Structures Congress 2014

A contractor erected multiple reinforced concrete mat foundations over the spring and summer construction season to support large tower structures. Six weeks into the construction, after nearly half of the nineteen foundations were cast, twenty-eight-day compressive strengths for the first several pours showed an alarming rate of below-strength results. The contractor, engineer, and concrete supplier scrambled to determine why the concrete was understrength. Was it the aggregate size? The withholding of trim water? The initial curing process? Testing procedures? As the team investigated and worked to remedy the problem, construction was delayed by nearly two months, which jeopardized the project delivery schedule. This paper describes the analysis of available data to determine what went wrong and how, from the submittal process through placement and cylinder testing.

The structural engineering community is being subjected to a series of changes that are altering the way our business is conducted. The focus of interest, in relation to these changes, is on integrated delivery practices and the usage of Building Information Modeling (BIM). Current successful implementation of these methods has been widely publicized. That said, the structural design and construction process still is inherent with numerous barriers and limitations on effective and efficient collaboration with other disciplines. Research has indicated that the creation of an integrated delivery process promoting computational technologies can enhance and facilitate a better resulting project for the owner. The discussion here will focus on the ongoing development of an integrated process model from the perspective of a project utilizing BIM-enhanced methodologies. The ongoing work correlates the critical integrated tasks at different lifecycle stages that define and impact the structural system/s modeling, design and construction. It is believed that ultimately, upon completion, this research could be implemented into practicing firms. There, the model would guide a firm to become more effective, as well as efficient, in the structural process through emerging methods and technologies.

How does a structural engineer juggle all of the tasks required to complete multiple projects on-time, with quality and still have a quality life at home? Development of personal mission statements, personal values, and goals helps to set the foundation for setting priorities. Once priorities are understood, decisions can be made on how to discern between the urgent and the important tasks. Writing down every task as it comes to mind and routinely assigning priorities is necessary to keep from becoming overwhelmed. When there are concurrent multiple projects, Post-it® notes will not be adequate to keep track of everything. The entire process — from recording the task, to scheduling the task, to delegating a task, to completion of a task — will be described. One online task management software tool will be demonstrated as it relates to engineering projects. The structural engineer will take away some ideas for organizing life and increasing efficiency on the job, still attending to the tasks required for the important relationships in life.

In regions of the world that receive snow, increased structural loading caused by drifting is typically considered by designers. In the USA, the American Society of Civil Engineers' (ASCE) design standard, Minimum Loads for Buildings and Other Structures (ASCE 7), is relied upon by structural engineers when designing roofs to resist snow loads. When roofs become large and prevailing winds in blizzards are not perpendicular to a ridgeline, notable snow drifting can occur in areas not predicted by ASCE 7. This can result in non-conservative design loads for the roof structure in those areas. The abnormal drifting patterns can be worsened by irregularities such as clerestories, monitor roofs, and other projections. This paper focuses on post-event forensic analyses of five pre-engineered metal buildings in the high plains of Colorado that were located adjacent to each other and that sustained snow load damage during three different blizzard events. Although quantitative snowdrift data were not obtained through this case study, the qualitative information is useful to designers and code/standard developers in recognizing where additional research may be needed to improve ASCE 7 snow provisions. This paper will help designers recognize when ASCE 7 may result in un-conservative design snow loads, in which case, the designer would do well to consult with individuals who understand local wind phenomena during blizzards. Alternatively, the designer should consider increased design snow loads in those situations.

With the advent of Integrated Project Delivery and BIM, there are growing demands on structural engineers who design buildings to become more integrative in their work. This paper presents architects' views on integration and the skills they are seeking from engineers as found in a qualitative analysis research study conducted with architects and structural engineers on the topic of integration. It was found that architects emphasized the integrative process and the final articulation of the structure. The ability of structural engineers to understand architectural design was seen by architects as a critical to integrative work. Responsiveness, flexibility, and willingness to investigate solutions were valued traits in a collaborative relationship. The initial results of this study presented here allow engineers to understand how integration is seen by architects and to gain information to improve their own practices.

This paper investigates an analytical framework for the seismic risk assessment of unreinforced masonry (URM) building structures. Integral to each URM building model with door and window perforations is a macro-element that represents each solid masonry panel within the structure. The macro-element includes multiple discrete elements to model different characteristics of unreinforced masonry behavior, including sliding, rocking, and diagonal tension/compression. Validation of the model is conducted through comparison of the analytical predictions with observed behavior from previous masonry tests. The simplicity of the macro-element modeling approach together with its material/geometry-based ability to predict URM behavior permits the semi-automatic extension of this framework to a wide range of analyses (e.g., ground motion records, material properties, building geometry, transverse walls).

Charts in the UFC-3-340-2 design manual are used to compute peak incident overpressures and impulse generated by a detonation of an explosive as a function of scaled distance and angle of incidence. These charts assume either a spherical or hemi-spherical charge and do not account for the variation in charge shape, charge orientation and the point of detonation within the charge. A numerical study was performed using AUTODYN to study the influence of charge shape, charge orientation and point of detonation within the charge on the free-field overpressure distributions and the response of an A992 Grade 50 W14 × 257 column. A set of analyses was performed with cylindrical charges with different aspect ratios. Results were compared with those involving a baseline analysis of a spherical charge. The resulting peak incident overpressure and impulses, and the pressure contours were compared in the near-, mid- and far- fields. In the near-field, the overpressure distributions are influenced significantly by charge shape and the point of detonation in the charge. The influence of these variables diminishes with distance. The loading and subsequent response of the W14 × 257 column to a near-field detonation showed significant dependence on the charge shape and charge orientation and clearly demonstrated that SDOF assumptions are inappropriate for blast-resistant design against detonations of improvised explosive devices at small standoff distances.

Both maximum displacement and displacement ductility factor should be considered in the design of a blast-resistant structure since both the parameters correlate with an expected performance level of a reinforced concrete (RC) structural member during a blast event. Assuming that the actual responses of a RC member are equal to those of the equivalent SDOF system, an iterative design procedure is developed for RC structural members on the basis of non-dimensional energy spectra (NES), which are constructed from an elastic-perfectly-plastic single-degree-of-freedom (SDOF) system. By converting a RC member into an equivalent SDOF system and controlling the responses of maximum displacement and displacement ductility factor to exactly reach the corresponding design performance targets, the effective depth and the longitudinal reinforcement ratio of the RC member are specifically determined against the given blast loading within the design process. To evaluate the design validity, numerical analysis is carried out on the specifically designed member to compute its actual responses under the given blast loading and compare these with the design performance targets. Some differences have been observed due to simplifying assumption of converting the RC member into an equivalent SDOF system.

The rise of intentional or unintentional explosions, on both defense critical and conventional buildings, is of domestic and international concern and requires the development of enhanced, cost-effective solutions for the blast protective design and rehabilitation of structures. This study explores the feasibility of a simple, cost-effective building envelope connector that provides an energy-absorbing mechanism for mitigating the effects of air-blast pressures onto a building from a ground explosion. The blast resistant ductile connectors (BRDC) are intended to be sacrificial and easier and cheaper to replace compared to building envelope panels and/or the primary lateral force resisting system (LFRS). The primary objective of the BRDCs is to provide improved blast protection over a wide range of blast scenarios offering an additional mitigation strategy for design professionals and advancing building performance for facility owners. The feasibility of the BRDCs was assessed through closed-form theoretical calculations applying principals of conservation of energy, conservation of momentum, and a generalized single degree of freedom dynamic-mechanical model to estimate the response of a concrete building envelope panel. Transient nonlinear finite element analyses are used to verify the theoretical results. This study found that, for a reasonably wide range of blast scenarios, the BRDC was able to fully dissipate the energy from a blast event, leaving the LFRS and building envelope panel undamaged. The results of the finite element model correlated well with the results of the theoretical evaluation within an appropriate design range. Designs of a potential BRDC using standard structural sections with minimal fabrication were evaluated through nonlinear finite element analyses and experimental testing. The BRDC system could be especially beneficial for the rehabilitation of existing buildings since the envelope connectors are more practical to replace than enhancement of envelope panels or LFRS.

One of the greatest challenges blast engineers face is securing enough standoff for facilities that need to be protected against attacks by vehicle-borne bombs. One solution might require the use of a perimeter blast wall. Depending on their location relative to the protected facility and the standoff distance to the bomb, perimeter blast walls might reduce the blast pressure and impulse from a vehicle bomb. Generally, erecting a blast wall at some distance from the building might provide no appreciable increase in protection for the majority of buildings. However, constructing a blast wall immediately in front of the building might provide significant protection. The blast wall effectively reduces the pressure from a reflected pulse to an incident pulse, permitting reduced safe standoff distances. Additionally, a properly designed perimeter blast wall will stop the effects of fragmentation. Empirical equations, developed by military researchers, might be used to predict the blast pressure and impulse reduction capabilities of a perimeter wall. However, the application of such equations is severely limited by the test parameters used in the equation development. Some design guidelines require that blast walls have a height equal to 1.5 times the protected structure height, and a width equal to twice the protected structure width. Furthermore, the wall must be constructed no further than one story height from the protected face of the building. Hence, blast walls can be massive and aesthetically not unpleasant. This paper will examine the effectiveness of blast walls in reducing blast pressures and impulses behind the walls. Three-dimensional, Computational Fluid Dynamic (CFD) simulations will be used to calculate the blast pressures for various blast environments. Where applicable, the calculated blast loads will be compared with those obtained using the empirical approach.

Steel plate-reinforced concrete (SC) structures are ideal for protective construction. Tests have demonstrated improved resistance to projectile perforation and construction benefits when compared to conventional reinforced concrete (RC). By placing the reinforcing steel at the extreme fiber of the section, SC walls have higher strength and stiffness than an RC wall of the same depth and reinforcement ratio. This paper presents results from a preliminary analytical study of the blast response of SC structural members. The focus of this study is on one-way slabs subjected to uniform blast loads, as are common for far-field explosions. Design parameters for blast protective design of SC walls are explained and necessary modifications to existing RC blast resistant design methods to account for SC behavior are recommended.

SDOF analysis is widely accepted for blast design, but many designers are not aware of the large database of available comparisons between results from single-degree-of-freedom (SDOF) analysis and blast test data. This paper collects a large amount of this data, excluding test data that is proprietary or restricted from public distribution, and presents comparisons of SDOF analysis results with test results for different types of structural components. This comparison includes typical structural components included in the SDOF-based blast design tool SBEDS from the U.S. Army Corps of Engineers, Protective Design Center (PDC). This comparison provides a comprehensive view of the degree of accuracy and conservatism of SDOF as a design method. This information is valuable for both researchers and designers of structural components subject to blast effects.

Close-in blast effects can cause catastrophic damage to both steel and reinforced concrete (RC) columns. Moreover, a large size column may not inherently afford much more protection than a small one for close-in charges. This paper describes issues that must be addressed in the design of RC columns to resist blast loads, especially those generated by nearby or in-contact detonations. Also shown are results from experiments showing the sorts of protective-design concepts that have proved effective in insuring the survival of RC columns subjected to the close-in blast loads. In particular, for close-in blasts, determining the effectiveness of a particular column design requires developing an effective means to consider the damage imparted to the concrete by the shock front and to assess the remaining capacity of the column given this damage. Another major aspect in realizing a protective design for columns is assessing the vulnerability of the support provided at the column's base, which may be severely damaged by a close-in blast. To facilitate the design of RC columns for such situations, a new class of simplified design and analysis tool was developed, which is described in the paper.

This paper summarizes recent testing, analysis, and applications to blast design for non-load-bearing, reinforced concrete wall panels. This includes solid, precast, and insulated sandwich panels reinforced with conventional and pre-stressed reinforcement. The measured peak response of these types of reinforced concrete test panels in blast tests is compared to the response calculated with the single-degree-of-freedom (SDOF) method commonly used for blast-resistant design. The observed damage in test panels is also used to develop response criteria which correlate the amount of peak panel response to the corresponding level of damage in the panel. The observed response of connections in precast test panels is also used to assess connection design for blast-resistant, precast panels. This paper recommends that cast-in-place and precast concrete, non-load-bearing panels, including solid concrete panels and insulated sandwich panels, can be designed to resist blast loads using the SDOF design methodology with new recommended response criteria.

Protection Engineering Consultants (PEC) has supported PPG Industries, Inc. (PPG) in the development of Mil-Tough® Light Weight Protective Panels for commercial façade and military protective application since 2008. Mil-Tough® panels are composed of (at most) three main components: an unreinforced strike-face (for ballistic resistance), inorganic ceramic binder (ICB) with reinforcement consisting of fiberglass fabric (for blast resistance), and MilTough^TM polymer (to reduce debris into the occupied space). During 2009, an early version of the façade panels was installed in a building overseas. As a result of the installation, additional research was performed to improve the panel fabrication and design process for future projects. The latest phase of the research and development in 2012 focused on developing a predictive engineering performance tool [flexural resistance function for use in a single-degree-of-freedom (SDOF) analysis] to facilitate the specification and design of the latest generation of Mil-Tough® panels for blast and fragmentation applications. This phase of the research program was accompanied by constituent material testing and characterization as well as, multi-scale static flexure testing and full-scale dynamic arena blast testing for validation of the design tool and determination of appropriate response limits for design. Concurrently, PPG updated the panel fabrication and production process resulting in a more robust and efficient assembly line producing a more consistent and higher quality panel. Most recently, the predictive engineering performance tool has been used to develop in-house "quick-design" tables for use by product specifiers and has also been used to develop designs for various proposals. This material is based upon work for PPG supported by the Air Force Research Laboratory under Contract No. FA4819-11-C-0007. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Air Force Research Laboratory.

Mullion members of storefront or curtain wall systems subjected to blast loading are commonly analyzed using the Single Degree of Freedom (SDOF) approach regardless of the interaction of the stiffness of the supported glazing. This approach does not include the effects of connection deformation. Further, static analysis is often used and this type of analysis does not typically incorporate the flexibility of connections. Mullion connections are typically designed based on the concept of ultimate or maximum required resistance (as shear force) which may be too conservative in some cases. The tensile force transferred by the mullion is normally neglected during the analysis and during the connection design. If proper detailing is not specified, the tensile force in the mullion may control the connection design. The typical SDOF model for flexure response cannot predict accurately the system response (including the reaction forces for the corresponding mullion connection design) because the model does not include the glazing and mullion interaction for large deflection and material non-linearity. This paper aims to discuss a more complex approach for modeling the mullion-glazing system subjected to blast loading, utilizing both:(1) large deflection and (2) material non-linearity concepts. The approach considers a system with three and four degrees of freedom (DOF) as transversal deflection of glazing and mullion, as well as joint sealant and mullion connection with in-plane deflection. A tool developed to solve the MDOF system and the validation with corresponding finite element analysis (FEA) models is also discussed. The proposed MDOF models can accurately predict the response of members as well as reaction forces in mullions when the system is subjected to blast loading when compared to the FEA models. In addition, the MDOF models allow shear or shear/tensile forces reactions computation.

In response to real world terrorist threats, the Defense Threat Reduction Agency (DTRA) has developed a fast-running vulnerability assessment software tool, Vulnerability Assessment and Protection Option (VAPO), which is used to characterize installations, facilities, and urban environments. VAPO can assess the vulnerability of an installation by predicting the effects of structural damage, equipment damage, and human injury due to a terrorist attack. For the 2014 Structures Congress, this paper will focus on the blast load predictions and structural response aspects of the program. This paper gives an overview of the current state of engineering calculations used in the VAPO program. The paper describes the individual methodologies of VAPO and illustrates how these pieces integrate into a package that provides capabilities that would otherwise be tedious to produce from independent tools. The process flow for the software program is broken down into four phases: characterization, environment modeling, vulnerability modeling, and results visualization. This paper's description of each phase provides the reader insight into how the program has evolved from solely a vulnerability assessment tool into an integrated software package useful for preliminary R&D problems, first-cut protective design, computational fluid dynamics geometry characterization, and DTRA reachback support for large events. The paper concludes with a discussion of future functionality and current engineering model limitations of the program.

This paper discusses a study using several analysis tools to make pre-test predictions of blast loads from an internal explosion test of a cased charge. The objective of the calculations was to generate best estimates of the blast loads, and because of the uncertainties associated with the different analytic tools, account for these uncertainties when analyzing or designing for the structure's response. The codes used included two fast-running models (FRM's) and two high-fidelity physics-based (HFPB) computational fluid dynamic (CFD) codes. The predictions from the simulations are compared to data from an actual blast test that was performed in a test structure that was designed to resist the loads while incurring only low levels of damage. The results of these comparisons are presented and the accuracy of the analysis tools is discussed

Often, when facilities are being renovated to meet blast requirements, budgetary constraints allow for upgrading window systems only and not the conventional exterior wall components. Designs of blast-mitigating window systems in accordance with the most current Unified Facilities Criteria (UFC) for Department of Defense (DoD) facilities and Interagency Security Committee (ISC) criteria for federal facilities are based on a specific design threat located at the appropriate available standoff, and do not consider factors beyond transferring the load into the building diaphragm. Existing historic structures typically have small standoff distances which result in very large blast loads on the façade. Where windows are the only component considered for upgrade, it is generally not practical or economically sound to develop window retrofit designs based solely on the design basis threat since the walls surrounding the windows will likely be much weaker than the window upgrades. The building façade should be treated as a system, with a balanced approach to mitigate hazard from blast loading. A balanced design requires the window glazing to be weaker than the window frame, the window frame to be weaker than the anchorage, and the anchorage to be weaker than the surrounding building component. In a balanced system, overloading one component of the system will not cause failure of subsequent levels of the system. In an unbalanced system, stronger windows can cause overloading of the walls and the safety provided by the window upgrades would be negated by the high-hazard fragments from the wall components. For a retrofit of an older, historical building, the wall components must be included in the evaluation of the window system so balanced window upgrades can be developed and incorporated. This paper presents a case-study involving the determination of the appropriate level of protection that should be provided for window systems as part of an upgrade of a multi-story historic building in an urban environment (with minimal standoff), where design loads exceed the wall capacities. This paper discusses the effectiveness of limiting the window upgrades to a capacity comparable to the wall capacity. The analysis results would be useful to design professionals that work on renovations of historic federal and DoD facilities.

As evidenced by available test data, steel columns are susceptible to failure due to large, localized deformations and fracturing of the k-area when subjected to near-contact explosive loading. This paper describes a case study performed on two different steel columns subjected to near-contact loading from a person-borne improvised explosive device (PBIED) along with a retrofit developed to reduce the expected damage to the columns. The analysis was performed using a loosely coupled computational fluid dynamics (CFD) and computational structural dynamics (CSD) code. The CFD code models the detonation of the high explosive, propagation of the shock wave in ambient air, shock reflection from the floor and column, and overpressure loading on the column flange and web surfaces. The CSD finite element (FE) code captures the local displacement and deformation of the column. In this coupled approach, the movement of the column influences the airblast which in turn affects the loading on the structure.

Recent changes to the two primary US criteria used for explosive load effects on buildings have led to increased blast loads on federal and military facilities. With recent reductions to the minimum construction standoff distances in United Facilities Criteria (UFC) 4-010-01 (dated 9 February, 2012, including change 1 dated 1 October, 2013), architects are able to site Department of Defense (DoD) housing facilities much closer to potential threat locations than before. Additionally, with the removal of capped loads for federal facilities allowed by the updated Interagency Security Committee (ISC) Physical Security Criteria for Federal Facilities (2010) has allowed for much higher design loads for federal facilities in an urban environment than in the past when incorporating the ISC criteria. While there are practical options for upgrading ductile reinforced concrete and steel components to meet the required response limits for the level of blast loads associated with minimal standoff distances, it is more challenging to design a brittle glazing material and the associated framing systems, particularly for curtainwalls, for the same level of loading. In response to the desire to maintain large areas of translucent glazing in locations where minimal standoff distances may be provided, this paper evaluates the potential use of a dual glazed curtainwall system, consisting of a combined interior and exterior curtainwall, to meet the required level of protection for building inhabitants. The system evaluated consists of a sacrificial conventional blast mitigating glazed system combined with a secondary high-performance "layer" to minimize the impact of the high pressures that correspond to small standoff distances. This paper provides an evaluation of the dual-layered system, and includes a comparison to the performance of a more conventional, single curtainwall system. Additionally, the distance between the two systems is evaluated to determine the impact of increasing/decreasing the provided gap. The analysis results and conclusions would be of interest to design professionals with an interest in federal and DoD facilities.

Dust explosions are a complex phenomenon that can occur when solid dust particles are dispersed as a cloud. In such configurations, solid particles can burn rapidly as the surrounding air acts as an oxidizer and sustains the combustion of the suspended particles once the reaction is ignited. If the expanding gases generated from the particle combustion are confined due to inadequate venting, the explosion can cause significant destruction to surrounding buildings and personnel. To protect nearby structures from such hazards, a methodology is needed to estimate the resulting airblast and debris. A methodology for predicting the airblast and debris loads generated from accidental dust explosions in grain silos is developed in this paper. The methodology is based on conservative assumptions which provide the initial conditions for coupled computational fluid dynamics (CFD) and computational structural dynamics (CSD) calculations. In the coupled analysis, a large CFD domain encompasses the grain silo CSD domain and a nearby structure. The silo CSD domain is a finite element (FE) model that models the concrete and reinforcing bars which compose the structure. The coupled high-fidelity calculation considers the fluid-structure interaction between the explosive products and the concrete walls during the breakup of the silo. In addition, the reflected airblast pressure is recorded at grid points located on the exterior walls and roof of adjacent buildings. These tracer point loads provide best estimates of reflected pressure and impulse loads on the nearby building as well as estimates of debris size and velocity. The intent of the methodology is to provide conservative load estimates for design purposes. The loads generated from this methodology can then be used for protective construction design and hazard mitigation. Depending on the situation, and as warranted, more refined calculations can be performed to resolve the level of conservativeness.

Current practice in blast-resistant structural design involves a component-by-component dynamic analysis to calculate the expected displacement for each structural component. The blast-induced displacement is then compared to limit values that are defined based on the component type and the expected damage level. Current provisions (such as ASCE 59-11 Blast Protection of Buildings and The Department of Defense Unified Facilities Criteria) identify limit values for increasing damage level in terms of end support rotations of steel frame components as high as 20 degrees. This paper considers the performance of simple shear tab connections at large beam end support rotations. In particular, it focuses on the residual shear strength of the connection at large rotation values. Limit values suggested by current blast-resistant design provisions will be discussed and compared to seismic design limit values and experimental evidence on simple shear tab connections. Simple analytical models will be developed to evaluate the impact of incorporating the connection effects on the dynamic response of simply supported beam elements.

As the requirement for blast-resistant design has become more common over the last few decades, significant advances in the analysis of glazing subject to blast loads have been made, along with the development of analytical tools based on theoretical and empirical data. A recent research test program funded by the US Army Corps of Engineers, Protective Design Center and conducted by Baker Engineering and Risk Consultants (BakerRisk) included a comprehensive literature search (Idriss, et. al 2012) and test program (Idriss, et. al. 2013) to evaluate the response of complete laminated glazing systems subjected to blast loads. The paramount goal of the research test program, literature search, and data evaluation effort was to document the critical response parameters characterizing the behavior of laminated glazing subjected to blast loads. Parameters and behavior for characterization include general glazing post-break performance, deflected shape, and glass edge reactions. Glass edge reactions of interest include both out-of-plane as well as in-plane reactions created due to the tensile membrane response of the laminated interlayer material. The collection of multi-direction glass edge reaction time histories in the test program provides significantly more response parameters than what was available through previous glazing research test efforts. The measured dynamic test data acquired in this program provides the basis for direct comparisons between the new and existing analytical glazing models. Initial comparisons to existing glazing model predictions indicate that although the existing codes generally predict glazing performance well, differences exist between predicted reaction forces and measured forces. The reaction data, along with other response parameter details, will be useful in the development of improved glazing analysis codes with more accurate prediction of reaction loads. Better prediction of glazing reaction forces leads to more confident design of window and curtain wall frame systems and edge capture and retention of the glazing itself. Significant work in the development of analysis code improvements will follow the completed research program. Other necessary related work includes specific research on the response of the glazing system support framing and its allowable dynamic response limits; which are addressed in this paper.

The objective of the project is to study the dynamic response of bridges for moving vehicles. The time history method of dynamic analysis is used in this study where a nodal time history of vehicle load is obtained for different speeds with loaded and unloaded vehicle conditions. Road surface roughness characteristics are also incorporated in the analysis. It is attempted to carry out dynamic analysis by taking into account the realistic vehicle type having maximum frequency of using the bridge than other lighter or heavy vehicle classes as given in IRC. Input parameters are vehicle weight and its varying speed. In the detailed study, various stress level calculations, impact factor evaluation and fatigue life estimation are carried out. Finally, based on the evaluated results, retrofitting measures are suggested to improve the bridge performance to dynamic loading. The evaluated results have been verified with IRC codal provision and available literature.

Previous studies have shown that using active confinement as a retrofit measure for vulnerable reinforced concrete (RC) columns using Shape Memory Alloy (SMA) spirals can significantly improve the seismic performance of these columns. However, the global seismic behaviors of bridges with SMA retrofitted bridge piers are not understood yet. Hence, one of the main focuses of this numerical study is to investigate the sequence of plastic hinge formation at bridge piers retrofitted with SMA when the bridge is subjected to multiple strong seismic events (e.g. strong main shock followed by an aftershock). In addition, this study investigates the changes in the demands imposed on various bridge components such as expansion joints and abutments due to the retrofit of the piers with SMA spirals. The numerical results illustrate the level of confinement required for all bridge piers to achieve a target performance of the bridge, which is measured by the aftershock peak ground acceleration (PGA) that the bridge can resist. Accordingly, the optimal retrofitting design of the bridge is identified. It is also found that the displacement demands on expansion joints and abutments increased when the bridge was subjected to increasing intensity of aftershock.

Bridges' response to extreme loading conditions, such as earthquakes and tsunamis, are critical to allow for continued evacuation and an effective emergency response. In this paper, dynamic responses and soil-foundation-structure interaction of bridges during earthquakes and tsunamis are analyzed by 3D, nonlinear, finite element modeling. This paper presents the research results of simple-span and two-span bridges with fully integral abutments, and the deep foundation type focused on is HP steel piles. The effect of pile orientations on bridge behavior is studied. The results show that it is more economical to orient the HP pile's web parallel to the bridge transverse direction.

Reinforced concrete (RC) bridge columns with inadequate lap splices in the longitudinal reinforcement are very vulnerable. They are even more critical in corrosive environments. Corrosion of steel bars decreases the steel section, reduces ductility, and deteriorates the bond between the steel reinforcing bars and the surrounding concrete. The base of a bridge pier, where the main reinforcing bars are lap spliced with starter bars, is a bond-critical region in RC bridges. This paper presents a model for estimation of the stress at corroded lap-spliced bars for tension-controlled RC column sections. The amount of stress in the steel bars at the ultimate limit state was estimated based on the experimental data of bond stress between the steel bars and concrete. Using the bond strength of corroded and non-corroded steel bars, stress of corroded lap-spliced bar is expressed in terms of corrosion rate and the original yielding strength. The results of this investigation suggest that corrosion of lap-spliced steel bars has significant impact on the load transfer between the lap-spliced bars and, consequently, drastic decrease in the flexural capacity of bridge columns.

A majority of the highly populated regions of the world are susceptible to multiple natural hazards such as earthquakes, tsunamis, tropical storms, inundation and flooding. In such regions, the potential multiple hazards that could cause damage and destruction of the constructed facilities are growing higher. To achieve an appropriate structural performance and to decrease the destructive effect of the natural hazards, a multiple hazard analysis is required. The current paper studies the combined effects of scouring and earthquake, as two uncorrelated extreme events, on the performance of reinforced concrete highway bridges. The results of the analysis indicate that the lateral load-bearing capacity of bridges is significantly affected with the increase in the scour depth which makes them more vulnerable to the future earthquakes. The outcome of this study directly contributes to the development of a multi-hazard framework for the performance-based design and assessment of highway bridges.

