Structures Congress 2012

Insulating concrete forms (ICF) have become increasingly common in commercial projects. In ICF wall construction, wall sections are built by stacking blocks atop each other prior to pouring concrete. A block consists of two foam panels with a cavity between connected by plastic webbing. ICF wall construction has several advantages over traditional assemblies of CMU and stick-frame walls, including: improved structural performance (demonstrated by wind projectile tests, ICF homes surviving hurricanes, and preliminary blast testing), energy efficiency, and speed of construction. STALA® integrated framing assemblies (IFA) were developed by STALA® Integrated Assemblies, LLC to streamline framing of openings in ICF wall construction. The IFAs act as the opening formwork and reinforcement. Protection Engineering Consultants (PEC) and STALA® performed an analytical study to evaluate IFAs used to frame ICF wall, door and window openings subjected to blast loads. The main goal was to develop design guidance for ICF walls with IFAs for Department of Defense (DoD) loads while meeting the DoD low level of protection (LLOP) response criteria (UFC 04-010-01). PEC developed a non-composite resistance function for each ICF wall and IFA combination for use in single-degree-of- freedom (SDOF) analysis program, specifically SBEDS v4.0. Design tables were constructed for DoD charge weights and standoffs based on the results of the SDOF analyses. The design tables illustrate how IFAs impact ICF wall blast performance as a function of opening width and clear spacing. In general, IFAs improve the performance of the typical ICF wall, such that all cases analyzed meet the DoD LLOP response criteria when subjected to DoD charge weights at conventional construction standoffs. This paper presents a summary of our assumptions, analyses, results, and recommendations for future work.

Mitigation techniques are continuously being developed to ensure public safety in the event of intentional or accidental explosions. Building material fragmentation is a major cause of human injury during such events. One of the most common methods of construction in buildings is the use of reinforced concrete material. Reinforced concrete structures are extremely susceptible to producing airborne debris that might cause severe injury to occupants or damage sensitive equipment housed within the building. Slurry Infiltrated Micro-Reinforced Concrete (SIMRC) is a new and innovative Ultra-High Performance Concrete (UHPC). The material consist of three dimensional mat system made from multiple layers of fine wire mesh infiltrated with a high-strength, self consolidating slurry. The slurry consists of Portland cement, supplemental cementitious materials, sand, and admixtures. The resulting product has an average compressive strength of 137 MPa (20 ksi), an average tensile strength of 20 MPa (2.9 ksi) and average shear strength of 15 MPa (2.2 ksi). It has a flexural strength and ductile performance that resembles steel. Detailed three-dimensional finite element models were generated using the explicit finite element software LS-DYNA. The finite element simulations are used to investigate the applicability of this material to various structural details and blast scenarios. This paper will present the analytical simulations, experimental testing and the uses of SIMRC for blast protection.

The paper presents experimental data generated for calibrating finite element models to predict the performance of reinforced concrete panels with a wide range of construction details under blast loading. The specimens were 1.2 m square panels constructed using Normal Weight Concrete (NWC) or Fiber Reinforced Concrete (FRC). FRC consisted of macro-synthetic fibers dispersed in NWC. Five types of panels were tested: NWC panels with steel bars; FRC panels without additional reinforcement; FRC panels with steel bars; NWC panels with glass fiber reinforced polymer (GFRP) bars; and NWC panels reinforced with steel bars and external GFRP laminates on both faces. Each panel type was constructed with three thicknesses: 152 mm, 254 mm, and 356 mm. FRC panels with steel bars had the best performance for new construction. NWC panels reinforced with steel bars and external GFRP laminates on both faces had the best performance for strengthening or rehabilitation of existing structures. The performance of NWC panels with GFRP bars was strongly influenced by the bar spacing. The behavior of the panels is classified in terms of damage using immediate occupancy, life safety, and near collapse performance levels. Preliminary dynamic simulations are compared to the experimental results.

Insulated Concrete Forms (ICF) have been used as residential and commercial building wall systems and in more recent years as floor and roof systems. The ICF consists of a reinforced concrete core formed between 2 panels of EPS (Expanded PolyStyrene foam) which acts as both permanent forms for the concrete core and the permanent insulation for the building. Typically only the concrete core with appropriate steel reinforcing is assumed to be the structural component of the building. Most of the ICF providers have load tables for resisting compression plus lateral pressure due to wind or seismic loads based on the thickness of the core and the amount and spacing of the steel reinforcement. Many building codes including the International Building Code (2009) include these materials in the chapters relating to concrete. FEMA 361 lists ICF as one of the materials to be used as a hurricane and tornado generated missile protection barrier with required core thicknesses depending on wind speed. This paper examines the possibility of the EPS foam panels contributing to the composite action of the ICF system to resist explosive blast loads. Both wind-generated missile impact tests and explosive blast tests have been conducted on ICF. The presence of the EPS outer form, which is usually about 2.5" thick, acts as a shock-absorbing cushion for both missile impact and the compression shock wave from an explosive blast. The plastic form ties that attach the inner EPS panel to the outer EPS panel restrains the hydro-static pressure of the uncured, wet concrete. These plastic ties and the inner EPS foam panel may also restrain any concrete fragments from penetrating into the interior of the building. This paper will summarize the results of these tests and present analytical evidence of the usefulness of not only the concrete core of the ICF, but also the EPS foam panels, as a blastresistant barrier.

A recent research program has generated uniform static and dynamic shock tube test results for unreinforced masonry walls retrofitted with spray-on polymers. The test program provided comprehensive static and dynamic data for developing SDOF based analytical models for three different polymer product applications. Two CMU wall thicknesses and two polymer application thicknesses were incorporated into the test program. The test data included mid-height displacement and support reaction time-histories. Multiple tests were run on several wall specimens, which allowed collecting dynamic response data in the light (Minor), moderate (Medium), and heavy (Severe) damage regimes for all three products. This paper focuses on the experimentation efforts and test results to generate necessary data for the validation of analytical models which were developed as part of the research program. These models consist of single crack and multiple crack (moment-curvature) SDOF models, along with engineering-level FEA models, both of which provide reasonable comparisons to dynamic test data. These models are not discussed in this paper.

Successful analysis of structural failures due to shock loading typically employs detailed three-dimensional codes that require excessive computational resources. Our interest is in developing more efficient approaches to evaluating the effects of damage on structures and personnel after a dynamic shock event. While several methods are currently available for a general analysis of structural failures under dynamic shock loads at a distance, we have developed a statistics based tool to predict the extent of damage for loads in close proximity to structures and quantify uncertainties. This tool is coupled with a fast-running, physics-based code that predicts the blast propagation in a tunnel of arbitrary complexity in order to form a single, user-friendly architecture to estimate the effects of blasts in tunnels. Use of such a fast-running tool facilitates scoping and planning of subsequent simulations using detailed, computationally expensive, models and provides a way to address parametric sensitivity.

The prediction of casualties and building damage, as well as the development of structural retrofits and blast mitigation methods, for blast in an urban environment depends heavily on the ability to accurately model propagation of air blast in such an environment. The Technical Support Working Group (TSWG) of the Combating Terrorism Technology Support Office (CTTSO) of the Office of the Secretary of Defense and the United States (U.S.) Department of Homeland Security (DHS) Science and Technology Directorate (S&T) have decided to address this issue through large-scale blast tests of simulated urban environments, as well as through the application of state-of-the-art numerical modeling, to assess how accurately the complicated reflection, diffraction, and diffusion of the blast wave can be predicted. The use of large-scale test specimens within a range of typical urban scenarios will provide a very large and realistic data-base. The ongoing, multi-year test effort is being performed by the Energetic Materials Research and Test Center (EMRTC) at their Simulated Urban Environment facility. Protection Engineering Consultants (PEC) is managing and directing the numerical modeling component of this program using a team of highly capable and well qualified organizations, which develop and apply their own computational fluid dynamics (CFD) codes and fast running models (FRMs). The experimental data collected by EMRTC will serve as a key benchmark for current numerical model assessment and for future code development and modification. Special care is being taken to ensure these tests yield the highest quality data possible, given the available resources. The breadth of the collected data will be more than sufficient to assess the current state of the art in numerical modeling. Numerous tests have been conducted to date. Two urban environment scenario layouts, with multiple charge configurations, have been tested at EMRTC. PEC is developing and populating a database of experimental and numerical results, defining the data analysis procedures, and statistically assessing the database to quantify the performance of each CFD code.

The blast load has a great effect on concrete structures; it can cause damage, which ranges from spalling to complete failure. This study presents an overview of the analytical models used to predict the spalling/cratering of concrete structures under close-in detonations. The study evaluates the current equations predicting the damage of concrete structures under blast loads comparing with the results obtained from a code developed by the authors. The routine was proposed using the MATLAB code, which is based on wave propagation through concrete members. The results were also compared to the existing damage level charts available in the literature. The results predicted by the developed code show a good agreement compared to the existing data available in the literature.

Typically, blast parameters at large distances from an explosive charge can be predicted with reasonable confidence with fast-running engineering models. However, when the charge is in close proximity to a target, the analyst's confidence in these engineering tools tends to diminish. Generally, there is limited test data available against which such tools can be validated for this purpose. A recent series of experiments conducted by the Air Force Research Laboratory at Eglin AFB, Florida, provides a useful data set that helps fill this historical gap. Two engineering-level methodologies are evaluated in this paper with reference to that body of test data. These are documented in the publicly available explosive safety manual, UFC 3-340-02: the Kingery-Bulmash formulation and the graphical method provided for Composition B cylinders. Parameters considered were the peak pressure as well as the total positive-phase impulse. The results provide instructive insight into the strengths and weaknesses of each model.

Pipelines are an extensive and critical part of the nation's infrastructure. Nationwide, there are 320,500 miles of natural gas transmission line and 168,900 miles of hazardous liquid line. Lines for local distribution of natural gas total 2.2 million miles [1]. Nearly all natural gas and 65% of hazardous liquids are transported by pipelines. Natural gas provides over 25% of residential and industrial energy needs, while oil products provide 97% of the energy used for transportation. In total, 62% of the energy used in the US is derived from these two sources [2].

The use of Single Degree of Freedom (SDOF) analysis for the design of columns under non-uniform blast load is investigated and, through comparison with dynamic finite element analysis, the limits of validation are identified for calculation of lateral displacements and dynamic reaction forces. First-principles derivation of the displaced shape of the element under a generalised load distribution, including account for shear deformation, permits the lateral displacement and flexural state of stress to be calculated with confidence, improving on the limits of validation of standard solutions for an equivalent uniform load and assume the location of plastic hinge formation. The dynamic reaction forces are considered and the extent to which higher modes affect the results of the analysis determined. Limits of validation of SDOF analysis for the calculation of reaction forces within reasonable accuracy are determined.

Vulnerability of buildings to disproportionate (or progressive) collapse has become an increasingly important performance issue in recent years. The current guidelines issued by the US Department of Defense use the alternative path method to assess the vulnerability of a structural system to disproportionate collapse. An energy-based nonlinear static pushdown analysis procedure is proposed in this paper to meet the need for a relatively simple procedure for preliminary vulnerability assessment of regular building frames subjected to local damage. This method can be used to check not only the vulnerability of the structure but also the possibility of structural instability during collapse. The predictions are found to be sufficiently close to the results of a nonlinear dynamic time history analysis (NTHA), even when failure involves more than one structural member and large displacements, that the method would be useful for collapse-resistant design of buildings with regular steel framing systems.

A collaborative research project supported by the American Institute of Steel Construction and the National Science Foundation is underway at the University of Washington, Purdue University and the University of Illinois at Urbana-Champaign to investigate the structural integrity of steel gravity frame systems. This comprehensive research program incorporates experiments exploring the behavior of critical components, including steel connections and composite concrete slab on metal deck, and also the behavior of complete steel gravity frame systems. This paper provides an overview of the key experimental components of the research program and presents results from the initial phases.

Beam-to-column connections play a critical role in a structural system's ability to resist widespread collapse by redistributing loads should localized damage occur due to an unanticipated extreme loading event such as a vehicular collision or an accidental explosion. Following the damage of a column in a steel frame designed to carry gravity loads, the strength and ductility demands on adjacent shear connections change substantially from those considered in conventional design. In addition to shear forces, large deflections can lead to the development of significant axial tension through what is known as catenary action. The behavior of steel shear connections under the combined effects of moment, shear, and tension has not been studied extensively and is not generally well-understood. However, this information is essential to assessing and improving the collapse resistance of structures. This paper presents the results of full-scale physical tests designed to investigate the behavior of common steel shear connections under load histories emulating the anticipated effects of the loss of an adjacent column, including large rotations and the development of axial tension. A variety of relative proportions of moment, shear, and tension were used for each type of connection, which included shear tab, single angle and double angle specimens, in order to permit a broad assessment of connection robustness applicable to different building geometries. This study examines the relative performance of these connection types, as well as the effects of connection geometry and combined loading. Observed connection capacities, ductility limits, and failure modes are presented and discussed.

This paper discusses the chapters of the newly published ASCE Standard, "Blast Protection of Buildings" (ASCE/SEI 59-11) on Structural Systems, Protected Spaces, Exterior Envelopes, and Fragmentation. This portion of the Standard addresses the features of structural analysis and design that may be used to improve the performance of structures in response to air-blast loading. It also includes the design of the exterior envelope, which is typically the weakest element of a building as well as the costliest to construct because of its large area. Chapter 6 addresses the protection of new versus existing construction; the relationship between aseismic design and blast resistance; analytical methods and modeling; characteristics of air-blast loads; and the prevention of progressive collapse. Chapter 7 addresses issues related to protected spaces and the hardening of interior partitions, walls, slabs, stairwell enclosures and plenums. The different levels of protection are related to performance-based design criteria. Chapter 8 defines the design intent for the building envelope in terms of the hazard-based and resistance-based approaches. Performance and construction requirements for new construction and retrofits are presented for glazing systems and doors; exterior wall systems, such as concrete, masonry and steel wall construction; roof systems; debris mitigating systems and venting. Finally, Chapter 5 addresses primary and secondary fragmentation and methods for predicting the hazards of airborne fragments.

Overhead protection (OHP) structures are used by major oil operators and government agencies in terrorist affected areas to protect facilities housing their personnel such as office facilities and dining facilities. Structural design of OHP structures to resist blast/fragment loads by 120 mm mortars and rockets is presented in this paper. The OHP structure consists of two layers: a pre-detonation layer and a shielding layer. The pre-detonation layer consists of plywood supported by steel beams, and this will cause the ordnance to explode upon impact. The shielding layer underneath consists of steel plates and sand bags supported by steel frames. The sand bags are intended to stop the fragmentation of the mortars or rockets while the steel plates and the supporting structural frames will resist the blast and impact loads. The blast and fragment loads caused by 120 mm mortar and rockets were calculated, and the required plywood thickness and sand bag thickness were determined. A finite element model for the OHP structure was developed using the general-purpose finite element program ABAQUS/Standard, and the structure was evaluated for the blast loads using the procedures in 2010 ASCE Guidelines, "Design of Blast Resistant Buildings in Petrochemical Facilities". In addition, the OHP structure was also evaluated for normal design loads such as wind loads and seismic loads based on 2006 International Building Code.

Vapor cloud explosions (VCE) cause considerable hazard in the chemical and petrochemical industries. They generate damaging levels of overpressure; the potential risk for human injury or death, damage to buildings and associated critical equipment becomes a concern. Predicting the possible consequences associated to vapor cloud explosions is important to ensure the safe design of existing and new installations. The accuracy of the assessments of such explosions is improved by carrying out experiments and by using theoretical models. To assess explosion hazards and to ultimately design safer structures several modeling approaches have been developed in order to estimate the air blast parameters at any given distance from a possible explosion source. Estimation of the overpressures that are generated from vapor cloud explosions is typically done via either simplified (empirical) models, phenomenological models or sophisticated computational fluid dynamics (CFD) models. This study includes a brief discussion on vapor cloud explosions and the prediction methods. The focus of this paper is on two of the most frequently used simplified prediction methods; the TNO Multi-energy (ME) model and the Baker-Strehlow-Tang (BST) model. The present study investigates the differences between the two methods and evaluates them in terms of resulting structural response and damage vulnerability caused by an explosion.

The design of three buildings, a control room, a large substation, and a medium substation are situated within a compression area for a natural gas facility. Owing to the close proximity of large gas compressors, these three buildings are designed to withstand blast forces from an accidental vapor cloud explosion. The control room is a single story building housing critical instrumentation controls and will be occupied continuously. The large substation and medium substation are two story buildings with the elevated floor housing critical electrical equipment and the lower floor provided for routing of connecting cables. This paper addresses topics pertaining to the rationale behind providing blast resistance, the determination of free field blast overpressure, structural engineering for blast resistance, and client-specific requirements. As applicable, topics are addressed with respect to the ASCE report Design of Blast Resistant Buildings in Petrochemical Facilities (ASCE 1997) and API Recommended Practice Management of Hazards Associated with Location of Process Plant Permanent Buildings (API RP752).

This paper presents an investigation into the influence that various idealized load shapes applicable to design in both the oil refining and chemical processing industry and the Anti-Terrorism Force Protection (ATFP) community have on the dynamic response of structural components. Although the most typical idealized load shape has an instantaneous rise to peak overpressure with a linear decay to ambient pressure over the duration of the load, other idealized load shapes that include a finite rise time to peak overpressure typically expressed as a ratio of the load duration are also used. More specifically, this paper explores the difference in structural damage between shock and blast pressure loading that are typically associated with detonations and deflagrations, respectively. As is common practice, Single-Degreeof- Freedom (SDOF) based pressure-impulse (P-i) damage curves for positive phase loading are utilized to compare load shape effects on dynamic structural component response. This paper also addresses the implications that the assumption of simplified, idealized blast load shapes for low fidelity analysis has on the assessment of structural component response.

Collapse performance of two existing buildings was investigated through experimental testing and computational simulations. Each building was tested in the field by physically removing four first-story perimeter columns from each building prior to building's scheduled demolition. Linear static and nonlinear dynamic analyses were performed using two- and three-dimensional building frame models. Experimental data from the field tests of two buildings were used to compare and verify the computational analyses. The measured strain data compared relatively well with the analysis results. In particular, 3-D model was more accurate than the 2-D model. The strain values calculated from the nonlinear dynamic analysis were smaller than those from the linear static analysis, and were closer to the measured strains. Also, linear static analysis resulted in larger remandto- capacity ratios (DCR) and vertical displacements than nonlinear dynamic analysis for both 2-D and 3-D models.

This paper investigates the role that flexural composite action between the concrete deck and underlying steel beams plays in the collapse resistance of steel structures. A 10-story, seismically designed steel building is used as a case study. The model employed in the simulation studies is a 3-D computational finite element model that accounts for the nonlinear, inelastic behavior of the most important structural components of the building. After validation, the simulation model is exercised to investigate system robustness when columns are forcibly removed, with specific emphasis on the role of the floor. The results show that slab-beam flexural composite action contributes significantly in the initial stages of collapse response, by reducing deformation levels and providing resistance against progressive collapse.

This paper presents several case-studies on a mid-rise (10 story) steel building subjected to compartment fire conditions and compares the results to understand the factors that can trigger and precipitate the collapse in a typical steel building. The study makes specific recommendations to reduce the risk of fire induced disproportionate collapse of steel structures. A 10 story steel building is designed following the current design specifications for a building located in the moderate seismic zone. Lateral load resistance (wind and earthquake) is provided by using moment resisting frames (MRFs) on the perimeter or a rigid elevator shaft at the center of the building. The Eurocode based parametric fire time-Temperature (T-t) curves are used to develop a representative fire loading. All the structural components are fire-protected according to the applicable building design codes. All the structural components, namely, steel columns, composite floor systems and connections are modeled in an FEM based software using macro level elements. The models were validated for accuracy and applicability in fire conditions against experimental data. The fire effects are simulated by assigning the pre-calculated temperature field for different structural components. Explicit dynamic analysis scheme used for predicting building collapse behavior includes the effects of degradation in material properties at elevated temperatures, concrete cracking, thermal strains, and plastic deformations in steel and concrete, etc. Some of the preliminary findings indicate that: (1) if all the components are designed for same level of fire safety, gravity columns are most likely to fail first in a typical steel building. (2) After a column fails, the load can be redistributed to the neighboring columns through a combination of flexural and catenary action in the floor system. (3) Reinforcement in the floor system can play an important role in safely redistributing the loads to the neighboring columns.

Design for progressive collapse resistance requires that the structure remains stable in the event that a primary structural member is removed following an extreme event such as blast or impact. However, these methodologies do not take into account the potential hazard of fire that is often a byproduct of an extreme event. This paper examines the fire resistance of a prototype steel high-rise building, which meets progressive collapse requirements per GSA. The building is modeled with the removal of a perimeter column thus simulating a consequence immediately following an extreme event. The building is then subjected to uncoupled thermal - structural analyses representing various fire scenarios based on the following parameters: (1) fire protection, (2) fire type, (3) location, and (4) fire spreading. The results show that even though the building meets progressive collapse design requirements, if the building sustains localized damage to the extent where nearby fire protection is removed or damaged, a subsequent fire may quickly lead to building collapse. While this finding is for one particular building prototype, it is a potential concern particularly for high-rise buildings, which must remain stable for a substantial time to completely evacuate building occupants.

This paper presents a new idea for retrofitting existing buildings and upgrading new buildings so that they are able to resist progressive collapse. The idea is to use vertical cables parallel to columns connected at the ends of the beams and hanged from a steel braced frame seated on the top of the building. A nonlinear dynamic analysis following the alternate path method (APM) recommended by UFC (2009) guidelines is adopted in order to investigate the viability of the proposed method. A ten story reinforced concrete building designed according to Australian Standard AS 3600 (2009) is adopted in this study. The structure is simulated using ANSYS 11.0 (2008) finite element software. The simulation results of the building example show that the proposed method of using cables and steel braced frame is efficient in absorbing the loss of a first floor column and eliminating the progressive collapse of the building.

Several studies have described the use of Fiber Reinforced Polymer (FRP) as a cost-effective retrofit to upgrade structural deficiencies, increasing gravity and lateral load demands as well as blast mitigation of existing structures. Specific applications of the FRP retrofits include increasing the flexure or tension capacity of deficient walls, beams, and slabs, providing continuous reinforcement for inversion in loading direction, and increasing the shear capacity of columns and beams. By combining these applications, FRP can also provide an effective upgrade to address the risk of progressive collapse. In this paper, the individual FRP applications are compiled to address applicability and limitations of FRP retrofits for each of the major progressive collapse upgrade methodologies. It includes a discussion of areas where the application has been verified by testing and areas where the application is analytically or theoretically based. Recommendations for future testing to address any gaps in the empirical information are also provided.

Perna Seca Hospital is considered one of the first reinforced concrete structures in Rio de Janeiro, Brazil. The structure is a sixteen story reinforced concrete structure with a total area of more than 25,000 m². Due to financial issues, the owner used only one half of the structure and left the other half unused. Over time, the unused half suffered severe deterioration and it became necessary to demolish it for the safety of the patients and employees of the occupied half. Before demolition, the contractor manually demolished a 15-meter strip between the two halves to completely separate them. A nonlinear dynamic analysis using the Applied Element Meothod (AEM) was used to verify and optimize the demolition plans proposed by the demolition contractor. The analytical results showed that AEM is a very good tool for simulating the progressive collapse of the structure. The analysis also showed that the impacting debris of the demolished portion of the structure with the ground had a minor effect on the remaining part of the hospital.

