Structures Congress 2006: Structural Engineering and Public Safety

The 2005 AISC Specification and its accompanying Manual of Steel Construction, 13^th Edition, incorporate many changes in the design of connections. Many of the changes in the 13^th Edition Manual make connections and therefore steel fabrication more economical. Among these are: (1) the removal of arbitrary minimum loads, (2) increased weld strengths based on direction of loading, (3) use of the plastic section modulus (This represents a 50% increase in bending capacity), (4) minimum fillet welds based on the thinner part joined, (5) column stiffener welds no longer required to develop the strength of the stiffener, (6) shear yielding strength increase over previous LRFD Manuals, (7) plate buckling strength increase over previous LRFD Manuals, (8) greater net section strength for bolted moment beams, (9) use of F_u instead of F_y in prying calculations, (10) elimination of eccentricity in most standard shear tabs, (11) improved design procedure for extended tabs, which eliminates the need for top and bottom stiffeners, (12) reduction of weld for shear tabs from 3/4 of the plate thickness to 5/8 of the plate thickness, and (13) the U factor used with shear lag calculation will be increased for "long" connections. A few changes will make connections and therefore steel fabrication less economical. Among these are: (1) reduced strength of slip critical connections when oversized holes are used, (2) in some cases block shear capacity will be reduced, and (3) the U factor used with shear lag calculation will be decreased for "short" connections.

Seismic isolation allows the engineer to control damage in moderate and large earthquakes for both a building and its contents using low-cost structural systems. At the present time, there are several types of isolation system in use, many variants of existing systems are being developed, and new systems are being proposed and investigated. The most widely adopted system uses elastomeric bearings that decouple the building or structure from the horizontal components of the ground motion by interposing the structural elements with low horizontal stiffness between the structure and the foundation. This soft layer gives the structure a fundamental frequency that is much lower than both its fixed-base frequency and the predominant frequencies of the ground motion. One of the factors limiting further seismic application of bearings has been a general lack of knowledge regarding the buckling behavior of this type of bearing. The buckling of multi-layer elastomeric bearings under compression loads is a reasonably well-understood phenomenon. What is not well known is that theoretical buckling analysis for compression predicts that the isolator can buckle in tension at a load close to that for buckling in compression. The explanation of this rather counter-intuitive behavior is that the deformation in tension or compression is mainly shear and shear is inherently symmetric. The linear elastic model that leads to both compression and tension buckling is an extremely simple one and it might be argued that the tensile buckling may be an artifact of the model itself and not of the isolator. For this reason, the results of this simple model have been verified by a numerical simulation, using a finite element model of a multi-layer elastomeric bearing. The paper presents the major findings of the numerical analysis for the buckling of elastomeric bearings. The theoretical results are compared with a finite element analysis conducted on numerical models with various shape factors. The rubber material in the numerical models is assumed incompressible or almost incompressible and can undergo large deformations when the stress-strain relationship becomes significantly non-linear. The study shows that the prediction of tensile buckling by the simple linear elastic theory is, in fact, accurate and not an artifact of the model. The numerical study not only confirms the theoretical prediction but also shows an excellent correlation between theoretical and numerical buckling loads in both compression and tension and with other aspects of the behavior of multi-layer elastomeric bearings in tension and compression.

Analytical investigations were undertaken to assess the seismic performance of a hospital building located in Southern California in seismic zone 4. The structure consists of a eight-story steel, and a bottom story reinforced concrete superstructure constructed over four levels of sub-grade parking stories. The building is rectangular, is 125 ft tall, and has total floor area of 130,000 ft². Steel and concrete moment-resisting frame along the grid lines of the building provide resistance to lateral loading. Project-specific design guidelines and FEMA, and SAC guidelines were used for evaluation. A comprehensive three-dimensional mathematical model of the structure was prepared. Nonlinear response history analysis of the existing building revealed that the performance was inadequate. In particular, story drifts and member nonlinear flexural rotations exceeded the limits specified in the design guidelines. The building rehabilitation consists of adding fluid viscous damper frames to the exterior faces of the building. The structure was then re-analyzed in the new configuration, and its performance was satisfactory.

Shape memory alloy (SMA) wires in their superelastic (austenitic) form are studied under a variety of loadings in order to evaluate their use in structural earthquake engineering applications as passive control devices. Past studies of superelastic wires have shown that SMAs have the ability to provide both recentering and supplemental damping at strain levels and strain rates consistent with a seismic event, but few experimental tests have been conducted to determine the optimal way to implement them into structures and how the mechanical behavior is affected by different types of earthquake loadings. The effect of mechanical training, pre-straining, and loading under both far-field and near-field type loading protocols on the forward transformation stress (loading plateau), residual strain, and equivalent viscous damping is explored. Mechanical training of SMAs is shown to stabilize NiTi properties. The optimal pre-straining of SMAs is explored to determine the strain level which provides the highest levels of supplemental damping. Finally, the effect of different loading protocols representing both near-field and far-field type motion on the properties of NiTi SMAs is studied to determine how large early strain cycles versus a gradual increase in strain level effects the behavior of NiTi. These results provide evidence of the ability of NiTi SMAs to improve the response of structures undergoing seismic events and suggest some ways to optimize this response based on the tensile properties of NiTi wires.

Building code provisions for the seismic resistant design of structures incorporate two basic types of requirements. The first of these is very similar to the code requirements for most other types of loading and comprises specification of minimum permissible strength and structural stiffness. The second is unique to design for seismic resistance and consists of prescriptive criteria on the detailing practice for the structural elements. While strength and stiffness requirements have been part of building codes for nearly 100 years, these detailing practice requirements, which include such things as prescription of the volumetric ratio and spacing of reinforcing in concrete structures, and permissible width/thickness ratios for elements of members in steel structures are a recent addition to the code. They were first introduced into the codes in the late 1960s and primarily affected the design of reinforced concrete structures. However, as researchers have continued to understand the importance of detailing to seismic performance and actual earthquakes have made clear to the profession that poor detailing practice directly leads to adverse structural behavior, the volume and complexity of these detailing requirements has steadily increased. AISC established a new ANSI standards committee, known as the Connection Prequalification Review Panel, in 2002 specifically to develop a standard containing pre-qualified connections and corresponding design procedures for critical connections in moment-resisting frames and eccentric braced frames designed under the AISC Seismic Provisions. Meanwhile, the American Welding Society commissioned Subcommittee 12-Seismic of its D1.1 Standards Committee, specifically to develop a seismic supplement to the D1.1 Structural Welding Code. As a result of these efforts, two new standards, AISC 358 and AWS D1.8 have just been published. The new AISC 358 connection prequalification standard contains design and detailing requirements for three types of moment-resisting connections: reduced beam section connections (Figure 4); unstiffened extended end plate connections (Figure 5); and stiffened extended end plate connections (Figure 6). Although it does not presently include several of the other pre-qualified connections contained in FEMA-350, it does significantly expand the limits of application for the connections that are included.