Damage due to age or accumulated damage from hazards on existing structures poses a worldwide problem. In order to evaluate the current status of aging, deteriorating and damaged structures, it is vital to accurately assess the present conditions. It is possible to capture the in situ condition of structures by using laser scanners that create dense 3D point clouds. However, extracting meaningful information from point clouds is automatically challenging, and the current state-of-the-art requires a certain amount of user-interaction. Previously in our research, widely accepted point cloud processing steps were used to divide laser scanner data into meaningful object clusters on which several damage detection methods were applied. Our current focus is on combining useful information extracted from laser scanner data with color information since novel laser scanners are capable of recording color data mapped on 3D point clouds. The color data provides additional information in the 4^th dimension, which makes it possible to detect damage types such as cracks, corrosion, and related surface defects that are generally difficult to detect by using only laser scanner data. It also helps to track volumetric changes on structures such as spalling. Even though crack and corrosion detection from images with varying resolution are extensively researched topics, damage detection by using laser scanners with and without images is a new research area that holds many opportunities for enhancing current practice in structural health monitoring. The aim of our research is to benefit from the best features of both laser scans and images, and combine them to create an automatic and effective damage detection method which will complement the need for skilled labor during visual inspections of damaged structures and allow documenting related information automatically. This work is of interest to researchers who are focused on structural health monitoring and interested in the use of new laser scanners and damage detection algorithms for structures. As well, practitioners will benefit from exploring new methods for improving their understanding of laser scanning technology and its capabilities for robust damage detection and documentation.

Bridges that have been damaged (but have not collapsed) due to a fire pose a problem for engineers tasked with determining whether a damaged bridge may be re-opened for full or partial traffic, or must be demolished and rebuilt. Depending on the significance of the bridge, this decision carries heavy economic costs due to both the price of building a new bridge and the impact of an out-of-commission bridge may have on regional mobility. Steel plate girder bridges are particularly susceptible to damage during a fire event. Web shear buckling at elevated temperatures has been observed in some cases. The work presented in this paper focuses on the residual post-fire shear buckling strength of steel webs that have reached their ultimate buckling load due to these fire temperatures. This initial study has found that, for most span-to-depth ratios considered, the web still retains a considerable amount of the postbuckling shear strength capacity that it had before the fire event occurred.

Construction of the new Indian River Inlet Bridge (IRIB) in Delaware was completed in 2012 and the bridge opened in time for the heavy summer beach resort traffic. A comprehensive Structural Health Monitoring (SHM) system was installed on the bridge during construction. The fiber-optic-based system includes more than 140 sensors to measure strain, acceleration, tilt, displacement, chlorides, and wind speed and direction on the bridge. Since the bridge opened, data has been collected automatically. Three controlled load tests have been conducted that will provide baseline data on the bridge response for the future. The test data has also been used to develop and calibrate live load models of the bridge.

As energy costs soar, public demand for massive transportation systems has increased. Massive transportation systems often include structures such as station buildings that are linked by elevated bridges. It is essential for these aerial structures to withstand large earthquakes. Structural engineers typically design station buildings according to the IBC which references ASCE 7, while bridge design is based on the AASHTO LRFD bridge design code and the Guide Specification for seismic design. IBC and AASHTO LRFD both use force-based design, but with different spectral loads, analysis parameters, and levels of acceptance. The newly published AASHTO Seismic Guide Specification applies displacement-based seismic design as its framework. However, there is no unified code for the seismic design of this kind of mixed structural systems in the United States. How will these codes be implemented in the design of mixed structural systems without violating either code? Based on displacement-based seismic design concepts, this paper uses a case study to show how the seismic design of mixed structural systems can satisfy the performance objectives of both the IBC and AASHTO codes without producing a design that is overly conservative.

Cable-stayed bridges provide an efficient structural solution over a wide range of span lengths and, as a structural form, are often used to build an iconic structure. Protecting them from threats, both malicious and accidental, presents a number of challenges. This paper presents a number of different mitigation decisions made as a consequence of Accident Threat and Vulnerability Assessment (ATVA), sometimes known as Risk and Vulnerability Assessment (RVA), in the design development of four cable-stayed bridges currently under design or construction in the US, and for which the authors have knowledge of the design. Details about each bridge are provided for the purposes of comparison and are limited so as to maintain the confidentiality of the threat and vulnerability assessment of the specific bridges discussed. Key considerations discussed for the bridges include: (1) main tower protection, (2) deck stability, (3) loss of cables, and (4) fire protection.

A new retrofit method for the distortion-induced fatigue problem in steel bridges by using adhesively-bonded FRP angles is developed in this paper. This retrofit method is relatively cheap and easy to use and does not require deck removal or any other modification to the steel girder. The FRP retrofitted specimens are found to have significantly longer fatigue lives than as-welded specimens and specimens repaired by means of two other conventional repair methods. The hot-spot stress method is used to quantify the effectiveness of the proposed retrofit method. A coarse finite element (FE) analysis is used to predict the effectiveness of the proposed retrofit methods in terms of the reduction in the hot spot stress value, and analytically calculated hot-spot stresses are validated with directly measured values. The effects of a number of the varied geometrical and mechanical parameters on the efficiency of the proposed retrofit are then studied using an FE analysis and recommendations are made to improve the efficiency of this FRP-based retrofit method.

There have been numerous examples of poor in-service performance of welded, tubeto-transverse plate connections within mast-arm sign support structures in the past several decades. A considerable amount of research has been devoted to identifying the structural response characteristics of these sign support systems and identifying how the connections within these systems can be repaired or designed to facilitate infinite service lives. Little attention has been given to using reliability-based approaches to assess the risk of fatigue-induced crack initiation in these structures. The present research effort focuses on systematically quantifying all sources of uncertainty found in these systems and formulating a reliability-based approach for prescribing inspection intervals corresponding to user-specified levels of risk of fatigue-induced crack initiation. The results indicate that implementation of state-of-the-art reliability-based assessment procedures can contribute toward formulating inspection protocols that are based upon owner-defined risk thresholds. The structural engineering community can use the results of this research effort to align inspection needs with limited fiscal and human resources. The procedures developed can also be readily extended to other infrastructure systems including bridges.

The special requirements of the San Francisco-Oakland Bay self-anchored suspension (SAS) bridge gave challenges in the design of the orthotropic decks. Many of the atypical details in this bridge are solutions to these unusual conditions. In the SFOBB-SAS, more than half the stress demand consists of axial dead load stress, the compression due to the main cable tension. Reinforcing for such stress is not simple, since adding material increases the dead load (DL) demands. Weight was reduced by the use of 14 mm decking and longer deck spans. Furthermore, as a bridge designed to resist extreme seismic demands, compactness and stability criteria apply for all longitudinal components of the deck. Testing of prototype decks was performed to confirm the design. The design criteria used in 2000 are compared with the FHWA Manual for the Design, Construction and Maintenance of Orthotropic Steel Deck Bridges (2012). The SAS design compares favorably with the current requirements.

Bridge designs in regions with moderate seismic hazard can be relied upon to provide an effectively isolated response and to protect super- and substructure components when the force transmission characteristics of the bearing components are properly accounted for in design and analysis. An experimental program for common bearing configurations employed in the state of Illinois investigated the peak capacity and transition mechanisms expected for non-seismic bearings subjected to seismic demands. Horizontal fuse capacity for elastomeric bearings ranged from about 0.2 to 0.6 times the bearing vertical gravity load when relying solely on friction between elastomer and concrete, and increased to about 0.7 to 1.0 in the bridge transverse direction due to stiffened angle retainer brackets anchored to the concrete substructure. The presence of polytetrafluroethylene (PTFE) decreased the fuse capacity to about 0.1 to 0.15, even accounting for contamination of the slip surface and velocity-dependence, and to about 0.4 to 0.75 with retainers in the transverse direction. Steel fixed bearings anchored to concrete demonstrated fuse capacities of about 0.85 to 1.15 prior to rupture of the anchors securing the bearings to the substructure, and subsequent coefficients of friction of about 0.2 to 0.4. These values consistently exceeded a target fuse limit of 0.2 times gravity load, as selected by the Illinois Department of Transportation. The experiments demonstrated that if fuses are intended to be used as part of an Earthquake Resisting System, performance of the components must be carefully considered and designs must be calibrated to ensure satisfactory response of the entire bridge structure.

Columns are the most critical components for the overall stability of a bridge. In many bridge fire cases, it is very easy to determine which fire-exposed columns are no longer functional. However, in special cases, a fire may last long enough to cause damage but not long enough to cause complete failure of the column. In fact, the damage may be undetectable by visual inspection, and a fire-damaged column may appear the same as an intact one. Officials are in need of a simple and cost-effective damage detection method which enables them to make quick decisions regarding the closure of a bridge with columns exposed to fire. Two one-fifth scale reinforced concrete (RC) bridge column specimens were designed in compliance with AASHTO specifications and subjected to two significant durations of extreme fire exposure at a fire testing facility. One specimen was subject to 1 hour of extreme temperature reaching 1285 degrees Fahrenheit, while the other was subjected to more than 2 hours of exposure at 1440 degrees Fahrenheit. Both of these durations cause significant damage to the concrete material but have very little visual indication. After the fire experiments, the columns were returned to the Next-Generation Multihazard Resilient Infrastructure Laboratory (NGMRIL) of the University of Connecticut where system identification and residual axial capacity tests were conducted on the undamaged and damaged columns. Modal analyses of both fire-damaged columns as well as an undamaged column were conducted, and the residual axial capacities of the damaged columns were obtained using a 400 kip loading frame. The capacity of damaged columns was compared with the axial capacity of the benchmark column. Possible methodologies for determining the residual capacities of fire damaged bridge columns are developed based on these experimental observations.

A method for quick repair of severely damaged, but still standing, concrete columns is developed and tested. Two ¼-scale, reinforced concrete (RC) bridge columns specimens were built and tested at a shake table facility of University of California, Berkeley. Both specimens had identical geometric and longitudinal reinforcement details, but different volumetric reinforcement ratios. A total of 11 ground motions with combination of horizontal and vertical excitations were chosen for testing the two specimens. Both specimens had moderate-to-high shear and flexural damage with cracking and spalling of concrete along the column height. Damaged specimens were then repaired and retrofitted with unidirectional Fiber Reinforced Polymer (FRP) composite sheets by wet lay-up method. The two repaired specimens were subjected to the same ground motions used for testing the performance of as-built specimens. Both repaired specimens exhibited better load-carrying capacity and ductility than the as-built specimens. FRP jackets on both columns remained intact and the residual displacements were negligible. From the experimental data, it was concluded that the proposed repair could be considered as a permanent strengthening solution of RC bridge columns.

Concrete-filled, fiber-reinforced polymer (FRP) tube [CFFT] columns were first introduced as an alternative to conventional reinforced concrete (RC) columns to enhance the durability and corrosion resistance of bridge piers. Recently, the CFFT column system has been validated as a high performance alternative to RC columns for multihazard resilience. This paper describes the superb seismic, blast and fire resiliency of this column system. First, the CFFT column was tested alongside a conventional RC column during shaking table experiments of a two-column bent at the University of Nevada, Reno. The shaking table experiments were the first to reveal the superb ductility and energy dissipation provided by CFFT columns. Next, the system was further tested at the U.S. Army Corps of Engineers Research and Development Center (USACEERDC) where the blast performance of the system was studied and compared against that of RC columns. Finally, fire testing of the CFFT column at a fire testing facility substantiated the system's fire resilience when properly protected. The CFFT system was able to endure more than two hours of extreme temperature exposure. Residual capacity tests conducted at the University of Connecticut on fire and blast-damaged CFFT and RC columns showed that the CFFT system provides much better axial strength and ductility retention after a damaging event. The three experimental studies solidly corroborate the applicability of CFFT columns for multihazard bridge design.

Bridge columns are the most critical components of a bridge for its overall stability. At the same time, bridge columns are one of the most vulnerable components to terrorist attacks. Recent studies conducted by the University of Connecticut at the Army Corps of Engineers - Engineer Research and Development Center (ERDC) have shown that reinforced concrete (RC) columns that are subjected to large explosions may undergo significant yielding without showing any observable signs of damage, like spalling or permanent deformations. The blast overpressure acts as a confining force on the pressure side and allows the columns to instantaneously resist larger loads and deformations compared to static and dynamic loading. This condition leads officials to believe a compromised bridge column has not lost any capacity. However, once the blast pressure wave has cleared, this increased resistance due to the confining effect of blast overpressure is no longer available. The column is left with significantly reduced ductility, but without any observable damage. The results of three one-fifth scale blast tests of varying severity conducted at ERDC, combined with residual capacity tests and analytical studies conducted at Next-Generation Multihazard Resilient Infrastructure Laboratory (NGMRIL) at UConn, are used to confirm this phenomenon. Experimental results are used to quantify the proposed blast overpressure confinement effect. Subsequently, possible methodologies to assist officials in making critical bridge closure decisions after columns have been exposed to blast loading are explored.

The American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Specification for bridges has its strength design limit state formulated and fully calibrated using the reliability-based approach. The extreme event design limit states, however, are constructed by combining the non-extreme load effects with the independently established extreme hazard load effects through professional judgment. Its margin of safety and adequacy could not be assessed quantitatively. A research project sponsored by the Federal Highway Administration (FHWA) has been carried out to explore principles and approaches for establishing multiple-hazard (MH)-LRFD based on the established rationale and reliability-based methodology of the AASHTO LRFD. An analytical framework has been established to consider the non-extreme and extreme loads on a common reliability-based platform. This paper will describe the formulation of specific extreme event design limit state (e.g. the limit state for non-extreme load with the earthquake load effects) by using the all-hazard, reliability-based approach. Future challenges towards the development of a comprehensive MH-LRFD will be described.

New England is home to many iconic and historic bridges. Within the Boston area, many well-known historic bridges cross the Charles River, connecting Boston to Cambridge. Typically, these bridges have a distinctive masonry component related to the timeframe of construction and the prevailing architectural influences of the surrounding region. Several years ago, the Massachusetts Department of Conservation and Recreation (DCR), which had jurisdiction over the Charles River bridges [these now belong to the Massachusetts Department of Transportation ( MassDOT)], began a systematic evaluation/renovation/reconstruction program to rehabilitate deteriorating bridges over the Charles River. Several bridges are currently in the design phase and two are in the construction phase. This session will discuss design considerations required when rehabilitating an historic masonry bridge, including: ≤ Assessing the historic masonry construction ≤ Design options to extend masonry service life ≤ Reuse of existing masonry materials in the new construction ≤ Construction techniques to facilitate ease and speed of construction for recreating masonry details The session will include examples from the author's experience and involvement with several historic masonry bridges in the New England area, including the Longfellow Bridge and the Anderson Memorial Bridge over the Charles River.

Designers working on historic bridge rehabilitation projects deal with conflicting objectives: rehabilitate and update the structure to meet current design codes and functional requirements or uphold the historic form, nature, and function of the structure. However, the requirements to satisfy each objective may be mutually exclusive. One obstacle commonly encountered is that current seismic code provisions were not required or even understood for 19^th century bridges. In rehabilitating the bridge to meet current seismic requirements, it may not be possible to maintain the historic form of the structure. At a certain point, the question arises as to how much can be changed before the structure loses its overall historic nature. If a bridge is no longer truly "historic", is the added expense justified in comparison to replacement? In other words, does a shell of an historic bridge satisfy the requirements for maintaining an historic bridge with just its original form but not true function? Is that bridge still considered "historic"? When is an historic bridge no longer an historic bridge? This paper will discuss and introduce the problem of historic bridge rehabilitation in general terms, and then present some examples. The paper concludes with a discussion addressing the title question and the tradeoffs.

Tropical Storm Irene swept through Vermont with 100-200 mm (4-8 inches) of rain, causing intensive flooding in the Southern and Central regions. Over 300 bridges suffered damage or failed as a result of heavy rains. Resources from the Vermont Agency of Transportation, Vermont Agency of Natural Resources, and Vermont Regional Planning Commission were joined to create a comprehensive bridge database. The database combines the stream characteristics and Irene damage along with the bridge attributes into a common resource that can be used for analysis. The examination of affected bridges showed scour as the dominant mode of damage from Irene. Bridges damaged tended to have floodplain contraction, and spans incapable of passing flood flows. Flow constriction and floodplain blockage were key indications of poor performance.

The Angus L. Macdonald Bridge, a major suspension bridge that crosses Halifax Harbour in Halifax, Nova Scotia, was opened for traffic in 1955. The bridge deck has reached the end of its service life, and the design of the new bridge superstructure and its replacement sequence have been completed. The entire suspended structure and hangers will be replaced sequentially during night closures while the bridge will be opened for traffic during daytime. The erection sequence has been supported by sophisticated automated erection analysis models which take into account the geometry of the existing bridge, positioning of the erection equipment on the deck, and necessary hanger and strand jack adjustments. Significant wind tunnel testing and analysis have been performed to ensure aerodynamic stability of the bridge during erection and in its final condition.

Historic masonry arch bridges were not designed to perform under the load levels typical of modern vehicles. Most of them still perform well due to their inherent strength; others experience various forms of distress. Load rating is the standard approach to assess the capacity of these structures; however, predicting the capacity of an arch bridge is difficult because of the complex behavior of the structure. Mathematical models are powerful tools to predict the actual performance of the structure, but they rely heavily on the accuracy of information provided by field investigations and engineering assumptions. Preservation and rehabilitation of these structures depend on both the success of in situ experimental investigations and numerical analysis. In this paper, a pragmatic approach to assess historic masonry arch bridges is described. The use of nondestructive evaluation (NDE) techniques to assess the existing condition of the structure is briefly discussed. The paper focuses on the load rating procedure provided by the AASHTO Manual for Bridge Evaluation (MBE) (AASHTO 2011). This method is reviewed based on results from a Finite Element Analysis (FEA) and diagnostic load test of a two-span masonry arch bridge over the Pascoag River in Burrillville, Rhode Island. The influence of the analysis assumptions on the bridge rating is evaluated with the aim of providing recommendations on how to improve the accuracy of the AASHTO load rating procedure for masonry arch bridges.

Intermediate diaphragms are used in precast concrete girder bridges for three primary reasons: 1) to prevent torsional girder rotations during girder erection and deck placement operations; 2) to increase the vertical load distribution between girders; and 3) to transfer and spread an impact load from an overheight vehicle to adjacent girders. Typical practice includes the design of end diaphragms, but there is significant variation in the practice of specifying or requiring intermediate diaphragms between state transportation agencies. Wide variations exist in the acceptance of steel alternates to traditional cast-in-place concrete. In addition to the lack of cohesion in material choice, there is also significant variation in the type and geometry of steel intermediate diaphragms, spacing within the span, and alignment relative to the girder. The importance of intermediate bracing in a span during construction is widely accepted as essential; however, their contribution to a bridge in service, after the bridge deck has hardened, is considered by some to be very minimal. As part of this research, a detailed survey of design practices by individual state bridge design agencies throughout the United States was conducted for all 50 states. To our knowledge this is the first effort to successfully profile the use of intermediate diaphragms in all 50 states.

Under bridge rehabilitation of an existing bridge originally designed in accordance to AASHTO Standard Specifications, the Colorado Department of Transportation (CDOT) currently requires a Load and Resistance Factor Rating (LRFR). The dual I-70 bridges being rated are located near Avon, Colorado. They were constructed in 1972 and carry two lanes of traffic over a railroad line, the Eagle River, and US 6. The bridges are five-span welded steel plate girders with 56° skewed supports. These bridges have been studied for the assessment of different structure rehabilitation alternatives, crack prevention strategies to reduce distortion induced fatigue, and crack repair options with the intent of increasing the remaining service life. In this paper we explore live load distribution factor sensitivity when steel girder bridges have a high skew angle and different configurations of cross frames, and their effect on the bridge load rating. A full load rating was performed that included an analysis of the inventory, overload, posting, and permit cases. This task was broken into two subtasks: Distribution Factor (DF) analysis and Load Rating analysis. The DF analysis evaluated live load distribution from AASHTO LRFD Equations and refined FE analysis methods using both SAP2000 and Virtis NSG applications. The results were compared and optimized to more accurately evaluate live load distribution for the rehabilitated structures. The Load Ratings of the rehabilitated bridges using the optimized distribution factors and the bridge load posting requirement for the Colorado State Legal Trucks were evaluated.

The paper describes analysis and design for the replacement of the Kenneth F. Burns Memorial Bridge (Route 9 over Lake Quinsigamond) in Shrewsbury and Worcester, Massachusetts. The replacement is actually two bridges, each consisting of five-span, post-tensioned, steel deck arches. The discussion includes the design approach, the construction sequence, the staged-construction analysis, the perched-pier foundation design, the approach for aesthetic design and detailing, and 3D modeling and visualization. The project uses the design-build project delivery method. The scope included fast-tracking of analysis and design to meet challenging project schedule milestones.

Vehicle collisions with bridge piers are one of the leading causes of bridge failures throughout the United States. The damage in a bridge pier caused by a vehicle collision can result in loss of axial capacity in the pier, fracturing of the longitudinal reinforcement, and failure of the bridge. Different performance levels can be established based on the various levels of damage the pier experiences. For this paper, a detailed finite element model was developed. The model consisted of a single, circular, reinforced concrete bridge pier with an elastic foundation and a vehicle model representing a Ford F800 single-unit truck. Various validation studies were conducted to assure the accuracy and to provide confidence in the analytical results. A detailed study was conducted to observe the effects of transverse hoop reinforcement spacing on the performance level of a bridge pier subjected to vehicle collision.

The Rocks Village Bridge is an historic 6-span truss bridge carrying Main Street over the Merrimack River at Haverhill and West Newbury, Massachusetts. It contains the oldest movable bridge in MassDOT's inventory and contains the only remaining manually-operated swing span in the state. Nearly every span of this truss bridge has a unique framing style or span arrangement. The spans were constructed over three different periods beginning in 1883. The 1883 spans, namely the rim-bearing swing span and adjacent west approach span, were built by the Boston Bridge Works. This is one of the earliest known surviving works of this nationally-significant bridge-building firm from the late nineteenth and early twentieth centuries. The bridge also contains one of the earliest riveted metal trusses identified in the state. The entire bridge is a contributing structure to the National Register listed Rocks Village Historic District (National Park Service, 1976)

The new Fore River Bridge is a hallmark project for the Massachusetts Department of Transportation's Accelerated Bridge Program. The project consists of a 324-foot-long Vertical Lift Span in addition to 2000 feet of approach superstructure joining the Boston, MA suburbs of Quincy and Weymouth. The structure will support four lanes of vehicular traffic, two bicycle lanes, and two pedestrian walkways, resulting in a roadway envelope over 73 feet wide. The new bridge structures will replace a temporary lift bridge and approach spans that replaced the previous bridge that was demolished in 2004. The project was awarded to the joint venture team of J.F. White-Skanska-Koch as a Design-Build Procurement, with Parsons serving as the lead designer. Extreme care in phasing and erection of this structure had to be taken to minimize disruption to vehicular and maritime traffic routes. Planning, analysis, design, erection and construction staging considerations have resulted in innovations in the lift span tower framing, lift span framing, and tower foundations.

Vehicle barrier systems are an important consideration in the security of protected sites. Standoff plays a critical role in controlling blast loads and vehicle control is necessary to address many attack scenarios not related to explosives. Without the ability to stop a vehicle, it is nearly impossible to protect buildings from determined attackers using vehicles. Therefore, on most projects, careful selection, siting, and installation of vehicle barriers, in combination with appropriate gate operations, are necessary to keep explosive devices and other threats at sufficient setback to achieve the desired protection goals. The selection of appropriate barrier systems should be the result of a process of weighing risks, tactics, and costs to arrive at a design vehicular threat. The threat determination should then be followed by a site evaluation to determine achievable impact angles and approach speeds and, finally, selection of appropriate barrier systems capable of stopping this moving threat at the required locations. To be successful, the process requires professionals with a wide range of skills and experience. The threat and risk evaluation process necessitates security professions with backgrounds in intelligence and law-enforcement. The site evaluation lends itself to professional with a background in transportation, roadway planning and vehicle dynamics. The barrier design process requires a background in engineering mechanics and structural dynamic analysis. Therefore, it is important that there is a common understanding among the various professions on the important barrier design parameters. This paper discusses barrier design requirements in terms of five major design parameters. Suggestions for common coordination documents are also provided, and design processes for five major classes of barrier are reviewed with the pros and cons of each. Readers will receive insights into common pitfalls in the barrier design process and should gain an understanding of how to fully describe barrier requirements on a project.

During the past few decades, several studies have been conducted to characterize the performance of in-service, girder-type bridge superstructures under operating conditions. Few of these efforts have focused on evaluating the actual response of the bridge systems — especially beyond the elastic limit of their behavior — and correlating the impact of damage to the overall system behavior. In practice, most of the in-service bridge superstructures behave elastically under the routine daily traffic. However, existing damage and deteriorating conditions would significantly influence different aspects of the structural performance, including reserve capacity, resilience and remaining service-life. The main purpose of this study is to evaluate the response of composite steel girder bridges under the effect of subsurface delamination in the reinforced concrete deck. Commercial finite element computer software, ANSYS, was implemented to perform a nonlinear analysis on a representative single-span, simply-supported bridge superstructure. The system failure characteristics were captured in the numerical models by incorporating different sources of material non-linearities, including cracking/crushing in the concrete and plasticity in steel components. Upon validation, non-linear behavior of the system, with both intact and degraded configurations, was used to evaluate the impact of integrated damage mechanism on the overall system performance. Reserve capacity of this bridge superstructure was also determined with respect to the nominal element-level design capacity. As vision to the future path, this framework can be implemented to evaluate the performance of other in-service bridges degraded under the effect of different damage scenarios, thus providing a mechanism to determine a measure of capacity, resilience and remaining service-life.

Debris impact forces generated during extreme events - such as floods, tsunami, and hurricane storm surge - can cause severe structural damage. To design the structures to resist such impact demands, it is necessary to be able to quantify debris impact forces. The goal of this study is to develop a simple model that accounts for additional nonstructural mass to estimate debris impact forces and durations accurately. Linear finite element models of a steel tube and shipping container were developed and validated by comparing with axial impact experiments. Parametric studies on the validated numerical models were carried out to investigate the effect of the amount and distribution of nonstructural mass on the impact forces generated. The results indicate that the impact force and duration are sensitive to the location and quantity of nonstructural mass present.

The Duck Bridge is a five-span, double-intersection, Warren-type through-truss bridge carrying Union Street over the Merrimack River in Lawrence, Massachusetts. Constructed in 1888 by Boston Bridge Works (Cambridge, MA), it is the oldest of its type in the state of Massachusetts. The structure underwent a $15.6M rehabilitation between September 2008 and March 2013, during which components of the substructure and superstructure were repaired or replaced. While the rehabilitation project was driven by the need to address safety concerns from structural deficiencies found in the bridge superstructure, it was important to maintain the historic nature of the truss bridge. The Duck Bridge has long been a significant part of the surrounding community, past and present. It is one of the primary features of the North Canal Historic District, which was added to the National Register of Historic Places in 1984.

This paper proposes nonlinear analyses of bridge pier-barge collision. A reinforced concrete bridge pier, a precast concrete deck and a Jumbo Hopper (JH) barge are modeled using LS-DYNA. The impact forces and structural responses of the reinforced concrete pier subjected to various barge impact loads are investigated. The AASHTO specifications and the previous studies on barge-pier collisions are used as baselines. It is demonstrated that the proposed FEA is effective to estimate the nonlinear behavior of the reinforced concrete bridge pier under barge impact loading.

This paper proposes a systematic, nonlinear, analysis framework for analyzing the structural impact responses of large infrastructural systems under various impact loads. The analysis framework is developed through the integration of a bridge pier equipped with a superstructure and high-impact vehicle model using the LS-DYNA finite element software. Both bridge pier and vehicle models are modeled using the solid elements. It was shown from the extensive simulations that the proposed analysis framework is effective in representing the complex behavior of bridge-vehicle collisions.

