the critical load capacity at zero lateral displacement is reduced by the ratio of the overlapping area between the top and bottom bearing end plates to the total bonded rubber area. This paper presents the results of a finite-element and experimental investigation aimed at improving the understanding of the stability of elastomeric bearing in the deformed configuration. The results of detailed nonlinear FE analysis and experimental testing of an elastomeric bearing with shape factor equal to 10 suggest the overlapping area method is overly conservative in predicting the critical load capacity in the deformed configuration.

Quantified risk assessment is performed for a typical light-frame wood residential building in the U.S. subject to mainshock and aftershock sequences. Mainshocks are simulated by a homogeneous Poisson process, while aftershocks are simulated by a non-homogeneous Poisson process. For mainshocks, pairs of ground motions are randomly selected, and geometrically scaled in accordance to the predicted spectra using an attenuation model. Transition and downtime costs are determined due to mainshocks and aftershocks, considering time discount factor. Aftershocks are found to be a significant factor for seismic risk analysis for wood constructions.

The new approach of Performance Based Design motivates the development of new methods for seismic retrofitting while two of the main performance indices are based on peak inter-story drifts and peak total accelerations. Previous research (Viti et al., 2006) has presented the concept of designing weak structures, or weakening some connections in existing structures, in addition to the installation of added viscous dampers. The new approach has been shown to effectively lead to relatively small drifts and accelerations. This paper presents a practical analysis based approach for the design of retrofitting of structures by weakening and damping. Alternatively, the algorithm can be used for the design of new structures equipped with viscous dampers to result desired levels of inter-story drifts while reducing total accelerations as well. The values of yield forces and damping coefficients serve as design variables. The physical behavior of yielding structures equipped with added viscous dampers is first analyzed and some insight to the strength and damping effects is gained. This insight is used to formulate simple intuitive criteria for the design that are then used to formulate a design procedure.

This paper examines the sensitivity of optimal designs of seismic retrofitting by means viscous dampers attained using the nominal properties of the structure to uncertainty in structural properties. Viscous dampers are first optimally designed for the nominal properties of the retrofitted structures and given ensembles of records. The behavior of the retrofitted structures considering uncertainty in their properties is then tested using monte-carlo simulation. It is shown that the uncertainty leads to larger mean drifts then expected and that some designs are more sensitive than others. The physical reason for that is discussed and some rules as to what designs are expected to be more sensitive are given.

Conventional concentrically-braced frame (CBF) systems have limited drift capacity before brace buckling and related damage leads to deterioration in strength and stiffness. A new type of CBF is being developed which has greater drift capacity before damage and which develops less permanent (residual) drift under seismic loading. This self-centering CBF (SC-CBF) system is motivated by the goal of minimizing structural damage under seismic loading and is intended to provide significant non-linear drift capacity while limiting damage and residual drift. The fundamental lateral load behavior of the SC-CBF system is rocking on its base, which occurs when the column under tension from overturning moment decompresses and uplifts from its support. The SC-CBF is designed to decompress at the base at a selected level of lateral loading, initiating a rigid-body rotation (rocking) of the frame. Vertically-aligned post-tensioning (PT) steel resists this uplift and provides a restoring force to return the SC-CBF to its support (to re-center the system). Experimental results show that SC-CBFs can be designed to sustain no significant structural damage under the design basis earthquake and only minor structural damage under the maximum considered earthquake.

This paper presents two approaches of estimating the control force magnitude in the building structure's seismic design. One is by spectrum average in frequency domain, and the other is by nondeterministic Monte Carlo analysis in time domain. The spectrum method is proposed to find the estimation by averaging the system's frequency response with an earthquake spectrum as a weighting factor. The nondeterministic method is based on sets of potential ground motions generated numerically. The approaches are developed in the concept of performance design, with studies based on the site potential seismic hazard and presenting results at different levels of displacement objective. The output of force estimation is arranged in tables or curves in terms of control ratio objective and the structural weight. The approaches are presented as a general concept and applicable to various controller types.

Research and experience of past earthquakes suggest the need for buildings that are less vulnerable to damage and easier to repair after a major earthquake. Our research aims to develop a new structural system that employs controlled frame rocking action and replaceable structural fuses to provide safe and cost effective resistance to earthquakes. The system combines desirable aspects of conventional steel-braced frame systems with energy dissipating shear fuses that are mobilized through rocking action. Vertical post-tensioning is provided to increase overturning resistance and enhance the self-centering characteristics to reduce residual drifts. This is the first of two companion papers to present research findings from a NSF-NEES Small Group Project on this topic. This paper examines the behavior of controlled rocking systems through large (1/2) scale rocking-frame subassembly tests conducted at the University of Illinois. Conducted using quasi-static cyclic and hybrid simulation techniques, the tests demonstrate the viability of the controlled rocking system and provide the basis for establishing design criteria to ensure an appropriate balance of overturning resistance, self-centering capacity, and energy dissipation.

This is the second of two companion papers that investigate the design and behavior of steel braced frames that resist earthquake effects through controlled rocking. By employing vertical post-tensioning and energy dissipating fuses, the controlled rocking systems can sustain large earthquake ground motions with minimal damage and without residual drift. This paper describes a series of large (two-thirds) scale dynamic shaking table tests, conducted at the E-Defense facility in Japan, to validate the system behavior for ground motions with intensities up to and beyond those of the maximum considered earthquake (MCE) level. The tests investigate response with alternative fuse designs and variable post-tensioning. Results of nonlinear dynamic analyses are shown to compare well with the shake table tests, which can be extended to assess the collapse performance of the controlled rocking frames, using procedures outlined in the FEMA P695 methodology to evaluate provisions for seismic design.

Design of a hybrid seismic device with energy-absorbing and re-centering capabilities is developed. The hybrid device consists of re-centering shape memory alloy (SMA) wires and energy-absorbing struts. In order to remain re-centering capacity, i.e., within the 6% target strain limit, the SMA wires should be designed to be sufficiently long. Another reason of using a 6% strain is to avoid the SMA stiffening phase that increases strength up to 5 times of its forward transformation yield forces, resulting in serious damage to the adjacent structural members. The energy-absorbing struts may be fabricated of mild steel or low strength aluminum. To reduce the possibility of buckling in the energy-absorbing struts when subjected to compression, they are designed to be stocky and seismically compact, or buckling restrained. An optimal proportion of the SMA wires and energy-absorbing struts is formulated such that the hybrid device retains re-centering capability while maximizing energy dissipation.

This paper summarizes the results of on-going research on the behavior of simple beam end framing connections in steel buildings subjected to fire. Connections are critical elements in maintaining the integrity of a structure during a fire. Very large force and deformation demands can occur at connections during a fire, and these demands are not well understood. In the US, one of the most common types of simple beam end framing connections is the single plate connection. In this study, the behavior of single plate connections in both the growth and decay phase of a fire using finite element analysis is presented. A refined three-dimensional finite element connection model was developed and used to study connection forces and deformations developed both during the heating and cooling phases of a fire. Residual forces and deformations in the connection after completion of the cooling phase are also examined. Design implications of the analyses are discussed.

In standard fire resistance furnace tests, structural specimens are unable to dissipate heat, as they are likely to do in building construction, by interconnection to cooler adjacent structural elements. Also, spray-applied fire resistive material (SFRM) coverage often is imperfect in buildings because it can be removed easily from steel, and poor application, natural deterioration, or other effects may cause localized deficiencies. Hence, standard furnace tests often do not capture the influences of important in situ features. This paper presents results of finite element, thermal-stress analyses that investigate the effects of connection proximity with respect to adjacent columns and the extent of SFRM coverage. More specifically, the performance of a series of model configurations that vary in connection proximity and SFRM coverage were studied under exposure from a typical office fire. These parametric studies demonstrate that minor changes to a connection assembly may have a significant effect on its fire performance. In some cases, relatively simple connection detailing changes can enhance the overall structure's fire resistance, even when SFRM coverage is not perfect.

Several reports and papers have identified a need for developing simple procedures to predict the response of structures in fire. Several performance-based models to calculate the performance of individual heated steel members have been previously developed. However, few approaches have developed simple methodologies for a frame-based analysis of steel structures exposed to fire. This paper shows a two-pronged procedure that predicts the behavior of a column on the perimeter of a building, considering both the individual member response (including thermal gradients) and the global response (including the interactions of adjacent members). All methods proposed in the paper are closed-form (i.e. they require no iteration) and can therefore be solved via spreadsheet or a simple mathematical algorithm. The framework is sufficiently simple for use in codified structural-fire design and could be included in a reference of performance-based analysis methods for steel structures. Although it addresses the performance of a specific member type (perimeter columns), the proposed framework has potential as a blueprint for the targeted performance-based analysis of other members types, such as floor beams.

Local buckling in floor beams has been one of the important observations in several fire events in steel buildings such as World Trade Center Tower 7 and large-scale fire experiments such as Cardington in UK. Utilizing three dimensional finite element methods for complex geometry and nonlinear behavior of such connections, local buckling of the web followed by the buckling of the lower flange is observed to occur in early stages in fire, which causes instability to the floor system, and a reduction in the connection strength. To fully capture the behavior of floor systems, one needs to be able to predict such buckling behavior of the beam. This paper contributes to such knowledge by investigating the local buckling of floor beams at elevated temperatures using nonlinear finite element models. The results are compared to AISC provisions of plate buckling under ambient and elevated temperatures.

This paper presents the experimental investigation of steel beam-columns under fire loading. Experimental tests have been planned to examine the fundamental behavior of steel beam-columns. Test specimens were sequentially subjected to: (i) constant axial loading, (ii) thermal loading on the plastic hinge region followed by ASTM E119 time-temperature (T-t) curve, and (iii) monotonically increasing flexural loading. The experimental approaches involved the use of: (a) innovative radiant heating and control equipment to apply thermal loading instead of using a conventional furnace and (b) digital image processing technique incorporated with close- range photogrammetry to measure the deformation and curvature over the heated region. The measured axial force-moment-curvature-temperature (P-M-Φ-T) responses of the steel members were compared to those obtained by 3D finite element models and analyses.

Case studies show that a lack of a model law structural engineer and a separate state structural Engineering Practice Act can lead to major disasters. For example the Cocoa Beach Florida collapse was attributed to engineers who did not know that they needed to check a concrete slab for shear strength. As a result a building collapsed under construction and caused the loss of life of several construction workers. In states with no Structural Engineering Act, it is more likely that errors will lead either to collapse or to extreme and expensive repair to buildings. Case studies are presented to discuss specific examples where structural failures would most likely not have occurred if the design engineers were licensed structural engineers as defined by ASCE Policy 524, SEI policy statement 101 and the NCEES Model Law Structural Engineer including the provision for additional 30 units of acceptable graduate course work beyond the B.S. degree, a minimum of 32 hours of written examination (includes FE/EIT exam) and a minimum of 4 years of experience working for a licensed Structural Engineer. Five case studies are presented.

Every engineer has an ethical obligation to hold paramount the health, safety, and welfare of the public. To many engineers, that obligation goes beyond policing oneself and one's own office. It also means doing everything in one's power to protect the public from sub-standard design regardless of its causes or origins. In this paper, I will explain what I think the engineering profession has to change in order to regain the grandeur and dignity of the profession — namely, college education requirements, experience reporting, technical examinations, continuing education requirements, ethics awareness, and enforcement — and why structural licensing and practice acts are the tools to make this happen.

The licensing of structural engineers is based on education, experience, and examination. In order to accomplish the goal of having all states license structural engineers in a consistent manner and thus provide comity between the states, a single structural exam needs to be used by all licensing jurisdictions. This paper reviews the last 94 years since the first structural exam was given in Illinois, and then turns to the future with a new NCEES structural engineering 16 hour exam. The new exam, with a new format, has challenges in satisfying the needs of states with different perceived requirements. This paper will review the process by which this new exam was developed and the test plan that will be used to write the problems.

A sea change has occurred over the past couple of years in the way that design firms document and deliver building designs. The era of 2D CAD drafting is slowly giving way to Building Information Modeling, or BIM. BIM provides for the complete 3-dimensional representation of building project data in a single file, database format. From this file, almost any information contained in the database can be extracted and presented in any documentation format. This conversion from 2D drafting to 3D BIM is dramatically changing the production process, and the firms that make this change are finding that they need to develop a whole new set of standards for this new process. This paper presents the process and results of implementing a new set of standards at a structural engineering firm that has converted to the BIM process. Standards regarding documentation, workflow, information exchange, project coordination, and conceptual design will be covered.

The ultimate success of Building Information Modeling will in part depend on the ability to capture all relevant data in the BIM model, and to successfully exchange data between the various project participants. One of the means of doing this information exchange is through a standardized file format. The objective of this standardized file format is to improve productivity in the design and construction industry by developing a basis for incorporating and integrating structural design, codes, and analysis tools and methods. Two of the file formats commonly used in this capacity are the CIS/2 standard and the IFC (industry foundation class) standard. This paper covers the challenges related to implementing the IFC standard, such as: What is the IFC standard? What information would be contained in this standard regarding structural components? What can structural engineering firms do now, if anything, to implement this standard?

All the different entities utilizing BIM technology in the construction and building industry including architects, engineers, contractors, and software developers, have diverse nomenclatures, diverse vocabularies, geometries, computing paradigms, data formats, data schemas, scales and fundamental world-views. They also have different requirements for accuracy, verisimilitude, and rendering performance. These various organizations have different standards and business processes for which they have developed their own paper and digital delivery procedures. To solve these problems, The National BIM standard (NBIMS) establishes standard definitions for building information exchanges to support critical business contexts using standard semantics and ontologies. This Standard forms the foundation for accurate and efficient communication and commerce that are needed by the construction industry. This paper investigates the general objectives of this standard, its relationship to structural engineering practice and focuses on the importance of involvement and contribution of structural engineering community to this standard. The standard is still in its infancy and the evolution and maturity of NBIMS will help to establish advanced design, communication and simulation tools that give the structural engineering community an opportunity to change the way it works in the industry, including open collaboration between stakeholders, design for optimum structure, increased energy efficiency, flexibility, constructability, comfort, and sustainability. It is important to note that agencies in the government and private sectors are currently adopting and enforcing the NBIM standard and it is becoming critical that the structural engineering community understands and delivers projects consistent with these NBIMS standards.