The American Institute of Steel Construction (AISC) document "Seismic Provisions for Structural Steel Buildings", has become the reference document for seismic design of steel structures throughout the United States. Since its initial publication in 2000, the International Building Code has incorporated these provisions by reference. Since their 1997 publication, the AISC Seismic Provisions have been updated on a regular basis in order to incorporate new developments from the FEMA/SAC project on moment frames and other work in this area. The latest revision culminated in 2005 with the publication of a completely new set of provisions that is in the same unified format as the main AISC design specification. In addition, this edition adds two new structural systems (Buckling Restrained Braced Frames and Steel Plate Shear Walls) and makes reference to a new AISC standard for the pre-qualification of seismic moment connections that was also completed in 2005. Major improvements to the quality control sections, based on FEMA 353, are also included for the first time. Coordinated efforts between AISC, ASCE-7 and the Building Seismic Safety Council (BSSC) will continue the process of keeping the seismic design provisions for structural steel buildings as current as possible. This paper will summarize the changes incorporated into the 2005 AISC Seismic Provisions and the use of the new moment connection pre-qualification standard.

A wind tunnel study to investigate wind pressures on single and multi-span saw-tooth roofs for a 1:100 geometrical scale model of a low-rise building was carried out in atmospheric boundary layer wind tunnel at the Wind Load Test Facility at Clemson University. The purpose of this investigation was to further investigate wind loads on low rise buildings with mono-sloped and saw-tooth roofs and study the validity of ASCE 7-02 specification on these buildings. By using larger models and a higher density of pressure tap than in previous studies, a greater resolution of the pressure variations was achieved. The paper presents representative results of the study that includes point and area-averaged wind pressure coefficients on models with varying spans and building heights. Local peak pressures and area-averaged pressures obtained in this study are compared with the design values specified in ASCE 7-02 and with results of previous wind tunnel studies. The results presented showed no significant difference in wind pressures between the windward span of the saw-tooth roof and the mono-sloped roof. Comparing results with ASCE 7-02 suggest that the current wind design provisions for mono-sloped roofs may be un-conservative.

This paper presents the methodology and results of an ongoing study of the performance of residential structures in the State of Florida. Site built single family homes constructed after Andrew-related changes to the standard building code were in effect were targeted for a detailed investigation of wind damage as a result of the 2004 hurricane season. The purpose of this study is to provide a quantitative statistical comparison of the relative performance of homes built between 1994 and 2001 with those built after the 2001 Florida Building Code replaced the Standard Building Code.

Contemporary wind load standards and codes of practice have placed an ever-increasing emphasis on the detailed determination of pressure coefficients appropriate for the design of low buildings of various shapes. In contrast, the evaluation of the upwind exposure is rather rudimentary, although its influence on the design wind loading may be at least as critical. Problems and discrepancies have been found in the provisions of exposure factors (Ce) when comparing different national wind standards and codes of practice, as well as when examining experimental findings in relation to code predictions. For instance, the minimum fetch length of suburban exposure required for equilibrium of wind speed profile is 460 m or 10 building heights, whichever is larger, as per ASCE 7, but 1500 m in the Canadian code NBCC 1995 (note the just released NBCC 2005 has modified this to 1000 m or 10 building heights; it also allows some interpolation of Ce values for upwind terrain patches greater than 50 m.) Problems have also been found in application of current Ce provisions for design in case of complex terrain or inhomogeneous extreme exposure. These problems may be attributed to the fact that the current codification approach is based on the assumptions that low building wind loads are well predictable with explicit analytical relationships of terrain roughness, wind speed and pressure coefficients. Roughness patches of different distance to site are considered of equal importance (as long as within a cut-off fetch length from site). Those assumptions appear to be oversimplified. The current analytical models may not predict well wind speeds at close-to-ground levels, i.e. `roughness sub-layer' [Raupach et al]. Moreover, those assumptions do not account for the turbulence loading effects which have not been fully understood yet. Wang and Stathopoulos noticed that patches of different distance to site have different strengths of impact. A wind tunnel study has been carried out investigating the low building wind load variation above different terrain configurations with particular attention to small-scale roughness changes close to site. It was found that the peak wind loads are dominated by the terrain configurations in a short distance upwind the site. This paper presents key results of this study and compares them with the ASCE 7 provisions for low buildings.

High mast lighting structures are being increasingly used to provide illumination for large intersections, particularly for highways located in rural areas. These structures, ranging from approximately 50 – 130 ft (15 – 40 m) in height, are exposed to high wind forces that in turn produce a tremendous number of loading cycles each year. A recent high mast lighting structural support failure in the high plains of Colorado near Denver International Airport served as the impetus for this study. Specifically, a numerical investigation to determine the nature of the complex dynamic response, estimate the fatigue life, and develop a prescriptive reliability-based selection (design) procedure for high-mast lighting structural supports. Morison's equation, which provides relative force for slender bodies as a function of flow velocity, was applied within a dynamic finite element framework in order to account for the relative motion between the wind and the motion of the structure. Then, a well-known random vibrations approach was coupled with Miner's rule to estimate the fatigue life of the structural support. Six different design parameters as well as mean wind velocities were examined.