A number of tests have been conducted by Karagozian & Case (K&C) to determine the effects of blast on the response and capacity of connections that are used in steel and reinforced concrete (RC) framing systems. Many of these tests were conducted using structural subassemblies comprised of a column with three girders framed into it using different types of connections. Connection responses were measured using two different protocols. One involved measuring the connections' performance after the column and girders were struck with a blast, while the other protocol involved measuring the response of pristine connections. In both situations, the lower portion of the column was removed to simulate a missing column design scenario, and an axial loading was applied to the top of the column to measure the capacity of the connections. For each test, a pretest prediction with a high-fidelity physics-based (HFPB) finite element (FE) model was made to assess the validity of HFPB FE modeling for this class of problem. This paper describes the results of this work, particularly focusing on the capability afforded by different types of steel connections.

Understanding of the behaviour of laminated glass under blast loading is fundamental to the successful design of curtain walling against explosions. Several engineering model are available which describe the pre- and post-crack capacity of laminated glass suitable for formulation in a Single Degree of Freedom analysis, but each suffers from limiting underlying assumptions and the lack of systematic examination of the behaviour of laminated glass under blast loading means there is no general agreement about the analysis methods for design. This paper reports the development of a validated engineering model of laminated glass under blast loading, which is an evolution of those currently adopted in the UK and the US and have their foundation in UK and US full-scale blast tests undertaken since the mid-1980s. The model defines the pre- and post-cracked phases of the material response. The energy absorption in the pre-crack phase relative to the post-crack phase is small; therefore this paper focuses on the post-crack behaviour. The model is based on smeared material properties representing the nonlinear behaviour of the laminated pane in the post-crack phase, which avoids the need for explicit assumptions about the crack patterns and densities or the development of bond stresses in the pvb-glass interface. The reaction forces applied by the pane are calculated from measured stresses/strains using digital image correlation and strain gauge data, and are employed as an indirect means of deriving the internal resistance of the system. A generalised SDOF algorithm is used to develop a revised resistance function fitted to the experimental test data and the findings of these SDOF assessments reported. Investigation is made of the time-varying nature of the load- and mass-transformation factors for incorporation into the ongoing development of the model, and the next steps in the development of the glazing model are outlined.

Cable-supported curtain walls are increasingly common architectural façade systems that can achieve long vertical spans through the use of a pretension force in the cable. These systems, however, are relatively unverified in terms of blast resistance because of the upfront cost of the system's construction and the additional analysis and physical testing costs associated with validating the performance under blast loads. The response of cable-supported curtain walls is unique due to their inherent light weight and flexibility when compared to conventional rigid frame systems. As a result, the blast industry's typical uncoupled, single degree of freedom analysis methodologies may not be appropriate to capture the coupled response of the glazingcable interaction. Furthermore, the industry required balanced design is challenging to achieve because of the flexibility of the coupled system, which results in higher glazing capacities than those obtained through fixed support analysis. As a result, energy dissipating mechanisms may be required in order to control the ultimate behavior of these façade systems. Recently, Hinman completed the finite element analysis of a 30'-0'' pretensioned cable-supported curtain wall using the high-fidelity finite element analysis program, LS-DYNA. The presentation of this case study will discuss analysis procedures and results, which will emphasize all pertinent design, analysis and construction issues along with subsequent solutions for the acceptable performance of cable-supported curtain walls as blast mitigating systems.

There has been an increasing interest in the use of advanced materials in the design of curtain wall systems to resist blast loading. This paper summarizes a series of tests on high performance concrete (HPC) and ultra high performance (UHPC) panels to characterize the panel strength in flexure and shear for several panel types under dynamic loading conditions. The tests were performing using three types of FORTOCRETE panels supplied by USG. One set of HPC panels was lightweight concrete fiber-reinforced FORTOCRETE structural panels developed by USG. Another set of UHPC panels consisted of FORTOCRETE Armor panels that use ultra high strength fiber-reinforced concrete with and without E-glass face sheets. The testing was conducted at the University of California San Diego (UCSD) Blast Simulator Test Facility. A series of 20 panel tests were performed using the three panel types. Each panel was instrumented to provide experimental data to characterize the response of the panels that are suitable for developing and validating analytical models for the various configurations of FORTOCRETE panels. The instrumentation consisted of three types of measurements: 1) load measurements of the dynamic panel reactions, 2) strain measurements of the dynamic flexural strains in the panels, 3) velocity measurements of the overall panel deflection histories, and 4) dynamic reactions. Each panel type was tested at different levels of blast loading to achieve a range of panel damage responses ranging from light to failure. The experimental data was used to develop material property data, validate analytical response models and to generalize the panel results into PI response diagrams. Based on these results, several blast curtain wall concepts were developed for GSA Level C blast loads and above and were validated in full-scale wall experiments with the UCSD Blast Simulator.

The intent of this paper is to describe a test program conducted at the ABSG Consulting, Inc. (ABS Consulting) shock tube research facility in San Antonio, Texas, where cable supported polycarbonate shield systems where tested to determine their viability as a curtain wall retrofit option. A total of five tests, using three different window systems, were tested to assess the capacity of each shield retrofit installed on the interior of an existing glazing panel. As a complement to the testing, high-fidelity numerical modeling was performed using the explicit finite element code LS-DYNA. The computational models were developed initially to establish the expected performance of the design. Additional testing was performed once the mechanism of failure was understood. Subsequent modeling was used to calibrate the tested system. The test program indicated a viable curtain wall retrofit system using a cable-polycarbonate shield. Information related to the test setup and observations from the program will be described. Details related to the modeling including material definitions, element formulations, boundary conditions, applied loading, and response predictions will be included. Finally, a comparison will be provided that illustrates the validity of numerical models with respect to the testing.

There is a growing need to reinforce historic structures to resist air-blast loading due to exterior blast events. The façade systems of these buildings are typically backed by unreinforced masonry walls, using either brick or hollow concrete masonry block (CMU), which must be retrofit in place to resist the design blast loading. Some of the associated design challenges include: installation of wall reinforcement while preserving the aesthetic qualities of the building façade, coordination of interior finishes and MEP elements with wall reinforcement and anchorage, and providing adequate load transfer from the reinforced walls to the structural diaphragm. Two options for the retrofit of existing masonry walls are the use of fiber reinforced polymers (FRP) and geotextile fabrics. FRP is a high tensile strength material directly laminated to the existing substrate that can significantly increase the flexural capacity of unreinforced masonry. Geotextile fabrics are effective as debris-catch systems that allow the wall to fail and prevent the masonry debris from entering the protected space. While both are viable options, the design, construction, and performance of FRP and geotextile fabrics under blast loadings are quite dissimilar from each other. Both options require careful coordination with the rest of the design disciplines for proper implementation. This paper will review the analytical tools that are available to predict the behavior of unreinforced masonry walls retrofit with FRP or geotextile fabric when subjected to blast loadings. Design considerations and options, anchorage detailing and construction aspects of both materials will be examined, and a discussion of the architectural implications will also be presented.

The value assigned to historic buildings goes well beyond their association with times long since past. The architectural aesthetic associated with this unique class of existing buildings provides visitors and occupants with an unparalleled experience of the built environment. It is, therefore, only natural that a key design objective of historic building renovation/retrofit projects be the preservation of building elements that have become integrally linked to the structure's iconic status. Recognizing the need to operate within these bounds, physical security design solutions must explore the "gray zones" of criteria documents and push the boundaries of innovative and cost-effective performance based design to optimally address identified risk. The resulting design efforts have the potential to introduce tailor made solutions to mitigate vulnerability without burdening the overall project vision or budget.

High Speed Railway (HSR) systems are playing an important role in modern transportation infrastructures all over the world. Resonant vibrations induced in railway bridges by light HSR trains may be more demanding than the effects of heavy freight trains at low speed. The dynamic allowances prescribed by design standards for railway bridges subjected to low-speed traffic do not cover resonance. Design of HSR bridges combines dynamic analysis of peak resonant accelerations for checks of track stability and strength checks for the dynamic allowance resulting from analysis.

This paper explores a novel form for movable bridges which uses linkages as the main kinematic and structural elements. The proposed linkage-based movable bridge form was designed through 1) physical shape-finding, 2) generating a parametric model and kinematic equations, and 3) multi-objective structural optimization for minimum self-weight and minimum power for operation. Shape optimization is performed to determine the lengths and relative angles of members using a Multi- Objective Simulated Annealing algorithm. A nested sizing optimization procedure, using the Descent Local Search algorithm, designs the section profiles of members to meet the specifications of current American bridge design code. The ultimate result of this optimization procedure is a pareto-optimal set of solutions from which an engineer can choose based on design priorities. This case study meets the design requirements for the mobile section of the Woodrow Wilson Bridge Design Competition (November 1998) for the crossing between Alexandria, Virginia and Oxon Hill, Maryland, USA.

Dynamic response of a prestressed concrete, box-girder bridge to passage of a light rail vehicle at design speed is expressed as a Dynamic Amplification Factor (DAF) - the ratio of effect of a moving vehicle (i.e. dynamic displacement of the bridge) to effect of the static, dead load of the vehicle. If the lowest natural frequency of the bridge indicates it may interact dynamically with the suspension of the moving vehicle - if lowest bridge frequency is about 3 Hz or less - the Owner's design criteria require a refined analysis. The present paper describes a detailed, dynamic three-dimensional finite element analysis combining models of the bridge, including curvature, and of a moving vehicle including multi degree-of-freedom suspension system. A main advance of the analysis is the procedure by which we move the model vehicle over the model bridge using the contact feature of ANSYS. The structure is a slender, prestressed reinforced concrete box girder bridge that is part of a metropolitan light-rail system. The bridge is a dual track light rail bridge with three spans that will span a total of 584 feet. To evaluate the design of the bridge, a rolling stock analysis was carried out to determine the DAF of a Light-Rail Vehicle (LRV) traveling over the bridge at 55 mph. The DAF analysis is based on a three-dimensional ANSYS model that combines the bridge and the LRV, including mass distribution of wheel sets, trucks, and vehicle body, and the primary and secondary suspension. Based on preliminary analysis of the natural frequencies of the bridge (flexural frequency 2.2 Hz) and the LRV, Owner's criteria require a detailed DAF analysis. We find that DAF is 1.06, less than the threshold value of 1.33 that would require stiffening of the bridge.

A preliminary structural evaluation of the historic Ann W. Richards Congress Avenue Bridge in Austin, Texas was conducted to determine its viability to carry a combination of existing roadway and pedestrian traffic with proposed light rail vehicles (LRV). This article describes the analysis process and findings developed in the preliminary phase of the Austin Urban Rail Advanced Conceptual Engineering Study. The goal of this phase was to perform a high level fatal flaw analysis of the bridge based on information collected from available documentation and considering both center-running and side-running track configurations. The age of the bridge necessitated a historical investigation to recover original drawings, construction records, geotechnical information, etc., and document several modifications made since the bridge's original construction. Additionally, recent inspection reports of the bridge were collected and confirmed with a site visit. Review of a number of Light Rail Transit (LRT) structural design criteria documents developed by several transportation agencies around the U.S. led to development of a set of structural design criteria used for evaluating the bridge structure and retrofit options. Results of simplified analyses of the superstructure and substructure showed that the bridge's box beams would require strengthening in order to accommodate LRV loads in addition to current loads. Substructure analyses indicated that the bent caps seem to have adequate strength while the piers show significant reserve capacity but that the foundation may need to be strengthened. Development of preliminary retrofit schemes was based on analysis results, bearing in mind the presence of a bat colony living in the bridge. Estimated approximate costs established an order-of-magnitude comparative value to help the owner decide if a more detailed study is worth considering.

Active transportation bridges carry non-motorised modes, principally cyclists, pedestrians, equestrians, stock animals and native fauna. Designers must consider aesthetics, collision risk, the user envelope, loads, limit state criteria, deflections and dynamic behaviour, access requirements (including the mobility impaired), security against errant objects, railings, kerbs and balustrades. These issues are explored via several recent bridge developments in Australia. Design references considered during the design of Australian active transportation bridges are discussed and compared with the predominant codes of practice adopted in Europe and the USA.

Halcrow Yolles was retained to design and install a glass bridge spanning across the top floor as part of a major renovation of Eaton's Center in Calgary. Its defining features are the 46 feet long laminated glass balustrades and the single slender steel mid-span support structure. Design work for the bridge was completed using a finite element model of the entire bridge allowing for a detailed analysis of stress concentrations in the glass at bearing bolt connections. Special attention was paid to the aesthetic demands of the project as well as the limitations to transporting and erecting large glass panels. This project demonstrates how state of the art glass production techniques in combination with leading edge design methodology can lead to architecturally interesting structures.

In the design of pedestrian bridges, it is not uncommon for the size of primary structural members to be controlled by user-induced vibrations. Building codes published by various government agencies provide a range of limiting values for acceptable bridge fundamental frequency limits that may prove to be excessively conservative. For simply-supported bridge spans, a more efficient design can be developed through a performance-based approach which accounts for the dynamic response of a bridge subjected to a harmonic load function. The design methodology outlined in this paper determines the adequacy of a simply-supported bridge structure through the application of a damping-dependent frequency response curve, where pedestrian-induced structural acceleration is compared to a calculated allowable acceleration limit. The applicability of the design methodology is then quantified through a case study that addresses the analysis and design of a simply-supported steel pedestrian bridge in Southeast Asia.

The main objective of this paper is to determine the possible increase in natural frequencies of the two joist supported laboratory footbridges when bottom chord extensions are installed in an attempt to reduce annoying floor vibrations. The results with bottom chord extensions installed after the concrete placement are compared to results when the bottom chord extensions are installed prior to concrete placement. Results from the static and dynamic tests on the single span footbridge indicate that installing the bottom chord extensions to the joists after concrete placement and with the center of the span jacked up increases the flexural stiffness and fundamental natural frequency considerably, but not as much as installing the bottom chord extensions before the concrete placement. For the three span footbridge, installing the bottom chord extensions also increases the flexural stiffness and fundamental natural frequency considerably, but there is no distinctive advantage of installing the bottom chord extensions before the concrete placement. For both of the footbridges, the magnitude of the increases in natural frequencies is sufficient to consider the installation of bottom chord extensions as a remedy to stiffen (and retrofit) a floor and reduce floor vibrations due to occupancy movements.

This paper deals with the allocation and sizing of multiple tuned-mass-dampers (MTMDs) in an attempt to retrofit footbridges with multiple critical modes resulting from the excitation of pedestrian traffic. The simple and practical methodology proposed herein includes the use of an iterative analysis/redesign type procedure that converges to a given allowable level of acceleration. An example that uses this methodology to retrofit an existing footbridge is presented.

A system to store and analyze bridge data collected during field inspections is presented. The management of an existing bridge asset is a multistep process that involves bridge inspectors, owner/agency for the overall management and maintenance, structural engineers for rating and design of repairs, fabricators and detailers for execution of repairs. The described approach is based on the integration of existing commercial bridge software and Building Information Modeling (BIM) techniques and other applications to the life cycle management of existing bridge assets. A case study is presented with an application to a medium span steel truss bridge. The model used for the truss bridge contains easy-to-reference databases built from record plans and field inspections data and is integrated with rating and analysis software. The use of the model allows the stakeholders to evaluate at various times different aspects that affect the structural safety of the asset.

The Hale Boggs Bridge, built in 1978, carries Interstate I-310 over the Mississippi River in Luling, Louisiana. The bridge has an overall width of 82 feet accommodating two 12 ft. lanes with a 4.25 ft. inside shoulder and a 10 ft. outside shoulder in each direction. The main river crossing of the Hale Boggs Bridge is a cable stayed bridge having a total length of 2,732 ft. configured as 260, 508, 1222, 495, and 260 foot spans. The cable stayed bridge consists of two A-shaped towers, fanned cables, and a steel box girder superstructure. The superstructure is composed of two steel tub girders connected with diaphragms and steel orthotropic deck. Recent bridge inspections revealed that cracks occurred in the deck plate and the fillet weld at the connections of the box girder web transverse stiffener to the orthotropic deck. Also, it was found that the cracks only exhibited in the outer web of the box girders under the outside lane of traffic. A three-dimensional structural model was developed for the determination of the likely causes of the cracks. It was found that the cracks are due to the stress concentration in the orthotropic deck due to the presence of the transverse stiffener of the tub girder. In addition, the remaining life of the fatigue detail was evaluated and repair schemes to suppress the cracks were developed and verified with the three-dimensional analysis model.

In recent years, it has been recognized that Negative Stiffness Devices (NSD) may be suitable for seismic protection of structures. Although the concept of negative stiffness may appear to be a reversal on the desired relationship between the force and displacement in structures (i.e., the product of restoring force and displacement is nonnegative), when implemented in parallel with a structure having positive stiffness, the combined system appears to have substantially reduced stiffness while remaining stable. Thus, there is an "apparent weakening and softening" of the structure that results in reduced forces and increased displacements (where the weakening and softening is of a non-damaging nature in that it occurs in the NSD's rather than within the structural framing system). Any excessive displacement response can then be limited by incorporating a damping device in parallel with the adaptive stiffness device. The combination of adaptive negative stiffness and passive damping provides a large degree of control over the expected performance of the structure. In this paper, a numerical study is presented on the performance of a seismically-isolated bridge model that is subjected to various strong earthquake ground motions. The results demonstrate that the addition of negative stiffness devices reduces the base shear substantially, while the deck displacement is limited to acceptable values. The seismic performance of the bridge model is being investigated as part of the NEES-ADAPT Project which includes shaking table tests of the bridge to validate the results from the numerical simulations.

This paper evaluates the seismic demands for a three-span curved bridge crossing fault rupture zones. Two approximate procedures which have been proved adequate for ordinary straight bridges crossing fault-rupture zones, i.e., the fault rupture-response spectrum analysis (FR-RSA) procedure and the fault rupture linear static analysis (FR-LSA) procedure, were considered in this investigation. These two procedures estimate the seismic demands by superposing the peak values of quasi-static and dynamic bridge responses. The peak quasi-static response in both methods is computed by nonlinear static analysis of the bridge under the ground displacement offset associated with fault rupture. In FR-RSA and FR-LSA, the peak dynamic responses are respectively estimated from combination of the peak modal responses using the complete-quadratic-combination rule and the linear static analysis of the bridge under appropriate equivalent seismic forces. The results from the two approximate procedures were compared to those obtained from the nonlinear response history analysis (RHA) which is more rigorous but may be too onerous for seismic demand evaluation. It is shown that the RSA and LSA procedures which require less modeling and analysis efforts provide reasonable seismic demand estimates for practical applications.

One of the key steps of the Performance-Based Earthquake Engineering (PBEE) framework is the probabilistic seismic demand model (PSDM) analysis which provides a probabilistic relationship between a hazard intensity measure (IM) and seismic demands of structures. Determining the optimum IM is still a challenge especially for coupled bridge-soil-foundation (CBSF) systems when soil failure and liquefaction conditions are considered, since soil-structure interaction and liquefaction make the seismic response of the CBSF system more complex. The objective of this study is to identify an optimal IM to estimate the seismic response of a bridge on liquefiable and non-liquefiable soils with soil structure interaction. A case study CBSF with deterministic geometry and soil and structural modeling uncertainties is used to test alternative intensity measures on the basis of selection criteria such as efficiency, practicality, proficiency and hazard computability. In addition, an alternative measure to obtain the coefficient of variance of the seismic response of the components is proposed. This measure provides a method to compare dispersions across different components and potentially inform monitoring and maintenance decisions. Results show that of the 18 IMs considered, velocity-based IMs (e.g. velocity spectrum intensity, VSI) and structure-based IMs (e.g. spectral acceleration at the fundamental nonlinear period, S_a-nonliner) are optimal IMs. However, when hazard computability is considered, structure-specific IMs are not a good choice and VSI and PGV are recommended for practical use. In addition, although duration has a great effect on liquefaction, all IMs related to duration are the least efficient. Conventional studies for evaluating the seismic response of CBSF systems are often based on PGA, but the findings of this study indicate that VSI and PGV display a good correlation between the seismic demand and seismic intensity, thus reducing the uncertainty in predicting the seismic response of the CBSF systems.

Modern structures are able to survive significant shaking caused by earthquakes. By implementing unbonded post-tensioned tendons in bridge columns, the damage caused by an earthquake can be significantly lower than that of a standard reinforced concrete bridge column by reducing the amount of residual displacement. Reducing the amount of damage will allow for speedy repairs on the bridge and minimal closure time. The objective of this research was to investigate new construction methods for unbonded post-tensioned bridge columns that will reduce the amount of damage caused by an earthquake. Two 0.4-scale columns containing unbonded tendons were selected for testing. The two columns are identical except for the amount of longitudinal reinforcement crossing the joint between the column base and footing. For the specimens to be true scale models, the amount of post-tensioning required in a full scale column was taken into consideration. The large amount of prestress needed in a full-scale column requires separate tendons being spread out around the center of the column cross section. Following an earthquake, the tendons may need to be inspected or replaced. Anchoring the tendons to the side of the footing as opposed to the base of the footing was introduced for ease of replacement. The introduction of the unbonded tendons showed a significant reduction in residual displacements.

Seaport activities play an important role in local and national economic growth, but are often located in areas of significant seismic activity. Because container wharf systems are responsible for the critical task of loading and unloading cargos, it is important to understand the factors which influence their seismic response. This paper studies the specific effect of wharf-crane interaction for a hypothetical wharf structure as part of the NEES-GC Seismic Risk Mitigation of Ports. Previous studies concluded that during earthquake events, container cranes may act as tuned mass dampers for the underlying wharf structures and thus suggest that it may be appropriate to ignore the dynamic interaction so long as some small portion of the crane's seismic mass is included in the wharf model. However, this conclusion was made based on a simplified wharf model. This study, on the other hand, utilizes a detailed model of a hypothetical wharf including nonlinearities in the piles, pile-deck connections, and soil structure-interaction. Subjecting the wharf and crane to timehistories of ground deformation and pore water pressure, it is demonstrated that considering the crane not only does not reduce wharf response in all cases but may actually amplify structural wharf response. These results suggest that crane-wharf interaction should be given more careful thought than is currently required when evaluating the seismic response of a wharf system.

Seismic isolation is an innovative design approach to minimize the effects of earthquakes on buildings and bridges. The intent is to reduce the seismic demand on a structure rather than increase its capacity, thereby avoiding structural collapse and reducing human casualties. To assist the design of an isolated bridge, the Simplified Method of analysis is recommended in the AASHTO Guide Specifications for Seismic Isolation Design, for initial design and the optimization of various design parameters. It is a displacement-based methodology assuming a single degree of freedom model of the bridge and elastic substructures. This paper describes an extension of the methodology to ductile substructures while maintaining all the attractive features of the original method. The modified method is applied to the analysis of a seismically isolated, 3-span, curved highway bridge of total length 362.5 ft. The results are compared to a nonlinear time history solution using SAP2000 software for three levels of input motion: 0.475, 1.0 and 1.4 times the 360⁰ component of the Sylmar ground motion. Displacements and substructure shear forces were found to be within 13% for the lowest level motion improving to within 8% for the highest level motion.