Developments of both online and "near-online" collaborative storage media are needed for continuing BIM implementation success moving forward. As model size, complexity and version control requirements increase, it is observed that increasingly automated data management capability is needed to improve project workflow. E-mail, ftp and other electronic delivery methods require a significant amount of man-hours that do not contribute directly to BIM productivity, but are actually overhead project functions embedded into the model (BIM) development costs. The author proposes a data collaboration strategy using IT for reducing this overhead burden to free up technical staff for more direct production rather than data management. Large data model transmission is a bottleneck for collaboration. Existing IT tools, combining hardware and software, can be reshaped to provide more robust data management to overcome "single-seat" data formats common in the Windows operating environment.

Building Information Modeling (BIM) is one of the most promising advances in the Architecture, Engineering and Construction (AEC) industries. Presently the AEC industry continues to inform their association members, stakeholders, etc., about BIM adoption in a variety of ways. However, at the core of all this BIM evolution is education. This paper focuses on the experiences gained in introducing BIM in the comprehensive design studio at different institutions. Using BIM as a framework for evidence-based design approach, BIM was implemented as the primary design tool for the final year architectural students at KSU to develop architectural, structural, MEP design for their studio's projects. The main objective of this studio is to provide students with means through which integrative pedagogical objectives are achieved through BIM. The interoperable devices are used to measure students' understanding and successful integration of the building design, the complex relationships between its components, and the construction processes through which their ideas could be realized. This includes documenting and evaluating students handling cross-disciplinary interests through use of Building Information Modeling knowledge and other tools into their practical design project. In addition, the paper assesses potential BIM future role in the building industry based on actual case studies and lessons learned, and suggested practical approaches to integrating BIM in AEC education.

This paper highlights the recent experiences garnered at the University of Cincinnati during a 3-quarter long capstone design course for structural engineering undergraduate students, working side-by-side with first year MS architecture students. The course was ideated to foster online collaboration among the students from the very start, using advanced videoconferencing and sharing software. The paper describes the challenges that were encountered and showcases the results obtained at the end of the course. Architecture and engineering students collaborated from the very initial phases on the "office building of the future", using Autodesk Revit as the common design platform. Engineering students then focused on the structural systems and attempted to analyze and design their structure using CSI ETABS, progressively updating the structural system into the Revit model. The results of the designs are summarized and commented, and some of the issues encountered are described in detail, both dealing with the interactions between architecture and engineering students, and with the interoperability capabilities of the software used. It is envisioned that in the next iteration of the course more engineering specialties will be involved, therefore broadening the scope of the projects, fully leveraging the potential of BIM.

The engineering profession is at a cross roads. Some professional associations are proposing that a Masters degree be required to enter practice while certain sectors of the structural engineering community feel a Bachelors degree should continue to be the requirement for entering the engineering profession. Regardless, both sides are trying to identify the minimum level of competency required to solve today's problems safely, economically, and efficiently (SEE). Engineering curriculum should be established that not only prepares graduates to SEE design projects, but also prepare students to face the problems of tomorrow and enable them to articulate those solutions to building owners, building designers and building contractors. The engineer of the future must possess the same skills as those of today, engineering dexterity, a bit of vision, and an ability to communicate with a variety of professionals. This requires a solid understanding of basic engineering principles, a solid understanding of how buildings behave, and a solid understanding of how a building is pieced together. Additionally, the engineer of tomorrow must look outward; beyond the confines or comfort zone of the traditional engineering world. The engineer of tomorrow will need to be prepared in the art of communicating: writing, verbal, and graphical and more importantly how the engineering profession is incorporated in the business world. Engineering education will continue to emphasize the basics of structural fundamentals, but there is also a need to expose students to those facets of the profession that enable one to bridge the gap between other designer professionals and between engineers and owners. But training structural engineers does not end at the university level, it continues through out ones career as a design professional. A goal of the education system is to create life long learners, so the assumption of continuing education in and out of a classroom after college is one of the premises of this paper. This paper will highlight the skill set necessary to succeed in the structures profession, reveal skills that industry insiders feel today's graduates lack, and propose how to teach the skills necessary to be successful in the future.

Integrated Steel Design and Delivery (ISDD) is an engineer-contractor-steel fabricator specific sub-set of Integrated Project Delivery. The project benefits of this progressive steel delivery process are numerous: (1) Accelerated material takeoff and mill order allowing for cost control through early steel acquisition (2) Reduced fabricator/detailer "Requests for Information" via early intervention by Structural Engineer. (3) Expedited shop drawing production/review/approval process via electronic review (4) Reduction in field coordination issues and conflicts with other trades. (5) Overall schedule savings by reducing start-to-finish duration for delivery of structural steel. However, all parties should recognize that challenges exist to successful implementation of ISDD. The ISDD process is changing the traditional standard of practice, and some contractors and fabricators are uncomfortable with embracing this change due to their inherent risk aversion perspective. As espoused in all the IPD publications, the only way to move beyond that paradigm is to assemble a team you can trust. This panel discussion will relate the experience of ISDD team members who successfully collaborated on a $110 million project in California. A panel member representing each of the key firms (structural engineer, steel fabricator and general contractor) will discuss the process from their unique perspective. Collectively, the panel will share with the audience what worked, and just as importantly, what did not work, when implementing ISDD. Topics will cover Direct Digital Exchange between structural modeling and steel detailing software, the communication process between engineers and detailers, and the relationship between steel fabricator, general contractor and designers. The session will end with a question and answer open dialogue with the audience.

There is widespread concern among practicing engineers that the clarity and usability of the building codes have radically diminished as the size and complexity of the codes have increased. One tool for assessing the ability of practicing engineers to consistently and reliably implement the code is the use of Trial Design Problems. The Trial Design Problem process consists of (a) developing a common engineering problem, (b) enlisting practicing engineers to complete the engineering problem using the code, (c) evaluating the engineering solutions submitted by practicing engineers, and (d) conveying the results of the problems to the engineering community and code development committees. The Design Practices Committee of the Structural Engineering Institute recently completed several Trial Design Problems related to wind loading per the ASCE 7-05 code and the new Alternate All Heights Method of the 2009 IBC. The quantitative analysis of the Trial Design Problem solutions indicated serious concerns with the ability of practicing engineers to reliably and efficiently implement several provisions of the ASCE 7-05 wind procedures including: (1) Using ASCE 7-05, only 1/2 of the practicing engineers properly accounted for the internal pressures. (2) Using ASCE 7-05, only 1/3 of the practicing engineers properly accounted for torsion or end zone pressures. (3) The new Alternate All Heights Method in the 2009 IBC yielded more reliable and accurate results in less than 1/2 the time as compared to ASCE 7-05 Method 2. Considering the Trial Design Problem results, a follow up study was performed to evaluate the committee structure of the ASCE 7 wind committee as compared with other ASCE 7 committees. The study indicates a clear connection between the usability of the code provisions and the number of practicing engineers on code committees.

There is widespread concern among practicing engineers that the clarity and usability of the building codes have radically diminished as the size and complexity of the codes have increased. One tool for assessing the ability of practicing engineers to consistently and reliably implement the code is the use of Trial Design Problems. The Trial Design Problem process consists of (a) developing a common engineering problem, (b) enlisting practicing engineers to complete the engineering problem using the code, (c) evaluating the engineering solutions submitted by practicing engineers, and (d) conveying the results of the problems to the engineering community and code development committees. The Design Practices Committee of the Structural Engineering Institute recently completed a Trial Design Problem related to snow loading per the ASCE 7-05 code and 2006 IBC. The quantitative analysis of the Trial Design Problem solutions indicated that while practicing engineers were able to consistently apply most of the basic ASCE 7 snow load provisions, some concerns with consistent application of the provisions were identified, including: (1) Using ASCE 7-05, approximately 10 percent of the practicing engineers incorrectly identified the roof exposure condition resulting in an under-estimation of the exposure coefficient and the snow load. (2) Using ASCE 7-05, over 20 percent of the solutions did not account for the projection drift load requirements at the parapet of the low roof. (3) Using ASCE 7-05, for those solutions which included a calculation of projection drift at the parapet, the value for the roof length upwind of the parapet in projection drift calculation was not uniformly selected. Based on the results of the quantitative analysis of the Trial Design Problem solutions, recommendations were made for clarifications to the Snow Load provisions of ASCE 7-05.

There is widespread concern among practicing engineers that the clarity and usability of the building codes have radically diminished as the size and complexity of the codes have increased. One tool for assessing the ability of practicing engineers to consistently and reliably implement the code is the use of Trial Design Problems. The Trial Design Problem process consists of (a) developing a common engineering problem, (b) enlisting practicing engineers to complete the engineering problem using the code, (c) evaluating the engineering solutions submitted by practicing engineers, and (d) conveying the results of the problems to the engineering community and code development committees. The Design Practices Committee of the Structural Engineering Institute recently completed one Trial Design Problem related to seismic loading per the ASCE 7-05 code and the 2006 IBC. The quantitative analysis of the Trial Design Problem solutions indicated serious concerns with the ability of practicing engineers to reliably and efficiently implement several provisions of the ASCE 7-05 seismic procedures including: (1) Experience is essential as engineers with less than 5 years experience had variations in base shear from 0.5 kips to 979 kips. (2) Selection of the Simplified vs. Equivalent Lateral Force Method was made only 20% of the time even though the simplified solution was applicable. (3) Using ASCE 7-05, by reading the seismic maps for S_s and S₁ or utilizing the USGS website contributed to variations in values. Discrepancies in reading these values resulted in 10% to 15% variation in seismic forces. (4) Determining the Seismic Design Category varied with 5% of respondents incorrectly selecting C. Recommendations going forward indicate efforts can be made to increase engineer's awareness to simplified procedures, increase professional development seminars, and increase training. Considering the Trial Design Problem results, training should include various options for obtaining S_s and S₁, including maps and software.

This paper evaluates the potential impact of hurricane damage risks to buildings due to climate change and adaptation strategies. The analysis includes a probabilistic hurricane wind field model and a hurricane vulnerability model. There is a great uncertainty on the potential change in hurricane hazard patterns due to climate change. To represent this uncertainty and to investigate the potential impact of climate change, the paper explores the scenarios of increases of –5 to 10% in mean annual maximum wind speed over 50 years. The effects of regional development dynamics, the rate of retrofit, cost of retrofit, reduction in vulnerability after retrofit, and discount rate are investigated. This risk-cost-benefit analysis is vital in indentifying optimal and cost-effective adaption strategies to the potential adverse effects of enhanced greenhouse conditions. Miami-Dade County, Florida is used as a case study to evaluate the economic viability of various adaptation strategies.

Hurricanes Katrina and Ike, and to a lesser extent Rita, Ivan and others that have struck the Gulf and Atlantic coasts over the last several years, have caused extensive damage to property. Much of the damage was to the foundation systems or was propagated to the building through poorly performing foundations. From damage investigations after the storms, it almost appears that there is insufficient information for the practicing engineers about how foundations should be designed for these highly vulnerable locations and buildings or the information that is available is being ignored. While the storm surge elevations were extensive for both Hurricanes Katrina and Ike, the performance of building foundations suggests that there is either little design being performed for these foundations or the expected loads on the foundations are not clearly understood by designers. Hurricane Ivan caused damage to shallow building foundations where survival was probably assured had the foundations been deep-driven piles. Many of the building and foundation losses were caused by extensive erosion and scour at the foundation and it is clear this important coastal `hazard' is not being sufficiently accounted for in the design of the foundation. This paper will explore not only some of the foundation damage mechanisms that have occurred along the U.S. coastlines but suggest design approaches that engineers should consider using to help insure greater survival rates of the foundation. The current foundation design guidance that is available for the practitioner from expert coastal construction sources is not sufficient in covering the many important aspects of foundation design that must be considered to resist failing under the extreme loads of coastal storm surge events.

A rational torsion model for RC members called the Softened Membrane Model for Torsion (SMMT) has recently been proposed, which can predict the entire torque-twist curve including the cracking point. In this paper the SMMT is extended to treat PC members subjected to pure torsion. The prestressing creates a complex initial stress state in PC torsional members. Previous torsion theories essentially circumvent the initial stress state by bypassing the pre-decompression stage. In the present paper, the SMMT is modified to incorporate the initial stresses due to prestressing. The modified SMMT for PC members is used to predict the torque-twist curves of 12 tested specimens and satisfactory agreements are obtained.

This paper discusses simulation methodology used to analyze static and dynamic behavior of foam insulated concrete sandwich wall panels through ultimate capacity. The experimental program used for model development and validation involved component-level testing, as well as both static and dynamic testing of full-scale wall panels. The static experiments involved single spans and double spans subjected to near-uniform distributed loading. The dynamic tests involved spans up to 30 ft tall that were subjected to impulse loads generated by an external explosion. Primary modeling challenges included: (1) accurately simulating prestressed initial conditions in an explicit dynamic code framework, (2) simulating the foam insulation in the high strain rate environment, and (3) simulating shear transfer between wythes, including frictional slippage and connector rupture. After validation, the models will be used to conduct additional behavioral studies and parametric analyses, and assess and improve methodology currently used in the design of foam insulated precast/prestressed sandwich panels for blast loads.

The use of precast/prestressed concrete and tilt-up concrete for exterior walls is common practice in the United States. This form of construction provides an economical, rapid, and high quality building technique making it ideal for military and government facilities. In most cases these building systems must be designed against a potential explosive demand. Current design recommendations are very restrictive when using precast concrete components due in large part to the lack of experimental research data. To address this issue, a series of over 50 experiments were conducted to assess the failure modes and load and deformation capacity of wall panel systems. Single span and multi-span panels were examined. Foam type, tie type, and reinforcement were varied to provide a thorough understanding of the effects of these variables on the failure modes of the panels. The response of the systems was found to be sensitive to the insulation foam used and the failure mode of the shear ties. The results indicate that insulated precast concrete panels exceed the current response limits used by the Army for Anti-Terrorism and Force Protection (ATFP) applications.