The current design wind loads for buildings and other structures are based upon model tests in low-speed boundary-layer wind tunnels that generate straight-line winds. However, winds resulting from tornadoes and microbursts that could occur during storm events such as thunderstorms or hurricanes are far from being regular atmospheric boundary-layer type winds. In recent full-scale measurements using Doppler radar, it has been observed that tornadoes could produce intense winds in the region below 20 m from the ground. Microbursts are characterized by a strong localized down-flow and an outburst of strong winds near the surface. Thus, microburst winds have significant vertical velocity components and mean horizontal velocity distributions that are different from usual boundary-layer winds. This paper presents quasi-steady and transient wind load effects on a tall building in a laboratory-simulated tornado and microburst. Experiments were conducted in the Tornado/Microburst Simulator at Iowa State University. The microburst is simulated as a round jet, 1.83 m or 6 ft in diameter, impinging onto a flat ground plane. The tornado was simulated with a maximum vortex core diameter of 1.12 m or 3.7 ft. A 1/500 geometrically-scaled model of a tall building, 216 m (708 ft) in height with a square cross section of 54 m (177 ft), is used for this study. Comparisons of peak loads measured in this study with loads specified in ASCE 7-02 showed that tornados of F2 strength or stronger would exceed the minimum design wind load provisions by a factor of 1.8 or greater.

Making accurate barometric pressure measurements in tornado cores using an in-situ probe is difficult due to very high wind velocities, heavy rain, and wind driven debris. Special considerations apply to the shape of the probe, as it must remain stationary during tornado passage. In-situ pressure measurements are particularly challenging as wind flow over any object will decrease the local static pressure and cause an erroneous barometric pressure measurement. This is especially important for the wind velocities exceeding 80 meters/second typical inside tornado cores. A specially-designed hardened probe called a "Hardened In-Situ Tornado Pressure Recorder" (HITPR) has been developed by the author at Applied Research Associates Inc.. The HITPR has addressed the above-mentioned challenges by using a novel probe geometry that compensates for air flow curvature when measuring pressure, and has a high degree of aerodynamic stability. With this method, accurate measurements of the free-stream static pressure, wind speed, wind direction, temperature, and relative humidity can be made inside tornado cores. The measurement technique will be described in the present paper, as well as actual pressure measurements of tornado cores, including the 100 millibar pressure drop measured for a violent F-4 tornado on June 24th, 2003.

Components and cladding on residential structures continue to be damaged in high winds despite improvements to building codes. Modern wind design codes that are helping to prevent structural damage to buildings are not as effective in preventing building envelope failures. Since 1998, a unique collaborative effort between Clemson University, the University of Florida, and Florida International University called the Florida Coastal Monitoring Program (FCMP) has been collecting full-scale pressure and wind speed data on residential buildings in suburban areas. The program, sponsored by the Florida Department of Community Affairs (FDCA), was developed to increase our limited full-scale data available on wind loadings of low rise buildings — none of which was obtained during sustained hurricane force winds until this project. Another objective was to determine the validity of current design wind load values that are based on wind tunnel tests using open-country exposure. This serves as the primary motivation to study pressure variation on roofs of suburban houses. This paper presents results of the field data collection and analysis of pressure coefficient data from field experiments and wind tunnel results obtained at Clemson University's atmospheric boundary layer wind tunnel.

Both High Frequency Force Balance (HFFB) and High Frequency Pressure Integration (HFPI) studies of the CAARC standard tall building were carried out at RWDI's boundary layer wind tunnel facility in Guelph, Canada. The results described in this paper are part of an ongoing detailed investigation aimed at quantifying the advantages and limitations of the HFFB and HFPI methods.

Recently, LC (load combination) method was developed by Holmes as a general method to derive effective wind load distributions (EWLD) for all types of structures. The LRC method used in the LC method, however, neglects resonant effect in developing background component of the EWLD. Also, it couldn't consider properly non-Gaussian pressures. The results of the LC method could be therefore quite different with actual wind load distributions (AWLD). In this study, advanced conditional sampling (ACS) method was developed to derive the AWLD and the EWLD was compared with it for a slender structure and a large span roof. Furthermore, a modifed method is suggested to compensate shortcomins of the LC method for convinient and practical use.

Modeling of wind loads on low-rise buildings is complicated by their variety of geometries and surroundings and remains a very challenging issue which is critical for cost-effective design and reduction of wind-induced losses. Current design practice often requires the transformation of spatiotemporally varying wind loads to the equivalent static wind loads (ESWLs). This paper addresses the analysis of wind load effects and modeling of ESWLs on low-rise buildings based on the full scale dynamic pressure data of the Wind Engineering Research Field Laboratory (WERFL) building at Texas Tech University. The ESWLs for different peak wind load effects of building frames under both alongwind and acrosswind excitations are examined using a number of approaches with a focus placed on developing physically meaningful and convenient wind load models for potential design applications. The results of this study demonstrated the advantage of the gust loading envelope approach for improved modeling of wind loads on low-rise buildings.

While there exists a relatively large body of technical information for the engineered design of wood-frame buildings to resist seismic ground motions, the quantitative assessment of seismic resistance of conventional houses built by prescriptive requirements is less well understood. Forintek Canada Corp., in collaboration with other research and industry partners, has embarked on a research project to address this topic. This paper will report on the first phase of this project, the seismic shake table tests of a full-scale wood-frame building. The two-storey specimen, 6 m x 6 m in plan, was built on the seismic shake table at Tongji University in Shanghai, China, according to Part 9 of the 1995 National Building Code of Canada and shaken uni-directionally in each of the two principal directions. Three different seismic table motions were applied at increasing peak ground motion amplitudes up to 0.40 and 0.50 g. The specimen was repaired after the above sets of seismic table motions, and successive runs were conducted for increased door openings. Measurements included specimen accelerations, displacements and anchorage forces. Static stiffness of the specimen was measured at low force levels, and natural frequencies were measured after each seismic loading stage by applying low-level random excitation. The results presented consist of the capacity spectra of the shake table tests, changes in specimen stiffness and natural frequencies with increasing seismic loading. These results and those from other recent shake table tests elsewhere will be compared with simplified engineering calculations based on codified values of strength, and on that basis preliminary conclusions will be drawn on the adequacy of the current code provisions and design guides in Canada and the USA for conventional wood-frame construction.

