Structures Congress 2011

Post-earthquake repair costs and repair times are important for evaluating the performance of bridges in a fundamentally different way than the traditional component-level metrics such as bearing displacements and column ductility demands. Repair costs and times are metrics that address the system-level response of bridges to a suite of seismic events, especially when cast probabilistically in the form of fragility curves. Traditionally, bridges are assessed and fragilities are generated according to enumerated component damage states (e.g., DS1 is minor damage). However, the level of system functionality that corresponds to each component damage state and whether individual components have risk or performance consistent with the system are of considerable interest in seismic assessment. In this paper, repair costs and times are calculated for a typical multi-span reinforced concrete highway overpass bridge in California. This system-level information is then used to back calculate consistent component damage states. The initial damage states are compared to the back-calculated states for forward prediction on different bridge configurations, and it is shown that it is difficult to achieve consistent performance using constant component damage states.

Seismic fragility estimates are computed for the Fabela Bridge, a five-span single-column bent reinforced concrete bridge, located in Toluca, Mexico based on previously developed probabilistic models for the capacity and demand of typical reinforced concrete bridges. The seismic fragility estimates are computed considering deformation failures in the columns. The approach used in this study properly accounts for epistemic and aleatory uncertainties of the problem. The properties of the bridge used to develop the fragility curves are estimated by matching the frequencies of a 3D finite element model to field data. For this purpose, a 3D finite element model of the studied bridge is created based on the available information of the bridge including drawings and field observations. Then the model is updated based on the modal frequencies obtained from measured accelerations in a series of forced vibration tests on the bridge. Fragility curves are generated to assess the seismic vulnerabilities of the current bridge. Different retrofit strategies are also applied to the bridge model to generate new fragility curves for a retrofitted bridge. The optimal retrofit strategies are determined based on the developed fragilities.

Seismic fragility modeling of highway bridges is becoming a well developed and accepted field among engineers. Within any fragility estimate exists many sources of uncertainty. One source of uncertainty which is key to robust fragility modeling is the aleatory uncertainty which exists within the ground motion suite itself. One obvious question an analyst must ask pertains to the appropriate number of ground motions which must be used to appropriately capture this aleatory uncertainty. This study looks to add to the existing knowledge base, established by previous research, by explicitly looking at the resulting uncertainty estimates as the size and make-up of the ground motion suite is altered. To explore this issue of ground motion suite size four bridge models which are representative of bridges in the Central and Southeastern United States (CSUS) are developed. Median value estimates for all bridge modeling parameters are utilized and held constant and no uncertainty in component capacities is used in an effort to decouple the aleatory uncertainty in the ground motions from the epistemic uncertainty present in typical modeling parameters. Utilizing a suite of 160 recorded ground motions as a pool, numerous subsets of this suite are created and used to generate fragility curves. To keep variation in median and dispersion estimates reasonable this preliminary study recommends that a suite of 80 or more ground motions be used. Such information is essential as fragility modeling gets closer to being an everyday reality for the practicing engineer.

A methodology is proposed to analyze the structural redundancy of bridge systems under lateral loads. The paper compares the results obtained from a probabilistic approach to those of a simplified deterministic analysis. A non-linear finite element analysis based on a 3-D frame model is performed for an example bridge considered to be representative of the behavior of structures with integral column-superstructure connections. The analysis accounts for material non-linearity using realistic models for the stress-strain relationships of the different constituents. The quantification of the available redundancy levels is evaluated using reliability as well as deterministic criteria previously proposed in NCHRP 458.

Measurement-data interpretation is especially costly when structural modeling is required. This paper summarizes results of three studies of anomaly detection without structural behavior models. In the first study, five signal-analysis methods were compared using an eight-year temperature/traffic loading vs. time history on a simulation of a two-span beam with four cases of damage scenarios occurring after four years and nine months. Moving principal-component analysis was identified to be able to detect damage most reliably. In the second study, ten signal analysis methods were compared using the same loading vs. time history as the first study. Fifteen cases of variations in daily temperature, traffic loading and sensor noise were used in this comparison. Results showed that moving principal-component analysis and robust regression detect damage more effectively than the other methods, especially in the presence of outliers and missing data. The third study involved the application of temperature cleansing methods to increase damage detectability and decrease detection time when using moving principal components analysis. The advantages of this method were compared with those of the robust regression method. Both methods are complementary. Complex relationships between frequency filtering, sensor/damage locations, traffic loading and noise were found to determine detectability and detection time. This has lead to several avenues for further study.

Damage prognosis for structural health monitoring is a challenging and complex research topic in civil engineering. Early and accurate damage detection is essential to maximizing the useful life of structures. The use of densely clustered sensor networks provides promising applications in the analysis of structural components and identification of local damage. The proposed localized damage detection method utilizes a linear regression analysis to monitor changes in the linear behavior of a structure with the onset of damage. The structural responses at various sensor locations along a structure are compared to those of other locations and pair-wise influence coefficients are estimated. These coefficients serve as damage indicators when damaged values are compared to healthy-state values. By statistically comparing the change in influence coefficients, structural damage can be accurately and effectively identified. The method is verified using simulations and an experimental prototype of a local beam-column connection, as well as a simulated model of a two-span bridge girder.

The Long Term Bridge Performance (LTBP) Program, sponsored by the Federal Highway Administration, is currently in the pilot phase. During this phase, seven bridges distributed throughout the United States have been subjected to an initial round of of bridge performance testing. This preliminary testing was conducted to establish a baseline for comparison with future bridge testing, monitoring, and evaluation. Long term instrumentation systems have been designed and installed at these sites. This paper will focus on three of the pilot bridges. For each bridge, the preliminary testing conducted and long-term instrumentation layout will be provided.

Structural vibration monitoring has received a lot of attention from the research community in the past few years. The objective is to create automatic structural assessment techniques that can be realized through programmed vibration analysis. Till now many vibration-based damage features have been proposed, yet to truly automate the damage identification process, reliable damage threshold construction techniques are also need. In this paper, two data-driven methods based on resampling and nearest neighbor rule are applied for threshold construction for damage features from autoregression (AR) analysis of vibration signals. Both threshold calculation techniques are rooted in empirical feature probability estimation. The proposed thresholds are then tested on features extracted acceleration measurements collected from a 5 DOF test specimen. The resampling method is applied to Mahalanobis distance of AR model coefficients, while the nearest neighbor rule is used on a combination of coefficient distance feature and the residual autocorrelation feature. Both methods perform well in this case study.

This study reviews different data analysis approaches to demonstrate possible means for getting information at different levels from the most commonly used strain sensors in an SHM system for short term and long term applications. The different methods are discussed from a real life monitoring study. First, the test bridge is presented with a brief introduction of the monitoring system and the sensor locations. Then, pre-processing and evaluation of raw strain data is discussed to identify the functionality of the installed sensors. Afterwards, strain data characterization by means of traffic and temperature induced strains is shown for more in-depth data analysis techniques. Finally, a new damage identification methodology based on strain correlation is discussed briefly. It is shown that there should be a suite of techniques and features to be available for implementation in SHM systems since one particular technique/feature may not be very reliable or sufficient for a particular case and/or structure.

Bridge structural health monitoring involves the collection and analysis of systematic measurements obtained from installed sensors on the bridge. While there are many quality certification systems available for civil engineering systems, e.g. American Society for Testing and Materials (ASTM), typical bridge monitoring specifications do not explicitly address performance requirements. As the applications of bridge structural health monitoring becomes more varied and advanced it will become necessary to ascertain the quality of measured data in order to check its suitability for new and varied applications. The quality of measured data has a direct impact on the results obtained from data analysis in structural health monitoring. The quality of measured data for a bridge monitoring system should meet three basic criteria: First, measured data should be devoid of anomalies such as signal clipping, intermittent noise spikes, temporary signal dropouts, and spurious trends. Second, the errors, including aliasing and quantization, and system noise should be within an acceptable range. Lastly, the measured data should satisfy required assumptions, such as stationarity and normality. Data qualification is defined as validating the quality of measured data and quantifying errors and noise to ensure the measured data sufficiently satisfies the above mentioned criteria. Despite the tremendous impact the quality of measured data has on bridge structural health monitoring, data qualification has not been formalized for bridge monitoring to provide a basis for bridge monitoring data specifications. This paper proposes measures of data qualification that can be used as a foundation for data specifications in bridge structural health monitoring. This paper will use data collected from monitored bridges in the Connecticut Long Term Bridge Monitoring program as examples of issues faced when using long term bridge monitoring data acquisition systems.

The recently designed highway for by-passing the city of Talavera de la Reina in Spain is currently under construction. The main structural element in the project is a cable-stayed bridge which for sure will become a landmark in the region. The bridge has a main span of 318 m, comprising a concrete box deck 36 m width and a single inclined pylon 164 m high. The singularity of the bridge has recommended a comprehensive analysis regarding wind effects on the structure. The aerodynamic coefficients of the deck have been obtained from wind tunnel tests and they have also been computed using CFD software considering two different turbulence models. Also the flutter functions have been evaluated by means of sectional model tests and the flutter velocity has been obtained. It has been found that the bridge enjoys a safe design for wind actions.

Catastrophic failure of steel bridge components can occur if the fatigue cracks reach critical levels. The purpose of the study described is to characterize the acoustic emission (AE) corresponding to crack extension from the stable to the unstable stage in steel bridge material. AE monitored fatigue tests were conducted using specialized compact tension (CT) specimens made of ASTM A572G50. A combined approach involving Swansong II filters and investigation of waveforms is employed in the discrimination of AE signals caused by cracks or noise. This approach is appropriate for data filtering and interpretation of sparse data as may be expected from field tests where wireless monitoring is essential. The results indicate that AE parameters from reduced datasets can provide warning for critical fatigue cracks under different test conditions. The transition of fracture mechanisms is reflected in the reduced AE dataset.

Experiments and computer simulations were carried out at the University of Kansas to investigate the use of composite materials for strengthening and repair of fatigue-vulnerable steel bridges. Prefabricated CFRP overlays were attached to welded coverplate specimens using a layer of epoxy resin. The specimens were then subjected to three-point bending under cyclic loading at a constant stress range. Early tests showed that bonding CFRP overlays to steel was an effective method to reduce the stress demand in areas susceptible to fatigue damage, and that this strengthening method could lead to substantial increases in crack initiation life. Fatigue tests also showed that maintaining the bond between the CFRP overlays and the steel was the most critical factor in the effectiveness of this strengthening technique. It was observed that the presence of a layer of breather fabric embedded within the layer of epoxy resin was the most important parameter affecting bond behavior under fatigue loading. This paper describes monotonic and fatigue tests carried out to evaluate the effect of the presence of breather fabric and thickness of the resin layer on bond strength and on the performance of the resin layer under fatigue loading. It was found that the mode of failure of the resin under monotonic and fatigue loading changed significantly due to the presence of the breather cloth. Although the presence of breather cloth had a negligible effect on the bond strength of thin resin layers, its effect on strength increased with the thickness of the resin layer. It was also found that the presence of the breather fabric had a very significant effect on the post-peak behavior of monotonic tests, which partially explains its beneficial effect on behavior under fatigue loading.

Since the Kansas Department of Transportation (KDOT) started its fracture critical bridge inspection program around the mid-1980s, many welded steel bridge details at the diaphragm (or floorbeam) to girder connections were found to have developed fatigue cracks, often due to the cause of out-of-plane distortion. While proper fatigue design philosophy has been developed and incorporated into the current AASHTO bridge design specifications, repair of existing bridges with fatigue cracking remains a challenge to the bridge engineering community, especially when the repair details happen to reside in locations with geometrical complexity, or when cracking is compounded by corrosion or impact damage. Beginning 1996, a series of research studies were performed through the collaborative effort between the KDOT State Bridge Office and the University of Kansas (KU). Five candidate structures were selected to examine the overall fatigue problem experienced by the KDOT steel bridges, using state-of-art finite element (FE) modeling technique. Two of these five bridges were then strain gauged, both before and after the repair, to ensure that the fatigue details were eliminated and the chosen repair method was effective. This paper discusses the research and repair findings of the first case study sponsored by KDOT, the Arkansas River Bridge.

When assessing the capacity of existing reinforced concrete slab bridges under the increased traffic loads prescribed in the current codes, shear may become the critical failure mode. To better evaluate the shear capacity of reinforced concrete slab bridges, a series of experiments is carried out on continuous one-way slabs loaded close to the support. Eight continuous slabs of 5m x 2,5m x 0,3m are tested. The loading position is taken at different a/d ratios. Six slabs with a standard concrete mixture and two slabs with a higher strength concrete are tested. The influence of the loading history, the shear span to depth ratio and the concrete compressive strength is discussed. Conclusions on the influence of these parameters on the one-way shear capacity of reinforced concrete slabs are drawn.

In areas of moderate seismicity, such as Mid-America, there is interest in developing alternate bridge design and construction methodologies to the typical approaches that are employed in high-seismic regions. One such method is to design so that various bearing components will exceed their ultimate capacities during a major seismic event in a specific sequence, leading to a global bridge structure response similar to a seismically-isolated system. Because the bridge would typically exhibit a stiff response, only developing an isolated response during major earthquakes, the bridge superstructure response may be described as quasi-isolated. This paper presents results for elastomeric bearing components obtained for an experimental program performed to investigate and characterize various bearing types that are being used for quasi-isolated designs. The elastomeric bearings investigated displayed approximately linear elastic response before sliding with a friction coefficient in the range of 0.3 – 0.45, at a shear strain in the range of 150 – 250%. The experiments also investigated the response of anchored retainer brackets used to prevent transverse motion for service loads and small earthquakes to characterize the combined effects of shear and overturning up to and including rupture of the concrete anchor. The test data indicate that the required horizontal force delivered by a bearing to a retainer to cause a failure of the anchor is slightly higher than the ultimate pure tensile strength of the anchor.

Recently a full scale prototype of a steel orthotropic deck was evaluated for a signature bridge in the ATLSS Engineering Research Center, Lehigh University. The deck was innovatively designed to be integral with the existing deck framing system. Since fatigue critical live load stresses at welded connections in an orthotropic deck can be produced by different loading dispositions, the response of the prototype deck was determined under a rolling tandem axle bogie in eight transverse positions. Global displacements at the specimen boundary were simulated by three under deck hydraulic actuators. The deck was instrumented using more than 300 sensors at critical locations. A 3D finite element model of the prototype deck was analyzed corresponding to the discrete axle positions and compared with experimental results. The prototype testing and the analytical studies provided critical understanding of the complex behavior of the deck and the influence surface/response envelopes under local wheel loads.

In the current design specifications, only the individual girder inside the double girder system is checked for lateral torsional buckling between the intermediate cross-frames. However, the overall lateral torsional buckling of double girder systems may be critical under bridge erection, due to the limited lateral bracing present at this stage. Therefore, close attention should be paid to the overall stability of double I-girders during construction, and research has been conducted for the simply supported case and the cantilever case under self-weight only. The results are presented in this paper. Through extensive finite element analyses, established formulas on the overall lateral torsional buckling capacity of simply-supported double girder systems were verified and then modified for the cantilever case. A stability index L/S was developed for estimating the stability of double girder systems under erection, which equals to the ratio between the girder span L and the girder spacing S. Formulae were then derived for the maximum span L_max and the maximum stability index (L/S)_max, beyond which the double girder system would lose stability under its self-weight. Parametric studies were conducted to determine the dominant parameters for L_max and (L/S)_max for various girder sections with different spacing. A quick and reliable method was also established to check the stability of double girder systems under erection using the L/S ratio.

Ultra high performance concrete (UHPC) is an emerging material which develops very high compressive strengths and exhibits improved tensile strength and durability properties. Recent construction of three UHPC bridges in the United States has sparked interest in the use of UHPC for prestressed bridge girders in several states. UHPC offers many advantages including longer spans, improved durability, and smaller structural members, making it an appealing material to use in prestressed bridge construction. This paper presents a case study conducted to investigate the feasibility of implementing UHPC in bridge design in New Mexico. Using a modified LFD procedure, bridge designs were developed considering the compressive strength, modulus of rupture, and modulus of elasticity of UHPC as well as design requirements for flexure and shear, girder cross-section geometry, and prestressing strand area. Comparisons with as-built bridge configurations show that using UHPC with compressive strengths between 100 MPa and 150 MPa may potentially lead to a reduction in required girder lines and reduce or eliminate mild steel shear reinforcement. Compared to regular concrete, a cubic yard of commercially available UHPC can cost as much as 10 times more, making designers and precasters hesitant to adopt this material. An economic analysis, assuming that local materials can be used to produce UHPC, indicates that the initial high cost can be offset by careful selection of materials, reduced construction time and maintenance, and the increased service life of the structure. Costs were evaluated based on local material prices, design parameters of the bridge, modified production practices, and a projected maintenance schedule. This study aids in the development of design procedures and recommendations for implementing UHPC as a prestressed concrete girder material.

Secondary bridge elements, such as barriers, curbs, or diaphragms, are not accounted for when calculating the distribution of load effects to interior and exterior girders, using the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications (AASHTO 2007). This paper shows that including the effect of barriers changes the distribution of loads and, therefore, bending moments in girders. The Florida Department of Transportation (FDOT) Structures Research Lab made field strain measurements on two bridges: a Florida Bulb-T girder bridge and an AASHTO Type IV girder bridge. The Florida Bulb-T bridge strain measurements were taken before and after barriers were placed, and the AASHTO girder bridge was tested only with the barriers. The bridge test results were used to calibrate finite element models, which showed that the barrier, the barrier joint, and the diaphragms affect both interior and exterior girder strains.

In this paper the cumulative effect of road surface roughness, vehicle dynamics, vehicle weight and speed is considered to find the impact factor for highway bridges. AASHTO HS20-44 vehicle is considered running on a very good road. The roughness of the road surface profile is found by using the power spectral density function. The AASHTO truck is modeled as a 12 degree of freedom system to consider the vehicle dynamics. First the forces coming on the bridge deck are calculated taking into account the road surface roughness, then the forces are input to find the vertical deflection by orthotropic plate theory. The deflection obtained is compared with the static deflection to find the impact factor. The impact factor thus obtained is compared with the impact factor calculated from the AASHTO formula. This study shows that the AASHTO formula underestimates the impact factor.

There are, enormous number of, steel truss bridges in the U.S. and around the world. Elementary theory of structural analysis or linear elastic small displacement finite element method is typically used for analysis and design of these bridges. However, steel bridges may face large deflections and inelastic displacements due to unexpected live loads and/or unfavorable environmental conditions. Therefore, there is a need for the second- or higher-order elastic and/or inelastic analysis of these bridges. This article presents a methodology for the elastic large displacement analysis of plane trusses that are novel in bridge engineering practice. Higher-order stiffness matrices and finite element procedure is used for the elastic nonlinear analysis of plane truss structures. The higher-order stiffness matrices are derived and formatted by using the updated Lagrangian description and the finite element concept. Then a numerical method, a modified Riks-Wempner approach, is used for the solution of geometric nonlinear plane truss problems. First, background on nonlinear truss analysis, the scope of this work, and the assumptions pertinent to this research are given. Second, the stiffness matrices, for nonlinear elastic plane truss analysis, are presented by using the incremental equation of equilibrium that is derived from first variation of increment of total potential energy. Third, a modified Riks-Wempner method is used for programming and software development. Numerical examples and results are presented next. The accuracy of the software developed is checked by comparing the results of numerical examples with theoretical results and examples published by other authors. In this research, the concept of Object-Oriented technology and C++ programming language are used for coding and software developed.

This study presents an inelastic non-linear three dimensional (3-D) beam element with axial, bending, shear force and torsion interaction for seismic analysis of Reinforced Concrete (RC) bridge columns. As a result of these load combinations the structural performances of RC bridge columns defer in strength, deformation capacity and failure modes. The shear mechanism along the beam is modeled by using Timoshenko beam approach with curved 3-D frame elements. The values of the concrete strength in principal directions 1, 2 and 3 are affected by the strain state in the other directions. The problem consists in solving a system of equations by combining the equilibrium conditions, compatibility conditions and constitutive laws of materials at section and structural level. The model is validated with the experimental tests subjected to real time earthquake motions.

Seismic analysis results of typical post-tensioned concrete bridges are presented considering the nonlinear behavior of transverse abutment shear. Current Caltrans and AASHTO bridge design criteria present overly general assumptions for the boundary conditions provided by abutment shear keys. This work uses a suite of ground acceleration time histories to compare the code specified assumptions to a more rigorous abutment shear key model that includes the lateral gap between the superstructure and the keys as well as the non-linear material response of the key itself. With the exception of the abutment shear key elements, the bridges are modeled using linear-elastic frame elements, as is typical in practice. Results of a sensitivity analysis are presented for typical parameters, including: record variability, bridge skew, bridge length, and bent heights. The analysis results precede a discussion which demonstrates the necessity for experimental work on this topic to verify the adequacy of the existing design code.

Computational systems analyses are described for bridge systems that employ quasi-isolation by using a set of fixed bearings in addition to isolation bearings such as elastomeric bearings with an elastomer-concrete sliding interface or elastomeric bearings with a PTFE (Teflon) to stainless steel sliding interface. The system uses stiffened L-shaped retainer brackets that limit transverse displacement of elastomeric bearings and the bridge is intended to respond predictably, reliably, and elastically under service loading (including small seismic events), but for larger seismic events, certain bridge bearing components are intended to "fuse" and experience nonlinear behaviors that can allow for passive quasi-isolation of the bridge superstructure. To facilitate the computational modeling, experimental findings from ongoing research are being used to formulate phenomenological element models that simulate nonlinear fusing behaviors in the bridge bearings and auxiliary components. Furthermore the substructure pier elements, the bridge foundations and the abutment backwalls were modeled as they can exhibit nonlinear behaviors under large loadings. A parametric study is being carried out to investigate the effectiveness of the isolation system for various bridge structures and bearing combinations, and the findings will provide guidance for confirmation and further development of quasi-isolation design strategies.

Integral abutment bridges are jointless bridges in which the deck is continuous and connected monolithically with the abutment walls supported typically by a single row of piles. Part of the research results from an ongoing project is presented in this paper, which focuses on the effects of two major parameters on the seismic behavior of an integral abutment bridge in Tennessee by considering soil-structure interaction around the piles and in back of the abutments: (1) clay stiffness (medium vs. hard) around the piles, and (2) level of compaction (loose vs. dense) of the abutment wall backfilling. Modal and nonlinear time history analyses were performed on a three dimensional detailed bridge model using the commercial software SAP2000, which clearly showed that (1) compacting the backfilling of the abutment wall will increase the bridge dominant longitudinal natural frequency considerably more than increasing the clay stiffness around the piles; (2) the maximum deflection and bending moment in the piles under seismic loading will happen at the pile-abutment interface; (3) under seismic loading, densely-compacted backfilling of the abutment wall is generally recommended since it will reduce the pile deflection, the abutment displacement, the moments in the steel girder, and particularly the pile moments; (4) under seismic loading, when the piles are located in firmer clay, although the pile deflection, the abutment displacement, and the maximum girder moment at the pier and the mid-span will decrease, the maximum pile moment and the maximum girder moment at the abutment will increase.

Designed by Populous (architects) and Buro Happold (structural engineers) and fabricated and erected by Watson Steel Structures Ltd, the roof over the London 2012 Olympic Stadium covers an area of more than 24,500m². The construction of the cable net roof posed many complex engineering problems, culminating in the erection of the 14 lighting towers, perched on the leading edge of the roof and supported by a secondary cable net. The entire main cable net, including access gantries, was lifted in one operation involving the simultaneous operation of 28 pairs of strand jacks to lift and pre-stress the cable net roof structure. The design of the staged lifting procedure meant that no additional strand jacks were required for the connection of other cables. An innovative method of lifting the lighting towers into position, using a single crane, was developed to save time and avoid the use of a second crane in a tight location. This paper covers the fabrication of the roof elements, the staged erection and pre-stressing of the main cable net and also the erection of the stadium's signature lighting towers.

BC Place Stadium in Vancouver, BC opened in 1983 as the first domed stadium in Canada covered by the largest air-supported roof in the world. As part of a major revitalization project the stadium dome is being replaced with a new retractable roof structure. The new roof, designed and engineered by an international team, is under construction with completion scheduled in late 2011. The new roof, designed for the 1 in 100 year snow and wind loads and current seismic requirements, is supported by the original stadium superstructure. The new roof structure is a post-tensioned radial cable truss, clad with tensile membrane with a center retracting pneumatic membrane. The paper presents features of the new roof and addresses some of the unique challenges encountered in this unprecedented project. While the challenges overcome in the roof construction, now nearing completion, are worthy and manifold, this paper is limited to roof design due to required brevity. The roof construction will hopefully merit future publication.

When the Florida Marlins began planning for a new baseball-only facility, the presence of a retractable roof was essential. The team owner had a vision for a modern structure different than many of the recently-constructed retro-ballparks. That vision included a retractable roof that was foreseen as more than an umbrella for field and fans. Armed with this direction, the design team embarked on devising a roof structure that could survive major hurricanes economically, while still satisfying the architectural and operational demands of the ballpark. The new ballpark, currently under construction and moving towards an opening day in April 2012, is situated near downtown Miami, Florida. On the one hand, the design team was challenged to support an architecture that did not overwhelm the surrounding residential neighborhood. On the other hand, traditional approaches to resisting hurricane-force winds forecast the need for either a potentially obtrusive or more costly structure. To resolve this dilemma, the roof team implemented an innovative storm preparation strategy to survive major tropical events. Leveraging the experience gained from previous collaboration on several retractable roofs, the team approached their design holistically, with each consultant balancing the efficiency and cost associated with their scope against the roof as a whole. The engineers also collaborated heavily with the project wind consultant to determine cost-effective operating parameters. Because of its unconventional functionality, the resulting three-panel roof, with spans up to 560 feet, exemplifies a new generation of retractable roof design. This session will present the challenges encountered, and solutions provided, by the structural team in charge of designing this new type of roof.

The common characteristics of wind-induced loads on building envelopes always vary in temporal and spatial dimensions. The variation of local wind pressures on building claddings and the total effective wind forces (base shear/overturning moment) on the main structural building systems have been investigated in the past few decades. However, very limited studies examined wind-induced torsional loads on the main resisting structural systems of buildings. This paper reviews these past studies and proceeds with a comparison of torsion provisions in three national wind loading standards, namely the American Society of Civil Engineers standard (ASCE/SEI 7-10), the National Building Code of Canada (NBCC 2010), and the European code (European 2004). Three low buildings located in an open terrain, in addition to three tall buildings located in suburban terrain were considered for this comparison. The low and tall building dimensions were selected to cover three different aspect ratios (length/width) varying from 1 to 3. The results demonstrated significant discrepancies among the provisions of these wind standards in evaluating torsional wind loads on buildings.

This paper presents a set of wind tunnel tests that are carried out to examine wind-induced torsional loads on low-rise buildings. Three low-rise buildings were tested in the Building Aerodynamics Laboratory located in the Engineering Complex at Concordia University, Montreal, Canada. Two low-rise buildings (scale 1:400) with a flat and 4:12 gabled roof slope (having the same dimensions) were examined in open and urban terrain exposures for a half wind direction cycle (every 15°). In addition, a model (scale 1:200) of an actual lowrise building in Fredericton, New Brunswick, Canada and its surroundings has been tested in three wind tunnel tests. Two of latter set of tests were conducted for the building model with a complete simulation of its surroundings in open and urban terrain exposures for a complete cycle by 10° increments. The building was also tested in an open terrain exposure without any surroundings. Peak, mean, and minimum base torsion and shear force for each azimuth were evaluated for all tests. In general, the measured results indicated that the maximum torsional moment on low-rise buildings could be simulated by applying 75% of the full wind loads (maximum shear) with additional 15% equivalent eccentricity of the facing building dimension.