Observation on damaged structures after recent earthquakes have shown that the force and deformation capacity of reinforced concrete bridge columns (RCBC) can be significantly affected by the combined effect of dynamic actions (axial, shear, bending and torsion); as a result of these load combinations, the RCBCs are subjected to unexpected large deformations and extensive damage that can seriously affect the seismic performance of bridges. To evaluate the impact of different loadings combinations on both circular and non-circular sections (double interlocking spirals), eight scaled cantilever-type RCBC specimens will be tested on the bidirectional shake table facility at the University of Nevada, Reno (UNR). As part of the study, a unique inertial loading system named the Bidirectional Mass Rig was developed to allow shake table testing of single cantilever-type RCBC under biaxial ground motions. Two sets of circular and interlocking RCBC will be subjected to different levels of biaxial, torsion and vertical loads through real time earthquake motions. The performance of the specimens will be assessed in terms of strength, deformation, and failure mode. Four of the eight specimens are reported in this paper

The paper investigates the drift at axial failure of R/C shear-critical columns tested under high axial load and repeated load reversals with increasing displacement. The tests discussed in this paper were part of a NEES Grand Challenge research program to study the risk of collapse of older reinforced concrete buildings during earthquakes. One of the primary goals of this column study was to learn about the difference in the failure mechanism of columns that experience simultaneous shear and axial failure, and those that are able to sustain axial load past the point of shear failure. It was found that the main parameters in the axial failure model adopted in ASCE/SEI 41/06 addendum do not properly reflect the failure mechanism of this type of columns.

This study is based on merging two promising materials to develop a new hybrid system. Engineered cementitious composites (ECC) allow optimization of the micro structure of the material to achieve ultra-high strength, ductility and fracture toughness. Studies during past two decades have also shown that fiber reinforced polymer (FRP) tubes can help eliminate the need for lateral steel reinforcement for confinement and shear in reinforced concrete (RC) columns, while also improving the flexural strength, ductility and energy dissipation. Analytical models were developed for several 1/6-scale bridge columns based on three different combinations of ECC, FRP tube and steel reinforcement. The models were simulated under constant axial load and reverse cyclic lateral loads. The results show a promising hybrid system, in which the FRP tube is filled with ECC only within the plastic hinge length and with conventional concrete for the remainder of the column. The proposed column does not have any lateral or longitudinal steel reinforcement, while performing the same as a typical RC bridge column. Furthermore, an experimental work has been designed and is already being carried out by the authors to validate the analytical simulation results. The study also focused on a series of uniaxial compression tests on FRP-confined ECC stub specimens with different fiber types and wrap thicknesses. The results showed that FRP confinement causes a significant enhancement in strength and ductility of FRP-confined ECC. Moreover, the study shows that the available confinement models for conventional concrete cannot predict the behavior of FRP-confined ECC columns.

The performance of multi-span steel-concrete composite (SCC) bridges in recent seismic events has shown that these structures are very sensitive to earthquake loading. Extensive damage can occur not only in the substructures, which are expected to yield, but also in the components of the superstructure involved in transferring the seismic loads. Thus, proper evaluation of the seismic demand and capacity of each structural component involved in the seismic loads path is crucial to assess the fragility of these bridges. The objective of the paper is to investigate the seismic vulnerability of SCC bridges with dual load path accounting for model parameter uncertainty. A benchmark model of a three-span SCC bridge with relatively slender piers is considered for this purpose. Monte Carlo Simulation with Latin hypercube sampling is used to build a probabilistic model of the seismic demand and capacity at the different bridge components. This paper considers both uncertainties of the seismic action and of model parameters defining geometrical, mechanical, structural and inertial properties of the bridges considered. Comparison between the response variability induced by seismic input uncertainty and by model parameter uncertainty sheds light on the importance of accounting for the latter when evaluating the safety of the class of SCC bridges considered in this study.

A probabilistic procedure for the Performance-Based Design of structures subject to wind action is illustrated. The central objective of the procedure is the assessment of the adequacy of the structure through the probabilistic description of a set of decision variables DVs. Each DV is a quantitative measure of a specific structural performance (no collapse, occupant safety, accessibility, full functionality, limited displacements or accelerations, etc.). The structural risk is conventionally measured by the probability of exceeding a relevant value of the corresponding DV; the probability is evaluated by taking into account the Aeolian hazard at the site, the calculated structural response and damage, and the correlation between the attained damage level and the relevant DV. The procedure is applied to an example case: the assessment of the comfort requirement for a high-rise building.

Coupled reinforced concrete (RC) shear walls are often used in zones of high seismic risk. The RC coupling beams that connect individual shear walls must transfer adequate force between adjacent walls and, at the same time, are expected to contribute significantly to energy dissipation through ductile deformation during strong seismic shaking. These stringent requirements usually result in a dense configuration of reinforcement, which complicates erection of RC coupled wall systems. High performance fiber reinforced cementitious composite (HPFRCC) materials have a unique strain hardening behavior in tension that translates into enhanced shear and bending response at the structural level. Recent research has shown that the use of HPFRCC in coupling beams can result in a relaxation in reinforcing details while maintaining good strength characteristics and deformation capacity. This paper discusses the seismic performance of an 18-story coupled wall system in which HPFRCC coupling beams are used instead of traditional RC beams. System performance is evaluated through various parameters including inter-story drift and rotation of critical structural parts. The ability of HPFRCC coupling beams to provide acceptable performance is discussed in light of the simulation results.

This paper proposes a design framework for CFRP liners for concrete pressure pipes with different levels of degradation in an attempt to form the basis of a design standard. Design approach considers non-degraded, degraded, and severely degraded pipes where the effects of loads on the CFRP liner may be different due to pipe flexibility, initial imperfections in geometry, and quality of bond to host pipe. Loads and limit states that govern the design are defined. A detailed nonlinear finite element analysis is presented to demonstrate the determination of loads on the pipe. The requirements for qualification of materials and contractor, and importance of quality control during and after construction are highlighted based on experience gained in design, construction, and inspection of CFRP liners.

This paper describes a project involving the evaluation and structural repair of post-tensioned (PT) concrete garage decks. The suspended parking deck slabs exhibited numerous signs of distress, deterioration, and other conditions which led to questioning the structural strength of the slabs. The scope of work involved assessing the structural integrity and condition of the parking decks; identifying the causes of distress and deterioration; identifying remedial work necessary to repair existing distress and deterioration; and correcting structural and durability deficiencies of the parking deck slabs.

This paper outlines the circumstances in which load testing is advantageous and describes various methods for load testing different types of structures, including reinforced concrete systems and those with composite strengthening. The authors discuss testing approaches and methods, use of load testing to evaluate repairs, and specific conditions and challenges encountered during load testing of specific projects, as well as research into new load testing methods. Both simple and sophisticated load testing methods, including static and cyclic loading, will be discussed.

Because modern theories of mechanical behavior of cementitious materials require information about fracture, it is important to develop a standard test that provides quantitative physical information about fracture behavior. This paper discusses progress toward a standard fracture test for concrete. ACI Committee 446 is developing a report entitled "Fracture Toughness Testing of Concrete". The first test in the report is a Level I test (requiring only measurement of peak loads), while the second is a Level II test, requiring a closed-loop testing machine. Both proposed standard tests use a notched beam in three-point bending, and are fracture theory-neutral. Methods of interpreting the test data in light of several fracture theories are provided in latter chapters in the report. Each chapter has been written in ASTM-style language and format, so that ultimately parts of the report may be adopted as ASTM standards. This paper describes the history and current status of the development of these standard fracture tests.

This paper presents results from a recent study in which a finite element model was used for predicting the performance of restrained shrinkage cracking in concrete slabs. The slabs will be used to evaluate the performance of different mixtures at "full scale" in a carefully controlled environment (relative humidity, temperature, and wind). The paper reviews some of the design considerations that have gone into the development of the testing system. The finite element model considers the concrete as an aging, viscoelastic material. The model uses non-linear fracture mechanics that is incorporated with cohesive law concepts. The numerical results from the model will be compared with experimental data. This work will specifically illustrate the role of specimen size and reinforcing materials in crack development.

The highly developed concrete composites used to realize the monumental structures of Imperial Rome are remarkable engineering materials. Their mechanical properties are attested to by the numerous constructions still intact after millennia of usage. The assessment of these mechanical properties — particularly in tension and fracture — is the objective of the present work. We begin with a brief overview of the current knowledge of the mechanical properties, obtained from other testing programs, and then describe our own testing program, which will fracture test both re-fabricated and authentic materials. The varying morphologies and compositions of the ancient samples require a unique experimental design, the fundamental aspects of which are described, along with details of the re-fabrication process of an Imperial mortar for initial testing.

Quasi-brittle engineering materials contain flaws such cracks, pores, voids and fissures. Mode I cracking from such pre-existing flaws is the major cause of brittle fracture of these materials in compression. It is commonly accepted that that failure in uniaxial compression is characterized by multiple cracks propagating parallel to the direction of compression, whereas brittle failure in tension is typified by the propagation of a single crack. The energetics of crack propagation in compression are clearly different to those in tension. We report on a method used to study compressive fracture of concrete and masonry with a single crack. Pre-set cracks with different shapes of crack tip were placed in specimens. These specimens were tested to study their effect on compressive fracture. Specimens with cylindrical pre-set cracks failed with a single crack parallel to the compression.

Reinforced concrete flat plate slabs and slabs with drop panels often exhibit radial cracking in the vicinity of column supports under normal service/construction loading. This behavior has been observed in slabs in which design and/or construction errors have been identified, and in properly designed and constructed slabs. As such, the occurrence of radial cracking is not itself indicative of either design of construction errors, much less unanticipated performance. Negative flexural stresses are typically responsible for a concentration of cracking in the immediate vicinity of the columns, which commonly manifests in a "star-burst" pattern of radial cracks, interspersed with orthogonal or circumferential cracking. Such cracking can be found in reinforced concrete flat plate slabs in buildings that have been in service for decades, as well as in new buildings shortly after removal of shoring. While this cracking may be of potential concern to building owners, building officials, and design professionals as it may signify high flexural stresses and may result in undesirable exposure of the negative flexural reinforcing to moisture and chlorides, it is normally not indicative of a serious structural problem, and can be readily shown by analysis to occur under normal service conditions. Despite this, radial slab cracking appears to be mistaken as indicative of design or construction errors, structural overload, or punching shear failure nearly as often as it is recognized as normal behavior. Multiple case-study structures in which radial slab cracking has occurred are presented to illustrate typical in-field radial slab cracking conditions, and nonlinear finite element analyses are provided that illustrate the propensity of a variety of slab configurations to develop radial cracking when subjected only to self weight. As the case studies and analyses show, radial slab cracking is not damage at all, but rather is a predictable and expected occurrence that should be anticipated in code-compliant flat plates under service dead load, without any design errors, construction errors, structural overload, or punching shear failures. The purpose of this paper is to provide real-life examples documenting cracking in concrete floor structures, to demonstrate via analysis why the cracking occurred, to identify factors influencing the appearance of the cracks, and to quantify the loading intensities required to form a well-developed system of cracks.

Floor and roof systems are designed to carry gravity loads and transfer these loads to supporting beams, columns or walls, and distribute earthquake-induced loads to the lateral load resisting systems by diaphragm action. In reinforced concrete buildings, the inplane flexibility of the floor diaphragms is often ignored for simplicity in practical design (i.e., floor systems are frequently treated as perfectly rigid diaphragms). Past research has shown that this assumption can result in considerable error when predicting seismic response of low-rise rectangular RC buildings with end shear walls with large diaphragm plan aspect ratio (>3.0). This error is further amplified when the influence of floor diaphragm openings (i.e., stairways, shafts, etc.) is not considered (Al Harash 2008). The ASCE/SEI 7-05, "Minimum Design Loads for Buildings and Other Structures" allows the use of a rigid floor assumption in buildings with plan aspect ratio of 3:1 or less, where no plan irregularities exist. In order to investigate the influence of diaphragm openings on the inelastic seismic response of reinforced concrete buildings, four 3-story reinforced concrete building with end shear walls are designed, as if in St. Louis, Missouri, as a Building Frame System according to International Building Code (IBC 2006). The buildings are 9 bays by 3 bays in plan - 3:1 aspect ratio - and carry openings symmetrically placed at bays 1 and 9, 2 and 8, 3 and 7, 4 and 6, respectively. The inelastic behavior of the building is investigated under both static lateral loads (pushover analysis) and dynamic (time-history) ground motions, where a well-known earthquake, having a dominant period close to the fundamental period of the building, is scaled down to model moderate ground motions in the St. Louis region. A parametric study involving diaphragm's opening location (4 locations) is conducted with three types of floor diaphragm models (rigid, elastic, and inelastic). The analysis summary of all twelve cases is presented and compared. It is observed that the base shear redistribution due to inelastic slab deformations increases the load subjected to the interior frames significantly (up to 49%), when diaphragm openings are located within the middle half of the building. It is concluded that, the true response of such RC buildings can only be captured if an inelastic diaphragm model is utilized; hence, assuming a rigid floor diaphragm assumption per ASCE/SEI 7-05 is inappropriate.

Reinforced concrete deep beams are used as primary load distribution elements in various civil engineering structures. Large openings often interrupt the load transfer by concrete struts in these beams and cause a sharp decrease in strength and serviceability. Although the strength evaluation and reinforcement details around the openings are essential considerations, the ACI Building Code does not provide explicit guidance for designing these elements with openings. Strut-and-tie models are commonly used for strength evaluation and design of deep beams with openings. However, reinforcement detailing based on these models can be very complex and the failure of deep beams may be due to localized damages that could not be predicted by the strut-and-tie models. In this study, an experimental investigation was conducted on two concrete deep beam specimens with large single opening, namely, reinforced concrete (RC) and steel fiber reinforced concrete (SFRC), to evaluate their performance under monotonically increased load. The reinforcement detailing in the SFRC specimen was considerably reduced since the steel reinforcement bars were only used for the tensile longitudinal reinforcements and the boundary elements. Both test specimens had significantly higher strength than the designed load computed based on one assumed strut-and-tie model.