One of the challenges associated with AASHTO-LRFD and Eurocode 8 (EC8) is predicting the failure of irregular bridges supported by piers of unequal heights, which is not effectively addressed by codes committee. EC8 currently uses "moment demand-to-moment capacity" ratios to somewhat guarantee simultaneous failure of piers on bridges, while AASHTO-LRFD relies on the relative effective stiffness of the piers. These conditions are not entirely valid, in particular for piers with a relative height of 0.5 or less, where a possible combination of flexure and shear failure mode may occur. In this case, the shorter piers often result in brittle shear failure, while the longer piers are most likely to fail due to flexure, creating a combination of different failure modes experienced by the bridge. To evaluate the adequacy of EC8 and AASHTO-LRFD design procedures for regular seismic behavior, various irregular bridges will be simulated through a non-linear pushover analysis using shear-critical, fiber-based, beam-column elements. The research will investigate the behavior of irregular monolithic and bearing-type bridges experiencing different failure modes, and investigate different ways of regularizing the bridge performance to balance damage. The ultimate aim is to obtain a simultaneous or near-simultaneous failure of all unequal piers irrespective of the different heights and failure mode experienced.

Unlike straight bridges with little or no skew, the behavior of curved, steel, I-girder bridges is dependent upon a complex interaction between the girders and cross frames. The ability to accurately predict loads and deformations within the frame system, therefore, requires correctly representing the stiffness of the girders and cross frames. This is particularly challenging when a 2D modeling approach is used, which requires making various assumptions and simplifications that impact behavior. A rare opportunity recently arose during construction of Ramp A5 on the Cleveland Innerbelt Bridge Project in Cleveland, OH, in which the modeling assumptions incorporated in the 2D model used to design the structure were validated through a field load test. The bridge consists of four continuous spans of composite, curved, steel plate I-girders. About two-thirds of the first span is horizontally curved with a radius at roadway baseline of 47.2 m (155.00'). Due to some concerns that arose during construction, a simple load test was performed to verify the behavior of the girder/cross-frame system prior to placement of the slab. A known weight was hung from the girders within the first span and deflections were measured along the girders. The predicted deflections due to the test load from the 2D model were in near exact agreement with those measured in the field. The load test, therefore, validated the assumptions incorporated in the development of the 2D model with respect to girder and cross frame stiffness, and clearly demonstrated the ability to accurately analyze a curved girder system using 2D methods.

This paper provides an overview of an innovative new approach for the safety inspection of highway bridges. The National Bridge Inspection Standards (NBIS) mandate a uniform 24-month inspection interval for most highway bridges. The uniform intervals were based on engineering judgment at the time the NBIS was implemented in the 1970's and do not consider the typical performance characteristics of bridges with different designs, materials, exposure environments, or existing condition. A more rational approach to determining inspection frequency and scope would consider the structure type, age, condition, environment, and other characteristics of bridges. This paper will discuss reliability-based inspection practices that utilize a risk assessment framework to determine appropriate inspection frequency and scope. This approach utilizes engineering analysis of typical damage modes and deterioration mechanisms for different types of bridges, combined with the exposure environments and loading, to assess the inspection needs for a bridge. Under such an approach, inspection efforts are focused where deterioration and damage are most likely and where consequences of that damage are greatest. The approach is intended to improve the safety of bridges by optimizing the use of resources, focusing inspection efforts where inspection needs are greatest.

Concrete-filled tubes (CFT) offer an efficient and economical alternative to conventional reinforced concrete construction; however, their implementation in the US has been limited mainly due to uncertain design expressions and reliable connections. A research program was undertaken at the University of Washington to develop connection details to use CFT columns in bridge systems. Two types of connections are being investigated, including column-to-foundation and integrated column-to-cap beam connections. Two variations of an embedded CFT-to-foundation connection were experimentally evaluated in which the steel tube was embedded in surrounding concrete. Results from the experimental studies were used to develop engineering expressions for design of the CFT column-to-foundation connection. The second phase of the study focuses on the column-to-cap beam connection which offers many unique design constraints including congested joint reinforcing and limits on geometry. Two variations of the CFT column-to-cap beam connection are being numerically and experimentally evaluated:(1)an embedded connection similar to the proposed foundation connection and (2) a connection in which headed reinforcing bars are welded to the inside of the steel tube and extended into the cap beam. Preliminary numerical and experimental results indicate that the embedded connection can achieve strength and ductility requirements within the constraints of the cap beam.

This paper describes the rehabilitation of the historic Anderson Memorial Bridge which carries North Harvard Street over the Charles River in Boston and Cambridge, Massachusetts. The structure is a vital transportation link that accommodates significant volumes of vehicular, pedestrian and bicycle traffic. The bridge is classified as an Urban Arterial, and it is listed on the State and National Registers of Historic Places as an integral component of the historic Charles River Basin. The Anderson Bridge, completed in 1915, is a three-span, earth-filled, concrete arch bridge with notable brick and granite aesthetic treatments adding to its appeal. Deterioration of the spandrel walls, parapets, brick arch rings and concrete arches necessitated bridge rehabilitation, and a $20 million project began in the Spring of 2012 to address these issues as part of the MassDOT $3 billion Accelerated Bridge Program. The project incorporated input from the public along with the interests of 18 stakeholders.

The ultra-modern, 245-meter-tall Federation of Korean Industries (FKI) office tower is a significant and recent addition to the skyline of Seoul, South Korea. The building, including below-grade parking and support spaces, consists of 170,000 square meters of gross floor area with 111,000 square meters above grade. A separate, free-form, glass and steel rib-shell structure at the podium also houses a 6,000-square-meter conference center. The tower structural system consists of a reinforced concrete core and composite perimeter columns coupled with steel outriggers and belt trusses to resist lateral forces. The superstructure is founded on reinforced concrete bored piles socketed into the local rock formation. Five below-grade levels were constructed utilizing top-down construction techniques. The exterior wall of the tower has been furrowed as part of the architectural expression and to provide optimal utilization of building-integrated photovoltaic panels. The unique exterior skin is a key factor in disrupting the organization of wind vortices for the purely prismatic tower geometry. All documentation was produced in 3D REVIT and TEKLA models.

The Pearl River Tower is a 71-story, 309-m (1015') office building in Guangzhou, China. The overall goal for the project was to create the most energy-efficient office building possible. Construction was completed in 2012. Close coordination and collaboration between the architects, structural engineers and MEP engineers was required to accommodate several of the energy-saving measures. In order to meet the demands of the sustainability initiatives, the architectural complexities of the building, and the Chinese Code Wind and Seismic requirements, the overall structural concept utilizes a highly integrated series of systems, including:reinforced concrete core walls, composite mega columns with structural steel Mega X-bracing, structural steel outrigger and belt trusses, structural steel columns, and composite floor framing. This paper will discuss the challenges that were presented by this project and how the various disciplines worked together to solve them. Particular emphasis will be placed on the structural role in this work.

The recently completed 40-story office tower at 250 West 55th Street in Manhattan demonstrates the best in innovative structural design and use of 3-D coordination tools for design and construction. This paper describes the integrated process that was followed and some of the challenges that were met along the way. It will be of interest to design professionals and others interested in integrated construction processes. The integrated 3-D process started with the use of Revit from the Schematic design stage, and was followed through the design, procurement, and construction phases, with all major sub contractors producing 3-D or 4-D models. These models were carefully integrated by the general contractor and enabled savings in the schedule, reduction of field conflicts, and reduced project risks. The progress of the project was complicated by a suspension of construction for two years after completion of the foundations. This paper describes some of the unusual steps taken to manage this process and allow for an accelerated schedule upon restart of construction.

Situated on a prominent waterfront site at the southern edge of the Korean peninsula, the Busan Lotte Town Tower will play a pivotal role in representing the city of Busan as the new gateway of East Asia. Standing at over 510 meters with 107 floors, the landmark tower incorporates 585,000 square meters (6.3 million square feet) of mixed-use program consisting of office, hotel, residential, retail and entertainment facilities, and underground parking. The tower is organized to maximize floor efficiency for each program while integrating a unique structural solution to minimize the effects of extreme wind. The tower's triangular shape and distinctive stacked massing are driven by the integration of a stacked multi-use programming on a very dense site coupled with a structural strategy to mitigate typhoon winds and limit motion perceptibility. Tower setbacks occur between major programmatic elements and are arranged in a reciprocal clock-wise fashion, animating the exterior façades while efficiently altering the lease span based on appropriateness for each program space. Structural steel belt trusses organized to mimic this dynamic reciprocal plan transfer each program stack to six mega-columns to successfully limit lateral uplift on the tower under extreme wind events. The concrete core wall and three sets of mega-columns are linked by structural steel outriggers to constitute the lateral resisting system and are arranged as contiguous vertical extrusions to simplify construction within this unique reciprocal plan. In turn, the outline of the building reveals these vertical edges throughout the height of the tower, creating the clean silhouette and emphasizing its verticality. Various sustainable measures will be used to ensure environmental responsibility, including a co-generation plant, radiant heating, exterior louvers, light shelf, and the utilization of sea-water for cooling.

Demand for a lighter and safer concrete floor system to improve the span limit resulted from the high weight-to-stiffness/strength ratios of a solid, reinforced concrete slab has led to the emergence of spherically voided biaxial slab (SVBS). However, the voids impart a non-prismatic nature in both in-plane directions of this new slab system. Because of this non-prismatic nature, determination of stiffness and structural capacity of a spherically voided biaxial slab is inherently challenging. The inclusion of the voids is intuitively expected to compromise the stiffness and structural capacity of the slab. However, the extent of the compromise is not explicitly known. Therefore, in this paper, the reduction of the stiffness and structural capacities of the spherically voided slab is investigated in comparison to a solid slab with equal dimensions. A 3D, non-linear. finite element analyses software - namely, ANSYS Workbench 14.0 -is used to conduct the investigation. The analyses indicated that the flexural capacities of spherically voided biaxial slabs are very close to solid slabs of equal dimension, especially when considering long span slabs. Moreover, the failure mechanisms of SVBS and solid slab system are evaluated and found to be almost similar under uniform loads. It is also concluded that the voids around the middle region of the slabs do not significantly compromise the flexural capacity and bending behavior of the slab system. However, the punching shear resistance of SVBS is determined to be considerably less than that of solid slab.

Pretensioned concrete ties are increasingly employed in railroad high speed and heavy haul applications. The bond between prestressing wires or strands and concrete plays an important role in determining the transfer length of pretensioned concrete members, but little research was done to characterize the transfer length in terms of steel reinforcement and concrete factors for railroad concrete ties. The Federal Railroad Administration is sponsoring a comprehensive test program at Kansas State University (KSU) aimed at quantitatively correlating prestressing steel and concrete variables with the transfer length of pretensioned concrete crossties. The Volpe Center has been applying the data obtained in the KSU test program to develop bond models that can be used in transfer length prediction and failure analysis of concrete ties. This paper describes finite element (FE) model development related to the smooth prestressing wire whose dominant bonding mechanisms with concrete are chemical adhesion and friction. The commercial FE software, Abaqus, is employed, and the steel-concrete interface is discretized with cohesive elements. A user bond model is developed within the elastoplastic framework and implemented for axisymmetric and 3D cohesive elements. The bond model defines constitutive relations in terms of normal and shear stresses vs. interfacial dilation and slips. The bond behavior is initially linear elastic, followed by adhesion and friction that are governed by a yield function and a plastic flow rule specific for the smooth wire-concrete interface. The main bond material parameters are normal and shear elastic stiffness, initial adhesive strength, plastic slip at which adhesion first breaks completely, and coefficient of friction. Except for the coefficient of friction, which is determined with reference to the open literature, the bond parameters are calibrated from untensioned pullout tests and pretensioned prism tests conducted at KSU. The calibrated bond parameters exhibit a dependence on the nominal compressive strength of concrete at the time of pretension release. Because considerable concrete creeping has been observed in the periods between pretension release and concrete strain measurement in the test program, an additional concrete material parameter, basic creep compliance, can be calculated and applied to adjust the concrete surface strain data. The user bond model is then validated with transfer length data measured on actual concrete crossties made with a smooth prestressing wire in a tie manufacturing plant.

Reinforced concrete flat slabs are used worldwide as a construction system in many multistory buildings. The problem that can occur in flat slabs is high stresses in the slab-column connection area that can result in a punching shear failure. Nonlinear Finite Element analyses can be performed in order to investigate the phenomenon of punching shear and to gain information on slab behavior. In this paper, a 3-D analysis of the reinforced concrete slab with the finite element software ABAQUS using the damage-plasticity model is presented. The choice of the adequate material model is important in finite element modeling for concrete structures. The simulations of the reinforced concrete slab are compared to the behavior of a specimen that has been tested at the University of Waterloo. This study involves the investigation on the punching shear behavior of reinforced concrete slab-column connections without shear reinforcement. The results of the FEA simulations indicate the reasonable response when compared to the behavior of the test specimen. The simulations give information on the punching shear capacity and the crack pattern.

The purpose of the study presented in this paper is to compare the current ACI 318-11 strut-and-tie modeling procedure to the previous ACI 318-99 sectional approach for the design of deep beams. To accomplish this goal, the author compiled a database of 905 deep beam tests from the literature. Of these tests, 438 specimens were isolated based on available specimen details, configuration of the test, or both. The shear capacity of these specimens was calculated according to the ACI 318-99 (Section 11.8) and ACI 318-11 (Appendix A) provisions, and compared with their experimentally measured capacity. Based on this analysis, it was observed that capacities calculated with both provisions are statistically similar for the experimental data available; however, the average of the capacities calculated per the ACI 318-99 procedure is increasingly unconservative as the specimen's cross-sectional area increases. The implication of this finding is that use of the ACI 318-99 provisions to design a conventionally sized transfer girder may potentially result in an unsafe situation. The strut and tie modeling procedure did not exhibit this downward trend because the method is founded in first principles. Thus, structural engineers can be assured that their transfer girders will be conservatively designed when using the strut and tie modeling procedure.

Punching shear design is a topic of international interest because it is critical for reinforced concrete slab-column connections, based on the fact that this type of connection can fail in a brittle way and without warning. Punching shear strength depends on many variables which may have some degree of uncertainty due to geometry, material properties, manufacturing processes, etc. In this study, reliability analysis will be performed by applying Monte Carlo Simulation due to random input parameters for current design codes (ACI 318-11, EC2-2004) and for an analytical punching shear model, such as Critical Shear Crack Theory, which was incorporated in the new fib Model Code (2010), so as to be compared and useful conclusions to be derived. For sensitivity analysis, valuable results will be derived on how specific parameters influence the output response (i.e., punching shear resistance). The sensitivity analysis will show how the uncertainty associated with the model's input parameters impacts the resultant uncertainty of its output, and which input parameters affect (most and least) the punching shear strength. Moreover, simulation results will give us an idea on which parameters are most important and which are the consequences of changing these parameters, regarding the punching shear strength of a slab-column connection, so as to improve punching shear design.

In this paper, a 3-dimensional finite element model is built by the author to analyse the progressive collapse potentials of high-rise buildings. Two different assessment methods are used in the analysis. In the first study, the alternative load path method is used for analysis. The full 3-D behaviour of the multi-story building under sudden column removal was studied. Based on this model, a direct simulation method of blast loading is also developed to assess the behaviour of the building under blast loading. The comparison between the two numerical assessment methods is made. The pros and cons of these two methods are compared.

The catastrophic after-effects of the historical collapse events have received considerable attention from government agencies, research communities, and practical engineers on the aspect of the evaluation of the risk of progressive collapse of buildings. In the recent decade, numerous studies have been conducted to answer the question: Are the frail designed to fail? In this paper, the research outcomes from experimental and analytical studies are discussed in an attempt to answer the critical question above, which mostly concerns building owners or decision makers. The findings from previous studies indicate that the buildings - which had a regular layout, moderate span, and cast-in-place construction method - may have lower collapse risk. This is mainly due to the slab and infill walls providing additional stiffness and strength to resist sudden column removal. Moreover, considerable second load-carrying mechanisms - such as catenary action, arch action, and compressive or tensile membrane actions - could develop in beams or slabs, which further reduces the possibility of progressive collapse. Furthermore, the recent dynamic tests have revealed that the dynamic effects were not as large as the value proposed by provision of guidelines. However, structures with irregular layout, which is very popular in nonseismic zones such as Singapore or Hong Kong, may undergo a much higher likelihood of collapse. Moreover, the high vulnerability of newly designed precast structures with extreme large design span could not be ignored. It should be further emphasized that multi-hazards due to terrorist attack (which were ignored in existing design guidelines) may lead to the collapse of the buildings, bringing about tragic consequences.

To study the influence of slabs on the progressive collapse resistance of reinforced concrete (RC) frame structures, two 1:3-scaled substructures - S1 (with slab) and B1 (without slab) - were comprehensively tested. Both specimens had two spans, and each span had a length of 2 m. The width of the floor slab for S1 is 1 m for each side of the centerline frame beam. The two opposite sides of the specimens were completely fixed, and the remaining opposite sides were free. Two hydraulic jacks were applied at the top and bottom of the middle beam-column joint. At the beginning of the experiment, these two hydraulic jacks applied a pair of small balanced forces synchronously. Next, the bottom jack maintained the constant force and, at the same time, gradually increased the force of the top jack. Displacement controlled loading was used to simulate the failure of the middle column. By analyzing the loadcarrying capacities of S1 and B1, the influence of the slab on the progressive collapse resistance of the RC frame structures was discussed.

This paper assesses the structural robustness of older RC flat plate buildings against progressive collapse. A finite element macro model is employed to simulate the complex nonlinear response of slab-column connections and their punching failures. The model is applied first to a multi-story flat plate building to examine its potential of progressive collapse. An energy-based static pushdown approach is validated for estimating the peak dynamic response. Parametric studies are then carried out to investigate the effects of slab reinforcement ratio, slab thickness and concrete strength on the progressive collapse resistance of flat plates. The dynamic increase factors specified in the current design guideline are examined.

To efficiently improve the security of buildings against extreme accidents, the Architectural Society of China organized a special committee to compile the Design Specification for the Collapse Prevention of Buildings. Based on the corresponding research in China and the relative design codes in various countries, this specification recommends design and analysis methods for the prevention of earthquake-induced collapse, progressive collapse, fire-induced collapse, construction error-induced collapse and so on. This paper provides a brief summary of the framework of this specification and presents the main innovative work in it (for example: the improved tie force method, the progressive collapse resistance demand based on energy method, the earthquake-induced collapse resistance evaluation based on incremental dynamic analysis and the fire-induced collapse prevention design calculations).

Standard S850, published by the Canadian Standards Association and entitled Design and Assessment of Buildings Subjected to Blast Loads, is the only Canadian standard that contains explicit and detailed disproportionate collapse mitigation criteria for buildings. The standard is non-mandatory and may be invoked by a building owner to meet design objectives if blast loading is deemed to be a required consideration. While the scope of the standard encompasses design to limit damage under loads caused by an explosion, one component of the coverage is a set of provisions that aims to prevent the occurrence of post-blast disproportionate collapse. As a result, these provisions are not based on the so-called "threat independent" philosophy, as is typically the case for stand-alone disproportionate collapse guidelines; rather, the blast-damaged structure is assessed to determine how the building would be expected to be compromised, and this forms the basis for the initiation of the required disproportionate collapse analyses. The paper also provides a brief overview of some of the recent research developments in Canada related to designing to minimise the possibility of disproportionate collapse occurring in steel-framed buildings in the event of a column loss due to blast or another unanticipated localised trigger. Over 70 full-scale physical tests have been carried out on a variety of common types of shear connections, with or without the influence of a composite floor slab. In addition, high-fidelity finite element models have been developed that are able to simulate the behaviour of the tests accurately. Simplified methods are currently under development for characterising the essence of the behaviour of the various types of shear connections under this unique loading regime. These connection models will be appropriate for use in full-building analyses for disproportionate collapse assessments.

The main goal of this research is to better understand progressive collapse mechanisms of buildings, and to evaluate the current modeling and analysis techniques and design methodologies. Field experiments and numerical simulations were performed to investigate the progressive collapse potential of several reinforced concrete and steel frame buildings. Up to four first-story columns were physically removed from the buildings to understand the subsequent load redistribution within each building. Experimental data from the field tests were used to compare and verify the computational models and analysis results. Due to the scarcity of data from full-scale tests, the experimental data of this research is a valuable addition to the state of knowledge on progressive collapse of buildings. The design guidelines typically recommend simplified analysis procedures involving instantaneous removal of specified critical columns in a building. This research investigates the effectiveness of such commonly used progressive collapse evaluation and design methodologies through numerical simulation and experimental data.

Structural integrity can enhance the robustness and, in turn, progressive collapse resistance of structures. Design loads as well as seismic detailing affect a structure's ability to resist extreme loading. The lateral loads used in design for seismic ground motions and wind loads differ and vary throughout the US. Furthermore, different levels of seismic detailing can be used in structural design. We will evaluate the effects of seismic detailing and the ACI 318 structural integrity requirements on the progressive collapse resistance of reinforced concrete structures. The main objective of conducting analyses with various design characteristics is to show how structural design and detailing affect the behavior of beams bridging over damaged areas.

In this research, the progressive collapse behaviour of a shear connection of a composite beam has been investigated experimentally. Steel shear/simple connections are widely used in composite gravity framing systems and their behaviour under conventional loading is well understood. However, their response and robustness under the column removal scenario is still largely unknown. While the slab itself can participate in maintaining the integrity of the overall floor system, its presence also amplifies the demand on the steel connections after experiencing initial flexural action. As the column pulls down progressively, which results in a large vertical deflection, the shear connection reaches its capacity under tension-dominant action. The contribution of the concrete slab to the steel connection demands plays an important role in determining the failure mode, load carrying capacity, and ductility of the connections. The main objective of the experimental program is to study the behaviour of steel shear connections in the presence of a concrete slab under a column removal scenario. The test results show the performance of the connection in terms of rotational ductility and ultimate load capacity.

The overall goal of this research is to evaluate the potential of disproportionate collapse in older, reinforced concrete, flat plate buildings subjected to the loss of a supporting column. The research program considers testing of isolated slab-column connections that represent the connection near the lost supporting column. The goal of the tests is to evaluate the effects of in-plane lateral restraint and post-punching capacity. The experiments provide critical data for validating the mechanical model of slab-column connections used to examine the disproportionate collapse resistance of the flat plate system. Five tests of restrained and unrestrained isolated slab column tests have been conducted at reinforcement ratios of 1.0% and 0.67%. The tests show that there is a marginal increase in punching shear capacity (2 to15%) due to the in-plane restraint, but is highly dependent in the level of lateral restraint. The tests also show that there can be significant post-punching capacity if the top bars are well anchored into the slab.

Lessons learned from designing against disproportionate collapse relevant to an international audience are discussed. Two structurally dissimilar buildings, designed against sudden column loss using two different methods of nonlinear alternate progressive collapse analysis, are selected for discussion. The first - a commercial, medium-rise office building with steel-braced frame and reinforced concrete cores - was designed using nonlinear static (pushover) methods with dynamic energy balance, and used simple (non-moment resisting) connections in the design. Such a structural arrangement is typical of non-seismic areas and is recognized as typically presenting challenges when designing against sudden column loss. The use of an energy-based approach permitted the fundamental behavior to be explored efficiently and different mechanisms of resistance in resisting the removal of corner, penultimate and typical perimeter columns to be studied in detail. The second structure, a seismically-designed transit center in California, is comprised of a steel superstructure (above grade) with a heavy park at the roof level and a reinforced concrete three-story substructure. Detailed nonlinear dynamic time history analysis in LS-DYNA was undertaken to assess resistance to sudden column loss. The model accounts for material and geometric nonlinearities and the inertial effects following column loss. Structural framing members were modeled using fiber elements in LS-DYNA. Material models were selected to model the concrete fibers to account for concrete cracking in tension, crushing in compression, post-peak strain softening, and strain rate effects. Element-level acceptance criteria in UFC 4-023-03 were translated to material-level failure criteria and incorporated into the analysis. The design of secondary beams and placement of slab reinforcement were shown in both structures to be critical to resisting collapse through the development of compressive arching and membrane action. Composite action of the slabs with the secondary beams was shown to play an important role in developing resistance against collapse and heavily influenced the demands on connections. The ductility of the connections in the moment-resisting frame influenced the ability to develop plastic hinges, but the selection and design of ductile shear connections in the steel braced frame was key to providing resistance against collapse. Catenary action, commonly held to be the principal mechanism of resistance, was found to be of limited significance.

An ongoing collaborative research project is studying the structural integrity of steel gravity framing systems composed of steel beams and girders with composite slab on metal deck. Experimental data has already been obtained at the component level for the behavior of the gravity connections and the composite slab during loading consistent with column removal. Half-scale floor system tests that include interior, exterior, and corner column loss scenarios are presently being conducted. These combined experimental data are now being used to evaluate the assumptions made in the various modeling approaches to simulate column removal in steel gravity frames. Subassembly models have been created to validate against the component level tests, and the lessons learned are being extended to system level modeling. Suggestions for further model refinement are made.

Large-scale floor system tests concluded a collaborative research project that studied the structural integrity of steel gravity framing systems composed of steel beams and girders with composite concrete slab on steel deck. Simple steel beam-column connection tests were conducted at the University of Washington, steel-concrete composite slab tests were conducted at Purdue University, and complete floor system tests were conducted at the University of Illinois at Urbana-Champaign. The complete floor system tests evaluate gravity systems subjected to severe demands consistent with column loss scenarios, complementing the previously-completed component tests. The floor system tests were conducted at half-scale on a three-bay square configuration that considers interior, exterior and corner column loss scenarios. The three-bay by three-bay configuration was chosen so that multiple tests could be conducted using one structure. For each test, the bays adjacent to the removed column were incrementally loaded with distributed load until the floor could not support more load. These experiments provide valuable data to validate existing numerical models, to identify critical limit states, and to determine system capacities under various column loss scenarios.

A computational assessment of the robustness of reinforced concrete (RC) building structures under column loss scenarios is presented. A reduced-order modeling approach is presented for three-dimensional RC framing systems, including the floor slab, and comparisons with high-fidelity finite element model results are presented to verify the approach. Pushdown analyses of prototype buildings under column loss scenarios are performed using reduced numerical models, and an energy-based procedure is employed to account for the dynamic effects associated with sudden column loss. The load-displacement curve obtained using the energy-based approach is found to be in good agreement with results from direct dynamic analysis of sudden column loss. A metric for structural robustness is defined by normalizing the ultimate capacity under sudden column loss by the applicable service-level gravity loading. The procedure is applied to two prototype, 10-story RC buildings, one employing intermediate moment frames (IMFs) and the other employing special moment frames (SMFs). The SMF building, with its more stringent seismic design and detailing, is found to have greater robustness.

This paper presents the results of an experimental study that was conducted to investigate the effects of key parameters on the compressive behavior of fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (FSDT). Hybrid FSDT columns have been introduced as a new form of hybrid columns. They consist of an outer tube made of FRP and inner tub made of steel, with sandwiched concrete between them. This paper investigated the effect of fiber angle and the ratio of steel tube diameter to its thickness (D_i/t_s) on the compressive behavior of FSDT columns. Six FSDT cylinders with different (D_i/t_s), in addition to two concrete filled-fiber tuber (CFFT) cylinders, were manufactured and tested under axial cyclic compression. The results of the experimental study indicate that the overall behavior of FSDT and CFFT is similar and the main difference is in the capacity load. Thecylinders with high D/t ratio achieve lower capacity than the normal capacity due to the local buckling of the steel tubes. Using the saturated fiber tube increases the axial ductility but does not give high confinement. These results are presented together with a discussion on the influence of the studied parameters on the compressive behavior of FSDTs.

Reinforced concrete (RC) highway bridges are subjected to deteriorating mechanisms during their life-cycle. These mechanisms have adverse effects on the durability of bridges and can potentially make them vulnerable in terms of serviceability and ultimate limit states. Corrosion-induced deterioration can be identified in several forms, such as mass and strength loss of rebars, cracking and spalling of the concrete cover, and loss of bond between the concrete and steel. The structural degradation must be evaluated on a regular basis to determine the available structural capacity and schedule the required preventive actions. The current paper studies the extent and likelihood of deterioration of RC bridges located in chloride-contaminated environments and investigates the effects of chloride-induced corrosion on the life-time performance of the aging bridges. In this study, the corrosion initiation time is calculated through a detailed computational model considering the most influential parameters, including ambient temperature, relative humidity, chloride binding capacity, and exposure conditions. Also, a detailed mechanical model is provided to consider the effects of corrosion on decreasing the cross-sectional area of steel, yield strength of steel and the loss of the concrete cover.