Recently developed steel-framed floor systems utilizing long-span metal deck have the potential of providing large column free areas with overall floor thicknesses approximately equal to concrete flat plates while typically imposing less dead load on the structure. The vibration serviceability of such floor systems is investigated in this paper. Two laboratory specimens, a full-scale mockup, and 13 in-situ floors were tested to measure their natural modes and responses to walking excitations. Natural modes were determined using experimental modal analysis techniques or heel-drop test results. Response to walking was determined by measuring the maximum peak acceleration due to individual walkers traversing the floor. The natural frequencies for the laboratory specimens and mockup were in the range of those measured for typical composite framing systems whereas all in-situ floors are high-frequency floors. The measured accelerations due to walking and subjective evaluations indicate that such floors will generally have adequate resistance to vibrations due to walking.

Laboratory and manufacturing facilities are frequently located in areas that experience high-frequency (greater than 30 Hz) environmental vibration. Such vibrations are a concern for the proper functioning of sensitive laboratory devices, precision manufacturing equipment as well as human comfort. A simple method to accurately predict the magnitude of high-frequency floor vibrations would allow detailed vibration assessment during the conceptual design phase, and provide physical insight useful for developing vibration mitigation approaches. This paper discusses a methodology for prediction of train-induced floor vibrations in buildings using a wave propagation technique. The data obtained from an experiment carried out at Tufts University on a scale model laboratory building have been used to validate the predictions. The proposed wave propagation method successfully predicted the measured velocities and impedances of the scale model building.

Floor vibration serviceability has become an area of interest over recent years. Lightweight electronic offices, especially those with slender architectural forms, and high-technology buildings with low vibration environments can often have excessive floor vibration due to human walking. This can result in a floor which is not fit-for-purpose. There exist a number of design guides which offer simplified formulae to analyse these floors. However, the simplistic methods are often shown in be inaccurate and inappropriate. The alternative, finite element analysis (FEA), which is often considered more accurate, can be expensive to implement and time consuming. In addition, modelling techniques required for dynamic analyses are different to that required for static analysis. This is often overlooked, resulting in poor inaccurate models. An accurate, simplistic, method is required which is suitable for everyday design. This paper examines the current simplified methods of predicting floor response to a single human walking. The inaccuracies are highlighted, as well as where the methodology is inappropriate. The paper also introduces new techniques and ideas to improve design guides in the future.

Improved design methods have led to the use of more slender structural elements in the construction of many newly built structures, especially office floors. These floors satisfy ultimate limit state criteria but can attract complaints arising from excessive human-induced vibrations. Active vibration control is a technology that has been shown to significantly reduce the level of response in this situation. This paper investigates the potential increases in slenderness and associated materials savings that can be realised whilst adhering to the vibration serviceability limits through the implementation of an active vibration control system. The decentralised control setup used was found to realise significant material savings whilst still achieving desirable vibration performance.

The strength and stability of connections in a floor system is an integral part of a building structure. A connection is subjected to large compressive and tensile forces during heating and cooling phase of a fire, respectively. Since shear connections are only designed for gravity loads that produce shear, their behavior in a floor assembly at elevated temperatures needs to be investigated. This paper compares the behavior of three types of shear connections (single plate, single angle and double angle) under fire conditions using the finite element software ABAQUS. The single plate shear connection was validated by a full-scale building fire tested in Cardington. Adopting Eurocode and AISC provisions on the shear connection design, the Cardington connection was redesigned using the single and double angles. While the single plate connections can provide substantial rotational ductility and tensile strength, it could fail during cooling phase of a fire by bolt-hole bearing or bolt shear. The bolted double angle connections are generally more ductile in tension which is advantageous during cooling phase; however they are prone to develop prying forces which could cause the failure of the bolts. In all of the connection models, the beam near the connection experiences local buckling at elevated temperatures.

This paper presents results of a numerical study on the effects of thermal expansion and support restraint conditions on the performance of composite floors in fire. Previously, two full-scale composite floor specimens were tested to investigate factors, such as the supports restraint conditions, that affected the failure of the World Trade Center buildings' floors. Although higher fire resistance was expected for the restrained floors, the test results showed higher fire resistance rating for the unrestrained floor specimen. The purpose of this research was to understand the rationale behind these results numerically. The structural analysis software SAFIR was employed to evaluate the response of the composite floor specimens in fire, such as strain and stress distributions and floor deflection. The results show that the concrete spalling during the first hour of the test for the restrained specimen would have been due to concrete compression failure caused by the restraint condition and thermal expansion.

RC bearing walls are one of the most common primary lateral and gravity load carrying systems in U.S. building practice. Severe exposure to fire can compromise the out-of-plane stability of these walls under service-level gravity loads, causing catastrophic overall or disproportionately large failure of the structure. Considering these issues, the authors are conducting a project with the overall objective of developing experimental and analytical evidence to demonstrate the structural design and performance of RC walls under fire. Eight full scale wall fire tests are scheduled to be completed as part of this project. This paper describes the finite element modeling of the full scale concrete wall structures, and initial pilot experiments conducted to validate the modeling approaches. The results of the finite element simulations will be paired with the experimental results of full scale walls to develop a predictive fire-resistant structural design procedure for the walls.

Composite action in floor systems plays an important role in enhancing load carrying capacity. Fire resistance of composite floors however remains an uncertain issue. As such, the fire response of composite floor assemblies during fire resistance tests is presented in this paper. Three composite floor slab assemblies were tested under different fire scenarios, connection configurations and fire protection schemes in the beam. It was observed that the concrete slab plays a major role in transferring forces from one part of the slab assembly to the other. Data from these fire resistance tests are being used to develop and validate numerical models for tracing the fire response of floor slabs.

This paper presents the behavior of A992 wide flange steel columns under fire loading. Experimental tests were conducted to investigate the structural-thermal response of steel columns subjected to axial loads and elevated temperatures. Two identical W14X53 specimens were tested under (i) non-standard fire loading to determine the axial load capacity at elevated temperature and (ii) standard fire loading to determine the buckling temperature of the axially loaded steel column. For the non-standard fire test (Test I), the monotonically increasing axial load was imposed on the steel column under steady-state heating condition. For the standard fire test (Test II), the steel column carrying the sustained axial load was tested under transient heating condition. The structural-thermal responses of steel columns observed in Test I and Test II were compared including column end rotations, lateral and axial displacements, and steel temperatures. The measured column buckling behaviors were also compared to those obtained by 3D finite element analyses. The results indicated that the end rotations and displacements of the steel column before buckling were affected by the sequence of applied loading. Both Test I and Test II provided the similar prediction of axial load capacity and buckling temperature of the steel columns.

The contribution of carbon emissions to the increase in the global average temperature is well established. It is nearly universally accepted that significant decreases in carbon dioxide and other greenhouse gas emissions must be realized in the near future, or the global community will face very troublesome and possibly even catastrophic climate-related impacts. Civil engineers have a professional duty to abide by the code of ethics adopted by ASCE. The first principle states "Engineers uphold and advance the integrity, honor and dignity of the engineering profession by: a) using their knowledge and skill for the enhancement of human welfare and the environment." The first canon instructs us that "Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable development in the performance of their professional duties" (ASCE, 2009). To these ends, structural engineers are tasked with finding ways to reduce the climate impacts of structures. This paper provides information on the currently available data pertaining to the carbon impacts of concrete and steel. The focus is on how to use the available data to make informed choices to minimize the climate impact of the material aspects of structural design. The first step is to understand the impacts, their relative intensities, and a little bit about climate science. The Carbon Working Group is dedicated to making this information available and usable.

Life cycle assessment is a means of calculating the environmental impact of processes. The ATHENA® Impact Estimator for Buildings was developed by the Athena Sustainable Materials Institute and software collaborator, Morrison Hershfield as a means of applying life cycle assessment to the construction of buildings. The Impact Estimator measures the environmental impact of the new construction of a building in the areas of: Primary Energy, Global Warming Potential, Human Health Respiratory Effects, Ozone Depletion, Weighted Resource Use, Water Pollution, and Air Pollution. It is the intent of this paper to use the software to evaluate a four story office building for four proposed structural framing systems currently under construction in Chicago. The building was designed with the intent of achieving LEED® Platinum certification. The results of the four life cycle assessments will be compared. During this comparison, the authors intend to examine the software to determine its validity as a tool for making sustainable design decisions based upon structural systems.

Life-Cycle Assessment (LCA) is the method which most fully accounts for the environmental impacts of structures. The method provides feedback for our engineering design and specification choices. Three case studies will demonstrate how LCA was used in different ways to answer different questions structural engineers had in the desire to reduce the environmental impacts of their projects. One uses Athena® EcoCalculator for an existing building while the other two studies employ LCA outside of currently available software models for new structures.

Life cycle assessment (LCA) can help bridge design engineers understand, measure, and evaluate the initial and long term environmental impacts of bridge projects, such as energy use and carbon dioxide (CO₂) emissions. LCA can be a helpful tool when comparing conventional construction materials with those that claim to be more environmentally sustainable because it provides the engineer with quantified information on impacts that cannot be identified by a typical bridge life cycle cost analysis (BLCCA). This study investigates the life cycle environmental impacts for a small single span bridge project. A life cycle inventory is completed using the PaLATE v2.1 tool as modified for use with the Greenroads^TM Rating System, and reports quantities for two key indicators of environmental impact for the project: energy use and CO₂. This research demonstrates that LCA tools can provide useful environmental information quickly and easily for structural engineers, but streamlined tools also require an understanding of the inherent limitations of their data sources and analysis methods.

Serviceability criteria in the form of lateral deflection and acceleration limits under wind loading are often the governing structural issues for tall buildings. Whilst the basis for acceleration criteria has been the subject of research, rational refinement and consensus over recent years, deflection limits are still rather arbitrary. Current guidance on deflection limits in international design codes is very limited and is based primarily on experience with typical low and medium-rise buildings. The issues with lateral deflection in very tall buildings are different to those of low-rise buildings, and depend on structural form. Rational choice of deflection criteria for tall buildings therefore requires further consideration of the nature of the deformations and the effects they have on the functional aspects of the building. This paper identifies the functional issues, the relevant deflection measures, and reviews current international practice. New design approaches are challenging previous design norms, and the paper describes a performance-based approach, which allows greater freedom in choosing appropriate constraints for structural and non-structural components. Whilst the subject matter is not new, the use of new design tools and processes leads us to re-examine rules of thumb previously used. The paper focuses primarily on wind events, but comparisons with seismic events are drawn.

When completed the Ping An Tower will be the second tallest building in the world and the tallest in China. Its design was being developed at the same time as the latest cycle of revisions to the China Code were being proposed and considered. Expert panel reviewers familiar with upcoming code changes considered them when commenting on the design. As a result, the analysis and design challenges experienced on the Ping An Tower provide a preview of likely effects of the forthcoming China Code. The paper will discuss and summarize extensive analyses required to satisfy the new China Code standards. The impending provisions in the China Code will establish more stringent design requirements that go beyond current international building design standards.

Structural nonlinear performance of the 126-story, 632-meter tall Shanghai Tower has been studied for 2475-year return period seismic events through nonlinear time history analysis. Seven sets of ground motions were selected as representative of potential local seismic excitation and scaled to meet the provisions of China Seismic Code, GB50011-2001 (2008 version) and Shanghai Seismic Code, DGJ08-9-2003. A detailed and complex finite element model (FEM) of the structure was created within Perform 3D (2008), a widely used software program for nonlinear analysis and performance assessment of structures. Global behavior of the structure was checked to meet serviceability requirement. For performance acceptance criteria at the individual structural element level, GB50011-2001 and ASCE 41-06 "Seismic Rehabilitation of Existing Buildings" (2006) were used as major references. The nonlinear time history analyses confirmed acceptable global and local performances of Shanghai Tower as designed.

Current shear design procedures calculate the nominal shear capacity, V_n of reinforced concrete (RC) slender beams with shear reinforcement (stirrups) by simply superimposing the shear capacity carried by concrete, V_c to that carried by stirrups, V_s. Previous studies concluded that current shear design equations do not only underestimate the resistance of concrete to shear, they also assume that the addition of stirrups does not alter the shear behaviour of RC slender beams. The addition of stirrups is known to provide confinement to concrete and therefore enhances the contribution of basic shear mechanisms to V_c. Current shear design provisions are yet to account for such enhancement and they simply calculate concrete contribution to V_n assuming that stirrups do not exist. In this paper, a previously developed artificial neural network (ANN) model trained on shear database of normal and high-strength concrete beams was used to investigate the effect of stirrups on the contribution of several basic shear design parameters to the overall shear capacity of RC beams. A sensitivity analysis was also carried out to evaluate the performance of several existing shear provisions in calculating the nominal shear capacity of reinforced concrete slender beams.

For many years, the design of reinforced concrete structures in the U.S. has been dominated by the use of steel reinforcement with a specified yield strength, f_y, of 60 ksi. Using steel reinforcement with a higher yield strength would introduce several benefits to the architectural, engineering, and construction industry. Not only would it allow for members with reduced cross sectional area, saving on material, shipping, and placement costs, but it would also help to overcome steel congestion, and facilitate concrete placement. This would directly lead to a better quality of construction, improved durability, and shorter construction times. One of the primary obstacles to the use of concrete members reinforced with ultrahigh strength steel (f_y greater than 80 ksi) is the paucity of experimental data. The applicability of using steel with f_y up to 120 ksi as primary reinforcement in concrete members is explored in this experimental study by subjecting beams and columns reinforced with ultrahigh strength steel to a cyclic loading protocol. The mechanical behavior of these members is compared to similar members reinforced with conventional steel. Test data from this study show that the use of ultrahigh strength steel is a viable option for earthquake-resistant construction.

Sections 21.9.4.5 and 21.9.7.4 of ACI 318-08 limit the nominal shear strength, V_n of concrete coupling beams, including short beams with diagonal reinforcement, to V_n≤0.83A_cw√f'_c (with f'_c in MPa units, or 10A_cw√f'_c with f'_c in psi units). Many experimental studies have been conducted on the design and detailing of diagonally-reinforced coupling beams for ductile behavior under seismic loading. The primary objective of the current ACI strength limit is to prevent the splitting and/or crushing of the diagonal strut in these beams. Through an analytical parametric investigation of isolated floor-level subassemblies, this paper shows that the boundary conditions utilized in the previous coupling beam experiments may not be adequate to investigate this important failure mode. The analytical model that forms the basis of the study uses a strut-and-tie representation of the forces developing inside a coupling beam under lateral loading. Multi-story coupled wall analyses are also conducted.

As part of a large infrastructure project in New York City, many load bearing brick masonry structures are located adjacent to areas undergoing excavation, tunneling and blast. Due to the numerous structures involved, simplified methods to rapidly assess stability issues of the brick masonry load bearing walls and facades have been developed. Based upon these methods, repair techniques have also been developed and successfully implemented. The methods of analysis and sample results are presented with recommended areas of improvement. The relative sensitivities of the various parameters and assumptions required are also presented.

Older load bearing brick masonry structures are often in a condition of advanced deterioration and may be leaning, bowing, cracking or suffering some other form of deterioration. Problems may arise from nearby demolition, excavation or just a general lack of maintenance. Many of these may be in danger of imminent collapse. The problem of detecting problems, effecting repairs and stabilizing these buildings is presented. Case studies showing examples of these problems and possible solutions are presented.

A structural reliability analysis was performed on concrete masonry under concentric axial compression to examine the reliability levels for masonry buildings designed to the current Canadian masonry standard CSA S304.1-04 (2004). The first order second moment method was used to carry out the analysis. Prism compressive strength for hollow and grouted concrete masonry was used as the model. Over 300 specified masonry compressive strength values were computed using test results available from North American investigations, mostly Canadian. The material and geometry statistical data needed were obtained from several Canadian concrete masonry producers. Based on the findings of this investigation, it is recommended that unreinforced masonry be assigned a material resistance factor (φ_m) different from reinforced masonry. For masonry members under compression, it is proposed that the current φ_m be increased from 0.6 to 0.65 for reinforced masonry and decreased from 0.6 to 0.5 for unreinforced masonry. The proposed factors correspond to reliability indices of 3.5 and 3.8 for reinforced and unreinforced masonry, respectively.

The use of wood blocking between wood rafters or trusses has been historically accepted by engineers as necessary to act as a wood roof diaphragm boundary edge member, to transfer chord forces to the chord and to transfer wind and seismic shear forces to the shear walls. However, the use of eave blocking has been abandoned by many design engineers who argue it is not specifically code-required and that empirical testing has shown it is not needed. They argue that chord and shear forces can be resolved through the use of other framing members and metal connectors. However, engineering mechanics and metal connector manufacturers' limits dictate that eave blocking cannot be omitted. In low load, low heel height cases, it could be argued that eave blocking may not be needed, but where roof diaphragms transfer wind and seismic forces, design engineers omitting eave blocking do so in denial of basic engineering principles.

Wood-concrete composite systems are well established, structurally efficient building systems for both new construction and rehabilitation of old timber structures. Composite action is achieved through a mechanical device to integrally connect in shear the two material components, wood and concrete. Depending on the device, different levels of composite action and thus efficiency are achieved. The purpose of this study was to investigate the structural feasibility and effectiveness of using truss plates, typically used in the making of metal-plate-connected wood trusses, as shear connectors for laminated veneer lumber (LVL)-concrete composite systems. The experimental program consisted of two studies. The first study established slip-modulus and ultimate shear capacity of the truss plates when used in an LVL-concrete push out assembly. The second study evaluated overall composite bending stiffness and strength in two full size T-beams when subjected to four-point bending. One beam employed two continuous rows of truss plates and the other employed one row. It was found that the initial stiffness of both T-beams was similar for one and two rows of truss plates but that the ultimate capacity was approximately 20% less with the use of only one row.

A common model of light gauge, metal joist hanger is tested on a wood-to-wood connection for two conditions. One condition follows the commonly used test standard for joist hangers, which allows the support beam to be restrained from horizontal and rotational movement. The second condition (unrestrained) allows the support beam to freely move horizontally and in rotation. The results show that the unrestrained case is much weaker than the standard restrained case. For the model of hanger tested, the average ultimate load for the unrestrained case was 28% of the standard restrained case. The mode of failure for the unrestrained case is different than that for the restrained case. This documents the importance of providing means of restraining the supporting beam by methods other than the connection via the joist hanger. The ASTM testing method for joist hangers may need to be adjusted to account for this possible mode of failure.

Strength is defined as the capacity of a material or element to resist load and can be graphically portrayed on a load-displacement curve by the point at which the maximum load is sustained, regardless of the displacement at which it occurs. It has long been recognized that the strengths of structural materials typically exhibit some sensitivity to load duration. Most strength of materials textbooks, for example, touch on the subject of strength versus load duration and indicate that structural materials subjected to very short term loading exhibit strengths that are enhanced relative to slower loading regimens. Less well-recognized is the fact that the strengths of some structural materials under very long duration loading are substantially reduced relative to what are typically taken to be their ultimate capacities, although for years, the wood engineering community has incorporated a factor into the codes that explicitly acknowledges wood's reduced capacity under long duration loads. This paper addresses the often misunderstood phenomenon of load duration effects in wood members.

The 14th Edition of AISC's Steel Construction Manual will be available in the summer of 2011. The new manual includes and is based on the 2010 AISC Specification for Structural Steel Buildings. Because of the new specification, as well as some other modifications to the connection design procedures, the 14th Ed. Manual will include revisions to some of the existing 13th Ed. tables. Many of the changes in the 2010 Specification are clarifications and minor adjustments, along with some important substantive changes in Chapter I, composite design, and a new Chapter N on quality control and quality assurance. Some of the other notable revisions include: (1) Revised scope statement related to seismic design (Chapter A) (2) Structural integrity is addressed (Chapter B) (3) Stability design procedures are reorganized (Chapter C, Appendices 7 and 8) (4) Revised the available shear strength values for bolts (Chapter J) (5) Revised the slip-critical strength limit state for bolts (Chapter J) (6) Tabulated the HSS connection design equations (Chapter K) (7) New Appendix on Inelastic Analysis and Design (Appendix 1) In addition to the changes to the Specification, several changes and improvements related to connection design were also made to the Manual. These include: (1) Revised bolt value tables for both bearing and slip-critical connections (Part 7). (2) Revisions and additions to the eccentrically loaded weld group tables (Part 8). (3) Clarifications to the discussion of connecting elements subject to flexure (Part 9). (4) Revisions to the design procedure for conventional single-plate shear connections (Part 10). (5) A revised discussion on the design of flexible moment connections (Part 11).

Seismic design provisions for use with steel sheathed cold-formed steel framed shear walls have been proposed for inclusion in the National Building Code of Canada with the associated detailing and design procedures found in the AISI S213 North American Lateral Design Standard for cold-formed steel structures. The design procedure, including recommended seismic force modification factors (R-values), was based on the results of an extensive series of monotonic, reversed cyclic and dynamic tests, as well as non-linear time history dynamic analyses of representative building structures. An approach adopted from the FEMA P695 incremental dynamic analysis procedure is being used to evaluate and improve the seismic design procedure. An overview of the process followed in the conception of the seismic design provisions is provided in this paper.

Diagonal strap bracing is a common means of providing lateral stability for a low rise commercial or residential structure in cold formed steel framing and can be used in wind and seismic design. When designing this type of force resisting system there are a number of design and serviceability considerations that should be investigated. These include loads, strap size, fastener quantity, connection detailing, and construction practices. In seismic applications it is particularly important to understand the behavior of diagonal strap bracing. Accordingly predicting the ductility of the system is critical. This presentation will discuss seismic design of diagonal strap bracing in using the provisions of AISI S213-07, the North American Standard for Cold-Formed Steel Framing — Lateral Design.

Metal Building Systems (MBS) make up a substantial portion of non-residential, low-rise construction in the U.S. Given their wide spread use, it is desirable to understand their performance during a seismic event. Previous pseudostatic, cyclic testing indicates an absence of ductility in these systems. This lack of ductility arises from the inherent design concepts behind using web-tapered frames with no flange or web compactness limits, causing buckling limit states to govern the strength of the frames. In light of the lack of ductility, it is obvious that the current practice of designing MBS moment frames as Ordinary Moment Frame (OMF) systems, with R=3.5, is inappropriate. Also, simple analytical studies suggest that MBS supporting large masses, such as concrete or masonry exterior cladding or interior mezzanines, may be particularly vulnerable to the lack of ductility. For these reasons, it is desirable to develop a safe, economic, and reliable design procedure for MBS. Earthquake simulation testing of MBS has been performed to provide test data to start this development. Three full-scale MBS specimens have been tested on the NEES/UCSD Large High Performance Outdoor Shake Table. Specimen 1 consisted of a single story MBS frame with metal side wall panels to represent the majority of MBS buildings. Specimen 2 was similar to the first, except with heavy concrete sidewall panels. Specimen 3 consisted of a MBS frame built with compact flanges, a mezzanine attached to one sidewall, and a concrete wall attached to the other. Results from each battery of tests will be presented in this paper.

Metal Building Systems (MBS) are frequently constructed with mezzanines contained in their floor plans. These mezzanines can be heavy and have a significant impact on the seismic design and performance of the MBS. When a mezzanine is attached to the MBS, it is not clear to the designer whether it should be treated as a one- or two-story building. It is also not clear how the seismic forces should be distributed vertically. Validity of common assumptions about mode shapes and the first-mode dominating system response was investigated. A codified design procedure was compared with a simpler procedure commonly used by MBS designers. A parametric study suggests that the current building code procedure for vertical distribution of seismic forces may be inapplicable to the design of MBS moment frames because it does not properly address the unique dynamic characteristics of the system. The parametric study and a recommendation for a design procedure are presented in this paper.

Research was conducted to investigate the seismic behavior of steel plate shear walls with in-span plastic hinges. Results show that the development of in-span plastic hinges has detrimental impacts on the behavior of the structure through inducing: (1) significant vertical and residual deformations on the HBEs (i.e. shakedown phenomenon); (2) only partial yielding of the infill plates; (3) lower global plastic strength compared to the values predicted by code equations; and (4) total HBE rotations greater than 0.03 radians after the structure was pushed cyclically up to a maximum lateral drift of 3%. Nonlinear time history analyses also demonstrated that the severity of the ground excitations accentuated the shakedown phenomenon.

This paper describes the recent experimental researches on the steel plate shear wall (SPSW) at National Center for Research on Earthquake Engineering (NCREE). In addition, the design implications learned from the test results are presented. In 2007, the cyclic tests of four full-scale two-story narrow SPSWs confirm that the yielding of the first story column can be confined in the bottom of the column when the proposed capacity design principle is followed. Test results also suggest that, when the column hinging is allowed at a location slightly above the column base, the column size can be cost-effectively reduced without comprising the seismic performance of the SPSW. In 2009, the cyclic test of a reduced scaled coupled SPSW (C-SPSW) substructure was conducted at NCREE. The specimen was the 2/5-scaled substructure of the lowest two-and-half-story of a 6-story C-SPSW prototype building. The C-SPSW specimen consisted of two SPSWs connected together by the coupling beams. In addition to a constant vertical force representing the gravity load effects, cyclic increasing displacements and the associated overturning moments were applied at the boundary of the specimen using the Multi-Axial Testing System (MATS) in NCREE. Test results suggest that the proposed design method, which aims to limit the hinging of the bottom column within the bottom quarter column height, could be a choice of design in the practice. The test results confirm that the effect of the coupling beams in reducing the axial forces in the inner boundary columns. The relationship between the coupling beam rotation and the story drift is explored based on the test data. Test results suggest that the cyclic responses of the C-SPSW specimen can be satisfactorily predicted using the general purposes frame response software incorporating the strip model.

The coupled steel plate shear wall (C-SPSW) system is emerging as a promising configuration for resisting lateral loads in high seismic regions. A C-SPSW is composed of two wall piers, which are special steel plate shear walls (SPSW), joined at the floor levels by coupling beams. The C-SPSW configuration is expected to retain the benefits of the conventional SPSW configuration and provide additional structural efficiency while introducing greater flexibility related to building services and function. However, current provisions do not address analysis and design of C-SPSWs and further research is needed to develop these guidelines. As part of a multi-institution NEESR project on steel plate shear walls, this research explores design procedures for C-SPSW, which build on current provisions for conventional SPSWs. These design procedures are evaluated in the context of a six-story prototype structure. The response of the prototype structure under static loading is studied using numerical models to investigate behavior and performance and to evaluate design procedures. To further study C-SPSW behavior and to validate the design procedures, a large-scale subassembly is being developed for laboratory testing. The preliminary experimental setup and specimen design are described here.

An innovative Self-Centering Steel Plate Shear Wall (SC-SPSW) system is proposed. It relies on post-tensioned (PT) beam-to-column connections that allow beams to rock about their flanges and provide system re-centering capabilities. A design procedure for the SC-SPSW system, developed based on a performance based design (PBD) approach, is presented, followed by analytical results for a prototype SC-SPSW building designed using this PBD approach, and subjected to a suite of ground motions simulating three different seismic hazard levels. The results of the nonlinear response history analyses show the proposed SC-SPSW design procedure to adequately achieve the desired enhanced performance objectives. Concepts of capacity design principle are integrated in the above approach, to prevent in-span plastic hinges of the beam considering reduced moment capacity due to the presence of axial and shear forces and to ensure that PT reinforcement remain elastic, among other things. To facilitate understanding of the behavior and design of an SC-SPSW system, the moment, shear and axial force distribution along the length of a boundary beam are established based on first principles. Closed form formulations describing the moment, shear and axial force beam diagrams are developed based on component capacity design approach and are used in the performance-based system design approach.