This analytical work focuses on utilizing the experimental results of RC columns that are tested under lateral cyclic loading after being retrofitted using a new active confinement technique. In the experimental work, the plastic hinges of nonductile columns are wrapped with prestrained shape memory alloy (SMA) spirals. The spirals are then heated to activate the shape memory feature in the SMA spirals, which consequently results in applying large external confinement pressure on the columns. Experimental cyclic tests show that this innovative type of confinement is superior to conventional passive confinement methods. This work presents a validated analytical modeling technique for RC columns that are actively confined with SMA spirals. The proposed analytical modeling technique is proven to be effective in capturing the global behavior of the columns. The developed analytical models are then used to conduct a parametric study to examine the sensitivity of the confined RC column to several parameters including external active confinement pressure induced by SMA spirals, volumetric ratio of internal steel transverse and longitudinal reinforcements, column's diameter and slenderness ratio, and the level of the axial load. Multi-factor analysis of variance (ANOVA) is used to design the parametric study. The ANOVA serves as a statistical tool to assess the impacts of possible interactions between the studied parameters on the columns' behavior. The goal is to determine the most significant interactions that ought to be studied and discard those interactions with low level of impact. The results of the parametric study are used to develop recommendations related to the optimum confinement pressure and column properties that are most important in designing the new retrofitting technique.

This paper describes preliminary findings from a Montana Department of Transportation (MDT) funded project focused on testing the seismic performance of concrete filled steel tube (CFT) pile to concrete pile-cap connections. These connections are common/critical components of the support structure for highway bridges in Montana and across the country, and it is essential for these connections to perform well during seismic events. Despite their widespread use, the design and expected performance of these connections are not necessarily well understood. The preferred failure mechanism for this connection is for the pile cap to possess sufficient capacity to force the connection failure into the more ductile CFT piles. Traditional design methods for this connection often lead to congested and complex reinforcing schemes, and this complexity can obscure the true behavior/effectiveness of the elements within the connection. In this research effort, nine half-scale connections were tested under a monotonic pushover load until failure. The piles were then cycled through several load reversals. As a result of this research effort, a new reinforcing scheme was developed that greatly simplifies the design and construction of the connection while increasing the capacity of the cap. This newly developed reinforcing scheme includes U-shaped reinforcing bars that encircle the embedded CFT piles within the cap that counteract the moment related demands introduced by the embedded pile. In particular, this paper presents the details and results of the nine specimens tested during this research effort. Data collected during these tests includes load, deformations, and strains. The structural efficiency of the newly developed reinforcing scheme is discussed and contrasted with conventional reinforcing schemes. Additionally, future directions of this research effort are presented.

Most bridge design specifications have few requirements concerning the inclusion of live load in the seismic design of bridges. Although it is recognized that live load provides not only additional gravity load but also dynamic force effects due to its sprung nature, the significance of these effects on the seismic response of a bridge is not clear. The main objective of this study is therefore to investigate and obtain insight into the effect of vehicle-bridge interaction during earthquake shaking. The study consists of both experimental and analytical investigations. This paper focuses on the experimental work, which includes shake table testing of a 0.4-scale model of a horizontally curved steel girder bridge loaded with a series of representative trucks. Preliminary experimental results show that the presence of the live load clearly had a beneficial effect on performance for small amplitude motions, but that this improvement diminished with increasing amplitude of shaking. Parameters used to measure performance include column displacements, abutment shear forces, and concrete spalling.

A 0.4-scale model of a highly curved, 3-span, steel girder bridge with two different configurations of protective systems was experimentally studied using the NEES shake table array at the University of Nevada. In the first configuration isolators are provided at all supports ("full isolation") while in the second configuration isolators are only provided at the abutments ("hybrid isolation"). The isolators in the first case were designed such that the columns remained elastic under the design earthquake. On the other hand, the isolators in the latter case were designed to not only keep the columns elastic but also substantially reduce the superstructure displacements. This paper presents and compares bridge response, isolator performance, and column performance for the two cases. It is shown that both techniques are successful at protecting the columns, even during the maximum considered earthquake (150% design earthquake). It is also shown that the hybrid isolation technique reduced the superstructure displacements by a factor of about one-half, accompanied by a corresponding increase in the abutment shear forces.

Seat-type supports are normally used at bridge ends to accommodate thermal expansion and eliminate the high stresses that would otherwise be present in the superstructure when the ends are rigidly held. However, during large seismic events, there is high possibility that the joint gap between the end of the bridge and abutment backwall would close and high acceleration impact would result. It is expected that this abutment backwall pounding would significantly affect the bridge response. Yet, limited experimental research has been conducted to investigate the extent, how, and what components are affected by such effect. As a part of a Federal Highway Administration funded project, a two-fifths scale curved bridge model was constructed at University of Nevada, Reno Large Scale Structures Laboratory for shake table testing. One of the six configurations of the bridge model was designed to experimentally study the seismic performance of seat-type abutments, abutment backwall pounding, and its effect on bridge response. An abutment setup was designed to facilitate the investigation of the abutment impact accounting for the nonlinearity of the backfill soil. A compression-only device with permanent deformation was developed to represent the soil passive resistance. This paper describes the experimental setup developed to evaluate the seismic performance of seat-type abutments and characterize the interaction between the bridge superstructure, abutment backwalls, and nonlinear soil backfill.

A project that is funded by the Federal Highway Administration (FHWA) is investigating the seismic performance of curved bridges. As part of this project, the effect of rocking foundations is being studied. Prior investigations on the effect of rocking bridge foundations or foundations that allow uplift under seismic loads concluded that rocking behavior, if it occurs, limits the damage of bridge substructures and accordingly, is a mean of isolating bridges. These prior investigations only examined individual column behavior and not systems effects. This paper describes the results of analyses on complete bridge systems with rocking foundations. Five 3-span, single column bent, bridges with different curvatures were analyzed with different footing sizes under biaxial seismic loads, using nonlinear time history analyses. Distribution of the demands on superstructure and the overall displacements were compared to systems without rocking. Findings indicate that foundation rocking reduces the damage in the substructures, but increases the superstructure and the abutments displacements. As part of the FHWA project at the University of Nevada Reno, a two-fifth scale of one of the analyzed curved bridges will be tested using shake tables. The experimental setup is also explained in this paper.

There are many components of a curved bridge system that influence behavior during seismic loading. The substructure, superstructure, and bearing types have a dramatic impact on system behavior. To study this impact, a 2/5ths scale, curved bridge was designed and tested on the multiple shake table array in the University of Nevada Reno, Large-Scale Structures Laboratory. In addition, extensive analytical modeling has been undertaken. This paper focuses on the design and performance of the single-column, dropped-bent cap, substructure for the bridge. A parametric study was conducted to determine the optimal column size based on conventional details typically used in practice. After completing this study, the column was designed according to the AASHTO LRFD Bridge Design Specifications and AASHTO Seismic Guide Specifications for LRFD Seismic Bridge Design. Specific elements of the substructure response were found to be determined by the global response of the system. These include the torsional stiffness of the system, abutment-column interaction, and column plastic hinging. In particular it was found that column behavior was a combination of single and double curvature despite being pinned to the superstructure. This was due to the constraints at the top and bottom of the column in the radial and tangential directions. This paper discusses the performance of the columns during the experiment and presents initial comparisons with analytical results. It was concluded that the curvature of the bridge directly impacts the torsional loading and rotations at columns and bearings when shear keys are still intact. Once the shear keys fail, torsional loading and rotations change as system torsional modes are excited. Along with these discoveries, reverse bending of the columns is also expected and should be considered when designing single column bents in curved bridges. Experimental column investigation in curved bridge systems has provided information that could not be determined from component testing.

Residual stress-based post-weld treatments such as needle peening, hammer peening, and ultrasonic impact treatment (UIT) offer a promising means for extending the fatigue lives of existing welded highway bridges. When applied to bridge welds in service, these treatments can be particularly effective, since the stresses due to the self weight of the bridge have already been imposed. In this paper, a finite element (FE) analysis study is performed to investigate the additional benefit that may result from applying post weld-treatments under load. Fatigue tests of small-scale weld specimens treated with and without preloading are first described. 2D FE models that simulate the treatment process are then described and used to model the treatment of the fatigue specimens. Effects of plate thickness, indentation depth, and preload level on the residual stress distribution induced by peening under load are then studied. Based on the results of this work, recommendations are made to aid in the prediction of the fatigue performance of bridge welds retrofitted by peening under load.

Ultrasonic impact treatment (UIT) offers a promising means for addressing detected or anticipated fatigue problems in steel highway bridges. Although the beneficial effects of UIT are well documented, a number of issues have slowed its adoption by authorities responsible for highway bridge maintenance. Among the more important of these is the need for simple, quantitative ways to independently verify the quality of the treatment after it is applied. This paper presents the latest results of a research project currently underway with the primary goal of addressing this issue. The scope of this project includes: 1) fatigue tests on welds treated by UIT, 2) experimentation with possible quality control (QC) procedures, and 3) finite element (FE) analysis and fracture mechanics studies conducted with the goal of relating the fatigue test and QC results. This paper discusses the latest fatigue test and FE analysis results, focusing on how characteristics of the treated weld toe, such as the radius or notch depth, can be measured and related to fatigue performance.

Transverse cracks frequently develop on concrete bridge decks. The materials used at this time to fill and seal the transverse, longitudinal, and other cracks on bridge decks have an elongation factor of 10%. It has been observed that once applied and cured, the crack filling material fails once loads are applied and deflections occur. Once the filling material fails, it becomes partially functional only, and in many instances water or moisture penetrates the crack again. An experimental study for the FDOT had been completed to better understand the performance of four different types of sealant materials and their structural performance. This research utilizes finite element methods to model and simulate the behavior of the tested bridge deck without the crack filling materials. Three-dimension finite-element (FE) models for the decks were developed using ANSYS. The models were used to evaluate behavior of deck before cracks were formed to identify crack formation and propagation. Cracked decks without sealing fills were also modeled and analyzed to investigate the performance of the decks after cracking. The models were utilized to study the mechanism of crack development. Computational results were compared to experimental results and are in good agreement. The models will be used to examine alternate methods of controlling or preventing cracking and to study the effects of different load patterns, load magnitudes, deflection limits, bridge span length, bridge continuity, and structural system (simply supported and continuous spans).

The paper presents the use of the Persistent Scatterer technique (PS-InSAR) to monitor displacements caused by tunneling in intra-urban areas for the assessment of building damage. The first part of the paper describes the applied PS-InSAR approach based on Synthetic Aperture Radar Interferometry and illustrates first results of measurements gained from a current tunnel building site in Düsseldorf (Germany). Data from TerraSAR-X satellite provided by the German Aerospace Center (DLR) are used. In the second part two approaches for structural analyses are given. On the one hand the movements of surface structures due to tunneling are visualized. On the other hand the results are used to categorize globally typical intraurban surface structures with respect to vulnerability due to settlements induced by tunneling. In order to do so, an equivalent building stiffness is derived by comparing the displacements of the upper parts of buildings (PS-InSAR derived) and foundations (terrestrial measurements).

Concrete bridge decks are susceptible to premature cracking and to the corrosion of reinforcing steel. Many agencies have shifted to using higher strength concrete as an attempt to improve the long term durability of bridge decks. Unfortunately, higher strength concretes have not completely solved the problem and in many cases this has exacerbated the problem of early-age cracking. Bridge deck concrete should be designed to minimize the potential for cracking while providing a dense microstructure that reduces the potential for chloride ingress. Concrete mixtures can be designed using a concept called internal curing. Internal curing minimizes cracking while reducing chloride ingress. The work will describe how internal curing, through increased cement hydration and ITZ depercolation, reduces chloride penetration. The impact on chloride ingress and corrosion will be described through a series of experimental measurements. The paper reports results from several transport tests on reference and internal cured concrete for several bridges that have recently been constructed in the state of New York and Indiana.

High volume fly ash (HVFA) concretes have been used in the past; however HVFA has been primarily advocated for use in mass construction applications. Recent interest in developing more sustainable construction materials has led to an increased interest in utilizing these HVFA mixtures in transportation structures such as pavements and bridges. These mixtures have a reduced carbon footprint, in addition to other improvements in the material performance. This paper presents a study utilizing the dual ring test to assess the benefits of the HVFA mortar mixtures with respect to reducing early age cracking. Three mortar mixtures were prepared with a water-to-cement ratio of 0.30. The first mixture is a plain cement mortar, the second mixture is a mortar where 40 % of the cement (by volume) was replaced with C class fly ash, and the third mixture is a mortar where 40 % of the cement (by volume) was replaced with C class fly ash and prewetted lightweight aggregate (LWA) to provide internal curing (IC). The cracking potential due to thermal and autogenous shrinkage was assessed. Results show a lower risk of shrinkage cracking in the HVFA mixture with internal curing. The IC mixture made using HVFA is more robust for construction at early ages.

Modular bridge expansion joints (MBEJs) are common large capacity bridge joints supplied throughout the United States. Most common are the single support bar service joints, though dedicated seismic variations exist at increased manufacture and installation cost. This paper assesses the effectiveness of a burgeoning subgroup of modular bridge expansion joints comprising of shape memory alloy (SMA) enhanced single support bar variations that maintain service performance and aim to improve seismic joint performance. Such an effective subgroup could potentially increase the inventory of bridges with seismically resistant joints and improve post-event functionality since joint damage often inhibits traffic passage. To this end a set of ten synthetic ground motions are used to simulate the behavior of both an as-built and an SMA enhanced modular bridge expansion joint. A simplified one-degree of freedom bridge-abutment model is used to estimate bridge-joint behavior. The differences between the standard MBEJ and the SMA enhanced MBEJ demonstrate that the addition of shape memory alloy properties improve the joint's ability to accommodate seismic movements.

Among the states, Florida has the largest stock of moveable bridges, most of which with open grid steel decks. These decks are often associated with poor rideability, high noise levels, susceptibility to fatigue damage, and high maintenance costs. To address these issues, two alternative lightweight shallow deck systems are proposed. One with a thin flange, narrow ribs across the deck span, and short transverse ribs, made with ultra high performance concrete (UHPC) and high-strength MMFX steel (HSS). Another one is a hollow core deck made with UHPC and fiber reinforced polymer (FRP) tubes. A large number of experiments, both static and fatigue, were conducted on simple and continuous two-span models of the UHPC-HSS deck system with single and multiple ribs in the cross section. Limited tests were carried out on the UHPC-FRP deck system. The UHPC-HSS deck system was shown to satisfy the strength serviceability requirements, whereas the UHPC-FRP deck system required additional stiffness. In addition, a series of pullout and beam tests were conducted to determine the bond and development for high-strength MMFX steel in UHPC. A detailed comparison between experimental results and the code recommendations showed that ACI 408R-03 compares more favorably than the ACI 318-08 for the development lengths of MMFX in UHPC.

Present inability to manage large amounts of data properly is a big barrier for a widespread deployment of structural health monitoring, especially when multiparameter data is involved and combined with camera images. Various sensors can measure strain, tilt, temperature, and weather, while live cameras can visualize traffic, and all the data can be registered both statically and dynamically. In order to combine the complex monitored data and make it available for multiple users, which can be the owner/manager of the bridge, researchers, practitioners, or students, a website portal with live data streaming can be a good solution. Historic data can then be consulted using another, "Playback" software package. Both Live Portal and Playback should have embedded algorithms for data visualization, statistical data analysis and reporting. This new solution for data visualization and accessibility, which combines internet omnipresence, computer science, and structural engineering, has been researched, developed and applied on the Tacony-Palmyra Bridge between Pennsylvania and New Jersey and presented in this paper.

Early damage detection and localization is very important for maintenance and retrofit of civil structures. In the past decades, a lot of research has been conducted on structural condition prognosis using vibration measurements, which can be very conveniently procured in large quantities at a moderate cost. Many of these approaches, however, concern only the identification of structural damage existence, and do not attempt higher level damage detection. In this paper, three regressionbased damage detection algorithms are be presented and applied for damage identification in a two-span steel girder in the lab. All of them can perform local damage detection and evaluation to a certain extent. They have different modeling complexities, and thus have different performance levels. Damage identification/localization/severity evaluation results obtained from these algorithms are compared and contrasted.

Bridges can be characterized through either full-scale static or dynamic testing methods to obtain a more reliable description of their in-service characteristics than is often available from idealized analytical models. The results obtained from a full-scale characterization can be used to support decisions related to serviceability problems, retrofits, and maintenance of a structure. A number of different dynamic testing methods are available for characterizing in-service bridges including ambient vibration testing, forced-vibration testing, and free vibration testing. The authors recently conducted a field testing program on an aged truss bridge. The bridge was dynamically characterized by ambient vibration and forced vibration testing methods. The objective of this paper is to compare the global characterization results obtained from each test method and to evaluate the advantages and limitations associated with each approach for characterizing similar structures.

The Congress Street Bascule Bridge is one of the few four leaf bascule bridges in the country and is located on a major route that serves the Chicago Loop. The bridge was completed in 1954 and spans the South Branch of the Chicago River. In 2010, the Illinois Department of Transportation (IDOT) embarked on a major rehabilitation of the movable bridge superstructure as well as the electrical and mechanical systems. Walsh Construction Company of Chicago Illinois (Walsh) was awarded the work for the project. Because of the complexity of construction work, IDOT required the contractor to retain the services of a Movable Bridge System Coordinator to work with the contractor to verify that all aspects of the work resulted in a fully operational bridge that met the requirements of the project specifications. Collins Engineers Incorporated of Chicago (Collins) was selected by Walsh to perform this work. The authors discuss the construction engineering design and construction techniques required to rehabilitate a movable bridge structure of this size and complexity. The construction engineering aspects of the work include modeling the truss under various stages of demolition and erection to determine stability and to ensure that there are no overstress conditions during the work, temporary jacking struts to replace load carrying members, pull down procedures prior to placing the leaf in operation, evaluation of crane loadings, bridge balancing both for temporary conditions and final completion, live load and anchor column adjustment, coordination of shop drawings and other submittals, and other temporary works required to complete the construction. The work required the close coordination between IDOT, the designer PB Americas, Walsh and Collins to complete the work efficiently.

For the erection of curved and skewed steel girder bridges, the Erection Engineer must be able to predict the bridge displacements, stresses, and stability with reasonable confidence at critical stages of the erection procedure. There are several analysis methods that can be used for the erection engineering analysis of curved and/or skewed steel girder bridges. These analysis methods can be categorized into three levels: 1D, 2D, and 3D. The results of each level of analysis can vary for a given structure, depending on the geometric parameters of the bridge. In this paper, bridge component responses such as girder deflections and stresses are compared for the different levels of analysis for the selected bridges. It is shown, that for some bridges, the levels of analyses predict responses that compare favorably with one another, while in other bridges the predicted responses compare quite unfavorably.

Low clearance bridges are susceptible to collision with overheight vehicles. Collisions of overheight vehicles can cause fatalities and injuries to the drivers and passengers of the overheight vehicles, and damage to bridge girders. The repair of the damaged bridges can be costly and time consuming. Overheight collision has become a significant cause for the damage of bridges and the number is expected to rise. A previous work by the authors showed that a protection system called bridge bumper can be designed that maximizes the energy absorption and decreases the likelihood of damages and fatalities. The current work presents the full scale implementation of the bridge bumper to a realistic bridge subjected to overheight collision with a heavy vehicle. A detailed Finite Element (FE) model of the bridge impacted by overheight vehicle is simulated. The unprotected and protected bridge with bridge bumper is analyzed by a full scale non linear transient analysis. The key parameters such as material and geometric properties of the bridge and bridge bumper are varied. The protection system consists of a plate made of steel to distribute the impact energy over a large area called stiff guard (SG). Energy absorbing material (EAM) are used to mitigate the effect of collision. Two materials viz. low density aluminum and visoeleastic material are investigated to maximize the absorption capacity. The system can be designed for any given impact scenario. A realistic impact scenario is simulated and the applicability of the protection system is shown. This is a novel system for the protection of bridge girders from overheight collision. It is a fairly cheap system when compared with the repair and closure costs. It is easy to manufacture, assemble and impalement on the bridge girder. The research can be further extended for the protection of bridge pier, building column against accidental collision or terrorist attacks.

Local wind effects due to adjacent structures can significantly impact the loading experienced by a building in a developed environment. Phenomena such as buffeting, channeling, and sheltering can have unique, and occasionally unpredictable, effects on the loading and response for a particular building. While sheltering is often beneficial, wake buffeting and channeling may result in increased responses for some wind directions. The consideration of these effects, whether advantageous or disadvantageous, has become a vital component of modern wind tunnel testing procedures. While accepting the influence of general terrain characteristics on wind speed and turbulence profiles many codes and standards, including ASCE 7, mandate that the beneficial effects of sheltering should not be relied upon. This is a conservative and justifiable provision, which grows in importance as an individual building begins to greatly exceed the height of its surroundings. Generally, the removal of an immediately adjacent building is required in order to separate the load reduction (from code-specified values) due to building aerodynamics from that due to sheltering. Building codes, however, do not have specifications targeting interference effects. This paper reviews the relevant underlying mechanisms driving aerodynamic interference in the context of arriving at recommendations of early detection of potential interference effects which should be considered in the wind tunnel testing program. Examples are given which illustrate situations where surrounding buildings significantly alter the mean and dynamic wind loads for a building, which could lead to increased dynamic response for some combinations of structural properties. Discussion of the assessment, treatment and prediction of interference effects is provided in the context of the interaction of the project building with its surroundings. The paper concludes with recommendations on the approach to identifying, dealing with and planning for local wind loading caused by interference effects.

The following paper outlines key challenges inherent in the design scheme of a super-tall linked tower (mega-structure) and the unique considerations associated with developing the design of such a complex project. Although 1 Dubai was put on hold as a consequence of the global financial crisis in October 2008, the early phases of building optimization, high performance material utilization, and constructability considerations provided unique lessons that can be applied in future ventures. Intuition and experience on comparable projects is essential in their design but so is keeping a thoughtful approach to building system performance and remaining flexible enough to allow modifications in response to unexpected challenges. To attain an end product that is both rational and efficient, all team members must be able to respond quickly and in a coordinated fashion.

The Hangzhou CBD project in Hangzhou, China is a mixed-use development of approximately 400,000 sq.m. Sharing a common basement that extends over the entire site, there are three separate building structures above grade, of which Tower A is the signature building (Figure 1). This 43-story tower, accommodating offices, serviced apartments and an hotel, is 200 m tall with a footprint of 165 m by 33 m. The width of the structure to the outermost columns is typically only 24 m. The architectural design presented many challenges in the design of this nonprescriptive structural system. Two 15 m wide vertical slots through the building height, 75 m and 96 m tall respectively, along with long span spaces in the hotel public areas, required the use of various multi-story high transfer structures. Long span cantilever floor areas up to 22 m in length, supporting extensive areas of hotel program, were integrated into the architectural and structural design. Core wall configurations were optimized to ensure satisfactory structural behavior resulting from the irregular floor areas. The design processes involved in accommodating the architectural features and ensuring that the structural design meets the rigorous standards demanded by the Chinese codes are described. These include an analysis of thermal effects and non-linear seismic analysis.