The goal of this research is to add to the knowledge base of bamboo-reinforced concrete (BRC) by focusing on a unique stirrup design and testing the lap-splicing of flexural reinforcement. Preliminary tests of the mechanical properties of bamboo were performed, and the results have been used in the design and construction of bamboo cages to reinforce concrete beams. This paper presents the preliminary results of tensile tests and pull-out tests on Moso (Phyllostachys edulis) bamboo. The test results show that bamboo is a viable alternative to steel as tensile reinforcement for concrete structures. As part of the on-going research, 14 Moso bamboo (Phyllostachys edulis) reinforced concrete beams will be cast and tested under monotonic gravity loading in early 2014 to assess the performance of bamboo as flexural reinforcement, shear reinforcement and lap-splicing.

An analysis approach to simulate the staged failure mechanism of corrosion-affected beam-column subjected to ultimate or seismic load using a simplified, non-linear, finite element model is proposed. The instantaneous axial and flexural rigidities at the sectional level are transferred to the element level, establishing the instantaneous structure stiffness at each load step. The approach efficiency and accuracy are verified through comparison with available experimental and analytical results. The proposed approach is numerically stable in all studied cases. It is found that the staged failure mechanism of the columns subjected to quasi-static load and cyclic load up to failure can be simulated with high accuracy. It is also found that corrosion-induced damage results in a large drop of the column load and displacement capacities, and a large shrinkage in the hysteretic relationship, which indicates similar drop in the energy absorption capacities of the beam-columns.

Concrete is the most synthetic material in the world and the most usable in the construction industry. Improving the problem of cracks and increasing tensile strength of concrete while maintaining its ductility in tension has always been essential. Since the discovery of carbon nanotubes/fibers in 1992 and recent advances in materials science, they are considered efficient fibers to be used in construction materials such as concrete. Previous experimental work has shown that incorporation of CNF in cementitious composites can enhance the mechanical behaviour of material by reducing the size of macro- and microcracks to nano-sized cracks, resulting in higher strength and ductility. Electrical properties of CNF give unique properties to concrete, which makes this fiber more beneficial compared to other fibers. Carbon nanofiber is a highly conductive electrical material which makes concrete highly conductive as well. In addition, due to tunnel conductivity effect, CNF concrete exhibits properties necessary for self-sensing ability. The electrical properties required for strain monitoring and damage evaluation of concrete is improved by CNF fibers. To date, exploitation of nanotechnology in concrete on a commercial scale remains limited with few results. This study aims to expand upon the use of such fibers in structural members. A general finite element model is developed to simulate structural members with CNF concrete. The model is based on fiber beam element formulation and accounts for the inelastic flexural and shear behavior of members. The FE model is validated against experimental results and the structural performance of CNF-reinforced concrete members is then evaluated. A comparison between members with CNF concrete against conventional concrete is made from the structural performance point of view. Results and discussion about the potential benefits of CNF concrete in structural applications are then presented.

This paper presents a methodology to simulate multi-dimensional non-Gaussian random fields and uses this to model, in a probabilistic sense, the spatial distribution of corrosion in a steel beam. In particular, the proposed approach is an extension of a recently developed iterative technique that generates one-dimensional, uni-variate sample functions of non-Gaussian random fields and processes. The contribution of this work is the extension to the case of multi-dimensional random functions and its application to a steel cantilever beam with simulation of corrosion penetration. The amount of corrosion is modeled as a random field and applied to a finite element mesh on the top flange. The field matches both the arbitrarily prescribed spectral density function and the non-Gaussian marginal distribution. The effect of the spatial variability of the corrosion on the flange is evaluated using the tip displacement as representative structural response metric, while a series of finite element analyses are performed for a Monte Carlo simulation. The results show that the spatial variability has a substantial effect on the structural response and an equivalent deterministic model with the same average corrosion uniformly distributed would not capture properly the structural behavior.

Computing is much more than a skill to be learned. It is an engineering science as well as a basic science. Many fundamentals of this basic science are relevant to engineers. This paper describes a course that describes important aspects to engineering undergraduates. Through more than ten years of experience, the course has been incrementally improved and materials are available for free by downloading from an ASCE website.

Technical mastery is only one condition for successful construction projects. Management skills should be considered as equally important. Architects and engineers are the backbone of project teams. When this team fails to work effectively together, project success is put at risk. Teaching and training of team and management skills in engineering and architectural education contributes to minimize this risk. It creates dynamics which will facilitate the application of innovative construction materials and methods for the benefit of the project. Introduction of those "soft skills" through an integrated teaching approach will foster joined up thinking and prepare students to deliver high quality projects during their professional career.

In the field of structural engineering, the ability of educators relate complex 3D spatial arrangements, such as connection detailing and lateral torsional buckling, has been limited to 2D drawings or physical models. Immersing students in a 3D virtual reality environment offers a promising and engaging means for effectively conveying complex ideas about structural connections and member response. With this purpose in mind, a fully immersive virtual reality environment has been developed to allow users to interact with a structure through a headmounted device and hand console. The system can also be deployed and used on any computer screen if a complete immersion environment is unavailable. The models can be conveniently modified, updated, and expanded, unlike a physical model which would be limited by cost and safety concerns.

More than ever, building information modeling (BIM) is being adopted by the A/E/C industry for the many benefits it provides in the management and execution of complex building projects. The University of Delaware, Department of Civil and Environmental Engineering, was encouraged by alums working in the field - consulting engineers, and project engineers with large construction companies - to provide our students with some exposure to BIM. To that end, the department created and offered, for the first time, a senior technical elective in BIM in the spring of 2013. The course was created to provide a basic introduction to the theory and application of BIM and to expose them to the key software platforms in use today. The course was deemed to be a real success from the perspectives of both the instructors and the students. The course will be offered for a second time in the spring of 2014. This paper provides an overview of the course, including the course goals, organization, student feedback, and lessons learned.

Pedagogical Content Knowledge (PCK) is the development of better understanding of the misconceptions that people hold that often confuse a person's deeper understanding of a concept. In earthquake engineering, these misconceptions can result in engineers making poor choices in their engineering decisions due to unclear application of code requirements, physical phenomena, and mathematical reasoning. While PDK has been established over several years for K-12 education, its' application to higher education and professional development is still under development. This paper looks at misconceptions held by college engineering undergraduate and graduate students while learning basic concepts of earthquake engineering. Many of the misconceptions likely apply to professional engineers, especially those not closely involved in earthquake engineering research and code development. Currently, the state of PDK development is at the preliminary stage, that of defining likely misconceptions and developing suitable instruments to monitor understanding. These preliminary steps will lead to better assessment of student capabilities and improved instructional strategies to help remove misconceptions and allow better conceptual understanding. This paper addresses issues related to engineering faculty teaching both higher education and professional development workshops. The audience will learn basic concepts of PDK, insights into struggles engineering students have with earthquake engineering concepts, and methods of monitoring student progress.

The authors discuss some of the challenges encountered in educating the millennial generation of civil engineers. This generation, born during the 1990's, may be characterized by their exposure to smart devices and computers connected to the Internet starting from their toddler years. They have developed a natural affinity and curiosity to take advantage of the computers for play and entertainment, reading, studying, and especially communicating. Meanwhile, most millennial students are proving to be less interested or uninterested in classical math and mechanics, group-thinking and group-studying, and in anything that involves non-virtual media. Alongside their special skills of naturally interfacing with software that promises instant digital and virtual rewards, there are justified concerns in educating this generation due to their general lack of interest in a physical, conceptual grasping of the real world. Without an interest in observation and exploration outside the virtual world, this generation also appears to trust what the virtual world presents to them. These challenges add to the difficulties of the civil engineering profession and education that are among the slowest in introducing technology and innovation.

Teaching engineering was identified as an area in need of improvement in many countries including the USA. While a typical course of structural engineering study focuses mostly on the engineering calculations, the great structures of our society come to existence not only by calculations, but also by (1) knowing and working with the related economic and political circumstances, (2) developing an appropriate and economical construction process, and (3) considering the environmental impacts of such a construction. However, modern educational systems often ignore these additional dimensions of engineering and, as a result, graduate structural engineers have a very narrow vision of their profession. At Princeton University, a new studio course was taught which explores these dimensions through multiple activities. This paper explores and presents an innovative approach for teaching successful engineering design and construction approaches, and discusses its impact to students and potential impacts to society in general.

The occurrence of fires following an earthquake in steel structures is an important scenario that can threaten the integrity of structural systems. Structural loss due to such combined events has been observed and reported. Despite such evidence, minimal studies have been conducted on the combined effects of the hazards on steel structures or any type of structures for that matter. The aim of this paper is to provide insight into the local behavior of reduced beam section connections during fire following earthquakes when representative time-dependent boundary conditions are utilized to simulate the restraint provided by the surrounding frame during the fire. This is achieved through investigating the response of two beam-column subassemblies designed for the Los Angeles region using 3D nonlinear finite element analyses. The models are developed and analyzed under several representative loading scenarios with continuously updated boundary conditions that characterize the nonlinear stiffness of the remainder of the frame. The results are presented and their implications discussed to protect against the hazard of fire following earthquakes in steel moment frames with reduced beam sections.

Multi-hazards, such as earthquake and/or impact followed by fire, represent major challenges for fire protection of steel structures. Spray-applied, fire-resistive material (SFRM) is one of the most widely used passive fire protection materials in North America. However, SFRM is inherently brittle and tends to dislodge or delaminate under extreme loading conditions (earthquakes or impacts) and even under normal service conditions such as wind-induced building movement. Such loss of fire protection material puts a steel structure in great danger under fire loading. As an alternative to conventional brittle cementitious materials, engineered cementitious composites (ECC) is a family of high-performance, fiber-reinforced, cementitious composites. ECC typically exhibits strain-hardening behavior with very high tensile ductility (3-5%) under static and high rate loading. In this paper, a new type of fire-resistive material that combines the desirable thermal insulation property of SFRM and the enhanced ductility of ECC is proposed as an alternative material to current SFRM. Two preliminary mixture designs are presented. The thermal conductivity of the new fire-resistive ECC is measured in accordance with ASTM E2584 and is shown to be similar or lower than a conventional SFRM within the same density range. The proposed material achieves tensile strength up to 3 MPa and tensile strain capacity as high as 2.9%, significantly higher than those of conventional SFRM. Fire-resistive ECC with enhanced mechanical performance is expected to improve the overall fire safety of steel structure under multi-hazards.

This paper discusses the through-thickness thermal behavior of two full-scale reinforced concrete (RC) bearing wall test specimens subjected to one-sided fire. The most probable fire exposure for RC wall structures is from one side of the wall only (i.e., compartment-type fire). This fire scenario causes steep thermal gradients through the wall thickness, leading to unsymmetrical fire damage and material degradation that can exacerbate out-of-plane eccentricity effects and compromise stability under service-level tributary gravity loads. A crucial step for the development of validated analytical tools to predict the structural fire behavior of RC walls is the ability to predict the through-thickness thermal gradients. With this objective, the measured thermocouple data from the test specimens is compared with 2D analytical predictions from two simulation software. The results generally show good predictions of the measured temperatures, with the largest discrepancies (in terms of percent error) near the unheated (i.e., back) face of each wall.

This paper presents the results of a full-scale experimental test on a composite floor beam designed according to American codes and standards that was subjected to elevated temperatures. The test focused on the fundamental behavior and mechanics of a composite beam with end shear connections that was subjected to combined gravity loads and thermal loading, simulating realistic fire effects that included both heating and cooling. The test was conducted on a 3.80-m-long composite beam that consisted of a steel beam that was composite with a flat, lightweight concrete slab through the use of shear studs. The beam was connected to a portal frame using shear tab connections. High-temperature, ceramic, radiant heaters with independent temperature control were used to heat the steel and concrete portions of the specimen. Results from the experimental test provide insight to the behavior of composite beams and the beam-to-column connections at elevated temperatures. The composite beam and connection survived heating to 600° C, but the shear tab connection fractured during cooling.

With the 2011 edition of ASTM standard E119 "Standard Test Methods for Fire Tests of Building Construction and Materials", a new standardized test type was adopted - "tests of loaded unrestrained beams supporting floors and roofs". At about the same time, a similar new test for loaded unrestrained beams was introduced into the 14th edition of ANSI/UL 263 standard "Fire Tests of Building Construction and Materials". The adoption of the new beam test marks the most significant development in over 40 years in standardized fire resistance testing in the United States. The authors review the historical background and evolution of fire resistance tests for beams, floors and roofs, and discuss the motivating reasons for the adoption of the new beam test. The distinctive features and parameters of the new test are described in comparison with the older methods. The potential applications of the new test method are also discussed.

Tuned Liquid Dampers (TLDs) are dynamic vibration absorbers used in suppressing the structural vibrations due to wind and seismic loads. They dissipate energy through liquid boundary layer friction, the free surface contamination, and wave breaking. In general, these devices could be designed and implemented easily with a low cost and they need low maintenance. In this study, instead of designing a single TLD tuned to the first mode of vibration of the structure, multiple TLDs are designed to increase the effectiveness of the control of vibrations. To shed light on the multiple TLD-structure interactions, an analytical solution and numerical simulations of multiple TLD - structure systems will be presented.

Real-time hybrid simulation (RTHS) has emerged as a feasible and economical means for seismic performance assessment of structural systems. It has been successfully applied to study the system-level response, combining experimental and computational substructures. However, existing substructure techniques are limited to interface boundaries where the influence of unbalanced forces are not significant. Because existing formulation procedures and experimental loading are both displacement-based, unbalanced forces are inevitable in conventional RTHS. In some cases (e.g., testing of extremely rigid specimens, soil-structure boundaries), force equilibrium becomes more critical than displacement compatibility. To accommodate such conditions, a force-based approach is essential and has to be developed in RTHS. This study presents substructure shake table testing as a case study of force-based RTHS. A four-story shear structure is divided into two substructures. The first story is tested on a shake table while the rest of the structure is computationally simulated. The interaction between the experimental and computational substructures is addressed such that the measured acceleration at the top floor in the experimental substructure is used as the base input to the computational structure while computed base shear in the computational substructure is fed back to the experimental substructure through a force-controlled actuator. As such, the overall simulation is performed at real-time with force-controlled actuators. This study presents the underlying theories of the substructure shake table test method, centralized actuator control and preliminary numerical simulations.

The resetting semi-active stiffness damper (RSASD) has proven effective in reducing the seismic response of structures. However, it relies on a multi-component feedback control system that is subject to reliability issues. Recently, research was conducted to replace components of the system with a mechanism that enables a similar control performance. The resulting resetting semi-passive stiffness damper (RSPSD) offers increased reliability without compromising effectiveness. To date, a model of the RSPSD has been developed and simulations have been conducted to evaluate its control performance. It was found that implementing the resetting control law in a numerical environment is complicated by building drift displacements that are characterized by local peaks. The present work details the development of the control logic that is required for simulating resetting of the RSPSD control force. It is demonstrated through numerical simulations of two single-story buildings equipped with the RSPSD and subject to a sinusoidal excitation.

Conventional concentrically braced frame (CBF) systems are commonly used in earthquake-resistant structural systems. However, they have limited drift capacity before brace buckling occurs. Self-centering, concentrically-braced frame (SC-CBF) systems have recently been developed to increase drift capacity prior to initiation of damage and to minimize residual drift. SC-CBFs have more complex behavior than conventional CBFs. The seismic response of SC-CBFs depends on many new parameters such as rocking behavior, post-tensioning bars, and energy dissipation elements. Additionally, uncertainty of mechanical properties (e.g., coefficient of friction in the friction-bearings) can affect the system response. To design SC-CBF systems, an accurate prediction of the statistical parameters of roof drift demand is essential. In this study, genetic programming is used to predict the mean and standard deviation of SC-CBF peak roof drift response under the design basis earthquake using the most effective mechanical and geometric parameters. The results of this study can then be used in the future to design more efficient SC-CBF systems with a more accurate roof drift prediction.

The second glued-laminated structure built in the United States was constructed at the USDA Forest Products Laboratory (FPL) in 1934 to demonstrate the performance of wooden arch buildings. After 75 years of use, the structure was decommissioned in 2010. Shortly after construction, researchers structurally evaluated the glued-laminated arch structure for uniform loading on the center arch. This structural system evaluation was added to the existing laboratory work on glued-laminated arches to develop the foundation on which the current glued-laminated arch design criteria is based. After 75 years of service and decommisioning, recovered arches were tested in the laboratory to evaluate the loss of structural performance. Loss of structural performance was evaluated by comparing original and current deformation. Based on a preliminary visual and structural assessment, the degradation of structural performance was minimal in the arches, except for two arches that were affected by the building fire.

The Hamptons at MetroWest, a wood-framed condominium complex located in Orlando, Florida, suffered extensive, long-term, large-scale, structural rot damage. Defective construction and installation of windows, weather protection systems (such as roof flashing), and the exterior wall stucco contributed long-term water intrusion flows into the building envelope and into wood-framed wall and roof cavities, causing extensive rot damage to the buildings' structural wood framing. This paper discusses the forensic investigation undertaken, the rot damage discovered, the temporary emergency shoring and patch repairs needed, and the large-scale repairs undertaken to save the project This topic would be of relevance in areas of the country where wood construction is used, and particularly those areas that receive a substantial amount of weather precipitation. The target audience would be primarily structural engineers who may come across similarly damaged existing buildings. It plays well upon a theme that existing buildings can be saved, rather than torn down and built anew. The investigative portion of the presentation shows that even when confronted with extensive damage, a thorough forensic investigation can identify the extent of damage and mitigate the potential for future rot. Attendees would be able to see the potential of forensic investigations of existing buildings in saving existing buildings. Whereas most of an engineer's training is focused on the design of new structures, this presentation provides an alternative path where existing structures are evaluated, repaired and saved, rather than torn down in a waste of natural and economic resources.

Tall buildings pose a challenge to the sustainability movement because they offer both positive and negative environmental impacts. Positive impacts include reducing urban sprawl, promoting alternative transportation, and allowing efficient energy use on a district scale. However, these benefits come with the cost of greater carbon emissions associated with both material production and building construction compared to a low-rise building. The goal of this research was to develop a structural system for tall buildings using mass-timber as the main structural material that reduces the carbon dioxide emissions associated with the structure. The structural system research was applied to a prototypical building based on an existing concrete benchmark for comparison. The selected concrete benchmark building is the Dewitt-Chestnut Apartments; a 120 m-tall, 42-story building in Chicago designed by Skidmore Owings and Merrill and built in 1966. This building was chosen as the benchmark because the geometry is a rectangular extrusion, the lease depths are consistent with contemporary residential buildings, and the concrete structural system is efficient in material usage providing a lower bound for comparison with the prototypical building. This paper discusses key design issues associated with tall mass-timber buildings along with potential solutions. Specific challenges include low structural weight and associated net uplift due to lateral loads, long-term differential shortening, floor vibrations, and fire performance. It is believed that the system proposed in the research and discussed in the paper could mitigate many of these design issues. The proposed system, the "Concrete Jointed Timber Frame", relies primarily on solid mass-timber for the main structural elements such as the floor panels, shear walls, and columns. The main structural mass-timber elements are connected by steel reinforcing through cast-in-place concrete at the connection joints. This system plays to the strengths of both materials and allows the designer to apply sound tall building engineering fundamentals. The result is believed to be an efficient structure that could compete with reinforced concrete and structural steel while reducing the associated carbon emissions by 60 to 75%.

In February, 2008, a 3-pound, pyramid-shaped piece of millwork fell from the ornate wood ceiling of Holy Name Cathedral (Holy Name) in Chicago, Illinois. The affected piece of millwork was originally located at the peak of the ceiling at the nave and transept intersection. Initial investigation of the fallen millwork indicated that movements (deflections) of the ceiling resulted in separations at the peak of the ceiling, which caused the millwork to become dislodged and fall. Further inspection of the ceiling revealed that the ceiling and roof were visibly deflected in the area where the nave and transept intersect. These observations led to a structural analysis of the roof trusses, which revealed that the calculated forces for the sloping tension bottom chord members of the scissors trusses were significantly greater than the published capacity of its 3/4-in. diameter, single bolt connections between the top chords and bottom chords. To address the observed roof deflections, and calculated overstresses, steel tension ties (rods) were recommended for the roof trusses.

As part of the renovation and expansion of a private residence in northern California, a new 3,600-square-foot, outdoor, open trellis was designed to provide shading and architectural unity to several building volumes. The trellis structure consists of a grid of aluminum plate joists and girders supported on solid aluminum extrusion cantilever columns. Curved, glue-laminated, timber struts of Port Orford cedar laminations span between adjacent aluminum joists to provide lateral bracing to the thin joists and create discrete diaphragm elements for lateral load distribution. Parametric design criteria were established for the curved glulam geometry including structural, architectural, and fabrication-related considerations. These criteria were used throughout the iterative design and fabrication process to rationalize the complex shapes and develop a structure that showcases the geometrical capabilities of glue-laminated timber.

Recent extreme weather events - such as Hurricanes Sandy and Irene and the winter storm, Nemo - have created a keen focus on the link between climate and the resiliency of both the built and natural worlds. This is particularly true for the water/wastewater sector which is impacted on several fronts, including hydrology, supply, demand, water quality issues and supporting infrastructure. The resulting damage incurred by these extreme events often creates an urgency to build against future impacts. However, jumping to adaptation solutions without fully understanding the most critical elements can result in the expenditure of limited funds on less pressing needs. This paper will review lessons learned from recent events and direct project experience to outline an approach to develop meaningful and implementable preparedness plans. Climate Change projects consist of three basic components: (1) climate change projections; (2) vulnerability assessment; and (3) preparedness planning. The vulnerability assessment is crucial to prioritize actions because of the limited funding that will be available to prepare for climate change impacts. This paper will focus on two important aspects of climate change impacts with implications to the water/wastewater infrastructure sector - translating climate change impacts into implementable design criteria and (2) developing a holistic water model that considers combined impacts of coastal, surface water and piped infrastructure flooding. The vulnerability assessment identifies the most at-risk elements which will be the focus of the adaptation plan. The feasibility of each adaptation plan should be judged using a combination of criteria including engineering feasibility, regulatory constraints, economic impacts and synergy with other initiatives

During the 2011 Mineral, Virginia earthquake, the Smithsonian Institute Museum Support Center (MSC) sustained considerable structural damage. An in-depth study was conducted to investigate the behavior of MSC during this earthquake and its potential implication on seismic risk of East Coast U.S. structures. The damage sustained by this building is documented and it is observed that the severity of damage is not uniformly distributed in the floor plan. A finite element model is created to perform the seismic response prediction using recorded ground motions in order to explain the cause of structural damage. A field vibration test was conducted to capture the dynamic characteristics of the building which are in turn used to calibrate the finite element model. Results from seismic analysis reveal that the main reason for seismic damage is local soil amplification and combined torsional and translational effects due to an eccentric floor mass distribution relative to the center of rigidity (CR) of the floor plan.

Stabilized earth masonry, which is made of compressed and stabilized earth blocks (CSEBs) and stabilized earth mortar, is emerging as a construction material that pairs sustainability with durability, energy efficiency, and extreme affordability. The appeal of CSEB masonry has prompted its use in numerous applications in developed countries ranging from modest to high-end houses. The availability and affordability of suitable soils in the US make CSEB masonry attractive also for high-quality dwellings in rural areas and farm lands where building with local materials becomes key to contain costs, reduce homelessness and create jobs. By engineering blocks and mortar combinations that maximize strength and deformability, it may also be possible to create dwelling structures that are capable of resisting extreme loads from natural hazards such as high winds and earthquakes. Prompted by the 2013 tragic events in Oklahoma and Illinois, this paper presents a proof-of-concept for the use of a prototype CSEB masonry in low-rise dwelling structures that can offer a safe shelter under extreme tornado winds. First, the prototype CSEB masonry, which is made with a widely available soil type in the US, and its salient mechanical properties are introduced. Second, the proof-of-concept is presented based on an analytical study aimed at understanding to what extent the prototype masonry is suitable for tornado-resistant dwelling structures. It is concluded that it is feasible to design one-story dwellings to resist severe tornado loads using the prototype CSEB masonry.

This work presents an investigation of the effects of tsunamis on bridge superstructures, with specific attention focused toward the differences between two-dimensional (2D) and three-dimensional (3D) analyses. For the most part, available research on tsunami-bridge interaction is based on 2D analysis. While 2D analyses can provide estimates of drag force, uplift, and overturning moment per unit length, they do not account for critical 3D phenomena such as channelization effects due to local bathymetry, bridge skew and other non-uniform geometric aspects. Using a high-fidelity, 3D, computational fluid dynamics approach, validated against existing experimental data, this work analyzes the temporal and spatial dynamics of tsunami loading on a model bridge and shows how variation in the local geometry - specifically, the skew angle of the bridge relative to the incoming wave - can affect the loading history on the structure.

The FEMA-developed Hazus-MH program was implemented in this study to estimate regional combined hurricane wind and wind-induced coastal flood losses using an ensemble of selected hazard-consistent hurricane scenarios. The hurricane scenarios were selected using site-specific mean return interval (MRI) contour plots considering the joint occurrence of hurricane wind and flood. The effectiveness of hurricane wind and flood mitigation strategies was also evaluated. The loss estimation results from Hazus-MH were discussed and compared between the cases with and without mitigation measures. It is shown that the combined effects of hurricane wind and flood should be properly addressed in order to correctly estimate hurricane losses. The wind mitigation measure is found to be more effective than the flood mitigation measure for a specific site under a given hazard level.

Reliability-based design of infrastructure requires the probabilistic assessment of jointly occurring natural hazards. For example, wind and temperature are hazards whose properties are of interest for design of transmission lines and energy infrastructure for both temperature extremes as well as offshore and enclosed structures. Increasing temperatures across the globe likely will increase the frequency of high temperature loading conditions and subsequently decrease low temperature conditions for infrastructure. A shift in location of areas of specific temperature loading conditions is also possible. In addition to infrastructure, the joint wind and temperature hazard can present problems for air quality, urban environment issues (e.g., urban heat wave and wind flows), energy demand and human comfort levels. High temperatures combined with high winds can become a significant hazard for wildland-urban interface (WUI) fires which also pose a significant threat to infrastructure and human life. In this paper, observed wind and temperature data are analyzed for locations in the Northern Plains and Southern California. These areas may be subject to more frequent wind, icing, and wind-driven wildfire events than most areas in the United States.

On May 3, 1999, an F5 tornado struck Moore, Oklahoma causing loss of life and destruction of property. On May 8, 2003, an F4 tornado struck Moore, Oklahoma. On May 20, 2013, Moore was struck by an EF-5 tornado with a similar path to the 1999 and 2003 twisters. This paper will compare our observations of damage caused by the 2013 tornado event to the damage documented by available sources during the 1999 and 2003 outbreaks. This paper will also review the history of the local building codes and ordinances and discuss their impact on the damage observed. The scope will include a summary of case studies of detailed damage evaluations in which construction defects and code variations may have contributed to the observed damage.

A precedent has been set by historical and recent hurricane hazard events that illustrates the importance of building more resilient coastal communities. Community resilience is dependent on the socioeconomic response after a hazard event; however, it is also heavily dependent on the vulnerability of the community to disaster. Therefore, it is beneficial to think of community resiliency in terms of mitigating the initial shock experienced by a community subjected to a hurricane hazard event so that it does not become a disaster event. The intent of this research is to determine the influence of community-wide disaster mitigation retrofits on community resilience and to identify the percentage of homes within a community that must be retrofitted against hurricane wind hazards to maintain the integrity of the community when subjected to a hurricane event. The results from this research have the capability to provide insurance companies with the information necessary to better set premiums within hurricane-prone coastal regions and provide homeowners with the incentive for individual members to work together towards a more disaster-resilient community.