Steel plate shear walls are generally considered to be economical only in high seismic regions, primarily because the high levels of ductility and resilience under cyclic loading have been demonstrated almost exclusively by tests on walls that contain expensive detailing at the beam-to-column connections. However, the lower demands on seismic load resisting systems in low and moderate seismic regions may permit the use of far more economical fabrication options. The use of modular construction methods is one option for reducing the costs associated with fabrication and erection. Modular components with repetitive fabrication processes can be produced in the shop and assembled in the field by bolts, eliminating the need for field welding entirely. This paper describes several potential modular options and discusses their advantages and disadvantages in terms of economics and constructability. The performance of one of these concepts (with different means of meeting capacity design requirements) is evaluated using detailed finite element models.

A fast nonlinear dynamic analysis algorithm is proposed based on modal superposition of structural response incorporating both material and geometric nonlinearities. Because linear modal superposition has found great acceptance in performance-based seismic engineering, it is here extended to the nonlinear domain by using the force analogy method to address material nonlinearity, where the stiffness force is computed by a change in displacement instead of using the traditional way of changing stiffness. Geometric nonlinearity is incorporated into the analysis using stability functions. State space method is used to explicitly calculate the dynamic responses of each modal single-degree-of-freedom system. Through the combination of force analogy method, stability functions, state space method, and modal superposition, numerical simulations are performed and results are demonstrated to be both accurate and efficient.

This paper describes the use of nonlinear analysis within the context of the ASCE 7 seismic load provisions. The methods of analysis that are discussed include P-Delta analysis, nonlinear static analysis, and nonlinear dynamic analysis. All methods of analysis are discussed at the systems (entire structure) level. The use of nonlinear static analysis to perform sub-system evaluation is also described. Also provided in the paper is an assessment of the adequacy of the current analysis techniques in the context of advances that have been made in computational power and analysis capabilities over the last 40 years. Recommendations for improvements in the ASCE 7 analysis procedures are provided at the end of the paper.

The need to perform cost-effective seismic rehabilitation of essential facilities has made the use of nonlinear analysis techniques an attractive option. The estimation of seismic demands on structures requires explicit consideration of the structural inelastic behavior. Therefore, nonlinear procedures such as pushover analyses are inevitably going to be more widely used. This paper presents a case study of a 10-story Pre-Northridge steel moment frame hospital building in California that was analyzed using nonlinear pushover analysis approach. Nonlinear force-deformation relationships and acceptance criteria of primary structural components were modeled in accordance to ASCE 41-06 and supplemented by experimental component testing results. Given the nature of steel moment frame buildings constructed during this era, existing connections are highly susceptible to damages during a major earthquake which could lead to an unfavorable failure mechanism. Based on nonlinear pushover analysis results, potential structural deficiencies will be identified and different rehabilitation methods will be presented. Besides, the comparisons of retrofit scopes between conventional and nonlinear methods will be highlighted. Finally and most importantly, this paper also addresses some challenges found by the authors in the implementation of nonlinear pushover analysis in seismic retrofit application, as well as recommendations from practitioner perspectives.

As part of maintenance and future planning for marine structures, a condition assessment and load rating are traditionally performed every 2 to 5 years, depending on the use and importance of the structure. Traditionally, the load rating of these structures only considers the "day-to-day" vertical service loading. As a greater understanding of the inherent, seismic hazards present in areas of the United States with marine infrastructure including those on the east and west coasts, vulnerability studies of existing structures are becoming more common. These studies estimate the expected behavior of the structure under a variety of loading conditions. This assessment helps determine if the facility needs to be repaired, given its current condition, or upgraded for changes in operational loading or use. This paper will demonstrate the implementation of non-linear static analysis techniques for assessing the vulnerability of existing marine infrastructure. In particular, the effects of concrete pile deterioration and concrete pile-to-pile cap connectivity on the service and lateral/seismic resistance of a typical pile supported marine structure is presented. The impact of considering the current condition state of the structure throughout the analysis will be emphasized.

In order to aid in post-earthquake response and recovery efforts, hospitals and other critical structures must remain operational after a design level seismic event. Protective systems (base-isolation and supplemental damping) provide a means to reliably and economically achieve improved structural and nonstructural performance. Viscous wall dampers (VWDs), originally developed in Japan, will be used in this first U.S. application to provide supplemental damping and enable a new 15 story hospital in San Francisco, California to achieve stringent performance goals. This paper introduces the innovative VWD devices, describes the results of full-scale prototype testing, summarizes VWD properties, and explains modeling techniques for implementation in nonlinear response history analysis. By using VWDs in this hospital application, the overall steel weight was reduced by an amount that more than offset the installed cost of the VWD devices and a unique lateral system was designed that will enable improved structural performance, when compared with traditional systems. Also, floor accelerations in the upper floors of the building were significantly decreased, thereby reducing the costs associated with nonstructural bracing, especially for the central utilities plant located on the top floor.

This paper summarizes the seismic analysis and rehabilitation design of a fifteen story steel moment resisting frame building in Oakland, California, less than five miles from the Hayward Fault. The building was constructed with connection details that were found to be vulnerable to fracture in the 1994 Northridge earthquake. Previous testing of the existing connections indicated that the welded connections were highly vulnerable to fracture, and consequently the building presented a risk to life safety in the event of a major earthquake. Seismic strengthening to meet the State of California Guidelines for the Seismic Retrofit of State Buildings Risk Level III resulted in a requirement to reduce the story drifts to 1.5% in a 475-year return period event. After considering several retrofitting schemes including connection strengthening, BRBF's and seismic isolation, a scheme that included strengthening sixty percent of the existing pre-Northridge moment frame connections and adding viscous dampers was selected. Since the existing moment connections had performed so poorly in previous testing, and because the size of the members in this building exceeded those that had been previously tested, a series of four full-scale tests were performed to confirm the validity of the connection upgrade design. Two phases of advanced analysis techniques were performed in the rehabilitation design; a study phase with multi-mode two-dimensional nonlinear pushover analyses along with single-degree-of-freedom nonlinear dynamic time-history analyses; and a working drawings phase with nonlinear response history analyses of building frames to refine the scheme and perform member checks. The extra steps taken beyond typical engineering practices were intended to provide better assurance that the project's performance goals would be met during the design basis seismic event.

The Bowls Project in San Francisco, California was synthesis of music, history, architecture, and engineering inspired by ancient Babylonian clay bowls. The structure is a base-isolated pair of intersecting masonry domes using the Mediterranean system of tile-vaulting. Construction of the domes as an unreinforced masonry structure would not be permitted by the San Francisco Department of Building Inspection if not for an alternate means of compliance through a base-isolated design. The typical ASCE 7-05 approval process for base-isolated structures is expensive and time-consuming — the review cost alone would have exceeded the entire budget for this small project. The Department of Building Inspections recognized the seismic protection that base-isolation would provide to the domes and agreed to permit the design using full scale testing of the completed structure to validate design properties of the isolation system. This not only made the project feasible, it allowed the schedule to move from conception to completion in only 2 months. The isolators use a Ball-N-Cone design by Worksafe Technologies. Upon completion of the masonry dome construction on the isolated plinth, the structure was pulled to maximum displacement and released in a series of "snap back" tests in orthogonal directions. The plinth and the top of the dome were monitored with accelerometers to capture the acceleration time history in free vibration. The data was used to confirm the maximum acceleration of the plinth, the damping ratio, fundamental period, and hysteretic behavior of the isolation system. This method to verify isolation system properties satisfies the intent of ASCE 7-05 by providing engineers with the design properties and surpasses the intent by providing these properties under actual load conditions. Future applications could provide artists, architects, and engineers the ability to build innovative, efficient structures in high seismic areas with the assurance that structure performs as intended.

The WorkSafe ISO-Base planks, Isolated Raised Access Floor and Isolated Equipment Platform take a new approach to protection of building contents in seismic areas by implementing isolation technology. Seismic isolation has been in use since the 1970s to protect buildings and other large structures from earthquake shaking in seismically active areas around the world. Seismic isolation technology works by decoupling the isolated component from the ground, essentially allowing the ground to move underneath the component without transmitting the damaging accelerations above the plane of isolation. WorkSafe Technologies owns the patents on the Ball-N-Cone isolation technology, which uses a steel dish and ball bearing to provide seismic isolation and has developed systems for isolating individual cabinets as well as entire access floors. The technology has now been extended to include large isolated platforms, suitable for large heavy items such as equipment, art installations and potentially light framed residential construction. The patented Ball-N-Cone isolators are well suited to the lighter vertical loads associated with building contents compared to those present in larger building and bridge structures. The WorkSafe ISO-Base planks are unique in applying isolation technology to individual server cabinets, or rows of cabinets. The Isolated Raised Access Floor (IRAF) applies the same isolation technology, but to an entire access floor by moving the isolation plane to the base of the access floor pedestals. The benefits of using isolation as opposed to conventional bracing are two-fold — critical equipment is protected against damaging earthquake accelerations and facility managers do not have to deal with installing traditional bracing, with the associated concrete drilling and relatively heavy construction in the sensitive data center environment. The Isolated Equipment Platform extends the use of the Ball-N-Cone isolator to heavier components such as large pieces of equipment, art installations and potentially light framed construction. This paper presents several case studies on the applications of equipment isolation and the benefits it provides.

The seismic responses for nuclear facilities are required to consider soil-structure interaction (SSI) effects. The upcoming revision of ASCE 4 establishes a goal of developing seismic responses with an 80% probability of non-exceedance. It is important to ensure the widely used deterministic analysis results to be in an 80th-percentile level response or higher as compared to the probabilistic analysis. The SSI analysis of the Lotung quarter-scale containment model is repeated using the probabilistic method using the computer program SASSI2000. The experimental Lotung results are used to evaluate the merits of the probabilistic approach and to make an assessment of the 80th-percentile responses with the responses obtained from recoded motion. The analysis is subsequently repeated at three sites with different soil depths and with modifications to the input parameters to observe their effects on the probabilistic analyses. Probabilistic analysis considers the variation of soil properties, layer thicknesses, and structural parameters. For all cases, a comparison of the seismic loads and in-structure response spectra (ISRS) at the 80th-percentile level is made with the envelope of three deterministic SSI analyses, demonstrating that the deterministic method envelopes the probabilistic ISRS, but probabilistic structural forces may exceed the deterministic. This paper further examines the effects of Monte Carlo and Latin Hypercube sampling methods and of the number of samples on the accuracy of results for the probabilistic analyses.

The forthcoming update of ASCE 4 includes expanded provisions for analysis, design of seismically isolated nuclear structures and testing of seismic isolation bearings. The paper describes the provisions and their technical basis. The analysis and design provisions are consistent with the ASCE 43-05 performance objectives for nuclear structures, namely, 1) 1% probability of unacceptable performance for 100% Design Basis Earthquake (DBE) shaking, and 2) 10% probability of unacceptable performance for 150% DBE shaking.

The subject of development of site specific performance-based design motion and its application to soil-structure interaction (SSI) analyses has been discussed in a number of guidance documents developed for both the Nuclear Regulatory Commission (USNRC) and Department of Energy (USDOE). NRC's Regulatory Guide 1.208 and upgrade to Sections 2.5.2, 3.7.1, 3.7.2 and 3.7.3 of NRC's Standard Review Plan (NUREG-0800) and DOE Standards (DOE Std 1020-94) have emphasized probabilistic approaches to development of seismic hazard and site response. These procedures are now used to estimate seismic response of critical facilities for design and evaluation purposes. Chapter 2 of the new revision of ASCE 4 attempts to captures all significant changes to the recommended site response analysis procedures with the goal of providing an industry consensus on this process. This paper summarizes the interpretation of the regulations and guides, and the industry agreement on the details of the development and application of the ground motion for SSI analysis. The objective of the recommended methodologies is to maintain consistency from development of the design motion from site response analysis to its application to SSI analysis and evaluation of results. Consistent use of soil property data and input motions developed based on the recommendations in Chapter 2 of ASCE4 for application to SSI analyses described in Chapter 5. Issues currently being emphasized in probabilistic site response analyses include (a) development of Foundation Input Response Spectra (FIRS) to be used as input to deterministic SSI analyses, (b) development of appropriate description of nonlinear soil properties to accommodate the incorporation of nonlinear behavior in the site response evaluation, and (c) consideration of layer-to-layer velocity correlation models in the column realizations

This article addresses engineering, detailing, and erection of shear connections which represent 95% of the connections on every steel project. While they are often unfairly regarded as simple, they are rarely simple. Shear connection are complex due to the many different types of connections, number of limit states to check, as well as geometry and erection complexity. This article will compare and rate the various methods the Engineer of Record (EOR) uses to provide shear demands. In addition, common types of shear connections will be presented and discussed. Shear connections are rarely controlled simply by the number and capacity of the bolts, and this paper will examine all limit states and discuss what to look out for during shop drawing review.

In the last 20 years, computer aided drafting and analysis software has allowed steel structure geometries to become more complicated. As the steel structure geometries become more complicated, the use of skewed t-joints for both tubular and nontubular connections has become more common. The American Welding Society Structural Welding Code - Steel (AWS D1.1) provides design and detailing requirements for skewed t-joints. Depending on the skewed t-joint geometry, designers are required to define the required weld leg or effective throat size. However, many designers are unaware of the AWS D1.1 skewed t-joint requirements and apply typical 90 degree fillet weld details to skewed connections. Contradiction between these 90 degree and skewed details in combination with the variety of AWS D1.1 prequalified joint configurations can lead to confusion and fabrication inefficiencies. AWS D1.1 design and detailing requirements for skewed t-joints are summarized and discussed.

This paper presents the design, and the examination of ductile structural behavior through finite element analyses, of super composite columns and their connections to the outriggers, double belt trusses, and mega bracing members of the Ping An International Financial Center Tower in Shenzhen, China. When completed, this 660m-tall structure will be the tallest building in China and the second tallest building in the world. Many complicated steel connections were analyzed and designed. Finite element analyses were performed on the super column, outriggers, double belt trusses, and mega bracing connections to evaluate the performance of the as-designed connections under 100 year wind forces and three levels of seismic action: frequent earthquake, moderate earthquake and severe earthquake. This paper also briefly presents the design of the steel connections; describes the ABAQUS finite element analyses model; presents the major results of the finite element analyses; and evaluates the performance of the connections based on the analysis results.

While architecture, engineering and construction continue to become more globally integrated, significant regional differences in practice continue. This paper explores the regional differences in structural steel detailing. There is significant global variation in who typically takes responsibility for the detailing (both for structural strength and for specifics of fabrication) of steel connections. Interviews with over thirty professionals (architects, engineers, fabricators and others) with expertise in ten countries and three regions of the US were completed to characterize four distinct methods of designing and detailing steel connections for construction. Case studies of three practices are presented to demonstrate established practices in which the distinction between engineer and fabricator is reduced or eliminated, explore the challenges and opportunities of the practice methods, provide examples for engineers, detailers and fabricators considering adaptation of their roles in an evolving market and present a framework for challenging basic assumptions and exploring alternate methods of project delivery.

Large-scale shake table tests were performed to examine the out-of-plane stability of buckling-restrained braces (BRBs). Two specimens were subjected repeatedly to a near-fault ground motion with increasing magnitude. The test specimens comprised a single-bay, single-story steel frame and a pair of BRBs placed in a chevron arrangement. The chevron braced frame specimens were not braced at the point of intersection in the beam, and was therefore susceptible to out-of-plane instability. Standard BRBs were used in the first specimen, while unique BRBs with a flexible segment at each end of the steel core were used in the second specimen. A simple stability model predicted the BRBs in the second specimen to fail due to out-of-plane buckling at a force smaller than the yielding strength of the steel core. The first specimen exhibited excellent ductility during the shake table tests, while the second specimen developed noticeable out-of-plane deformation. Observations from the tested are described along with design implications.

Large-scale shake table tests were conducted to examine the dynamic response of steel concentrically braced frames. The specimen was a single-bay, single-story frame with a pair of square-tube braces placed in a chevron arrangement. The gusset plates connecting the brace to the framing elements were provided with an elliptical clearance to permit free out-of-plane rotation. The specimen was subjected repeatedly to unidirectional ground motion with increasing magnitude until the braces fractured. The test results demonstrated excellent performance of the gusset plate connections. The specimen response was reproduced by a numerical model using fiber elements. This model was able to predict the occurrence of brace fracture and post-fracture behavior of the frame. Observations from the shake table tests and aspects of the numerical analysis are reported in this paper.

Although conventional earthquake-resisting structural systems provide adequate life safety when properly designed, they rely on significant structural damage to dissipate the seismic energy. This structural damage and the residual drift that may result from the inelastic response can make a building difficult, if not financially unreasonable, to repair after an earthquake. As a result, development of systems that return to their initial position (i.e., "self-center") following an earthquake and minimize structural damage is a crucial need. This research aims to address this need by creating an innovative self-centering brace for advanced seismic performance. In the present study, the seismic behavior and performance of self-centering buckling-restrained braces (SC-BRBs) is investigated. A SC-BRB consists of a typical BRB component, which provides energy dissipation, and pre-tensioned superelastic NiTi shape memory alloy (SMA) rods, which provide self-centering. The SMA rods are attached to the BRB portion of the brace using a set of concentric tubes and free-floating end plates that cause the SMA rods to elongate when the brace is in both tension and compression. Half-scale SC-BRBs are designed and fabricated for experimental validation. To characterize hysteretic response, the braces are subjected to a cyclic loading protocol adapted from the AISC Seismic Provisions for Structural Steel Buildings. The results of the experiments are used to validate a SC-BRB numerical model, which is used to conduct further parametric studies of SC-BRB behavior and to perform system studies of concentrically-braced frames with SC-BRBs.

The Cathedral of Christ the Light is an artistic celebration of modest and common building materials used to transform a site on the north end of Lake Merritt in Oakland California. The structure uses the most advanced geometric and scientific approaches to created a building that satisfied the Diocese of Oakland's need to construct a new cathedral with the service life of at least 300 years; a request that was not unexpected considering the venerable cathedrals of the Catholic Church that have survived for centuries. The project site exists only 4.6 km from the Hayward Fault, one of the most active seismic faults in the world, making the request substantially more challenging. Ground motions expected at the site could result in an earthquake of magnitude 7.0 or more on the Richter Scale. The approach to design embodies lightness (both visually and structurally) and luminosity, hence its name, The Cathedral of Christ the Light. The structure is defined by sacred geometries and designed for lightness by using seismic isolation to manage ground motions and reduce the demand on the superstructure during an earthquake. It is the light that transforms the structure and its material throughout the day creating what the cathedral's lead architect and SOM Design Partner Craig Hartman calls a space of "ephemeral lightness" with a "primordial connection to the earth." In developing the design, Hartman thought that "the cathedral must be in the architectural language of our time. The Catholic Church has historically applied the most advanced architectural thinking to create architecture that illuminates, inspires and ennobles the human spirit." The cathedral incorporates a highly innovative use of natural, yet ordinary, materials with an ethos of sustainability. Glued-laminated timber from sustainable forests, exposed reinforced concrete using replacement slag and fly ash, recycled high-strength steel, aluminum, and glass create the symbolic form. The 1,350-seat cathedral, located on the northern edge of Lake Merritt, is the centerpiece of a 224,000-square-foot complex with a complement of facilities that includes a mausoleum, a conference center, administrative offices, bishop and clergy residences, a bookstore, a café, and community-serving ministries. A landscaped public plaza, accessible from all directions, firmly links the center with the city's commercial downtown and surrounding neighborhoods. As a whole, the structure honors its religious and civic obligations to both the Catholic Diocese and the city of Oakland.

This paper discusses the analysis procedure adopted for performance evaluation of Ping An International Finance Center in Shenzhen, China. Upon completion, the 115 story tower 660 meters tall will become the world's second tallest building and tallest building in China. The selected structural system consists of a composite concrete core, seven exterior double layer belt trusses, four sets of steel outriggers, eight super columns and super diagonal braces between super columns. Given the scale and importance of this building, a rather sophisticated evaluation of seismic performance during a rare earthquake (2% probability in 50 years or 2475 year return period) was performed. Two synthetic and five recorded ground motions were selected for the nonlinear time-history analysis. These ground motions were scaled to meet the provisions in China Seismic Code; BG50011-2008. The performance levels for immediate occupancy, life safety and collapse prevention were set based on ASCE 41-06 "Seismic Rehabilitation of Existing Buildings" (2006). Complex 3D computer models with geometric and material nonlinearities were generated for nonlinear dynamic time-history analyses. The detailed performance assessments of main structural elements such as coupling beams, core walls, super columns, outriggers, belt-trusses and super-diagonal braces are presented in this paper.

This paper presents an overview of the "Enhanced" seismic design of the New San Bernardino Court facility. Designed for the Judicial Council of California under the jurisdiction of the Administrative Office of the Courts, the state-of-the-art Superior Court facility will be located in the City of San Bernardino, California — a region of high seismicity in close proximity to active earthquake faults. The 12-story structure with one below grade level was designed to meet "Enhanced" seismic performance objectives of the 2006 California Trial Court Facility Standards in accordance with the 2007 California Building Code. The final design features a cost-effective steel-framed superstructure with special moment-resisting frames and supplementary viscous damping devices supported on a triple-concave friction pendulum seismic isolation system. This paper focuses on the overall progression of the final design from early design phases through final construction documents. This includes architectural design development, site-specific seismic hazard evaluation, structural system options considered, as well as, seismic risk assessment and life-cycle cost analysis to help inform decision making and system selection.

This paper summarizes the case study of a four-story building with three additional levels below grade in the Pacific Northwest of the U.S. consisting primarily of precast and cast-in-place concrete elements. The lateral force resisting system consists of eight reinforced concrete shear wall towers located around the perimeter of the building and four shear walls down the centerline of the building. The building was analyzed and a retrofit scheme was developed using both linear and nonlinear static analysis procedures conforming to the requirements of ASCE 31 and 41. The retrofit scheme had to meet a number of criteria set forth by the owner. The retrofit had to visually promote the owner's commitment to seismic safety while embodying sustainability. The building had to remain occupied and operational while the retrofit construction took place; which required noise, dust and vibration be minimized. The HVAC system also had to remain in operation while it was modernized. To satisfy these constraints, the retrofit employed a mostly exterior strengthening scheme that included large horizontal steel trusses and steel collectors in order to engage previously unused exterior tower walls. Four strips of new roof over the existing roofs were added to confine the existing gypsum concrete roofs and provide support for a new HVAC system. Collectively, the retrofit scheme was a tailored solution which optimized use of the existing structural elements while providing the owner with an economical retrofit which is expected to meet or exceed the established performance goals.

The unfortunate collapse of the I-35W Bridge in Minneapolis, Minnesota in August 2007 has brought bridge safety to the forefront of the public. The immediate reaction to the incident was focused on highway bridge inspection and evaluation practices, especially related to inspection and evaluation of gusset plates on truss bridges. There were several directives from federal and state authorities to address these issues in the short-term and long-term. The short-term directives were to address the inspection and evaluation of gusset plates on truss bridges similar to the collapsed I-35W bridge. For the long-term, Congress and the bridge industry have focused on reviewing current practices in bridge inspection and bridge management, identifying gaps and issues with current practices and policies that can be improved in the future, and providing methodologies to effectively utilize available limited resources using risk based methodologies. This paper will discuss these issues from the owners' perspective based on the authors' involvement and experience in working with state and other transportation agencies on such issues.

The failure of a large steel truss bridge in Minnesota has been, in part, attributed to overstressed and buckled gusset plates. This catastrophic event signaled concerns of the potential for a similar overstressed state in gusset plates in steel truss bridges across the county. To provide guidance to bridge engineers, the Federal Highway Administration released FHWA Bridge Design Guidance No. 1 Load Rating Evaluation of Gusset Plates in Truss Bridges; however, the somewhat complex evaluation methods make rapid assessment costly for DOTs. A study supported by the Washington State Department of Transportation and FHWA has developed a procedure for rapid and reliable evaluation of the state of gusset plates, including the maximum stresses and likelihood of yielding. The development utilized a parametric study of several gusset plate configurations performed using advanced nonlinear finite element analysis. Parameters such as plate thickness, yield stress, and load distribution were considered for actual gusset plate connections from bridges primarily in Washington State. The selected gusset connections also had different geometries to ensure the resulting evaluation approach is sufficiently broad in applicability. The new approach should enable bridge engineers to more expediently evaluate the capacity of gusset plates, allowing gusset plates with near critical demand-to-capacity ratios to be identified for further, more refined analysis or retrofit. The paper and presentation will detail the analyses and resulting rapid gusset plate evaluation procedure.

Wading through the mechanics of writing a bill and getting support for structural licensing and practice acts can appear to be an overwhelming, difficult, and time-consuming experience. Working through the political process can especially be a challenge if you are unfamiliar with the motivating factors and back-room negotiations that typically influence a legislative decision. However, a number of Structural Engineers Associations (SEAs) have successfully worked through the legislative process and effectively lobbied for structural licensing and practice acts. Learning from their experience will provide you with the essential background information that you need to ensure success as you move forward toward structural licensing and practice acts in your state. Because the specific methods of changing the licensing laws will vary from state to state, this session will focus on general topics that each state should have in common. Specifically, this session will include important information about establishing a firm foundation of support, emphasizing the reasons for a practice act, creating a vision that will motivate and inspire, developing strategies for success, presenting talking points that will have impact, and explaining why structural licensing and practice acts are essential. Additional topics will include understanding your legislators and actually writing the bill.

In April 2011, National Council of Examiners for Engineering and Surveying (NCEES) will begin offering a new 16-hour Structural Examination to replace the Structural I and Structural II examinations. This new exam will also replace the state specific seismic structural examinations currently offered by California, Oregon, and Washington. The first half of this paper will focus on how and why the changes were made, including discussion of how different states use the current structural examinations, difficulties in mobility of structural licenses, the NCEES Structural Task Force, the NCEES Professional Activities and Knowledges Survey for the new 16-hour Structural Examination, and the new Test Specification. The second half of this paper will discuss the format of the new 16-hour Structural Examination, the new 16-hour Structural Examination writing committee, and how the new 16-hour Structural Examination is graded.

Science is widely perceived as an especially systematic approach to knowing; engineering could be conceived as an especially systematic approach to willing. In science, although the will is implicitly involved, the intellect is primary, because the goal is ideal—additional "objective" knowledge. In engineering, although the intellect is implicitly involved, the will is primary, because the goal is pragmatic— some "subjective" outcome, which is often selected by a manager or client, rather than the engineer. Furthermore, engineering problems are rarely well-defined; uncertainties and resource constraints dictate that they be conceptualized and solved heuristically. As a result, different engineers will follow different design procedures and develop different models, none of which is uniquely "correct." Because tradeoffs are always necessary, engineering decision-making—and human behavior in general—is more intentional than rational. Recognizing this can help today's society to engage engineers more explicitly in addressing the many challenges that it faces, technological and otherwise.

Structural building codes serve a number of purposes, but the primary one is to provide minimum standards of design that protect human health and safety. Codes have grown more complicated over the past 25 years primarily by providing increasing numbers of explicit provisions for the design of most structural members. Explicit provisions appear to be a good way to encode design knowledge, but too many of them will make the code difficult to decode. Encoding and decoding of design knowledge is best performed by a combination of implicit and explicit provisions providing general design principles and optimizing the number of explicit provisions in order to minimize the noise in the encoding/decoding process.

Most engineers today have heard of sustainability, but there are probably few who would feel comfortable defining what it means. Even well-intentioned and well-read practitioners struggle with a useful definition of sustainability. Depending on who is asked topics that fall under the umbrella of sustainability can include green materials, energy independence, pervious pavement, the heat island effect, health of local waterways, social justice, etc. The scope of topics is extremely broad and can create a lack of focus that is a barrier to making progress on technical issues and communicating an effective message about sustainability. In civil engineering, perhaps the two viewpoints on sustainability most commonly offered are a quote from the Brundtland Commission: "meeting the needs of the present without compromising the ability of future generations to meet their own needs" and the Triple Bottom Line of people, planet, and profit. These and other approaches contribute to our understanding of sustainability, sometimes from radically different points of view. In this paper the different approaches are discussed. Commonalities and differences are noted and a generalized framework of sustainability is developed. This framework can serve as a guide to analyzing some of the more popular topics in the discourse surrounding sustainability as related to civil engineering, to determine which do not fall within the scope of sustainability, which are the most important, and where we as technical practitioners should be focusing our efforts. Ultimately, the goal of this paper is to help engineers actively discuss and answer these questions for themselves.