Two-way reinforced concrete flat slabs are an efficient, economical and widely used structural system. Building codes and analysis methodologies have evolved to address both slab strength and serviceability requirements. With respect to serviceability, codes permit thinner slab thicknesses when computed deflections are within prescribed limits. However, computed deflections often will not correlate with measured values. This discrepancy has led to numerous serviceability deficiencies associated with excessive two-way flat slab deflection. In many cases, this excessive deflection is related to cracking in the slab. Commercially available structural software programs will often model the slabs as uncracked and with a uniform thickness. Some of these programs are unable to account for the parameters associated with excessive deflection. Consequently, computed deflections often do not represent those of the structure in place. In this paper, we examine the effects of cracking on two-way slab deflection and serviceability.

This paper examines the effect of member self weight on preventing upward buckling of a compression member with horizontal orientation. The unique case of continuous, one-directional bracing with constant brace force but with zero brace stiffness is considered for a practical range of members and applied axial loads. The concept is further explored through an analysis of the stability of an exterior curtain wall that is laterally supported by suspended horizontal tube steel trusses. Under outward wind loads, the compression chord of the truss may be considered adequately braced against upward buckling by its own self-weight.

The Shanghai Center will be the tallest building in China and the second tallest building in the world. Its iconic shape, predominantly because of its unique curtain wall support structure, will make it one of the landmark buildings of the twenty first century. The outer curtain wall support structure consists of ring of pipes held off from the inner cylindrical building by radial spokes. The outer curtain wall looks like a triangular cam in plan that twists around the inner cylindrical building. Between the two skins is an atrium created by the void. Every 12 to 15 floors the inner tower extends out to support the outer skin creating a "mini plaza" as a result. Many structural challenges were created by this curtain wall support system including hanging the façade support structure every 60m to 70m (12 to 15 floors) vertically, thermal forces created by the exposed support structure, interaction with the primary tower structure and generation of the geometry. Each aspect of the design and analysis will be explored in this paper.

Over the past decade, extensive experimental and analytical research has been conducted on the behavior and resistance of unreinforced masonry (URM) walls retrofitted with methods for increasing ductility. This includes numerous experiments conducted by the Airbase Technologies Division of the Air Force Research Laboratory (AFRL). These retrofit materials varied from soft elastomeric coatings to very stiff composites and metal sheets. Some retrofit materials were strongly bonded to the masonry wall, which resulted in an integrated system response, while others were not bonded to the masonry and the membrane simply acted as a barrier that prevented secondary fragmentation from entering the occupied space. Previous research programs by AFRL and others have focused on the development of the retrofit materials, with the predominant exploratory measure focusing on the maximum inward transverse displacement. However, little emphasis was placed on the real behavior of the boundaries of these systems and the proper and efficient design of connections. This paper discusses an appropriate analytical methodology for the design of retrofit connections to resist impulse loads due to blast. In addition, typical support conditions for URM walls, and the shear, flexure and friction interaction of blast-impulse-loaded retrofitted URM walls at their support boundaries are discussed. The ideas and conclusions presented herein are based on component-level static testing, full scale explosion arena testing, and high fidelity finite element modeling.

Past research has demonstrated that steel stud walls can perform well when subjected to large blast events. The construction methods needed to achieve good performance that take advantage of the inherent ductility offered by steel, however, have been costly and have often required the use of specialized connection details that allow a stud to reach its full flexural and/or tensile capacities prior to connection failure. The goal of the current study is to develop techniques for mitigating large blast loads acting against steel stud walls using conventional construction materials and techniques. Two issues of concern for the current research are: 1) the performance under blast loads of typical connections, either commercial clips or the standard screwed-stud-to-track, has yet to be fully examined, and 2) current methods of design do not incorporate the mechanical interaction of veneer layers for potentially increasing the blast resistance of steel stud walls. To better understand the role played by connection design details and wall system construction details, research for this project includes laboratory testing, field testing, and computational modeling. In this paper, the authors provide an overview of the research program and a summary of the findings that have been developed to date. From the data collected during this project, designs that exhibit a balance of simplistic, economic, and adequate protection will be developed.

Exterior façades being designed for dynamic blast loadings traditionally have used cast-in-place concrete, precast concrete or reinforced concrete masonry unit construction. These systems, although very effective in resisting blast loading, can add substantial weight and cost to the building's structure. Light gauge metal stud façade systems are commonly used in conventional construction projects because they are relatively light weight, cost effective, and can be constructed in unitized systems pre-fabricated off-site thus minimizing erection and building enclosure schedules. Due to these benefits, their use is becoming more prevalent in blast resistant applications. Light gauge metal stud systems can be designed for blast loads using traditional single degree of freedom (SDOF) dynamic analysis techniques; however, inelastic dynamic finite element modeling (FEM) tools can be used to optimize the design of these flexible and ductile systems, particularly for more complex wall geometries and systems with multiple connected components. Finite element models can provide a more in-depth understanding of the overall wall system behavior, the interaction and phasing of the system components and the sensitivity of the system to variations of connected elements and span lengths.

Criteria for designing hardened, heavily-reinforced concrete structures to resist blast effects from accidental explosions are defined by Unified Facilities Criteria 3-340-02 formerly Army Technical Manual TM 5-1300 (Departments of the Army, Navy, and Air Force. 1990). Lap splicing of the required steel reinforcing bars is the current practice in the construction of these reinforced concrete structures. Lap splicing of reinforcing bars often creates congested areas within the formwork that limit working space and hinder proper placement of concrete. In 1971, a limited number of splice types were tested at the ERDC (formerly Waterways Experiment Station) to investigate their performance under dynamic load conditions (Flathau 1971). Subsequently, several types of mechanical couplers have been tested and validated for developing the strength of reinforcing steel for cyclic loading and strain rates expected during earthquakes. The ERDC recently conducted a series of high strain-rate tests on five different types of American Concrete Institute 318 type II mechanical couplers, used for splicing of flexural reinforcing steel, to obtain their measured performance when loaded at high strain-rates. This paper compares the performance of the different types of mechanical couplers to control bars tested at the same high strain rates, and evaluates their performance to meet the service requirements of UFC 3-340-02.

This paper presents several unique design features and various analytical approaches used for a specific curtain wall proposed for a federal building that was required to withstand potential external high explosive threats. The building is a large reinforced concrete frame building with precast concrete wall panels and a glass curtain wall. The curtain wall consists of glass units supported by mullions that are attached to pretensioned steel cables spanning from the foundation to the roof. The glazing is designed using a single-degree-of-freedom (SDOF) approach using GSA's WINGARD code, which is compared to results obtained using BakerRisk's proprietary SDOF glazing analysis program. The cables are analyzed as tension membrane components using the SDOF methodology. A three-dimensional finite element analysis (FEA) model of the windows and cables has also been developed using both the commercially-available ADINA and LS-DYNA FEA codes. The SDOF results are compared to the FEA model results.

Finite element simulations of modern flexible high energy dissipation blast resistant curtain walls will be presented and compared with test results. Within the models the whole structures with all relevant components of windows, frames and anchoring are included by using a special nonlinear material algorithm for laminated glass, contact definitions, a detailed mesh etc. The focus of the presentation is the prediction of different processes of fracture and damage. Additionally some common design parameters like ductility factors and member end rotation limits will be discussed and compared with simulation and test results. Often too rigid handling of deformation limits instead of using more realistic failure criteria is counterproductive for well balanced structures and leads to increased stiffness of all parts and high support forces.

Application guidance and engineering performance parameters are being developed by PPG Industries (PPG) and Protection Engineering Consultants (PEC) for PPG's spray on and trowelable (hand applied) polymers. These materials are offered by PPG (Mil-Tough^TM) for use as structural wall retrofits for strengthening and debris reduction for blast loading applications. The application guidance has been developed through full scale static and blast testing and analysis of those results by PEC. Both anchored (wall head and base) and unanchored solutions were investigated and are offered by PPG. This paper presents an overview of testing and analysis, and will illustrate the use of the application guidance in an example application.

Russian loading and design standards present many challenges for Structural Engineers from North America. Structural Engineers have to deal with language, wind loading, load combinations and design methodologies that are presented in a different manner than in the United States. Design for Steel Buildings in Russia is based on requirements of the State Standards "Building Norms and Rules", SNiP (Stroitelnye Normy i Pravila), SNIP 2.01.07-85 for loads and SNIP 2.23-81 for "Steelwork". Structural design using these standards is mandatory. In addition, guidance for steel design is found in "General Rules for Steel Structure Design" SP 53-102-2004 This paper describes how SNIP 2.01.07-85 , SNIP 2.23-81 and SP 53-102-2004 are used in the design of steel buildings under wind loads as well as comparing designs wind loads to Canada and the United States.

In September 2007 the Spanish version of eurocode, UNE-EN 1991-1-4 has been published; also in road bridges the Spanish IAP code is considered by designers as a feasible tool for the evaluation of wind actions on conventional road bridges. Additionally the AASHTO LRFD Bridge Design Specifications is a feasible comprehensive code. The aim of this work is to analyze the approaches followed for the aforementioned codes for the design of short road bridges in terms of wind loads values and "user-friendliness". Thus the general procedures are described in order to get a grasp of their stipulations. Finally, two examples of simple bridges have been considered to evaluate the wind loads to be considered in their design according to the two codes. It has been obtained that eurocode and AASHTO LRFD give higher wind loads than the IAP code. Moreover IAP and AASHTO LRFD are easier to use for practitioners as they are specific bridge norms.

The first consensus wind load design criteria were published as ANSI A58.1-1972 by the American National Standard Institute (ANSI) in 1972. This document delineated wind load criteria based on probabilistically determined wind speed and tabulated forms of design load parameters. Since then, the wind load criteria have gone through major changes as revisions of the standard were made in ANSI A58.1-1982, ASCE 7-88, ASCE 7-93, ASCE 7-95, ASCE 7-98, ASCE 7-02 and ASCE 7-05. Major changes occurred in the wind load criteria in ANSI A 58.1-1982 and in ASCE 7-95. The most significant change is the reference wind speed, which changed from fastest-mile to a 3-second gust. Each revision made changes and adjustments in several different factors including the importance factor, terrain factor, directionality factor, gust effect factor and the pressure/force coefficients. This paper outlines only the significant changes in the wind load criteria as they have evolved over the last three decades.

Buildings need to be designed to withstand wind loads regardless of where they are located and the laws of physics governing wind loads do not change when crossing political boundaries, nor do basic statistical principles. Likewise in the colder regions of the world snow loads need to be designed for and design values should again be governed by the laws of physics and statistics. However, as any designer working internationally knows, the requirements of building codes can be very different in different parts of the world. Part of this is understandable due to the geographic dependence of climate. Some is also due to historically different approaches to risk and different rates of advancement technically. However, the largest cause is the large gaps in knowledge that still exist in many aspects of wind and snow loads, and these gaps will continue to exist, making international consensus difficult, unless some of the advanced countries decide to increase considerably the research funding directed to these topics. This presentation will discuss some of the differences and similarities of wind and snow provisions in the codes of various countries and discuss approaches to improving consistency and uniformity of methods.

This paper discusses rational approaches to the design of structures for wind loads, at locations where tropical cyclones, including hurricanes and typhoons, are the dominant windstorm event. The characteristics of the windstorm event itself, including current knowledge of mean velocity and gust profiles are discussed. Structural safety and reliability principles are discussed, in relation to design for wind loads in the extreme wind environments affected by tropical cyclones. It is shown that the greatest uncertainty is the wind speed itself. Typical variations of the basic wind speed with return period (annual risk of exceedence) and appropriate return periods and wind load factors for design are proposed.

The city of La Coruna is located in the northwestern coast of Spain on the Atlantic Ocean coast. The total population comprising the surroundings is about half a million of inhabitants. The most densely populated part is in an isthmus, thus conventional roads on the narrow mainland have reached a high level of traffic congestion. As a consequence, there is a social demand for alternative routes joining the city downtown and the residential areas around it. Therefore to solve this traffic problem the local authorities demanded the authors to elaborate the conceptual design of a bridge spanning the La Coruna Bay in order to improve communications of the main city with the growing areas at the North in the other side of the bay. The targets of the conceptual design work have comprised the evaluation of the most adequate location of the bridge, the study of alternatives and the final decision of the typology, the geometrical definition of the towers and the deck and the layout of the road to connect the bridge with the pre-existing communication network. As a matter of fact, this work has offered a great occasion to apply non-conventional tools in the bridged design process. Computer renderings have been done since the initial steps of the design work in order to verify the aesthetic values of the proposal. CFD has been employed to evaluate the aerodynamic coefficients of the deck cross-section in order to anticipate the aerodynamic and aeroelastic performance of the bridge. Moreover, the optimization of the cables cross-section of the cable-stayed bridge has been carried out considering constraints associated with the cables stress and the deck displacements. In this paper the final definition of the proposal is presented, describing the cable stayed bridge selected after the alternatives study and significant attention is paid to the set of design tools employed along the design process.

Elbow River Bridge is a single-span, cable-stayed bridge spanning the Elbow River near Downtown Calgary, Alberta. The bridge has a span of 48.5 metres (m) and is the first vehicular cable-stayed bridge in Alberta. Limiting roadway elevations at the top of the deck and free-board limits at the bottom left very little room for deck thickness. A cable-stayed bridge was suggested as an option by the design team, as it reduced the deck-thickness requirement and eliminated the need for a pier in the river, which also helped with the tight construction schedule. The project delivery method was similar to design-build except that both the consulting engineer (CH2M HILL) and the contractor (Graham Construction) were hired by the owner. This paper describes the different aspects of the bridge's design and construction, including the selection and design of main components, analysis of the bridge, and interaction between design and construction.