Steel-plated composite (SC) concrete walls, which consist of a poured concrete core between two studded steel plates, have been utilized in many applications in lieu of conventional reinforced concrete (RC) walls. For this type of wall, the steel reinforcing plates serve as formwork, which allows for modularization of the design and correspondingly accelerated construction. Recently, both overseas and domestic nuclear power plant (NPP) projects have incorporated SC walls into their designs. When installed in nuclear plant facilities, such walls may be required to resist the effects of extreme loadings such as tornado missile and aircraft impact. The analysis of the structural response of conventional RC walls to such extreme loadings is well understood and is amenable to a simplified and well known inelastic single-degree-of-freedom (SDOF) approach which treats the wall as an effective mass with an easily defined inelastic spring. The purpose of this investigation is to study the SC wall load deformation behavior or resistance function, under missile impact, for input to an SDOF model. Based on pseudo-static nonlinear finite element analyses, the SC wall load deformation behavior under a central concentrated load is investigated for some typical wall panel configurations. System parameters are varied to assess their effects on the resistance function.

Storm surge vulnerability functions have found widespread use in describing, assessing and modeling damage to buildings and their contents in the built environment from hurricane storm surge. Although several models with different levels of complexity are used to quantify the hazard component of storm surge, the fundamental link between the hazard and the associated loss to the built environment is not well addressed. Exacerbating this situation is the lack of granularity of the vulnerability functions currently being used in risk assessment. The aim of the present study is two-fold. Firstly, it is to summarize the state-of-the-art in the field of hurricane storm surge damage estimation by drawing on existing literature, empirical field damage surveys and reconnaissance reports from past hurricanes in the United States. The underlying assumptions and limitations associated with the existing vulnerability functions provided by United States Army Corps of Engineers (USACE) and currently employed in the risk assessment package, Hazards United States (HAZUS-MH) are identified. Some of these include the lack of differentiated vulnerability functions by building attributes such as year of construction, foundation type and first floor elevation. Secondly, insights are provided on the betterment of the approach involving damage and loss estimation in the perspective of Catastrophe (CAT) modeling.

This paper presents a study to assess the impact of possible future climate change on the joint hurricane wind and rain hazard along the US eastern coastline. To characterize the hurricane wind hazard, climate change scenarios were coupled with state-of-the-art hurricane genesis, wind field, and tracking models to examine possible changes in hurricane intensity (maximum wind speed) and hurricane size (radius to maximum winds). A postulated climate change model (IPCC scenario) was considered. The scenario suggested changes in sea surface temperature (SST), which is the driving parameter in most modern hurricane models. A rainfall hazard model was then developed using recorded rainfall data associated with hurricane events and a probabilistic model relating wind and rain was constructed. The annual maximum wind speed (or rate of rainfall) distribution and the joint distribution of maximum wind speed (or rate of rainfall) and storm size, under 2012 (current) and 2100 (future) climate scenarios, were then compared. Finally, a joint wind, rain and storm size hazard model is constructed that includes consideration of projected climate change impacts.

Transportation networks are necessary infrastructure elements to provide aid to impacted areas after the occurrence of an extreme event. Without functional roads, recovering other damaged facilities and lifelines would be slow and difficult. Therefore, restoring the damages of transportation networks, specifically bridges as their most vulnerable elements, is among the first priorities of disaster management officials. This paper presents a new methodology for scheduling the restoration of damaged bridges. The problem is formulated as a multi-objective combinatorial optimization solved by Genetic Algorithms, which minimizes the time to connect the selected critical locations and maximizes the resilience of the transportation network. The main purpose of developing the algorithm was to provide a restoration plan which is practical to be used by decision makers at the time of an event, yet based on solid computations rather than mere engineering judgment. The algorithm is examined with a numerical example. The presented algorithm can be considered as the enhancement of previous work performed at Lehigh University. The results show that the new optimization setup improved the solution quality and efficiency compared to the previous techniques.

Data collected from recent tornadoes in Tuscaloosa, Joplin, and Moore shows a consistent pattern of damage to residential structures. For an EF-4 or EF-5 tornado, damage levels increase from the outer edges toward the center line of a tornado track. This is not just because of higher wind speeds at the center of a tornado vortex; the wind velocity fields around structures are also different at the tornado center. Analysis from the damage pattern from the tornado showed that the failure progression of residential structures within a tornado wind field depends on the relative location and direction of the house to the tornado track. With the same wind speed, different damage levels can be observed if structures located in different relative distances from the center-line of a tornado damage track. This should be considered when predicting tornado wind speed based on residential structural damage.

Storm Sandy-induced structural damage of New York City buildings is presented. The paper presents findings based on statistical analyses that used the population of over 17,000 ATC safety assessment reports prepared by consulting engineers. The surge affected mostly wood frame, low-rise buildings and the paper focuses on the different response of one- and two-story buildings. Engineering observations and statistical results indicate that the weight of a building is a simple and reliable predictor of the level of structural damage.

Laboratory tornado simulators, intended for estimating tornado-induced wind loading on structures, have been in development for a little more than ten years with the first such facility being developed at Iowa State University. The ideal validation of such facilities would compare pressures on buildings in the lab to pressures on buildings in the field. Since this is nearly impossible from a practical standpoint, other validations must be sought. In the past, the Iowa State facility's performance has been compared with Doppler radar velocity profiles, with surface pressure profiles and with damage patterns for individual structures. This paper summarizes how the simulator's results compare with the newly acquired damage data from the Moore, Oklahoma tornado of May 21, 2013. The data from this tornado consists of geo-located, structural damage data. The structural damage was plotted as a function of radial distance from the center of the damage path. This function was then compared with lab simulator estimates of how tornado-induced forces vary with distance from the center of the vortex. The lab simulator over-predicted the damage for most radial positions, but the analysis highlights the promise of the lab simulation. The shape of the curves was reasonably consistent and could be improved with a more rational connection between predicted forces and resulting damage.

The Moore, OK, tornados provide a rare glimpse of an extreme tornado event (EF-5) occurring at the same relative geographical location twice in fourteen years. Evidence from the May 3, 1999 and May 20, 2013 events were considered with a special emphasis on the lateral load bracing systems and the influence of building code requirements. The team focused on residential structures and the lateral bracing failures evidenced in these types of buildings. Residential homes built using the continuous sheathing method (R602.10.4 of the 2009 IRC) were compared to the intermittent bracing methods (Table R602.10.2 of the 2009 IRC) or the prior local codes (CABO 1995) which did not incorporate wind speed design parameters. The long-term focus is to improve residential construction techniques so that the structures will generally perform better, with a higher structural survivability and a narrower damage path due to a tornado.

Natural hazards, particularly extra-tropical (winter storms) and tropical cyclones, could have devastating impacts on human life, structures, the environment, and the economy. It has not been long enough to forget the destructive impacts of the 1998 ice storm and, more recently, the costly impact of Hurricane Irene in 2011. In terms of today's economy, the 1998 ice storm would have caused insured and economic losses of about 3 and 6 billion Canadian dollars (CAD), respectively. More recently, Hurricane Irene left an impact across Ontario, Quebec, and New Brunswick, causing approximately 200 million CAD in damage to insured properties. To estimate possible damage and losses within Canada due to extra-tropical cyclones, a comprehensive probabilistic model was developed which incorporates the meteorological hazards (wind, snow, freezing temperatures, and ice accumulation) and the associated vulnerability of Canadian built structures. In addition, a methodology for accounting for the temporal and regional vulnerability of structures was also implemented, reflecting changes in the wind and snow load design methodologies as well as the construction practices in Canada. A similar approach is used to develop a model for assessing the tropical cyclone risk in Canada.

The paper presents a methodology to evaluate economic resilience at the community level which can be applied to any type of disruptive event rather than earthquakes. The goal is to help decision makers to understand the economic resilience problem of inter-dependent networks from a community level to a business level. The case study chosen in this paper is the San Francisco Bay Area, a region which is very sensitive to natural disasters as proven by the numerous projects and institutions working on identifying performance levels to be achieved to obtain a resilient city. The two approaches - which aim to compute economic resilience and identify the effects arising from different investment allocation - are compared. Some insights on how these approaches can be implemented to evaluate the life-cycle costs of structural systems and the return of investments on preparedness measures (like building structures with higher performance with respect to the minimum required performance levels) will be investigated.

The frequent occurrence of severe thunderstorms (ST) in recent years has caused substantial life and property losses in the United States. The 2011 severe thunderstorm outbreaks alone caused a record-breaking 26 billion dollars in losses for the North America insurance industry- as per Property Claim Services (PCS). In 2012, total insured losses reported by PCS were on the order of 15 billion dollars. The majority of the time, these storms affected the non-hurricane-prone regions of the US - "Midwest and Central Plains". Hail, tornadoes, and straight-line winds were the main contributors to damage from such events. Apart from significant levels of wind and hail hazard from these events, vulnerability of buildings in these areas also exacerbated the level of damage and losses. Buildings in these regions are generally designed to a lower wind speed than those imposed on by extreme wind events such as hurricanes. Experimental and numerical techniques are generally employed by engineers to study the impact of extreme weather events on buildings. However, tornado wind fields and falling hail are difficult to accurately simulate. Hence, engineers have mainly depended on post-disaster survey data to rate the hazard intensity and assess the level of damage. In catastrophe modeling - a study area in which risk from natural catastrophes is assessed - damage survey data can also be supported by actual insurance claims data and used to inform the vulnerability assessment of buildings. In this paper, blending of the insurance claims data and post-damage survey data for the assessment of building vulnerability from tornadoes and hail is studied. The relationship between the damage ratio (repair cost divided by the replacement value of a building) from insurance claims data of various companies and the EF-scale's degree-of-damage from the field surveys, along with the progression of damage across the tornado path and the impact of several building characteristics on the damage at a given hazard intensity level were investigated. In general, the data and the practical experience gained from the damage surveys proved to be instrumental for validation and calibration of resulting vulnerability functions.

Nuclear Island (NI) fill concrete is an essential element in the design and construction of nuclear power plants that are founded on rock. To specify the various factors required in the concrete placement process - such as mix formula, lift thicknesses and delay time between lifts - would be difficult without taking full advantage of experience and lessons learned from constructing other similar projects. This paper collects the most relevant points of the NI fill concrete design and testing from plants currently under construction and summarizes them in one single document. The information presented will help designers of NI fill concrete address licensing concerns on the subject and make the final product capable of supporting the various loads from the NI structures.

Design of third-generation-plus nuclear plants incorporate many design concepts and construction methods developed by other industries before 2008. Many concepts and methods, including modular and open-top construction methods, have been proven quite effective and practical. On the other hand, the incorporation of some newer structural systems, such as adaption of eccentrically braced frames in the turbine building (TB) and inclusion of base-isolation systems in the steel turbine-support structure, have met more challenges than what were anticipated. Fortunately, the re-engineering of the turbine building for use in Europe may present the design engineers with another opportunity to incorporate the latest structural systems in that building. Because of the difficulties encountered in the current, a due-diligence study was conducted on the steel buckling-restrained brace frame (BRBF) structural system. The quick literature review was performed with a singular aim to see whether this new structural system can be qualified to be included in the TB design. The time span of the study is extremely short. The information gathered and accessed was at best sketchy, and some may be out of date. This paper presents basic information used for determining future re-design methods of the TB.

Engineers designing conventional, rectangular, reinforced concrete, liquid containing structures (LCS) often rely on the Portland Cement Association's (PCA) publication, "Rectangular Concrete Tanks", to analyze two-way panels. Several scenarios that would benefit designers are not included in the publication. This article expands on the scenarios presented in PCA's publication. In lieu of printed tables, an Excel database application has been developed to publish desired tables. Designers often encounter partially filled panels where contained fluid is below the propped support. In addition, designers may want to check shear at a critical section following ACI 350-06 "Code Requirements for Environmental Engineering Concrete Structures". The out-of-plane forces and displacements have been determined using finite element software and converted to non-dimensional coefficients in an Excel database. The coefficient tables are automatically generated in a similar format as the PCA publication. These tables are very useful for designers because LCS walls response can be obtained without finite element analysis. Discussion of the formulation is presented, including relevant finite element model information. Also, an example is presented using the tables in accordance with ACI 350-06. (Please note that the tables and Excel files mentioned in the abstract are not included in this paper.)

From the 1960s to around 2000, approximately 100 large, hyperbolic cooling towers(HCTs) with heights up to 160 meters (about 525 feet) were constructed in the US. This period roughly coincides with the expansion of the nuclear power industry. Since 2000, apparently very few towers have been built in the US, with the Braydon Pt. project (Smith, 2013) reported at SEI 2013 featuring the first new towers constructed in many years. Of the large US towers, some have been demolished (such as the iconic Trojan Tower in Washington State) and some have been permanently shut down (such as the Three Mile Island towers), but many remain in operation, either continuously for base power production or intermittently for peak load demands. Given the age of these towers and the often severe service environments, it is expected that most are in need of rehabilitation. The consensus documents for cooling tower design and construction produced in the 1970s were widely used for the design and construction of many of the large towers during that era but have not been updated. While deteriorated towers have been cosmetically repaired, is desirable in many cases to carry out the rehabilitation in a manner that facilitates the determination of the structural capacity and service life of the restored structure. Given the vintage of the original consensus documents, it is evident that they are an insufficient basis for the complete rehabilitation of existing towers. In the decades since the US recommendations were produced, there have been many advancements in design methodologies and assessment provisions and technology, primarily in Europe. In this paper, key factors that affect the rehabilitation of deteriorated towers are reviewed and prioritized with consideration of current capabilities and developments so as to provide a reasonable basis for restoring any lost structural capacity and extending the service life.

Restrictions on power plant emissions have required owners and utilities to build and upgrade flue gas ductwork structures. Flue gas ductwork structures are generally designed as rectangular box-girders made of thin wall plates which are stiffened by W-shapes or Channels. Ductwork is designed for dead, ash, wind, live, and seismic loads at a high temperature and pressure. Better understanding of some critical issues, such as geometrically nonlinear analysis of ductwork, can help engineers to strengthen existing ductwork and design new ductwork more economically. This paper researches and compares different modeling methods per design experience and, for nonlinear analysis of ductwork, proposes an efficient approach to solve the problem. Ductwork is designed per ASCE's "The Structural Design of Air and Gas Ducts for Power Stations and Industrial Boiler Applications". Since the guide was published in 1995, it hasn't been updated per current codes and developed finite element software. The linear small deflection theory and allowable stress design methods are proposed. Ductwork is generally made of thin steel plate, around 0.25 inch, with stiffener spacing L, around 3 feet. The ratio of span to thickness is larger than 80, which is the borderline used to consider the membrane force for a plate under lateral loads. The deflection to thickness is mostly above 0.5, which is the standard line from small deflection theory to large deflection theory per Timoshenko in 1959. Therefore, nonlinear analysis should be considered for most ductwork, especially when existing ductwork is to be evaluated for new loads. The nonlinear analysis is important because duct plate should support shear and axial membrane stresses instead of only bending stresses caused by flue gas pressure. For these cases, small deflection theory may not be the more conservative solution compared to large deflection theory. This paper summarizes flue gas ductwork design per ASCE design guide, and compares different solutions of fixed-edge-rectangular plates based on small and large deflection theories from recent technical papers and books to further understand the behavior of duct plate. This article discusses ductwork design loads per large deflection theory, and provides a typical example of finite element nonlinear analysis for a ductwork structure. This research can be used for similar structures using stiffened steel plates such as boiler casings, bridges, and other non-building structures.

A large water tank, 21 m (69 ft) in diameter and 15 m (50 ft) high, was constructed within a power generation plant in the state of Michigan. Field measurements indicated that the tank's foundation was settling up to 380 mm (15 in) during the tank filling process. The settlement continued to increase as more water was added to the tank. Therefore, it was crucial to investigate whether such excessive movement was due to bearing failure of the supporting soil or to clay consolidation. Also, assessment of the maximum anticipated settlement and the time required to reach the maximum settlement were required since the project was being turned over to the owners. Due to the complex drainage behavior at the tank site, finite difference and finite element models were used to analyze the behavior of the soft clay layer. The objective of the analyses was to recreate the time settlement history of the tank and then use these models to predict the potential for additional settlement in the future. Soil parameters were adjusted in order to be able to recreate the time-settlement history recorded in the field with analytical models. Having "calibrated" the models in this fashion, various time-dependent load cases were introduced to predict probable future soil movements. The analyses indicated that the long-term settlement is expected to be about 420 mm (16.5 in) when the tank is filled with water. Among other things, that level of settlement would likely damage any pipes attached to the tank. Therefore, it was crucial for the pipe connections to be completed after the tank had attained its maximum predicted settlement. The other option was to design a forgiving connection that could accommodate a certain level of tank settlement. It was recommended that pipe connections to the tank should be designed to accommodate 25.4 to 38.1 mm (1.0 to 1.5 in.) movement. It is prudent to consider remedial action should the observed settlement exceed the flexibility limit of the pipe connections. Remedial measures, including jet grouting and supporting the tank on deep foundation, were among the options considered for the project. Numerical simulations indicated that the full tank was producing stresses that are close to the bearing capacity of the soil. Therefore, it was recommended that the water level should not exceed a maximum height of 14.0 m (46.5 ft), and that determined the location of the overflow pipe connection.

Wind turbines are typically designed for a target service life of 20 years because of fatigue-related failures, which often occur in moving components such as the rotor and blades. Designing the tower to have the same lifetime as other components is required for optimizing the wind turbine. This study focuses on fatigue life of the wind tower due to a mode I fatigue of the welded base connection only. A model for fatigue assessment, including crack propagation, was developed for the tower base connection. The allowance of crack propagation is expected to extend the service life of the tower in comparison to conventional fatigue life analysis using the S-N curve approach. An illustrative example of fatigue life design for a typical 5-MW wind turbine in Colorado for different operational conditions is then presented. The results of this study will benefit the design of new wind turbine towers and condition evaluation of existing wind turbine towers.

Cylindrical structures -such as grain storage silos, liquid storage tanks and other bulk storage bins - have been widely used for industrial facilities. Wind load design requirements in the current ASCE 7 are lacking for such structures. It has been found that the determinations of wind loads for tanks varies in US industrial standards such as API 650, API 620, AWWA D100, AWWA D103 and NFPA22. The design requirements or approaches are defined in different ways in other standards such as those for Australia and New Zealand (AS/NZS1170.2) and India (IS875 part 3). Detailed wind tunnel tests of such structures in Australia started in the 1980s. Results indicated that the distributions of wind pressures on the walls and roofs of silos and circular tanks are different from those on regular buildings and are functions of aspect ratios (height to diameter), roof slopes and tank spacings. In this study, wind tunnel test results and design provisions from the Australian Standard for wind loading (AS/NZS 1170.2) are reviewed. A proposed codification for ASCE 7 is made. Comparison of wind loads using AS/NZS 1170.2, the proposed ASCE 7 procedure, and those in IS 875 part 3, API 650, API 620, AWWA D100, AWWA D103 and NFPA22 are included.

Modular structural steel industrial structures are commonly adopted in order to reduce construction costs associated with expensive labor at remote installation sites and to improve construction schedule due to weather constraints. Even small maintenance or construction issues at such sites could become very costly operations. Utmost care is required when performing the analysis and design of such modular structures, especially for heavy rotating or reciprocating machines requiring a dynamic analysis. The dynamic response of the structure due to machine-induced vibratory loading has to be acceptable despite an inherent lack of mass in a steel structure, and despite a potential range of climate conditions which could impact the dynamic properties of soil. The impedance (stiffness and damping) of soil- or pile-supported foundations is a function of the dynamic properties of soil and operating machine frequencies. In addition, a module could house a number of machines requiring an analysis for dynamic loads, with the machines in various combinations of operation and shutdown. This paper presents one such design performed for a project in Russia covering the unique aspects of steel modules, sub- and super-structure modeling, determination of pile dynamic parameters under different weather conditions, and dynamic analysis and design. The design process proceeds until vibration amplitudes are within the allowable limits (as specified by machine manufacturer) for satisfactory operation of the machines, and for the comfort of nearby working personnel.

Pre-assembled units (PAUs) or modules have been widely used for industrial pipe racks. Compared with traditional stick-built construction, using PAUs or modules can accelerate the construction schedule for maximization of shop fabrication, resulting in lower field installation cost. It can be suitable for a plant revamp project due to space limitations and turnaround period requirements, or a project located in a remote or an environmentally sensitive area. However, modular construction requires considerable construction planning and involves logistical challenges. Structural members and connections need to be detailed and suitable for construction sequencing and various types of conditions: shipping, setting, lifting, modular assembly, and fitting for final installation. This paper addresses such challenges, primarily focusing on the considerations of structural analysis and construction detailing.

In the coming years, a number of offshore wind projects and demonstration pilots are poised to commence construction along the coastal states of the Northeast. These projects have the potential to generate up to 5 gigawatts (GW) of zero carbon energy and displace the region's aging and highly polluting coal-fired power plants. The paper provides an overview of these important developments in the American offshore wind industry, including public policy, lease areas, commercial projects and marine infrastructure. Current efforts in the Northeast are discussed in light of ongoing efforts in Germany and Denmark. Special attention is given to the role that the Commonwealth of Massachusetts and the Massachusetts Clean Energy Center have played in stimulating this industry via the construction of critical infrastructure projects, working with offshore wind developers, and working to permit and lease offshore wind sites.

Currently under construction, the New Bedford Marine Commerce Terminal (NBMCT) will be the first purpose-built offshore wind logistics port in North America. In order to become an essential logistics hub for the growing offshore wind industry in the Northeast, this terminal was designed not only for immediate use, but also for operational support and service to future generations of offshore wind turbines. For this reason, the bulkhead was designed to support the use of crawler cranes capable of picking 500 tonnes at a distance of 30 meters. This paper discusses the circular cofferdam bulkhead design and its relation to the specific geology and logistics requirements of New Bedford Harbor. At quayside, the cofferdams are protected by a reinforced concrete relieving platform on steel pipe piles. The authors discuss the uniqueness of this system design and its responsiveness to the requirements set forth by the offshore wind industry and the Massachusetts Clean Energy Center.

One of the barriers to reducing the cost of wind-generated energy is the cost of manufacturing wind turbine towers which are usually designed with conical steel shells. Such towers are currently manufactured manually at centralized plants and then transported in sections to the installation site. The necessity of transporting these sections often limits the base diameter of large tower designs, requiring an increased use of material when compared to an optimized (i.e. least-weight) design. A new manufacturing technology, based on an adaptation of spiral welding, enables on-site and automated fabrication of taller, more economical towers. On-site fabrication precludes transport-based limits that currently inhibit turbine size. Automated fabrication enables production at lower cost than other methods. Spiral welding is a mature technology in the pipeline industry where resistance to internal and external pressures is the primary loading mode. However, for wind turbine towers, flexure is the primary loading mode and the design of spirally-welded tubes for this application is not fully established. Moreover, this application of spiral welding requires larger diameter-to-thickness ratios than are currently used in the pipeline industry. This paper examines existing design standards for slender shells and assesses their applicability to shells manufactured by spiral welding. The research considers two limit states - local buckling and fatigue - and emphasizes the differences in imperfections and weld details between traditional turbine towers and those manufactured with spiral welding.

Most offshore wind turbines (OWTs) are designed according to the international standard IEC 61400-3 which requires consideration of several design load cases under extreme sea state conditions during which the wind turbine is in survival mode (i.e. the rotor is parked and blades are feathered). Each of these load cases depends on combinations of two random variables, the mean wind speed and the significant wave height, both with a mean return period of 50 years. The response of an offshore wind turbine under wave loading is known to be sensitive to both the significant wave height and a frequency measure of the sea state such as the peak spectral period. The IEC standard states that design calculations for the extreme sea state should be based on values of peak spectral period which result in the highest loads acting on the structure, but does not provide additional guidance. The Standard does provide a deterministic range for the period of the extreme wave conditioned on the significant wave height, and this can be converted to a range of peak spectral period using published empirical relationships. This paper considers an offshore location off the coast of Georgia, where NOAA buoy 41008 is located, and shows that a deterministic range of peak spectral period converted from the range provided in the IEC Standard may not accurately represent measured data. Moreover, the paper shows that the response of a hypothetical offshore wind turbine, installed at this location and supported by a monopile foundation, is sensitive to variation in the peak spectral period, emphasizing the importance of modeling the turbine for an appropriate and possibly site-specific range of peak spectral periods. A probabilistic approach is proposed to find an appropriate and site-specific range of the peak spectral period for the design of offshore wind turbines under the extreme sea state.

Onshore wind offers a green and renewable energy source, and onshore wind energy harvesting is one of the fastest growing industries in the world. The cumulative wind power capacity of the United States has grown from 3,000 MW in 2000 to over 20,000 MW in 2010. The major portion of the construction cost of wind farms is due to turbines, while the cost of the towers constitutes approximately 20% of the total cost. However, in such a growing market, there is still room and interest to reduce the cost of projects through achieving economy in tower design. The selection of proper turbine height and size depending on the location of the wind farm is the key factor in optimizing the installation cost. This paper evaluates and compares the cost of energy (COE) for a total of 10 tower height-turbine size combinations. Lattice (rather than monopole) towers are investigated for providing a cost-effective solution for small and medium size turbines as the ones considered here. With the number of wind farms increasing, it is inevitable that a significant number of wind turbines will be established in seismically active areas where the design forces are severe. Therefore, an earthquake-prone region is selected for the case study and seismic forces are included in the analysis. The results provide direct insight on the selection of the optimal tower alternative for a given location considering the height and turbine size despite the fact that the effects of the total number of towers in the farm and their location with respect to each other are not evaluated here.

In this paper, the static and dynamic buckling of cylindrical storage tanks is studied. The nonlinear static buckling analysis was performed on the tank with height-to-diameter (H/D) ratio of 2.0 and diameter-to-thickness (D/t) ratio of 960 when it is subjected to a horizontal shear force at the top. Then, three different geometries of tanks were analyzed for dynamic buckling when subjected to the El Centro earthquake at the base of the tanks. The procedure by Budiansky and Roth was used to identify the dynamic buckling load for empty and liquid-filled tanks up to 90% of their depth. It is noted that that the tanks fail by static buckling when they are empty, whereas the tanks fail by dynamic buckling when they have liquid in them because of added mass. The empty tanks do not buckle under the action of earthquake load. The peak ground accelerations (PGA) for the three models of liquid-filled tanks studied here are 0.25g, 0.39g, and 1.50 g.

North America has an aging fleet of coal plants which contain substantial ductwork systems. This ductwork is exposed to harsh conditions associated with plant operations and environmental conditions. These harsh conditions increase risk of metallurgical deterioration over time. This paper will discuss the effects of high temperature operations and the resulting graphitization effects within ductwork. Graphitization is the breakdown of the material's metallurgical microstructure, thus forming a weakened failure path. There have been documented failures in coal-fired power plants due to graphitization which have caused plant shutdowns and injuries to personnel. Currently, there is no industry consensus document providing information on the formation of graphitization and how to combat this problem. Multiple individual reports and technical papers on graphitization and its effects have been written in the past 50 years. The formation of a single source document outlining guides and standards would be beneficial to the power industry. The primary goal of this report will be to condense the relevant industry information on this topic into a summary discussing the formation characteristics of graphitization. Additionally, the report will provide technical information on the graphitization process, including critical components, design considerations, and inspection and remediation methods to correct possible existing conditions. Through research of top industry documents, it has been concluded that the effects of graphitization need to be closely considered and monitored as temperatures exceed 800.F. Temperatures below 800.F may experience graphitization, but at such a marginal rate that it can be neglected over the design service life. By providing a single location outlining the formation characteristics of graphitization, engineers will benefit from standardized procedures for the inspection, analysis and design of existing and new hot-side ductwork components, thus yielding improved consistency and product quality.