Seismic code provisions are now adopting performance-based methodologies, where structures are designed to satisfy multiple performance objectives. Most codes rely on approximate methods to predict the desired seismic demand parameters. Most of these methods are based on simple SDOF models, and do not take into account neither MDOF nor degradation effects, which are major factors influencing structural behavior under earthquake excitations. More importantly, most of these models can not predict collapse explicitly under severe seismic loads. This study presents a newly developed model that incorporates degradation effects into seismic analysis of MDOF structures. A new energy-based approach is used to define several types of degradation effects. Collapse under severe seismic excitations, which is typically due to the formation of structures mechanisms, was modeled in this work through the degrading hysteretic structural behavior along with P-Delta effects due to gravity loads. The model was used to conduct extensive statistical dynamic analysis of different structural systems subjected to a large set of recent earthquake records. To perform this task, finite element models of a series of generic MDOF structures were developed. An ensemble of recent earthquake records was used in the work, and a variety of degrading MDOF structures that cover a wide range of periods, yield values, and levels of degradation were considered. For each MDOF structure, collapse was investigated and inelastic displacement ratios curves were developed in case collapse doesn't occur. In addition, seismic fragility curves for a collapse criterion were also developed. The findings provide necessary information for the design evaluation phase of a performance-based earthquake design process.

This study is focused on a 115 meter high reinforced concrete chimney located at the Tüpras refinery, Turkey, which collapsed during the 1999 Kocaeli earthquake. The stack was designed and constructed according to international standards and is representative of similar structures at refineries throughout the world. This structure is of particular interest because several similar chimneys at the site survived the shock with only moderate damage. The particular distinction of this chimney appears to be an unusually large rectangular opening, located about 1/3 of the height above the base, which appeared to be the region of collapse initiation. The main focus of the research is the dynamic response of the stack due to an earthquake motion recorded at a nearby site. Results from a response spectrum analysis of the Tüpras stack as well as from a basic nonlinear static pushover analysis using a demand-collapse comparison have been published. These results provide a strong indication of the collapse mechanism of the stack and are consistent with the post-collapse remnants. Since the available spectrum had a peak close to the second period of the stack, the higher mode participation is of interest. In this paper, different methods for the consideration of the higher mode effects are evaluated by comparison with a full nonlinear dynamic analysis. Results are presented that include the effects of the higher mode contributions on the nonlinear static collapse loading.

The events of September 11, 2001 had a profound impact on the building design community. Although the weapons employed that day were fully fueled commercial aircraft, the industry turned considerable attention to the most common tactic historically employed in terrorist attacks around the world: the improvised explosive device. While information for addressing this threat existed, it was largely confined to military and other government publications that were neither readily available nor directly applicable to facilities constructed by the private sector. Recognizing this, in 2002 SEI began the process of establishing a new Codes & Standards Committee on Blast Protection of Buildings. Chaired by Donald O. Dusenberry, P.E., M.ASCE, of Simpson, Gumpertz & Heger in Waltham, MA, the committee set out to develop a new ANSI-accredited Standard for the planning, design, construction, and assessment of new and existing buildings subject to the effects of accidental or intentional explosions. Six task committees have been developing the mandatory provisions and accompanying commentary: (1) General Provisions, (2) Fuels and Loadings, (3) Structural Systems, (4) Building Envelope and Glazing, (5) Materials Detailing, and (6) Appurtenant Systems and Performance Verification. The resulting document is now in draft form, and the committee hopes to ballot it sometime in 2006. The purpose of this paper is to summarize the structure and content of the first four chapters of the Standard, which are the responsibility of the first two task committees listed above and address the following subjects: (1) General, (2) Design Considerations, (3) Performance Criteria, and (4) Blast Loading.

This paper discusses the work to date of the Task Committees of the ASCE Blast Standard on Structural Systems, Protected Spaces and Exterior Envelopes. This portion of the Standard addresses the features of structural analysis and design that may be used to improve the performance of structures in response to air-blast loading. It also includes the design of the exterior envelope, which is typically the weakest element of a building as well as the costliest to construct because of its large area. Chapter 6 addresses issues such as the protection of new versus existing construction; the relationship between aseismic design and blast resistance; analytical methods and modeling; characteristics of air-blast loads; and the prevention of progressive collapse. Chapter 7 addresses issues related to protected spaces and the hardening of interior partitions, walls, slabs, stairwell enclosures and plenums. The different levels of protection are related to performance-based design criteria. Chapter 8 defines the design intent for the building envelope in terms of the hazard-based and resistance-based approaches. Performance and construction requirements for new construction and retrofits are presented for glazing systems and doors; exterior wall systems, such as concrete, masonry and steel wall construction; roof systems; debris mitigating systems, and venting. Chapter 9 addresses primary and secondary fragmentation and methods of predicting the hazards of airborne fragments.

Research is currently being performed at the Engineer Research and Development Center (ERDC) of the U.S. Army Corps of Engineers to understand the structural response of buildings subjected to blast loadings from high explosive devices such as terrorist bombs. The focus of this research is to develop methodologies to produce designs that will provide protection to building occupants and maintain structural integrity for rescue operation purposes after the blast event. In particular, the U.S. Department of State-sponsored research on cold-formed steel stud wall systems using conventional steel construction materials and methods has application to exterior walls subjected to severe blast loading. The elements of this research and their interconnections are presented and include: quasi-static stud component testing; mechanical property testing of materials; connection testing; steel stud design program development; finite element quasi-static and dynamic numerical simulations; and full-scale blast testing of typical wall system designs. Although the research is still in progress, results have culminated in a preliminary methodology and a PC software program based on a single degree-of-freedom dynamic model for the design of blast-resistant steel stud exterior wall systems.

Blast resistant design has come to the forefront of engineering concerns in the wake of recent terrorist threats to the United States. Safety and security are of utmost concern when designing structures, and there has been a significant rise in the demand of researching new methods of reinforcing and retrofitting structures to provide better resistance to blast loading. The focus of this research paper is on the use of steel sheathing as a method of such retrofit. Research is done to ascertain the steel strength, analyze the response of the steel to static pressure, explore strength and ductility limits, investigate connection details, and develop an analytical model of the static resistance function, which will be verified by experimental data. The analytical model for the resistance function will be used in a single-degree of freedom (SDOF) dynamic model to predict the response of steel sheathing blast-retrofitted wall systems. Coupon tests were performed to establish the stress-strain behavior of the steel material, and component beam tests were used to determine the response of the sheathing under static pressure. In addition, connection methods were analyzed and tested in an effort to determine the most suitable blast-retrofit design for a given blast, without exceeding strength or ductility limits for the steel sheets, and to develop the limit states for the retrofit system. The results of the experimental program and the analytical static and dynamic models were incorporated into a user-friendly wall analysis code for the design of steel sheathing for blast retrofit of CMU walls.