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 has recently completed evaluating two different Design Problems. One design problem was for the application of ACI 318 Appendix D cracked concrete anchor bolt design. The second problem was the analysis and detailing specification of Wall-to-Roof anchorage in masonry construction intended to be per ACI 530-08. These problems have exhibited and proved that new code sections are routinely misinterpreted or not applied by practicing engineers. The application of these important and more recently instituted code sections has proved to be a subject that can cause confusion and misapplication as will be evidenced in the session. A movement is in progress to encourage greater collaboration between Code writing authors, and application and interpretation of code sections by the practicing engineers. The purpose of this session is to present the results of these trial problems and encourage further collaboration to advance the practice of structural engineering as it relates to code interpretation and design of elements and components. The objective is to improve clarity regarding current issues in the profession such as application of code sections, the complexity of codes and their detailed application. Presentations will introduce these topics, allowing time for comments, questions, and further discussion with members of the audience in attendance.

The study of failures, particularly in a design course, can help teach students how to ensure the satisfactory performance of buildings and bridges. Some of the shear design provisions in the current ACI 318 Building Code can be traced back to two collapses of Air Force warehouses in the mid-1950s. Three building collapses in the 1970s and 1980s showed the importance of punching shear. There is also much to be learned from reinforced concrete building performance under extreme conditions, such as the terrorist attacks on the Oklahoma City Murrah Building and the Pentagon (9/11). Another classic case is the collapse of a major section of the Ronan Point apartment towers in the UK in 1968, illustrating the need to properly tie precast building elements together. The relatively recent collapse of the Laval, Quebec concrete bridge abutments in Canada shows the importance of providing continuity of reinforcement.

A new undergraduate course was developed to introduce civil engineering students to the field of forensic engineering and foster an awareness of how engineers can and should learn from failures. Several other individuals and engineering departments have made commendable efforts to integrate information about specific failure cases within civil engineering courses while others have developed graduate-level courses designed to teach the students to become forensic engineers. This undergraduate course was designed to fit somewhere in between. The goals were two-fold: to improve the general knowledge base of historic and common failure modes and to introduce the field of forensic engineering and what it requires in an effort to encourage continued education in the field. The development of such a course was difficult for a number of reasons including the vast scope of the field, the scarce supply of teaching materials, and the disparity between the level of student knowledge at an undergraduate level and that required to fully understand an engineering failure. This paper describes the educational objectives and resources utilized in the preparation of the course, the variety of teaching methods and techniques undertaken during the course of the semester, and the successful components of the course as well as the difficulties and challenges encountered. Several considerations and suggestions are presented for others in the development of similar courses and recommendations for improving future offerings of this course are also presented.

To this day, the 1981 skywalk collapse in the Kansas City Hyatt Regency resulted in the worst loss of life from a structural engineering mistake in United States history. While many important engineering lessons can be drawn from this disaster, it is just as important to recognize the broader lessons learned in the design and construction process as a whole that can be successfully brought into the classroom. Numerous organizations have undertaken the task of envisioning how engineering education can meet the demands of the future. ABET's baccalaureate degree accreditation criteria, ASCE's Body of Knowledge and Body of Knowledge 2 as well as the National Academy of Engineering have documented the need to change engineering education from its historical focus on technical content knowledge to include greater emphasis on professional issues and to integrate engineering practice into education. To this end teaching methods such as project based learning, active learning and the use of case studies are being explored to address these broader learning outcomes while actively engaging students. Because of the attraction students have in extraordinary events, the Hyatt disaster provides an ideal backdrop to introduce many of the professional issues needed to broaden the undergraduates' learning experience. This paper discusses the use of the Hyatt Regency skywalk collapse in design coursework with specific application to third and fourth year civil and architectural engineering student learning. Besides the traditional concepts of load flow analysis and member design, broader concepts relating to professional roles and responsibilities, design team interplay, the design process, the construction process and professional practice ethics are emphasized.

Reasons for including failure case studies within the undergraduate engineering curriculum have been made by various authors. Specific cases have been integrated into the syllabi of engineering mechanics, structural analysis, and structural design courses. The case studies used are typically catastrophic structural failures, where failure can be defined as a structural collapse, often with significant loss of life. Many civil engineering undergraduate programs include a course in construction planning and management. The American Society of Civil Engineers (ASCE) Civil Engineering Body of Knowledge (BOK) for the 21th Century, Second Edition emphasizes a need for Civil Engineers to understand not only the technical areas of analysis and design, but also more of the project management issues that enable a project to go from design to fruition. Hence, it is likely that more programs will include construction management courses. This paper deals with the integration of failure case studies into a construction planning and estimating course. In addition to structural failures, this course looks at the definition of "failure" from an engineering/construction perspective. It explains that failure includes the inability of an engineered facility to perform as designed. It further opines that failure to be constructed within reasonable time and budgetary constraints falls within the definition of failure. While most students may have the pre-conceived notion that failures are only caused by design deficiencies and perhaps natural hazards, the examples used in this course emphasize how many failures are caused by deficiencies in the design and/or construction process itself. In addition to the use of more typical and catastrophic failure case studies, such as the Hyatt Regency Walkway Collapse (Kansas City, Missouri), and the L'Ambiance Plaza Collapse (Bridgeport, Connecticut), the course makes extensive use of the Montreal Olympic Facility design and construction to demonstrate how deficiencies in the design and construction process can lead to extreme constructability issues and exorbitant cost overruns. The author also shows how the inclusion of the case studies addresses some of the more difficult areas to address in the Accreditation Board for Engineering and Technology (ABET) evaluation criteria, such as the understanding of the impact of civil and environmental engineering solutions in a global and social context.

Fully biodegradable composite materials fabricated using natural fiber reinforcements and biopolymeric matrices derived from poly(β-hydroxybutyrate) (PHB) and PHB- co-poly(β-hydroxyvalerate) (PHBV), are being investigated as potential alternatives to traditional residential construction materials. The materials are envisioned to be rapidly renewable by using biogas from their anaerobic biodegradation as the feedstock for microbial production of the biopolymer and using plant-based materials for composite reinforcement and fillers. These biobased composites are being engineered to satisfy acceptable stiffness, strength, ductility, and in-service durability performance criteria while maintaining the propensity for rapid out-of-service anaerobic biodegradation. In this paper a brief overview of research on material development, mechanical properties, and multiscale modeling, as well as moisture absorption and long-term durability of PHBV-wood fiber filled composites with and without fiber treatments is given. This research is an interdisciplinary collaboration between structural, environmental, and chemical engineers.

Many studies have shown that fiber-reinforced polymer (FRP) laminates are an effective alternative for structural retrofit and repair of insufficiently reinforced concrete members; however, achieving the full tensile capacity of the externally bonded FRP is often very difficult. This is especially true when FRP is used on elements where there is inadequate length to develop the full tensile strength of the FRP laminate, leading to premature debonding failure. Anchorage systems attempt to mechanically restrain the FRP or improve the FRP-to-concrete bond, thus reducing the length required to develop its full design strength. Many types of anchorage systems have been tested by different investigators, but mixed and inconclusive results have been presented. Additionally, no evidence exists to show that one particular type of anchorage system is completely effective in developing the full tensile strength of FRP. The lack of conclusive results is exacerbated by the absence of a consistent testing procedure for evaluating anchorage strength and a system for categorizing the purpose of the anchorage system, despite the current design guide's recommendation that anchorage testing should precede the strengthening of a structure with FRP. An overview of previously tested anchorage systems is presented along with applicable testing procedures from existing literature. The limitations of each anchorage system are mentioned with respect to specific structural strengthening applications. The existing anchorages are then categorized according to their specific application to FRP anchorage, and the applicability of testing procedures to each anchorage category is discussed. Finally, the need for systematic testing is discussed and potential research topics are explored.

Concrete has been used as the major construction material for many years in the field of civil engineering because of its high compressive strength and constructability. In order to restrict the growth of micro cracks, Carbon-Nanofibers (CNF's) were added to the concrete mix. The concentration of CNF in concrete mix also yields higher strength and ductility. Uniaxial compression tests on CNF concrete were conducted to find the best CNF concentration. To evaluate the performance of CNF concrete, experiments were conducted at the University of Houston (UH) and an inelastic non-linear fiber beam element with bending, shear and axial force interaction for the analysis of reinforced concrete structures was developed and evaluated to correlate with the experimental results.

Post-earthquake functionality of essential facilities, like hospitals, relies heavily on operation of its nonstructural components such as piping systems, fire suppressors, elevators, and medical equipments. This paper presents the findings from experiments performed on welded and threaded hospital piping subassemblies, with and without cable braces, subjected to various intensities of equivalent inter-story drift. The subassemblies were tested between a stationary frame and a biaxial shake table with an input motion compatible with ICC-ES AC156. A simplified computational model was developed in SAP2000 and calibrated with the experimental data. The model was used to investigate the dynamic characteristics of the piping subassemblies. The effective stiffness of the cable bracing system was found from the computational model to be approximately 10% of full stiffness due to initial looseness that typically exists in piping bracings.

As part of the project entitled "NEESR-GC: Simulation of the Seismic Performance of Nonstructural System," a series of system-level full-scale experiments of ceilings-piping-partition systems will be conducted at the University of Nevada, Reno NEES Site. This project is aimed at understanding the seismic response of these systems and their interaction with each other and the parent structure. A two-story, two-bay steel braced frame spanning across three biaxial shake tables was designed as a Test-Bed structure to simulate a variety of dynamic environments. After introducing the design considerations of the Test-Bed structure within this paper, the method proposed to develop the shake table drive motions is explained. To obtain the drive motion, a transfer function (TF) was formulated for a multi-support dynamic system under differential support excitation and combined with a TF previously developed for target floor acceleration of a generic structure. A suitable high-pass filter was suggested to limit exerted demands on the shake tables.

In this study, 38/ 34kV Highway N Substation, St. Charles County, Missouri was analyzed with a finite element model (FEM) for its vulnerability during earthquake excitations. Every component of the substation was modeled with due considerations of mass density, stiffness and geometries. Based on the FEM, modal analysis was conducted to identify the natural frequencies of structures along with their corresponding mass participation factors. In response spectrum analysis, the dynamic responses of main components such as `rigid' buses and switches were evaluated. In time-history analysis, both site-specific synthetic ground motion and spectrum compatible ground motion were considered. The numerical results under both ground motions were compared and the magnitude and location of the maximum moments in each case were identified.

Design, assessment and prediction of the performance of structures and infrastructures based on component analysis have been the conventional methodologies enforced by the specifications. Nevertheless, system-based performance indicators can provide more efficiency and dependability in performance-based design, assessment, and prediction of structures and infrastructures. The objective of this paper is to provide a general overview of performance indicators applicable to civil structures and infrastructures. Definitions and formulations of selected performance indicators are presented. Information on what level (section, component, system, system of systems) these indicators are useful is provided. Interaction between life-cycle cost and lifetime performance is presented.

The drive for alternative energy sources has resulted in many proposals for offshore wind farms in the United Sates. Offshore wind turbines are subject to harsh environmental conditions including but not limited to simultaneous action of extreme wind and wave loading as well as hurricanes. From a structural reliability point of view, there are several failure mechanisms of a wind turbine such as blade or other component fatigue, tower local or global buckling and foundation failure such as sliding. In addition, there are several mechanical components and a control mechanism that could be studied from a traditional reliability point of view. Given the complexity of the problem which involves a combination of structural and electromechanical systems, an approach based on annual power generation is considered here to evaluate the performance of offshore wind farms.

As an important clean and renewable energy, tidal energy is attracting more and more attention, and various plan and projects are being made worldwide to generate power. First, this paper discusses the current status of tidal power generation, and then describes Marine Hydrokinetic (MHK) energy turbines and related facilities. Then, the paper proposes performance indicators of the power generation systems in aspects of their power output estimate and reliability.

Transmission tower networks, consisting of lattice support towers and conductor cables, play an important role in the infrastructure system of many countries throughout the world. Lattice support towers are typically comprised of two different components: the vertical tower body and the horizontal conductor support cross-arms. Much research has been directed towards the evaluation of aerodynamic coefficients of the compact lattice form typical of the vertical tower body sections of transmission towers, which now can often be calculated (based on solidity ratio) to an acceptable accuracy. However, the horizontal lattice form of the conductor support cross-arms have not been studied in depth. In this paper, results from wind tunnel tests on a typical conductor support cross-arm are used to show that the aerodynamics of these types of horizontal lattice sections are not as easily predicted as those for vertical lattice sections. The results from the wind tunnel tests are compared to the values calculated through the use of ASCE Manual No. 74: Guidelines for Electrical Transmission Line Structural Loading, and reasons for these discrepancies are discussed. This comparison is used to illustrate two examples where Manual No. 74 may or may not provide a conservative design estimate for tower and line loading at skewed wind directions, depending on the relative contributions of the cross-arm and tower body sections to the total wind loads. This is attributed to the underestimation of the wind loads on the cross-arms at skewed wind directions. Examples are used to show that the ratio of cross-arm area to total structure area is important for the consideration of the design wind direction. In light of the emphasis on efficiency in the world of transmission tower design, recommendations towards an improved evaluation of cross-arm force coefficients are provided.

Connections between steel and concrete were not yet covered by codes until 2009. A European Technical Specification was published in 06/2009 with the aim to provide design rules for anchorages to concrete. This work of the European committee CEN TC 250, published as prCENTS 1992–4, led to a European Technical Approval (ETA) for anchor channels. Following the technical approach, a fib design guide was developed. This design guide will be published approx. in 2010 and gives design rules for several fixing methods such as dowels, headed studs and also anchor channels. This fib design guide will present the basis for a future international approval for anchor channels. This approval will be issued approximately in 2010/2011. In the present state of the art, technical approvals basing on test results only confirm a defined amount of applications with definite boundary conditions. A building product (here: a fixing construction) can only be used in accordance to these regulations. Diverging from the boundary conditions of the technical approval means using a non licensed product e.g. to infringe the approval. With a design guide which describes the general application of a product, a universal calculation becomes possible without constraints towards boundary conditions. A technical approval then "only" proves the applicability of the design rule and the suitability of the product to this documented state of technique. It should be a clear aim of the holders of approvals to support the efforts obtaining design guides and standards to document the technical state of the art which then can be incorporated into technical approvals. This paper gives an overview of these new methods of calculating the resistance of fixing constructions, in this case: anchor channels. The practicality of these formulas on the products is stated by an adequate approval. The design rules are explained and the experimental results are illustrated.

For many years, tubular steel poles have been utilized in various industries. A popular support structure for the sports lighting industry due to their strength, reliability, and ease of installation, the steel pole has served the industry well. The industry has steel pole installations that have been in service upward of fifty years. However, in recent years, there have been numerous failures of sports lighting structures. While manufacturing, installation, and maintenance issues have contributed to these failures, design issues have also contributed. Careful attention to the design requirements for these structures will prolong their lifespan and ensure public safety. As with any steel support structure, consistent application of a design standard is critical. Historically, the sports lighting industry has not utilized a consistent standard for the design of its support structures. Some pole structures are purchased to meet a recognized structural code with appropriate load and strength safety factors and others are sold as general "commercial" design. Design issues include improper factors of safety, inadequate base plate design, insufficient anchor bolts, improper application of wind and wind coefficients, undersized welds, improper material specifications, and ignoring fatigue issues. Standardizing the design process will improve the safety of these structures and reduce confusion during the procurement process. This article will present current methods used to design sports lighting structures to the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaries, and Traffic Signals, 5th Edition, 2009. The document is specifically for pole structures, specifies factor of safety, addresses fatigue issues, and addresses wind induced vibration issues.

This paper presents the results of a preliminary numerical investigation into the interaction between precast concrete cladding systems and moment resisting frames. Macro-scale models of cladding systems are implemented in existing lumped plasticity models for moment resisting frames. Different failure mechanisms and various configurations are considered in order to show the effect of the entire cladding system upon a structure's seismic behavior. Several parameters are varied in order to establish their associated influence on the overall structural response. Results show that it is clearly more advantageous to have a failure mechanism governed by the connection than one governed by either the panel or the frame. An experimental program is now underway building on what has been learnt from the parametric investigation. The authors intend to continue the research to successively develop improved or innovative low-damage cladding-moment resisting frame systems. They also aim to produce simple design tools that provide easy inclusion of the seismic effects of cladding-frame interaction.

Over the past two decades fatigue failure of cantilevered highway sign and traffic signal structures are increasingly being reported around the United States, primarily due to wind induced oscillations. For aesthetic reasons many of these structures are built with multisided tubular sections with sharp corners. Fatigue performance of fillet-welded tube-to-end plate connections in multi-sided sign/signal structures were evaluated by laboratory testing and parametric finite element analyses (FEA). Seven full size galvanized sign/signal structure specimens having eight sided cross section were fatigue tested under constant amplitude loading simulating wind induced aero-elastic galloping oscillation. Fatigue cracking in multi-sided sections mostly initiate at the bend corners of tube-to-end plate welded connection, and may appear early in service. Flexibility of the end plate, the number of sides, and the corner bend radius are the important parameters that affect fatigue resistance of multi-sided tubular structures. The existing specification does not address the effects of the connection geometry on their fatigue design. The experimental and analytical studies established the fatigue design provisions of tube-to-end plate connections in multi-sided sign and signal structures.

The current practices used in blast design for reinforced masonry are largely based on single-degree-of-freedom analyses. These analyses use a resistance function, i.e., a load-deflection response, to define the behavior of the structural system (in this case, a wall). This paper presents an improved method for determining the resistance function for reinforced masonry walls. The new approach is capable of more accurately capturing the true behavior of a reinforced masonry wall loaded out-of-plane. The improved method is compared to current blast design practices and test data.

The U.S. Army Engineer Research and Development Center (ERDC) is currently conducting material research on advanced cementitious composites with randomly distributed fiber reinforcement. The successes of the research are well documented, and unconfined compressive strengths on the order of 200 MPa are not uncommon. However, as with most cementitious materials, these materials exhibit a brittle tensile failure response. To improve the material's response to blast and ballistic loads, the tensile capacity must first be quantified and subsequently enhanced. This paper presents findings of three laboratory experimental series conducted to characterize, quantify, and enhance the tensile failure response of a new rapid-set, field-curable geopolymer concrete that offers distinct advantages over other cementitious composites. Individual fiber, single fiber pull-out, and direct uniaxial tension experiments were conducted for a geopolymer concrete capable of achieving 44 MPa in 24 hours, and 62 MPa in 28 days in ambient temperatures with no additional curing requirements. Three fiber types were examined at various embedment lengths in the matrix. Load versus displacement curves are presented for each type of fiber, as well as the mechanical properties of the fiber itself. Direct tension samples were cast with each type of fiber at 2% by volume in the matrix and tested in a direct uniaxial experiment. The corresponding load versus displacement responses are presented and discussed. Key steps are identified for ongoing research to optimize the fiber matrix interaction, thus maximizing ductility for enhanced material response to tensile forces.

In this paper we present a comparative study of precast prestressed concrete façade panel analysis using single degree of freedom (SDOF) and finite element methodologies. LS-Dyna was used to develop the finite element formulation. The goal of the study is to identify simple, easy and economical analytical procedure to determine the reaction loads for the precast panels. This study was motivated by a real project, with the requirements dictated by UFC 4-010-01 DoD Minimum Antiterrorism Standards for Buildings. The reaction forces obtained from the two analysis methods are juxtaposed and the differences are discussed. This paper presents a summary of our findings, conclusions and recommendations.

This paper presents the results of testing and analytical developments sponsored by the U.S. Department of State to provide recommendations for support connection design of through-edge bolted laminated glass. Design equations are presented that capture the capacity of the through-bolted laminate material in reaction to in-plane membrane induced loading. A simple analytical treatment of edge-clamping and tear-out resistance forces is presented. Specific recommendations for bolt pre-load and gasket characteristics are presented. Test data are presented to support the validity of the calculations and recommendations. The various tests were executed by the Force Protection Branch of the Air Force Research Laboratory (AFRL) at Tyndall Air Force Base, Florida and Southern Research Institute in Birmingham, Alabama.

The Federal government mandates blast protection for all of its facilities, which can be particularly challenging for existing buildings, especially those of historic interest. The blast protection of historic façades is one of the most challenging aspects since historic window structures offer little blast resistance and it is critical to preserve the existing aesthetic. As a solution to this issue, Hinman Consulting Engineers, Inc. (Hinman) investigated the potential application of a window cable catchment system as a means of cost-effective blast protection. This paper discusses the unique design features and analytical modeling of the cable system on exterior windows to resist potential external blast threats. The cable catchment system consists of steel cables installed behind glass panes and anchored into the structural system above and below each window. A three-dimensional finite element (FE) model was developed to investigate the performance of the window catchment system. This analytical model was then validated by the results of shock tube tests sponsored by the General Services Administration (GSA). Finally, the key parameters of interest in the performance of different cable system configurations including the interaction between cables and glass panels, details of the system configuration, and the reliability of the system are outlined. The results of this study show that the cable systems demonstrate considerable potential to provide efficient blast protection for existing window systems.

The application of blast resistant design principles has become more prevalent for buildings due to risk of accidental industrial explosions and terrorist attack. This has precipitated to more attention to exterior doors subjected to blast loadings, including the publication of ASTM F2247-043 "Standard Test Method for Metal Doors Used in Blast Resistant Applications (Equivalent Static Load Method)". However, the evaluation of doors subject to blast loadings lags significantly compared to the documented analytical tools and methodologies for other structural components, as well as windows. This paper lists and compares several techniques for evaluating doors subject to blast loadings, including testing and analytical approaches. A recent research program has generated static and dynamic shock tube test results for various low-range hollow metal door types. The static data was used to develop single-degree-of-freedom models which were used to predict the door response for several dynamic tests. The comparison of the analytical predictions and test data provides a basis to adjust the dynamic model to better predict the response of the subject door. The results of the effort may allow blast designers to utilize existing static data for commercial doors to develop reasonable dynamic models for blast evaluations.

The flood loads that are covered in Chapter 5 of ASCE 7-10 have not changed in any substantive way since ASCE 7-05. The same flood forces are discussed with formulas exactly as they were in ASCE 7-05. The issue for the designer using the flood standard is in trying to understand the unknowns inherent in the formulas so they can make good decisions about how to apply the formulas to real problems. The paper will describe the issues that designers must consider for each of the flood forces delineated in ASCE 7-10 and where continued work needs to be done to improve the understanding we have about the magnitudes of flood loads. The paper will also offer guidance on the magnitude of the load factors used in strength and allowable stress design situations.

The new edition of ASCE 7, ASCE 7-10 Minimum Design Loads for Buildings and Other Structures, contains new, revised and updated provisions for dead and live loads to be used for structural design since the previous edition, ASCE 7-05, was published five years before. The provisions of this Standard, adopted by reference by building codes across the nation, impact the structural design of nearly every building in the country, and are used by all who are responsible for these designs. New material has been introduced which provide for the live load requirements for structures not previously covered in prior editions, specifically for helipads and screen enclosures. Revisions to the live load requirements for balconies and decks, roofs, and vehicle barrier systems have been made which better define the nature of live loads acting on these particular occupancy areas or structural elements. There has also been a revision to the live load reduction provisions for structural members in one- and two-family dwellings supporting more than one floor load. The rationale for the new live load provisions and for the substantial technical revisions to previous live load requirements are presented, relating the discussions and comments by committee members during the five-year balloting period since the previous Standard was published in 2005, and incorporating guidance from the Commentary to the Standard where this helps to clarify some of the new or revised loading requirements.

The fundamental load combination requirements for strength design (or load and resistance factor design) appearing in Section 2.3 of ASCE Standard 7-10 incorporate major revisions, among them the treatment of self-straining actions, fluid and soil loads, load combinations for extraordinary events, and probability-based load requirements for non-specified loads. The last item is based on suggested reliability levels for the new performance-based design procedures in the Section 1.3.1 Commentary. The Commentary to Section 2 of ASCE Standard 7-10 presents the technical basis for these changes. Since the basis of the traditional allowable stress design combinations was purely judgmental, the ASD combinations in Section 2.4 have been brought into alignment with the strength combinations in Section 2.3, which have a rational reliability basis.

Since its inception, the purpose of the ASCE 7 standard has been to set minimum design loads for buildings and other structures, such that they would provide safe and reliable service. It has never been intended to comprise a complete design standard, deferring for the most part to other industry standards for requirements for determination of strength and detailing. Because reliable seismic performance is as much dependent on structural detailing as it is strength and stiffness, the seismic chapters have also included detailing requirements as a condition of loading determination. The 2010 revisions to Chapter 1 of the standard take a major step towards conversion of the document into a comprehensive design standard with the introduction of a performance-based design alternative. The Performance-based design process is one of setting performance criteria then evaluating the ability of a design, either through testing, simulation or a combination of these, to meet these criteria. As such, design loading, in the conventional sense is not used, but rather design scenarios, which include consideration of inherently uncertain loading events and equally uncertain structural response, must be evaluated. Initially, the performance-based option is likely to see most application in seismic and force-protection design, where it already experiences wide use. However, as engineers become more familiar with this approach and the freedom it provides, it will likely see wider use with satisfaction of performance criteria being the primary objective of design.

ASCE 7-10 "Minimum Design Loads for Buildings and Other Structures" contains several changes regarding wind loads. The major editorial change is a complete reorganization to a multiple-chapter format as done previously for seismic loads with the objective being to make the provisions easier to follow. Technical changes include the introduction of new wind speed maps to be used with a 1.0 load factor for LRFD and a 0.6 load factor for ASD, the reintroduction of Exposure D for water surfaces in hurricane-prone regions, and revised wind-borne debris regions. A new simplified procedure for buildings up to 160 ft has been added based on the provisions for buildings of all heights.

UFC 3-340-02, "Structures to Resist the Effects of Accidental Explosions," was recently approved by the Services. Publication of UFC 3-340-02 represents the culmination of a 5-year, Department of Defense Explosives Safety Board (DDESB) effort to update DoD's mandatory blast design requirements for explosives safety applications, as provided in Army TM 5-1300/NAVFAC P-397/AFR 88-22 (TM 5-1300), revision 1, November 1990. As an unlimited distribution document approved for public release, TM 5-1300 has long provided both government and private sector engineers with an invaluable source of blast effects and loading data and with step-by-step procedures for blast analysis and design. UFC 3-340-02 continues this tradition, using straightforward guidance and examples to illustrate and explain protective construction design requirements. While based upon TM 5-1300, UFC 3-340-02 incorporates several beneficial changes to the manual's reinforced concrete design requirements. This presentation provides an overview of the more significant of these changes. Anticipated, future revisions and additions to other chapters also are presented and discussed. UFC 3-340-02 may be downloaded from the Whole Building Design Guide website. For users who have the DPLOT computer program, readable versions of some manual figures also are available through this website. In 2003, the Department of Defense Explosives Safety Board (DDESB) established a Technical Working Group to revise the tri-service blast design manual, "Structures to Resist the Effects of Accidental Explosions," Army Technical Manual 5-1300/NAVFAC P-397/AFR 88-22. As an unlimited distribution document approved for public release, TM 5-1300 provides both government and private sector engineers with an invaluable source of blast effects and loading data and with step-by-step procedures for blast analysis and design. This paper provides a status update of TWG activities and plans for future work. Emphasis will be given to revisions to chapter 4, "Reinforced Concrete Design." Anticipated revisions and additions to other manual chapters also will be presented and discussed.