The 56-story, 232 m tall Jinao Tower in Nanjing, China, incorporates steel bracing placed at the outside of a reinforced concrete frame providing an unusual lateral load resisting system. The Tower form was derived from the juxtaposition of an innovative double-skin façade and an external lateral braced steel frame that wraps the tower from crown to base and defines the dimensions and folds of the building envelope. The bracing was conceived three dimensionally by considering the faceted form as a volume rather than a planar system. Introducing the diagonal steel brace system on each side of the structure (outside of the tube-in-tube structure and between the double-skin facade) resulted in additional stiffening of the structure and a 40% design reduction in concrete and rebar in the concrete lateral load resisting system and a 20% design reduction in concrete and rebar for the overall building structure. Several studies beyond typical code checks were conducted to explicitly ensure the redundancy, ductility, and overstrength of the proposed structural system including a 3D nonlinear pushover and time history analysis, enhanced design criteria of key members and components, reanalysis after brace removal, and testing.

Skidmore, Owings & Merrill LLP (SOM) has been designing tall and complex buildings in China for close to two decades. The process of design of such buildings in China typically involves a detailed review by a panel of experts at the end of the Design Development phase. These expert panel reviews (EPR) are intended to validate the building designs, particularly when the buildings exceed the prescriptive limits and requirements of the codes. In specific instances, for instances where complex or new connection types are used or a when unique building forms or structural systems are proposed, the reviewing experts recommend that physical testing be performed as part of the approval requirements. Several of SOM's structures have involved testing; of components as well of the entire building structures. The paper presents a summary of the testing performed on several projects as it relates to the validation of the component design and system selection.

Officially opened in November 2011, the 413 m tall Al Hamra Tower in Kuwait was the 12th tallest building in the world upon completion. Setting it apart from other structures of this height is its complex non-prismatic form. The tower is approximately square in plan, but has an internal open atrium that is formed by cutting a 90 degree slice from the typical floor plate. The opening to the atrium spirals up the building height. The building's superstructure consists of a reinforced concrete core with moment frames along the building perimeter and hyperbolic paraboloid shear walls that bound the spiraling slice. With its complex shape and structure, load distribution to the foundations was concentrated in specific locations. A pile supported raft foundation, where both the raft and piles support the tower loads was recommended by the geotechnical engineers. Two approaches to determination of the contribution of the piles were evaluated; one in which the pile load capacities and stiffness contributions were based on the piles acting individually, and one based on the group action of piles. A design methodology that considered the two approaches was ultimately developed, substantiated by a Plaxis non-linear analysis of the soil-foundation interaction. The paper will discuss the development of the design parameters, the foundation design itself taking into account the load distribution and fast track construction schedule, the pile load testing, foundation settlement prediction and monitoring of the actual settlement.

High frequency floors are often used to support sensitive medical, manufacturing, and laboratory equipment to minimize accelerations due to walking and because most types of equipment are less sensitive to high frequency vibration. Therefore, it is important that structural engineers have accurate methods for predicting the magnitude of high frequency floor vibrations and several candidate prediction methods are found in the literature. This research investigates the accuracy of seven most widely accepted high frequency floor vibration prediction methods. In-situ modal and walking tests were performed on four high frequency floors of different types: steel framed floors supporting an operating room, an intensive care unit, and a research laboratory, and a concrete floor that would be suitable for supporting most types of sensitive equipment. Measurements are compared to predictions generated using the widely accepted methods to assess the accuracy of each method. The SCI P354 simplified method most accurately predicted the narrowband acceleration spectrum peak magnitudes and the SCI P331 method most accurately predicted the one-third octave peak magnitudes.

Buildings in major cities may be affected by vibrations from many sources such as trains, and subways. These ground-born vibrations are received at the building foundations and propagate up throughout the structures. The prediction of building floor vibrations plays an important role in the design of buildings for human comfort, the operation of sensitive equipment, and in nano-scale manufacturing. The ability to quantify and to predict building floor vibration levels enables engineers to take sufficient preventive measures based on a site condition. The accuracy of Finite Element Analysis (FEA) used for the prediction of building floor vibration depends on the mesh size used for modeling and the frequency range of the excitations. Although fine mesh sizes in FEA leads to greater accuracy, it becomes computationally prohibitive to achieve accurate predictions in higher frequency ranges. An impedance model provides an alternative simplified technique for the prediction of building floor vibration with great accuracy even in higher frequency ranges. This paper successfully illustrates the robustness of impedance modeling as compared to finite element (FE) modeling, in the prediction of building floor vibrations due to measured vibrational excitation at the foundation level. Impedance modeling provides the vibration response with a high degree of accuracy across the full frequency spectrum. Such models show the axial wave propagation along the length of a column when the floors are treated as point impedance discontinuities where they are attached to a column. Compared to FE models, it provides much higher accuracy with a method that is far more computationally efficient. Impedance modeling is a powerful tool for the simplified prediction of train and subway induced vibrations in the design phase of new buildings and may help with mitigating the effects of floor vibrations in existing buildings.

Historically, the effects of buildings on the environment have been solely evaluated based on mechanical, electrical, and plumbing building system energy use related to daily operations. Structural systems themselves are typically given little or no consideration for environmental effects; yet, in fact, they contribute significantly to the effects of climate change. Structural systems contribute to carbon emissions not only when they are built, but also over their service life, especially if they are located in regions of high seismic risk. The carbon footprint associated with the damage, repair, and partial reconstruction—or in some cases the full demolition and reconstruction—have considerable effects on the environment. The carbon footprint of a building is sensitive to its structural system with results that may be significantly more favorable with enhanced seismic resistance systems such as base-isolation or viscous dampers. Integrating environmental performance with seismic risk provides opportunities to communicate the benefits of enhanced seismic performance with regards to damage mitigation and environmental impacts to owners, developers, and the general public. Since currently available carbon assessment tools do not fully address the long-term environmental impact of structures, especially as it relates to probabilistic seismic damage, the Environmental Analysis Tool^TM has been developed and is capable of considering the environmental impact of structural systems over the entire life cycle of the building. The program is capable of predicting carbon emission equivalents at the conception of design simply by knowing the location of the proposed building, the size of the project, the structural material type, and the expected service life. The program is also capable of performing analysis during the later stages of design, for specific project information. The program can be used to evaluate new and existing structures. Several example projects are overviewed and the impact of probabilistic seismic damage on the carbon footprint is evaluated. Furthermore, a cost-benefit analysis considering enhanced seismic systems conducted. The Environmental Analysis Tool^TM is also implemented in a parametric environment for the assessment of buildings at an urban-scale. With the generated carbon footprint results, designers and planners can consider carbon emission equivalents of proposed buildings in the earliest phases of design.

Recent disasters and organizations such as SPUR have identified and highlighted a need for a shift away from designing code-minimum buildings that are life-safe but often "disposable." An important piece of this shift requires an understanding of buildings' life-cycle costs including a consideration of the associated environmental impacts induced by earthquake damage. Appropriate detailing of nonstructural components, the use of high-performance structural systems that outperform typical code-based designs, and consideration of the interactions between structural and nonstructural systems can greatly reduce expected damage and minimize the environmental impacts associated with seismic damage throughout a building's life. To evaluate seismic force-resisting systems and weigh their relative long term environmental impacts, the expected seismic damage throughout a building's lifespan and the environmental impact associated with that damage must be quantified. A method for performing such an evaluation has been developed by the authors and is discussed. Results of case study projects are presented and compared, along with lessons learned from the case studies and applications.

The Federal Emergency Management Association (FEMA) has sponsored a project by the Applied Technology Council (ATC) to develop next generation performance-based seismic design guidelines, FEMA P-58, that can be used to design new buildings or upgrade existing buildings to reliably and economically attain desired performance goals, and to assist stakeholders in selecting appropriate design performance goals for individual buildings (ATC, 2011). The project includes the establishment of a methodology for predicting the earthquake performance of buildings characterized in terms of probable life loss, repair costs and time out of service resulting from earthquake effects, expressed in a variety of formats useful to different stakeholders and decision makers. As part of this effort a Performance Assessment Calculation Tool (PACT) has been developed to gather and organize building information, perform loss calculations and evaluate loss information. In the spring of 2011, the project was expanded with the initiation of the ATC 86 to develop a draft methodology to quantify the environmental impacts (in terms of carbon footprint and other measures) of seismic damage and potential environmental benefits of performance based seismic design and retrofit. The project team is currently developing strategies to link life cycle assessment data to the damage and repair estimates generated by the P-58 methodology and as of December 2011 is approximately half way through the project. This paper outlines the seismic and environmental performance measures being integrated by the ATC-86 team and identifies critical issues to address as the project moves forward.

At this time, embodied energy and carbon impacts related to the design and construction of buildings in general, and load-bearing structures in particular, are not (yet) considered as a matter of course during the design process. Consequently, the relative magnitude of such impacts associated with fundamental structural design parameters is generally not well understood. This paper reviews some of the scientific background related to structural embodied energy and carbon and conceptually introduces two tools developed by Thornton Tomasetti that are aimed at quantifying and optimizing the embodied energy and carbon impacts associated with the design and construction of structural systems.

Model checking frameworks employ rule-based systems to a proposed design, with results such as "pass", "fail" or "warning", or `unknown' for cases where the needed data is incomplete or missing and generally they do not modify a building design, but rather assesses a design on the basis of the configuration of objects, their relations or attributes. The complexity in the building design and building construction process is increasing and the need for automatic model checking is becoming critical. This work presents an overview of existing frameworks for model checking in building design and particularly structural BIM (Building Information Models). The study reviews main concepts for SmartCodes and model checking and examines rules checking systems that assess building designs according to various criteria. This includes evaluating and reviewing the functional capabilities of both the technology and structure of current BIM model checking systems. The paper suggests a new framework for automated rule and code conformance systems for the structural domain.

This Case Study presents the design and construction of a new high performance building for the East Bay Municipal Utility District (EBMUD). The 5,600 square foot commercial building with offices, open cubicles, conference/meeting rooms, and locker/shower rooms serves 22 ranger staff that work in the Mokelumne River Watershed in the Sierra Nevada foothills approximately 30 miles northeast of Stockton, California. The designers created a unique building that included several sustainable and high performance features by employing a combination of "low technology" methods using design strategies from pre-modern historical practices with "high technology" analyses and controls. The sustainable features include water saving systems (rainwater collection, gray-water irrigation); low energy HVAC systems (radiant floors, natural ventilation, earth tubes, stack effect); and energy generation (PV, future wind turbine). The project goal was to achieve "net zero" annual energy use. Furthermore, the building was designed for steel-frame custom modular construction to minimize construction waste and provide a cost-effective building solution. This case study presents the design strategies employed in this project, the goals of minimizing water use and construction waste, the importance of reducing the energy demand, the benefits of non-conventional and low energy HVAC systems, and the potential for "net zero" energy use with a combination of power generation with PV and low-energy use features. The design strategies include project siting for optimum passive and active solar gain, using bioclimatic analysis for active and passive design strategies, high performance building envelopes to minimize thermal loss, floor slab mass for temperature moderation, and architectural features to reduce energy demands and to optimize day-lighting and minimize solar gain. Some of the unique sustainable features of the project include rainwater collection for HVAC hydronic systems, rainwater use for toilet flushing, a "night-sky-spray-chiller" for cooling water in lieu of a conventional chiller, earth tube preconditioning of ventilation air, and separate plumbing for gray-water collection to be used in irrigation. The project includes a 10kW photovoltaic system and options for a future wind turbine for backup power generation. This case study also presents building performance concept drawings, design schematics and renderings, performance specifications for a complete building as a product, key elements for competitive bidding, construction photos, cost analysis of conventional and high performance features, and lessons learned during the design and construction of the project.

Tornadoes like all natural hazards posses a full range of intensities with the majority having winds below 130 mph. In this paper, a dual objective-based tornado engineering design philosophy is explained that has the simultaneous objectives of (1) reducing monetary losses due to damage; and (2) reducing loss of human life. While these objectives may seem an obvious goal for any design code related to natural hazards they have not yet been adequately addressed within the context of tornado hazard by engineers and scientists. Consider that at the center of a tornado swath for a large Enhanced Fujita (EF) 5 tornado there are slabs swept clean of the residential building that once stood there, corresponding to a degree of damage (DOD) of level 10. Moving out perpendicular to the direction of the tornado path the DOD reduces at some gradient to a DOD of 1, which is the threshold of visible damage. To date, it has been widely agreed upon that there is little that can be done against intense tornadoes in woodframe buildings except seeking shelter. There are two considerations or design objectives for the approach outlined in this paper: damage (D) and life safety (L). Damage can be controlled at lower levels of the Enhanced Fujita scale wind speeds, i.e. EF0 and EF1, through the use of engineered connectors, design ensuring continuous vertical uplift load paths, and horizontal load distribution and load path. This is handled typically at the component design level, i.e. connectors, single load paths. For wind speeds corresponding to EF2 and EF3 level, both component and system-level loading must be considered to enable better performance. System level performance is related to load sharing amongst wall lines and distribution of the lateral load path as a whole throughout the building as it is racked by wind and amplified further by windborne debris catching on the structure. In tornadoes with wind speeds corresponding to EF4 and EF5-level damage, the major issue becomes system effects and focuses on other alternatives to provide life safety to the building occupants. These alternatives are above or below ground safe rooms and neighborhood safe shelters.

The spring 2011 tornadoes were record breaking in their intensity, severity, and loss of property and life. The Federal Emergency Management Agency deployed a Mitigation Assessment Team (MAT) to observe building performance in five states. Critical facilities, such as hospitals, fire and police stations, schools, and emergency operation centers, were a key area of study. The tornadoes significantly affected many critical facilities. Poor building performance resulted in occupant deaths and injuries, and also placed additional burdens on response and recovery personnel as they endeavored to assist their communities. To facilitate improved performance of critical facilities and enhanced protection of building occupants, the MAT developed Tornado Recovery Advisories for owners and designers of critical facilities located in tornado-prone regions. This paper presents the evolution of critical facility tornado design strategies over the past 40 years, with a focus on new strategies that were developed by the MAT in the aftermath of the 2011 tornadoes.

In the tornado of May 22, 2011 that struck Joplin, MO., two large schools were significantly damaged by the intense winds of that storm. Those schools together had space for over 2700 students. The high school was built in 1968 and the middle school was built in 2009 yet the performance of these two complexes from the tornadic winds was very similar. This paper will describe the damage to the schools and discuss some possible reasons for those results providing important lessons for rebuilding. The damage to the high school was extensive, particularly in high bay areas like the gymnasium and the auditorium. However, exterior walls also collapsed in courtyardfacing single-story classrooms and the exterior walls of the center section of the school were shredded with wind-borne debris while newly built walkways managed to remain standing because of strong load path continuity. The concrete floors and roof of the center section of the school provided sufficient strength to keep those elements of the structure intact. The middle school was also extensively damaged in the high bay areas of the gymnasium and auditorium. The one story sections of the school survived quite well except for some broken windows, but none of the roof or exterior walls of those one story sections were damaged. In the high bay areas, it appears the roofs lifted or were shifted from their connection to the walls and this allowed the walls to collapse in both the gymnasium and auditorium. The gymnasium wall was precast or tilt-up concrete covered with a brick veneer and the auditorium wall was CMU covered with brick. There were many failures in both schools at connections of common materials easily detailed in the type of construction utilized by both schools. This paper will also address the frequently observed condition of a lack of load path continuity in both the older and newer school and offer some mitigation strategies for rebuilding in this community where design wind speeds are only 90 mph (ASCE 7-05) yet where severe winds from tornadoes are a known and frequent hazard.

The year 2011 was one of the deadliest tornado seasons on record. As of August a total of 1543 tornadoes had been confirmed by the NWS and 2011 is on pace to becoming the most active years to date (NOAA 2011). Contained within this total are two of the most violent and costly tornadoes on record; one striking Tuscaloosa, AL on April 27th and the other Joplin, MO on May 22nd. Both were part of much larger storm systems that spawned numerous other tornadoes across these regions. The authors formed a team after each storm and conducted investigations of the damage with intent of gathering perishable data of damaged structures, paying particular attention to wood-frame residential homes. By looking at the nature of the damage, recommendations can be made to change construction practices and implement structural retrofits to reduce damage and fatalities.

The paper describes firstly the overview of the earthquake and tsunamis. Then, the observed ground motion characteristics are addressed. Features of structural damage by shaking will be provided in relation to ground motion characteristics with long duration. The damage in some area is addressed from the view point of the damaged area due to past earthquakes such as 1978 Miyagi-ken Oki earthquake. Regarding structural damage due to tsunamis, the tsunami load investigation based on the damage survey is also discussed from. Finally some aspects of lessons from the earthquake and tsunami are addressed.

This paper presented the investigation of reinforced concrete building structures by 2011 East Japan Earthquake. Generally, reinforced concrete structures in Miyagi region performed very well during the earthquake and effect of seismic retrofit was found in mitigation of damage, although severe damage to some seismically retrofitted buildings was noticed. A good correlation was observed between calculated seismic capacity Is-index and observed damage. Moreover, buildings designed according to the current seismic design code had minor damage in its structural members. However, major damage to non structural elements was commonly observed. Some typical damage observed by author's field survey in Miyagi pref. which is conducted mainly as an activity of the AIJ committee is described. Damage to structural members was not found in most of RC buildings which suffered tsunami, although damage to non structural elements was generally severe. However, severe structural damage induced by devastating tsunami was observed in some buildings.

The author has kept warning the danger of the failure of non-structural components in large rooms since Kobe earthquake in 1995. The Japan earthquake in 2011 has brought about the damage to the non-structural components, especially to the suspended ceilings in large rooms, in a very wide scale. The examples of failure are reported and discussed.

The 2011 Tohoku-Chiho Taiheiyo-Oki Earthquake (2011 Tohoku earthquake for short) caused widespread damage to steel building structures. The Steel Committee of the Architectural Institute of Japan (AIJ) conducted earthquake damage reconnaissance over cities where severe ground shaking was recorded. In general, steel office and industrial buildings exhibited excellent seismic performance. Buildings that used older cladding installation methods sustained damage to their claddings even if their structural performance was excellent. Damage to a few braced frames offer valuable insight into gusset plate connection design. It is widely recognized that a devastating feature of the Tohoku earthquake is the vast damage over the north-east coast of Japan caused by tsunami. This tsunami claimed nearly 20,000 lives. This coast is a rich fishing area and hence housed many fishing ports and facilities among other major buildings. At the port town of Onagawa, where the tsunami reached an extreme severity and height of 15 meters, a three-story steel building fell sideways after its piles failed. While the majority of steel buildings stood upright after the tsunami subsided, these buildings sustained heavy damage to its external and internal finishes. This paper summarizes findings made by the authors and their AIJ colleagues.

This paper explores the post-earthquake building assessment program that was utilized in Christchurch, New Zealand following the Canterbury Sequence of earthquakes beginning with the Magnitude (M_w) 7.1 Darfield event in September 2010. The aftershocks or triggered events, two of which exceeded M_w 6.0, continued with events in February and June 2011 causing the greatest amount of damage. More than 70,000 building safety assessments were completed following the February event. The timeline and assessment procedures will be discussed including the use of rapid response teams, selection of indicator buildings to monitor damage following aftershocks, risk assessments for demolition of red-tagged buildings, the use of task forces to address management of the heavily damaged downtown area and the process of demolition. Through the post-event safety assessment program that occurred throughout the Canterbury Sequence of earthquakes, many important lessons can be learned that will benefit future response to natural hazards that have potential to damage structures.

The aftershock that struck Christchurch, New Zealand on February 22, 2011 had a significantly smaller magnitude and duration than the September event in the same region, although the damage was much more significant. This paper explores the damage, both structural and non-structural, to low-rise, industrial buildings, primarily those with precast concrete cladding. Industrial buildings observed in and around Christchurch were typically comprised of either load bearing tilt-up panels with steel roof framing, or pre-engineered steel frames with pre-cast cladding panels. At buildings with load-bearing tilt-up panels, damage was observed in the panels as well as the connection between the panels and roof framing members. Buildings with steel frames supporting gravity loads and tilt-up panels for lateral resistance experienced damage in the connections between the precast and steel columns that were not designed for the required deformation. Recommendations for connections with better performance are suggested. Non-structural damage due to ground shaking and geotechnical damage is also discussed.

In less than six months the city of Christchurch, experienced two major earthquakes on September 4, 2010 and February 22, 2011. The former was generated by rupture of the previously unknown Greendale fault releasing a magnitude (M_w) 7.1 earthquake at 30-40km away from the city, while the latter event, a M_w 6.2, was less than 10km from the Central Business District on a buried fault at beneath of the city. Lifelines sustained widespread damage in Christchurch City and the closest districts of Selwyn and Waimakariri. However, no major bridge collapses were registered, and only twenty bridges required closure due to damage caused by the two earthquakes. Canterbury soils are susceptible to liquefaction, and the resulting lateral spreading caused extensive damage to roads/bridge approaches and the associates lifelines. Authors aim to provide a seismic damage assessment overview of Canterbury bridges, emphasizing unexpected issues that are still not properly detailed in New Zealand and overseas standards.

The performance of retrofitted unreinforced masonry (URM) bearing wall buildings in Christchurch is examined, considering ground motion recordings from multiple events. Suggestions for how the experiences in Christchurch might be relevant to retrofit practices common to New Zealand, U.S. and Canada are also provided. Whilst the poor performance of unretrofitted URM buildings in earthquakes is well known, much less is known about how retrofitted URM buildings perform when subjected to strong ground shaking.

As a result of new research, building codes have been altered to include increase the robustness of structures against extreme loads. One newly implemented structural integrity provision for the 2009 International Building Code (IBC) includes the need to provide a minimum tensile capacity in simple shear connections. One of the most economical shear connections, a bolted single-angle, has been analytically modeled to determine its ability to meet the new code requirements.

Exemplifying the integration of architectural and structural form, the Virginia Beach Convention Center is defined by a striking 80' (24 m) tall glass curtain wall at the entry to the Prefunction Hall. The window wall is inclined and subtly curved along its height to suggest the billowed profile of a ship's sail in wind, and is supported by vertically spanning, lens shaped bow-string trusses which act as cablestayed masts. The bow string trusses consist of an 8" (200 mm) diameter double extra strong pipe compression chord flanked on each side by 1 5/8" (40 mm) stressed steel cables acting as tension ties. The compression chord is extremely slender when considering its height between its pin-ended support points. This central spine relies upon the adjacent cables in tension to maintain its stability. Under lateral loads, the bow string truss central spine develops destabilizing axial compression while the cable tie develops stabilizing axial tension. Essentially, the individual bow string trusses are self-stabilizing mechanisms; the compression chord's tendency to buckle is resisted by the cable's tensile stabilization forces. Rigid cruciform arms act to link these balancing mechanisms, and therefore serve as brace points along the height of the compression spine. The system maintains a visual `lightness' as its stability does not rely upon direct member connectivity between compression chords. This paper describes the design of the bow string truss system supporting the curtain wall, with emphasis on the stability design of the individual trusses and of the overall system. Analytical methods which account for the geometrically nonlinear load-deformation relationship of the structure are described, as well as the means by which to account for the variation in stiffness of the compression chord as a function of stress level.