Military and diplomatic facilities are targets of terrorist bomb attacks. Unfortunately, terrorists also commonly target populated public facilities such as residential buildings, office buildings, and restaurants. Most casualties and injuries sustained during external explosions are not caused by the pressure, heat, or container fragments resulting from a bomb detonation. Rather, most injuries are blunt trauma and penetration injuries caused by the disintegration and fragmentation of walls, the shattering of windows, and by non-secured objects that are propelled at high velocities by the blast. Ensuring that the exterior walls of a structure are able to withstand a blast without producing deadly fragments is a critical part of minimizing injuries to building occupants. Most common building wall structures are not designed to withstand blast loading. The resistance of a wall to blast loads can be enhanced by increasing the mass and ductility of the wall with additional concrete and steel reinforcement, which can be time consuming and expensive. For these reasons among others, a need has arisen for cost effective methods of designing and constructing walls that can resist significant levels of blast pressure. The overall objective of the research described herein is therefore to investigate and describe the effectiveness mechanisms of walls comprised of permanent concrete formwork for resisting blast loads, and to develop an engineering definition of the resistance provided by polymer-encased concrete wall systems subjected to blast loading. Static flexural tests and full-scale explosive tests were conducted. Also, high-fidelity finite element simulations were used to further understand resistance mechanisms. Efforts thus far have focused on walls without internal steel reinforcement. Future efforts will involve other configurations of stay-in-place forms and resistance definitions that include internal steel, reinforcement. This paper highlights static testing, dynamic testing, finite element modeling approach, engineering resistance definitions, and implementation and accuracy of single-degree-of-freedom (SDOF) models.

An integrated experimental, analytical, and computational effort is being made in the Center for Explosion Resistant Design, in collaboration with national laboratories and industry, on the structural design, first-principle simulation, and development of an empirical model and PC-based code for predicting the responses of a blast barrier. To catch the essential feature with an effective simulation tool, an axisymmetrical model is formulated to predict the blast environment in the presence of a barrier with the use of a coupled computational fluid dynamics (CFD) and computational solid dynamics (CSD) simulation procedure based on previous work. This coupled CFD and CSD simulation procedure is designed via the Material Point Method (MPM) in spatial discretization that is an extension from CFD to CSD. The scaled blast experimental databases from small-scale tests performed by the national laboratories are employed to determine the gaps in the database that indicate a need for additional experiments. An empirical model is developed based on the experimental data and the first-principle simulation model. System identification models are then established to predict the blast pressure based on a range of parameters such as bomb size and position, wall dimensions, angle of incident, and location of target. In collaboration with the Air Force Research Laboratory (AFRL), the proposed model-based simulation procedures are verified and improved with full-scale experiments, and the structural design of the barrier prototype is examined for near-field blast loads to evaluate various confinement strategies and materials. Based on the above results, the empirical model will be implemented into a user-friendly PC-based code for predicting the blast pressure and impulse on structures in the presence of the prototype blast barrier. In the presentation, recent research results on the coupled CFD and CSD simulation of blast-barrier responses will be discussed.

Two new design concepts are presented for constructing barriers that provide protection from blast. These concepts have performed well in blast tests, remaining relatively undamaged when struck with the blasts from large amounts of explosives placed near them. The two barriers use radically different concepts to achieve their purpose. One concept employs a structural panel composed of two sheets of steel plate with a concrete core placed between. The panel is supported by a steel posts sunk into the ground around 10 feet. Depending on the configuration and threat, panels range in size from 1 to 2 feet in thickness, with steel plates of ¼ inch to 1 inch thick with heights ranging from 4 to 16 feet. The other barrier represents a new and effective use of soil and sheet metal materials. Here, the sheet metal is used to form cells that are then filled with soil. A simple pinning mechanism is used to attach adjacent sheets to one another. No foundation is required. A range of wall configurations have been developed, some with wall heights up to 80 feet. Karagozian & Case has developed high-fidelity physics-based finite element models for these barriers that are used to select design parameters for specific threats and deployment options. This paper describes some of the designs, analytic results, and verification tests that have been developed. This paper also describes the features needed by such barriers and how the features of these designs contribute to their success.

The work documented herein is a portion of a multi-organizational effort lead by the University of Missouri-Rolla (UMR) Rock Mechanics and Explosives Research Center, with the following participants: Kontek Industries, the Air Force Research Laboratory Airbase Technologies Division, UMR's Department of Civil, Architectural, and Environmental Engineering, the Department of Architectural Studies from the University of Missouri-Columbia (UMC), and UMC's National Center for Explosion Resistant Design. The ultimate goal of this multi-year project is to establish prototypical functionality and architectural standards for blast-resistant barricade systems through applied research, design, and test efforts. This paper specifically addresses the results of efforts by UMR and Kontek to design and test barrier structures that protect other structures, and mitigate pressure loads and shock hydrodynamic effects on structural barriers, columns, beams, and bents. As a part of this effort, we are examining structural load path transfer during a blast, in order to provide additional support to portions of structure under attack. Continuation of the current close coordination among the authors in the areas of analytical modeling and blast design and test, as well as the commercial constructability, allows the design of mid-scale and full-scale experiments to populate and validate empirical models for blast barriers, to include off-axis pressure prediction and the development of empirical-based algorithm for prediction of blast pressures around structures and barriers.

Urban planners often consider the use of barrier walls as a means of protecting structures and other assets from terrorist vehicle bombs. Barrier walls offer a means of halting the approach of vehicle bombs, thereby limiting the proximity of the bomb to the at-risk asset. Depending upon their height and structural integrity, barrier walls may also provide significant shielding from the airblast produced by the bomb. Several methods exist for the prediction of this shielding effect. Unfortunately, these methods tend to be rather inaccurate, due primarily to the complexity of the airblast/barrier wall interaction, and to the lack of a comprehensive database upon which to form a predictive methodology. During the past four years, the US Army Engineer Research and Development Center has conducted an extensive series of small-scale experiments and hydrocode calculations to examine barrier wall shielding of structures. This database is now being used to develop an improved methodology to predict peak reflected pressure and impulse behind barrier walls of various heights for a wide range of explosive-to-wall and wall-to-structure distances. A wide range of target heights on the shielded structure are also addressed. This paper provides an overview of the experimental and computational database, and the new predictive methodology now under development.