This paper presents a brief overview of historical and current practices for the design of windows and glass curtain walls subjected to short-duration, high-energy loading from blast shock waves. General discussion is provided that describes typical treatment of force-displacement relationships, boundary conditions, pre- and post-cracked behavior of laminated glass, and failure criterion. Various practical examples from design projects are presented that demonstrate limitations or misapplications of methods that are often used in blast engineering. Developments from parallel research are cited to highlight some of the current deficiencies.

Current United States design provisions for post-installed mechanical anchors are typically tailored toward conventional static and dynamic load regimes, such as seismic and wind loads. In fact, the dynamic behavior of post-installed anchors in reinforced concrete is primarily based on seismic loading effects. Yet, dynamic loads that produce extremely short duration impact, such as air-blast, are not addressed in design criteria, including anchorage to concrete. Usually this is not an issue as most structures are not designed to withstand these forces; however, when blast applications are considered, there is no clear method to determine how these anchors will perform. With little research on the behavior of anchor bolts under impact loads, in comparison to other long term cyclical loadings, properly designing concrete anchorage to meet these demands is difficult.

In 2003, the Blue Ribbon Panel on Bridge and Tunnel Security issued its recommendations for risk assessment and mitigation of bridges and tunnels. The report gives general guidelines to help decision makers improve the security of bridges and tunnels. However, the actual implementation can be highly dependent on the methods used to carry out the assessment. Variability in risk assessments may prevent limited funding from going to projects where it is needed most. The factors that determine the relative risk of a bridge include: Occurrence — the likelihood of an event taking place, whether intentional or unintentional; Vulnerability — the consequences of an event; and Importance — the tangible and intangible value of the asset. The product of weighted scores for each of these factors determines the relative level of risk. A real life example of risk assessment is presented with special attention paid toward the calculation of the weighted score for vulnerability. The threats listed in the Blue Ribbon Panel report were used to determine the consequences of various terrorist tactics of a real-life group of movable bridges over a waterway used for shipping. Potential consequences of attack included damage to bridge, downtime of bridge and waterway, human casualties, and collateral damage to surrounding area. Conventional blast resistant engineering methodology, more commonly used on buildings, was used where applicable and compared to high fidelity modeling. The damage expected on each component in the bridge was used to estimate the vulnerability scores. The Blue Ribbon Panel report discusses possible mitigation measures and how to prioritize their implementation. Mitigation measures usually focus on reducing either occurrence, though deterrence measures, or vulnerability, through hardening or increasing standoff. Both types of mitigation measures are applied to these real life examples as a model of how bridge owners can most effectively reduce terrorist risk on their assets.

As an original member of the Blue Ribbon Panel (BRP) that developed the "Recommendations for Bridge and Tunnel Security" published in September 2003 by the Federal Highway Administration and AASHTO the author reviews the use of this and other subsequent homeland security related risk assessment guidelines in practice by sharing observations on how threat and vulnerability assessment (TVA) of existing bridges has evolved and where it may be going. The paper focuses on the original objectives of the BRP recommendations, how they align with the latest National Infrastructure Protection Plans for the Transportation Sector, how well their application has worked in practice, whether they assist DOTs and other agencies in obtaining DHS grant funding for security related projects, their application to rail bridges and tunnels, and why they are an essential part in the decision making process for implementing security improvements and countermeasures for bridges and tunnels. This will be discussed in the context of a case study. Since the BRP recommendations were issued best practices for TVAs conducted by some state DOTs have given way to simplified decision tables for risk equations and risk values used with electronic spread sheets that can be used to sort security mitigation costs for critical bridges using cost-benefit factors. The prioritized mitigation projects for existing bridges are then included in the rehabilitation project scope for each bridge when they are contracted out based upon the DOT's state-of-good-repair program. Many states, however, have not yet embraced the BRP recommendations based upon the judgment that funds for repairing deficient bridges are their first priority and they will not deal with security related issues until those needs are addressed. Independent of the availability of funds to repair or secure bridges in a given state or agency, there is a need to prioritize the criticality of the bridge and tunnel inventory because whether a bridge fails due to deterioration, an accident, natural hazards, or intentional attack, the owner should know where the first dollar of funding should be spent, be it for repair of deficiencies or for hazard reduction.

In recent times, the use of sandwich panels as sacrificial claddings in the blast/impact protection of structural systems has been the subject of much investigation. Popular sandwich panels systems include core consisting of regular metallic-lattice and metallic-foams. These systems have been proven to be beneficial when used as sacrificial claddings because of their propensity to sustain large deformations and plastic energy dissipation. This allows the panels systems to absorb more energy than a single metallic plate consisting of the same mass. In case of metallic-lattice cores, energy absorption capacity depends on the topological structure and the optimal topology for these cores is not yet established. In this study the effect of topological parameters on the performance of sandwich panel systems with metallic-lattice cores is investigated. Nonlinear finite element analyses of cladding systems with different core topologies are carried out to investigate the effect of core parameters on their performance. The simulation results shows that the performance of the sandwich panel systems is highly influenced the topological parameters.

There are a few related researches that provide well-defined models to predict the damage size under close-in explosions. This paper presents a prediction of the damage size experienced by reinforced concrete (RC) slabs subjected to close-in detonations using numerical data and a neural network—based model. To train and validate the artificial neural network (ANN), a data base is developed through a series of measurements of the damage diameter (crater/spalling) size induced in reinforced concrete two-way slabs under blast loads. The data was obtained by performing various simulations using the dynamic explicit finite element code LS-DYNA. The principle parameters controlling the breaching size are charge weight, standoff distance, and slab thickness, which were used to develop the ANN training input data set. The trained and validated neural network was used to develop an ANN model capable of predicting the breach size of concrete slabs under close-in detonations.

A type of enamel coating that contain hydraulically reactive calcium silicates have been developed to improve the performance and service life of steel used as reinforcement in concrete structures. To demonstrate the effect of enamel coating on the mechanical performance of concrete structures subject to blast loading, two wall barriers with identical dimensions, which were often used to keep the terrorism attack (such as car bomb attack) away from critical buildings, were fabricated and tested in a military base. One of the wall barriers was reinforced with coated rebar and the other with regular rebar. Four equivalent TNT weights, 4 lbs, 10 lbs, 30 lbs and 45 lbs explosive were applied to observe the deformation, cracking and failure mode of the two barrier walls. Generally, the test results indicate that the barrier wall reinforced with enamel coated rebar has much better integrity than that with regular rebar: fewer cracks on the front and back faces of the wall, more stress transferred to the steel rebar, and mitigated catastrophic failure of the wall. The new coating can be of great value in increasing the performance and the service life of defense-critical infrastructure.

Dynamic modeling and field testing of full-scale window systems using a shock tube are presented in this paper. The modeling includes numerical simulations using LS-DYNA. The dynamic response in terms of the center deflection as well as the dynamic reactions around the window frame is measured and compared to the modeling results. In addition to the positive phase of the blast loading, the response of the window system to negative phase is also investigated. The modeled dynamic deflections and reactions correlated well within the first few peaks of the measured response of the window systems. The results of this study can be used to improve the existing methods for predicting the dynamic response of windows under blast and to provide affordable design recommendations.

The paper presents an overview of the issues related to the application of tower crane loads to buildings under construction. Intended for the structural engineers who design these buildings, it provides a primer on the derivation of these loads by the crane installation designers. Based on a review of tower cranes installations designs executed in New York City, the author finds that the attachments at the top of the structure can develop horizontal loads of same order of magnitude as the wind loads used for the base building design. Interaction and responsibility between crane and building engineers is examined. The building designers are better suited to evaluate the effects on the main lateral load resisting system. The crane installation designers need to use more consistency and clarity when presenting the loads for evaluation by the engineers of record.

On 16 February 2004, one of two identical launching gantries used for the parallel construction of the approach viaducts for the I-280 Maumee River Bridge crossing collapsed. The collapse killed four workers and injured four others. Each launching gantry consisted of two overhead steel trusses and a central lower steel-box-girder underbridge. The trusses spanned between adjacent piers and supported precast concrete segments for post-tensioning. Once a concrete span was post-tensioned, the trusses were moved forward across the newly completed span and the underbridge, which was advanced before the subsequent span. The process was then repeated. Simpson Gumpertz & Heger Inc. (SGH) was on site after the collapse to observe and record the debris in place and as it was removed. SGH also had access to the second, essentially identical, launching gantry in its position on the approach viaduct. From review of the two launching gantries and construction records, it was clear that modifications were made to the method and extent of anchoring the gantries to the new bridge. The results of our analysis indicated that the failure to install prestressed rods at the stools supporting the rear legs of the gantry trusses meant there was insufficient resistance to movement when the underbridge was reversed backwards into a pier. This paper presents our investigation of possible failure sequences and their correlation to the facts observed on site.

There currently is no peer reviewed or broadly accepted protocols for conducting vulnerability assessments on the structural frame of buildings. This lack of protocols and lack of uniformity in vulnerability assessments is particularly important when the building is located in an area that might be subject to a natural hazard event such as a hurricane, a tornado, an earthquake or a flood. The design firm conducting the assessment is required to determine what might constitute a vulnerability based on their knowledge of the building, the hazard, or the owner's stated operational intent during or after any or all of these potential hazards. The vulnerability of the structural frame of a critical facility (or any other building) depends on: (1) Age (which influences the codes and standards that were available at the time of design) (2) Quality of design and construction (3) Type of construction (wood, concrete, steel, masonry or combinations of these and other materials) (4) Risk to the structural frame from events such as an earthquake, a hurricane or a tornado, or from a man-made hazard such as a bomb blast (5) Number and extent of past modifications to the building (6) Deterioration (corrosion decay, termite damage) These issues are crucial in understanding how vulnerable any particular building is to an unexpected load (i.e. hurricane or bomb) or to an expected load but one that has not ever occurred or not occurred recently. These issues are very important for the vulnerability assessment team to understand before they can state with some confidence that the building that is being assessed can be expected to perform in some stated manner when future catastrophic events might occur. This paper will explore what a vulnerability assessment protocol for the structural frame should include, how a standardized protocol would be helpful to both the engineering profession and the building owners, and how such a protocol might reduce potential liability and misunderstandings with owners or future building buyers if a "standardized gage" could be developed that would give an owner a comparative basis for understanding the condition of the subject building vs. the condition of others within the use type (critical facilities) or construction type (wood, concrete, steel, etc.).

This paper presents a preliminary protocol for assessing the wind vulnerability of roof systems and rooftop equipment on critical facilities. Such facilities include emergency operations centers, fire and police stations, hospitals, jails, nursing homes, power plants, schools, water supply and treatment plants, and other buildings that are essential for the delivery of vital services or protection of a community. Roof systems and rooftop equipment are key building elements that are frequently damaged during high winds. Leakage from damaged roofs or rooftop equipment has interrupted numerous facility operations, and many critical facilities have been forced to evacuate due to roof leakage. By identifying wind vulnerabilities, mitigation efforts can be undertaken to avoid future damage and disruption of services. The preliminary protocol can be used by design professionals to systematically guide their assessment of these building elements.

One of the most vulnerable areas for critical facilities in severe windstorms is the exterior building envelope. Loss of roofing, cladding or glazing exposes building occupants to life safety risks and renders facilities inoperable at the time they are most needed. Engineers, Architects and Building Professionals are in need of guidelines for how to assess building envelopes to predict performance during severe windstorms and identify required upgrades. This paper outlines the necessary steps for assessing severe windstorm threats to cladding and glazing on existing critical facilities. This outline includes developing appropriate design criteria for wind pressure, windborne debris and water infiltration, as the code mandated minimum may not be enough, depending upon the location and use of the facility. A staged analysis approach is presented to allow the user to determine the condition of existing cladding and glazing. An initial assessment would include a review of project documents and a visual survey. Higher level assessments include field testing and destructive analysis. The included methodology for assessing and analyzing various cladding and glazing systems provides the reader with guidance for make a determination about the resistance of components and overall systems in severe windstorms. The assessment can then be used to identify needed upgrades and plan for safe operations during severe windstorms.

This paper proposes an innovative fully probabilistic Performance-Based Hurricane Engineering (PBHE) approach for risk assessment and design of structural systems located in hurricane-prone regions. The methodology is based on the Total Probability Theorem and disaggregates the risk assessment analysis into independent elementary components, namely hazard analysis, structural characterization, interaction analysis, structural analysis, damage analysis, and loss analysis. The proposed PBHE methodology accounts for the multi-hazard nature of hurricane events by including the separate effects of, and the interaction among, hurricane wind, flood, windborne debris, and rainfall hazard. A review of existing models with the ability to describe the different sources of hazard is performed, and a consistent vector of intensity measures for hurricane hazard analysis is proposed. The PBHE approach illustrated in this paper represents a first step toward a rational methodology for risk assessment and design of structures subjected to multi-hazard scenarios.

The net effect of changes incorporated into ASCE 7-10 Minimum Design Loads for Buildings and Other Structures for wind design is often described in broad terms. These include use of uniform recurrence intervals for wind speed contours and removal of conservatism in the hurricane prone region. This paper will explore the net effect of changes on calculated wind pressures for specific locations both within the hurricane prone region and outside of the hurricane prone region. Design velocity pressure calculated using ASCE 7-10 and ASCE 7-05 will be compared and implications on relative vulnerabilities of buildings (between those designed under ASCE 7-05 and ASCE 7-10) will be explored.

This paper presents an overview of the damage from the 2010 Chile Earthquake observed by a field reconnaissance team from the Mid-America Earthquake Center. Seismic performances of structures in Santiago, Biobío, and Maule regions in Chile are summarized based on field observations and discussions with researchers and city officials. In addition, post-earthquake analyses of a damaged bridge and a building structure are presented. The analyses are carried out with detailed documentation from the field and the acquired design drawings of the structures. For the building structure, the focus of the analysis is to understand the effect of masonry infill walls on the shear force demand of columns. The analysis results confirm that the infill walls of the building may have caused the damage to columns by increasing the shear force demand. For the bridge structure, the effect of seismic bars on the bridge response is investigated. The seismic bars in the bridge reduce the displacement demand of the superstructure by increasing the energy dissipation capacity of elastomeric bearings.

Field observations and plausible reasons of damaged bridges are presented and their implications to bridge design are discussed. In general, bridge substructures behaved satisfactorily except that a few columns suffered shear failure. Reinforced concrete shear keys served their design purposes, performing well when they functioned as part of the lateral restraint system at the bottom flange of girders. Vertical seismic bars were widely used to restrain the vertical motion of decks and they also performed well. Lateral steel stoppers were also used to provide vertical and lateral restraints on girders but were largely unsuccessful due to their weak connection to capbeams. Many spans of precast, prestressed, discontinuous girder bridges with continuous decks fell from their supports due likely to significant rotation of their superstructure. Other types of bridge damage were related to ground shaking, ground settlement and liquefaction-induced lateral spreading.

The earthquake that shook the island of Hispaniola on January 12, 2010 devastated Haiti. The resulting damage was widespread due to the construction methods, poor material quality and lack of rigorous design procedures. Post-event reconnaissance has brought to light deficiencies in all these areas. Construction, especially residential, is typically completed by the building owner who may or may not have the necessary skills to design or build safe structures. Very few structures are designed by an engineering professional. The two most common construction materials are masonry block and reinforced concrete. Building response to the ground shaking is demonstrated through damage surveys in downtown Port-au-Prince and Leogane and specific case studies generated through reconnaissance efforts which highlight the infrastructure problems which led to the deadly structural performance.

Performance of reinforced concrete buildings in Viña del Mar, Chile following the M7.8 1985 earthquake led to changes to the Uniform Building Code (UBC-94) and the American Concrete Institute Code for design of reinforced concrete buildings (ACI 318-99). In 1996, Chile adopted, with minor modifications, the ACI 318-95 Code. Reinforced concrete buildings are the predominant form of construction in Chile for buildings over four stories. Over the last 10 to 15 years, a construction boom similar to that in the US and other countries resulted in the construction of a substantial number of new buildings. Thus, the Feb. 27, 2010 earthquake provides a unique opportunity to assess the performance of modern reinforced concrete buildings designed using modern codes similar to those used in the US. Preliminary observations on building performance and the potential impact on US codes and practices, particularly with respect to ACI 318 seismic provisions, is presented.

High strain dynamic pile testing is widely spread in the pile driving industry. Evaluation of pile capacity from field testing is the primary application of the dynamic method, but the accuracy and the area of utilization (soil conditions and pile type) of this method are vague. The application of hardware and software is only partially established because different hardware and software produce substantially diverse pile capacities. Engineering evaluation of pile capacity is not established at all. Statistical analysis of pile capacities is unable to find out applicability of the method to specified site conditions. Uncertainties are available in signal matching technique and comparison of the results of static and dynamic tests. Quality of dynamic measurements together with the software features and the engineering factors affect pile capacity obtained by dynamic testing. Engineering research is needed to ascertain the accuracy and the area of application of high strain dynamic pile testing.

A low-rise high school building constructed on the site of an existing construction debris landfill included initial site preparation using Deep Dynamic Compaction (DDC) to mitigate potential future settlement of the building's first-floor slab on grade. Within the first six years of building occupancy, the first-floor slab on grade settled up to 6 in. because of consolidation of the landfill. Differential settlement of the first-floor slab relative to the pile-supported building frame caused severe distress to the interior partition walls, buried storm and sanitary drainage systems, interior piping, mechanical and electrical systems, and other finish work. This paper presents our evaluation of the landfill consolidation effects using precision settlement surveys as well as measurements from vibrating-wire borehole extensometers to model the settlement rates throughout the entire building footprint. The paper also summarizes the final repair design and construction procedures used to mitigate future settlement damage. The cost for repairs completed to date is approximately $10MM.

In south Florida, mortar-set roof tile applications are commonplace. This type of installation, when completed properly, can perform as a durable and long lasting roofing system. A properly installed system includes the tiles having been rigidly affixed to the roofing underlayment by mortar paddies. Problems can arise, for a homeowner experiencing an improper installation, when they discover that the tiles are not rigidly attached and that many individual tiles are loose and easily lifted by hand, during inspection. This is usually discovered sometime after a hurricane event and well after the original installation. Subsequently, the homeowner's insurance company may be called upon during a roof related property loss claim and tasked with determining what, if any, loose roofing tile is categorized as damage due to winds from a presumed and associated storm and/or other causes, unrelated to storm events. Mortar-set installation of roofing tiles is generally covered by the Concrete and Clay Roof Tile Installation Manual. The mortar paddy is intended to provide the necessary bond between the tile and the roofing underlayment, in order to create resistance against wind uplift forces. Uplift resistances for available properly-installed systems are documented with published values obtained through rigorous testing, which is required prior to a "Notice of Acceptance" (NOA) being issued for each and every roofing system included on the product approval list in Miami-Dade County, Florida. Each approved system has a corresponding NOA that provides documented values, in tabular form, which indicate resistances for an individual tile due to self weight alone, as well as the resistance provided by the "mortar-set fastening/attachment method", which has been documented to provide anywhere from 3 to 5 times additional uplift resistance. This resistance helps to prevent wind forces from removing the tiles from the roof. The NOA is a valuable resource to aid in determining if/that an existing tile condition, being "loose"/"not bonded" on any particular home, is not automatically or necessarily the result of storm induced wind uplift forces. The fact that the loose tile remains on the roof, in its original position as installed, helps to affirm that the wind forces in question were not large enough to overcome simply the tile's own weight.

For many years, steel poles have been reliable sports lighting support structures. Tubular steel poles have performed admirably at some of America's most popular sporting venues. However, in recent years, there have been numerous failures of sports lighting structures across the country. Planned maintenance and inspection of steel poles including careful attention to the base welded connection will ensure the safety of the structure, prolong their lifespan, and protect the public. A pole base plate connects the structure via the anchor bolts to the foundation. As the only connection and one that is non-redundant, the structural adequacy and integrity of this connection is crucial to the performance of the pole structure. A failure, if one was to occur at this joint, will in almost all cases be catastrophic resulting in the collapse of the pole. A crack in a pole base plate weld connection can occur during fabrication, galvanizing, or after loading of the structure. It is imperative that inspections of this connection are carried out by qualified personnel with CWI and non-destructive ASNT credentials. This article will present current methods used to inspect sports lighting structures from a non-destructive examination standpoint. Specific techniques for non-destructively examining the base weld connection including visual testing, magnetic particle testing, and ultrasonic testing will be discussed.

The behaviour of masonry under seismic loads has recently become of great interest. New methods for design and analysis, as well as models for resistance, have been developed. The main focus has been on experimental and analytical research for the development of new brick and mortar material whilst the characteristics of old brick material and mortar have been neglected. With the introduction of Eurocode 8 (EC), the behaviour of old masonry structures under seismic load became an interesting topic for architects and engineers. In particular, the available resistance capacity of existing masonry structures is highly relevant to the retrofit and/or improvement of existing buildings. Deformation energy, or ductile response, is a source for energy dissipation of structures. Since normal levels of internal damping represent only a small portion of energy dissipation, large material deformations such as those required in building components to perform a ductile behaviour, are often associated with cracking and degradation of its stiffness, particularly in masonry structures. The stiffness identification of masonry walls in an uncracked state is examined by laboratory tests. Further, stiffness degradation due to an imposed pseudo dynamic horizontal load pattern is evaluated. In particular, the wall specimens are distinguished by different mechanical characteristics like old and new brick units, low and high strength bricks and two common brick layouts. Beyond the effect of stiffness degradation in masonry on the inelastic response characteristic parameters for energy dissipation are compared within the varying masonry specimens. Due to damage propagation, caused by imposed shear load, typical failure states are determined. The results of a series of laboratory tests are analysed. Resistance and deformation characteristics of masonry under shear are compared to specifications according EC 6.

The question of commonality of damages was posed in a proposed class of members that was intended to represent the city of New Orleans as a whole. Were patterns of damage common such that they were identifiable by predictive means without individual site assessments? The authors were presented this question in the Katrina Canal Breaches Consolidated Litigation Levee with a putative class size of 36 members. Data collection efforts, which involved site specific testing, resulted in detailed class property information such as watermarks; levelness; plumbness; architectural and structural condition; and mechanical, electrical, plumbing (MEP) condition. Hurricane forces of wind and water and degradation of materials affected structures differently; the extent of subsequent material degradation was related to characteristics unique to each structure (age, design, construction, materials, soil condition, and maintenance). Focusing on flood damages due to canal breaches, predictability was not found due to unknown variables of building height, characteristics, and length of time flood water was present. The type and degree of damage varied considerably not only in the global putative class but also in the local subclasses, indicating a lack of meaningful subclass boundaries. Damages were not predictive by formula and therefore commonality was not present in the class. The only reliable method of damage assessment due to hurricane related distress is by individual site evaluation. Based on the scientific method, a test methodology is developed for assessing commonality of damages.

Water ingress into unbonded post-tensioning tendons can lead to serious and expensive structural problems. The severity of this condition can be difficult to detect as often there are limited signs of distress until one or more tendons have lost tension as a result of section loss from corrosion. This paper presents a case study illustrating the investigation and the rehabilitation of tendon failures in a two-way, unbonded post-tensioned roof slab. Techniques for identifying deficiencies with the tendons are summarized as well as the proprietary cable drying procedure that was used for tendon rehabilitation. The authors' observations regarding the effectiveness of the tendon drying based upon continued monitoring of the structure are presented.

Located on Oregon Inlet on the Outer Banks of North Carolina, near the town of Nags Head, is the Bodie Island Light Station, a collection of buildings constructed circa 1872 to serve as an aid to navigation along the dangerous section of the Atlantic coastline known as "The Graveyard of the Atlantic." Listed in the National Register of Historic Places, the Light Station today consists of the historic Lighthouse, Oil House, Light Keeper's Quarters, storage buildings, brick walkways, and a modern Visitor Comfort Station. The Light Station is within the environs of the Cape Hatteras National Seashore, which is maintained by the National Park Service.

This paper provides guidance to engineers, property owners, property managers, and contractors on the mitigation of damage to lightweight, flat (or low slope) roof structures by snow removal. The objectives are to minimize large deflection, prevent blocked drainage paths, minimize snow-induced ponding, and most importantly, to prevent the collapse of roof structures caused by overload due to snow. The structures most susceptible to overload are lightweight, flat roof, commercial structures, such as "Big Box" stores, warehouses, recreation centers, and shopping malls. These structures commonly have low permissible snow load to dead load ratios making them sensitive to extreme snow loads. In February 2010, there were three successive snowstorms extending from Washington, DC to New York, New York that challenged snow removal efforts. Each storm was a significant event and together in quick succession, these storms caused the collapse of roof structures throughout the region. The collapse of roof structures and the forecast for significant accumulation after the first storm prompted property owners and managers to take precautions to protect their property from damage. Conditions and events motivated the development of these snow removal guidelines to protect against overload. Factors influencing a successful snow removal strategy include the amount of snowfall (i.e., depth of snow, unit weight of snow, and drifting snow), design capacity and condition of the roof structure, potential to exceed the design requirements and/or code specified requirements, size of the roof structure, safety of the snow removal crews, economic aspects of snow removal, etc. This paper considers strategies for snow removal, such as taking no action, removing a uniform depth of snow throughout the roof structure, removing channels of snow from the field of the roof, or a combination. The methodology presented may also be adapted to roof structures undergoing rehabilitation, such as re-roofing.

Clark County, Nevada has completed the Nation's very first effort to map earthquake hazard class systematically through an entire urban area. The map will be used in development and disaster response planning, in addition to its direct use for building code implementation and enforcement. The County and the City of Henderson contracted with the Nevada System of Higher Education to classify about 550 square miles of Las Vegas Valley. The Parcel Map includes more than 10,000 measurements that classify individual parcels on the NEHRP hazard scale. We introduce a "C+" Class for sites with Class B average velocities but soft surface soil. The measured Parcel Map shows a clearly definable C+ to C boundary on the west side of the Valley. The C to D boundary is much more complex. Using the parcel map in computing shaking in the Valley for scenario earthquakes is crucial for obtaining realistic predictions of ground motions. We computed using our "ShakeZoning" process 50 separate earthquake scenarios, yielding estimates of earthquake ground shaking in Las Vegas Valley based on physics and geology rather than on statistics. Despite affecting only the upper 30 m, the Vs30 geotechnical shear-velocity from the Parcel Map shows clear effects on 0.1-Hz to 0.3-Hz shaking predictions.

A dramatic new concrete arch joins the setting of the historic Hoover Dam, spanning the Black Canyon between the States of Arizona and Nevada, USA. This 1060 foot (323 m) long arch span is the 4th longest concrete arch in the world, and the longest in the United States. The scale of concrete construction for the bridge is impressive. Four form travelers advanced to the crown of the cast-in-place arch supported by 88 carefully tuned stay cables, while precast segmental construction was used for the tallest precast columns erected to date.

In order to expand the use of FRP in new structures, a satisfactory degree of understanding is required for the behavior of members reinforced with FRP rebars. The aim of the current study is to investigate the concrete contribution to shear strength for beams reinforced with FRP longitudinal bars. A review for the available test results for members reinforced with FRP longitudinal bars without shear reinforcement results a database of specimens from different researchers. The available equations for predicting the value of the concrete shear strength for FRP reinforced members were also collected. An experimental test program was conducted to verify the results for beams with low longitudinal reinforcement ratios. A comparison was made between the experimental results and the shear strengths calculated using the different available equations. Based on the comparison and the experimental program results, the equation adopted by Building Research Institute (BRI)-Japan was found to fit best with the experimental results.