Silo structures are used all around the world to store granular bulk solids such as grains, coal, plastic pellets, and mineral ore among many others. As bulk solids processes increase in complexity and size in industrial facilities due to plant improvements and increased global demand for products, many storage silos are designed or modified to discharge eccentrically. Even though those designs or modifications meet all the requirements at the basic and functional engineering level for the envisioned process, they may have severe implications for the storage structural system. Silo shells are efficient structures if internal pressures are applied uniformly. However, eccentric discharge changes the loading behavior to non-uniform pressures around the circumference of the silo. These non-uniform pressures cause high membrane stresses in thin metal silos which may deform the shell and, in some cases, cause catastrophic failure. In concrete silos, these non-uniform pressures result in bending moments that may cause severe damage to the walls by developing dangerous cracks. These structural damages are intimately related to the loading pattern which, in turn, is related to the bulk solids behavior developed during eccentric discharge of silos. Design of new or modified silos discharging eccentrically is a challenging task that requires not only understanding the structural analysis and design of these types of structures, but also bulk solids flow behavior as well as their loading patterns.

A growing trend in petrochemical industry capital projects is the modularization of facilities. The decision to modularize a new petrochemical facility depends on various factors such as schedule, local labor conditions, facility shutdown period, constructability and the geographical location of the facility. The decisions on type and level of modularization should be made early in the project due to their considerable impact on cost and schedule.

Modularized petrochemical projects are sometimes located in regions of high seismicity. When this occurs, the designer is required to balance the structural stiffness and overall strength requirements of transportation loads with the ductility and detailing requirements of earthquake design. If the seismic and transportation loads are not handled effectively, then the resulting modular design can become unnecessarily costly, bulky, and inefficient.

This paper provides a technical overview of a new reference document titled "ASCE/AWEA RP2011: Recommended Practice for Compliance of Large Land-Based Wind Turbine Support Structures." This paper discusses the features of RP2011 as a design and permitting resource for structural engineers and plan reviewers engaged in utility-scale wind farm tower design or permitting. The US wind industry has been developing utility-scale wind farms for over three decades, and in that time there has been no clear guidance in the US for the design and permitting of wind turbine support structures. In the absence of specific design guidelines or standards, demonstrating building code (i.e., "Code") compliance has been a challenge, especially since the wind industry primarily utilizes international (European) design standards. The lack of guidance may have been tolerable in the early days when large utility-scale wind energy projects were very few, but conditions and priorities in the US are changing. There is an increased demand for green/renewable energy in lieu of fossil fuels, and there is now more interest in American energy independence from foreign sources. RP2011 is specifically targeted to help and inform structural engineer designers and plan reviewers of wind farm towers. Since wind turbine support structures are addressed neither in the Code nor in any Code reference standard, design professionals might not be aware of the many idiosyncrasies and complexities involved in wind industry tower design. Design professionals will learn about several key issues in wind tower design: (1) how to properly apply Code wind and seismic provisions; (2) the importance of fatigue assessment and the reconciliation of Eurocode and AISC fatigue provisions; (3) the importance of frequency separation; and (4) cautionary examples where general attempts to apply Code provisions would result in unconservative tower designs that do not meet wind industry standards. To address these and other issues, an effort was started in late 2009 to develop a US Recommended Practice for the design and permitting of wind energy structures. This task was undertaken by a joint committee of the American Society of Civil Engineers (ASCE) and the American Wind Energy Association (AWEA) with the main goal of reconciling the regulatory requirements of US Code versus those of international wind industry commercial certification. The result of this effort is ASCE/AWEA RP2011.

Shipping logistics and transportation form integral parts of modularization design and are influenced by the geographical location of the facility, the type of modularization, and the location of the module fabrication yard.

The United States' Occupational Safety and Health Administration (OSHA) has numerous requirements that govern the design, use, evaluation, and testing of permanently dedicated facade access equipment such as davit systems, outrigger beams, and fall arrest anchorages. These requirements are part of the US Code of Federal Regulations (CFR). Although the relevant structural requirements are contained within 29 CFR 1910 and 29 CFR 1926, the requirements are interspersed with thousands of other requirements that are not related to structural engineering. The intent of the provisions related to structural engineering is often less than clear due to use of terminology that is not common in the structural engineering profession. For this reason, the Architectural Engineering Institute (AEI) supported development of a guideline for engineers to better understand the structural engineering requirements governing this equipment. This paper introduces the AEI's Guideline for the Structural Design, Evaluation, and Testing of Permanent Building-Supported Facade Access Equipment, and Commentary, including its general scope and intent.

The United States' Occupational Safety and Health Administration (OSHA) has numerous requirements that govern the design, use, evaluation, and testing of facade access equipment. These requirements are part of the US Code of Federal Regulations (CFR). Although the relevant structural requirements are contained within 29 CFR 1910 and 29 CFR 1926, the requirements are interspersed with thousands of other requirements that are not related to structural engineering. The provisions that are related to structural engineering are often less than clear in terms of their intent due to their use of terminology that is not common in the structural engineering profession. For this reason, the Architectural Engineering Institute (AEI) sponsored an effort to develop a guideline to help engineers better understand the structural engineering requirements that govern the design, evaluation, and testing of permanent building-supported facade access equipment. The purpose of this paper is to review OSHA's requirements and explain how they might be converted into easily understood, unfactored design live loads. This paper is associated with three other companion papers regarding facade access systems, including "Introduction to the Guideline for the Structural Design, Evaluation, and Testing of Permanent Building-Supported Facade Access Equipment, and Commentary" (Lewis et al., 2014), "Evaluation and Testing of Building-Supported Facade Access Equipment" (Hill et al., 2014), and "Case Studies and Practical Examples Related to Facade Access Equipment" (Larson et al., 2014).

The United States' Occupational Safety and Health Administration (OSHA) has numerous requirements that govern the design, use, evaluation, and testing of facade access equipment. These requirements are part of the US Code of Federal Regulations (CFR). Although the relevant structural requirements are contained within 29CFR1910 and 29CFR1926, the requirements are interspersed with thousands of other requirements that are not related to structural engineering, and the provisions that are related to structural engineering are often less than clear in terms of their intent due to their use of terminology that is not common in the structural engineering profession. For this reason, the Architectural Engineering Institute (AEI) sponsored an effort to develop a guideline to help engineers better understand the structural engineering requirements that govern the design, evaluation, and testing of permanent building-supported facade access equipment. The purpose of this specific paper is to introduce attendees and readers to OSHA's requirements and explain how new and existing facade access equipment can be load tested to verify that it meets the minimum requirements of OSHA. This paper is part of three other companion papers regarding facade access systems, including "Introduction to the Guideline for the Structural Design, Evaluation, and Testing of Permanent Building-Supported Facade Access Equipment, and Commentary" (Lewis et al., 2014), "Structural Design Recommendations for Building-Supported Facade Access Equipment" (Searer et al., 2014), and "Case Studies and Practical Examples Related to Facade Access Equipment" (Larson et al., 2014).

The United States' Occupational Safety and Health Administration (OSHA) has numerous requirements that govern the design, use, evaluation, and testing of facade access equipment. These requirements are part of the US Code of Federal Regulations (CFR). Although the relevant structural requirements for facade access equipment are contained within 29 CFR 1910 and 29 CFR 1926, the structural requirements are interspersed with thousands of other requirements that are unrelated to structural engineering. For engineers tasked with designing or evaluating facade access equipment, the structural provisions are often less than clear due to OSHA's use of terminology that is not common in the structural engineering profession. For this reason, the Architectural Engineering Institute (AEI) sponsored the development of the Guideline and Commentary for the Structural Design, Evaluation, and Testing of Permanent Building-Supported Facade Access Equipment to help engineers understand the structural engineering provisions related to the design and evaluation of facade access equipment. This paper, along with three other companion papers, including "Introduction to the Guideline and Commentary for the Structural Design, Evaluation, and Testing of Permanent Building-Supported Facade Access Equipment" (Lewis et al., 2014), "Structural Design Recommendations for Building-Supported Facade Access Equipment" (Searer et al., 2014), and "Evaluation and Testing of Building-Supported Facade Access Equipment" (Hill et al., 2014), are intended to introduce the new AEI guideline and OSHA's structural requirements for permanent building-supported facade access equipment. The purpose of this paper is to demonstrate practical examples of how these requirements can be applied to actual equipment on actual buildings.

Past earthquakes have shown widespread damage to nonstructural systems in various types of buildings. The damage led to the loss of functionality or evacuation of several buildings and, in extreme cases, to loss of life. As part of the project titled "NEESR-GC: Simulation of the Seismic Performance of Nonstructural System" a series of system-level, large-scale experiments were conducted at the UNR-NEES site from December 2012 to April 2013. These experiments focused on the investigation of the system-level responses and failure mechanisms of nonstructural systems, including: steel-studded gypsum partition walls; suspended ceilings; and fire sprinkler systems. The preliminary observations included: failure of perimeter and in-field connections of ceiling systems, damage to the boundaries of partition walls, and failure of piping hangers. In addition, observations showed that interaction between partition walls and ceiling systems could cause damage in the ceiling systems.

Bidirectional shake table tests are performed on standard hollow brick partitions, subjecting the partitions simultaneously to interstory relative displacements in their own plane and accelerations in the out-of-plane direction. Five couples of accelerograms are selected matching the target response spectrum provided by the U.S. code for nonstructural components (i.e., AC156) in order to investigate a wide range of seismic demand. Three damage states are considered and correlated to an engineering demand parameter, i.e. the interstory drift ratio. The tested specimen exhibits significant damage for 0.3% interstory drift and extensive damage for displacement close to 1.0%. The correlation between the dynamic characteristics of the test setup - in terms of damping ratio and natural frequency - and the recorded damage is evidenced.

Bidirectional shake table tests are performed to investigate the seismic behavior of innovative plasterboard partitions. Such partitions are designed in order to not interfere with the hosting structure up to moderate level of interstorey drifts (about 0.5%). The table input is provided through acceleration time histories representative of expected/target ground motion at a given story. The time histories are artificially defined in order to match the ICBO-AC156 code prescriptions. To investigate a wide range of interstorey drift demand and seismic damage, the shakes are performed scaling the accelerograms at 11 different intensity levels. The tested plasterboard partitions exhibit a good seismic behavior, both in their own plane and out of plane, showing limited damage up to 1.1% interstorey drift ratio. The correlation between the dynamic characteristics of the test setup and the recorded damage is evidenced.

A ceiling system is composed of interlocking grid members including 4-ft.-and 2ft-long cross-tees. These members are held together at each intersection by interlocking clips attached to both ends of the members. A series of component-level experiments was performed on such members. The 4-ft.- and 2-ft.-long cross-tees were subjected to tensile and compressive forces to obtain their axial strength and stiffness characteristics. Tension and compression tests were also performed on the 2-ft. and 4-ft. clips to define their strength. Finally, the behavior of the interlocked cross-tees under cyclic axial load was investigated until failure of the connection. The experimental results were used to calibrate an integrated OpenSees model of a ceiling-sprinkler assembly that was tested at the E-Defense shake table facility in 2011. A full-scale, five-stor,y steel moment frame building was subjected to a number of biaxial and triaxial excitations. In these experiments, more than 900 ft² of suspended ceiling with lay-in tiles was installed on the 4th and 5th floors of the building, along with 100 ft. of sprinkler piping. The results from the analytical simulation were compared to the experimental results. This research promotes the experimentally validated computer simulation of non-structural systems and establishes a modeling methodology for future studies.

Six full-scale experimental studies of precast concrete facade have been completed in 2011/12 to evaluate the seismic performance of nonstructural building components. Experimental testing of cladding panels was completed at the nees@berkeley lab facility. Research findings are particularly relevant to seismic regions of the United States and other countries. The paper is targeted toward engineers directly responsible for façade design as well as the Engineer of Record for a building project. Researchers involved in code development and expansion of Performance Based Earthquake Engineering will also benefit from the paper. Specimens included full-width, half-width, and return column covers supported by an articulated steel test jig simulating a building structural frame. Steel connections between the panels and the supporting frame included slotted connections at the tops of panels and welded connections at the base of panels. The static loading protocol compared cyclic loading with increasing amplitude to a seismic loading protocol based upon the nonlinear time history drift of the prototype structure. The horizontal slotted connection at the top of panels allowed inter-story drift matching the building code requirements to occur with minimal damage to the panels. However, once the inter-story drift increased above a point where the slotted connection reached the allowed travel, damage to the panel occured in the form of severe cracking at embedded connections. Force-deformation graphs of the global specimen and individual connections quantify the hysteretic behavior. Horizontal slotted connections clearly show minimal resistance to lateral movement while the displacement remains below the maximum allowance of the slot. Once this free clearance is reached, bearing of the slot significantly increases and the connection quickly increases lateral resistance. Welded connections show very little hysteretic behavior due to low levels of relative displacement. The concrete embeds of the weld plates show more pronounced hysteretic behavior as this is the main location of damage and cracking at the base connections. The primary goal of evaluating the connection force-deformation relationships is to develop suitable analytical models for use in nonlinear studies of the façade system. The presentation will clarify performance of modern façade systems and define the analytical modeling input data for researchers exploring holistic building performance.

Several people have been injured because of the overturning or sliding of furniture, or falling objects from the furniture during past earthquakes. For these reasons, it becomes more important to find the criteria of overturning of furniture and its prevention against overturning during earthquakes. The overturning of a non-anchored body (such as furniture) during an earthquake is caused by the rocking motion. The purpose of this study is to compare and improve the equation proposed by Kaneko which expresses the relation between overturning ratios of rectangular rigid bodies of parallel pipe shape and the input excitations. Numerical simulations have been conducted using several non-structural elements of rectangular shape with different widths and heights. They were subjected to real earthquake floor motions of different typical buildings in California which have been monitored in real time. Based on the numerical results, a new formula has been proposed while results are compared with the ones obtained from Kaneko and with the model proposed by G.W. Housner in 1963.

This paper summarizes the initial developments of a research project that integrates experimental and numerical analyses to study the seismic performance of rooftop cooling towers and their isolation/restraint vibration protective systems. The numerical models used in the study are evaluated using available experimental data on the seismic responses of a rooftop cooling tower and its isolation/restraint system on a full-scale, 5-story building, atop of the NEES@UCSD earthquake simulator. The paper makes conclusions on: (a) the effects of isolation/restraint systems controlling the seismic responses of rooftop equipment; (b) the main variables controlling the earthquake accelerations in upper floors of a fixed base and a base-isolated building; (c) how rooftop amplification of accelerations affect the seismic responses rooftop equipment; and, (d) the capabilities and limitations of existing modeling methodologies for isolation/restraint systems in a commonly available software.

The peak inelastic displacement of a building during strong ground motion (GM) correlates with the elastic period of the structure. Algan (1976) observed this while subjecting laboratory scale reinforced concrete building structures to dynamic base excitations. Later, Lepage (1996) expressed the relationship in a simple form after carrying out regression analysis on dynamic response data from a wide range of buildings. Both Algan and Lepage focused on reinforced concrete buildings. In this study, the presence of a similar correlation between peak inelastic displacement and initial, elastic period in steel special moment resisting frame (SMRF) type building structures is investigated. Two sets of GMs are used in response simulation of 3-story and 9-story SMRFs using OpenSEES. The uniaxial Giuffre-Menegotto-Pinto model, with isotropic strain hardening and uniaxial bilinear behaviors, is considered to have two steel material properties of the structures. The structures are subjected to a series of ground motions with ascending peak ground accelerations. The results are compared with the corresponding responses from non-deteriorated (pristine) structural systems subjected to the highest intensity ground motion from the mentioned ground motion series. Each ground motion is scaled to a target spectral acceleration with respect to the first period of the structure. It is found that a simple empirical expression could be used to estimate the peak inelastic displacement. The source of this rather unexpected behavior is investigated through extensive high-performance computational simulations of how fundamental dynamic characteristics relate to damage and/or softening in a building structural system, including damage accumulation.

A large-scale experimental study is presented to investigate the wind loading mechanism on concrete roof pavers on the flat roof of a low rise building. The experiments were performed in Wall of Wind, a large-scale hurricane testing facility at Florida International University. Both wind blow-off tests and pressure measurements on the top and bottom surfaces of the pavers were performed. Attention was focused on accurate investigation of the net pressure distributions and the effect of the pavers' edge-gap/spacer height ratio on the wind performance of roof paving systems. The results showed that increasing the edge-gap to spacer height ratio parameter decreases the net pressures on pavers. Results of the wind blow-off tests are compared with those obtained from pressure measurements.

This paper presents an application for the optimization of tall buildings under lateral loads. The aim of this application is to show how engineering and scripting can be integrated to improve workflow and increase the accuracy of design.

One of the phenomena that reduces durability of concrete is plastic shrinkage cracking (PSC). Traditionally, the initiation and propagation of PSC has been controlled by minimizing its exposure to detrimental weather conditions or by adding fibers. In this study, concrete re-vibration technique was used, as an alternative, to reduce development of PSC because of the limited availability of fibers in developing countries. The time of re-vibration was selected to be 90 minutes after casting of slab which was based on ASTM C1579 procedure. The length of re-vibration was varied from 15 to 45 seconds. To identify influence of water on PSC, the water-cement ratios were selected to be 0.5, 0.55 and 0.6. In addition, an image analysis approach was implemented to process digital images of the cracks to estimate crack widths and lengths. The test results showed that the cracks' widths and lengths were reduced depending on the water-cement ratios and the re-vibration time lengths. Both fibered and re-vibrated showed similar levels of PSC reductions. Since both techniques reduced PSCs to similar levels, it is proposed to use re-vibration technique because it is more cost-effective in developing countries.

The effect of aerodynamic interference on tall buildings due to adjacent and upstream structures is routinely assessed for a building of interest (i.e., the project building) through wind tunnel testing. Due to the complexity of most urban environments, it is often challenging to attach the underlying aerodynamic mechanism (cause) to an increased response (effect) for particular wind directions. To broaden the understanding in this regard, research has been carried out by many parties focused on a singlebuilding or on multiple interfering buildings. However, in each instance found in the literature, the only buildings present in the wind tunnel tests are the interfering building(s) and the building of interest. While this approach improves the understanding of individual interference effects, it may not reflect realistic urban density. In reality, there are often many buildings in between the significant interfering buildings and the building of interest, which are likely characterized by varying height and geometry. Thus, the interference factors obtained in the experiment without these intermediate buildings, while useful, reflect values which may not be representative of true urban interference factors. It is often assumed that the interference factors obtained without the inclusion of intermediate buildings provide an upper bound of interference effects and are, therefore, on the conservative side. However, the extent of this conservatism, or whether they do indeed reflect a conservative estimate, remains to be seen. Wind tunnel tests were carried out based on a single upstream building and multiple configurations of simplified intermediate buildings to provide a comparison to the traditional approach to interference effects. Results from previous experimental work provide estimates of the peak response interference factors for the traditional approach to interference effects, which serve as the basis of comparison for experiments including intermediate buildings.

The seismic performance of a three-story building isolated with superelastic-friction base isolator (S-FBI) systems is evaluated relative to ground motion intensity associated with a risk level of 2% probability of exceedance in 50 years. The S-FBI system consists of a flat steel-PTFE sliding bearing and superelastic shape memory alloy (SMA) elements. An analytical model of the isolated building with the S-FBI system is developed to determine the response of the structure subjected to a seismic event. Seismic response of the non-isolated building is also evaluated for comparison purposes. Nonlinear response history analyses are conducted under a suite of 22 ground motion records. Peak interstory drift ratio, peak isolator displacement and residual isolator displacement are selected as the primary response quantities. Performance objectives based on the story drift ratios are defined. The effects of mechanical properties of the S-FBI system on the performance of the isolated buildings are examined.

This paper presents research towards the behaviour of reinforced concrete columns subjected to complex loading environments characteristic of internal blast. Historic events have demonstrated that confined blasts can induce significant upward tensile forces on load-bearing columns. These time-dependant upward forces act simultaneously with lateral blast pressures, coupled with the strength of concrete columns falling rapidly due to a net reduction in the axial compression force. To date, a large body of research exists regarding the vulnerability of concrete columns to external explosions, but no comprehensive studies have been conducted to understand column behaviour under complex internal blast environments. In this research, numerical models of concrete columns are constructed utilizing the Applied Element Method and benchmarked through comparative studies against experimental data. Internal detonations and the subsequent wave propagation featuring multiple reflections and blast venting are accurately simulated using CFD with independent load verification using Autodyn. Parametric studies were conducted to understand the influence of perimeter wall type, (i.e. rigid, open) in relation to blast wave reflections and the upward tensile effect on internal column members. The results of this research will benefit both academics and practitioners involved in designing protective structures covering both civilian and military construction.

The cold bended parts of pipelines are prone to geotechnical movements due to discontinuous permafrost, slope instabilities and seismic activities. Sen et al [1] carried out an extensive experimental study in 2006 in order to understand the buckling behaviour of cold bend pipes under applied curvature. In one of the experiments in this study, a high pressure X65 pipe specimen failed under applied curvature due to tension side fracture. This fracture was observed after the development of a wrinkle on the compression side. In this paper, the behaviour of this cold bend pipe specimen under applied curvature and bending is investigated using finite element method to understand the conditions leading to pipe body tension side fracture in the post-buckling phase of a cold bend. The finite element analyses - with and without internal pressure and the plastic strain and von Mises stress distributions - showed that the tension side fracture occurs under equal amount of applied curvature only in the case of the pressurized pipes. These results were in accordance with the experimental results obtained by Sen et al [1] . The effect of internal pressure is analyzed further in order to determine a transition point of the mode of failure from compressive to tensile. A parametric study is conducted for a series of internal pressure values ranging from 20% Specified Minimum Yield Strength (SMYS) to 80% SMYS. A failure criterion based on the equivalent plastic strain reaching a critical value was used to assess the models behavior up to failure. It was observed that load cases having an internal pressure less than or equal to 60% SMYS exhibit higher equivalent plastic strains on the compression side throughout the simulations and up to failure. However, for internal pressure values higher than or equal to 67% SMYS, the equivalent plastic strain on the tension side of the cold bend starts increasing dramatically at some point during the loading process, exceeding the equivalent plastic strain values on the compression side up to failure.

Structural behavior of reinforced concrete beams with corroded reinforcement is studied in this paper. The degrading effects of corrosion on the structural response of reinforced concrete beams has been simulated considering factors such as the reduction of cross-sectional area of steel, change in steel and concrete material properties and bond deterioration. A three-dimensional, finite element model, which is capable of considering the nonlinearity in material and geometric properties, is proposed to investigate the structural performance of reinforced concrete beams with different reinforcement ratios and arrangements under varying corrosion levels. Nonlinear relationship for the bond-slip deterioration as a function of corrosion level has been developed and implemented into the finite element model. At the final stage, the results have been verified with the available experimental data.

Highway networks can sustain extensive damage after extreme events such as earthquakes. Bridges are known as the most vulnerable component of the highway network, and their failure may result in lengthy service disruptions that can hinder the daily activities in the region. It is important to increase the resilience of the network by planning effective repair and recovery strategies that will expedite reconstruction of the network and further enhance its resilience. The repair process for the bridges can be lengthy. To counteract this, bridge repair acceleration techniques can be applied in order to shorten the repair time and restore the network to an acceptable level of functionality. Competitive bidding and daily incentives for finishing ahead of the schedule will decrease the repair time. This paper aims to show the applicability and benefits of incentivizing and accelerated bridge construction techniques in recovery actions after extreme events. It is shown that, although carrying a larger construction cost, these techniques reduce the indirect costs associated with network disruption.

Many buildings located in industrial and petrochemical facilities require protection from accidental external explosions. Due to the difference in basic characteristics of the two loading types, design of these buildings to resist external explosions or blast loading poses significant challenges when the facility is located in in a region with high seismicity. Seismic loads are cyclic, inertial loads with long durations, whereas blast loads are short duration impulse loads. Seismic loads are defined by ground acceleration response spectra while blast loads are specified by blast overpressures and durations. In blast-resistant design, building owners determine hazard return periods and acceptable performance and damage levels based on risk evaluation of personnel safety and property loss. Current seismic code provisions have been developed with the intent of achieving performance through prevention of building collapse and protection of life safety. Next-generation, performance-based seismic design will be based on performance and damage levels similar to those used in blast resistant building design. For purposes of demonstrating an optimized design process for both seismic and blast loading using performance-based design philosophy, this paper presents a blast-resistant design of a reinforced concrete building in a petrochemical facility located in a region with high seismicity. Selection of effective structural systems, performance levels, acceptable damage levels, structural modeling, structural analysis methods and ductile design and detailing of structural components are discussed in this paper.

The use of multi-tower sky bridges is a growing trend in tall building design, expanding the programmatic opportunities beyond the tower footprint. More than just pedestrian link bridges, the scale of these immense structures can accommodate a diverse range of program and amenities. Recent examples include the CCTV building in Beijing, China and the Sands SkyPark® at the Marina Bay Sands® Integrated Resort in Singapore. The means by which towers are linked together has considerable implications to the structural design, architecture, and construction of the project. Typically, these massive elevated structures are either monolithic to the connected towers (CCTV) or made structurally independent via a series of movement joints (Sands SkyPark®). However, the design proposed for the new 300-m-long conservatory atop the Raffles City Chongqing development employs an innovative use of seismic bearings to structurally isolate the sky bridge. This approach has been demonstrated to benefit both the conservatory and the four 250-m towers that support it. This paper provides a survey of various typologies of sky bridges, introduces key considerations for their design, and highlights the results of an extensive non-linear time history investigation recently completed to assess a matrix of bearing options considered for the Raffles City Chongqing conservatory.

The penetration of ogive-nose projectiles into concrete targets is investigated using finite element analyses. The Elastic-Plastic Impact Computation (EPIC) is used to examine the velocity vector fields of high- and low-strength target material during concrete penetration. The velocity fields represent the flow of the target material around the nose of the projectile and provide information about the concrete's penetration resistance behavior. The simulations show that material flow patterns transition during a penetration event. The dependence of this transition point as a function of concrete strength and impact velocity is presented. A Spherical Expansion Comparison Methodology (SECM) is developed to provide possible physical interpretations of the observed transition points. Structural engineers and model developers looking to improve the accuracy of current analytical concrete penetration models will benefit from the findings of this paper.

Soil-structure interaction modeling techniques are presented for bridges supported on large gravity caissons at deep-water sites. The fundamental mode of vibration of these massive caisson foundations tends to be in the short period range, in contrast with the longer period superstructure response. This results in an overall system with complex behavior during an earthquake, which needs to be carefully considered in the analysis and design. Modeling techniques with varying levels of complexity are demonstrated based on project experience from three bridges in highly seismic regions including: Second Tacoma-Narrows Bridge (WA), Strait of Messina Bridge (Italy) and South Park Bridge (WA). Use of numerical model pushover analyses to develop nonlinear distributed soil springs is shown to help overcome several of the limitations of the more basic lumped linear stiffness matrix approach. The relative importance of wave scattering effects and the evaluations of earth pressure distributions considering seismic loading scenarios for assessment of required reinforcements are also addressed.

This paper focuses on investigation of a new seismic rehabilitation method to mitigate soft-story failures in deficient, multi-story, steel, concentrically braced frames (CBFs). The considered method consists of a sufficiently stiff rocking core (RC) that is pinned to the foundation and connected to an existing deficient CBF building to re-distribute seismic forces along its height, creating more uniform inter-story drift and ductility demand distributions. Two benchmark steel CBF buildings - including one 3-story and one 6-story - designed for Los Angeles, California, were selected and retrofitted using the considered method. Nonlinear static pushover analyses were conducted to demonstrate the beneficial contribution of RC in mitigating non-uniform, inter-story, drift distribution. It is shown that the RC is effective in reducing inter-story drift concentration in both buildings when they reach the maximum inter-story drift limits associated with collapse prevention, lift safety and immediate occupancy recommended in FEMA 356 for performance-based seismic design.

At a remote US air base in northern Greenland, 700 miles inside the Arctic Circle, a Danish contractor worked with US engineers and US materials to construct a radar tower and supporting equipment building. Problems with site access, material shipping constraints, a short construction season, and aggressive project delivery schedule necessitated a change to European building materials partway through the building erection. The changes were not routine substitutions because the structure needed to withstand extreme sub-freezing temperatures and wind conditions. The designer, owner, contractor, and fabricator worked closely during construction to: (1) select materials suitable for arctic conditions; (2) re-detail a building designed with US steel shapes to utilize European steel shapes; (3) detail connections between the elevated US steel floor frame and European steel superstructure; (4) design components and cladding for high wind pressures; (5) meet a tight fabrication and material delivery schedule; and (6) collaborate to address multiple technical, delivery, and constructability challenges.