The Wind Technology Testing Center (WTTC) was designed to help position the United States as a global leader in the development of wind energy. Located just north of Boston, the WTTC is the largest facility of its kind in the world, and has the capacity to test wind turbine blades up to 90 m in length. The laboratory is enclosed by eleven steel trussed frames 140 ft wide, 82 ft high, and 30 ft on center. The 7 ft deep, three-dimensional frames are fixed at the base and self-stabilizing in all directions. These frames also stabilize columns and runway beams for an overhead crane system with two 50 ton cranes. The crane columns consist of round HSS sections, supported in the plane of the crane girder by attachments to the nose pipes of the trussed frames. These attachments allow vertical slippage so that the crane columns are not subjected to trussed frame overturning forces. In the plane of the runway beams, the crane columns are supported by the bending stiffness of the attachment and nose pipe assemblies. The investigation of tolerances with regard to eccentricity of the crane rails and runway beams required the interaction between crane girders, crane columns, and trussed frames to be studied in detail. This study included elastic system stability including second order effects, crane runway beam stability analysis using direct analysis methods to account for second order effects, and inelastic system stability accounting for maximum crane column eccentricity and second order effects. The paper discusses this study as well as its relationship to approximate methods of analysis for conceptual design of systems that are driven by stability considerations.

Design provisions for reinforced masonry shear walls (MSJC, 2011) differ in several significant ways from design provisions for reinforced concrete shear walls (ACI 318-11, 2011). Masonry shear walls have distributed flexural reinforcement, while reinforced concrete shear walls often have longitudinal reinforcement concentrated in confined boundary regions. In this paper, the reasons for these differences are reviewed, and areas for possible future harmonization are presented. Designs are compared for masonry shear walls and geometrically similar reinforced concrete shear walls in Seismic Design Category D.

Engineering education is distinct from education in other disciplines because it teaches the budding engineer to think in ways that other disciplines typically do not. The primary driver for that difference is the need for engineers to be able to perform engineering design. Engineering design requires knowledge of engineering science, how to use heuristics, and how to visualize a system that does not exist yet. These three traits partially demarcate engineering education from other disciplines. Furthermore, engineering education is based on a balance of non-engineering courses and engineering science courses, primarily knowing-that, versus the art and practice of engineering embodied in engineering design, knowing-how. This balance continues the demarcation of engineering education with respect to other disciplines. The required balance is hard to keep and has been nearly lost in the past. The realization that the balance between knowing-that and knowing-how is necessary also demarcates engineering education from other disciplines.

When someone asks, "What makes an engineer an engineer?" it is no different from an engineer asking, "Who am I?" This question is fundamental to understanding not only who we are, but also how we can grow as individuals. The easiest way to approach this question is to understand how and why we choose this as a profession. What made us think that engineering might be what we want to do? What makes an engineer unique? What we find are character traits that are common to most engineers. We are partly mathematicians and scientists, as one would expect, but we are also creative artists and inventors. We tend to be visual thinkers, who are attentive and self-reflective. Engineers are also confident risk takers temped by worry, who value intuition, logic, and living meaningful lives. We are in constant search for the know-how to be able to actively participate in creating a better built world.

Engineers often complain that non-engineers do not really understand what engineers do for a living. Some of this can be attributed to the persistent failure of engineers to reflect thoughtfully on the nature of their work so that they can recognize and articulate its truly unique aspects. The distinctiveness of engineering is often sought in the specific knowledge that it requires, but a frequent mistake is to focus on propositional knowledge-that, rather than practical knowledge-how. Engineering routinely requires the use of fallible heuristics and non-deterministic design procedures to formulate technical problems in a way that is manageable and then develop creative solutions to them. It involves skill and judgment that can only be acquired through experience.

Solar collector or photovoltaic (PV) systems placed on building roofs have been used extensively in recent years. These systems are sensitive to wind loading but design standards and codes of practice offer little assistance to the designers regarding provisions for wind-induced loading. The paper reports on a detailed literature survey, which has reviewed and compared the findings of some of the most recent and older experimental and numerical studies carried out for different solar collector system configurations. Results show significant differences among different studies, some of which correspond to similar configurations. Comparisons are made in terms of mean and, if available, peak pressure coefficients for different wind directions. The data are organized separately for solar collectors on flat and pitched roofs. Also the slope of the collector, as well as its location on the roof, has been taken into account. The review explains clearly the lack of design provisions in wind loading standards and codes of practice. It would indeed be very difficult to yield to an acceptable set of design provisions for solar collector and PV systems. The paper concludes that a new comprehensive study would be necessary in order to put together a set of provisions for different configurations including both point and area-averaged loads.

In this study, 3D unsteady Reynolds-Averaged Navier-Stokes (RANS) simulation is performed to predict the wind loading on a set of ground mounted photovoltaic (PV) panels immersed in atmospheric boundary layer. Attention has been given to proper modeling of inlet profiles, boundary conditions and turbulence model constants to minimize stream-wise gradients between the inlet and incident profiles. Distributions of pressure coefficients on top and back surfaces of the panel are investigated. Force and torque coefficients are also reported and the effect of Reynolds number on these coefficients is also discussed.

This study assesses the reliability improvements that could be achieved by attaching a tuned liquid column damper (TLCD) as a vibration control system to emerging wind turbines. The study employs a dynamic model of the wind turbine-TLCD coupled system and stochastic wind forces to obtain displacement response distributions. The reductions in structural responses gained by the damper are assessed in a probabilistic framework to account for system inherent uncertainties. Results indicate that the TLCD minimizes wind turbine responses under wind speeds ranging from 5 m/s to 30 m/s by up to 32.3% and 21% in peak and root mean square displacement, respectively. The study further develops wind-induced fragility curves for wind turbines with and without TLCD for operation and maintenance decision making by capturing failure probabilities conditioned on wind speeds for predefined displacement limit states. The curves show considerable reduction in the fragility owing to the TLCDs. The paper also examines the benefits of the damper in terms of site-specific probability of damages by weighting the computed fragilities with the likelihood of observing wind speeds in a specific location, such as West Texas. The study demonstrates that the TLCD is an effective control mechanism that reduces the annual expected damage probability by 13.8%. Minimization in fragilities and annual damage probability gained by the damper consequently reduces the expected number of stoppages, lost time, lost revenue and recovery cost for a given year.

Utility-scale wind farm development has been underway in the US for approximately three decades, and in that time, the tower structural systems (for supporting large wind turbines) have changed dramatically—from relatively short 20 m to 40 m steel lattice towers and guyed or self-supporting poles; to moderately tall 40 m to 60 m thin-shell steel fabricated tubes; and to the current wind industry standard of taller 80 m to 100 m steel fabricated tubes. Moreover, the observed evolution stages in wind tower design seem to have occurred approximately every ten years. So as the US wind industry enters its fourth decade, it is not surprising that wind tower design appears to be at a new threshold. Recently, the wind industry's attention has turned to a new generation of very tall 100 m to 160 m concept and prototype tower structural systems that include: flexible steel fabricated tube "soft" towers; multi-petal steel towers; hybrid towers constructed of both steel and concrete; all-concrete towers of post-tensioned concrete construction, either cast-in-place or precast; and next generation steel lattice towers, i.e., "space frame" systems. This paper provides a historical overview of these changing wind tower designs and describes the pertinent technical aspects of their structural engineering. The paper then explains the tower changes by discussing their underlying causes and effects. It discusses the changing design conditions in the wind industry that have been and are continuing to drive and shape the rapid evolution of wind turbine tower support structures.

Structural supporting systems for elevated drums - which consist of deck levels and the required systems for supporting drums and other operating equipment - can be complicated for operational purposes. Structure design can be even more challenging when dealing with drum replacement, which is different from a regular retrofit project. Replacing drums requires not only the verification of existing structure but also, during construction and after drum replacement, the consideration of module lifting, center of gravity, setting, and existing structure verifications. Drum replacement can be required for new technology application, increased production, or damage to existing drums. Due to a limited turnaround period for drum replacements, good planning and constructability reviews are essential for project success. Such an effort includes careful investigation of existing structure elements, the retrofit options, and construction detailing. This paper is focused primarily on the consideration of design loads, structure analysis, and construction detailing affected by construction sequencing.

The use of Advanced Fiber Wrap Composite systems has been widely used in buildings and bridges during the past two decades. As the global structural engineering community has adopted the fiber wrap technology for structural repair, so has the industrial infrastructure community. This paper will cover in detail the use of this relatively novel technology in the repair and strengthening of a reinforced concrete frame supporting a refinery coker unit. The Wilmington Refinery was commissioned in 1960's, and is responsible for much of the asphalt supply in Southern California. Due to the evolving building codes, the concrete structure, a refinery coker frame, was found to be seismically deficient. Advanced Fiber Wrap Composite Systems were utilized to supplement shear capacity to existing concrete columns and beams of the frame. Also, the use of proven concrete repair methods, and the special fire coat finish which were implemented as part of the retrofit will be discussed. The aim of this paper will be to discuss the Advanced Fiber Wrap Composite Systems method of repair and to compare with the current alternative conventional methods of repair. The benefits and deterrents for the different repair methods which were discussed by the engineer of record and owner alike will be discussed both from the construction, structural, and from the financial standpoint.

Open-framed structural steel industrial and petrochemical structures are susceptible to corrosion due to exposure to natural elements and chemicals within the facilities they support. Complete replacement of these structures is neither economical nor practical because it would require taking the facilities they support out of service. These facilities contain equipment, piping, electrical, and controls critical to the operation of the plant, and are normally kept online until a planned shutdown or turnaround. Certain precautions are required to repair and retrofit these structures while the facilities they support are in operation. This paper examines typical situations of corroded open-framed industrial and petrochemical structural steel structures, and provides potential solutions and recommendations for analysis, in-situ repair and retrofit of structures that are practical and economical. Retrofit and repair topics addressed include field welding, field bolting, component replacement, temporary supports, shop preassembly, repair of galvanizing, painting and other coating systems.

Steel pipelines, whether buried in the ground or exposed to the atmosphere, are susceptible to corrosion, which may impact their structural integrity. Pipeline failures can be catastrophic, especially for pipelines that transport hazardous materials. Maintenance actions, however, are often deferred following detection of localized corrosion due to operational requirements and financial constraints. Consequently, pipeline owners are often confronted with decisions as to whether a corroded pipe is still fit for service with an acceptable reliability or what is the remaining service life of the pipe before it poses a serious threat to public safety. The methodology presented in this paper to predict remaining service life of pressurized steel pipelines can be used to support decisions related to continued safe pipe operation and optimal pipe inspection intervals and maintenance schedules.

This paper will detail the major structural refurbishment required to an existing station to accommodate the new Second Avenue Subway. The existing mined and open cut structure was completed in the 1980s and today only half of the tracks and ancillary spaces are in use. As part of the Second Avenue Subway project, these unused spaces, platforms and tunnels will be reconstructed to enable trains to connect into the existing subway network. The major reframing of the deep station box will be described, including the complex sequencing and temporary supports required. The renovation of existing entrances and the construction of new street level entrances and ancillary structures integrated into residential and commercial buildings will be included. The challenges posed by the renewal of an underground space with restricted clearances and limited geotechnical and structural parameters will be highlighted.

This paper will highlight examples of the issues and possible solutions associated with constructing deep excavations adjacent to existing buildings in Manhattan for the new Second Avenue Subway. While some of the adjacent buildings are modern high rise buildings constructed on deep foundations, many are 4 to 5 story masonry brick buildings supported on shallow foundations that were built over 100 years ago and are often in poor condition. It will describe the existing geology of the site; methods used to monitor and survey; construction methods used on the project; and the different types of structural strengthening and repair details provided such as masonry, timber, steel and concrete reconstruction, underpinning, reframing and façade tie backs.

This paper will focus on the design of a new station entrance for the Second Avenue Subway with multiple elevators. Located on a small corner lot in Manhattan, the challenge was to create an efficient entrance with a minimal footprint that also included a large atrium space below ground with natural light from above. The principal constraints will be discussed, these included: maintaining capacity and access requirements, accommodating existing sensitive utilities, protecting adjacent existing properties, constructability issues and meeting the high end architectural requirements. The design and analysis methods will be outlined and the unique solution adopted will be described. This scheme incorporates architecturally exposed structural steel trusses spanning vertically between hoistways to support the shaft lining. This permits a high and open strut-free space in front of the elevators. Innovative and practical detailing of the steel trusses to accommodate the required elevator hoistway clearances will be discussed. The use of preloading to control deflections during construction due to the rock and hydrostatic loadings will be described.

The design of new underground subway stations in a complex urban environment will be discussed. Major topics covered will include both cut-and-cover structures and mined caverns, the factors in determining the applicability of each, and the main requirements and challenges of designing and constructing these systems in a highly constrained environment. The key determinants in the choice of the type of structure will be investigated. Loading, types of analysis utilized and constructability issues will be discussed. The discussion of cut-and-cover structures will include the use of both secant pile walls and slurry walls. The advantages, disadvantages, suitability and design considerations of each system will be examined. A key topic of discussion will be constructability issues related to these types of construction in a metropolitan area and the solutions that may be implemented. The close relationship with geotechnical data and its impact on geometry will be covered.

Two full-scale precast concrete cladding panels were tested in 2011 on a full-scale five-story steel fame building at the E~Defense shake table facility in Japan. The panels were designed according to common U.S. practice. Two issues evaluated were: 1) the effect of acceleration on the cladding panel, and 2) the effectiveness of the current slotted-bolt sliding connection to allow for inter-story earthquake motion. The cladding tests represented one type of standard US cladding façade design where cladding is designed to accommodate inter-story drift though racking of individual panels. Panels were cast in Japan but steel connections were designed and fabricated in the US to accurately simulate the behavior of American cladding construction. A 50 mm vertical seismic joint was installed between the two panels. Two full-height column cover panels were tested, a return cover 3D shape, and a flat panel. Instrumentation measured the acceleration of the panels and the movement of the slotted connections. Findings include the ability of slotted connections to slide while being accelerated in a full scale 3D seismic motion and development of fragility curves relating damage to panel and/or floor acceleration.

Nonstructural systems constitute a significant portion of the total property of a typical building. Recent earthquakes have repeatedly demonstrated that nonstructural damage results in significant loss of property and function with major catastrophic impact on communities. In a collaborative project between the NSF NEES program and the National Research Institute for Earth Science and Disaster Prevention of Japan, a full-scale, five-story steel moment frame building was subjected to a number of 2D and 3D ground motions using the E-Defense shake table. The building was tested under three different configurations: 1) base isolated with triple pendulum bearings (TPB), 2) base isolated with a combination of lead-rubber bearings and cross linear bearings (LRB/CLB), and 3) base fixed. As part of a NEESR-GC project on the "Simulation of the Seismic Performance of Nonstructural Systems," more than 75 m² (800 sq-ft) of suspended ceiling with lay-in tiles and 3 sprinkler branch lines were installed on the 4th and 5th floors of the building. The ceiling was enclosed by light gauge stud gypsum partition walls. This paper presents some of the preliminary observations on the response of nonstructural systems from these experiments.

Electric switchboards are essential pieces of equipment that manage and control the building electrical power system. For the evaluation of seismic vulnerability of electrical equipment, conventional shake table testing or highly detailed finite element models have practical and economical limitations due to the many different configurations of electrical switchboards. To address this problem, this study suggests simplified numerical models for characterizing the dynamic performance of switchboard cabinets. Numerical models for switchboard cabinets are generated using the finite element approach, and their nonlinear dynamic behavior is analyzed considering the material properties of cabinet frames, force-deformation of bolted connections, and the anchored constraint conditions. Through nonlinear time history analysis, seismic responses of the cabinets are investigated. It is found that the proposed model is capable of including nonlinear effects of switchboard cabinets while requiring low computational demand.

An extensive test program was conducted to investigate the mechanical performance of a wide range of passive fire-resistance systems during simulated earthquakes and their performance in subsequent fire tests. Since no general guideline for such tests is currently available, a test setup and measurement metrics were developed. The results show that different passive fire-resistance systems have different capacity to tolerate deformation while maintaining their smoke and fire rating. Consideration of earthquake-induced deformation in the assessment of passive fire-resistance systems will contribute to more robust post-earthquake fire performance of critical infrastructure.

This project involves earthquake and post-earthquake fire testing of a full-scale five-story building furnished with nonstructural components and systems (NCSs). A broad array of NCSs are incorporated in the test building, including a functioning passenger elevator, stairs, exterior walls, interior partition walls, piping, HVAC, ceiling, sprinklers, building contents, as well as passive and active fire systems. The NEES-UCSD outdoor shake table facility is utilized to support this full-scale testing program. In this paper, the design and construction of the test building and its NCSs are summarized. Testing is projected for March 2012, and pending this progression, preliminary data may be presented at the conference. Data obtained from this program will be used to evaluate and refine current code assumptions and computer models regarding nonstructural components and systems, and to find ways to minimize undesirable damage to NCSs during an earthquake.

The damage and failure of computer equipment typically supported by raised access floors in critical data processing facilities could have serious safety and economic implications. Current design provisions provide general guidance on how to estimate the seismic demand on non-structural elements within a structure. However, the possible lack of conservatism is of particular concern at locations near active faults where the vertical ground motion components have high amplitudes. Through reduced-order simplified modeling of a frame building and its raised access floors and computer equipment, we present findings on the insufficiencies of current industrial spectra considering a suite of risk-targeted ground motions with both vertical and horizontal components. Excessive seismic axial force demands are found for both access floors and computer equipment. This paper concludes that caution needs to be taken for seismic qualification and design of raised access floor and computer equipment systems considering vertical ground motions.

Base isolation of mission critical data center equipment provides high performance seismic protection of sensitive systems in seismically active regions. Base isolation technology works by decoupling the isolated elements from the horizontal component of strong ground motion shaking, essentially allowing the ground to move underneath the component without transmitting the damaging ground accelerations above the plane of isolation. The accelerations imposed on base isolated equipment can be five or more times lower when compared with a traditional fixed-base anchorage system, depending on location. This significantly improves the probability that the data center can continue to function following a seismic event. Base 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. WorkSafe Technologies owns the patents on Ball-N-Cone isolation technology, which uses two steel dishes and ball bearing to provide seismic isolation and has developed systems for isolating individual cabinets as well as an entire access floor. The Ball-N-Cone isolators are well suited to the lighter vertical loads associated with data center components 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 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 allowing for operational performance 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.

A full-scale, 5-story building was designed and constructed on the NEES-UCSD shake table. The building is outfitted with a wide range of common nonstructural components and systems (NCSs). Amongst these are two large computer servers donated by industry, with one supported on a raised access floor and the other conventionally anchored to the floor slab. In this paper we present the scope of the broader test program, an overview of its building structural design and numerical modeling, and relevant to this session, pre-test numerical simulation of the access floor - computer rack system. Pending the test schedule, preliminary test results for the computer rack - access floor system may be presented at the conference.

Designing a mainframe computer structure that can withstand seismic events requires significant testing and analysis. The computer frame and anchorage system must have adequate strength and stiffness to counteract earthquake-induced forces, thereby preventing human injury and potential system damage. However, this same frame and anchorage system must also meet the requirement of ensuring continued system operation by limiting overall displacement of the structure to accepted levels. Therefore, the test and analysis scope need to include the mainframe structure and its anchorage attachment to the building's concrete floor via a raised floor structure. This paper discusses the numerical modeling and its verification to quantify the robustness of a high end computer server structure subjected to a severe seismic event. The frame of the computer is the structure where components are installed (e.g., the central processing unit, the input-output drawer, the power supply component, etc.). The dynamic response of this structure is highly related to the weight of the components, the assembly's inherent natural frequency, and the location of the structure's center of gravity. The natural frequency of various mainframe configurations were analyzed and measured by either changing the weights (i.e., adding or eliminating components) or by changing the structural stiffness (e.g., adding reinforcement brackets). The main objective of the modeling was to ensure structural integrity following a seismic test of a functional server system. Finite element analysis (FEA) was employed as part of the overall frame's structural robustness design verification, whereby the simulated modal analysis results were compared to both the experimental modal data of the frame structure as well as measured swept sine data. This design study builds toward the objective of constructing a verified model of the server frame and components, which lead to a guideline for implementing optimized reinforcement. As part of the verification, the mainframe structures were subjected to horizontal table vibration tests simulating the loads and environmental conditions endured during seismic events. During experimental verification, the dynamic responses were recorded and analyzed in both the time and frequency domains.

Several earthquake related items should be considered in order to have a successful petrochemical project in a region of high seismic risk. One of the first things that should be established for the project is the seismic design criteria. The essential seismic parameters required for design include the design response spectra, Seismic Design Categories (SDC) assigned to structures, and liquefaction potential of local soils. These are essential for proper seismic evaluation of a petrochemical facility. Over estimation of these parameters can lead to costly over design. Under estimation of these parameters can only be corrected by even more costly retrofit. There are many petrochemical plants located in areas where there is a high probability of large ground motions due to earthquakes. Structures within these facilities are typically assigned to higher Seismic Design Categories which trigger special seismic detailing of structural steel, concrete, and equipment. The impact of these seismic detailing requirements is that there will be increased design and engineering man-hours, increased fabrication costs, and increased construction costs compared to comparable projects without seismic detailing. It takes knowledge of the applicable codes and standards, experience in planning and executing such projects, and coordination of efforts between engineering disciplines to mitigate the impacts of high seismic risk considerations. This paper not only identifies the major considerations for petrochemical projects in areas of high seismic risk but also makes recommendations for the mitigation of impacts due to these considerations.

The Federal Occupational Safety and Health Administration (OSHA) maintains standards (Standards) that define design and usage requirements for elements that support suspended scaffolds (e.g., davits, davit bases, outrigger beams) and fall arrest lanyards (e.g., dedicated roof anchorages) when this equipment is used to access facades and other elevated portions of buildings. Ensuring that applicable requirements are met is the responsibility of what OSHA terms a "qualified person"—typically a professional engineer. However, navigating and applying the OSHA structural provisions can be difficult primarily because relevant requirements are not located in a single document, structural requirements vary for different uses, and structural requirements are not always written in a manner consistent with typical structural engineering practice. It is important for engineers to promote and practice the rational application of sound engineering principles during both the initial design of this equipment and any post-installation load testing that is used to confirm continuing compliance with OSHA Standards. Unfortunately, certain trends and recent developments in the facade access equipment industry have made proper certification more difficult than it needs to be; irrational approaches and conclusions are, at times, actually encouraged by industry groups. In this paper, the authors' experience designing, evaluating, and load testing hundreds of equipment installations will be used to illustrate key principles of properly designed facade access equipment and to convey important considerations for performing post-installation load testing.

The wind load provisions of Chapter 6 in ASCE 7-05 Minimum Design Loads for Buildings and Other Structures have been reorganized into six chapters in the 2010 edition. 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. The present guideline Wind Loads and Anchor Bolt Design for Petrochemical Facilities (1997) by ASCE Petrochemical Energy Committee is commonly used in the industry for calculating wind loads on nonbuilding structures and components. The new edition of this publication Wind Loads for Petrochemical and Other Industrial Facilities was released in September 2011 based on the provisions of ASCE 7-05. This paper addresses the important changes to the wind load provisions of ASCE 7-10 for non-building structures and components. This paper also provides comparative parametric studies of wind loads calculated using the analytical procedures based on the 2011 edition of Wind Loads for Petrochemical and Other Industrial Facilities and the provisions of ASCE 7-10 for new non-building structures and components, including pipe racks, open equipment structures, and vertical vessels.