An overview of the many recent cases of roof collapse and the collapse of other portions of buildings in the United States and Canada is given. This paper discusses many of the recent cases of collapses of buildings or portions of buildings that usually get only local news coverage. In most cases roofs collapse under heavy snow loads, although some also fail under wind or rain loads. Many example cases are given based on information collected from local news coverage and other sources. In most cases, the collapse occurs in ordinary buildings and there are few, if any, serious injuries. In many cases the building gives the occupants some warning of collapse and people escape. One exception to the lack of injuries occurs when a wood deck fails. When a wood deck fails, the deck is usually loaded with people. Surprising, the frequency of collapse may be higher in schools and firehouses. Collapse of a portion of a school or a firehouse is upsetting to the public, even when there are no injuries.

The intent of the study is to incorporate discrete, short, mechanically deformed, small diameter steel fibers into high strength concrete (f'_c > 69 MPa) in an attempt to eliminate or reduce the need for steel rebar in concrete construction. This paper presents the rheological properties and behavior of high strength steel fiber reinforced (SFR) / self-consolidating (SFRSC) concrete mixture with different dosages of steel fibers, ranging from zero to 2% by volume in 1% increments. The effect of high range water reducing agent (HRWR) and viscosity modifying agent (VMA) on the fresh properties of SFRC/SCC are studied. Concrete mixtures include fly ash and silica fume. The fresh properties studied are: the flow-ability (spread diameter), the pass-ability (J-Ring and U-Box test) and fill-ability (V-Funnel test). The study shows that, the addition of steel fibers to the mixture results in the reduction of flow-ability, pass-ability, fill-ability and workability, which was mitigated through the adjustment of HRWR and VMA dosage.

Adhesive-bonded anchors are increasingly adopted as structural fasteners for connections to hardened concrete. The strength of these anchors relies on several factors such as geometric parameters and adhesive bond strength. Due to the complexity of the interaction of these factors, it is difficult to estimate their tensile capacity. Furthermore, these anchors have not yet been incorporated into the design provisions of ACI 318-08. This study aims at estimating the effect of different parameters on the tensile strength of concrete adhesive anchors in uncracked concrete using artificial neural networks (ANNs). The ANN model will be able to capture the complex relationship between the tensile strength of anchors and different parameters.

The Aria Tower is the principal hotel and iconic centerpiece of the MGM Resorts International CityCenter Las Vegas mixed-use complex making its mark on the Nevada skyline. The Aria is designed in an elegant, sophisticated and contemporary architectural style with a floor plan based on interlocking arcs that is distinctly different from the linear, T, Y and X floor plans common to casino hotels. It also has three separate elevator cores with dedicated entry lobbies to provide guests with the experience of entering a smaller, exclusive hotel and avoiding long walks to their rooms. Visual massing of the hotel exterior is minimized by varying the heights of different building areas while fitting over 4 million square feet of hotel/casino spaces in up to 52 stories above ground and two stories below ground within the Federal Aviation Administration (FAA) height limitation of 600 feet. The unusual floor plan, separate cores and varied heights presented unique structural analysis and design challenges. This paper discusses the process and results for structural engineering of the Aria tower, including development of its "Core-Moment Frame" lateral system, its deep foundation interacting with caliche, and its unconventional post-tensioned (PT) slab system applied to a high rise building in a region of moderate seismicity. Guiding the project through turbulent economical times, completing the project on schedule, and achieving the coveted Green Building LEED (The Leadership in Energy and Environmental Design) Gold status were the results of the professionalism, dedication, commitment, and cooperation of the entire Aria Tower ownership, design and construction team.

Engineering structures such as wind turbines require continuous monitoring to ensure structural safety, to reduce the overall maintenance and repair costs and, ultimately, to achieve extended lifetimes and a greater economic viability. For that purpose, an automated SHM system for wind turbines has been developed and installed on a 500 kW wind turbine in Germany. During its operation, temporary malfunctions of the installed sensing units have been observed. These malfunctions, such as temporary sensor breakdowns which are well known from real-time SHM systems, might cause the loss of valuable monitoring data if not detected timely. A multi-agent system, which is capable of self-detecting system malfunctions and notifying the human individuals automatically, has been developed and integrated into the existing SHM system. The SHM system and its subsystem, the multi-agent system, have been in continuous operation since 2009. Since then, various malfunctions have automatically been detected and appropriate actions have been taken in a timely manner. As a result, the malfunctioning of the sensors did not lead to significant data loss, thus enhancing the quality of the SHM system.

Civil infrastructures are generally a country's most expensive investment, and concrete is the most widely used material in the construction of civil infrastructures. During a structure's service life, concrete ages and deteriorates, leading to substantial loss of structural integrity and potentially resulting in catastrophic disasters such as highway bridge collapses. A solution to prevent such occurrences, is the use of Structural Health Monitoring (SHM) technology for Smart Concrete structures. Smart Concrete is concrete reinforced with Carbon Nanofibers (CNF). CNF concrete has many structural benefits. CNF restricts the growth of micro cracks in addition to yielding higher strength and ductility. Additionally, test results indicate a relationship between electrical resistance and concrete strain. A series of RC columns were built and tested under a reversed cyclic loading using CNF as a SHM device. The SHM device detected and assessed the level of damage in the RC columns, providing a real-time health monitoring system for the structure's overall integrity.

Structural sensing and dynamic monitoring of critical infrastructure is essential to maintain the ageing critical infrastructure of US. To this end various sensing mechanisms and innovations have been used in the recent past such as strain sensors, accelerometers etc. Measurement of strain gives first hand information about the state of stresses in a structure. The effectiveness of multiwalled carbon nanotube (MWCNT) films as strain sensors has been demonstrated by the authors (Vemuru et al. 2009) and other researchers. In this paper the real time dynamic response of MWCNT polystyrene nanocomposite thin film sensors is studied and experimental results presented of both its dynamic response as well as its response to temperature. Experimental results demonstrate a linear response from the MWCNT nanocomposite. Further electromechanical properties observed are completely reversible and stable. The temperature response of the nanocomposite film is also studied experimentally and results presented. It is demonstrated that the nanocomposite thin films monitors the strain very effectively and can be used as a multifunctional material in civil, mechanical and aerospace applications.

For structures located in a moderately or highly aggressive environment, multiple environmental and mechanical stressors lead to deterioration of structural performance and, therefore, create maintenance issues. Such deterioration will reduce the service life of structures. The main purpose of this paper is to discuss a methodology previously proposed by the writers for the evaluation of long-term seismic reliability of reinforced concrete (RC) bridge piers in a marine environment and present new results. This methodology consists of three steps: (1) investigate the relationship between material deterioration and structural performance on an experimental basis; (2) consider both the seismic hazard and the hazard associated with marine environment; and (3) perform an analysis of the long-term seismic performance of RC bridge piers in an aggressive marine environment.

This study presents a stochastic method to optimize the inspection of reinforced concrete structures subjected to chloride penetration. The strategy is oriented to find the time interval between two consecutive inspections that (1) minimize the costs of inspection, preventive and corrective repair; and (2) ensure a given level of safety. The optimal interval is therefore determined by using stochastic processes and decision theory. The chloride penetration phenomenon is represented by a Markov chain whose transition matrix is determined from simulations.

A structural risk evaluation methodology is introduced in this paper for the offshore platforms against major hazard events (hurricanes and earthquakes) during the operating life of the platforms. The primary objective is to evaluate the risk level from the major hazard events to identify possible risk reduction solutions. Firstly a non-linear progressive collapse analysis approach is presented to investigate the platform capacity to resist the loads imposed by major hazard events. The structural reliability method is then proposed to estimate the probability of platform failure under major hazard events. The platform failure limit state function is defined in terms of hazard loads and platform capacity. Uncertainties are included in the parameters associated with hazard loads and platform capacity. Finally the platform failure consequence and the probability of platform failure are combined to determine the platform risk associated with the major hazard events. Case studies are presented to illustrate the application of the developed structural risk evaluation approach.

Bridge infrastructure faces both continued aging and deterioration throughout its lifetime, as well as potential exposure to natural hazards such as earthquakes in hazard prone regions. Consequential damage requires increased monetary investments, energy spent on subsequent repair/replacement, as well as carbon dioxide (CO₂) emissions associated with the manufacture/transport of repair materials. This paper will derive and compare estimates of three important metrics associated with the life cycle performance of aging bridges given seismic exposure, namely, life cycle cost, embodied energy and associated CO₂ emissions. A case study is presented for a representative multi-span simply supported (MSSS) concrete girder bridge to evaluate the life cycle sustainability metrics of the corroded bridge system given uncertain performance and repair under lifetime exposure to seismic hazards. The results underscore the importance of capturing the effects of time dependent structural deterioration when conducting life cycle analysis of bridges based on different indicators. The proposed framework is also anticipated to help guide the selection of optimal rehabilitation or retrofit measures for bridge infrastructure based on target sustainability metrics related to life cycle cost, energy usage, and harmful emissions.

A proposed probabilistic framework for performance-based durability engineering is motivated by the successful implementation of the Pacific Earthquake Engineering Research Center's framework for performance-based earthquake engineering. Both approaches combine several stages of analysis linked through a limited set of "pinch point" variables, which allows modeling flexibility. The analysis extends to the computation of information useful to decision makers, and can also provide sensitivity analysis of the modeling stages to be used to direct future research. The major stages, variables, datasets, and models to be used are outlined with corrosion in reinforced concrete as the cause of deterioration.

The devastation inflicted on civil infrastructure by natural disasters has the potential to result in numerous deaths and huge economic losses. Natural hazards such as hurricanes, earthquakes, floods, and tornadoes have led to extreme property damage and the loss of many lives. While the occurrence of these hazards is beyond our control, novel structural engineering approaches to design and construction have the ability to reduce their consequences. Structures along the coast are particularly susceptible to a variety of natural hazards. Coastal construction practices, however, as they exist today, may not be sufficient to resist their extreme loads. Design and construction in a coastal environment must consider the effects of multiple hazards concurrently rather than focusing on each hazard in isolation. Multi-hazard engineering strategies can be incorporated into design to enhance the inherent resilience and improve the robustness of structures. Current design approaches also lack a probabilistic backbone that can be used to relate specific structural performances with different hazard intensities. Performance-based engineering (PBE) allows for a structure to be designed for specified levels of performance under particular hazard scenarios. Currently, arbitrary importance factors are integrated into design to account for uncertainties in hazards and their loads. In comparison, PBE uses direct analysis procedures to predict the performance of a building under hazard loads over the entire life of the structure. The probabilistic basis of PBE allows future changes in hazard frequencies and intensities due to global climate change to be taken into account. An integration of multi-hazard engineering with PBE promises to significantly improve structural reliability for a wide range of loading scenarios. A possible methodology for assessing response of structures in coastal environments vulnerable to winds, storm surge, tsunamis, and earthquakes is presented.

The seismic performance of structural systems exposed to aggressive environments has to be considered time-variant. Current capacity design criteria are time-invariant and do not account for the interaction with environmental hazards. In fact, for aging systems the energy-dissipating collapse mode may vary over time due to a reduction of both strength and curvature ductility of critical cross-sections where plastic hinges may occur during a seismic event. In this study the lifetime seismic performance of concrete structures is investigated in both probabilistic and deterministic terms. Static and dynamic non linear analyses are carried out on a three-story concrete frame to evaluate the effects of damage on the time evolution of seismic performance indicators. The results show the important role of a life-cycle approach for both seismic assessment of existing structures and seismic design of new structures.

This paper issues a call to improve the conceptual underpinnings of community resilience to disasters as it relates to critical infrastructure. It is argued that, broadly, infrastructure is the combination of both capital and services. Loss and recovery, and thus resilience, of infrastructure do not make practical sense without consideration of both. Specifically, infrastructure is characterized by its relationship to other infrastructure, agents, possible disruptions, possible interventions, jurisdictions and markets. Based on this and previous development work related to the resilience simulation model ResilUS, the beginnings of a new conceptual model are proposed. The comprehensive nature of the model suggests it is appropriate for planning purposes. The conceptual model provides opportunities for advancing ResilUS, specifically, and infrastructure and community resilience research and planning broadly. It facilitates the creation of a database schema for infrastructure loss and restoration and its impact on indicators of community resilience. Population of this schema will push understanding of community resilience and facilitate the development of better tools for supporting resilience planning.

This paper proposes a three-stage framework to analyze the smart grid resilience. In each stage, a series of resilience improvement strategies are introduced to realize the smart grids, and appropriate metrics are also identified and then combined to establish an annual resilience metric. Taking the power transmission grid in Harris County, Texas USA as case study, this paper establishes an original power grid model and several smart grid models to compare the effectiveness of resilience improvement strategies in different stages. Results show that the annual resilience of the smart grid with all three-stage improvements increases 0.035% compared to the original grid. Although the improvement is small in magnitude due to the high reliability of real power grids, it may save hundreds of millions of dollars. This framework can provide insights to design resilient smart infrastructure systems and retrofit present ones.

A distinction is made between the reliability of a structural system and its resilience. The former is generally measured probabilistically, evaluated by means of computer algorithms capable of handling multiple failure modes, and forms the basis of design codes. Resilience must incorporate the time history of performance following significant disturbance, include imprecise definitions and evaluations, and reflect the effects of system performance (physical, economic, social and political) on the community served. Reliability analysis, including code calibration, has generally been the purview of structural engineering risk professionals. Resilience, on the other hand, should integrate community input on the degree of inconvenience and time trajectory of recovery, even incorporating concepts of sustainability. Resilience must often use generalized uncertainty, including fuzzy logic, to transform societal goals into metrics, and recognize sensitivity to sources of uncertainty in terms of acceptance of diminished performance. At a minimum, this requires keeping epistemic and aleatory uncertainty separate.

The concept of Disaster Resilience has received considerable attention in recent years and it is increasingly used as an approach for understanding the dynamics of natural disaster systems. The goal of this paper has two distinct tasks: (i) conduct a literature survey analyzing asset-based approaches for defining and measuring disaster resilience for physical infrastructures that is one of the seven dimensions of the PEOPLES Resilience Framework; (ii) identify the gaps between asset-based approaches and community-scale approaches. It is offered an overview of the models developed in literature to quantify resilience and performances of electric power, water, wastewater and natural gas utilities; communication companies and transportation networks as well as health care facilities. Discussion will be added related to strengths and weakness on how these approaches could facilitate the comparison of alternative resilience options/strategies and measure the speed with which disruptions can be overcome and community functions restored. A new geographic approach will be introduced to measure community resilience, focusing on spatial, temporal scale of resilience.

The process of community recovery in the aftermath of a disaster is complex, long lasting, resource intensive, and poorly understood. Insights described here result from an ongoing project that aims to monitor, quantify, and evaluate the process of post-disaster recovery for two events, Hurricane Charley (2004, Charlotte County and Punta Gorda, Florida) and Hurricane Katrina (2005, Harrison County and Biloxi, Mississippi). A mixed-methods approach using statistical data, interviews, and remote sensing-derived data is applied in an effort to understand as well as monitor, measure and evaluate the recovery process and its outcomes. Observations associated with the post-disaster course of moving residents from temporary to transitional, and ultimately permanent housing serves as the focus for this paper. This work represents a discrete portion of a multi-sector project where Economic, Environmental, Housing/Infrastructure, and Social elements of community recovery are explored. Understanding community recovery can inform community resilience-building strategies.

This paper deals with the concept of "resilience" and proposes its use as optimization criterion for the rehabilitation of a transportation network subject to earthquake. The most earthquake damage prone components of a transportation network are certainly its bridges; therefore, the proposed approach focuses on bridge rehabilitation interventions. The design variables of the optimization problem are the application times and durations of the interventions on bridges of the network. These durations are determined by the amount of funding invested on each bridge. Hence, the proposed methodology provides the optimal rehabilitation schedule and cost breakdown for all the bridges of the network. A numerical application is presented to illustrate the proposed approach and to show its capabilities.

This experimental study focuses on investigating the feasibility of using shape memory alloy (SMA) spiral to conduct emergency repairs on severely damaged reinforced concrete (RC) bridge piers. The studied repair technique can be implemented in less than 24 hours and hence can be used to rapidly restore the functionality of lifeline bridges that are severely damaged by an earthquake. The proposed repair technique can also ensure the safety and structural integrity of important bridges against strong aftershocks. Unlike other repair techniques such as composite jackets, which utilize the concept of passive confinement, this proposed technique relies on the concept of concrete active confinement to enhance the strength and ductility of severely damaged concrete. Research has shown that active confinement is a more superior confinement technique to passive confinement; however, with conventional materials, its fast application on-site in case of an emergency could be a challenge. This study presents an easy and fast method to apply active confinement using SMAs. The thermally activated shape recovery feature of SMAs is used to apply the active confining pressure at the damaged locations. To examine the proposed technique, two 1/3-scale RC columns which were severely damaged are repaired using SMA spirals and retested. The damage sustained by the two columns is localized primarily at the column base (i.e. at the plastic hinge zone), which is typical in seismically damaged slender columns. The damages in both columns are in the form of concrete cover spalling, concrete core crushing, and buckling and rupture of at least one of the longitudinal rebars. The repaired columns are tested under quasi-static cyclic loading. The results are compared with those of the as-built columns. The experimental results show that the repaired columns have fully restored their lateral stiffness, strength and hysteretic energy dissipation capability. The results of this study clearly illustrate the effectiveness of the proposed technique for emergency repair applications.

This study compares the performance of two smart isolation systems that utilize superelastic shape memory alloys (SMAs) for seismic protection of isolated bridges during strong earthquakes. The first isolation system is an SMA/rubber-based (SRB) isolation system and consists of a laminated rubber bearing that decouples the superstructure from the bridge piers and an SMA device that provides additional energy dissipation and re-centering capacity. The second isolation system, named as superelastic-friction base isolator (S-FBI), combines the superelastic SMAs with a flat steel-Teflon bearing rather than a laminated rubber bearing. Seismic energy equations of a bridge structure with SMA-based isolation systems are established by absolute and relative energy balance formulations. Nonlinear time history analyses are performed in order to assess the effectiveness of the isolation systems and compare their performance. The program RspMatch2005 is employed to generate spectrum compatible ground motions that are used in dynamic time history analyses of the isolated bridge. The results indicate that SRB isolation system produces higher seismic input energy, recoverable energy and base shears as compared to the S-FBI system. Also, it is shown that combining superelastic SMAs with a sliding bearing rather than rubber bearing significantly reduce the amount of the required SMA material.

Failure of expansion joints is a leading cause of damage to bridge superstructures. Cohesive and/or adhesive failure of joint sealant material facilitates decay of the structures beneath it. The objective of this study is to develop a novel smart joint sealant to self-heal cohesive damage and eliminate adhesive failure of expansion joints. This sealant will be a shape memory polymer (SMP) based syntactic foam material. A key feature of this sealant is that it utilizes the shape memory functionality for the purpose of self-healing damage. In particular, internal cracks can be narrowed or fully closed by confined shape recovery of the smart sealant. Also, the sealant can be programmed to consistently and autonomously apply a compressive stress to the edge of the concrete deck and restrict the upward expansion, so that adhesive failure or debonding can be eliminated and a smooth joint can be maintained. In this study, a shape memory polymer (SMP) based syntactic foam sealant was prepared by dispersing 40% by volume of glass microballoons into a SMP matrix. After curing, this foam sealant was first programmed under 2-D stress condition (compression in longitudinal direction and tension in transverse direction) by a specially designed 2-D test fixture and then freely recovered. The effect of the prestress levels and the number of programming-recovery cycles on the thermomechanical behavior and shape fixity and shape recovery ratios, was investigated. The potential of this sealant for eliminating adhesive failure and healing cohesive damage was discussed.

The ASCE SEI Committee on Disproportionate Collapse Standards and Guidance is developing a guidance document for design against disproportionate collapse of structures. A Terminology and Procedures Sub-Committee was created to focus on definitions of terms and to develop a conceptual framework. The Sub-Committee prepared a draft that was discussed and accepted in principle by the Committee at its meeting on 13 May 2010. The draft is published here in its latest but shortened version for rapid dissemination and discussion. The complete draft is available on request. The draft starts with a comprehensive and consistent set of definitions of relevant terms such as collapse resistance, robustness, vulnerability, exposure, direct design, indirect design, threat-specific design, non-threat-specific design, and many more, which up to now have not been consistently defined and used. These definitions are strongly cross-referenced and a hierarchical system of interrelated definitions thus emerges. On this basis, a conceptual framework of design criteria comprising design requirements, design objectives, design methods, and verification procedures is developed. This framework will serve as the outline for the Committee's design guidance document. Specific content for a number of sections and an appendix still need to be developed by dedicated Sub-Committees (SC). These tasks are clearly defined by the framework. The draft consists of recommendations and commentary. In the following, recommendations are set in normal font and commentary in italics. The section numbering of the draft is substantial to cross-referencing and thus retained. Specific content still to be developed by dedicated Sub-Committees is indicated in brackets. Numbers given in tables are intended to illustrate the possible final content of these tables and to stimulate discussion. They should be understood as placeholders for the final content to be specified by the respective Sub-Committee.

Civil infrastructure systems are complex networks of tightly coupled, interdependent subsystems that involve many factors and system constraints. Their resiliency is critical for the proper functioning of society during and following extreme events such as hurricanes and earthquakes. The goal of this paper is to outline the formulation of a framework that provides strategies for increased resiliency. These strategies will be expressed in a common rule-based form of "If- Then" statements. A rule-based model is flexible and can incorporate social performance measures in addition to traditional metrics. The rule-based model also has the capability to reflect the performance of interdependent networks of multiple systems. These rules may be formulated in a manner so as to be incorporated in a multi-objective optimization algorithm that can improve system performance. A brief example of the proposed framework is provided.

This paper aims at presenting an innovative approach for an optimised/full-controlled seismic design of structures which combines recent contributions in the field of earthquake engineering and overcomes the traditional design approach leading to the identification of the characteristics of the lateral-resisting system capable of satisfying multiple seismic performance objectives. In this respect, it is fundamental the total conceptual separation between the structural systems resisting to vertical and horizontal loads. With reference to both (1) a braced pendular frame structure and (2) a shear-type frame system coupled with a lateral-resisting element (such as a reinforced concrete core or a bracing system), the approach here presented identifies the characteristics (strength, stiffness, ductility, energy-absorption) of the system resisting to horizontal loads which enables to satisfy prescribed seismic performance objectives. This is achieved through the identification of an objectives curve, in the Force-Displacement diagram, of the mechanical characteristics of the structure. The lateral-resisting system is obtained by means of (1) special braces in the case of the braced pendular frame structure and (2) special connection elements in the case of the shear-type system coupled with a lateral-resisting element.

This paper focuses on blast vulnerability assessment of concrete masonry infill walls retrofitted with nano particle reinforced polyurea. Quarter scale model concrete masonry infill walls made of scaled down brick units were retrofitted with Polyhedral Oligomeric Silsesquioxane (POSS) reinforced polyurea and subjected to a pre-adjusted airblast pressure and impulse in the ERDC Blast Load Simulator facility. A computationally-efficient model was built using an explicit hydrocode called ANSYS AUTODYN to replicate with reasonable accuracy the behavior of retrofitted infill walls subjected to blast loads. A series of finite element analysis was conducted. The focus was to study the effect of some factors such as boundary conditions, thickness and arrangement of retrofitted layers, and ductility of retrofitted materials on the behavior of the system during and after blast. Results from blast experiments showed that POSS reinforced polyurea significantly enhanced the performance of masonry walls sustaining blast load. The finite element parametric evaluation results show that for the case of retrofitting with elastomeric materials it is better to apply the retrofit at the back side since this will be associated with no failure, when compared to front side retrofit, and a larger deflection (e.g. more energy dissipation) when compared with two side retrofit with a smaller amount of material.

ASCE 4, "Seismic Analysis of Safety-Related Nuclear Structures and Commentary," was first issued in 1986. It was expanded, revised and re-issued in 1998. The second revision of the standard will soon be completed by the Working Group on Revision of ASCE 4, which is part of the ASCE Committee for Dynamic Analysis of Nuclear Structures. This standard provides prescriptive criteria for the analysis of safety-related (Seismic Category I) structures, systems and components (SSCs). It is designed to be used in conjunction with ASCE-43/SEI 43-05, "Seismic Design Criteria for Structures, Systems and Components in Nuclear Facilities." It addresses all aspects of seismic analysis: site response, modeling, and analysis for all types of SSCs. The standard also provides guidance on Quality Assurance requirements and Peer Review needs. Taken together, ASCE4 and ASCE/SEI43-05 may be adapted by federal agencies such as the U.S. Nuclear Regulatory Commission and the U.S. Department of Energy as the minimum expected seismic analysis and design requirements for nuclear facilities. This overview paper highlights the proposed changes to the ASCE 4-98 Standard proposed by the Working Group. These changes, if adapted, will become effective following consensus balloting and public comment of the proposed changes.

Parameters of interest in the seismic analysis of liquid-containing tanks include reaction forces, slosh heights, and peak wall pressures. Numerous references including Section 7.4 of ASCE 4 have simplified expressions for wall pressures, overturning moments, and slosh heights for tanks with excess freeboard. For tanks with insufficient freeboard, less guidance is available. As an example, ASCE 4 requires that if tanks have insufficient freeboard, the liquid level must be lowered or the tank roof and wall must be designed to withstand the impact of the sloshing fluid. However, ASCE 4 does not provide specific guidance on evaluating the impact of liquid with the tank roof. The present study evaluates seismically induced fluid-structure interaction in flat-top and domed tanks with insufficient freeboard using the explicit finite element program MSC.Dytran® and the results of the study are compared to approximate solutions. For the systems considered, the study shows that the peak wall pressures in the domed tank are nearly the same as for a vertical-walled tank with excess freeboard. However, for the flat-top tank, the peak roof pressures are significantly higher than predicted using the approximate methods. In all cases, peak wall pressures lower in the tanks are unaffected by local roof or dome interactions.

Nuclear structures are typically reinforced concrete shear wall buildings constructed either embedded in or on the ground surface. Nuclear structures contain equipment, systems, and components that are safety-related and generally require seismic qualification by either full-scale testing or analysis. Evaluation of a safety-related nuclear structure is typically performed by dynamic analysis of a finite element model of the structure considering three orthogonal components of input motion. The paper addresses updates to ASCE 4 in the areas of finite element modeling, damping for multiple levels of response, modal response combination, frequency domain response methods, multi-step analyses, and nonlinear seismic analysis.

Section 7.6 of ASCE 4-Rev 2, Seismic Analysis of Safety-Related Nuclear Structures: Standard and Commentary, provides updated guidance for analysis of rocking and sliding of unanchored structures and components subjected to seismic load. This guidance includes provisions both for simplified approximate energy-based approaches, and for detailed probabilistic time history analysis using nonlinear methods. Factors to be applied to the analytical results are also provided to achieve demand estimates at the 80% non-exceedance probability level. The present paper surveys the published literature supporting these provisions. The results of available testing and analyses are compared to results produced by both simplified and probabilistic approaches. In addition, adequacy of the standard's provisions for analysis methods and factors is assessed. A comparison is made between the achieved level of conservatism and the standard's non- exceedance probability target.

Codes, standards, and guidelines commonly used in the evaluation and rehabilitation of existing buildings recognize and allow various performance-based engineering analysis methods, but much of their focus is on nonlinear static procedures (NSPs). The NSPs codified in those documents are based on single-degree-of-freedom (SDOF) models, which are easy to understand but may not capture adequately the complex behavior of structures with multiple-degree-of-freedom (MDOF) effects. The NEHRP Consultants Joint Venture has completed a project (ATC-76-6, with results published in NIST GCR 10-917-9) to improve the practical application of NSPs and nonlinear response history analysis (NRHA) to structures with MDOF effects. The NIST GCR 10-917-9 project report summarizes both recent MDOF modeling research and current structural analysis practice as specified in codes, standards, and guidelines and as implemented by leading practitioners. The work of the project includes synthesis of available research and performance of new problem-focused studies. The primary studies compare results from NSP and NRHA for both detailed structural archetypes and simplified models. Issues addressed in ancillary studies include examination of demand parameter sensitivity to ground motion selection and scaling methods, direct determination of NSP target displacement, and practical implementation of the nonlinear analysis methods. Based on available past research and on the new studies, the project report provides guidance on selection of simple nonlinear analysis methods appropriate for design, on implementation of nonlinear analysis methods, and on incorporating uncertainty in nonlinear dynamic and nonlinear static analysis. Related to the ATC-76-6 project, this paper provides background, a summary of the work performed, and a summary of key findings and recommendations. Related papers provide more detail of the technical work performed.