Multiple hazards affect the stability and service life of structures, and should be considered during design and analysis. Due to recent events, design of structures for blast and impact are also becoming very important. It is anticipated that multihazard design considerations will result in overall cost reduction while maintaining the needed safety levels. This paper briefly describes the application of theory of multihazards considering life-cycle costs for making appropriate retrofit decisions.

There are some similarities between seismic and blast effects on bridge structures: both major earthquakes and terrorist attacks/accidental explosions are rare events that can induce large inelastic deformations in the key structural components of bridges. Since many bridges are (or will be) located in areas of moderate or high seismic activity, and because many bridges are potential terrorist targets, there is a need to develop structural systems capable of performing equally well under both events. The objective of this research project is to develop a multi-hazard bridge pier concept capable of providing an adequate level of protection against collapse under both seismic and blast loading, and whose members' dimensions are not very different from those currently found in typical highway bridges.

The purpose of the ATC-58 project is to develop next-generation seismic design procedures that will address these issues and also provide a more reliable means of predicting and designing desired for performance. Initial planning for the project was outlined in an action plan, FEMA-349, developed by the Earthquake Engineering Research Institute. The project is being executed in two phases, each with an anticipated duration of 5 years. The first phase is currently underway and includes development of a comprehensive building seismic performance assessment methodology. This methodology will be suitable for direct application to performance-based design of new buildings or performance-based retrofit design for existing buildings. The second phase of the project, which will be conducted upon conclusion of the first phase will focus on the development of design guidance to assist the engineer in efficiently identifying designs likely to be capable of providing the desired performance.

Terrorist bombings of buildings in the United States of America over the past decade have created an urgent need for all governmental and code agencies to provide guidance for the analysis and design of structures to reduce the potential for progressive collapse under abnormal loading conditions. This paper presents the results to date of a first-ever, multi-year steel frame blast research program sponsored by the General Services Administration (GSA) of the Office of Chief Architect (OCA), as part of an historic integrated inter-agency test program with the Defense Threat Reduction Agency (DTRA) as an integral part of DTRA's Blast Effects Tests Series. GSA's primary program goals and objectives are threefold, viz. 1) to evaluate the behavior of steel frame connections subjected to large scale arena explosive tests, 2) to determine their post-blast integrity for the purpose of mitigating progressive collapse, and 3) to identify and prescribe effective solutions. This paper examines the blast resistance and overall structural performance of selected steel frame beam-to-column moment connection configurations when subjected to direct air blast attack, including the effects of high strain rates in critical components and welds, and evaluates the post-blast integrity of those same moment connection configurations needed to arrest structural mechanisms that are known to trigger progressive collapse. Gaining this knowledge is of strategic importance to the GSA in light of the fact that the GSA has found steel framed structures to be characteristically cost-effective to build due to their light weight when compared to concrete structures, and because they are typically erected much faster with a corresponding reduction in construction time.

In a truss, dynamic effects may arise not only due to external dynamic loads but also due to sudden reduction in the stiffness and load carrying capacity of a member. The sudden reduction in the load carrying capacity of a member may not only occur due to complete member failure, but also due to postbuckling and subsequent inelastic cyclic member behavior. The resulting dynamic redistribution of internal forces may lead to progressive collapse of the entire truss structure. In the present study, an analytical method to model the dynamic nature of progerssive collapse is presented. A numerical scheme has been developed to track and generate the a complete inelastic cyclic force-diformation characteristics of every member of the truss at each iteration step of the solution scheme of the dynamic equations of motion. The solution methodology is based on the finite element technique and considers elasto-plastic material and large deformation geometric nonlinearities using Pseudo force technique. As an illustration, this methodology is applied to the failure analysis of a two-dimensional redundant truss structure consisting of forty members. The truss is subjected to a slight quasistatic overload such that the failure is initiated by buckling of a member. The results show that postbuckling and subsequent cycles of inelastic force-deformation behavior of truss members give rise to adverse member force redistribution that leads to complete collapse of the structure even if it is built with redundant members.

With the 1995 bombing of the Murrah Federal Building in Oklahoma City and the more recent terrorist attacks in New York and Washington D.C., attention has been focused on the ability of both new and existing structures to withstand significant structural assault while maintaining the degree of structural integrity sufficient to allow building occupants to safely exit. None of the major United States Building Codes (IBC, UBC, SBC, BOCA) or the structural design codes (American Institute of Steel Construction, American Concrete Institute, The Masonry Society, American Forest and Paper Association, etc) provide specific design requirements for evaluating or reducing the vulnerability of a structure to progressive collapse. However, government standards have been developed by the U.S. General Services Administration (GSA) and the Department of Defense (DoD) and are currently used to provide progressive collapse considerations in the design and retrofit of their respective building inventories. The analysis procedures contained in these documents, as well as strengthening approaches and a range of progressive collapse retrofit costs for various building types will be addressed.

Detailed finite element simulations are used to investigate the large deformation behavior of seismically designed beam-column subassemblies. The numerical model employs a micromechanical fracture model for steel that is calibrated to existing test results. The developed simulation tools are used to understand the role of a number of parameters that influence the formation of catenary action in steel moment resisting frame (MRF) connections.

Currently the designers of buildings in North America rely on the results of standard fire tests to ensure building structures meet the fire resistance rating requirements prescribed by national building codes. With the development of performance based building codes throughout North America it is important that the design community have the tools necessary to take advantage of these new codes. In order to provide structural engineers with these tools a method is being proposed that will facilitate the design of structural steel for fire conditions using a performance based approach. This approach is simplistic in nature and only considers a two-dimensional thermal response of structural steel to the fire. A method has been proposed that allows the designer to predict the time-temperature relationship expected in a compartment fire with a reasonable level of conservatism, which can be used to determine the required level of protection.