Existing frame finite elements for modeling the response of structures in fire are limited to the stiffness method of analysis, in which the element formulations are based on an assumed displacement field. Such stiffness-based elements tend to experience loss of accuracy in highly nonlinear problems since the basic conditions of equilibrium are often violated. This problem can usually be remedied with the use of more elements along the length of a member, a solution that also leads to significant loss of efficiency. Recent efforts in the analysis of structures at ambient temperatures have demonstrated that flexibility-based and mixed formulation elements tend to offer greater accuracy and computational efficiency, since the element formulations strictly enforce equilibrium. This paper considers the development of a flexibility-based fiber beam-column element for modeling the response of structures under fire. A fiber discretization over the element cross-section is used to account for gradual yielding of the member. The element formulation accounts for thermal expansion of the material as well as geometric nonlinearities, temperature-dependent material behavior, and residual stresses. Analyses of benchmark experimental tests of steel structures demonstrate that the flexibility-based element yields excellent accuracy. In addition, comparisons with stiffness-based frame elements show that the flexibility-based element offers greater computational efficiency since fewer elements are needed along the length of the member.

A new method is developed for reducing train—induced floor vibrations in buildings. Vibration transmitted through building columns to the upper floors can be mitigated by considerably increasing the thickness of a lower floor, which is named the "blocking floor". This can be a desirable and inexpensive solution for vibration mitigation. The work presented by this paper shows the ability of an impedance-based wave propagation model to capture the blocking floor behavior by comparing the analytical predictions of the velocity rations with the measured velocity ratios in the frequency domain. A 4-story scale model building was designed and constructed for measuring floor vibrations induced by excitations at the base. The effectiveness of using different blocking floors with different thicknesses in the scale model to mitigate vibrations was examined. Additionally, a sandwich floor with an integral damping layer was added to the scale model building to examine the effect of enhanced energy dissipation in the blocking floor slab.

Dynamic responses of constructed systems are of interest due to issue of life-safety related to earthquakes, blast, and impact loadings. There are two common approaches to understanding the dynamic behavior of constructed systems: field testing and small-scale physical model testing in a laboratory. Both of these approaches are needed. Field tests are guaranteed to be representative of actual constructed system behavior, but are difficult to interpret and understand completely. Physical models are easier to understand and interpret, but may not be representative of actual constructed system behavior. There is currently an incomplete understanding of how reliable the theory and application of dynamic similitude laws are for physical model studies, and thus there is uncertainty associated with the validity of the results from a large number of experimental studies. Several key sources of uncertainty associated with construction of physical models, scaling and execution of input, elastic behavior-specific mechanisms and inelastic behavior-specific mechanisms have been identified. This paper establishes how they influence the use of small-scale physical models to simulate the dynamic behavior of constructed systems. The final goal of this thesis is to serve as class notes for a graduate course on experimental mechanics partly based on physical modeling with focus on dynamic similitude and structural dynamics.

Laser scanning technology is quickly expanding into many fields and is becoming an essential tool for accurate non-destructive 3D measurement of an object's shape. This technology enables users to capture millions of object's points with high accuracy. Depending on the size of the object, its proximity to the scanner and its type, a laser scanner can deliver results with an accuracy ranging from 0.050 mm to 4 mm. So called 3D point cloud representing the object's surface is delivered as the result. The paper presents several representative applications of this technology, and shows the use of the laser scans to document and assess earthquake damages in structures that can be utilized for finite element modeling of the structure and its components and/or for subsequent determination of adequate retrofitting techniques.

In addition to a number of editorial changes, the 2010 edition of ASCE 7 will contain a number of important changes that affect nonbuilding structures. This paper discusses these important changes and how these changes will impact the design and construction of nonbuilding structures. The significant detailing requirements for large breech openings in reinforced concrete stacks combined with a change in R and Ω_o values added to the standard in response to damage of reinforced concrete stacks in a major earthquake in Turkey are reviewed. The modifications to the seismic requirements of ACI 350.3 to bring that document into compliance with ASCE 7 for the design of ground supported concrete tanks are discussed. The revised provisions that provide some relief to the excessive sloshing wave heights calculated under ASCE 7-05 for ground supported storage tanks are reviewed. Anchorage requirements for many nonbuilding structures are clarified. Steel storage rack requirements, updated to meet FEMA 460 and ANSI MH 16.1–2008, are discussed.

Seismic restraint of nonstructural components (i.e., building contents and all building elements not part of the building structure) has gained in importance over the past decade. The primary objectives associated with seismic design of nonstructural components can be stated as: 1. Mitigation of falling hazards, particularly in or around paths of egress; 2. Mitigation of the release of hazardous materials; 3. Ongoing operability of structures and buildings vital to post-earthquake recovery (e.g. hospitals and fire stations); and 4. Mitigation of property and commercial losses. The requirements of ASCE/SEI 7–10 Chapter 13 are specifically intended to address the first three concerns, i.e., reduction (not elimination) of risks to building occupants associated with dislodgement and disruption of fixed building contents and systems, prevention of haz/tox release, and improvement of the likelihood that essential facilities will continue to function after an earthquake. While not a stated goal, some degree of property protection may result from successful implementation of the provisions; however, significant reduction of property losses, e.g., associated with pipe rupture and consequential flooding may require implementation of a greater degree of protection (such as leak tightness in piping systems). In this context the provisions of ASCE/SEI 7–10 are reviewed, specifically with regards to highlighted changes from the 2005 edition in the areas of anchorage, the treatment of architectural, electrical and mechanical components, system certification, and exempted components.

The ASCE/SEI Seismic Design Provisions embody the seismic design requirements enforced by U.S. Building Codes. Since 1998, the basis for these seismic design requirements contained in ASCE 7 has been the NEHRP Recommended Provisions for Seismic Regulation of Buildings and Other Structures, developed and published by the Building Seismic Safety Council of the National Institute of Building Sciences under contract to the Federal Emergency Management Agency. BSSC has published the NEHRP Provision since 1985. The BSSC Provision provide a forum for new seismic design criteria including to be developed under an informal consensus process, and readied for adoption in ASCE 7 and other standards. Traditionally the NEHRP Provisions have provided a vehicle for the development of new analytical procedures, new structural systems and even entire design procedures. The 2009 NEHRP Provisions were instrumental in the development of new seismic hazard maps included in ASCE/SEI 7–10 as well as design provisions for AAC wall systems and cold–formed steel moment resisting frame systems, as well as extensive requirements for nonbuilding structures. Importantly, the NEHPR Provisions are accompanied by a complete commentary to the ASCE/SEI-7 seismic requirements as well as recommended new technologies that are not yet ready for adoption into the standard, but which may be suitable for such adoption in future years.

New provisions for computing peak ground acceleration (PGA) for soil liquefaction and stability evaluations have been introduced in Section 11.8.3 of the 2010 NEHRP Seismic Provisions and the ASCE 7–10 standard. The PGA provisions consist of maps of the Maximum Considered Earthquake (MCE), geometric mean, horizontal component, bedrock PGA, plus a site-coefficient (F_PGA) table to convert the bedrock PGA value to one corresponding to another site class. Of particular note is the requirement that liquefaction must now be evaluated for the MCE, rather than the design earthquake, as currently required in the 2006 International Building Code (IBC) and ASCE 7-05.

This paper describes work by the Seismic Design Procedures Reassessment Group (SDPRG) of Project 07 to update the seismic design maps and procedures of the 2009 NEHRP Recommended Provisions. Project 07 was a joint effort of the Building Seismic Safety Council (BSSC), the Federal Emergency Management Agency (FEMA and the United States Geological Survey (USGS). As part of Project 07, the SDPRG worked with the USGS to incorporate new (2008) hazard data and improved earthquake ground motion criteria in the 2009 Provisions. Work by SDPRG resulted in three significant changes to design ground motions: (1) "probabilistic" ground motions are now defined in terms of uniform risk, rather than uniform hazard, (2) ground motion intensity is now defined in terms of the maximum spectral response in the horizontal plane, and (3) "deterministic" ground motions are now defined by 84th percentile spectral response (rather than 1.5 times median spectral response).

This paper presents an experimental program using real-time hybrid simulation to verify the performance-based seismic design of a two story, four-bay steel moment resisting frame (MRF) building with compressed elastomer dampers. The laboratory specimens, referred to as experimental substructures, are two individual compressed elastomer dampers, while the remaining part of the building is modeled as an analytical substructure. The proposed experimental technique enables an ensemble of ground motions to be applied to the building, resulting in various levels of damage, without the need to repair the experimental substructures since the damage is within the analytical substructure. Statistical experimental response results incorporating the ground motion variability show that an MRF with compressed elastomer dampers can be designed to perform better than a conventional steel special moment resisting frame (SMRF), even when the MRF with dampers is significantly lighter in weight than the conventional SMRF.

The landmark Theme Building at the Los Angeles International Airport was evaluated for seismic loading. This structure is comprised of a reinforced concrete annular core and four steel arches placed at 90-degree orientations. Performance based engineering was used to assess the seismic performance of the concrete core. A detailed mathematical model of the structure was analyzed using site-specific acceleration histories. Analysis showed that the concrete core had insufficient flexural and shear capacity to resist the seismic loading. A comprehensive retrofit strategy consisting of increasing the capacity and lowering the demand was employed. The focus of the seismic retrofit is a tuned mass damper placed at the roof of the structure to reduce the seismic demand. Additional strengthening for flexure and shear are also incorporated in design. The retrofitted structure met its performance goal. Confidence analyses were conducted to assess the probability of reaching non-ductile limit states.

This paper contains the findings of an experimental study on the seismic response of two types of standard frictional bridge bearings: (a) steel-reinforced elastomeric bearings with PTFE disks, and (b) PTFE spherical bearings. The experimental program which was conducted partly at UC San Diego and partly at UC Berkeley included cyclic tests at various velocities and displacements for which these bearings have not been designed but may experience during an earthquake. The primary conclusions of these tests are that PTFE-elastomeric bearings perform adequately but cannot accommodate rotations reliably. Spherical bearings featuring general-purpose adhesives perform very poorly under seismic conditions; however, when high-temperatures adhesives are used in their construction, these bearings perform very well under seismic conditions.

The seismic isolation code which must be used for all seismic isolated buildings in the United States is conservative in many of its provisions. While seismic isolation is flourishing in other countries, it is underused in the United States. For static analysis and for the selection of time histories, the spectrum is constant-velocity for periods of one second and longer, leading to large displacements for long period systems and forcing the designer to use added damping to reduce these displacements. The damping systems used are hysteretic with the characteristic that damping decreases with increasing displacement. To achieve the damping needed to reduce these large displacements, expected from very rare seismic input, means that at smaller displacements, caused by realistic levels of seismic input, the damping will be very much higher, and there may be stiffening of the isolation system, meaning that the building may not act as isolated and there may be an impact on sensitive internal equipment. This paper shows how highly damped isolation systems are counterproductive to isolation and suggests an alternative approach that will conform to code requirements but ensure that, at moderate earthquake inputs, the equipment remains protected, and the large code-mandated displacements are kept to acceptable levels.

The number of base isolated building in Asian countries, especially Japan, far outstrips the number in the United States. Base isolated buildings in Japan number in the thousands while the number in the U.S. remains around one hundred. Unlike its use in Japan, isolation technology in the U.S. has remained within mainly essential, public buildings such as hospitals, city halls or 911 centers. The technology has not spread to use in typical office or residential buildings, which may also see increased safety and performance benefits. This paper compares the codes and practices for designing seismically isolated buildings in the U.S. and Japan. The design spectra are developed for buildings of the same occupancy rating located in comparable seismic regions in both countries. The design process is discussed from determining the ground motion demands through peer review and isolation device testing. Special attention is made to the code design methods for isolated building in the two countries with focus on the displacement demands for isolation devices. A comparison of the displacement demands for a three-story office building is made.

This paper briefly summarizes the ongoing research about concentrically braced steel frames that are widely used in north America. In the analytic phase, a series of nonlinear dynamic analyses and parameter studies are carried out to improve better understanding of the seismic behavior of concentrically braced frames to identify improved performance based design and analysis procedure. Analytical results of a two-story model building with bracing configuration identical to the test specimen are presented here. In the experimental phase, four large-scale two-story tall special concentrically braced frames and two buckling restrained braced frames are designed and tested in the NEES facility at Berkeley. Test reults and experimental observations of the first two braced frame specimens using square and round hollow structural section as bracing components are presented in this paper.

The WTC 7 investigation by the National Institute of Standards and Technology (NIST) identified several factors that alone, or in combination, led to fire-induced failures of the floors, and subsequently, total collapse of the 47-story WTC 7 building. At the present time, a sensitivity study is being conducted to determine the relative contribution of the identified factors, which includes the presence or absence of shear studs on girders, connection types, asymmetric framing, and bay span lengths. The technical basis for the identified structural factors is presented in this paper.

"Break elements" were developed to efficiently and accurately capture progressive failures of components and connections with temperature dependent properties for use in finite-element models of structures. These elements were used to model bolted and welded connections and shear connectors between concrete slab and floor framing used in the development of the finite-element modeling of the World Trade Center (WTC) Towers in the National Institute of Standards and Technology (NIST) investigation of the collapse initiation. Break elements account for geometric effects such as gaps, sliding off of seated connections, and temperature-dependent failure modes such as bolt shear, tear-out, block shear, and weld failure. The break elements were incorporated into the finite-element models of the structural components, subsystems, and global models of the WTC buildings. Validation of the models developed using break elements was achieved through comparison of the results obtained with detailed finite-element models. The models developed using break elements were able to capture the temperature-dependent response of components and connections with only a few degrees of freedom.

The National Institute of Standards and Technology (NIST) has published a comprehensive set of best practice guidelines for structural fire resistance design of buildings as part of its World Trade Center (WTC) Response Plan. The Best Practice Guidelines is a result of a collaborative effort initiated by NIST that involved experts in the design and construction industry and academia. It features information on current best practices in fire resistance engineering in the United States and overseas, and current best knowledge in fire risk assessment and characterization, material properties at high temperatures, and thermal and structural response calculation methods. The document integrates state-of-the-art information into a single source document to enable the use of the performance-based approach for fire resistance design, and to provide engineers and code enforcement officials with a technical resource for use in their approach to fire resistance design and evaluation of concrete and steel structures.