Vibration-based structural health monitoring (SHM) has become a tool in evaluating the condition of civil structures. For bridge structures, vibration-based SHM systems may use the dynamic response of a bridge to measure modal parameters. A change in a structure's modal parameters may indicate damage or other changes to the structural system. These same modal parameters are also sensitive to environmental conditions, primarily temperature. Statistical models have been utilized to differentiate the modal parameter changes caused by temperature and those caused by physical changes. Statistical models also help describe the relationship between modal parameters and environmental conditions. The Lambert Road Bridge is a concrete integral abutment bridge located in California on Interstate 5 (I-5), south of Sacramento. In this study, a SHM system installed on the Lambert Road Bridge was utilized to monitor the bridge's modal parameters and temperatures. The measurements from the SHM system were used to create multiple linear regression models that helped describe the relationship between the structure's modal parameters and temperatures.

The 2007 collapse of the I-35 West Mississippi River Bridge in Minneapolis has raised questions as to the integrity of steel truss bridges throughout the United States, causing owners to become more concerned about the safety and performance of these bridges. The capacity of the Riverside-Delanco steel truss Bridge (Bridge) was evaluated due to this heightened concern. This historical bridge consists of three pony truss spans, including two simple approach spans and a unique center bearing swing span. These bridge spans were analyzed for their structural integrity. The objective of this evaluation project was to provide the Bridge owner with a comprehensive load rating of the Bridge. The Bridge load rating analyses included allowable stress rating (ASR), load factor rating (LFR), and load and resistance factor rating (LRFR) methods. In addition, a baseline 3D finite element (FE) model of the Bridge, which realistically mimics the behavior of the Bridge, was constructed to help understand the response of the Bridge under various loading conditions. This FE model was utilized in the bridge load rating development and the gusset plate assessment procedures.

Environmental corrosion and vehicle dynamic impacts are among the major threats to the safety of existing bridges. The structural reliability is greatly endangered by their combined effects, which could possibly lead to a catastrophic failure. In this paper, the fatigue reliability of existing deteriorating steel bridges is evaluated. The dynamic stress ranges were obtained based on vehicle-bridge dynamic analysis. Varied material corrosion rates, vehicle types, vehicle speeds, and time-varied road surface conditions are considered. In the fatigue damage assessment approach, the bridge deteriorations of the road surface condition and structural components are included. At the end of each stress block, the fatigue life is estimated by evaluating the cumulative probability of failure. The effects of the corrosion induced area loss and moment of inertia reduction are limited and are much less than the random effects from road surface condition. Corrosion-induced fatigue strength reduction has a large effect on fatigue life. More than 60% reduction of fatigue life is predicted for different corrosion levels. The fatigue strength reduction is found more sensitive for the fatigue life estimation. Last, a new dynamic amplification factor for life-cycle bridge fatigue design (DALC) is proposed which is defined as the ratio of the life-cycle nominal live load stress range and the maximum static stress range. Fatigue damages from multiple stress range cycles due to each vehicle passage at varied vehicle speeds under various road conditions in bridge's life cycle and progressive deterioration are included.

Experiences over the last few years have given us the impression that the structural engineering profession is suffering from "ethical drift". An increasing number of engineers appear to be seeking recognition as "experts" via their pursuit and delivery of creative opinions that have no bases in long-established engineering principles. While such creativity may cause great and unjust harm to others, these experts are themselves insulated from harm by the apparently universal, though tacit, accommodation of the profession itself, which seems to have pre-judged all such opinionating as fair play and harmful to none. Moreover, the boards that license engineers and are charged with protecting the public have demonstrated that they are generally unwilling or unable to police the professionals under their control. The incredible extent to which engineers will bend the truth in order to provide "good" service to their clients or to protect their own interests is truly eye-opening and deserves a closer look by both the boards that govern our profession and the profession as a whole. In this vein, a number of case studies are presented that demonstrate the widespread problems with the ethics of the structural engineering profession.

Structural engineering software continues to evolve through the addition of more capabilities, interfaces with other software, and updated reference standards. These are all for the benefit of streamlining the process of design in the hope that significant time can be saved for structural engineers. However, with this increase in capabilities comes an increase in the complexity of the software to the point where some people may conceive the software as a "black box". Additionally, there is still a lack of understanding in knowing how to confidently check the results. Defined herein are specific steps that structural engineers can take to reduce the chance of making errors and to simplify the process of verifying results by creating a software error reduction plan (SERP). In addition, a discussion on tips and steps to reduce errors for integrating structural engineering software with BIM software will be discussed.

"Progressive collapse" occurs when a localised failure of a structural component triggers propagation of failure to adjoining elements, eventually resulting in collapse of the entire structure or a major part of it. This phenomenon in steel structures is mitigated primarily through beam-to-column connections. In particular, simple shear connections are critical as they are the most common beam-to-column connections in steel structures and experience different load combinations than those considered in conventional design. They experience extreme rotation and axial tension due to catenary action developed in the frame after the removal of an adjoining column. With increasing experimental evidence and detailed numerical models, prediction of the behaviour and failure of shear connections is increasingly feasible. However, uncertainties in such predictions are unavoidable due to the uncertainties in the material and geometric properties. This paper aims to investigate the reliability of the connection capacity predictions due to variability in the connection parameters. As such, high-fidelity, finite-element-based models - including the connection components (plate, bolts, beams) - have been analysed to examine the performance and behaviour of the shear connections under different geometric variables. Models include a single 6-m-span beam with shear tab connections at both ends and application of a concentrated load at the removed column. Uncertainties in the plate dimensions - such as end distance, plate thickness, and hole diameter - have been considered for the reliability and sensitivity assessments. Explicit quasi-static analysis using ABAQUS is employed to overcome the convergence difficulties related to contact, geometric and material nonlinearities, large deformation, and fracture simulation.

The prediction of collapse of structures has gained growing attention recently, as it is important to be able to predict and model structural collapse due to extreme loads. A lack of accurate and validated structural collapse models significantly limits the structural engineering community to predict possible extreme loads that precipitate collapse. This paper proposes an integrated platform for validated prediction of collapse of steel structures that accounts for material softening followed by elimination of finite elements to enable simulation of fracture. The proposed approach employs a void growth model (VGM) to simulate the initiation of softening and the Hillerborg model for modeling the softening itself, followed by an element deletion strategy that is developed in this framework. The parameters of these models were calibrated to a comprehensive set of experimental test results of circumferentially notched tensile (CNT) coupon specimens. These calibrated models were then validated through comparison with a broad array of experimental test results of steel structures, ranging in complexity from tensile coupons to moment-resisting beam-to-column connections. The proposed approach is shown to be accurate. Through element deletion, the formulation can account for complete structural component separation, thus precipitating modeling of the collapse of structures. This approach thus enables high-fidelity parametric simulation capabilities of interest to researchers, practitioners, and code developers who address collapse of structures.

Cold-formed steel stud load bearing walls have three framing components that can be utilized to enhance the resistance to disproportionate collapse in case of wall section removal from the structure: the wall lateral bracing, the wall studs, and added diagonal tension straps. Strengthening of the walls with tension straps has shown to redistribute the load of the lost wall section to the system and to enhance the resistance to disproportionate collapse in a previous paper of the authors. This paper extends the findings of the single multi-story wall system to the full 3D structure. The effects of the 3D interaction and the membrane action of the composite floor deck are investigated. The redistributed load after wall section removal is supported by the added wall strengthening system. The double studs showed effectiveness in preventing the wall from experiencing disproportionate collapse. Due to the rigidity of the composite deck floor, the diagonal strap system did not carry much force but it helped to redistribute the loads to other parts of the building.

Simpson Gumpertz & Heger, Inc. recently developed a cost-effective, non-load-bearing steel stud wall system for blast protection of building envelopes. Field tests at Tyndall Air Force Base (AFB) using equivalent vehicle bombs validated the system's ability to resist high blast impulsive pressures. The load-bearing capacity of such systems is the focus of an ongoing research and development program undertaken by the Air Force Civil Engineering Center (AFCEC) at Tyndall AFB. This paper presents quasi-static ABAQUS/Explicit finite element analyses which demonstrate the potential use of these wall systems as primary, load-bearing, structural components in multi-story buildings. This study addresses typical load-bearing steel stud framing approaches including single-span, infill walls in platform construction, as well as multi-span walls in balloon or ledger framing. Use of composite and non-composite sheathing for enhanced blast resistance is assessed through a parametric study.

Understanding the response of primary, load-bearing structural components in Antiterrorism/Force Protection (AT/FP) applications is important because of the critical role they play in ensuring building structural integrity. According to current AT/FP design standards established by the U.S. Army Corps of Engineers (COE), there is insufficient information available to develop response limits specifically for members in combined flexure and compression. For this reason, stringent response limits are defined for many blast-resistant structural systems including steel stud walls, thus essentially eliminating their use in many Department of Defense facilities. This paper discusses an ongoing study into the performance of load-bearing steel stud wall systems, currently underway at the Engineering Mechanics and Explosive Effects Research Group (EMEERG) at Tyndall Air Force Base, Florida. EMEERG has recently expanded its laboratory capabilities to study structural systems and components under combined axial and flexural demands. These studies will shed light on the residual load-bearing capacity of different building components and fill a knowledge gap with the possible benefit of relaxing response limits prescribed by the COE. Such lab tests are useful in characterizing response at a fraction of the cost of full-scale field tests using live explosives.

This paper describes both full-scale testing and detailed finite-element modeling of a precast concrete moment-frame assembly extracted from the perimeter moment frame of a 10-story prototype building. The assembly comprises two beam spans and three columns, and the unsupported center column is subjected to monotonically increasing downward displacement to simulate a column loss scenario. Failure of the assembly was due to non-ductile fracture of the bottom anchorage bars near the welded connection to the center column. Component-level testing of the welded connection detail revealed reductions in ductility of the anchorage bar in the heat-affected zone where the bar was welded to a connecting angle. Finite element analyses revealed that large bending moments, due to eccentricities in the welded connection details, also contributed to the premature fracture of the anchorage bars in the moment-frame assembly. Finite element analyses and comparisons with experimental measurements also provide insight into the load-carrying mechanisms of the precast concrete assembly, including initial flexural action followed by arching action.

Recent efforts to develop progressive collapse guidelines in the United States reveal an interest in improving design requirements to address disproportionate collapse, especially in the context of blast-resistant design. As a result, several ongoing research projects are investigating structural response under disproportionate collapse conditions. Generally, disproportionate collapse considers the complete loss of a critical load-carrying element - typically a column - that leads to a disproportionate collapse of other parts of the structure. However, simply considering disproportionate collapse through a complete member removal, as is typical per current design procedures, does not account for disproportionate failures that may occur due to localized effects. Engineers need to consider all possible failure mechanisms in design, including disproportionate collapse, for a more accurate determination of the initiation of a global failure. Inspired by such tragedies as the Hyatt Regency walkway collapse where the localized connection failure led to the disproportionate collapse of two entire walkways, this study examines expanding the definition of disproportionate collapse to consider local failures and their effect on members or systems. By characterizing the response and behavior of a structural member after localized failure occurs, appropriate design considerations can be developed. Results from this study will highlight the localized effects on the structural capacity considering disproportionate collapse and show why these types of failures must be considered by design professionals, code developers, and research efforts.

The significant advances recently accomplished in the fields of modeling, analysis, and design of deteriorating civil engineering systems are far from being explicitly addressed in design codes and effectively implemented into practice. There is, therefore, a strong need to promote further research in the field of life-cycle performance of structural systems under uncertainty and to fill the gap between theory and practice by incorporating life-cycle concepts in structural design codes and standards. An effort is currently ongoing within SEI/ASCE to meet this need. This paper is part of this effort and it is aimed at presenting a short overview of the main principles, concepts, methods and strategies associated with life-cycle assessment and design of deteriorating structural systems under uncertainty.

Infrastructure systems are continuously subjected to various deterioration mechanisms. Due to the presence of uncertainties associated with the loads, material properties, damage occurrence and propagation, and modeling the structural performance, among others, the life-cycle management of deteriorating structural systems represents a major challenge, especially when considering the effects of sudden damage. Although various performance indicators can be used within the life-cycle management of infrastructure systems, risk-based approaches are well-suited for this task. This is due to the ability to integrate the probabilistic performance with the consequences arising from structural collapse or failure of different components within an infrastructure system. This paper presents a general framework for the probabilistic risk-based optimization of life-cycle management of infrastructure systems under the effects of gradual and sudden deterioration. The management scheme covers the identification of optimal inspection, monitoring, and maintenance/repair activities which minimize the life-cycle cost, extend the service life, and/or maximize the performance of the structure throughout its projected service life. Uncertainties associated with the various stages of the life-cycle management are included. Additionally, several case studies for the implementation of the framework are discussed.

Structural reliability is commonly approached by evaluating observations of system failures over time. Although this approach has been very useful, it leaves out the insights of the process leading to failure. The understanding of this process, which is referred to as "deterioration", plays a significant role in life-cycle analysis. Degradation depends on the type of structure and the nature of the external or internal demands (i.e., frequency, intensity, mechanism). Therefore, there are important challenges in managing the uncertainty of this process. In this paper, we describe the problem of degradation and the associated uncertainties and suggest different modeling alternatives - among which we emphasize the use of Phase-type distributions as a convenient way to handle problems such as convolution - which emerge frequently in this type of problem.

Superstorm Sandy was one of the largest hurricanes ever recorded in the Atlantic Ocean, with a radius of maximum winds that extended over 100 nautical miles (185 km, NHC 2013). Prior to landfall in New Jersey on October 29, 2012, the storm was declared post-tropical with sustained winds of approximately 80 mph (129 kph).

In the maintenance planning,life cycle cost (LCC) can be reduced by treating multiple bridges simultaneously. However, it is difficult for a practical case to establish an optimal plan that reduces LCC because there is a large number of bridges to be maintained. In this study, an attempt is made to propose an optimal planning method for a large number of bridges in two stages by using a genetic algorithm (GA). In the first stage, the proposed method optimizes a maintenance plan for a single bridge with considering for preventive maintenance. Here, this optimal plan involves some periods in which maintenance works can be postponed without increasing LCC under the same safety condition. Then, in the second stage, the proposed method minimizes the total LCC of a large number of bridges by using each maintenance plan obtained for a single bridge, modifying it using such flexible periods involved in the maintenance plan, and calculating the total LCC by summing up the LCC for single bridge. Furthermore, the effects of budget constraints on LCC minimization are discussed. Numerical examples are presented to demonstrate the applicability of the proposed method.

The ASCE Sub-Committee on Disaster Resilience of Structures and Infrastructures initiated a testbed study on Resilience-Based design (RBD) considering two critical strategic structures (Town Hall and Hospital), a University Campus and the water distribution network of a small town. These structures were chosen because of the widespread interest in critical structures and infrastructures. In particular, the first two structures are considered critical, because they must not only survive the shaking, but must remain in operation. They require the largest investment of resources to insure that they can provide services following an earthquake. The test bed study will be developed using discrete event simulation models which are going to be calibrated using real data collected in the field. The development of these test beds will facilitate the comparison among different resilience frameworks which are available in literature. The paper presents an overview and problem definition of a hospital testbed which intends to help move the earthquake engineering community another step toward the realization and implementation of resilience-based design strategies.

The Federal Highway Administration has developed a framework document to help better define key decision points for effectively integrating security measures into project development. This paper will explore ideas from this framework that can help transportation planners meet owner needs for project development. Local, state, and regional planning organizations have well-defined processes to plan transportation projects, but incorporating security is a relatively new area for the highway community. While planning for security poses challenges, at the same time such planning has potential to produce structures with a level of resilience expected by the owners at the best possible cost. This paper's focus is on highway projects involving bridges and tunnels. The processes described apply to the design-bid-build method of contracting, but because many recent bridge and tunnel security projects use the design/build approach for contracting, the paper will also describe how the processes and considerations for traditional planning are just as applicable and even more important for design/build projects.

The increased dependability of modern societies on deteriorated water infrastructure (i.e., transmission and distribution systems) places special emphasis on its continuous functioning. Consequently, disaster resilience of these systems during and after hazards is vital for the response and recovery to the event. Water infrastructure system managers must understand the critical aspects of resiliency such as planning for hazardous conditions by anticipating the impacts and subsequently taking necessary measures to minimize consequences, and also prevent the disruption of other infrastructure systems (e.g., electrical infrastructure) by understanding and dealing with the critical interdependencies. A majority of these aspects are not always clear until the system has been exposed to the hazard, which is why we can learn so much from recent disasters. This paper will outline the key aspects of drinking water infrastructure system resiliency (e.g., system vulnerability, redundancy, management and response plans, etc.) and the parameters will be analyzed using historical hazardous events (e.g., earthquakes and hurricanes) to determine what the best practices were and should be moving forward. Recommendations for incorporating the best practices into rehabilitating existing systems and future designs will be discussed.

This paper proposes an object-oriented, consequence-based framework for lifecycle risk assessment to aid design of bridges subjected to multiple hazards while considering the effects of structural deterioration. Such a framework constitutes an essential foundation for a transition to multi-hazard, risk-based design. In the proposed framework, losses (i.e., consequences of damage such as cost or downtime) are introduced to provide a common performance metric for multiple hazards. Surrogate models are used to condition loss potential upon the intensity measure(s) of the hazards and structural design parameters. The loss estimates are coupled with hazard information to obtain expected annual losses from each hazard. The fragility of the bridge and, consequently, the expected annual loss change with time due to aging of the bridge. This time-dependent feature is also accounted for in the proposed framework. As a case study, the proposed framework is applied for multi-hazard design of multi-span simply supported (MSSS) concrete girder bridges in coastal South Carolina, which is susceptible to earthquake- and hurricane-induced wave and surge loads in addition to corrosion. The framework's applicability in facilitating safe and economical lifecycle-based design is shown by investigating the effect of variation in design parameters and structural deterioration on the lifecycle costs (LCC). The effect of deterioration on lifecycle performance of bridges under different hazards is studied along with relative contribution of each of the hazards towards total expected loss and its variation with time.

Although it has not always been the case, requirements for design of buildings to resist earthquake effects are currently mostly uniform throughout New England. At this time, virtually all jurisdictions in New England have based their design requirements on a model building code that adopts ASCE/SEI 7 for most seismic design requirements. Not only are the current design requirements similar throughout New England, practicing engineers approach design similarly. For example, structural engineers generally design buildings with seismic-force-resisting systems that are commonly used. These systems are generally lower ductility systems, and systems intended to provide high ductility are rarely designed and constructed. Although design approaches similar to current approaches will likely continue, more interest in higher ductility systems is likely as new ductile systems that are less difficult to construct and more cost efficient are introduced. Also, there should be continued interest in requirements for masonry construction and how to address unreinforced masonry existing buildings. Initiatives are currently underway that will impact seismic design provisions in the future. Several of these initiatives, if incorporated into ASCE/SEI 7, will affect seismic design requirements and structural design practice in New England. The initiatives likely to affect design for earthquake effects in New England include creation of design provisions that are applicable only to seismic design category (SDC) B buildings, revisions to the Simplified Seismic Design Procedure in ASCE/SEI 7, improved estimations of diaphragm force levels and ductility, a design approach applicable to buildings dominated by the response of a roof diaphragm, strength design for foundations, revised soil site factors, revised seismicity maps, and revisions to seismic design category criteria. These initiatives are described herein.

This study examines the seismic performance of steel frame buildings designed for wind, without consideration of seismic loads. The prototype building from the 2013 AISC Design Examples is selected to illustrate the possible seismic behavior of a typical mid-rise steel building designed for moderate wind and low seismic loads. The results indicate that, in many areas of the central and eastern United States, moment-frame buildings designed for wind may provide adequate performance for serviceability in frequent and occasional seismic events. Reserve strength in the structural wind and gravity systems then provides sufficient life-safety protection and prevention against collapse for very rare events.

In the central and eastern United States (CEUS) seismic hazard is distinct compared to the western United States (WUS) due to lower earthquake recurrence rates, generally slower attenuation of wave propagation, unique site response, and increased high-frequency content in ground motion. These differences have profound implications for performance-based design. In the CEUS, ground motion data for harder bedrock (V_s = 2,000 m/s) is more appropriate than the conventional (V_s = 760 m/s) data. Spectral accelerations caused by small and medium events are on the order of 5-15% of the MCE, on average, for the CEUS, compared to 13-20% of the MCE for the WUS. As a result, serviceability-level ground motions are unlikely to be significant for new buildings. In the CEUS, hazard is often dominated by distant earthquakes and overall duration of ground motion is likely to be longer, inferring that non-ductile structures may be more susceptible to damage.

Current codes allow engineers in moderate seismic regions to ignore seismic detailing as long as they design the structure using R = 3. However, recent research has raised questions regarding the reliability of such systems. When subjected to the maximum considered earthquake seismic hazard, the collapse of these systems becomes inherently dependent on their reserve lateral load-resisting capacity. Several sources of reserve capacity in these structures have been identified: connections in the gravity framing system, connections in the braced frame system, column continuity, base fixity, and brace re-engagement. In this paper, the results of several parametric OpenSees studies are presented in order to evaluate the effect of these sources of reserve capacity in traditional R = 3 systems, with focus on a three-story prototype chevron concentrically-braced frame. Nonlinear, inelastic, static analysis, as well as nonlinear, inelastic, incremental dynamic analysis for a suite of earthquake ground motions was performed. Various limit states for these structures were identified, and failure of the welded connection between the brace and gusset plate was identified as the prominent event affecting collapse performance.

Recent work on the seismic behavior of low-ductility, steel-braced frames has suggested that adding top and seat angles to gravity-framing connections can increase a building's reserve capacity and, hence, its collapse performance. To this end, a comprehensive suite of 133 tests has been developed and is currently in progress to establish a baseline of ultimate capacities under monotonic and cyclic loading. Angles range in size from L4x4x5/16 to L8x6x3/4 and will be fastened using 3/4" A325, 1" A325, and 1" A490 bolts. The distance from the heel of the angle to the bolt centerline in the vertical leg, referred to as the gage, has previously been shown to be an important parameter, particularly in relation to the thickness of the angle. Low gage-to-thickness ratios indicate stocky configurations, while high ratios indicate slender, flexure-controlled configurations. The ratios within this study range from 1.25 to 8.00. Based on the test results, this study aims to develop simple analytical models that can reasonably predict ultimate moment capacities and rotations of beam-to-column connections reinforced with top and seat angles.

Self-centering, concentrically braced frame (SC-CBF) systems have higher drift capacity than conventional CBF systems prior to damage. To fully demonstrate the effectiveness of SC-CBF systems, a comparison study is performed considering both structural and nonstructural seismic performance. First, two prototype buildings are designed with the same configuration, but different lateral load resisting systems (CBF or SC-CBF exclusively). Nonlinear dynamic analysis is conducted using finite element numerical modeling to obtain seismic responses under a suite of earthquake records with various hazard levels. The numerical results are then utilized to build probabilistic demand models of inter-story drift, floor acceleration, and roof acceleration. Finally, fragility curves for structural and nonstructural components are generated for various performance levels with demands and capacities. The comparison of the fragilities of the two structural systems reveals that the SC-CBF has better seismic performance than the conventional CBF; however, nonstructural components must be designed for higher force demands in the SC-CBF.

Low-ductility braced steel frames are widely used in moderate seismic regions of North America. A research project has been initiated to examine the possible benefits of considering the moment resistance of beam-to-column connections in the gravity load-carrying system to provide such braced frame building structures with minimum dependable lateral reserve capacity. Beam-to-column moment connections are constructed using top and seat angles acting together with beam web clip angles. A first test program has been developed to characterize the inelastic behavior of individual angles subjected to monotonic and cyclic demands. Test results are presented to illustrate the influence of several parameters, including the angle geometry and the loading sequence. A second test program has been undertaken to examine the cyclic inelastic response of the proposed beam-to-column joints. The test program is described and joint rotation capacity predictions based on individual angle test results are presented and discussed.

In regions of moderate seismic hazard, the costly structural detailing necessary to ensure adequate ductile performance of a braced frame during an earthquake event can be difficult to justify economically. Structural engineers, however, are permitted to design low-ductility systems if larger demands are assumed. In regions of moderate seismic hazard, this philosophy has proved to be economical and has resulted in widespread use of such low-ductility braced frame systems. Despite this popularity, the inelastic behavior and collapse performance of these systems are not currently understood at a fundamental level. A broadened understanding of the inelastic behavior of low-ductility braced frames can lead to an improved seismic design philosophy and provide practicing structural engineers with a coherent, rational, and transparent design approach applicable to moderate seismic regions. This research aims to identify low-ductility braced frame failure mechanisms and the sequence in which they occur, as well as to draw conclusions on the implications of the observed behavior contextually in building collapse performance.

In low-ductility, concentrically braced steel frames (CBFs) with traditional fillet welds between the gusset plates and slotted HSS braces, fracture of the fillet welds or net section rupture of the tube are viewed as the most likely connection failure modes. After such failure, the braces lose all their tensile strength but may still re-engage in compression to provide some degree of reserve strength to the structure. A test program was recently completed to verify the behavioral limit states and probable re-engagement strength of brace connections. Six specimens with slotted-HSS welded-gusset plate connections were examined in this research. The connection specimens were part of a 9-story prototype building with chevron CBFs located in eastern North America and designed with an R factor of 3.0. The connection specimens were proportioned to exhibit weld or net section rupture failure modes. The tests showed that connections can re-engage in compression after weld or net section rupture when the edge of the HSS slot comes into contact with the edge of the gusset plate. For slender gusset plates, connection buckling occurred due to the eccentricity resulting from unsymmetrical damage modes - such as coupled weld and net section ruptures - before substantial connection re-engagement can develop in bearing.

Although several self-centering seismic systems have been developed, their use in practice has been relatively limited. Complicated or unusual field construction, perceived initial cost premiums, and deformation incompatibility with the gravity framing may be some of the factors restricting their use. A self-centering beam moment frame (SCB-MF) has been developed that mitigates several of these issues. The self-centering beam (SCB) can be shop fabricated with self-contained restoring force which eliminates deformation incompatibility and allows conventional field construction methods. The strength and stiffness of the SCB are decoupled resulting in a cost-effective system that may be competitive with conventional moment frames. This paper describes the SCB-MF concepts, construction and modeling. An upcoming experimental program on two-thirds scale test specimens will also be presented. Computational simulations of the SCB-MF are presented and the results are analyzed.

Post-tensioning (PT) strand systems have been employed in a number of self-centering seismic systems as part of their restoring force mechanism to eliminate residual building drifts following seismic loading. Because of their large elastic deformation capability, PT strand systems have been shown to be effective in these applications. Although typically designed to stay elastic during design basis earthquake events, PT strands can be subjected to inelastic strains during extreme seismic events. Furthermore, the yielding and fracture behaviors of PT strand systems are central to understanding and predicting the collapse behavior of self-centering systems. The loading conditions associated with prestressed/post-tensioned concrete applications are vastly different, and only limited research has explored the behavior of PT strand systems as subjected to inelastic cyclic loading. To better characterize the behavior of PT strand systems subjected to inelastic cyclic loading, a testing program was conducted to investigate important parameters related to self-centering system applications. The testing program consisted of both monotonic and cyclic tests of PT strand systems to failure. Variations in the test configuration included strand obtained from two manufactures, two types of multiple use anchorage systems, and several levels of initial post-tensioning strand stress. Characteristics of the response that were investigated included seating losses, deformation capacity prior to initial wire fracture, additional deformation capacity after initial fracture, and the overall load-deformation behavior. An equation was developed that provides the reduction in PT strand force due to seating losses. Other practical information is also summarized, including suggested strain limits to prevent PT wire fracture.