This paper discusses the effectiveness of simplified nonlinear static methods for predicting the seismic response of various steel moment resisting frames (MRFs) and shear wall structures. Different nonlinear static analysis procedures are discussed. Results from focused studies of different archetype structural systems are compared with nonlinear response history analysis (NRHA). The main engineering demand parameters considered are story drift ratios, story shear forces and overturning moments. Suggestions are made for improving accuracy and required effort of alternative nonlinear static procedures used to predict the seismic response of steel MRF and shear wall structural systems.

The applicability of nonlinear static procedures for estimating seismic demands in a variety of building types was evaluated within the recently concluded ATC-76-6 project. Results are reported herein for several pushover methods applied to three RC moment frame buildings, relative to baseline data provided by nonlinear response history analysis. Response quantities include peak interstory drifts, floor accelerations, story shears, and floor overturning moments. The single-mode pushover methods that were evaluated include the N2 and ASCE 41 coefficient methods. Multi-modal pushover methods include the modal pushover with elastic higher modes, and the consecutive modal pushover. Target displacements were estimated using typical R-C₁-T relationships. Results indicate that the good performance of the single-mode methods for low-rise buildings rapidly deteriorates as the number of stories increases. Multi-mode techniques generally can extend the range of applicability of static pushover methods, but at the cost of significant additional computation and with uncertainty about the reliability of the results.

This paper discusses the pros and cons of predicting structural behavior and important engineering demand parameters (EDPs) by means of either nonlinear static pushover (NSP) analysis or nonlinear response history analysis (NRHA) with simple hysteretic models. It will be demonstrated that NRHA comes out as a clear winner if the issue is quantification of EDPs, except for low-rise first mode controlled structures in which torsion is not an important consideration. It also will be demonstrated that NSP analysis has much value in understanding important behavior characteristics that are not being explored in a NRHA in which engineers usually focus on a demand/capacity assessment rather than visualization of response. The conclusion is that both NSP and NRHA have intrinsic value and that it is advisable to employ a combination of both to understand seismic performance and quantify important engineering demand parameters.

The study describes a procedure to identify bridge fragility parameters utilizing its vibration response recorded during experimental study. For this purpose, bridge damage data observed in a near full-scale shake table experiment is utilized. The bridge was tested under a sequence of earthquake ground motions with increasing intensities. Low and high amplitude tests were performed in series to observe the seismic performance of the bridge starting from yielding to complete failure. In the present study, recorded bridge acceleration during high amplitude tests is utilized and further analyzed to evaluate the degraded performance of the bridge after each high amplitude test. This is done by using extended Kalman filtering (EKF) technique as a tool. The degraded performance of the bridge after each run is measured in terms of degraded stiffness of the bridge at pier ends. In parallel, finite element (FE) model of the same bridge is developed in order to perform time history analysis under a set of earthquake ground motions with various hazard levels. Before applying the ground motions, the FE model is updated with the degraded stiffness of the bridge obtained from EKF after each high amplitude test. This is important to numerically simulate the gradual progression of bridge damage when subjected to earthquake ground motions in sequence. After each time history analysis, bridge response is obtained in terms of the rotation at bridge pier ends. Thus obtained response from time history analyses is used for fragility curve development. The change in fragility parameters represents the progressive damage of the bridge when subjected to ground motions with incremental intensity.

The objective of the presented study is to evaluate the sensitivities of the random variables and Average Daily Truck Traffic (ADTT) on the evaluated reliability of bridges. The reliability analysis is carried out for the Strength I Limit State in the AASHTO LRFD Bridge Design Specification. The Weigh-In-Motion (WIM) data recorded at 24 WIM stations in Missouri are processed and used as an input to simulate realistic live loads due to truck traffic. Gumbel Type I extreme value distribution is used to represent daily maximum positive moments and extreme value theory is used to project the daily maximum values to the maximum values in 75 years of bridge lifespan. Sensitivity analysis is conducted to understand the relative effects of random variables and ADTT on the calculated reliability index. The result shows that the ADTT affects the reliability index as sensitively as other random variables, such as dead load, girder distribution factor, and dynamic impact factor. Hence, explicit consideration of uncertainties in ADTT is suggested for future calibration studies. Alternatively, the reliability index needs to be assessed conditioned on deterministic ADTT.

Post-hurricane functionality of the transportation system is vital for emergency response and recovery activities. Coastal bridges are among the most critical components of the transportation system susceptible to hurricane induced wave and surge loads that may hamper this functionality. This study explores alternative approaches to develop probabilistic statements of coastal bridge damage potential conditioned upon hazard intensity, known as fragility. Fragility surfaces for a representative bridge structure of the Houston/Galveston area are developed using two different approaches: static analysis and nonlinear dynamic simulation. The static approach is efficient and can provide sufficient fragility models for simply supported bridges with limited connectivity between the super structure and substructure, since their predominant mode of failure is deck unseating or shifting due to connection failure. Nevertheless, for bridges with strong connection between sub and superstructure, the force transfer can cause other components to exceed their limit state. Hence the full dynamic behavior of structure becomes more critical in the fragility modeling of bridges with high strength connections.

A team of engineers, funded by an NSF RAPID Grant, investigated selected critical electrical equipment, such as switchgear, motor control centers and inverters, at ten sites located in the Port-Au-Prince region that were subjected to strong ground motion during the 12 January 2010 Haiti earthquake. The investigations included a site survey of both damaged and undamaged electrical equipment, and included not only documentation of the physical damage to the equipment, but also consideration of the resulting consequences of the loss of use of the specific equipment and related systems. While the observed damage modes for the selected equipment when subjected to strong ground motion were not unexpected, it was the consequences of the loss (actual or potential) of the use of the damaged equipment that presented important lessons for the investigating team. This paper will detail the observed damage for selected non-structural elements subjected to strong ground motion during the 2010 Haiti earthquake. In addition, the paper will discuss the consequences of the loss of critical equipment at selected facilities in the Port-Au-Prince region and possible implications for the seismic design of critical non-structural components required for post-earthquake recovery operations in developing countries.

Although the majority of devastation in the January 12 2010 Haiti earthquake was from non-engineered structures, the earthquake also damaged several modern engineered buildings in the capital city of Port-au-Prince. Data gathered on the observed performance of a selection of these structures is being used for the purposes of comparison with, and calibration of, analysis-based predictions used in seismic assessment procedures. Structures were selected for investigation based on their damage state, available design information, and accessibility. These buildings are a small set of important engineered reinforced concrete structures within Port-au-Prince. The available information is being used to construct analytical models using state-of-the-art techniques for nonlinear dynamic analysis. Seismic hazard levels are being estimated by indexing to the level of demand required to bring about the observed damage. Conclusions on the efficacy of these methods are being drawn through comparisons of the predicted response to actual outcomes. The final deliverable is a report documenting the structure and design information; the post-earthquake state; the modeling techniques; analytical results/comparison and evaluation of the methods. As an interim report, this paper presents: (1) general Haiti earthquake information; (2) damage mapping of candidate structures; (3) preliminary analytical modeling.

Design processes and design calculations are reviewed for the 1925 Valtschielbach Bridge by Robert Maillart and the 1998 Ingolstadt Bridge by Jörg and Michael Schlaich. This review emphasizes the importance of conceptual transparency in structural design and demonstrates the interconnected nature of theory and practice in actual design processes. It helps to establish engineering thinking as distinct from scientific or mathematical thinking, and allows detailed consideration of how structural design processes may be taught in the university. Examples from the author's own practice and teaching demonstrate the potential for learning environments where university students are introduced to the tools and disciplines essential to creating original work based on fundamental understanding of engineering concepts.

Félix Candela is widely acknowledged to be one of the great structural artists of the twentieth century. Candela was born in Spain, and was exiled in 1939 to Mexico where he created all of his major thin shell concrete constructions. This paper examines Candela's process of design and illustrates through his major works that he acted first as a builder who not only constructs, but also makes the engineering design. He also takes a general form and plays with it to make structural art. Structural art implies efficiency, economy, and elegance; but we also illustrate how structural art also implies a sustainable design. Finally, we show that the inspiration for the designs of structural artists come from a process that begins with imitation, followed by innovation. Education is crucial for the future of structural art, and in studying it, educators, practitioners, and the general public can recognize the potential for this new art form in the 21st century.

This study examines engineering design processes and organization at the Tennessee Valley Authority in its early years from 1933 to 1936. During this time, Norris and Wheeler dams were constructed and plans and designs were begun for several additional dams. The TVA experience provides insights into how design processes evolved and were managed in a large engineering organization. A particularly innovative decision was the choice to build TVA dams by force account, i.e. by hiring their own employees, rather than by selecting contractors through a traditional bidding process. TVA engineers believed this approach would reduce overall design and construction costs, as well as reduce time to completion. Case studies of civil engineering history, like this one, provide an important tool for introducing students to design processes and engineering decision making.

This damage assessment relied heavily on the use of remote sensing technology. Never before has the availability of high-resolution satellite and aerial imagery been so open and accessible. Data from different missions (World Bank-ImageCat-RIT Remote Sensing Mission (15cm optical and 2 pt/m2 LiDAR), Google (15cm optical), NOAA (25cm optical), Pictometry, as well as satellite imagery from GeoEye and Digitalglobe) has allowed damage from the Haiti earthquake to be viewed through multiple sensors and at different times. These multi-dimensional perspectives have been invaluable in understanding the magnitude and scope of damage caused by this earthquake.

This research applied the nondestructive testing (NDT) technique of acoustic emission (AE) to monitor fatigue cracking in steel structures and utilized artificial neural networks (ANNs) for fatigue life prediction. The neural network classification network known as a Kohonen self organizing map (SOM) was first used to classify the AE data into the different source mechanisms occurring during fatigue cracking. This research developed methodologies for placing sensors, collecting acoustic emission data and eliminating noise from the raw data. The ultimate goal of this research was to monitor for steel fatigue cracking and accurately predict remaining fatigue lives using AE flaw growth data and back propagation neural networks (BPNNs). The procedures for doing so are presented herein.

Two large-scale experiments are currently in progress in the structural laboratory at Hunan University, China to assess the progressive collapse behavior of reinforced concrete (RC) building systems: the first system comprises a flat-plate structure while the second is a beam-column moment frame. Results from the first test are reported in this paper while construction of the second system is in progress with collapse testing scheduled during the summer of 2011. The collapse experiment of the flat-plate structure consisted of a push-down test to simulate the loss of an interior column. The next proposed test will assess the system response of a half-scale three story RC frame building to sudden column removal. The tests will enable a clearer understanding of force redistribution, slab contribution and catenary effects during progressive structural collapse.

A number of analytic tools have been applied to or developed for progressive collapse modeling. However, the lack of relevant experimental test data makes it difficult to validate these tools or identify which aspects of the modeling approaches or software formulations may need additional refinement. The cost of full scale testing to validate these analytical tools is extraordinarily expensive due to the physical size of the structures that need to be tested and the range of phenomenology that needs to be investigated. This paper investigates the use of small scale building models, which can be tested in a centrifuge to provide properly scaled gravitational loads, for studying progressive collapse of damaged buildings. For this effort, a reinforced concrete building (3-bay x 4-bay, 4-story) was designed, constructed at 1/18th scale and tested in a centrifuge while several ground floor support columns were dynamically removed. The test data, including overall collapse response, were compared with the results of pretest analyses performed using a high fidelity, explicit finite element code. This testing effort was designed to contribute to improved validation of simulation tools for progressive collapse modeling.

Due to highly fragmented nature of the of Architecture Engineering Construction (AEC) industry and time constraints, little attention has been devoted to the conceptual design process. Multidisciplinary teams start with a limited set of requirements, mostly imposed by the Architect, to work on only a restricted number of design alternatives. Therefore, final designs often lack satisfactory performance throughout its life. This paper uses a decision support tool, the IVCG, which combines the searching power of evolutionary computation with the exploration power of an interactive visualisation tools to assist designers at the conceptual design stage. This approach facilitates members of the different disciplines involved to interact with the system independently to identify those regions of the search space which best satisfy the requirements of their individual disciplines. It then allows them to agree on a `mutually inclusive' region that partially satisfies the needs of all parties involved in the design. The system also uses the Pareto optimisation algorithm to focus on a limited number of solutions, inside the Pareto front, for the multi-disciplinary team to interactively explore solutions within this region. This enables selection of a workable number of `compromised solutions' that are acceptable to all parties involved.

Few will argue the importance of civil infrastructure to society, yet its condition has been allowed to deteriorate to a staggering level. Meanwhile the research and design practice dedicated to it has relied only upon limited, fractured resources scattered physically across the community with little formal collaboration. As the information used in the design, analysis and even management of civil infrastructure is trapped inside proprietary systems, these essential public works projects often do not benefit from the full expertise and latest advances available in the wider engineering community. To address this problem, a new virtual organization has been launched: Open Sourcing the Design of Civil Infrastructure (OSD-CI), welcoming Citizen Engineers to engage in four dimensions of collaboration (sharing hardware, software, knowledge and manpower). This paper presents the ongoing development of this concept, specifically focusing on two recent prototypes allowing this crowd to contribute and assess engineering data.

Following the events of 9/11/2001, FHWA together with AASHTO commissioned a Blue Ribbon Panel (BRP) on Bridge & Tunnel Security. It was charged with the task of examining the issues and developing the initial road map for improving the bridge and tunnel security in the United States in the face of this new reality; organized terrorism on American soil. The recommendations of the panel was published in September of 2003, and has been a key reference and a source document for assessing vulnerability and planning of structural hardening of many key bridge and tunnel facilities in the US. Even though a considerable knowledge existed in related areas, especially within the military type organizations, at the time the BRP, bridge and tunnel security was in its infancy. Over the decade since 9/11, much progress has been made in both infusing the considerable knowledge that existed in other areas. These include counter terrorism intelligence, monitoring and enforcement as well as structural hardening and blast resistant design applied to military buildings and other facilities of sensitive nature. In addition to this cross-over of operational and design methodologies, considerable new knowledge and experience in vulnerability assessment and mitigation has been generated specific to bridges and tunnels. One key aspect of this evolution is the crystallization of the idea that any holistic vulnerability assessment and risk mitigation of the transportation infrastructure must consider multi-hazards and just not terrorism. However, many challenges and considerable difficulties still remain in improving safety and security of many existing bridges and tunnels to a meaningful level. The paper examines the evolution of bridge and tunnel security, the progress to date and also the challenges and opportunities as we as look to the future in developing promising new approaches and initiatives. It can be shown that viable approaches are available to bring bridge and tunnel security to the next level in a cost effective manner in a relatively short time; same way how the earthquake security initiative of the 70's improved the seismic worthiness of bridges and tunnels in America and beyond.

It has been roughly three decades of utility-scale wind farm development in the US without much clear guidance for the design and permitting of these structures. However, since late 2009 an effort has been underway to develop a US Recommended Practice for the design and permitting of wind energy structures. This task has been undertaken by a joint committee of the American Wind Energy Association (AWEA) and the American Society of Civil Engineers (ASCE). While the stated goal of a practical design guideline for Code compliance is straightforward, technical challenges and unresolved issues have been encountered during the Recommended Practice's development process. This paper describes several of those technical issues including the following: (1) Reconciling the regulatory requirements of American Code versus those of International and European wind industry commercial certification. (2) Reconciling the fatigue provisions of Eurocode and AISC. (3) Reconciling extreme wind speed profiles of ASCE and International Wind Turbine Standards (4) Establishing Code-compliant seismic design parameters and procedures for the combination of earthquake plus turbine operational loads. (5) Handling specialized design procedures used in the wind industry that are based on foreign reference documents that have not been translated into the English language. This paper discusses possible solutions and the ongoing efforts to resolve these technical issues. The paper also makes suggestions for needed research and calls for dedicated U.S. national leadership focused in shaping an industry that is known for producing safe and reliable structures that produce alternative and cost-effective energy.

It is not unusual in petrochemical plants for two adjacent nonbuilding structures to be connected together by large diameter pipe. Common examples of these nonbuilding structures include pipe racks, equipment modules, and heat exchanger structures. Typically, these structures are modeled separately from each other without considering the effects due to large diameter pipe connected to adjacent structures. The pipe is typically modeled and analyzed independent of the nonbuilding structures by considering the equipment as anchor points and the supporting structures as supports, guides or anchor points. This method of modeling nonbuilding structures connected by large diameter pipe is acceptable for static loads; however, the results can become very misleading when applied to earthquake loads. It is even more difficult to rationally apply the effects seismic displacements to these independent models. In this paper three methods of seismic analysis and corresponding results are presented using a simplified 2-D example of two nonbuilding structures connected by a large diameter pipe. The first method uses the traditional method of analyzing the two structures independently and accounting for loads due to seismic displacements from an independent pipe model. The second method utilizes a combined model which includes two nonbuilding structures connected by a large diameter pipe. The seismic load is applied statically to the structures. The third method utilizes the same combined model as the second method with analysis done using Response Spectra Analysis. The results of each method are graphically compared. The paper also includes the results and conclusions drawn from the methods which were investigated.

This paper discusses the nonlinear analysis of a structural steel frame subjected to low level far field blast loads. Such blast loads are considered typical for buildings designed for petrochemical plants. The analysis involves the use of a beam and hinge model similar to what can be used for a nonlinear seismic design. An example frame, based on Chapter 12 of ASCE 2010, "Design of Blast-Resistant Buildings in Petrochemical Facilities", is analyzed. The resulting dynamic response is compared to a simpler SDOF equivalent analysis and a to more comprehensive nonlinear finite element analysis. For simple steel frames in typical petrochemical plant applications, the use of a nonlinear hinge model provides a reasonable level of accuracy.

The design of foundations for vibrating machinery involves solving the equations of motion. To do this, the basic values of load, mass, and impedance need to be determined. Soil / pile impedance is easily the most complex of these values. Current means of evaluating soil impedance is through the use of computer software. Because of the complexity of the calculations, such software is often seen as a "black box" that takes user input data and reports a result. Familiarity with the assumptions and formulas behind computer calculations is important, as is a visual grasp of how results will be affected by changes to input data. Also of significance is having the ability to confirm the reasonableness of computer results. This paper addresses these subjects.

Modular construction is a well-proven technique for the North Slope of Alaska and the offshore petrochemical industry and is often preferred because of site conditions. Modularization is not a technique generally associated with conventional land-based petrochemical facilities, but certain project conditions, such as limited manpower availability and severe weather conditions, can make it the best construction execution method to achieve cost savings. Structural engineering for modular structures is more complex than for conventional structures due to requirements associated with transport, handling, and final placement of complete modules or major sub-assemblies. A primary source of the additional complexity is the need for structural engineers to participate in the Weight Management process. Determination of module weight and Center-of-Gravity (COG) location is a key component of the Weight Management process. This paper provides an overview of the Weight Management process and presents a structural engineer's roles in this process. An implementation example is provided to show how the weight control data is generated by the weight reporting scheme to be used to assist project planning and management, specifically in material procurement and transportation logistics planning.

Built 100' deep into dolomite bedrock, the influent pump station at Valley Creek Wastewater Treatment Plant in Alabama is approximately 360' long and 230' wide. Several elements of this underground structure failed in April 2005 only a few weeks after its commissioning, partially flooding the pump station and rendering it inoperable. After the causes of the failure were determined, the engineer presented several repair options. The accepted repairs included wall and floor thickening using 25,000 epoxy grouted steel dowels, uplift stabilization of the entire underground structure using 700 high-capacity rock anchors, installation of concrete and steel transverse bracing for previously laterally unsupported basement walls, modifications to various structural elements for reconfigured load paths by new transverse bracing, hydrophilic urethane crack injection in the mat slab to reduce groundwater infiltration, and epoxy injection of numerous cracked structural concrete elements. Despite the magnitude and the challenges of the repairs, the pump station was restored within three years of the failure and is fully operational.

To expedite the design of foundations for the SCR support structure (40 m wide x 170 m long x 85 m high) at a Southeastern U.S. coal fired power plant, a number of STAAD Pro v8i (Bentley Systems, Inc., 2008) models were developed and Excel (Microsoft 2003) spreadsheets utilized. The forces were summarized in Excel to assist in the reinforcing design. There were a large number of primary load cases which resulted in thousands of service and strength load cases that needed to be analyzed. The large amount of data generated required post processing using Excel to consolidate and summarize the information. Typically, information is copied from STAAD Pro v8i and pasted into the appropriate location in the spreadsheet, however, one spreadsheet was utilized which uses Open STAAD (A library of exposed functions) to extract the pertinent information and combine the plate forces (Mx, My & Mxy). This spreadsheet was enhanced by graphics of the foundation plates that were then color coded to represent the extent of the required reinforcing. This provided a convenient visual representation of the extents of the required reinforcing. Due to poor soil capacity and large loads, micro piles to rock were required to support the pile caps. The micro piles were modeled in STAAD Pro v8i and the forces extracted to an Excel spreadsheet which compared the values to allowable capacities. Foundation thickness was confined due to existing obstructions (feed water pipes, electrical duct banks, etc) which limited the foundation shear capacity. In a number of locations micro piles were located within d of the columns requiring a deep beam shear check of the foundation. Another spreadsheet was developed to provide this check by extracting the plate moments and shear for each load case and applying it with the appropriate deep beam shear formula. A comparison between the allowable deep beam shear and the actual was then made.

Concrete pedestals of elevated water storage tanks support a steel vessel, schematically shown in Figure 1, or a concrete vessel, schematically shown in Figure 2. ACI Report 371R-08 [1] recommends that elevated tank pedestals be designed in accordance with ACI 318 (Code) [2]. The Code permits the shear strength of members to be calculated as the sum of the strength provided by concrete alone and the strength provided by shear reinforcement. For the concrete contribution to shear strength, Chapter 11 of the Code allows the designer of tank pedestals the choice of considering the pedestal as a compression member or as a shear wall. The Code provisions for compression members are based on tests of beams and beam columns of rectangular and solid circular cross sections. The Code provisions for shear walls are based on tests of walls of rectangular sections. The pedestals of tanks exemplified by the pedestals shown in Figures 1 and 2 are of thin-walled circular hollow sections. In addition, Chapter 21 of the Code provides requirements for structural walls subjected to seismic forces. This paper discusses the concrete shear strengths of elevated tank pedestals obtained from ACI 318, proposes alternate concrete shear strengths based on theory and test results on plain concrete, and presents concrete shear strength and limit state obtained from a pushover analysis of the pedestal shown in Figure 2.

Wiss, Janney, Elstner Associates, Inc. (WJE) was asked to investigate cracking and spalling of the concrete foundations of a number of liquid storage tanks at an ethanol manufacturing plant located in western Oregon. The plant was new at the time and the cracking and spalling of the foundations occurred immediately after the tanks were put into service. An initial attempt by the plant to repair the foundations failed immediately. WJE was asked to investigate the cause of the cracking and make recommendations for repairs. There were twenty metal liquid storage tanks at the plant ranging in size from 62 feet in diameter and 52 feet in height to 14 feet in diameter and 5-1/2 feet in height. All twenty tanks were constructed on foundations with a 1 in 12 slope. The only attachments of the tanks to the foundations were hold down bolts spaced evenly around the perimeter of the tanks, which were intended to prevent overturning. Although analysis indicated that friction between the base plates and the compacted fill was sufficient to resist sliding of the tanks due to gravity, wind and earthquake forces, it was evident that the tanks were sliding down slope. A study of the thermal expansion and contraction characteristics of the tanks by WJE found that thermal cycling would cause the tanks to migrate down slope. Ultimately, WJE was tasked with determining which of the twenty tanks were at risk of additional damage and determining if (and how) the process could be arrested. This paper discusses the problems with constructing metal storage tanks on sloped base foundations and proposes an innovative method to prevent downward sliding of these types of tanks.

Pipe bridges are widely used to cross over roads, highways, railroads and obstructions. Retrofitting of existing pipe bridges are required for many reasons such as additional levels, outriggers, and past modifications which were not considered in the original design. There are many items to consider when evaluating, analyzing and reinforcing existing pipe bridges such as operating loads, test loads, seismic loads, wind loads, analysis methods, and reinforcement plans. Pipe bridges are classified as pipe rack structures, which belong to non-building structures. The nature of pipe bridge structures are not similar to regular building structures, which have less redundancy to resist seismic or wind loads. Wind load determination can be a challenging topic due to the lack of research and design guidelines. In this paper, there is a comparative study of wind load determination, which is based on ASCE 7, ASCE Wind Loads on Petrochemical Facilities, a reference calculation performed in the 60s, current design practices and AASHTO wind pressures. The consideration of operating loads, test loads, seismic loads and load combinations for pipe bridges are also discussed in this paper. Usually, existing pipe bridge evaluations and retrofit plans will rely on a structural analysis of the existing bridge. In order to eliminate or minimize the extent of upgrades and satisfy client expectations, several design approaches and options need to be tried and compared. These efforts are also important to meet the project schedule and budget requirements. In some cases, obstructions will add to the difficulties of the retrofit project that requires additional efforts for passing code check, connection verifications and foundation reinforcement. Spring boundary conditions and analysis modeling options are discussed in this paper. It is found that the force redistribution among the structural members and foundations is important for retrofit projects, especially for pipe bridges located in congested areas. The enhancement for pipe bridge members, connections and foundations are also discussed and presented in this paper.

Built in the early 1970s, Aloha Stadium is a welded plate girder and steel frame structure located in Honolulu, Hawaii that was not designed for contemporary hurricane wind loads, much less the large earthquake design forces that current code now prescribes. The owner of the stadium elected to voluntarily upgrade the structure to resist current-code-level wind and seismic events. This paper presents the results of a multi-year detailed structural analysis and a multi-year structural strengthening project for Aloha Stadium.

With increasing knowledge of structural performance during seismic events, new building design has evolved to include redundancy, building regularity, ductile detailing, and continuity among many changes that set precedence for the retrofit of existing buildings. Many existing buildings require a seismic retrofit not only to perform to the level of similar new buildings during an earthquake but to even perform at all. However, it is impractical to seismically retrofit all existing buildings. This is why priority is given to retrofitting various essential facilities and in many instances, enforced through regulations. Many municipalities are required to seismically retrofit many of their essential facilities because of the economical and life safety impacts of not doing so. This paper will outline the seismic retrofit of an essential water storage facility for the City of San Francisco in accordance with ASCE 41-06. In addition, this paper will discuss in brief the temperature analysis performed on the reservoir.

In 2007 Walter P Moore relocated its corporate headquarters in Houston, TX, in 2007 to three floors in a tall building in downtown Houston designed by the firm. Working with the architecture firm Gensler, initial planning efforts identified the need to connect the workflow of the office via a new, common central stair atrium cut into the existing floor plates. The final design for the stair was chosen from an internal design competition that sought to identify a lightweight, progressive structural solution that highlighted the creative abilities of the firm. The design implemented for the stair consists of a cantilevered, stringerless arrangement that takes advantage of the intrinsic elements that exist functionally in a stair by rewriting the structural behavior of the stair through manipulation of the boundary support conditions. Using this design framework, individual elements of the stair were minimized through the use of high performance materials, including ultra-high performance fiber reinforced concrete (UHPFRC) and high strength steel cables. In addition to the optimization process that enabled the ultra-thin sections, a unique approach to vibration design was taken. The stair was intentionally designed to be somewhat flexible, allowing a platform for discussion of vibration perception topics with the clients who visit the office. The stairs are outfitted with a small tuned mass damper (TMD) and instrumented with accelerometers whose output is displayed on a large screen at the bottom of the stair.