Exodiagonal building structures are defined as those having a regular series of intersecting diagonal members, completely or partially encompassing the building's exterior face, that carry both gravity and lateral loads. Exodiagonal building structures normally lack vertical members on the exterior walls. The highly redundant exodiagonal structural system facilitates the immediate redistribution of internal forces away from damaged portions of the shell in the case of an extreme loading event. Structures of this type are uniformly resilient without any inherent vulnerabilities. Several completed buildings utilizing this type of structural system are in use today around the world. The general performance characteristics of exodiagonal building structures with respect to redundancy are examined in this study. In this study, two hypothetical building structures, a high-rise and a low-rise, each using a three-dimensional, exodiagonal structural grid, are analyzed. For purposes of this study, the exodiagonal members in the models are sized to meet the minimum requirements of the ASCE 7-02 Code for gravity and moderate lateral loads. Both of the building models are then subjected to the removal of a vertical support and reanalyzed in a manner similar to standard progressive collapse procedures. A vertical support for an exodiagonal structure is judged to be a pair of adjacent diagonal members. Redistributed loads are calculated for pertinent members and compared to the original Code-based member designs. Next, additional exodiagonal members are removed from the model, adjacent to those previously removed. The models are reanalyzed and the loads are recalculated for pertinent members so that the redistribution of internal forces can be considered. This process is repeated through numerous member removal steps. The results of the above redundancy analysis is summarized and presented.

The predication of nonlinear response of steel buildings under elevated temperatures from fire loading can be achieved by sequentially using heat-transfer analysis and stress analysis. A combined computational fluid dynamics (CFD) and structural stress investigation was conducted to study the 3D response of a two-story framed steel building. After an extensive literature review on the CFD modeling used in the heat transfer analysis, it is concluded that for practical considerations, the important factors such as thermal buoyancy, thermal radiation, and flow turbulence were considered while the effects of combustion and the associated chemical reactions were neglected. The fire was modeled as a high-temperature zone whose temperature changed with time according to a prescribed manner. Walls consisted of typical construction materials (gypsum, wood, and fiberglass) while the floor systems consisted of concrete slabs supported by steel beams. Free convection of air and thermal radiation were both included in the analysis. The governing differential equations of flow and energy were solved by FLUENT. The air turbulence was modeled by the standard k-ε model and the radiation was simulated by the Discrete Transfer Radiation Model. The result of FLUENT analysis indicated that the air velocity was high in the middle of the room above the fire and adjacent to the ceiling. The temperatures of the beams and columns generally decreased away from the center, with a more rapid decrease toward the ends. It was also observed that radiation played an important role in fire modeling where 20–40% of the heat transfer took place by radiation. Subsequently, the temperature of the beams and columns obtained from the CFD analysis were used in the nonlinear stress analysis to obtain the complete structural response using ANSYS where the floor loads due to gravity were included. It was assumed that the stress analysis results had no bearing on the heat transfer analysis, which is a reasonable assumption for most conventional structures. The following research paper will provide a summary description of the structural model used in ANSYS, and the corresponding results obtained.

The region of a slab in the vicinity of a support could fail in shear by developing a failure surface in the form a truncated cone or pyramid. This type of failure, called `Punching Shear Failure, is usually the source of collapse of flat-plate and flat-slab structures. Punching shear failure of slab-column connections is a subject on which there are theoretical guidelines and there are wide divergences in different empirical treatments adopted by different codes. In this paper the shear strength of slab-column connections for internal columns are critically reviewed. Shear reinforcement in the slabs is not considered in the strength evaluation. The effect of various parameters, such as, ratio of side width of columns, ratio of side width of column to the effective depth of slab, concrete compressive strength, and percentage of flexural steel, on punching shear capacity are examined.

The high-speed rail project to improve Taiwan's transportation systems is an effort by the Taiwanese government to further the island's economic development. The planned route is 345 km long, and the viaducts and bridges are approximately 207 km long. Hence, there are many bridge piers in the project. To maximize structural efficiency in terms of the strength/mass and stiffness/mass ratios and to reduce the mass contribution of the pier to seismic response, it is desirable to use a hollow section for the piers. To consider both the ductility and constructability, a hollow section with special confinement reinforcement has been used in the bridge piers in the high-speed rail project of Taiwan. During the past three decades, various studies on the confinement effects of lateral reinforcement in columns have been conducted, and the analytical models have been proposed. It is not clear that if any of the stress-strain models of confined concrete proposed in the past is appropriate for the hollow sections used in Taiwan. Therefore, such hollow sections need to be studied by both tests and analysis. The seismic performance of rectangular hollow bridge piers is a significant issue of the high-speed rail project in Taiwan, because the shear capacity of such piers with the configuration of lateral reinforcement used in Taiwan is not clear. Such piers were tested under a constant axial load and a cyclically reversed horizontal load to investigate their seismic behavior. This paper presents the experimental results of three specimens of such piers. The parameter of the test program was the height to width ratio of the piers. The seismic behavior of the piers, including flexural ductility, dissipated energy, and shear capacity is presented. On the other hand, shear research at the University of Houston performed over the past two decades resulted in a series of constitutive models. The Cyclic Softened Membrane Model (CSMM) is the latest developed constitutive model, which is able to accurately predict the cyclic shear behavior of the reinforced membrane elements. By adopting the finite element framework OpenSees CSMM was implemented into OpenSees and a nonlinear finite element computer program "Simulation for Reinforced Concrete Structures (SRCS)" was developed. The program is capable of predicting the nonlinear behavior of reinforced concrete structures subjected to static, reversed cyclic, and dynamic loading. In this paper, the SRCS was used to predict the seismic behavior of the piers and the predicted results are compared with the test data. It is found that the proposed analytical model can well predict the load-displacement relationships of such piers under reversed cyclic loading.

Column shear failures observed during recent earthquakes and experimental data indicate that shear deformations are typically associated with insufficient transverse reinforcement, low aspect ratio and a few other parameters. It was shown that in some relatively tall columns, shear displacements can be as large as displacements due to flexure and longitudinal bar slip at column ends. However, very few researchers attempted to predict the lateral load-shear displacement relationship. In this paper, a piecewise-linear model is proposed to predict the lateral load-shear displacement relationship. Part of the new model is developed using the analysis results from Modified Compression Field Theory (MCFT). The results from the proposed model, which uses simplified equations, are evaluated and compared with the predictions from existing models as well as column test data. The proposed model is fairly simple, and predicts the lateral load-shear displacement relations relatively accurately at critical stages including shear cracking, peak strength, onset of lateral strength degradation, and loss of axial load carrying capacity.