It is not uncommon to have petrochemical facilities such as refineries, natural gas processing facilities and pipe line projects located in cold and arctic regions. The snow and ice considerations of the non-building structures and the components present unique design considerations for engineers. Non-building structures such as pipe bridges, pipe racks, multi level open equipment structures, storage tanks, electrical cable tray, air coolers, and equipment supporting structures retain snow differently than buildings. ASCE 7 does not have specific provisions for snow and ice on non building structures and components. Process Industry Practices (PI) and American Petroleum Institute (API) recommendations do not give comprehensive design procedures or guidelines for calculating snow and ice loads on non-building structures and components. Engineering judgment is used for adapting the snow and ice provisions for buildings to non-building structures. Calculation of the snow and ice loads becomes even more critical if the facility in a high seismic zone due to the added seismic mass. This paper provides recommendations for calculating the snow and ice loads for non-building structures and components based on the knowledge and experience of the authors. Snow loading on specific non-building structures are examined and recommendations based on current industry practices are presented

The Ivanpah Solar Electric Generating Facility will be the largest concentrated solar electric generating facility in the world when it is completed. This power plant consists of three identical 340 foot tall lattice steel towers, each supporting a 2,062 ton 120 foot tall steam generator capable of producing approximately 125 megawatts of electricity. Each tower receives solar flux reflected from more than 55,000 mirrors. Although these towers are classified as seismic design category C, due to their dynamic characteristics the controlling lateral loads are due to wind. Early in the design process, it was postulated that a cross-wind excitation of the structure, as a result of vortex shedding from the steam generator, could be a critical portion of the wind load. This dynamic response of the structure was confirmed by a wind tunnel study. A tuned mass damper (TMD) was ultimately selected as an established, economical solution to mitigate the cross-wind loading. Use of the TMD resulted in a substantial savings in structural steel and foundation costs when compared to a tower designed to resist the un-damped cross-wind loading. This paper discusses the structural design of the tower, and the chosen solution to mitigate the cross-wind excitation. Results of the wind tunnel study are reviewed. The effect of spatial constraints on the design of the TMD is highlighted. Structural design considerations, including the combination of cross-wind with along-wind loads, are addressed.

The presented work deals with the seismic design and response evaluation of elevated steel containment tanks. The focus of the paper is on the behaviour of the supporting structure, since a horizontal ground motion will mainly cause damage to this part of the overall structural system. A case study has been considered, where, according to common practice, the supporting structure is a steel concentrically braced frame. In both design and response evaluation processes, particular attention has been paid to the consideration of internal fluid sloshing phenomena and on their implication on the overall dynamic response of the system. Two design methods have been considered: one in accordance with the relevant international codes and a second proposed method that allows considering the strength of braces in compression. The dynamic response of the elevated tank has been evaluated through linear and non-linear analysis. The different analysis strategies considered are compared and the influence of the design process on the global response is highlighted.

The Tunnel and Reservoir Plan (TARP) is the Chicago area's plan for cost-effectively complying with Federal and State water quality standards. TARP's main goals are to protect Lake Michigan - the region's drinking water supply - from raw sewage pollution; improve water quality of area rivers and streams; and provide an outlet for floodwaters to reduce street and basement sewage backup flooding. Phase I of TARP (operational since 1980 and completed in 2006) captures and stores combined sewer overflows (CSOs) that previously discharged at hundreds of outfall locations. After storms fill the tunnels with the first flush from combined sewers, the captured CSO is pumped to water reclamation plants for full secondary treatment. Phase I includes 109.4 miles of 8' to 33' diameter rock tunnels, 150' to 350' below the ground, providing 2.3 billion gallons (BG) of CSO storage. Phase II of TARP consists of three large reservoirs that will increase the TARP system storage volume to 17.5 BG. The 350 million gallon (MG) Majewski Reservoir has been in operation since 1998. The dual purpose Thornton Composite Reservoir is scheduled to be completed in 2015 and will provide 3.1 BG of flood water storage and 4.8 BG of CSO storage. The 10 BG McCook Reservoir is being constructed in two stages, with 2017 and 2029 completion dates. At both reservoirs, there is a mining agreement with a local quarry operator to provide the reservoir hole, and several construction contracts to turn the hole into a functioning reservoir. The mining, design, and construction activities are currently underway. Close coordination with several different stakeholders is required to bring these projects to completion Since its inception, TARP has abated flooding and pollution in the Chicagoland area and preserved the integrity of Lake Michigan. Area waterways are once again abundant with many species of aquatic life and have been reclaimed for recreation. The full benefits of TARP will be reached when the McCook and Thornton Composite Reservoirs are completed.

In this paper, a numerical study of the seismic performance of an innovative light-gauge cold-formed steel mid-rise building designed using direct displacement design (DDD) is presented. This innovative system includes floor trusses, open panels, V-braced panels, columns and connections between components. A series of reversed-cyclic tests of sub-assembly structures were conducted to understand the performance of the system under cyclic loading. The test data was then integrated into a numerical model for non-linear time history analysis of the building. A super shear element was developed to represent the panels as well as the floor diaphragm in the numerical model. The results show that the building performs very well based on the ASCE Standard 41 criteria at the global level. However, it can be concluded that further development of DDD should be pursued to account for torsion and to investigate localized response in these types of structures.

Lightweight cold-formed steel (CFS) framing is an effective building solution for low and mid-rise structures. However, systems level response and component contributions as well as their interactions such as those from lateral-load resisting systems, floor diaphragms, studs to track connections, etc., are not fully understood. Existing building codes for the CFS frame buildings are based solely on the stiffness of the lateral-load resisting frames and do not explicitly incorporate systems response. This paper presents the first-phase of a multi-year project aimed at generating knowledge and tools needed to increase the seismic safety of CFS frame buildings. The first phase of the study focuses on the design, instrumentation plan, and preliminary analysis of full-scale two-story CFS frame buildings that are tested on shake tables at University at Buffalo NEES Facility in the second phase. Design of the two-story CFS buildings incorporates a "state of the practice" ledger framing system that attaches floor and roof joists to the inside flanges of the load-bearing studs via a combination of track and clip angles. The instrumentation plan for the shake table tests is developed to capture both systems and component level response of the buildings. The preliminary analysis includes development of new modeling capabilities that incorporate cross-section limit states (local and distortional buckling) into frame analysis engines such as OpenSees to enable more accurate incremental dynamic analysis. This paper provides detailed design of a prototype CFS frame building and instrumentation plan for the shake table tests at Buffalo.

This paper summarizes results from an experimental program designed to evaluate the tension-compression cyclic axial response of cold-formed steel C-section structural studs. Establishing the hysteretic response will allow energy dissipation from cross-sectional deformations unique to cold-formed steel members to be included in seismic models, resulting in more accurate predictions of seismic performance. A new cyclic loading protocol for cold-formed steel members is presented that establishes the target axial displacement based on elastic buckling parameters like the Euler buckling load. The protocol is used to explore the cyclic response of unbraced structural studs experiencing global buckling deformation, and weak axis flexural buckling in compression is observed. The buckling causes local folding of the stiffening lips which become stress concentration points during the tension cycles. Post-bucking energy dissipation was observed as well as tension stretching and softening. The studs failed with a tensile fracture initiating at the damaged stiffening lips near the stud midheight or at the welded end supports.

This paper compares the measured lateral load behaviors of two 0.4-scale "hybrid" precast concrete wall test specimens - one wall with solid panels and the other with perforated panels. The test specimens have the same overall geometry and utilize a combination of mild [i.e., Grade 400 (U.S. Grade 60)] steel and high-strength unbonded post-tensioning (PT) steel for lateral resistance across horizontal joints. The mild steel reinforcement is designed to yield in tension and compression, providing energy dissipation. The unbonded PT steel provides self-centering capability, reducing the residual lateral displacements of the wall after a large earthquake. The comparisons between the two walls focus on the applied lateral load versus displacement behavior, energy dissipation, shear deformations, and behavior along the critical horizontal base-panel-to-foundation joint. Both specimens demonstrated excellent re-centering and energy dissipation capabilities as well as ductile behavior over lateral displacements at or greater than the ACI ITG-5.1 (2007) requirement. The perforated specimen was able to achieve greater lateral drift due to improvements made to the details of the panel reinforcement at the wall toes. Ultimately, these results are expected to support the successful code approval of hybrid precast shear walls for moderate and high seismic regions of the United States.

Performance-based seismic design has brought about innovative rocking and self-centering structural systems such as the controlled rocking steel braced frame (CRBF). This lateral force resisting system has recently received focused attention in academic research however has seen limited application in practice to date. This may be due in part to the unconventional load path and plastic mechanisms formed during response. The transfer of forces through a CRBF with a few configurations of passivie energy dissipating devices (steel yielding and viscous) is described and illustrated. The structural demands on primary CRBF members including dynamic load effects are evaluated through nonlinear transient finite element seismic analyses. Additionally, the demands placed on non-structural components contained on each building floor was investigated through the computational model by calculating critical response quantities such as inter-story drift, peak floor acceleration, and floor spectra. Structural and non-structural demands are compared with a conventional (fixed-base) ductile braced frame structure to illustrate the differences in seismic behaivor and potential benefits of a well designed controlled rocking steel braced frame.

Gravity forces could lead to unsymmetrical lateral resistance capacity in a building structure. This phenomenon, called "gravity bias", could result in detrimental behavior in structure's seismic response. In order to investigate this issue, a series of nonlinear time history analyses were conducted for representative single degree of freedom structures with variation of several parameters. The analyses results showed that both maximum relative displacement and ductility demand of a structure increases due to gravity bias. The influences of structural period of vibration, hysteretic characteristics, and site class on the gravity bias effect were also investigated. Based on this study, it is suggested that a smaller response reduction factor should be chosen for design when gravity bias exists.

Ground motion selection and scaling comprises one of the most important components of any seismic risk assessment study that involves response history analysis. The related research to date has been based on analytical studies of mostly single-degree-of-freedom systems, with fewer studies conducted using multi-degree-of- freedom systems. By contrast, the research effort described in this paper focuses on an experimental evaluation based on shake table tests of a small-scale six-story building frame specimen utilizing a calibrated, reusable, rotational, nonlinear beam-column connection. The paper focuses on the development and calibration of this connection and an associated analytical simulation to quantify the uncertainty introduced into the shake table results due to the variability in the calibrated strength of the connection. It is shown that the six-story frame structure outfitted with nonlinear connections at each beam end is effective in filtering the variability in the local connection behavior such that the uncertainty in the global response of the structure is often less than that of the connection. Ultimately, these results will be used in conjunction with the shake table test data from the six-story frame structure for the development of guidelines and procedures to achieve reliable demand estimates from nonlinear response history analysis in seismic design.

The Steel Slit Panel Frame (SSPF) has promise as a lateral force resisting system, exhibiting good energy dissipation and ductile behavior. Further benefits include ease of fabrication and erection and use of Steel Slit Panels (SSPs) as replaceable fuse elements. However, issues of residual drift and cumulative story stiffness reduction should be addressed further before the SSPF can be implemented in practice. Cumulative story stiffness reduction in the SSPF is the result of SSP-frame interaction. Preliminary design guidelines are refined through a parametric study of various SSPF configurations. Residual drift may hamper installation of new SSPs after a seismic event. However, preliminary analysis results suggest that some simple detailing could be used to accommodate residual drift. SSPF residual drift and possible replaceable fuse strategies are investigated.

A self-centering steel plate shear wall (SC-SPSW) system has been developed to achieve enhanced performance objectives following earthquakes, including recentering. The SC-SPSW consists of thin steel infill web panels as the primary lateral load resistance and energy dissipation of the system providing a high initial stiffness, where the moment resisting connections of conventional SPSW construction are replaced with post-tensioned (PT) beam-to-column connections that allow the beam to rock about its flanges to provide system recentering. The system and component behavior of SC-SPSWs have been investigated experimentally through a series of quasi-static and shake table tests. Quasi-static subassembly tests at the University of Washington have been conducted to study the effects of various design parameters on overall cyclic response and component demands. The University at Buffalo experiments focus on third-scale 3-story SC-SPSWs subjected to quasi-static and shake table testing to investigate system behavior. These experiments consider three different PT rocking connection details: 1) connections that rock about the beam flanges, 2) connections that rock about the beam centerline, and 3) an innovative NewZ-BREAKSS connection that rocks about the top beam flange only. The latter two PT connections have been proposed as methods to essentially eliminate floor system damage due to frame expansion that occurs with typical PT connections where the beams rock about their flanges.

The Linked Column Frame (LCF) was developed as a braced-free structural steel framing system intended for rapid return to occupancy earthquake performance level. The structural system consists of moment frames for gravity and closely spaced dual columns interconnected with bolted links for the lateral system. The links are sacrificial and intended to be replaced following a design level earthquake. This paper outlines the LCF system analyses conducted in preparation for large-scale system experiments. The system experiments are being planned to be hybrid experiments; a combination of physical test of a critical substructure tied to a numerical model of the building. The experimental substructure will consist of a 1-bay and 2-story LCF frame while the remainder of the building will be numerically modeled. A preliminary non-linear pushover analyses were used to validate the system ability to achieve the rapid return performance level. The objectives of these analyses were to detail design the physical specimens while considering laboratory constraints and as such have shed light on some of the important design considerations of the LCF system.

This paper presents results from two experimental programs of quasi-static testing and dynamic testing which investigate the re-centering and energy-dissipating behavior of a one-tenth-scale smart hybrid brace. Smart hybrid braces, that tend to prevent a soft-story mechanism, restore the original configuration and can be rapidly rehabilitated, are composed of three main components: (1) a set of superelastic shape memory alloy (SMA) wires anchored in a re-centering mechanism, (2) two struts with energy-absorbing capabilities, and (3) two high-strength steel tubes to guide the movement of the smart hybrid brace. A prototype smart hybrid brace was designed in compliance with the optimal proportion design methodology. The 1/10-scale smart hybrid brace was fabricated according to the similarity rules and then was tested in a uniaxial MTS 810 material testing machine. When the smart hybrid brace without the energy-dissipation struts was conducted under a series of quasi-statically cyclic tests, a double-flag-shaped hysteresis was clearly revealed. Subsequently, the energy-dissipation aluminum struts were added into the hybrid brace and then the same low-frequency cyclic tests was performed until the SMA strain approached the design strain limitation of 6%. The maximum residual displacement, 0.02 in, is smaller than the reverse transformation yield displacement of 0.03 in, meeting the proposed design concept. The hysteretic response in the last cycle exhibits a similar double-flag shape with nearly zero residual displacement, indicating that both the recentering SMA-wire mechanism and brace main body in the smart hybrid brace remain intact. The smart hybrid brace was further tested using dynamic loading with a frequency of 0.25 Hz. The dynamic results reveal a similar hysteresis to that under the quasi-static tests, except for the increased strain hardening. These tests reveal the features of the smart hybrid braces - repeatable SMA wire recentering mechanism and replaceable energy-dissipation components.

California legislation requires acute-care hospital buildings designed prior to the 1973 code to be evaluated, and if necessary, retrofitted to Life Safety (LS) in order to keep providing acute care until 2030. Innovative and cost-effective solutions are required in order to meet the requirements of the regulatory agency, namely the Office of Statewide Health Planning and Development (OSHPD), as well as the owner expectations. This paper presents a case study of a six-story steel moment frame structure built in 1972 that is retrofitted using supplemental viscous damping. The building is located near two major Southern California active faults. In addition, the building is triangular in plan with non-parallel lateral force resisting systems. Because of the retrofit methodology, Non-linear Dynamic Procedure (NDP) per ASCE 41-06 is required. The building will be retrofitted by adding new primary external damped 3-bay moment frames and modifying the existing moment frame base connections to prevent brittle failure by allowing controlled frame uplift. The basic retrofit criterion is to upgrade to LS under an earthquake with a 10% probability of exceedence in 50 years (475 year return period), namely BSE-1 earthquake. This paper presents some of the challenges found by the authors from a constructability perspective, as well as in the implementation of the NDP for a non-conventional building geometry near two major fault lines while satisfying the acceptance criteria delineated by OSHPD and ASCE 41-06.

The rocking foundation mechanism has proven to be an effective means to dissipate seismic energy, and thereby reduce the seismic demand on the superstructure. Its use has been broadly applied in both the building and bridge domains. Nonetheless, a common concern remains regarding its global behavior in a building system. Specifically designers must understand how the rocking foundation dynamically interacts with other inelastic components, particularly those designed into the structural components. To advance understanding, this paper presents and compares the seismic response of two extreme structural configurations, namely, a structural hinging-dominated (SHD) system and a foundation rocking-dominated (FRD) system. These two structural systems were recently tested in a 9-m-radius centrifuge-based shake table at UC Davis. Results indicate that the SHD system is more prone to localize the seismic energy at the structural fuse element, with relatively little energy transferred to the rocking footing. As a result, the structural fuses have a fairly large demand, which in turn cause significant transient and residual deformation in the superstructure. The FRD system, on the other hand, with broad moment-rotation hysteretic response of the foundation effectively minimizes the superstructure seismic demands in terms of roof drift and base shear, while the structural fuse element remains linear-elastic, even under intense base shaking.

This paper presents the results of an ongoing research project on the seismic performance of concentrically braced steel frames of the Conventional Construction category designed according to NBCC 2010 and CSA-S16 seismic provisions. The braced frames studied are of the tension-compression X-bracing configuration and special attention is devoted to the response of the connection at the brace intersection point. Numerical simulations were performed to determine the inelastic demand on the braces and brace connections. A test program including four full-scale quasistatic cyclic tests was carried out to verify the findings of the numerical simulations. The results indicate that the behaviour of the bracing members is influenced by the type of mid-connection. In particular, connections with single lap splices at the intersection of the braces may be prone to local instability. In all tests, failure occurred in the connections, indicating that more attention must be paid in design to prevent premature and brittle failure in connections.

The performance of passive tuned mass dampers (TMDs) has generally been assessed by parametric studies using numerical models, primarily with the purpose of selecting optimal damper parameters. Alternatively, limited full-scale and experimental verifications of the performance of TMDs have been undertaken; however, these have the inherent shortcoming of not being able to accurately quantify the performance of the TMD to the same excitation time history. Therefore, a hybrid approach is proposed, where the modal characteristics of a full-scale structure equipped with a pendulum TMD (PTMD) are determined through a measurement program and system identification. Subsequently, the responses of a numerical model with natural frequencies, primary mode shapes, and modal damping ratios consistent with the full-scale structure are found using excitation data gathered from a boundary layer wind tunnel by the high frequency base balance (HFBB) method, commonly used to predict the responses of structures through wind tunnel studies. Using a Lagrangian approach, the equations of motion for a three-dimensional PTMD coupled with a flexible main structure are determined, and the time-domain HFBB method is adapted to accommodate the directional coupling of the non-linear, three-dimensional PTMD, where both the planar and spherical motion of the auxiliary mass is considered. The results are compared to the responses predicted using simplistic models excited by broadband white noise, where motion of the tuned mass is linearized to the planar direction. The findings demonstrate the value of passive PTMDs, shed new light on the effect of using simplistic models to predict their performance, and demonstrate a practical approach to quantifying PTMD performance using full-scale measurement data.

This research investigates a parametric approach for optimizing the use of passive friction damping as a means of seismic alleviation. Two building models were constructed to simulate steel frame structures and subjected to several seismic excitations. One model was equipped with adjustable diagonal-cross-bracing passive friction dampers, and the other was left unequipped with friction dampers. Both models were subjected to one-directional shaking, and instantaneous values of acceleration and deflection were recorded. Acquired data was used to determine the effect the dampers have on the behavior of the structure and to verify a mathematically derived correlation between structural stiffness and damper frictional settings. Preliminary results show that the efficacy of the dampers varies significantly with respect to their frictional settings and the parameters of ground motion. Additional tests are expected to yield a correlation of these parameters, allowing for optimization of the frictional force for a particular ground motion.

This paper presents a methodology for scaling and modifying ground motions that best represents the seismic-hazard characteristics of the site, minimizes the amplification and modification to the records and uses the minimum number of ground motions required while still meeting all the code requirements. The objective of the ground-motion modification method is to scale and modify the ground motions such that the average of the spectrum resultants matches the scaled design spectrum over the entire period range of the design spectrum. This method reduces the ground-motion amplification needed to meet the code requirements when amplitude scaling is implemented. It also reduces the record modification needed for spectral matching. The proposed methodology was used in generating the ground motions used for the design of a hospital expansion project. The implementation of this methodology and its effects on the design are presented in the paper.

There are configurations of a structural-system model where soil-foundationstructure interaction (SFSI) effects need to be considered. The objective of incorporating these effects is to model the system more realistically than as a theoretically flexible building structure on a rigid-base foundation that is subjected to free-field ground motions. Effects such as foundation and soil inertia, damping, flexibility and strength can be incorporated directly into the numerical model. Of interest in this paper are the kinematic effects, base-slab averaging and embedment effects, which result in spatial variations of input motions on the foundation boundaries. Because this variation of ground motion cannot be modeled directly when using current state-of-the-practice numerical-simulation tools, modifications accounting for these effects need to be made to the ground-motion records a-priori. This paper presents a case study where soil-foundation-structure interaction was incorporated in the numerical simulation used for design.

In the design of new structures subject to earthquake loading the use of nonlinear response history analysis (NRHA) can be an extremely effective tool for optimization of the lateral system, however it can be a time consuming endeavor. In the process of optimization the necessity of running multiple analysis iterations, each subject to a suite of ground motions, is computationally intensive and can slow down the design process. However, by utilizing a simplified simulation technique, the extended consecutive modal pushover (ECMP) analysis method, the analysis and data reduction effort in design optimization can be reduced. The consecutive modal pushover (CMP) analysis method (Poursh et al. 2009) is a multi-mode nonlinear analysis technique involving sequential application of different modal based load profiles. An extension of the CMP procedure, termed the extended consecutive modal pushover (ECPM) method has been developed by the authors to improve the predictive capabilities of the CMP method. In an ECMP analysis the sequence and sign (direction) of modal load patterns are varied, encouraging formation of different inelastic mechanisms with the goal of replicating the various mechanisms that are observed to develop in NRHA when using a suite of ground motion records. Since the results of an ECMP analysis are similar to that achieved in a more computationally intensive NRHA, the ECMP procedure is an ideal simplified method to use during design optimization, and when model size makes NRHA computationally unfeasible. This paper will present the ECMP analysis method and will describe a procedure for using ECMP analysis as a design optimization tool coupled with NRHA. The results of ECMP and NRHA will be compared for two actual buildings to demonstrate the new ECMP analysis procedure and its use as a design optimization tool.