A major impediment to the advancement of Tropical Cyclone (TC) intensity forecasting and infrastructure damage mitigation is the void of data describing the near ground behavior of wind and water at the marine-coastal interface. The Digital Hurricane Consortium (DHC) is the newly formed umbrella organization that coordinates existing field deployment activities to collect and analyze wind, rain, storm surge and wave data via instrumented towers, mobile Doppler radars and surge/wave sensors. This coordination will produce an adaptive, event-driven observing system applied to the TC. Three-dimensional wind structure, precipitation, and surge/wave height will be collected at sub-kilometer resolution on time scales less than 1 min in the most severe region of the TC, and spanning from deep through shallow waters into surge inundated areas. A high-resolution surface intensity database will be created to assist modelers in prediction verification. These data will also be analyzed by a multi-disciplinary team of atmospheric scientists and wind/coastal engineers to investigate three areas: (1) air-sea momentum exchange/IBL formation, (2) wind-wave coupling and (3) mesoscale phenomena, such as eyewall mesovortices and rainband core downdrafts. The protection of coastal infrastructure from hurricane damage will be improved by this detailed quantification of the impinging forces.

This paper provides an overview of the research programs within the Department of Civil and Coastal Engineering at the University of Florida (UF) that focus on characterizing and mitigating the effects of hurricanes on the built infrastructure. The UF wind hazard research group specializes in "full-scale" hurricane research, i.e conducting experiments at landfall to quantify loads and damage mechanisms as well as recreating the damaging nature of hurricane winds and wind-driven rain at sufficient scale to test actual building systems. These programs include the Florida Coastal Monitoring Program, which collects weather data during hurricane landfall to guide post-damage assessments. A critical component of this program includes the collection of wind pressures on residential housing. Researchers are also conducting destructive experiments on formerly occupied homes provided by the State of Florida to learn how actual buildings respond to hurricane wind loads. Computer-based numerical simulation complements this research. UF is developing numerical techniques to simulate fluctuating loads on low-rise structures. Finally, researchers have undertaken several projects to evaluate the structural and water penetration resistance of building components using full-scale testing apparatuses built at UF. The centerpieces of this research are a portable 2800 hp Hurricane Simulator, which can recreate Category 3 wind loads on residential construction, and several dynamic pressure loading actuation systems based on the Three Little Pigs project at the University of Western Ontario (UWO).

There are several industry-accepted test protocols to evaluate the wind uplift resistance of commercial roofing systems (ASTM E1592, UL1897, UL580, FM 4470 etc.). These tests apply pneumatic pressure to full-scale roof specimens installed on a pressure chamber, and increasing the pressure until failure. The wind uplift design pressure is then determined by reducing the peak pressure by an accepted factor of safety (e.g. 1.5 or 2.0). A critical question to be asked on the results is the meaning or validity of these static test results when hurricane winds produce dynamic roof pressures that are constantly fluctuating in time and space? The presenter reviews similarities and limitations of common wind uplift test methods for standing seam metal panels, and mechanically attached single ply roofing systems that have been the industry-standard for many years and reports on research results for these systems. Most of the test protocols provide comparative results, absent any verifiable relationship to roof performance in actual wind storms. Of particular interest now is the determination of the wind design pressure for light-framed wood roof systems, for which there exists no industry-accepted test protocol. The fastener schedules and minimum fasteners included in current ICC building code today appear to be based on research conducted immediately after Hurricane Andrew. Recent experimental studies at the University of Florida revisited those studies and developed a new dynamic test protocol for wind uplift testing of roof sheathing panels. The results have shown inconsistency in previous tests and that static pressure testing of wood roofs may over-estimate their failure capacity when compared with dynamic pressure test methods. The presentation concludes with a proposal for standardizing the wind uplift testing of wood roof systems based on dynamic pressure fluctuations. The conclusion has far-reaching implications as similar modifications may be required to calibrate current static pressure test methodologies for commercial roof systems so that they for hurricane-prone locations.

This paper discusses current structural engineering issues related to steel telecommunications monopole structures. Over the last decade there has been ever increasing use of cellular telephones, including new `smart' phones, for voice and data communication, and wireless internet access, which drives increased demand for wireless data transmission bandwidth. As a result, there has been a large increase in the number of monopoles installed around populated areas to support antennas. Monopoles have become an important part of our communications infrastructure. The design of new and the analysis of existing monopoles are affected by code and standard changes such as the TIA-222-G Standard. Other issues related to strengthening and reinforcing of existing monopole structures to carry the new required antennas are discussed. Also current methods used to strengthen pole base connections due to loading overstress and fatigue considerations are discussed; and opportunities for needed research in these areas are identified.

This paper presents methods to calculate the forces in the circular tank wall and base. The impacts of the changes in the ACI 350 and ACI 318 on circular tank design including load factors, allowable stresses and crack control are presented.

There are many parameters for the successful design of rectangular concrete tanks. The basic premises are sometimes buried under the details involved in the complexities of the overall design. Critical elements of the design criteria are reviewed and presented. The designer is presented with the concepts associated with concrete mix design including guidelines for admixtures. The concepts associated with concrete curing are reviewed. The critical elements of design for joint sizing, detailing and spacing are presented. Seismic impacts and references for design detailing are reviewed. Although there are many facets of rectangular concrete tank design, which are not addressed, the criteria reviewed provides the designer with critical design issues for consideration.

Anchorages of tanks, vessels and other significant structures in petrochemical facilities are subject to code requirements and must be engineered so that their design strength equals or exceeds the factored loads from load combinations that include earthquake (seismic) load effects. Depending on the Seismic Design Category, there are additional requirements in codes and standards that either require a ductile failure mode for the anchorage or require elastic behavior of the anchorage when it is subjected to the displacement demands of the design seismic event. There are additional seismic design considerations that are recommended for anchorages within petrochemical facilities in order to provide adequate performance when subjected to seismic loads, and are dependant upon the type of nonbuilding (petrochemical) structure under consideration. The state-of-the-practice report Design of Anchorages in Petrochemical Facilities soon to be issued by the ASCE Task Committee on Anchorage (Petrochemical Committee) provides guidelines that should help practicing engineers design anchorages in industrial facilities for earthquake loads. Topics related to petrochemical facility anchorage seismic design that are addressed in this guideline include references to and highlights from building codes and industry standards for determining seismic design loads; recommendations for implementing ductility requirements; and special detailing considerations for anchorage of typical nonbuilding structures within petrochemical facilities.

Vertical vessel anchorages present unique design considerations for engineers because of the nature of loading, the geometry of the anchorage, and the constraints of typical construction techniques. The nature of the loading is primarily tension due to transient lateral loads such as wind or earthquake. Vertical vessels that are set directly on a foundation are typically set on an octagon pedestal, which requires a different design procedure for calculating concrete breakout strength in tension for anchors than that of a square pedestal. The updated ASCE "Design of Anchorage in Petrochemical Facilities" includes recommendations for calculating concrete breakout strength in tension of anchors in an octagon pedestal. Methods for calculating concrete breakout strength in tension should be practical, quick to perform, and follow the methods of current codes and standards. Several methods for determining the breakout capacity in tension of anchors within an octagon pedestal are presented, compared, and example problems are provided.

Appendix D of ACI 318 Building Code Requirements for Structural Concrete [ACI (2008)] and Appendix B of ACI 349 Requirements for Nuclear Safety Related Concrete Structures [ACI (2006)] provides the practicing engineer guidance on the subject of anchorage to unreinforced concrete, however the subject of anchorage to reinforced concrete is left without guidance. In an effort to update the Design of Anchorage in Petrochemical Facilities [ASCE (2010, proposed)] for consistent application with the current design codes and state of practice, ASCE re-established the Task Committee on Anchorage. The Task Committee's primary objective is to establish and evaluate the impacts of published reference data, research development, and changes in material specifications and code provisions that have occurred since the original publication. With this in mind the committee has tried not to repeat information or provide interpretation on the subject matter covered within the afore mentioned design codes, but to expand the design concepts to and apply sound engineering principles to situations and geometries that are not covered by the design codes. The 2010 edition continues to provide guidance on the design of tensile reinforcement of anchors, but expands this discussion to include detailed methods and examples for determining the need and amount of reinforcement required to transfer shear on a pedestal, and reinforcement for side face blow-out of anchors near an edge. New to the ASCE document is an in depth coverage of post-installed anchors and headed studs. The addition of these anchorage methods have been included throughout the document to provide guidance on material properties, anchorage design, and installation and repair methodologies. The 2010 edition is intended to be a State-of-the-Practice for the design and evaluation of cast-in-place, weld stud, and post-installed anchorages and as with the development on any design guide a comprehensive review of current practices, internal company standards, and published documents was conducted, and a list of references is be provide for additional information and further individual research. As a result of this update the ASCE document may continue to serve as a source for uniformity in the design, fabrication and installation of anchorage for the petrochemical industry consistent with current design codes and industry practices.

One of the major additions incorporated in Appendix D of ACI 318-08 is the definition of anchor reinforcement in addition to the previously defined supplementary reinforcement. However, ACI 318-08 does not provide the specific guidelines for designing such reinforcement. This paper presents methods for designing a typical anchorage in reinforced concrete pedestals for both tension and shear forces. It addresses the failure modes to be checked (steel failure of the anchor in tension, and shear if applicable, concrete side-face blowout, concrete pull-out), and how to properly size and detail the pedestal reinforcement to transfer both the tensile and shear forces.

The paper and presentation will show a new innovative type of glass staircase, where transparent laminated safety glazing treads are bonded to local stainless steel fittings (Sentry-glass Plus autoclave lamination process) that are connected to thin stainless steel cables, pre- stressed in between the floor and ceiling of a specialty glazing shop fabrication facility in Long Island near New York City. The full flight is supported entirely bending- free (without any risers) and designed as a tensegrity structure, where tensioned cables transfer loading to treads in compression. The cables are placed in a poetic way with varying angles and integrated lighting next to each other that remind the user of musical harp strings, making the treads entirely 'flow within space'. Underneath the transparent treads is a single fish-bow truss that assures lateral stability and increases natural frequencies to an acceptable level, high enough to minimize staircase vibrations. From a structural engineering point of view, careful calculations were carried out, both for the glazed treads (assuming post- failure scenarios) as well as for the cable structure and required pre- stress levels (using special third-order form-finding software for cable structure analysis). From a precision manufacturing point of view, one single type of adjustable structural connection from cable to glass tread was invented to take all different cable angles in an economic and elegant way. The presentation will show the architectural intend, concept engineering design, all required calculations, fabrication and erection of this one-of-a-kind new transparent prototype staircase made in the US.

ETFE-foil cushions belong to the lightweight construction methods. These structures lead to ecological and economical advantages ostensibly because of its low weight. However, the transparent air inflated cushions are advantageous in more than this one and only discipline. ETFE-foil cushions also fulfill the second and the third criteria of lightweight constructions. They can be designed as intelligent systems fulfilling several functions additional to the load transfer and, a priori, they constitute very efficient structures which follow the best pathway of forces a load can take to the primary structure and, at last, to the ground. The thin tension elements of ETFE foils, placed at the boundary surface of the cushion, combined with the inner compression element of inflated air lead to a very effective way of building. Therefore ETFE-foil cushions tap the full potential of the three kinds of minimization concerning light constructions: building with light materials, building with light systems and building with light structures.

This paper describes how the application of special glass laminates enables new developments and concepts in the field of structural glass façades. The first part addresses the use of oversized glass laminates and the design principle for the glass laminates with shear stiff interlayers, such as SentryGlas from DuPont, which are usually selected for oversized glass laminates. Using an example, it will be shown that the use of a shear stiff interlayer in the laminated glass provides a huge load carrying capacity. It also will be shown that, beside the general design concept for glass laminates, it may become necessary to adopt additional considerations to ensure a safe design concept for the shear stiff glass laminates. The second part focuses on the idea of using a shear stiff SentryGlas interlayer system to generate laminated `cold'-bent glass. The specific structural and structural-physical advantages of the laminated `cold' bent glass will be explained. Apart from this a schematic overview about the very complex manufacturing process and the structural design requirements is given.

Adhesive bonds offer a high potential for glass connections in structural applications. The strength, rigidity, durability and other material parameters of selected adhesive systems and substrates need to be assessed by intensive testing to identify suitable adhesives. The test programs cover short, long-term and dynamic load scearios. Current research is also increasingly focused on hybrid products, where several tasks are combined in the same structural element. The combination of brittle glass and ductile materials expands the scope of potential applications beyond the initial limitations of glass. Glass-polycarbonate composite panels and glass-steel beams offer a distinctly improved post-breakage behaviour compared to standard products. Experimental research focuses mainly on the ageing behaviour, post-breakage performance and manufacturing technology. Further impulses arise from studies on specific applications of bonded glass, which are developed from a first idea to the final solution in close collaboration with industrial partners. To demonstrate this, the experimental analysis for bonded frames of an all glass cabinet is presented.

In recent years, three major ceiling grid manufacturers in the United States have conducted extensive earthquake simulator testing of suspended ceilings. The tests to date have followed the ICC-ES AC-156 protocol and have been performed on an elevated test frame of limited size. The test protocol was developed to be applicable for a wide array of nonstructural components and is referenced in the building codes as a standard when testing nonstructural components. The tests have provided researchers and engineers with invaluable data and have enabled manufacturers to assess the seismic performance of their components with a degree of reliability. However, the tests have also revealed shortcomings in the current experimental and evaluation procedures. It is proposed to develop a second-generation test protocol that takes into account the unique properties of suspended ceilings such as multiple attachment points and large floor plan, and to address evaluation questions including qualification levels and performance targets.

There are considerable changes in the sections on suspended ceilings between ASCE 7-05 and ASCE 7-10. These changes fall into two categories: changes in the requirements and changes in the cited references. Additionally, many requirements have been relocated from ASCE 7 to the cited reference, reducing conflicts between the two documents and greatly simplifying the understanding of the requirements. Since the commentary for these code sections is currently limited, this paper will also review the history and rationale behind the current requirements. This is to aid in applying the requirements to field conditions as well as designing custom applications to constructions not covered by ASCE 7.