Modular construction is a relatively new technique where prefabricated units are assembled on-site to produce a complete building. Due to detailing requirements for the assembly of the modules, these systems are prone to undesirable failure mechanisms during large earthquakes. Specifically, for multi-story modular steel buildings (MSBs), column discontinuity coupled with possible high inelasticity concentration in vertical connections can be an area of concern. Diaphragm interaction, relative displacements and rotations between modules, and the way forces are transferred through horizontal connections are other important aspects that are considered in this study. To have an assessment of seismic demand and capacity of MSBs, using OpenSees, three-dimensional (3D), nonlinear dynamic analyses of a detailed, 4-story, MSB structure with 48 modules have been carried out. Since nonlinear analysis is inherently sensitive to ground motion characteristics, Incremental Dynamic Analyses (IDA) have been performed and conclusions have been made to provide a better understanding.

Steel-plate composite (SC) walls are composed of steel faceplates, infill concrete, shear studs bonding the faceplate to the infill, and tie rods linking the faceplates. In new build nuclear power plants, elastic response is sought of SC walls in design basis earthquake shaking and numerical and experimental studies on SC walls have focused primarily on response to design basis loadings. The inelastic response of SC walls for beyond design basis earthquake shaking has yet to be explored and characterized. The experimental and numerical responses of four SC walls subjected to cyclic in-plane loading are summarized in this paper. The walls have an aspect ratio of 1.0 and are flexure-critical. A number of design parameters are investigated, including infill concrete thickness, reinforcement ratio, stud spacing, and tie bar spacing. Numerical models of these walls are constructed using the general-purpose finite element code LS-DYNA. The numerical analyses, and key experimental results are presented.

Shear walls are the primary lateral load-carrying elements in tall buildings. The steel plate-concrete composite shear walls have good advantage in mechanical properties for the combined effect of two kinds of materials. It is composed of two steel plates with studs inside, side columns made of steel tube and an infill of concrete. This paper focuses on the effective stiffness and the ultimate loading capacity of the composite shear walls. Many design practices currently deal with shear stiffness by employing a stiffness reduction factor. In this paper, however, a plane combination truss model (PCTM) is built for effective shear stiffness of the composite wall based on the theory of fixed angle truss model. The formula for calculating the effective shear stiffness of the composite shear wall is derived based on the model. A numerical model for elasto-plastic analysis of the composite wall is built to find the key factors for the effective flexural stiffness subjected to axial force and bending moment, the simplified design formulae for which are obtained based on the parameter analysis. The effective stiffness is obtained by combining the flexural stiffness and the shear stiffness. The predictions of effective stiffness correlates well with experimental results of a series of composite shear wall specimens.

Modern structures are increasingly being constructed ever more slender and with longer spans between columns. These aesthetically pleasing designs, however, are more susceptible to high levels of vibration caused by their human occupants. This has led to research into technology, such as active vibration control (AVC), that can significantly reduce vibrations whilst maintaining the slender structural form. Previous research in the area of AVC for human-induced vibrations in floors has focused on single points where the control is located. This paper investigates the effect over the entire area in a multi-panel floor. Simulations are performed on a finite element model of a real office floor with a realistic walking force applied, simulating the in-service conditions of an office environment. The power demand of the active control system is then investigated, in particular, consideration of the trade-off between performance increase and power demand reduction. The benefits of using high feedback gains to control the entire area of this multi-panel floor are shown to be limited. Subsequently, power and cost savings could be realised through the use of reduced gain and/or a switching-off rule.

Topology optimization methods have recently been used as a tool for conceptual tall building design. These techniques were originally developed in a deterministic setting despite the inherently uncertain nature of the real-world environment. If uncertainties are neglected during the design process, there is a possibility that the final constructed designs may perform unsatisfactorily. Thus, it is necessary to account for uncertainties affecting the problem, including stochastic environmental loads and time-invariant uncertainties. Furthermore, the dynamically sensitive nature of tall buildings must be considered during the design process. This paper presents a methodology for the topology optimization of tall buildings in this setting using a framework based on the PEER Equation. A novel decoupling approach is developed that defines approximate sub-problems that can be solved using established topology optimization techniques. The successive resolution of the sub-problems until convergence results in an optimal design that satisfies the original performance constraints. A case study is used to demonstrate the validity of this framework.

In the pursuit of a highly efficient high-rise structure, structural engineers have been developing new systems. Almost all of these techniques involve use of the entire width of the building. Legacy systems - such as outriggers, belt trusses, and perimeter braces - provide efficient systems, but they have an impact on the ductility, redundancy, and uniformity of the stiffness of structure. In regions of high seismic activity, the cost of adopting such legacy systems can be significant in terms of structural and architectural efficiency. The design team for Shum-Yip Tower One developed a structural system which allows for maximum architectural flexibility without compromising efficiency of the structure. This system has been named the Ladder System. The architectural requirement of unobstructed views has resulted in fewer perimeter columns. Gravity loads at the perimeter are directed through eight mega-columns; the resulting higher gravity loads have eliminated tension due to overturning. This gravity system is instrumental in the success of the Ladder System.

Several practical tools for the characterization of the optimal layout of material in a structure have been developed in recent years based on both numerical and analytical approaches. Within the numerical methods, discrete and continuum methodologies have been successfully used in a variety of applications. This paper describes an integrated topology optimization framework using discrete and continuum elements for buckling and stiffness optimization of high-rise buildings. The focus of this work is on linearized buckling and stability as objectives. Examples are discussed to illustrate the proposed methodology for high-rise building design.

Slender monumental stairs are major architectural features in hotels, condominiums, hospitals, and other high-end building structures. Architectural requirements for these are usually very aggressive, with long spans and slender stringers being the norm. Slender stairs often have fairly massive treads and guardrails which, combined with slender stringers, results in natural frequencies within reach of the very large lower harmonics of the force caused by a person descending the stair. Stair designers must be able to predict the vertical vibration response of a stair during the design phase. Current prediction methods rely on finite element analysis-based response prediction methods which are outside the reach of many structural engineering firms. This paper presents a simplified response prediction method based on the fundamental natural mode of the stair, which is suitable for manual calculations. Response predictions are compared to experimental measurements to show that the predictions are accurate enough for design use.

A 40%-scale reinforced concrete coupled core wall structure with novel unbonded post-tensioned coupling beams was recently tested under quasi-static reversed-cyclic lateral loading combined with tributary gravity loads. This paper provides an overview of the design, analysis, and testing of this specimen. The specimen represented the most critical bottom three stories of an 8-story prototype structure consisting of two C-shaped wall piers, six post-tensioned coupling beams, tributary post-tensioned slabs at each floor, and the foundation. The less critical upper stories of the prototype structure were simulated analytically to impose lateral forces, axial forces, and overturning moments at the top of the laboratory specimen. Overall, the structure performed as predicted and validated the design approach, which was conducted for a maximum roof drift ratio of 3% for the full 8-story structure. Strength loss during the final cycles of the test was largely caused by the fracture of the vertical reinforcing bars in the wall pier toes at the base. The post-tensioned coupling beams performed well, demonstrating the advantages of the new system.

Discontinuities in FRP retrofit laminates used to increase the in-plane shear capacity of concrete slabs (diaphragm shear) could introduce a serious interference in the anticipated load path. Discontinuity may occur where the continuity of laminates is interrupted due to the presence of other structural members. In the case of multi-span reinforced concrete slabs retrofitted from below, discontinuities in the FRP system occur where beams are intersected. A novel anchoring system was successfully developed and tested to introduce an effective means of connecting the FRP system to the substrate and creating continuity across the beams in multi-span reinforced concrete slabs. This innovative anchoring system was implemented in a seismic retrofit project to enhance the in-plane shear capacity of third floor and roof slabs in a high revenue telecommunication center. The proposed anchoring scheme ensured the continuity of the retrofit system and therefore created a viable load path for diaphragm shear forces.

This paper presents the application of advanced seismic design methods and technologies to achieve enhanced seismic performance objectives for the New San Diego Central Courthouse project. The building superstructure consists of a cost-effective, steel-framed superstructure with two-way lateral special moment-resisting frames utilizing ductile reduced WF beam section "RBS" connections with WF cruciform and built-up box column sections. The steel moment-resisting frames incorporate 106 nonlinear viscous damping devices to provide a distributed supplemental energy dissipating damping system over the height of the structure to reduce seismically-induced building story shears, story drifts, floor accelerations and inelastic rotational demands on moment frame beam-column joints. This paper is intended to document the enhanced seismic performance objectives in the application of advanced seismic design methods and technologies to share with a broad audience in achieving resilient and sustainable structures systems in regions of high seismicity. It describes the step by step approach to selection of the final lateral system for the project.

Vibration serviceability assessments were carried out on the floors of several "units" of an industrial complex in Singapore. Floors tested were within large, two-level, structural units described as detached, semi-detached and terraced and having usable single floor areas up to 2100 m². All floors were constructed from hollow core slabs with spans up to 12 m and all nominally behaved as high frequency floors. Occupancy conditions ranged from empty and untenanted to usage for warehousing, instrument assembly and testing, electronic equipment manufacture to light manufacturing and machining of metal structures. Forms of loading included internal and external vehicles, human footfalls and excitation by machinery. The study identified the most onerous form of loading and provides guidance for facility owners with mixed vibration serviceability requirements.

The lack of clear guidance regarding the value of elastic flexural rigidity (EI) that should be used in the analysis of steel-concrete composite columns is a significant unresolved issue that hinders the design of frame systems that include these members. The common approach of utilizing the rigidity of either the steel or the concrete only tends to be overly conservative. Other approaches that combine the rigidities have not been fully validated for use in strength and stability design procedures or for the determination of lateral deflections. To address this issue, research has been conducted to develop comprehensive recommendations for the elastic flexural rigidity of composite columns. A complimentary goal has been to validate common strength design procedures - including interaction diagrams, axial compression and bending moment anchor points, and analysis procedures - to determine required strengths. In this paper, an assessment of current strength design methodologies is presented along with recommendations for potential improvements. Both the AISC Direct Analysis method and the ACI elastic second-order analysis method are investigated.

This paper presents a method to evaluate plastic deformation capacity of welded beam-to-column connection used for moment frames until ductile fracture due to cyclic loading with varying deformation amplitudes. Constant deformation amplitude loading tests were conducted to investigate the relationships between deformation capacity until fracture and deformation amplitude. From test results, the crack propagation is formulated as the function of number of cycles and the deformation amplitude to evaluate the damage to the welded connection of a beam flange. In order to verify validity of the proposed crack propagation formulation, varying deformation amplitude loading tests were conducted. From test results, it is found that the deformation capacityaffected not only the amplitudes but also the orders, which indicates that the Miner rule is not suitable for the prediction of fracture with varying deformation amplitude. The proposed formulation well evaluates damage and simulates crack propagation until fracture.

Gusset plates are used in steel buildings and bridges to connect diagonal members to other members in the structural system. In design, gusset plates are currently modeled as rectangular columns with an effective cross-section defined by a 30° stress trajectory. The buckling strength is calculated using a standard column curve with empirical effective length factors. Previous tests showed that local yielding allowed the stresses to redistribute and create a wider stress trajectory. Because slender gusset plates cannot redistribute stresses without buckling, a variable stress trajectory has been established, which is dependent on the lateral buckling slenderness parameter. This paper describes an improved method to calculate the buckling strength of gusset plates using variable stress trajectory angles. The effective length factors used in design were also evaluated, and revised values were proposed. The design model is valid for single- and double-plane corner gusset plates in steel buildings and bridges, including extended corner gusset plates commonly used for seismic design. Compared to the results of 159 specimens from 15 previously-published research projects, the design model is reasonably accurate.

Even though partially-restrained, bolted, beam-to-column connection systems are not explicitly certified to be used for moment resistance in current building specification jurisdictions, they represent a promising solution in modern steel moment-resisting frames (MRFs), showing their significant potential to be able to mitigate some of the major drawbacks inherently related to the geometry of welded connections. In order to quantify the influence of this attractive solution, applicable both to new construction and to the retrofitting of existing structures - on the global response of whole MRF buildings under seismic loads - a numerical procedure, based both on refined three-dimensional solid and one-dimensional fiber-based finite element (FE) models, has been developed and validated using past experimental results. This validated numerical approach has been used to assess the seismic performance of T-stub connection systems within entire MRFs, in comparison with the response of other top-and-seat angle joints. A series of conventional and adaptive pushover and incremental dynamic analyses, accounting for material and geometric nonlinearities, has been carried out to quantify behavioral changes as a consequence of geometric variations in the connection system.

Low-rise metal building systems are widely used in the United States and worldwide as complex production facilities and warehouses, retail stores, shopping centers, schools, libraries and medical facilities for their cost effectiveness, easy fabrication and quick turnaround times. In most cases, the current practice is to assume zero rotational stiffness ("pinned") for the base-plate-foundation connection of web-tapered columns in low-rise metal buildings for both serviceability and strength design. The underlying reason for this assumption is the lack of design guidelines and experimental data. On the other hand, prior research indicates that this approach may result in a significant underestimation of the rotational stiffness of the connections, thereby increasing the cost of the structure. The objective of this paper is to study the rotational stiffness of column base-plate connections in low-rise metal building systems through testing of eight full-scale base-plate connections with varying base-plate dimensions, number of anchor rods, anchor rod diameters, gage distances, and tapers of the column sections.

This study aims to quantify slab contributions in eccentrically braced frames (EBFs) by investigating the dynamic performance of two 3-story EBF configurations with and without concrete slabs — one configuration having long (flexural yielding) links and the other having shorter (shear yielding) links. Particular effort is spent investigating the relative accumulation of ultra low-cycle fatigue damage within the link regions during dynamic loading. All slab and major frame geometries are modeled using shell elements. Linear springs and nodal constraints model the discrete slab-to-beam interactions. Recorded earthquake ground accelerations, scaled to design-level intensities, load the EBFs. Ultra low-cycle fatigue damage is investigated using a calibrated micro-mechanics-based ductile fracture model. Results indicate reduced system-level frame demands (inter-story drift, residual drift, and link rotation) due to increased system stiffness from the concrete slabs. Reductions in these demands were larger for EBFs with long (flexural yielding) links as compared to the short (shear yielding) links. Even with reduced rotation demands, EBF models with slabs sustained similar link fatigue damage (as compared with the bare-steel models) due to increased plastic strain demands, presumably from a neutral axis shift.

Multitier concentrically braced frames (MTCBFs) are often employed as the lateral force-resisting system in structures where a tall, single story is required. To create an MTCBF, a braced frame is subdivided into a series of tiers with intermediate struts. Out-of-plane bracing is not provided at the tier levels, however. Prior studies on the seismic behavior of MTCBFs demonstrated that frames designed according to contemporary seismic provisions are susceptible to inelastic drift concentration within a single tier. Concentration of inelastic drift may lead to brace fracture and in-plane flexural yielding of the columns. In this study, three-dimensional finite element models of full MTCBFs were used to investigate their seismic behavior. Results from static pushover and nonlinear response history analyses revealed that the gusset plate connections at the tier levels aid MTCBFs in preventing inelastic drift concentrations and flexural yielding in the columns. Nevertheless, refinements to existing seismic design provisions appear necessary since excessive panel drifts were observed.

Thin cold-formed steel (CFS) structural members in building construction can be designed using one of several approaches: the "effective-width" plate buckling concept, the Direct Strength Method, or through implementation of a full finite element analysis. While a finite element analysis gives the most complete picture of member behavior, the effort involved in its use and implementation often limits its use to academic or forensic applications. Traditionally, CFS members have been designed using the effective width approach, but the development of the Direct Strength Method (DSM) represents an exciting new tool for use in determining cold-formed steel member capacity. As the steel building industry adjusts to DSM and finite strip analysis, knowledge of how members are analyzed and how strength is determined using this process is critical in giving the practicing engineer the tools to judge the appropriateness of a given computer-based solution for the actual conditions. The goal of this paper is to introduce the practicing engineer to the concepts behind finite strip analysis and show how its results are employed in determining strengths using the Direct Strength Method.

Experiments are performed to validate the American Iron and Steel Institute's Direct Strength Method (DSM) for cold-formed steel design applied to a unique, thin-walled, 3-radius, cold-formed steel oval tube. The tube segments make up a structural system for long span domes with surface areas over 20,000 m². While it is expected that the dome design will be governed by overall global buckling under dead load, the compressive strength of the individual tubes experiencing local buckling is also checked. Strength prediction methods are limited for thin-walled steel tubes, especially for non-rectangular cross-sections, leaving engineers with few validated approaches for predicting axial capacity including local buckling. Stub column experiments are conducted to evaluate local buckling behavior and tested capacities are compared to DSM predictions employing finite strip elastic buckling analysis. It is confirmed with elastic buckling studies and the experiments that local buckling tendencies are reduced with radial curvature.

A seismic design strategy is presented to design the columns of multi-tiered steel braced frames. Minimum strength and stiffness requirements are introduced for the columns under the seismic loads. The proposed method aims at reducing the concentration of ductility demand in one of the tiers and, thereby, the in-plane bending moment demand on the columns and the ductility demand on the bracing members. Nonlinear static and dynamic analyses are performed to validate the design procedure. Moreover, detailed finite element analysis is carried out to investigate the stability of the columns. The results show that the proposed design method can efficiently reduce the column in-plane flexural demand and the brace ductility demand.

This paper presents an experimental investigation on the behavior and performance of the cold-formed steel (CFS) framed shear walls sheathed with a composite panel which contains a 0.0686-mm (0.027-in.) steel sheet and a 15.9-mm (5/8-in.) gypsum board bonded together. The shear wall framing configurations were selected to be suitable for mid-rise buildings. Both monotonic and cyclic tests were conducted and the research was focused on the seismic performance. It was found that the composite panel provided considerably higher shear strength than the traditional wood-based sheathing and the 0.838-mm (0.033-in.) steel sheathing. The composite panel demonstrated a similar failure mechanism and post-peak behavior as the steel sheet sheathing. It is concluded that the tested composite panel is a suitable structural sheathing material for mid-rise buildings, particularly the Type I and II constructions, in seismic areas.

This research studies the wireless strain sensing performance of a slotted patch antenna sensor. In our previous work, a folded patch antenna was designed for passive wireless strain and crack sensing. When experiencing deformation, the antenna shape changes, causing shift in electromagnetic resonance frequency of the antenna. The wireless interrogation system utilizes the principle of electromagnetic backscattering and adopts off-the-shelf 900MHz radiofrequency identification (RFID) technology. In this research, a new slotted patch antenna sensor is designed and tested. The antenna detours surface current using slot patterns so that the electrical length is kept similar as previous folded patch antenna. As a result, the sensor footprint is reduced and the antenna resonance frequency is maintained within 900MHz RFID band. To accurately describe both mechanical and electromagnetic behaviors of the antenna sensor, a multi-physics coupled simulation approach is pursued. Implemented through a commercial software package, COMSOL, a multi-physics finite element model of the antenna uses the same geometry and meshing for both mechanical and electromagnetic simulations. Wireless strain sensing performance of the antenna is first simulated using the multi-physics model. In addition, experimental tensile tests are performed to investigate the correlation between wirelessly interrogated resonance frequency and the strain experienced by the antenna. The strain sensing performance is tested.

Elevated water tanks are generally located at higher elevations within a particular geographic area. The locations and height of these structures often makes them desirable for siting wireless and cellular communications antennas. The impact of this practice on the long-term serviceability performance of the primary structure is not clear and could be an important consideration deserving further analysis. This paper presents a case study on the structural identification of an elevated water tank that was motivated by this particular consideration. The structure had been retrofitted with cellular antennas during its service and later experienced fatigue cracking at the fill pipe-tank interface. The owner wished to determine if the addition of the cellular antennas had contributed to this damage. This paper presents a structural identification program that was implemented to develop a calibrated FE model suitable for evaluating the source of the damage. The water tank was characterized by ambient vibration testing under different operating conditions, including wind speeds and water levels, and the impact of these conditions on the behavior of the water tank and the calibration of the FE model are discussed.

Structural topology optimization is increasingly being used to generate design ideas for efficient structural systems (including gravity and lateral systems) for buildings. The optimization objective is typically to minimize weight (material cost), or to maximize performance subject to a fixed system weight. While useful for generating design ideas, this falls short of actual structural design objectives as it neglects constructability of the structural system, which is typically the primary governing cost in the construction of structures. This paper summarizes new advancements for addressing constructability objectives and constraints in topology optimization, moving towards design for minimum total constructed cost. These include treatment of standardized patterns, member orientations, and integer design variables. These ideas are presented in the context of truss and frame structures, and in optimizing rebar schedules in reinforced concrete design. While quantifying these costs remains a challenge, the presented tools provide a means for exploring the design space as a function of material and construction costs.

This paper presents a conceptual framework of how some recent efforts aimed at using data gained from automated and robotic structural sensing systems can be incorporated into Building Information Modeling (BIM) systems leading to a comprehensive, intelligent structural health management system. Robotic and similar automated systems may extend the reach of structural sensing systems to realms and modes that are impractical with other systems. This paper begins with a brief discussion of the operational principles of the following automated inspections systems: (1) Multisensor assessment of concrete corrosion damage; (2) Low-cost high-quality image processing for structural condition; (3) Quadcopter UAV for remote imaging of structural condition; (4) Suction foot robot for climbing on brick and concrete walls; (5) Wheeled robot with active stereo imaging system that measures structural shapes; and (6) Lidar imaging system with integration into BIM. These systems carry onboard sensors, such as 3-D optical imagers and ground penetrating radar. Issues when using these systems include: (1) Position registration and navigation; (2) Sensing system performance and operational procedures; (3) Safety; and (4) Intelligent integration of sensing data into structural database. The present state of the art is that these types of systems work reasonably well and can generate large data streams that quickly overwhelm manual management methods. A possible path of automated data management is to tie the data directly to a structural database. BIM is presented as a potential framework for data integration, synthesis, retrieval and rapid display of data in graphical formats tied to the structure, in a level of detail hierarchy.

This paper primarily presents a comparison of traditional and advanced sensing techniques in the field of structural health monitoring for use in damage detection in reinforced concrete (RC) structures. The accuracy of these methods is evaluated through standard laboratory tests on concrete cylinders. Furthermore, a damage detection method for RC structures is introduced where strains measured from densely clustered sensors are used to develop damage sensitive features. This method is verified through simulation data from a fiber element model of a new earthquake resistant RC coupled shear wall system. A large scale specimen of this system with a dense network of embedded strain gauges, displacement and rotation transducers, as well as digital image correlation systems was recently tested. The data collected through this experiment will be used to experimentally validate the proposed damage detection method.

This paper presents a heuristic algorithm for discrete design optimization. Practical applicability is the first concern; special attention is therefore paid to the implementation of buildability constraints. The method is used in this paper for the optimal design of a Warren type truss composed of steel CHS members with welded joints. For each member, the optimal section is chosen from a given steel catalog. Following Eurocode 3 and the CIDECT design guidelines, restrictions are imposed on the deflections, the member forces, the layout of the joints, and the joint forces. The buildability of the design is ensured by requiring all top chord members and all bottom chord members to have the same outer diameter. Practically all methods that have recently been proposed for this type of optimization problems are based on evolutionary computing. However, these methods are slow, and they involve algorithmic parameters that require careful tuning. A new algorithm is therefore proposed in the present paper, based on the optimality criteria method. The algorithm is faster than an evolutionary method and free of tuning parameters. It is successfully applied to the example truss design optimization problem.

Launched bridges are a usual typology for medium span length up to approximately 100 m. An important device in this construction procedure is the launching nose, a steel structure located in front of the deck and intended to decrease the bending moments of the cantilever portion of the bridge during launching. The research conducted by the authors on this type of structures was aimed to decrease the amount of material and, thus, the cost of the bridge. Two different problems were tackled. First, the length of the launching nose was chosen as the objective function with the aim to diminish the bending moment in the bridge. Secondly, an optimization problem was defined considering both the length of the launching nose and the internal dimensions of bridge deck as design variables and defining the weight of the bridge and the launching nose as objective function. To make it easier for practitioners to deal with this design procedure, a graphical interface was written and is also presented.

Facade bracing systems are applied all over the world in structural design to limit deflections and guarantee stability. Efficient distribution of bracing over a structure is an important concern for structural design professionals and is often based on intuition and previous experience. Meanwhile, the limited amount of academic research on this topic often focuses on one aspect of the design, neglecting the practical design process itself. This research presents a topology optimization procedure for cable bracing of the hanging steel facade of a new museum in the United States. In this procedure, the use of a multiobjective genetic algorithm allows for flexibility during design modifications and accounts for uncertainty of deflection constraint values. Since the allowed position of the cables is limited and only certain standard cable sections can be used, the design variables are discrete and the cost function is easily defined. The presented method achieves practical solutions to a series of cost-minimizing problems, giving the designer a range of optimal bracing configurations which can be selected in response to the continuously changing structural and architectural requirements throughout the design process. The application of the method to the design of the museum facade demonstrates the strength of the proposed approach. This research aims at stimulating discussion on optimization methods which are capable of taking the design process into account, and the possibility of using multiobjective optimization to deal with these practical design uncertainties.

Advancements in sensing and data acquisition technology have made monitoring of infrastructure more affordable and, at the same time, more comprehensive. Examples of such advancements are application of wireless technology for communication, automated systems for long-term monitoring, and remote control of the sensing networks. These advancements have assisted in alleviating many challenges in application of traditional structural health monitoring (SHM) systems. As a result, with minimal efforts, reliability of existing structures can be achieved through measurement and assessment of the structure's response. This paper presents application of combined wired and wireless sensor networks -which benefit from advantages of both systems - in performance evaluation of an in-service, 16-story building structure that is suffering from perceptible vibration in different directions and different locations. A broad range of structural responses - including acceleration, displacement, strain, wind speed and wind direction - are measured/recorded in this work, and the dynamic behaviour of the structure is investigated. This investigation includes identification of the vibration propagation in the building (its path and attenuation trend) along with development of the finite element model of the building structure for prediction of the structure's response at different locations. The information obtained in this study is used to evaluate potential mitigation strategies for maintenance and serviceability of the building in its future operation.

Various research studies have been carried out to improve wireless structural monitoring. The improvements can be categorized into two general categories: data processing (software) and sensors technology (hardware). Advances in data processing offer new strategies for analyzing the data while novel sensor technologies mostly solve the challenges in power consumption and data transmission. These hardware challenges may also be affected by improvements in the data analyzing process which can help in reducing the quantity of data that needs to be transferred and significantly decreases the power consumption. In this study, the random decrement (RD) technique along with the Ibrahim Time Domain (ITD) method were evaluated for modal identification of structures through both wired and wireless sensors. This paper shows how smaller segments of data can be used for extracting the modal properties with similar accuracy. A simple laboratory beam test was performed to compare the data from co-located wireless and wired sensors in the time-domain. Then, the modal identification of the beam through RD and ITD method shows the comparison between wired and wireless structural identification. Additionally, this study investigates the capability of the wireless sensors in providing accurate modal parameters through different data analyzing processes and system identification techniques under actual field conditions. These techniques were used for structural identification of a bridge located in Perry, Utah. The performance and capability of these methods were evaluated and show that detecting the modal parameters of a bridge can be achieved by not transmitting the entire collected package of data.

The ability to accurately measure bridge deflections is an important aspect of bridge monitoring and maintenance, both in the US and internationally. Static deck deflections are used to provide load ratings while dynamic deflection measurements may be used to track changes in the dynamic behavior of the bridge due to environmental, loading, and condition changes. Directly measuring bridge deflection has proven challenging, requiring either a fixed reference point or the use of non-contact laser sensors. This presentation introduces wireless, continuous wave radar sensors developed for bridge monitoring applications. The small, bridge-mounted sensors provide a practical and low-cost solution for a range of measurement conditions. As the bridge moves, the radars send a continuous wave that is reflected by a stationary target (either the ground below or a fixed transponder, depending on the application). The reflected signal contains the information necessary to extract the bridge motion. While the theoretical operation is straightforward, there are challenges associated with signal demodulation and data processing in the presence of noise due to interference or long detection ranges. Characterization of the static and dynamic performance of the radar is presented, as well as guidelines for their practical application. The audience of this presentation will be both researchers and practitioners working to improve bridge inspection and monitoring practices. Specifically, the audience will learn about a novel technology to improve bridge testing, gain an understanding of the advantages and challenges of applying radar technology to structural monitoring, and be presented with strategies for achieving a network of distributed radar sensors to capture bridge responses.