Due to the inherent variation of wood as a biological building material, the seismic performance of nominally identical wood buildings can be highly variable. In light-frame wood construction, the performance of the structure under lateral loads depends on the performance of the wood shear walls which are part of the main lateral force resisting system. In this study, the seismic performance of typical wood shear wall configurations such as fully sheathed shear walls and walls with garage and pedestrian door openings are investigated. The variability in the wood shear wall strength arises from the inherent uncertainty in the connectors and framing materials, and also the input ground motions. The far-field ground motion ensemble developed as part of the ATC-63 project is used in nonlinear time history analyses to capture the ground motion uncertainty. In addition, the drift performances of the NDS-compliance shear walls considering the performance levels prescribed in ASCE-41 for immediate occupancy (1% drift), Life safety (2% drift) and collapse prevention (3% drift) are discussed.

This paper describes the use of post-tensioning for timber gravity frames. These frames can be used for multi-storey commercial and office buildings. Two different configurations are described, one with prefabricated post-tensioned timber beams and one with post-tensioning through the full length of the frame. In the latter, beam-column connections are created by the clamping force due to the posttensioning. It is shown that post-tensioning of timber beams can create a precamber which helps to satisfy deflection criteria. This makes it possible to create long span timber beams while limiting the section height. Key design issues including deflections, tendon profile, deviators and tendon anchorage are addressed. The behavior of these connections is presented and the three deformation components of the connection are explained. A design example of a post-tensioned timber frame is also included.

This paper describes initial experimental testing to investigate feasible sources of passive damping for the seismic design of post-tensioned glue laminated timber structures. These innovative high performance structural systems extend precast concrete PRESSS technology to engineered wood structures, combining the use of post-tensioning bars or cables with large post-tensioned timber members. The combination of these two elements provides elastic recentering to the structure while the addition of damping using a specialised energy dissipation system gives the desirable `flag shaped' hysteretic response under lateral loading. Testing has been performed on a full scale beam-column joint at the University of Basilicata in Italy in a collaborative project with the University of Canterbury, New Zealand. The experimental testing uses engineered wood products, extending the use of laminated veneer lumber (LVL) structures tested in New Zealand to testing of glue laminated timber (glulam) structures in Italy. Current testing is aimed at further improvement of the system through additional energy dissipation systems. After initial benchmark post-tensioned only testing an innovative source of hysteretic damping was added and tested. These tests show that the system is directly applicable to glulam considering testing both with and without additional damping devices exhibited excellent results. The addition of damping devices increased values of equivalent viscous damping from 2% for the post-tensioned only system to a maximum of 16%.

Soft-story woodframe buildings are recognizable by their large openings at the bottom story which are typically for parking or other storage. During an earthquake, these large openings lead to large inter-story drifts and potential collapse, even before the upper stories experience any significant drifts. In order to improve the seismic performance of these at-risk buildings, a retrofit technique is designed using a Performance Base Seismic Retrofit (PBSR) method which applies the direct displacement design (DDD) approach. Torsion is eliminated based on structural analysis and then the DDD procedure is applied. The seismic performance of the retrofitted building is evaluated through multi-record incremental dynamic analysis (IDA). This paper focuses on the retrofit of a full-scale three-story wood-frame building that will be tested in 2012 at the NEES@Buffalo laboratory as part of the NEES-Soft Project. Two different types of retrofits models were developed, namely the inverted steel moment frames (IMF) and wood shearwalls resulting in the building achieving the prescribed performance objectives at all stories.

Many older multi-story woodframe buildings in the United States were not designed according to the earthquake engineering principles. Most of these older buildings have a soft first story due to the existence of large garage doors or retail store window openings. These soft-story buildings are prone to large lateral movements (displacements and rotations) and even pancake collapses in the first story during earthquakes. Analyzing the stability and seismic performance of soft-story buildings that undergo large deformations require a geometric nonlinear analysis. This paper presents a new three dimensional (3D) model for nonlinear dynamic analysis of woodframe buildings under large deformations. In the proposed 3D model, the floor and roof diaphragms are modeled using a 3D two-node twelve degrees of freedom (DOF) corotational frame element. In corotational formulation, the orientation of the frame elements is updated in each modeling time step. The use of corotational formulation and 3D frame element allows the numerical model accurately captures the in-plane and out-of-plane motions of the diaphragms under large rotations. Two-node six DOFs (three translations and three rotations) link elements which represent the shear walls and wall studs are used to connect the diaphragms in a 3D space. To reduce the computational demand, shape functions are utilized in the proposed 3D model to eliminate the DOFs of the link elements from dynamic analysis. In other words, the size of the building stiffness matrix for dynamic analysis does not increase as more link elements (shear walls) are added to the structural model. An example application of the proposed 3D model for modeling a three-story building with soft first story is presented.

Under extreme earthquake loading, light-frame wood building collapse is often caused by excessive inter-story drift at one or more story levels, which can lead to catastrophic P-Δ failure once the shear walls, and subsequently the entire structure, become unstable. Current performance-based seismic design for light-frame wood structures typically uses very conservative drift limits to prevent the collapse of the system, such as 3% drift in the ACSE Standard 41. The collapse drift limit for wood shear walls has not been studied extensively to date. A series of full scale collapse tests for wood shear walls was conducted and is presented in this paper with the objective of investigating the influence of wall configuration and gravity load on the ultimate drift level at which P-Δ collapse occurs. The shear wall collapse limit was found to be a function of wall strength and vertical load. Assigning a single ultimate drift level for light-frame wood building collapse limits appears to be justifiable based on the test results.

Many multi-story buildings have a structural weakness due to large openings in their perimeter walls and to a lack of interior walls at the ground level. The open condition results a ground story that is significantly weaker and more flexible (softer) than the upper stories. In addition, if the flexible wall lines of the ground story are irregularly distributed in plan, torsional response is triggered, adding to the soft-story effect. During earthquake shaking, these soft-story buildings are prone to damage, including pancake-like collapse in some severe cases. In this study, a high-performance retrofit is investigated wherein an energy dissipation system is incorporated within the soft story of wood-framed buildings. The system consists of damping devices that are installed in parallel with the narrow wall piers of the flexible wall lines using scissor-jack bracing to amplify the damper motion. The analysis indicates that the energy dissipation system is effective in dissipating a significant portion of seismic input energy, thus reducing inelastic energy dissipation demand on the wood framing system within the soft story. In addition, through strategic placement of the damping devices (location and magnitude of damping), the story drifts and seismic forces within the upper stories can be controlled while simultaneously minimizing torsional effects, especially within the soft story.

The San Francisco Community Action Plan for Seismic Safety (CAPSS), among other tasks, addressed the threat that regional earthquakes pose to 4,400 older, soft-story, high-occupancy woodframe residential buildings, like the apartment buildings that collapsed in the 1989 Loma Prieta earthquake. They house 8% of the city's population, in a city with a rental vacancy rate near 3%. A risk analysis was performed to estimate their post-earthquake safety and repair costs under 4 scenarios and 4 what-if conditions. We used a method related to HAZUS-MH, but using detailed characteristics of 4 index buildings that served as proxies for the broader population. Post-earthquake safety was characterized in terms of ATC-20 (Applied Technology Council 1989 et seq.) tag color, plus a collapsed/not collapsed metric. Results were peer reviewed by respected engineers who added their own judgment. Results were presented to approximately 80 self-selected stakeholders, including tenants, owners, and other parties. The stakeholders identified, discussed, and selected policy recommendations that included a City ordinance for mandatory retrofit. It seems likely that the City will enact such an ordinance. If that outcome is deemed "success," we attribute it to four factors that might be emulated elsewhere. First, these buildings probably do represent a leading threat to the City's viability. The memory of the 1989 Loma Prieta earthquake and photographs of similar damage in 1906 are evidence of a real, ongoing threat. Second, the risk estimate focused on an important community value: safety tag color, rather than repair cost (though we presented both). Third, while acknowledging the many uncertainties involved, we limited our discussion of probabilities, focusing instead on realistic outcomes of a few realistic earthquakes that could occur any day, and certainly will occur eventually. Fourth, we made no policy recommendations, allowing the public (through the stakeholder committee) to determine what they thought was best for them and for the City.

Hundreds of laboratory experiments have been conducted to date to investigate the punching shear behavior of two-way reinforced concrete (RC) slabs at interior supports. These experiments provide a mandatory frame of reference for the development, calibration and evaluation of punching shear design provisions. Unfortunately, because of the lack of dissemination and unavailability of some of the references together with some level of arbitrariness by researchers and code developers in selecting reference data, code provisions have been developed based on a rather limited subset of the available test results. To overcome these limitations, a task group was formed within ACI Committee 445 to gather, compile and post-process the results from laboratory tests studying the concentric punching shear behavior of two-way RC slabs without shear reinforcement at interior supports. The development of the databank involved two stages: first, the creation of a "collected" databank, where the characteristics of test specimens and test results were compiled as faithfully as possible to what was reported by researchers. Secondly, the development of a "selected" databank based on a series of Data Acceptance Criteria (DAC), with the goal of endorsing a test result into an evaluation-level databank. This paper describes the creation process and main features of the collected databank and discusses several important aspects in databank development including the selected platform being used to disseminate the information to users.

The unidirectional shear design and behavior of typical reinforced concrete (RC) structures has been extensively studied in the past several decades. Such design requires knowledge of the constitutive behavior of RC elements subjected to a biaxial state of stress. The true behavior of many large complex structures, however, requires knowledge of the constitutive laws of RC elements subjected to a triaxial state of stress. In particular, nuclear containment vessels are subjected to a combination of tangential, peripheral, and radial shear stresses. The goal of this research is to develop new constitutive relations for RC elements, representative of nuclear containment structures, and subjected to tri-directional shear stresses. The paper discusses the development and upgrade of the Universal Panel Tester at the University of Houston to be capable of testing full scale RC panels subjected to tridirectional shear loads. An experimental program to test several RC elements subjected to different combinations of in-plane and out-of-plane shear loads was conducted. The experimental investigation confirmed that there is a strong interaction between the behavior of the shear loads in the in-plane and out-of-plane directions. Based on these findings, a tridirectional shear interaction diagram was constructed.

This paper describes recent findings of an experimental and computational program to investigate the effect of mismatch when concrete materials are subjected to rapid heating and drying. The main foci are interaction effects in heterogeneous composites when the constituents with different thermal expansion and hygral shrinkage properties are subjected to severe environmental load scenarios. This paper addresses the question, whether spalling in concrete materials is caused (a) by the contrast of constituent material properties, or (b) by thermal-shock instabilities of subdomains subjected to compression. This discussion reaches beyond the traditional arguments of thermal stress spalling due to restrained thermal expansion, or due to pore pressure spalling caused by the phase change of the free pore water under high temperature.

The implementation of finite element models on the last three decades, enable the solution of sophisticated structure-soil interaction. Underground structure diaphragm wall (D-wall) soil interaction is one of the needful for using finite element analytical model. A finite element analytical model is developed in this paper and obtainable to fulfill the huge under ground construction Tunnel Pump Station (TPS2), constructed on Ameria-Cairo-Egypt. The TPS2 is used for collecting the wastewater from Cairo and redistributed this wastewater to the treatment plant. TPS2 is designed for about forty two meter diameter and abut thirty meter underground depth, as wastewater retaining structure. The construction methodology needs to be open-cut with thick plug for restrictive the water table during construction course of action. D-wall with thick plug for the TPS2 is used as preeminent choice for the construction development. The model developed in this paper is strain-induced orthotropic model for concrete representation and spring element to represent the soil-D-wall structure interaction. The behavior of concrete is presented on this paper using concrete crack-controlled serviceability model to satisfy wastewater retaining structure code requirements. The model represent, precisely all compartments of the outer wall, inner wall flooring system in addition to entire columns, ties and core wall. Finite element representation utilizes orthotropic shell elements for walls, core and flooring system, while the beams and columns are represented using axial frame elements. D-wall is considered, on this model, to perform as rigid pad for load transitions between outer soil and outer reinforced concrete wall. The over all behavior of TPS2 is confined by reinforced concrete diaphragm cantilever panels, arranged to perform the circular shape of the open earth-cut off. According to the straining action at different levels; the compression-only spring stiffness is intended, on this model, to take on the true behavior of the soil-over all structure-integrity interaction. All the results are extracted from this model to develop the concrete dimension and reinforcement details according to adopted design code. Finally, this predicted results adopted from finite element implemented model shows good agreements with the expected structure behavior under applied load combinations and state of circumferences. The results and design methodology are well recognized according to extracted results from the adopted finite element model.

Steel-plate composite (SC) walls are of significant interest for designing containment internal structures for third generation nuclear power plants. As part of containment internal structures, these walls may be exposed to seismic loading and combined thermal and mechanical loading in the event of a postulated accident scenario. Experimental and analytical evaluations indicate that SC walls subjected to accident thermal loading develop nonlinear temperature gradients through the wall thickness and undergo concrete cracking. This concrete cracking significantly reduces the stiffness of the SC walls, and thus the thermally induced forces and moments. The paper includes recommendations for: (i) estimating the structural stiffness of SC walls subjected to accident thermal loading, (ii) estimating the maximum moments induced due to thermal gradients, and (iii) developing linear elastic finite element (LEFE) models of SC walls for conducting dynamic seismic analysis.

Impact analysis of nuclear plant structural walls composed of surface steel plates, tie-bars, shear studs and concrete are discussed utilizing a simplified model of a fictitious wall to perform the analysis using LS-DYNA. The concrete constitutive model is based on Winfrith concrete model which covers all aspects of concrete behavior including cracking. The model was used to conduct a series of numerical studies to evaluate the effect of several parameters affecting the behavior of the wall. These parameters include thickness of the wall, thickness of the steel plate and diameter of tie bars. These studies resulted in several conclusions regarding the global and local behavior of the steel plated concrete wall system.

Reinforced concrete structures rely on steel reinforcing, acting in unison with concrete, to produce the essential ductile behaviour required to resist earthquake loading. Corrosion is known to affect bond performance and loss of adequate bond between these two materials introduces increased risk of brittle failure through pull-out of reinforcement. Reinforcing is put through the greatest stress in plastic hinge regions of structures where it is detailed to rupture before pulling out. Such regions are the primary locations for cracking damage, heightening corrosion susceptibility following even minor seismic event. Bridges and wharfs in marine environments are particularly susceptible to deterioration with these key regions coinciding with the highly aggressive `splash zone'. This becomes of particular importance in older, or poorly designed structures which have been designed with laps in plastic hinge zones This paper looks to assess the impacts of bond degradation due to corrosion on seismic behaviour. It follows on from a series of experimental pull-out cyclic testing carried out on corroded steel bars. Testing assessed two parameters; the level of corrosion, ranging from 0% to 25% section loss, along with reduced confinement associated with corrosion of confining steel. From this testing a numerical bond-slip model was developed which included the effects of corrosion and reduced confinement. This paper utilises the developed model in a series of multi-spring models, simulating the reinforcement development and plastic hinge region of bridge piers under various levels of deterioration. Analyses were then performed to determine the seismic susceptibility under degraded bonding conditions. Analysis found that inclusion of the corrosion effects resulted in increased displacement, reduced strength, altered ductility and an overall reduction in seismic performance.

The seismic performance of concrete structures should be considered time-variant, since in aggressive environments the corrosion phenomena affect the characteristics of both reinforcing steel bars and concrete matrix during lifetime. Seismic design criteria should therefore account for the environmental hazard, especially if bridges are considered, because of the direct exposure of the structure to the atmosphere. This paper investigates the seismic performance of bridges by considering the interaction between the diffusion process and the corresponding mechanical damage in both deterministic and probabilistic terms. Lifetime moment-curvature analyses are carried out at cross-sectional level of the bridge piers under different scenarios of environmental aggressiveness, accounting for uncertainties involved in corrosion parameters, material properties and structural geometry. Static and dynamic analyses are then performed on a bridge structure to assess how the time-variant seismic performance depends on the environmental exposure. Results show that a bridge designed for the same seismic action could have a different lifetime performance depending on the level of corrosion. This confirms the important role of a life-cycle approach for seismic assessment and design procedures which should be revised to consider both seismic and environmental hazards.

An earthquake can cause multiple disasters. For the reliability estimation of coastal structures and infrastructures in Japan, seismic hazard, tsunami hazard and hazard associated with airborne chlorides need to be taken into consideration. Firstly, this paper presents the damage of bridges during the Great East Japan Earthquake and Tsunami on March 11, 2011 based on the Japan Society of Civil Engineers (JSCE) damage investigation. Especially, the damages condition and the possible failure mechanisms of bridges due to tsunami are discussed based on the field survey. Secondly, the tsunami fragility curves are presented. These are used to estimate the structural fragility under the tsunami hazards. Bridge failure probability can be estimated using the tsunami hazard curve and the fragility curve. Finally, an illustrative example quantifying the effect of bridge pier height on the reliability of a bridge under tsunami hazard is presented.

Understanding how structures exposed to natural threats affect the environment is required in order to evaluate them from a sustainability perspective. Since natural hazard risk mitigation has evolved independent of consideration for sustainable development goals, there tends to be a disconnect amongst stakeholders, lack of consistent language and understanding across the field of natural hazard mitigation and those embracing sustainable development concepts, and need for an overarching framework to enable consideration of both perspectives. This paper presents a thorough examination of research and concepts developed to date related to integrating life cycle analysis of structures with sustainable engineering assessment, natural hazard risks, and their joint consideration. This review is expected to facilitate research and development of advanced life cycle analyses integrating and linking sustainable design with natural hazard mitigation design. Proposed future work required in this area to address existing gaps is also presented.

Engineering computing is much more than a specialized skill that enables engineers to create programs and use commercial tools. The science of computing involves the study of representation and reasoning strategies as well as fundamental topics such as computational complexity. The core ideas associated with such topics are expected to have an important impact on decisions related to computing during the careers of current engineering students. This paper describes a course on the fundamentals of computing that has been taught to second-year civil-engineering undergraduates in Switzerland for ten years and more recently, to undergraduate and graduate students in India and the USA. Practical outcomes include a sustainable knowledge of fundamentals for competence across a wide band of technologies, agile adoption of future developments, better collaboration with computer scientists for large, and often out-sourced, projects in practice and more informed purchases of software.

Effective force testing (EFT) is one of the force-based experimental methods for structures that incorporate dynamic force control using hydraulic actuators. While previous studies have shown successful implementation of the force control, control-lable frequency ranges are limited to low frequencies (10 Hz). This study presents the EFT method using a robust loop shaping force feedback controller that can extend the frequency range up to 25 Hz or even higher. Unlike conventional proportional controllers, loop shaping controllers can provide robustness for a high level of force measurement noise. This study discusses investigation of actuator dynamics and a design of a loop shaping controller that compensates control-structure interaction as well as suppresses oil-column resonance. The designed loop shaping controller is successfully implemented into an EFT setup at the Johns Hopkins University. Experimental investigation of the loop shaping controller was performed under step, random and earthquake force loadings. Experimental results showed that the loop shaping controller provides excellent force tracking performance as well as robustness for dynamic force loadings. It was also shown that the loop shaping can have the gain margin of 3.0 even at the frequency of 28 Hz.

Over the past several decades, structural testing has become ever more expensive, and researchers from many leading funding agencies are pushing to capture more and better data with each structural test conducted. Three dimensional digital image correlation (3D-DIC), is a tool that is gaining popularity as one way that more detailed information can be captured as part of testing programs. In 3D-DIC, the measured object is photographed with a pair of digital cameras before, during and after a load event and a stochastic pattern marked on the object is tracked from one set of images to the next such that a full field of displacements is derived. Historically, along with the cost of the system, factors such as how to correctly specify appropriate testing protocol and how to correctly interpret the results have limited the application in structural testing. The current paper focuses on three main aspects of 3D-DIC technology. First, a treatment of the basic theory behind the method is provided, highlighting the strengths and limitations of use for structural testing. Included are recommendations and guidelines for accuracy and other lessons learned during deployment over a broad range of projects. Second, the flexibility of the technique and the wide range of applications where it can prove useful will be discussed. Several case studies show how the technology has enhanced understanding of structural behavior in applications as far ranging as testing of rammed earth walls under gravity loads, testing of concrete bearing walls under fire and gravity loading, testing of post-tensioned shear walls under earthquake loading, and dynamic testing of a moment frame under earthquake loading. Finally, an experimental set-up designed to develop a protocol for deploying multiple 3D-DIC sensors simultaneously during the same structural test will be presented. The experiment is designed to allow four camera pairs to capture the deformations of key structural components of a coupled post-tensioned shear wall system.

Wood has been used as a construction material long before concrete and steel were available as structural materials. Wood is easy to work with and can be used for many different types of framing. Wood trusses have been used for long span roof framing in the United States since the 1800's. Over time the material, wood, has remained largely unchanged; however, the connections have evolved as well as the standards to which they are designed. Before the 1850's, truss connections typically consisted of mortise and tenon joinery. These connections make good use of the inherent strength of the wood members with little or no reliance on fasteners or engineering analysis. During the late 1800's and early 1900's these connections evolved into side lapped joints with steel bolts which bear on the wood in order to transfer shear through the joint. During the mid 1900's the invention of shear plates and split rings allowed joint forces to be transferred with fewer bolts. During the late 1900's pressed plate connections were developed which permited wood trusses to be readily pre-fabricated. In addition to the evolution of the connections, advancements in the testing of materials and creation of design standards have evolved into what they are today. This paper provides examples of actual woods connection failures from the different time periods mentioned above and discusses the cause of the failures. Also provided is a comparison of historic references versus modern design methods for the evaluation of the failed connections.

Due to increasing global challenges for the building industry such as urban growth, scarcity of resources and complex construction work, an international research consortium led by Cree GmbH intends to face this situation by developing a wood-hybrid construction system for high-rise buildings. Therefore, the result of the research project is a unique product, the LifeCycle Tower, which functions as a solution for use in an urban context, offers high resource-efficiency by focusing on a renewable resource - timber, and is developed as a standardised universally usable modular system. The LifeCycle Tower concept is featured by a highly energy-efficient building services concept, industrial series production, supply chain management and life cycle-oriented design. In order to turn the LifeCycle Tower into reality, Cree GmbH was set up and the first two real projects will be built soon. LCT ONE will be an eight-storey demonstration building in the form of an office block in Dornbirn, Austria reporting the advantages of the building concept on a public stage. Illwerke Zentrum Montafon (IZM) is the first commissioned project and will be one of the largest wood-based office buildings in the world in Montafon, Austria.

The subject of this paper is the investigation, load testing, and repair of a 1920's vintage public school building located in Chicago, Illinois. This school is one of thirty-two similar schools that were the subject of substantial controversy at the time they were built. Shortly after construction was completed, selected portions of the reinforced concrete roof structure were shored with supplemental steel beams to address alleged design and construction defects. The roofs have since been plagued with recurring maintenance issues related to the supplemental steel beams. An engineering study of the existing roof framing and supplemental steel reinforcement was performed to determine if the existing reinforcement was necessary. Full scale load tests of various portions of the roof structure were performed to verify the capacity of the original concrete framing. Repairs were developed to address locations where deterioration was observed or additional capacity was required, which allowed the complete removal of the existing structural steel reinforcement in place. Fiber-reinforced polymer (FRP) reinforcement, used for the first time in the Chicago Public School System, was chosen to reinforce selected concrete beams and joists. This paper will review the investigation, structural analysis, load testing and the design and installation of the externally bonded FRP reinforcement.