Suspended ceilings have suffered major damage in past earthquakes. This damage has been non-proportional, has occurred in moderate events even for adequately designed buildings, and has led to the loss of building functionality. In recent earthquakes, damage to suspended ceilings has resulted in significant business interruptions and financial losses. Structural engineers strive to design buildings that perform well in earthquakes. However, without adequate design and installation of non-structural components and suspended ceilings, this effort might well be compromised. Survey of observed damage, the resulting business interruptions, and recommendations for sustainable design of suspended ceilings are presented in this paper.

An ongoing study within the framework of the project on seismic behavior of nonstructural components, sponsored by the research program of the National Science Foundation's Network for Earthquake Engineering Simulation (NEES), is developing a new testing facility for suspended ceilings and other systems, for use with either single or tandem shake tables. The experimental facility is necessary for the evaluation of full size suspended systems for which modeling is either too complex or cost inefficient. Moreover, in the frame of the aforementioned research, methods of analysis and design are being developed. The authors developed a large frame to test a continuous suspended ceiling of up to 20 x 50ft (1,000 ft.²). The frame has dynamic characteristics with variable frequencies characteristic to typical roofs (or floors) for the suspension of ceilings and flexible walls. However, the frame cannot deliver precisely the desired "floor" motion unless a special procedure is employed. Such procedure using interactive control principles was developed to provide a "command drive" signal to the shake table in order to obtain a "desired floor motion" at the roof level. The combined designs of the physical frame and of the shake table motion allow for testing a variety of suspended systems while eliminating side effects of high frequency ringing or wall distortions. The paper describes the design parameters and introduces the motion design procedure, which can be implemented in any experimental facilities as well.

NASA, Kennedy Space Center has designed a new, lightweight mobile launch structure (Mobile Launcher) for the Ares I launch vehicle. The challenge was to build the new Mobile Launcher (ML) at or below the weight of the Space Shuttle Mobile Launch Platform while adding a 120 m tall by 12 m square tower to support the Ares I. The weight of the Mobile Launcher is limited by the capacity of the existing Crawler Transporter, which is 5.7 x 10⁶ kg. Previous Mobile Launcher designs used primarily plate girders, rolled sections, and flat plate. The lightweight design combines a mixture of plate girders, HSS and rolled section trusses, and corrugated plates and sheets. The design team was challenged by specific requirements for stiffness and natural frequencies, reversing loads, multiple indeterminate restraint conditions, and the natural and induced (launch) environment.²

This paper deals with the statistical quantification of peak floor acceleration (PFA) demands and peak component acceleration (PCA) demands for acceleration-sensitive nonstructural components attached to or suspended from shear-wall structures with fundamental periods from 0.15 to 1.5s. Dynamic analyses are conducted with a set of 40 ground motions recorded in stiff-soil sites. Median PFA and PCA demands are compared to ASCE-7 estimates of component accelerations for rigid and flexible components, respectively. The results from this study indicate that the estimation of component acceleration demands should explicitly consider the dynamic properties of the supporting structure, the relationship between the period of the component and the modal periods of the structure, the ground motion intensity and the location of the component within the structure. In some cases, ASCE-7 estimates of component accelerations severely underestimate median PCA demands, especially for components located at the roof level of shear-wall structures with periods greater than 0.45 s when the component period lies in the vicinity of the higher modal periods of the supporting structure.

In order to better understand the seismic performance of nonstructural components, equipment and building contents, and to develop effective mitigation measures, the University at Buffalo has commissioned a dedicated Nonstructural Component Simulator (UB-NCS). The UB-NCS is a two-level modular testing frame capable of simultaneously subjecting displacement and/or acceleration sensitive nonstructural systems to realistic full-scale floor motions expected within multistory buildings. The UB-NCS can subject nonstructural systems up to 3g acceleration, 100 in/s (2.5 m/s) velocity and ±40 in (1 m) displacement amplitudes. An innovative dynamic testing protocol was developed for the seismic performance assessment of nonstructural systems, taking full advantage of the UB-NCS testing capabilities. The testing protocol consists of a pair of displacement histories for the testing platforms that simultaneously match a seismic hazard consistent ground or floor acceleration response spectrum and a target generalized interstory drift. The input parameters for the protocol are a local seismic hazard and the location above grade of the nonstructural system. The protocol motions were applied to assess the seismic performance of a full-scale hospital emergency room containing typical nonstructural components and life support medical equipment.

Partition wall and fire extinguishing sprinkler piping nonstructural subsystems constitute a significant portion of the total investment in building infrastructure. Past earthquakes and numerical simulations have demonstrated that damage to these nonstructural subsystems can cause substantial earthquake losses and degrade the overall functionality of buildings. Nevertheless, the data obtained from field observations, previous experimentations, and numerical simulations are insufficient to fully characterize their mechanical response under seismic actions and to develop effective solutions to improve their seismic performance. As part of the NEES Nonstructural Grand Challenge Project: Simulation of the Seismic Performance of Nonstructural Systems an experimental program is underway to evaluate the seismic performance of full-scale light gage steel studded gypsum partition walls and fire suppression piping subsystems. Fifty partition wall specimens, corresponding to 22 wall configurations, were constructed following standard construction techniques typically used in commercial and institutional facilities. Quasi-static and dynamic tests were carried out to assess the in-plane and out-of-plane seismic performance of the gypsum walls. Testing of piping systems is ongoing with two of the most common joint configurations, tees and elbows, being tested to determine the moment and rotation capacities at which leakage or fracture occur. Subsequently, a full scale two-story subsection of a typical commercial fire suppression system will be tested under dynamic loading. This paper reviews the failure mechanisms observed in the walls and in the piping systems and the application of the ATC-58 framework to develop a seismic fragility database for gypsum partition walls and fire sprinklers. Further, the experimental observations are used to propose a set of innovative construction details and configurations that minimize the seismic damage in these subsystems.

Arup provided structural engineering for a structural glass pavilion designed by Desai/Chia Architecture for a private residence in New York. The glass pavilion is a 25ft wide by 60ft long by 15ft tall cube. The pavilion's exterior will be clad entirely in glass with the exemption of a small area of solid roof above the core. The glass pavilion includes a glass panel roof supported by a combination of structural steel frames and glass beams. The mullion free perimeter glass wall supports the exterior edge of the glass roof panels. The main lateral force resisting system consists of structural steel frames at the core and perimeter glass walls acting as shear walls. This paper covers the basic design approach and structural system for the glass pavilion including the importance of redundancy and some of the analysis techniques used in the design the glass structure.

This paper discusses unique design and construction issues of a glass stair, which comprises of a custom made stainless steel elliptical shaped stringer, glass treads and glass balustrade. State-of the-art finite element analyses were performed to ensure that the stresses at the interface of the glass-stainless steel pieces were within allowable limits. Furthermore, dynamic footfall analyses were performed to ensure that vibration due to walking activity was within an acceptable limit of human comfort. Finally, manufacturing and erection of the glass stair had unique features due to the brittle nature of glass.

The expansion at Dulles International Airport in Washington, D.C. features an Automated People Mover system with interior glazed enclosures along the length of the station platforms. These structural glass enclosures were designed to undergo extreme in-service loadings, be structurally redundant in the event of breakage and remain intact for a short period of time in the event of a train fire within the enclosure. The design process addressed issues concerning glass technology, processing and procurement, material selection for compatibility and rationalization of detailing. Full scale testing was conducted to demonstrate the behavior of the structural glass enclosure under the design fire conditions as well as verifying the structural redundancy of the enclosure when key glass elements were broken. The design process was influenced by client demands, material properties and the ability of the industry to deliver reliable façade products in a cost effective way. The selection and detailing of laminated glass, as well as safety, procurement and fabrication are examined.

Wind farm towers are the steel fabricated-tube towers, typically 80 m (262 ft.) in height, serving as the support structures for large, utility-scale power-generating wind turbines. The modern multi-megawatt wind turbine machine is a complex piece of high-tech equipment costing 2 to 3 million dollars each. The turbine's design applies state-of-the-art aerospace and mechanical engineering. In contrast, the structural design of its 20-story tall steel support tower structure is an orphan of structural engineering, for no dedicated US design standard exists for wind farm towers. In US practice, in the absence of specific design guidelines, demonstrating basic building code (i.e., "Code") compliance can be a challenge. It is a struggle that has been faced for many years by structural engineers in the fledgling domestic wind industry. Code compliance is determined using a variety of standards--from AISC, ASME, Eurocode, and miscellaneous textbooks--cobbled together using engineering judgment. Further, wind turbine and tower commercial certification by European agencies requires compliance with various European standards and agency-specific guidelines. For this reason, the application of any US standards must then be rationally reconciled with the European standards serving as the basis of the commercial certification. Further complications are unusual design issues that are seldom encountered in routine building design for which the Code is targeted. Modern utility-scale wind farm towers are thin-shell tubular structures sensitive to local buckling. Subject to turbine operational loads, towers undergo very high-cycle fatigue and must meet frequency separation criteria to avoid resonance. Sensitivity to vortex shedding must be considered. Towers are subject to European certification loads that may in some instances exceed typical Code lateral forces. This paper presents an overview of Code compliance issues and describes some practical approaches and solutions developed over the last decade of wind farm tower structural design.

This paper presents an alternative technique to the modal analysis of machine foundations. The frequency dependent soil impedance (stiffness & damping), soil-foundation-machine system modeling techniques and the system natural frequencies and mode shapes are addressed in the paper. Through comparative study of the methodologies for identifying the foundation rigid body motion modes and local member motion modes, this study proposes the use of the Dynamic Magnification Factors (DMF) to determine the acceptability of natural frequencies and mode shapes. This paper introduces an alternative technique for analyzing the excitation potential of the natural modes of vibration and presents a practical methodology by using a Dynamic Magnification Factor (DMF) curve to analyze the dynamic behavior of the foundation members within the full range of machine operating speeds. All analysis studies, techniques, criteria and methodologies presented and described in the paper are using an actual engineering project as an example.

Earthquakes pose a significant threat to seaports in the United States and around the World. Container cranes, used to load and unload goods, represent one of the most vulnerable components of ports. Cranes are critical to the economy and post disaster response of a region. In order to better understand how cranes behave under earthquake loading, shake table experiments are conducted on a 1:10 scale model of a typical container crane found on the west coast of the USA. During previous earthquakes, three failure modes have been observed: derailment, local buckling of the legs and collapse. To investigate the various failure modes, a 1:10 scale model is constructed and tested on the six-degree-of-freedom shake table at the University at Buffalo. For ease of testing, the model is simplified by modifying the boom structure, while still preserving the most influential vibration modes. This paper presents important results from the study.

Very large heavy centrifugal compressors are required in the design process for petrochemical, liquefied natural gas (LNG) plants, and power plant facilities. In a LNG plant, it requires multiple compressor units that contain methane, ethylene and propane compressors for converting natural gas to LNG by cooling the liquid temperature to –270°F. The heavy compressor vibrating machines are supported on concrete table top pedestal that consists of concrete slabs, beams, columns and mat foundation. For plant site located in a high seismic area, the dynamic analysis using the response spectrum method is applied to calculate the seismic force for design of the machine anchorage and the tabletop pedestal/ foundation. Also, the steady-state vibration analyses of the table top pedestal are performed to ensure that during the normal operating condition, the resultant maximum dynamic displacement (or velocity) amplitudes are within the limiting amplitudes set by machine manufactures and industrial standards. Both concrete cracked and un-cracked properties are considered in the analysis. Concrete members and connections are designed to comply with the seismic provisions in Chapter 21 of ACI 318-08 to ensure that the concrete pedestal will behave in a ductile manner during severe seismic events. This paper presents the design of a typical concrete table top structure supporting two compressor units. The plant is located in high seismic area. The presentation includes foundation sizing criteria and design loads, finite element modeling of the concrete table top structure, dynamic steady state vibration analysis due to machine imbalances, vibration response limit criteria, seismic response spectra analysis, and evaluating seismic design forces based on the static and dynamic analysis results. Due to heavy weight machines and deck, the P- Δ effect is considered in the static design. The reinforced concrete structural structural members are designed in accordance with ACI 318-08 seismic provisions.

This paper describes the verification of the structural integrity for the gates of the flood spillway of the hydroelectric dam Malpaso (Chiapas, Mexico), which height was increased about 1 m because they had to operate close to the extraordinary maximum water level. The increment on the water level of the reservoir was originated because of the weather conditions that had recently caused the sliding of a mass that had obstructed the river, downstream of the dam. Works had to be done on the obstruction zone, and the Malpaso dam had to stop its energy production. The gates were instrumented with strain gage rosettes, an analysis of the theoretical model subjected to those conditions was generated, and their performance was evaluated. The analyses showed that the performance of the gates do not represent a risk for the service of the structures.

The main objective of this paper is to identify the dynamic characteristics of a realistic model of a commercial transformer (230 kV) and identify the critical components that influence the dynamic response of three high voltage porcelain bushings installed on its flexible roof. For this purpose, a finite element model of the transformer is appropriately modified and enhanced. The improved model is subjected to a wide band random motion excitation and the responses at various locations are processed in the frequency domain. The dynamic response of the high voltage porcelain bushings (196/230kV) and the amplification that occurs between the base and the top of the transformer's oil tank, is assessed through detailed sensitivity analysis for a variety of potential structural modifications of the model. Each structurally modified model is investigated using a random ground motion, compatible to IEEE-693 spectrum. The accelerations are monitored at the bushings, at the corners of the cover plate and at the top of the turrets for each model and comparisons are made for the effect of each modification to be assessed. The ground motion amplifications at the cover are obtained from the spectra at the corners of the cover and at the top of the turrets. The sensitivity shows that the cover plate has the predominant influence on the response of the bushings.

Electric power substation systems are critical facilities as lifeline systems for sustaining society from earthquake events. The composite hollow core electrical post insulators are important parts of the electrical substations equipment and their failure may have consequences to the local network and to the entire grid. In this study, a macroscopic analytical model is developed, which consists of gravity mass, two linear springs, viscous damping, and friction characteristics. The macroscopic model is formulated with high order differential equations derived with a state-space form solved by using Runge-Kutta method. Several prototype insulators have been tested at the University at Buffalo and the developed models are verified through comparing with the test results. The comparisons of acceleration and displacement responses are conducted and show good agreements.