Feature staircases are very popular in the architectural design of institutional and commercial buildings in North America and elsewhere. Generally, the iconic staircase is constructed from steel, has long unsupported spans and often consists of unique geometries. The gravity design of such staircases is trivial; however, designing the staircase to be insensitive to vibrations due to human activity is often challenging. The long spans, low mass, in conjunction with a low damping ratio, can result in a low-frequency system that responds with high human-induced accelerations. The damping ratio and the pace frequency have a significant influence on the vibration behavior of the structure. The AISC 11 design guide, which is the document used predominantly in North America for vibration design, does not contain any specific requirements for staircases. The UK design guide SCI P354, however, provides some specific information pertaining to their design. This paper examines the approaches of different vibration design guidelines and, along with the assumptions used in the analytical model, presents their application to the design of a feature staircase at a prominent academic institution in Toronto, Ontario, Canada. The four-story steel staircase, analyzed for vibrations using the finite element program SAP2000, has a nine meter cantilever span, with stone finishes and composite steel landings. To determine the best estimate for the actual damping ratio needed to be used in the analysis, acceleration measurements were performed on an existing staircase with similar characteristics. The study demonstrates that a large and inconsistent scatter of accelerations is obtained using the approaches specified in the different guidelines. It also emphasizes that the damping ratios recommended in the guidelines may not be indicative of the actual values and should be used with caution. Recommendations for damping ratios and pace frequencies for staircases are also provided.

This paper presents a case study of a 39-foot long, curved, conventionally framed monumental stair. The stair experienced considerable vibration issues under normal loading. A retrofit solution was designed and implemented to mitigate the vibrations. Before and after vibration results are included, as well as the design calculations for determining the repair. The paper includes an additional case study of a concrete slab on steel beam framed office building that started to experience vibration problems when the Owner removed steel and glass partitions during a remodel. The design solution, equations, and before and after results are presented.

In December 2009, Louis Vuitton opened their largest North American store in the retail component of the CityCenter development in Las Vegas. The three retail floors of the flagship store are interconnected with an elegant feature staircase clad in polished stainless steel, glass, and exotic hardwood. The steel structure is comprised of stepped stringers with folded plate to form the treads and risers. The staircases finishes are closely fitted to three sides of each stringer∖. The slender profile of the staircase was achieved by minimizing the depth of the stringer to 8 in even though the mi-landing is cantilevered 20' from the supporting landings. Extensive structural and vibration analyses and precise detailing of the integral glass guard ensure the performance of this monumental staircase. This paper presents a review of the analysis, design, and detailing of this feature stair steel structure and integral glass guard.

Transformation AGO is the recently completed renovation of the Art Gallery of Ontario by Frank Gehry. Within the building, visitors are intuitively drawn to Walker Court, the heart of the AGO bathed in natural light. The focal point of Walker Court is the Feature Spiral Staircase. From the ground floor the stair is experienced as a sculptural form clad in douglas fir panels. Upon entering the staircase at the 2^nd floor level, visitors travel through the roof of Walker Court and upward 90 ft on the north elevation of the new Contemporary Tower with landings on the 3^rd, 4^th, and 5^th floors. On the south elevation, an enclosed staircase, clad in stainless steel and glass, cantilevers 30 ft from the face of the building directly above the 4^th oldest surviving building in Toronto. The staircase has been dubbed the "Barnacle Stair" for the manner in which it appears to cling to the face of the Contemporary Tower. This paper will provide an overview of the design and construction processes related to the two monumental stairs.

As the entertainment industry continues its efforts to attract audiences and audiences search for ever more dramatic events, engineers are being asked to design and analyze a widening variety of temporary entertainment structures. Whereas concert tours and music festivals typically employ a standard range of modular stages, some events have started using stage structures that are unique and used for one event only. Wrestlemania XXVI in the spring of 2010 at University of Phoenix Stadium is an especially interesting example of this. Standard Stageco rental equipment was combined with several custom-built pieces to create a four-legged pyramid over the main event wrestling ring. In all, 40,000 lbs' worth of truss supported rigging loads equaling 63,000 lb. Unique, one-off entertainment structures present specific challenges for the engineer, not least because of the normally tight schedules. The loads and structure dimensions can be significant despite the temporary nature of the installations. And it is most often not feasible when problems arise to take the time to determine the cause(s). Usually, issues must simply be worked around if the event is to take place safely and on time. In working on entertainment projects, engineers need to be flexible and creative.

The ever increasing load demands placed on existing theaters by modern live entertainment pose unique challenges for the structural engineer. One of the more difficult aspects for the engineer is the fact that many of the older theaters have limited, or no, design/construction documentation in existence. In the absence of drawings, investigations must be based solely on surveys of the existing conditions of the stage supporting structures and the grid-iron and fly systems. Typically, one finds that structural modifications have been made over the years for various shows without the benefit of engineering reviews. The Hammerstein Ballroom Theater (circa 1906) and the Howard Gilman Opera House at the Brooklyn Academy of Music (circa 1908) are two particularly interesting examples of old theaters requiring structural reviews for recent productions of new shows whose loads would impose a high demand on the existing structures.

This paper presents the experience of the authors engineering stages for touring productions for outdoor concerts in stadia and other large outdoor venues. Stage structures spanning as much as 30m (100 ft) capable of supporting as much as 50 tons of entertainment equipment are regularly erected, dismantled, trucked and re-erected dozens of times in a major tour. Structures assembled in three days from modular steel components and platforms supported on scaffold systems are employed to create large stages often for a single performance at a venue. Most structures are designed to be supported at grade, often on sports turf fields, creating unique engineering challenges.

During structural design of reinforced concrete liquid containing structures, it is very important to visualize how shear and moments are transferred from the wall to the foundation slab. This article presents simple explanations to understand the behavior of the shear/moment connection in reinforced concrete tanks. This includes figures and sketches to aid engineers in properly locating reinforcement, splices, and hook requirements. The proper reinforcement location, taking into account the development of the stresses transferred, is one of the most important detailing challenges in liquid containing structures in order to avoid crack formation and potential leaking. Using the tips and explanations presented, the engineers will be able to minimize cracking in the connection, as well as to understand the structural behavior of the wall/slab joint of liquid containing structures.

The Meck Plot is an adapted version of the well-known Southwell method for determining experimentally the critical load of a structure undergoing lateral-torsional buckling. It has been demonstrated that lateral displacement and rotation are directly coupled when lateral-torsional buckling occurs. Recently, it has also been interestingly shown that lateral displacement of an I-beam undergoing lateral-distortional mode of buckling is directly coupled with the web transverse strain, and satisfactory results have been obtained as a result of application of the Meck's method on these deformation variables. In this paper, one further step is taken in this regard and it is shown that web transverse strain may even be used with either web longitudinal strain, vertical deflection, or angles of twist of top and bottom flanges of an I-beam undergoing lateral-distortional buckling and still good results be obtained as a result of application of the Meck Plot on each pair of these deformation variables.

The new Deacero Headquarters in Monterrey, Mexico is a building focused on the changing world. The building was designed and engineered in a holistic fashion around two central tenents- flexibility and sustainability- while presenting it in a cutting edge architectural form. The structure was developed to maximize flexibility of the space. The structure was designed on a 17m x 17m (56 ft. x 56 ft.) column grid without the use of internal columns or bracing. All bracing is accomplished through a unique Vierendeel Truss framing system. The dry, hot environment of Monterrey presented a number of challenges to the façade system. To minimize heat gain on the structure, a sophisticated façade and louver system was developed. Some of the interior architectural features, namely a very slender elevator support frame, presented a challenging structural problem. These features required careful consideration of the analysis and the design to fully capture its architectural intent. The building has an extensive and sophisticated water management system that allows the building to be highly sustainable in a hot, dry environment. The system employs on-site water reclamation, bio-treatment and water recycling strategies. All of this results in a surplus of water which can be returned to the city.

Welcoming guests to Aria, CityCenter's 4,004 room hotel and casino, are two feature porte cochères: the Harmon Canopy to the north at the Aria Hotel lobby, and the Casino Circle Canopy to the east at the City Center Casino entrance. The canopies, with heights of 102' and lengths of 157', are large, three dimensional structures that use their geometry to resist loads and integrate into the surrounding program. The primary system to create the canopies' cantilevers are a series of cable stayed box girders on a radial grid attached to box columns. A single cable between the box beam and column is tensioned against pairs of compression struts to resist uplift forces in the canopy. Perpendicular to the frame of the box beam and column is a lattice work of stayed girts that support the inverted glass roof hung below. A series of in plane rods, bracing and radial struts create a diaphragm between the box girders to resist both seismic and wind lateral loading. In addition, the diaphragm stiffens the frames to reduce both periods and deflections. The extreme fast-track nature of the CityCenter construction schedule led to unique problems and solutions in executing the design and construction of the two canopies.

It is very common to consider the cross girder of a slab-girder bridge as a stiff-Rigid-girder rested on springs while distributing loads to main girders for simplification. This approach gives suitable results for primary manual analysis for bridges that have cross girder depth almost equal to main girder depth, small spacing between main girders, large spans of the bridge vent, and monolithically casted elements. Two simplified models were studied in this paper: an infinitely rigid beam rested on springs having an applied concentrated load, and an imaginary very flexible beam rested on springs having the same loading condition. These two models were studied to indicate the extreme conditions of the cross girder. An approximate governing equation is proposed to correlate the bridge geometry to the accuracy of applying the stiff girder approach. Concrete sections of main and stiff girders were considered to be cracked sections in either working or ultimate stages. It was obvious from the results that the bridge deformation) which is calculated by the stiff girder approach) is changing dramatically while changing bridge geometry. But the straining action of the bridge may not exceed the resistance values, before or after plastic hinges deformation.

The Alabama Department of Transportation (ALDOT) is in the process of transitioning from the AASHTO Standard Specification for Highway Bridges to the LRFD Bridge Design Specifications. One significant difference between the two specifications is the seismic design provisions. From a practical point of view, the desire is that typical details can be developed for the worst case scenarios which can be implemented for bridges throughout the state without a significant cost premium. To determine the effects of the updated seismic provisions on current practice, an initial study of existing bridges was completed. Three typical, multi-span, prestressed concrete I-girder bridges were selected for the study. In order to bracket the demands for typical bridges, the primary bridge geometry variables were span length, pier height and pier configuration. The bridges' Earthquake Resisting Systems were re-designed for the worst conditions for the state of Alabama. After doing the initial calculations with Site Class D as the soil condition, it was found that the Seismic Design Catergory B was the worst case for Alabama. The AASHTO Guide Specifications for LRFD Seismic Bridge Design was used for analysis and design of the three bridges. This paper discusses the changes made to two of the bridges in order to meet the requirements. The reinforcing detailing requirements in the pier for the hinge location were increased, the pier cap and drilled shaft were designed in accordance with capacity-based design, and the connection between the pier cap and girder was re-designed.

A new component-based, two-node, simplified, semi-rigid beam-to-column-connection element than can easily be used in conjunction with many available structural-engineering software products is proposed for computer-oriented structural analysis. Relevant connection element properties, such as its stiffness matrices, have been established. The proposed model circumvents the iterative procedure proposed by several code standards for determining the resistance capacity and rotational stiffness of beam-to-column connections while at the same time it also alleviates the inapplicability of four-node elements that have been proposed by several researchers for use in commonly available high-end structural engineering software products. In the process of formulating the analytical model, panel shear deformation of the joint has been taken care of by allowing the joint region of the column to undergo shear deformation. Numerical experience has been gained by processing several frame structural models. Application will be demonstrated using the general purpose finite element package ANSYS by way of applying to study a typical frame. Results have also been compared with those obtained by other researchers and a high-quality correlation between and among results have been obtained. In all cases, values obtained by the proposed two-node connection model have been acceptable for design purpose.

In mid-to-high rise structures, dual systems (DS) enable a structural designer to satisfy the stringent drift limitations of current codes without compromising ductility. Currently, ASCE 7-05 permits a variety of structural systems to be used in combination as a dual system yet the design requirements are limited to the following: Moment frames must be capable of resisting 25% of the seismic forces while the moment frames and braced frames or shear walls must be capable of resisting the entire seismic forces in proportion to their relative rigidities. This paper assesses the significance of the 25% design requirement for the secondary moment frames (SMF) in dual systems with consideration of current structural engineering practice. Three 20-story buckling-restrained braced frame (BRBF) dual system structures have been designed with varying relative strengths between the braced and special moment frame systems. The SMF system has been designed for 15%, 25%, and 40% of seismic demands and the BRBF system design has been adjusted accordingly based on its relative stiffness with respect to the moment frame. These structures have been examined with nonlinear static and nonlinear dynamic procedures with guidance from ASCE 41-06. The drift, displacement and ductility demands, and the base shear distribution results of this study show similar responses of the three prototype structures. These results indicate a secondary moment frame designed to less than 25% of seismic demands may be adequate for consideration as a dual system regardless of the 25% rule.

Tampa international airport interchange consists of two sub-interchanges: Courtney Campbell Causeway (CCC) and Spruce Street/S.R. 60 sub-interchanges. The objective of this paper is to present the unique and economic design of the steel bridges in the CCC sub-interchange. First, a brief description of the whole project is given. Then, a detailed discussion is presented of the most important bridge design issues influencing the selection of the best bridge alternative. Finally, some unique and innovative designs are discussed. The information presented in this paper is of benefit to both the novice and experienced bridge engineers.

Confined masonry (CM) consists of masonry panels surrounded by cast-in-place RC boundary frames that provide confinement to the panels. When a CM panel is perforated for the needs of opening, the confining effect becomes questionable. This research is aimed at the slender CM panel segments between openings and tie columns. A series of test was carried out to study the failing behavior of this type of panels under in-plane loading. The main variables are the position of tie columns, the number of panels, and the loading pattern. Three specimens were tested under monotonic loading, including two single wing-walls with a tie column placed at the tensile and compressive side respectively and one twin wing-wall with the tie column place at the middle. Another single wing-wall and twin wing-wall specimens were tested under cyclic loading for comparison. The test result indicated that the failing behavior of the specimens was considerably affected by the position of tie column but not by the loading pattern.

As engineers are being guided with greater frequency to ASCE 31, Seismic Evaluation of Existing Buildings, and ASCE 41, Seismic Rehabilitation of Existing Buildings, by state and federal government requirements as well as model building codes, greater numbers of buildings are being evaluated, upgraded, and even designed in accordance with the methodologies and criteria prescribed therein. By using these flawed standards, harm is being inflicted by the structural engineering profession on society-at-large. While the contributors to the original documents have been well aware of major technical problems with these documents since long before publication, efforts to mitigate the problems have been slow, and engineering studies of buildings across the country — including all buildings considered for lease by the Federal Government — are being impacted by these problems. To our knowledge, no formal efforts have yet been put forth to warn anyone — not engineers, not building owners, not government officials, and not building officials — that reliance on the documents can easily lead to wrong results — even though engineers most familiar with ASCE 31 and 41 acknowledge that in their own practice, use of the documents often entails modifying or ignoring major components of the published methodologies. In fact, despite the recent renewal of efforts by the associated ASCE committees to improve these standards as much as seven years after publication (and much more than a decade after the bases of these documents, FEMA 310 and 356, were published), these so-called standards remain highly flawed and continue to adversely affect the public interest. This paper discusses a selection of mind-boggling problems with ASCE 31 and 41, focusing on some aspects about which every engineer planning to use the documents ought to be aware.

Force-based seismic evaluation techniques for low ductility braced frame buildings generally will classify a braced frame structure as a potential collapse hazard if the brace connections are not capable of developing the force capacity of the associated braces. However, anecdotal evidence from major earthquakes has shown that most steel braced frame buildings have performed to a life safety or better performance level, even when brace connections have fractured. One reason for this lies with the contribution of the gravity framing participating as partially restrained moment frames. This paper discusses the seismic evaluation of a two-story 1980's braced frame building located in California. A nonlinear static analysis in accordance with ASCE 41-06 Seismic Rehabilitation of Existing Buildings was performed, with brace connection fracture and all the gravity frames modeled as partially restrained moment frames. The analysis showed that the building was very stiff, until the brace connections fractured. Following the connection fracture, the building became more flexible, but the gravity frames had sufficient flexibility to accommodate the earthquake induced drifts without compromising the stability of the building. The analysis showed that the building met the Life Safety performance level.

Firstly, a plastic-damage constitutive model for concrete complying with the laws of thermodynamics is proposed based on continuum damage mechanics theory. The damage constitutive equations, damage evolution equations and plastic deformation of concrete are derived. Secondly, Fiber damage analysis model(FDAM) for RC beam-column member is established by analyzing section of fiber beam column element, which was developed with VUEL subroutine based on ABAQUS/Explicit platform, with the uniaxial damage constitutive relations of concrete proposed in present paper being used. The member damage index is defined, which can describe the nonlinear damage behavior of RC members under any loadings. Accuracy of the model is identified preliminarily by comparing with the analysis results of solid element. Finally, a numerical analysis model based on finite element program ABAQUS combined with the proposed damage model is built to analyze the seismic damage of a high-rise structure, and the structure analysis results are compared to the data from shaking table test.

Wall-type precast reinforced concrete (WPC) residential buildings, which are assembled using prefabricated concrete panels for the slabs and walls, were widely constructed during the 1960–70s in Japan. The number of existing WPC residential units constructed before 1980 is approximately 470,000. Although these buildings are of high quality in terms of structural condition, they are not fully utilized due to their small and uniform unit plans that do not suit modern living styles. Creating new openings in the walls could widen the possibility of plan changes during renovation; however, a design methodology for new openings, including the addition of structural reinforcement, has not been developed for this unique structural system. In this research, reinforcement design for new openings was developed and improvement of seismic performance was examined in half-scale cyclic loading tests. Numerical analysis models were also developed and the behavior of the walls was well simulated.

A hexagonal space dome was analyzed to investigate the relationship between structural vulnerability and failure mechanism. The analysis of stress ratios under design loads has shown that the bars that have greater stresses are closely correlated to the deteriorating bars in structural vulnerability. This provides a new approach for structural vulnerability analysis. By calculating the vulnerability parameters of bars of greater stresses, a variety of failure modes can be found and the structural vulnerability can be estimated. Moreover, the relationship between vulnerability characteristic parameters and design ultimate load was discussed by analyzing the structural failure modes under El Centro and artificial earthquake ground motions.

The dynamic characteristics of the long-span corridor in a stadium are usually very complicated. The vibration may be significant when subjected to heavy walking excitations, which requires vibration control systems, such as dampers, to be implemented. In this paper, a stadium corridor using Tuned Mass Dampers (TMDs) for vibration control was studied. The eigenvalue analysis of the corridor showed that a vertical vibration mode is prominent, and the frequency of this mode is close to human fast-walking frequency, which can cause resonance in the corridor. Simulated walking excitation loads were applied to the finite element model. A variety of walking scenarios, and different TMD frequencies and distributions were investigated in order to optimize the frequencies and layout of the TMDs. The analysis results indicated that TMDs can significantly reduce the vibration response of the corridor due to walking, particularly near the resonance frequency. Though the TMDs were tuned to or near the resonance frequency, when subjected to other walking frequencies, the corridor's responses with TMDs also reduced substantially. The sensitivity of TMDs to structural frequency necessitates the field dynamic tests before fine tuning the dampers to optimize the vibration control effects.

From funding to design and construction, the Cross Street Bridge in Middlebury, Vermont is an infrastructure accomplishment that can serve as both inspiration and a blueprint others desiring to integrate infrastructure improvements into the fabric of the community. This paper discusses the development of the bridge —the longest simple span spliced girder known in the US—from conceptual design through final design and construction, providing detail on the team's design-build approach and the challenges faced and overcome.

This paper highlights the importance of accounting for three dimensional effects when modeling progressive collapse behavior. Two types of nonlinear, inelastic models are first presented: 1) a planar comprised of beam-column elements to represent key structural members, and 2) a 3-D model that accounts for the most important components of the building. After validation, the simulation models are exercised to investigate system robustness when columns are forcibly removed. The importance of 3-D effects is quantitatively investigated through comparisons of system responses captured by the planar and 3-D models. In addition, the effect of modeling the slabs is demonstrated by comparing the responses of a 3-D model without slabs and the same 3-D model, but with slabs. It is shown that the slab plays a crucial role in progressive collapse response.

The Alternate Path Method is used to examine the vulnerability of a 5-story barracks building to progressive collapse based on DoD criteria UFC-4-023-03. The building is composed of composite deck floor system and steel roof trusses, all supported by cold-formed steel stud load bearing walls. Two different wall section removal scenarios at the first story of the building were considered for the analysis. The analysis was performed using the "Extreme Loading® for Structures" software, a 3-dimensional nonlinear dynamic analysis software. The results show the ability of the composite deck floor slabs to bridge over the removed wall sections. The slabs were able to re-distribute the gravity loads to adjacent wall components, while some of the loads were picked up in tension by the stud walls above the slabs. The study provides a good understanding of the composite deck floor-cold-formed steel stud bearing walls building system in resisting progressive collapse.

The ability to perform accurate nonlinear simulations is a key component in the assessment of the behavior of seismic force resisting systems. A three-dimensional distributed plasticity formulation for composite beam-columns suitable for nonlinear static and dynamic analyses of composite seismic force resisting systems has been developed. New uniaxial constitutive relations are developed for the concrete and steel elements to simulate the cyclic response of steel reinforced concrete (SRC) members. The relations account for the salient features of each material, as well as the interaction between the two, including for concrete: varying levels of confinement within a section, cracking, crushing, and spalling, and for steel: cyclic plasticity and residual stresses. The accuracy of the formulation is validated against a comprehensive set of results from monotonically and cyclically loaded beam-column specimens. The formulation is suitable for use in parametric studies to quantify the seismic performance factors of special moment frames using steel reinforced concrete columns and structural steel beams following recommendations of the recently released FEMA P695 report.

Structure-Soil-Structure Interaction (SSSI) is defined as the effect that a neighboring structure has on the dynamic response of a given structure on a common soil site. The significance of SSSI is sensitive to the characteristics of the soil, structures, and ground motion, as well as the spatial distance between structures. The Hanford Site, a Department of Energy Facility, contains a complex of structures that exhibit significant SSSI behavior. The SSSI effect is measured in this paper by considering two models, one including the entire complex of structures and one including only the structure that exhibits the most critical SSSI response. The amplification is quanitifed through a comparison of transfer functions and seismic member demand accelerations. A realistic study of the sensitivity of soil parameters is accomplished by replacing the Hanford Site soil parameters with those of the Savannah River Site (SRS). SRS is also a Department of Energy Facility. As this Site is located in the state of South Carolina, the soil stiffness is less rigid and provides for a practical comparison. The sensitivity of the soil stiffness is quantified by taking a ratio of the response of the combined model to the response of the individual model for both soil types.

For a secondary mass damper such as tuned liquid damper (TLD) or tuned liquid column damper (TLCD), whose moving mass is liquid, it is impossible to pre-fabricate the damper in a factory for the identification of dynamic properties. Also, it is not easy to pre-fabricate a concrete tuned mass damper (TMD) in a factory whose moving mass is made of concrete. In this paper, an identification method of dynamic properties of secondary mass dampers based on the forced vibration test is presented. Decoupled equations of motion are derived from a coupled equation of motion of building and damper. The decoupled equations of motion are then applied to the system identification using the response of the damper as an input and the response of the building as an output. The proposed method is applied to numerical examples and an actual TMD and TLCD installed in buildings.

Column forces, displacements and accelerations experienced by the structure during strong ground motions can be reduced by weakening and (or) softening the structure and adding a supplemental damper. Although this approach proved to be promising analytically, the concept of "structural strength reduction" leads to inelastic behavior and large permanent deformations in the main structural system. In this paper a new concept is developed to emulate weakening in a structural system by adding an "adaptive negative stiffness device" (NSD) and shifting the "yielding" away from the main structural system; leading, to the new idea of "apparent weakening" with reduced inelastic excursions in the main structural system. This is achieved through an adaptive negative stiffness system (ANSS), which is a combination of NSD and a damper. Engaging the NSD at an appropriate displacement (simulated yield displacement), that is well below the actual yield displacement of the structural system, will result in a composite structure-device assembly that behaves like a yielding structure. The NSD has a re-centering mechanism thereby avoiding permanent deformation in the composite structuredevice assembly unless, the main structure itself yields. Essentially, a yielding-structure is "mimicked" without any, or with minimum yielding and permanent deformation in the main structure. In summary, the main structural system undergoes less acceleration, less displacements and less base shear, while the ANSS "absorbs" them. This paper presents the working principle and details on development and study of the ANSS/NSD. Through numerical simulations, the effectiveness and the superior performance of the ANSS/NSD as compared to a structural system with supplemental passive dampers is presented.

Shear connections in beams are conventionally designed to transfer shear forces only. It is assumed that there is no substantial moment transfer due to the fact that beam end rotation is allowable. The shear tab, or fin plate, connection is one of the simplest and most cost-effective shear connection types and, although its behavior under gravity and cyclic loading has been established, its response to the column removal scenario that is commonly considered for progressive collapse analysis is still relatively unknown. In this paper, challenges involved in numerical studies for simulating the performance of shear tab connections when a column has been compromised are discussed. Modeling definitions for performing highly nonlinear analysis are discussed and recommendations are made regarding obtaining verification by available experimental data. Shear, axial force, and moment versus chord rotation diagrams are presented for both numerical and experimental results and conclusion are made.

Several methods have been proposed to reduce the moment and axial force demands on the columns of steel plate shear walls. One such method is to reduce the strength of the infill plate by introducing a regular pattern of perforations in the form of circular holes. The decrease in shear strength of the system depends on the diameter of the holes and their centre-to-centre distance. It was found using a variety of finite element models that although introducing the perforations may reduce the lateral strength of the system, the total demand on the columns can in some cases actually increase. Also, the perforated system is sensitive to the pattern of holes selected in that a small change in the arrangement of the holes can have a significant effect on the moment demand on the columns. Moreover, the flexibility of the beam-to-column connections affects the column demands considerably and also influences the sensitivity of the column design forces to the pattern of holes selected. An appropriate design method is proposed and the suitability of this system is summarized.

One of the critical factors affecting the strength of steel columns at elevated temperatures is the influence of material creep. Under fire conditions, steel columns can exhibit creep buckling, a phenomenon in which the critical buckling load for a column depends not only on slenderness and temperature, but also on the duration of applied load. Although material creep and consequently the phenomenon of creep buckling can significantly impact the safety of steel columns subjected to fire, they have received relatively little research attention, and are not currently explicitly considered in code-based design formula for columns at elevated temperatures, such as those in the Eurocode 3 or in the AISC Specification. This paper will propose a preliminary methodology to study the phenomenon of creep buckling in steel columns subjected to fire. Preliminary analytical solutions are presented, and compared with computational predictions for creep buckling. The analytical and computational results clearly indicate that accurate knowledge of material creep is essential in studying creep buckling phenomenon at elevated temperatures. In addition, the results show that neglecting creep effects can lead to erroneous and potentially unsafe predictions of the strength of steel columns subjected to fire.

A column failure caused by an explosion, impact, or other accidental events can propagate in a flat plate/slab structure through punching shear and lead to progressive collapse. The local post-punching behavior of flat slabs has been investigated experimentally and theoretically at the EPFL, Switzerland, and a mechanical model capable of predicting this behavior was developed. Using the mechanical model, an analytical model is developed here to estimate the initiation of punching shear failure as well as post-punching shear response of flat plates/slabs. The analytical model is used to study the system level post-punching response of structures and nonlinear dynamic finite element analyses are performed using a general purpose finite element software ABAQUS. The analytical model and the results of system level study can be of interest in assessing progressive collapse resistance of existing structures and in design of new structures.