For the last century, steel has been used as a reinforcing material for most of the reinforced civil engineering structures. Despite requisite stiffness, strength, ductility and serviceability properties, steel reinforcing bars have shown deterioration over time due to corrosion. Fiber reinforced polymer (FRP) reinforcing bars have been used in concrete structures as alternate to conventional steel reinforcement, in order to overcome corrosion problems. However, due to their linear elastic behavior, they are not considered in structures which require ductility and damping characteristics. The use of shape memory alloys (SMAs) with their nonlinear super-elastic behavior in the composite could potentially provide solution for this problem. Small diameter super-elastic SMA wires, coupled with polymer matrix and FRP is sought in this research as reinforcing bars in reinforced concrete (RC) moment resisting frames (MRFs) to improve the performance of the frames in terms of reduced residual inter-storey drifts and damage under quasi-static and seismic loading, while still maintaining the elastic characteristics associated with FRP. The new SMA-FRP composite reinforcement is placed at the plastic hinge region of the MRFs, where the nonlinearity is expected to accumulate. A three storey one bay RC MRF prototype structure is designed with steel reinforcement using equivalent static force procedure given in International Building Code (IBC) for particular seismic hazard. The RC MRF is then modified by replacing steel at the plastic hinge region in the beams with conventional Glass-FRP (GFRP) and SMA-FRP composite reinforcement using design acceleration response spectra achieved based on seismic demand. Incremental dynamic analysis is conducted to investigate the behaviors of the frame with the three different reinforcement types under a suite of ground motion records. From this study, it is found that the frame with SMA-FRP composite reinforcement exhibits higher performance levels including lower residual inter-storey drifts, high energy dissipation to residual drifts ratio and thus lower damage, which is of essence for the structures in high seismic zones.

Currently, there are only a few common methods that can be used to strengthen reinforced concrete columns. These methods, including steel jacketing, section enlargement by concrete jacketing, and fiber reinforced polymer (FRP) composite wraps, were are used to strengthen 15 column specimens. The ease of application, economy and efficiency of each method are discussed and compared. In this study, three exterior reinforced concrete beam-column joint specimens were tested under reverse cyclic loading. The damaged specimens were repaired by replacing the damaged concrete and then strengthened using FRP strips. The strength was restored and deformation capacities of the strengthened specimens were much larger than those of the original specimens.

This paper reflects on potential broader benefits the structural engineer can bring to individual communities when undertaking design services; whilst particularly relevant to developing countries, there are also clear benefits when designing projects in developed nations in adopting the approach illustrated. A case study - The Sustainable Kindergarten School, Ghana is used to illustrate the benefits of structural engineers operating as "Global Workers and Local Thinkers" - an important theme in the global mission of the Institution of Structural Engineers.

This paper considers several of the major challenges which face structural engineers in applying sustainable thinking to projects in developed countries. It refers to the Heathrow Terminal 5 and London Olympics 2012 projects, completed recently in the UK, and highlights key attributes that assisted in their successful delivery. Through these examples, the paper demonstrates the distinct economic advantages of taking a holistic sustainable approach to construction. Key findings are that a cooperative partnering contract strategy, coupled with an open-minded holistic approach to design are crucial when delivering complex projects. It is also apparent that rigorous investigation and planning work beforehand, coupled with the earliest possible involvement of the supply chain, will yield the greatest commercial benefits, while at the same time minimising material use and maximising project sustainability.

In this paper, a study is carried out to investigate the stress concentrations at junctions of cylindrical-conical shell structures using the finite element method. A finite element solution is developed and used to model the structure. The solution utilizes curved finite elements that are capable to model the cylindrical and conical shell surfaces with high degree of accuracy. Elevated storage cylindrical-conical tanks and silos supported by "unyielding" stiff ring girders, which sit on a cylindrical skirt or on multi equally spaced columns, are analyzed. The opportunity is also taken to investigate the effects of various geometrical parameters, such as the conical angle, the height/radius ratio of the cylindrical shell, the location of the ring girder relative to the junction and the influence of adding ring stiffeners on the behavior of the structure. It is concluded that the geometrical discontinuity at the junction causes concentrations of compressive inplane as well as bending stresses. These stresses can be significantly reduced by either increasing the inclination angle of the conical bottom or by placing the ring girder closer to the junction.

Bottomless culverts are three sided culverts that are founded on either spread footings or pile supported footings. The absence of a bottom slab connecting the walls makes these culverts different (more flexible) than their four-sided box counterparts. These structures are increasingly used in highway facilities such as waterway crossings, fish passages, and pedestrian undercrossing. They are considered environmentally friendly because they allow natural stream beds to remain unchanged, thus they continue to provide habitat support for native plants and animals. For this reason alone, it is anticipated their use will continue to grow in the future. Traditional methods of analysis and design rely on simplified soil pressure "envelopes" to obtain the forces in the culvert walls and top slab. These traditional methods, by virtue of their historical record of success with minimal failures, enjoy a high level of credibility among practicing engineers. In most cases, this credibility is well justified and should not be ignored. However, this approach appears to be too conservative for bottomless culverts, since the "semi-rigid" nature of these structures affects the soil pressure distribution from the surrounding fill, and hence, the forces within the culvert walls and top slab. It follows that analysis methods that are better able to capture a more accurate soil-structure interaction provide better means of estimating the soil loading and structural response for these culverts. The computer program CANDE (Culvert ANalysis and DEsign) by NCHRP provides this capability through detailed soil modeling and finite element analysis. As the effort towards implementing the LRFD code continues, it is important for engineers to look for opportunities - not only to migrate to the new code - but to also upgrade their analysis methods and design assumptions to take advantage of the more modern and refined analysis tools. This is especially true where modern analysis tools also allow for the incorporation of more detailed material properties based on laboratory testing. By upgrading their analysis tools while transitioning to LRFD, engineers stand to benefit from the new technology by achieving better designs, and realizing what could be significant cost savings in both design and construction. The focus of this paper is to identify and preserve the salient features of traditional methods of designing bottomless culverts while they are transformed into a new and improved LRFD based approach.

Optimum detailing of reinforcement bars for biaxial columns is a hard problem. Conventional methods of producing a single design solution and the use of optimisation methods to find a single global optimum solution are not what practicing engineers require. This paper introduces an innovative approach to design, in which the emphasis is on the interactive use of evolutionary computing, as a powerful search tool, supported by visualisation techniques, as a powerful exploration tool. This approach replaces the `black box' nature of the optimisation techniques with an interactive approach in which the designer is in full control of the process. Instead of attempting to locate a single solution, clusters of good designs are identified which allows the designer to conduct a more focused search inside these areas of high performance designs. Case studies presented in this paper demonstrate how this approach enhances role of designers as decision makers and enable them to gain a deeper understanding of the design issues.

The failure of structural members under blast, impact, wind pressure and earthquake is highly dynamic phenomenon. One of the mechanisms of failure during such event is referred to as "Progressive Collapse". In the present study progressive collapse potential of 4-storey and 10-storey asymmetrical concrete framed building is evaluated. Linear static and dynamic analysis is performed by following the General Service Administration and Department of Defense guidelines for evaluating progressive collapse potential. Modeling, analysis and design of the buildings are performed using SAP2000 for five different threat-independent column removal conditions by following the alternate load path method. It is observed that demand capacity ratio (DCR) in beams and columns are exceeding the allowable limit for all the cases. This indicates the building considered for study is having high potential of progressive collapse. To reduce the potential of progressive collapse various approaches for mitigation of the progressive collapse are presented in this paper. Three different approaches like providing bracing at floor level, moderate increase in the size of beam at all the storey level and major increase the size of beam at bottom storey level are studied. Comparison between all the three approaches is presented for building taken into study. Among all the three approaches, bracing at floor level emerges as the most effective and economic approach for mitigating the potential of progressive collapse.

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. The phenomenon of time-dependent buckling can have a significant impact on the safety of steel columns subjected to fire. This phenomenon has received relatively little research attention, and is not currently explicitly considered in code-based design formulas for columns at elevated temperatures, such as those in the Eurocode 3 or those in the AISC Specification. This paper presents some results of on-going research, which aims at developing analytical, computational and experimental predictions of the phenomenon of creep buckling in steel columns subjected to fire. Analytical solutions using the concept of time-dependent tangent modulus are developed to model time-dependent buckling behavior of steel columns at elevated temperatures. Results from computational creep buckling studies using Abaqus are also presented, and compared with analytical predictions. Material creep data on ASTM A992 steel is also presented in the paper and compared to existing creep models for structural steel at high temperatures. Both analytical and computational methods utilize material creep models for structural steel developed by Harmathy, by Fields and Fields, and by the authors. Predictions from this study are also compared against those from Eurocode 3 and the AISC Specification. Results of this work show that neglecting creep effects can lead to erroneous and potentially unsafe predictions of the strength of steel columns subjected to fire.

Hybrid masonry is a new technology for seismic building construction. The system utilizes reinforced masonry panels with a framed structure, as well as steel connector plates to tie the surrounding steel frame to the masonry wall. To date, the system has been only used for construction of several low-rise buildings in the eastern and mid-western United States. Current research extends the application of hybrid masonry for use in seismic hazard regions. Both capacity design and performance-based seismic design of hybrid masonry systems are studied. The steps of two capacity design process for hybrid masonry structural systems are presented, by dictating two favorable failure modes to the structure, i.e., steel connector plates acting as fuses or flexural yielding of the vertical steel bars of masonry walls. Moreover, for the case of plasticity concentrated to the steel connector plates, a performance-based method is also proposed for seismic design of hybrid masonry Type I building systems.

DoD UFC 4-023-03 requires anchoring of horizontal internal ties into peripheral ties when the "Tie Forces" method is used to satisfy the progressive collapse design requirements. The criteria recommend anchoring of longitudinal and transverse rebar reinforcement ties using seismic hooks. No reason is stated in the document or its commentary for this recommendation. Nonlinear dynamic numerical analysis has been carried out to investigate the behavior of floor slabs, designed to the UFC Tie Forces criteria, in the cases of existence and absence of these seismic hooks. A numerical computer model has been developed to study the deformation of composite deck slabs and the development of tie tension forces when the slab is subjected to loss of a vertical load bearing wall. The results of the study show the ability of the composite deck slab to bridge over the missing wall support in the two cases of existence and absence of seismic hooks. Slab deflection and cracking occurred and stresses developed in the metal deck as expected after wall section removal. There were minor behavior differences with the absence of seismic hooks. Further studies are needed for composite deck slab systems as well as other slab systems to evaluate the effectiveness of seismic hook anchoring for the purpose of resisting progressive collapse condition.

Renovation and rehabilitation projects frequently require the reinforcement of the high-moment portions of existing structural framing which see new loading. The method for determining the necessary extent of new reinforcement on an existing beam to meet strength demand is relatively straightforward and well established. However, once a beam is reinforced it becomes non-prismatic, with discreet changes in its flexural rigidity EI. Significant additional calculation complexity or additional computer modeling is required to accurately determine the beam's deflection in its reinforced state. This paper presents easy-to-use graphical design aids which simplify the determination of the maximum post-reinforcement deflection of a beam which is reinforced over a portion of its length, essentially providing it with different constant flexural rigidities in two regions. A sample derivation using basic mechanics of materials principals is also provided. The design aids presented address common beam support and load configurations, as well as widely varying reinforced flexural rigidities and reinforcement extents. Applicability and use of the design aids are discussed, and examples of their use from the author's professional experience for both renovation and new construction projects are provided.

The initial content of this paper presents results of a survey-based study that identified simplified displacement monitoring of railroad bridges under trains as the main research interest of railroad bridge structural engineers. The second part of this publication describes a railroad bridge classification towards structural health monitoring (SHM) applications, based on current structural engineering problems and challenges identified by the railroad industry for each railroad bridge type. Finally, this paper briefly describes ongoing research related to attempting to monitor railroad bridge deflections by means of using simplified wireless sensors, and preliminary field experimentation and proof of concept validations.

Tuned liquid dampers (TLDs) are cost effective and low-maintenance dynamic vibration absorbers that are being used in flexible and lightly damped structures. A TLD is a passive control device that dissipates energy through the liquid boundary layer friction, the free surface contamination, and wave breaking. In this paper the dynamic behaviour and performance of TLDs are investigated through a series of the real time hybrid simulations on a steel frame equipped with a TLD on the roof level. The tests were carried out using a Quanser shaking table, and by implementing the real-time hybrid simulation algorithms in MATLAB Simulink, Real-time Workshop and WINCON. By combining computer simulation with physical testing, the real-time hybrid simulation method provides the response of the structure-TLD system by only testing the TLD. This way, the structure-TLD interaction will be captured without testing a scaled-down model of the entire system in the laboratory. By better understanding the TLD behaviour and its interaction with the structure, the results presented here will contribute to the improved design of the TLDs which will in turn result in the wider application of these devices.

Hybrid testing, as an advanced seismic response simulation method, combines experimental physical models with analytical numerical models; its versatility and capability of testing large-scale specimens make it particularly applicable to the study of seismic performance. Hybrid testing has been applied in approximately twenty George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) research projects. This paper provides a review of hybrid testing techniques used in these projects based on the information available at the NEEShub project warehouse. An overview of hybrid testing is firstly presented. Then a list of NEESR projects involving hybrid testing methods are discussed in details, including experimental specimen, substructuring, integration algorithms, rate of loading and testing results validation. The paper concludes that hybrid testing is an effective experimental method in earthquake engineering simulation but needs further development in the areas of providing more realistic structural responses and validated general hybrid testing procedure for broader application.

In this paper, the issue of actuator-structure interaction in dynamic testing of structures is approached from the novel standpoint of impedance control. It is shown that an effective strategy to design controls for dynamic testing is by designing the test system impedance and that this can be achieved using feedforward compensation. The analysis is carried out in the context of displacement controlled dynamic testing, when the tested structure has a high and nonlinear stiffness. It is demonstrated that stable and accurate dynamic testing can be achieved using the proposed strategy, when this is not possible using traditional feedback control techniques. Furthermore, the impedance control and feedforward strategies are applied in the context of hybrid simulation, a technique of coupling computational and physical substructures applied in earthquake engineering. Here, a delay compensation scheme is necessary in addition to feedforward. Experimental results are presented that demonstrate both improved dynamic testing performance when impedance control is employed, and its applicability in hybrid simulation.

This study investigates the stability and accuracy of a new substructure shake table test method that utilizes controlled masses. The method allows for an earthquake simulation of large and complex structural systems by decomposing the specimen into experimental and computational substructures. The dynamic interaction of the computational substructure is incorporated into the experimental substructure through the inertial force of a controlled mass. Acceleration measurements of the experimental system are used as input to the computational system. Because the mass is controlled by either acceleration or displacement commands, the method does not require the use of dynamic force control techniques that are needed in previously proposed methods. To validate the feasibility of the method a computational simulation is performed using detailed models of the system components. This work serves as an analytical validation of the substructure shake table test method and as preparation for the experimental implementation that is ongoing at Johns Hopkins University. This paper presents theoretical formulation, details of the simulation models, computational simulation results, and suggestions for the experimental study.

Reinforced concrete buildings in low-to-moderate seismic zones are often designed only for gravity loads in accordance with the non-seismic detailing provisions. Deficient detailing of columns and beam-column joints can lead to unpredictable brittle failures even under moderate earthquakes. Therefore, a reliable estimate of structural response is required for the seismic evaluation of these structures. For this purpose, analytical models for both interior and exterior slab-beam-column subassemblages and for a 1/3 scale model frame were implemented into the nonlinear finite element platform OpenSees. Comparison between the analytical results and experimental data available in the literature is carried out using nonlinear pushover analyses and nonlinear time history analysis for the subassemblages and the model frame, respectively. Furthermore, the seismic fragility assessment of reinforced concrete buildings is performed on a set of non-ductile frames using nonlinear time history analyses. The fragility curves, which are developed for various damage states for the maximum interstory drift ratio are characterized in terms of peak ground acceleration and spectral acceleration using a suite of ground motions representative of the seismic hazard in the region.

New technologies involving passive control devices have matured to the level of practical use. Although such devices may have the ability to reduce inter-story drifts and absolute accelerations, the two main measures for structural and non-structural damage, the variety of types of devices raises an important question: What type of device is best suited for reducing either absolute acceleration or inter-story drift, or simultaneously reducing both? In order to rigorously answer this question, we adopted an evolutionary, multi-objective optimization approach, wherein inter-story drifts and absolute accelerations served as objective functions. We estimated the set of all Pareto optimal solutions for retrofitting typical medium-rise framed structures by considering different configurations and types of passive energy dissipation (PED) devices. The results of numerical simulations indicate that some types of PED devices show superior performance in comparison to others. These findings could assist designers with a robust choice of PED device types, configurations, and sizes to address specific design problems.

RC bridge columns are subjected to combined bending moment, shear force, axial and torsional loads during earthquake excitations, particularly for skewed and curved bridges, and bridges with unequal spans or column heights. The combined loading would affect the seismic performance of reinforced concrete (RC) bridge columns in terms of strength, stiffness, deformation and progression of damage limit states. Performance based design approach for RC square columns under combined loadings including torsion is investigated in this paper. Different damage limit states are evaluated from performance based design approach using proposed damage index model, which permits decoupling these combined actions according to the test data. The main variable considered in the experimental study is the ratio of torsion to bending moment (T/M). The effects of combined loading on the torsional and flexural hysteretic responses, plastic hinge characteristics, rotational and displacement ductility limits, progression of damage states are discussed. The progression of damage states, quantified according to the proposed damage index model, can be correlated to the observed damage from practical point of view, which exhibit reliable indication of failure stages of RC square bridge columns. Based on experimental and analytical results, progression of damage was found to be amplified by the effect of increasing torsion; and the displacement as well as rotational ductility is decreased due to the effect of combined loading. Hence it is necessary for the performance based design procedures to consider the effect of torsional loadings.

This work summarizes the salient features of a study on the dynamic characteristics of 27 mid-rise and high-rise reinforced concrete shear wall buildings in Montreal. Ambient vibration measurements were performed and dynamic properties extracted using frequency domain decomposition of the measured records. The extracted dynamic properties were then used to evaluate different models proposed in building codes and in the literature to predict the natural periods in various response ranges. Results obtained for modal damping are also discussed.

The configuration of backfilled construction clearances may significantly impact the seismic response of an embedded structure. At rock sites where the free-field consists of a rigid rock profile, it is anticipated that a more flexible backfill, surrounding the embedded portion of the structure, will alter the seismic motion transferred to the structure. In this paper, the Soil-Structure Interaction (SSI) response of a deeply embedded massive structure is computed with backfill explicitly modeled and with the backfill neglected. These seismic responses are compared and a determination on the sensitivity of seismic response due to backfill modeling techniques, for the case considered, is presented in this paper.

This paper investigates the workability, compressive strength, and elastic modulus of normal strength concrete mixtures that use recycled concrete aggregates (RCA) as replacement for virgin coarse natural aggregates. To provide a regional geographical representation of the variability in material quality and properties, a total of 144 mixtures with 16 different RCA sources are used in the experimental program. Three RCA concrete mix design methods utilizing varying amounts of direct volume aggregate replacement, direct weight replacement, and equivalent mortar replacement are compared. It is found that the RCA material properties do not affect the workability of RCA concrete designed using the direct volume replacement method. However, for the equivalent mortar replacement method, there is a significant reduction in workability even when the maximum recommended amount of water reducer is used. The compressive strength and elastic modulus of concrete are not significantly affected by the mix design method. Depending on the RCA source, the compressive strength of RCA concrete is generally comparable to the strength of concrete with virgin aggregates. However, there is a greater effect in the elastic modulus as the amount of RCA is increased. The results suggest that the RCA material properties that most affect the mechanical behavior of concrete are the aggregate water absorption and deleterious material content.

Current structural design methods are generally based on an iterative approach of member sizing after subjecting a system to a suite of load combinations, and then selecting the governing combination for each member. With the recent emphasis on performance-based design, it is important to advance this concept into the next realm, and ask what the consequence is of individual member behavior on the performance of the structural system. In a reliability and multiple performance framework, this is a generalization of the notion of progressive collapse. A major objective of this paper is to define the sensitivities of current code philosophy on the overall design. Structural system reliability concepts are adapted for multiple performance evaluation of systems with multiple levels of interdependent limit states, and some ideas are indicated for new approaches. This concept is further extended from a system composed of members of an individual building to a community scale, where a suite of structures forms the set of basic units, rather than individual structural members. The resilience function for the community served becomes the objective function, in place of the reliability of a single structure. By defining the resilience of a community through the relationship of its building reliabilities, structural design becomes an inherent tradeoff for societal investment in structures in terms of their role for community physical, social and economic well-being.

As part of a research project conducted at McGill University, in-situ dynamic properties of 80 low-rise school buildings located in Montreal, Quebec, were identified from ambient vibration measurements. Natural periods determined for the two most common lateral load resisting systems (concrete shear wall buildings and concrete frame buildings with unreinforced masonry infill walls) are presented. They are compared to approximate equations that estimate the fundamental period as a function of building height, given in the 2010 National Building Code of Canada. It is shown that the fit between the experimental periods and approximate code formulae is poor, with code expressions grossly overestimating the periods. Linear regression on the experimental data resulted in the development of better fitting expressions. The periods obtained from ambient vibration measurements were also compared to generic capacity curves used in the Hazus-MH MR4 multi-hazard loss estimation methodology. The measured periods seem to be slightly low, but they are generally in agreement with the theoretical capacity curves.

Post-tensioned box girder bridges are considered one of the most structurally efficient bridge systems and are widely used in the U.S. This study investigates numerical results of progressive collapse for post-tensioned box girder bridges under blast loads. Limited data is published on this topic; however there is available literature on the analysis of the progressive collapse of cable-stayed bridges under blast loads. Accidental detonations are assumed to take place under the bridge deck. Numerical simulation is conducted using the Applied Element Method implemented in "Extreme Loading for Structures" software. The numerical model of the bridge structure and simulation results of the main bridge components, piers, and main span deck are investigated. The parameter studied was in terms of the weight of the explosion at two different locations simulating a large vehicle bomb (LVB) placed underneath the bridge. The progressive collapse analyses of the bridge structure after damage in either one of the two main bridge components are investigated. Damage mechanism and severity in the bridge pier, and deck are examined. Numerical results presented in this study could help departments of transportation and engineers and owners of similar bridges to determine appropriate measures for bridge protection against possible explosion threats.

Structural collapses that are caused by fire have always attracted the attention of researchers concerned with fire safety in building design. In its latest statement of research interests, the American Institute of Steel Construction (AISC) lists connection performance and safety as one of the fields in need of further exploration. This study investigates the behavior of steel beam-to-column moment connections under fire using a numerical simulation. Fire is always a concern after earthquakes and understanding the behavior of structural components during a possible after shock is essential for making sound engineering decisions. The study reported herein focuses on Reduced Beam Section (RBS) moment connections. This type of connection can be used to mitigate seismically induced failure as per the recommendations of the AISC seismic provisions. The study is conducted using the finite element modeling software ABAQUS, which can account for material and geometric nonlinearities and contact behavior. This type of modeling can provide a better understanding of the complex 3D behavior of steel joints under fire loading. The RBS moment connection is experienced many deformations under the fire loading. This study introduces preliminary results of ongoing research regarding the RBS moment connections under fire.