This paper is aimed to show that concrete members designed to have the same initial performance may exhibit different reliabilities over time depending on the shape of the cross-section. The lifetime structural performance of three cross-sections, designed to have the same initial bending strength with the same amount of reinforcement, material properties and concrete cover, is investigated both in deterministic and probabilistic terms. The results show that the equal performance of the cross-sections in the undamaged state is lost in time due to damage, and that the shape of the cross-section significantly affects their reliabilities over time.

This paper presents the current status of bridge management and life cycle performance in Japan. The outline of bridge management system is illustrated and problems to be overcome are clarified. In Japan there are 150,000 bridges with spans of more than 15 meters are in use so that it requires an enormous budget to maintain them in satisfactory conditions. Furthermore, sufficient data, experienced maintenance engineers, special technologies, and good ordering system are needed. In order to develop a bridge management system, the concept of Life-Cycle Cost (LCC) has been paid attention as a promising tool for the achievement of rational maintenance programs. Several suggestions are provided to realize the rational and economic maintenance program and to develop a practical bridge management system.

Structural assessment is a key part of the structural integrity management (SIM) process for ensuring the fitness-for-purpose of offshore fixed platforms. This paper presents a comprehensive life cycle structural performance assessment approach for the offshore fixed platforms. Non-linear pushover analysis is used to perform the structural assessment, in which the platform capacity is characterized in terms of the platform's reserve strength ratio (RSR). Comparison of the platform RSR and the target RSR specified in the acceptance criteria determine the fitness-for-purpose of the platform. A structural reliability methodology is proposed for the development of the regionally specific acceptance criteria. The annual probability of platform failure is calculated using the first order reliability method (FORM). The assessment results are used to develop a long term risk-based underwater inspection strategy. A case study for the platforms located offshore Eastern Caribbean is used to illustrate the application of the developed structural assessment approach.

The current AASHTO LRFD highway bridge design specifications have been calibrated with the stated goal of achieving uniform reliability levels for all bridge configurations, components, and material types for a 75-year design life. Although this goal has been met for checking the strength and fatigue limit states of main bridge members under the effect of live loads, several criteria for other limit states and hazards were simply adopted from previous generations of design codes while other extreme event limit states were developed using different probabilistic bases than those used for the live load effects. This paper presents an overview of current code-specified criteria for evaluating the performance of bridge systems under various types of hazards, summarizes ongoing studies to extend the reliability-based calibration to new types of members and components and outlines remaining issues that should be addressed in order to develop criteria that will achieve consistent levels of bridge system safety and reliability.

In the current AASHTO LRFD Bridge Design Specifications [AASHTO, 2007], a fracture critical member is defined as a "component in tension whose failure is expected to result in the collapse of the bridge or the inability of the bridge to perform its function." All bridges designed with fracture critical members or components are designated as fracture critical bridges. The bridge design process is affected by many factors including economics, aesthetics, and function, and many popular bridge structural systems are classified as fracture critical. In fact, approximately 11% of all steel bridges in the United States have this designation [Connor, et al., 2005]. As long as the risk of a brittle fracture of an integral component of a bridge's main load path is minimized, a fracture critical bridge is not inherently unsafe. For this reason, the design of fracture critical bridges is permitted, but a major requirement in the fracture critical member provisions is that a full inspection of all fracture critical bridges be performed every two years. Fracture critical bridge inspections are labor intensive—and therefore costly—requiring the examination of every weld throughout a structure. The fracture critical provisions in the AASHTO Bridge Design Specifications [AASHTO, 2007] assume that, when a fracture critical member fails, the remaining bridge structure lacks a redundant load path to support its loads. A number of incidents involving the full-depth fracture of in-service two-girder bridges (all designated as fracture critical) provide evidence that, in certain cases, a redundant load path does exist in these structures even though they have not been given credit for such. The Texas Department of Transportation (TxDOT) owns and operates a vast inventory of more than 50,000 bridges throughout the state. Many of these bridges are two-girder bridges and are classified as fracture critical by the AASHTO guidelines [AASHTO, 2007], contributing to large annual inspection costs. In search of guidance in reevaluating the inspection schedule for fracture critical bridges, TxDOT and the Federal Highway Administration (FHWA) cosponsored a large-scale research program at the Ferguson Structural Engineering Laboratory (FSEL) at The University of Texas at Austin. The overall goal of the project was to provide transportation engineers with methods for evaluating the redundancy of fracture critical steel bridges. The research focused specifically on investigating the redundant capacity of fracture critical twin steel box-girder bridges, which are common throughout the state of Texas (Figure 1). Using tools to estimate the load carrying capacities of their structures in the event of a failure of a fracture critical member or component, bridge owners would be able to appropriately tailor their maintenance schedules to their bridge inventory. Supported by significant experimental, computational, and financial resources, the comprehensive research program at FSEL continued for four years and comprised a set of interrelated experimental initiatives. The techniques used to work toward the ultimate goals of the research included simplified structural analyses performed by hand or through the use of spreadsheets, analyses performed through detailed finite element simulations, the testing of laboratory specimens to quantify experimentally the capacity of specific bridge elements, and the full-scale testing of a twin steel box-girder bridge (i.e., a fracture critical bridge) reconstructed at FSEL for use in this project. Detailed information on the testing program can be found in Neuman [Neuman, 2009] and Mouras [Mouras, 2008], and a description of the simplified procedure to predict the capacity of twin steel box-girder bridges can be found in Samaras [Samaras, 2009]. The current paper provides an overview of the detailed finite element simulations performed as part of this project. The simulation models include inelastic material behavior and nonlinear geometry, and they also account for the complex interaction of the shear studs with the concrete deck under progressing levels of damage. In addition, the contribution of the bridge rail, including the presence of expansion joints, has been successfully modeled in the finite element analyses carried out for this study. These simulation models have been validated using small-scale laboratory tests and results obtained from full-scale tests on a twin steel box-girder bridge. A brief description of the test program and the finite element models developed for this research are provided below.

The Nation's infrastructure is at risk from aging, increasing the potential for deterioration in safety and functionality of buildings, bridges and other civil infrastructure facilities. Quantitative time-dependent reliability assessment tools have matured in recent years to the point where they can assist in establishing priorities and strategies for managing risk of aging infrastructure through an extended service life. A life-cycle reliability assessment can determine whether the deterioration is significant from a safety (or serviceability) point of view, whether acceptable performance can be expected during a projected service life, and what additional requirements, if any, should be imposed as conditions for continued service. This presentation will explore a number of practical issues that arise in answering these key questions in general terms, touching upon common degradation mechanisms, practical time-dependent reliability analysis tools, and perspectives on risk that are germane to civil infrastructure decision-making.

The continued growth of Building Information Modeling (BIM) has prompted new contractual arrangements, of which the best known is Integrated Project Delivery (IPD). In IPD, early contributions of downstream partners provide crucial credibility of design information, and require that fabrication knowledge be engaged much earlier in the process. What does this mean for structural engineers and fabricators? Also, what is the current state of BIM? In this session, the presenters—an engineer and an architect—will outline their firm's extensive experience with BIM in all design disciplines, as well as their ongoing efforts in working with contractors on BIM models. They will also outline the many "levels" of BIM—including space management and direct fabrication—and how the next steps in BIM maturation will involve going straight to the source, allowing engineering fabrication models to become part of the design Contract Documents. Attendees will leave the session with a new understanding of BIM, along with strategies to apply to their own projects.

Since the 1960s, post-tensioned concrete construction has grown and is now one of the most common and economical systems used for multi-story buildings and parking structures. Over the years, post-tensioning (PT) systems have evolved and the industry has learned about various serviceability issues that are magnified in coastal and other aggressive environments. The evolution of the PT systems and potential differences in the long-term performance of each system will be reviewed. In addition, various techniques used to evaluate deteriorated PT and possible repair and monitoring methods used to address deteriorated single-strand systems will be discussed. Several case studies of system and installation specific concerns that can contribute to premature deterioration of PT single-strand systems will be reviewed.

Corrosion of metallic embedments in concrete and masonry structures is recognized as one of the main causes for damage to the surrounding material ultimately resulting in aesthetic damage, structural failures, safety hazards and significant costs. In addition, the historic and aesthetic value of some of the affected structures can be significant and sometimes it is irreplaceable. More than 20 billion dollars per year are spent in the US alone repairing damaged concrete structures. Most of this is the result of steel reinforcement corrosion. This paper will address the agents, mechanisms and process of corrosion of metallic components in concrete and masonry structures in a variety of environments. In addition the corrosion process will be analyzed from a lifecycle perspective: initiation, propagation and ultimate impact on the overall structure. Mitigation technologies will be described and case histories will be presented along with costs associated with mitigation of this problem at each stage of the corrosion lifecycle.

Safe, efficient structural forms are abundant in nature. The challenge, however, is to quantify these forms and to derive behavior that is adaptable, constructible and cost effective. Adaptations and mathematical derivations that use nature's mechanics in structural design have led to innovations in structural systems. These organically-inspired structural systems typically exhibit interesting aesthetic qualities which are not necessarily intuitive. Natural structural systems may also incorporate devices that understand and respond to demand, alter behavior, and ensure optimal performance. Three conceptual structural systems are considered which example the use of organic and natural forms in building design. First, bamboo geometric properties as they relate to structural efficiency are examined and applied to the China World Trade Center Tower Competition. Second, organic growth patterns form the perimeter structural framework of the Transbay Transit Tower Competition. Third, nature-inspired genetic algorithms are used to optimize the perimeter cable filigree of the Al Sharq Tower.

In the search for ever more efficient structural forms, the emerging field of biomimicry offers a near limitless source of inspiration. The natural world surrounding us is filled with organisms that have adapted over tens of thousands of years to be highly suited to their environment. As builders strive to realize more sophisticated manmade structures that incorporate lessons from highly evolved natural forms in similar environments, engineers are faced with realizing these structures through construction methods that have evolved only over the last few centuries. Some initial rudimentary efforts are now being made by engineers to emulate sophisticated natural forms. Often these efforts can only borrow one or two simplistic guiding principles from far more complex organisms due to the limitations of readily available construction techniques. Beginning steps to connect biological concepts to structural design methodology are best focused on connecting more advanced structural forms with rather simplistic biological constructs. To this end, this paper presents an example of a new method for form-finding of tensile structures informed by the growth principles that govern basic cell geometry. The patterns of cell growth and cell wall spatial arrangement are mechanisms driven by surface tension in the growth medium. Such mechanisms have been well understood by biologists for nearly a century, and a close examination of the cell growth literature exhibits a striking analogy to the mathematical form-finding methods that have been developed since the 1970's for tensile structures. By combining the principles of the force-density form finding method with a series of rules derived from cell growth theory, a robust new form finding method is possible. This method allows the specific tensile form to "grow" according to a series of rules, rather than be a result of arbitrary boundary conditions imposed by the designer. A series of examples are presented to demonstrate the implementation of the biomimicral form finding method. These cases illustrate in simple ways similarities to mechanisms found in natural forms. For example, insect wings often demonstrate a network of stronger veins that serve to compartmentalize weaker infill cell material. Similarly, in a tensile form isolated cables can be "grown" where needed to suit the particular abilities of the infill membrane material used. Such biologically inspired form finding processes offer exciting possibilities for future development of truly organic structural systems.

Nature shades the forest floor from the hot summer sun by the intricacies of the tree canopies made from the patterns of leaves. As summer turns to winter the dense patterns open as trees drop their leaves, allowing light to penetrate deep into the forest, and the solar transmittance of the forest changes as a whole. Just as these individual elements within nature work together to change the performance characteristics of larger systems, ETFE foil systems can alter its components configuration to adapt to environmental conditions. ETFE (ethylene tetrafluoroethylene) has been used over the past 25 years for transparent roof and wall systems around the world but the material and technology only made it onto the world stage with the debut of the Allianz Arena for the 2006 World Cup in Germany and with the light filled entrance of the "Water Cube" as the National Swimming Center at the 2008 Beijing Olympics. Now the material with its diverse aesthetic and performance capabilities is being considered the material of choice for traditional skylights, long span structures, and building facades. This paper will explore how this system takes its cue from nature and actively adapts to environmental conditions, producing enlivened and energy efficient building skins.

The Jinta Tower is a 75-story building located in Tianjin, China, with slender steel plate shear walls (SPSW) used as the primary lateral load resisting system. Construction detail, method and schedule constraints result in the steel plates being subject to gravity loads. Chinese codes require that steel plates not buckle in frequent (50 year) seismic events in addition to the typical performance requirements in the moderate (475 year) and rare (2000 year) seismic events. To address these constraints, a buckling restrained slender steel plate shear wall system - SPSWs with vertical stiffeners to enhance gravity load carrying capacity of the plates and delay buckling is developed. The approach for stiffener design included use of buckling and interaction formulae as well as pushover, parametric and sensitivity studies. The rare earthquake performance was studied and prescribed performances were verified by nonlinear dynamic analyses. The SPSWs were finely meshed to a 0.1m x 0.1m grid incorporating geometric and material nonlinearities. Geometric imperfections were also taken into account. Other structural members such as concrete filled tube columns, floor slabs, steel beams/braces and stiffeners were also meshed to a similar size to accurately model their nonlinearities. A ten million degree of freedom nonlinear model of the structure was created for three 40s earthquake time history analyses on the ABAQUS parallel platform. Despite the high initial gravity stresses, the stiffeners were demonstrated to push the inception of plate buckling out beyond the frequent events and provide great ductility and ability to absorb the earthquake input energy through significant tension field action in the larger events.

In order to obtain seismic review approval for the Nanjing State-Owned Assets & Greenland Financial Center's Main Tower, one of tallest structures in the world to date, enhanced design measures and performance-based evaluations were utilized. The critical parts of the lateral system were designed for earthquake forces between two and six times that typically required by Chinese code. In addition a full 3-Dimensional Non-Linear Elasto-Plastic analysis for a 2500-year earthquake was completed to determine the structures response and serviceability. A multistage axial shortening, creep and shrinkage analysis was also performed to evaluate the long-term load sharing between the central core and the perimeter of the Tower via the outrigger truss system.