Presented is a detailed case study on structural Finite Element (FE) modeling and Modal Pushover Analysis (MPA) of a 14-story office building instrumented for seismic response investigation. The system identification tool was used to identify the structural dynamic properties, including the natural periods of vibration of the structure and level of critical damping based on seismic data recorded during small seismic ground motions. A series of FE models were created to improve the modeling technique. The final "corrected" FE model was refined and calibrated to match the identified structural natural periods. It was found that a FE model can be calibrated to give a good prediction of earthquake response. Using the calibrated FE model, the structural seismic behavior has been examined using the MPA procedure. In the MPA procedure, an improved analysis based on structural dynamic theory with invariant force distributions was used to generate the push loads. Four recorded ground acceleration time histories were used as input data for the MPA procedure. Five sets of push forces, corresponding to the effective earthquake forces from the first five modal expansions, were applied to the FE model. The final MPA results were combined from these five push-over cases using the Square-Root-of-Sum-of-Squares (SRSS) rule and the Complete Quadratic Combination (CQC) rule to get the total response. The MPA results were also compared with the Incremental Dynamic Analysis (IDA). It is found that the MPA and IDA results are reasonably matched. The MPA procedure is an improved tool for estimating seismic demands on buildings. Using the MPA procedure, the structural behavior can be examined during seismic loading and future performance of the building during damaging earthquakes can be predicted.

This paper describes the innovative seismic retrofit of the Webb Tower located on the campus of the University of Southern California in Los Angeles. The existing 14-story residential structure was constructed circa 1972 using light-weight concrete. The lateral system for the building consists of perimeter non-ductile post-tensioned concrete moment frames supported on isolated spread footings. A preliminary evaluation of the building revealed several seismic deficiencies, including the following: (1) non-ductile detailing, (2) excessive building deflection and (3) joint shear overstress. After considering several alternate retrofit schemes, a unique retrofit scheme was developed utilizing a single bay of buckling-restrained steel braces in combination with a reinforced concrete beam-column frame on each side of the building. The selection of this system provides several advantages for this project over other retrofit schemes, including: (1) provides partial views from the existing windows, (2) requires significantly less demolition than an interior scheme, (3) more cost-effective than an interior solution, (4) reduces building drift and demands on the non-ductile moment frames, and (5) buckling-restrained braces do not exhibit strength degrading and aesthetically unacceptable post-buckling deformations. A three-dimensional nonlinear computer model was developed capable of capturing the nonlinear behavior of the buckling-restrained braces, the existing concrete beams and columns with consideration for the post-tensioning effect, and the new concrete beams and columns. The seismic performance of the retrofitted building was investigated by time history analyses using seven sets of ground motion records.

One hundred years ago, St. Louis enjoyed a golden age of commerce and notoriety including the construction of many mid to high-rise buildings. After suffering through a period of urban decline, the city is reviving many old buildings. With millions of square feet of warehouse and factory buildings being turned into lofts, offices, schools, museums & retail centers, buildings are being renovated with changes in occupancy. Rehabilitation of these structures to suit their new uses can be challenging. One unique engineering aspect is the rehabilitation of buildings with masonry/concrete floor systems. In this paper we will give a general overview some of the types of masonry floor systems that we have encountered. Also, presented are two case histories of floor systems that presented unique challenges. The first is the Ely Walker Dry Goods Building at 16th & Washington Avenue. The seven story building has a steel skeleton structure with a segmental arch floor consisting of hollow clay tile and cinder concrete fill spanning 20 feet. The second is the Marquette Building. This 23 story building is also a skeleton steel framed structure with concrete rib joists spanning 12 feet between columns. Instead of pans, the space between concrete joists is filled with hollow clay tile.

The prediction of joint mechanical response is an important issue for the advanced analysis of metal structures. On the other hand, it is recognized that the behaviour of connections is very complex, because it includes many local effects, giving rise to complicate stress redistribution among the basic components. Therefore, for a reliable understanding of connection behaviour and setting up of relevant calculation methods the direct experimentation is required. While several tests have been carried out for steel, allowing some consistent calculation procedures to be set up, only few are concerned with aluminium alloys. On the basis of the above considerations, a large research project dealing with aluminium joints has been recently carried out at the University of Naples Federico II, sponsored by the Italian Ministry of Education, University and Research (MIUR). It was mainly concerned with the behaviour of bolted T-stub joint components, which has been deeply examined under analytical, numerical and experimental points of view. In fact, T-stub is one of the more important joint components. It may be regarded both as stand-alone connection and as a part of several, more complex bolted joint configurations. In previous papers, the authors have already proposed an analytical method to determine both the collapse mechanism type and the corresponding load bearing capacity of aluminium T-stubs based on the existing formulations adopted into EC3-Part 1.8. It is important to remind that for steel T-stubs, three possible failure modes are recognized: type-1 mechanism, with complete yielding of the flange through the onset of four plastic hinges, two of which are located at bolt axis location; type-2 mechanism, when the bolt failure takes place together with the yielding of the flange at the sections corresponding to flange-to-web connection; type-3 mechanism, due to bolt failure with the overall uplift of the flange. Due to the limited ductility of the material, for aluminium T-stubs, the intermediate failure mechanism (type 2) has to be split into two different mechanisms: the first one (type 2a) is characterized by the failure of the flange material with plastic engagement of bolts; the second one (type 2b) is distinguished by the failure of bolts and plastic engagement of the flange material. Besides, in order to account for the hardening of the material, a special procedure has been defined for the evaluation of plastic strength of aluminium T-stub flange sections and aluminium bolts.

Gusset plates are used in steel buildings to connect bracing members to other structural members in the lateral force resisting system. Horizontal bracing is commonly used to resist lateral loads in industrial structures and in commercial buildings where floor and roof diaphragms cannot carry the loads. Wrap-around gusset plates are L-shaped plates that are used where an opening is required at the comer of the plate. This typically occurs at horizontal bracing where the gusset plate is cut out around a column. Finite element models were used to determine the behavior of wrap-around gusset plates. The plates were modeled using material and geometric nonlinearities. Five different gusset plates were modeled with geometry and material properties matching the experimental specimens of Dowswell. All of the models were loaded in tension. The loads from the finite element models were compared to the experimental loads.

The use of reduced beam section (RBS) moment connections has become popular in the seismic resistant design of steel special moment resisting frames (SMF). Deep columns in SMFs are desirable because they offer more economical drift control compared to shallower columns. The lack of knowledge about the behavior of RBS connections to a deep column under seismic loading conditions led to the experimental study presented in this paper. The seismic performance of the deep column RBS connection test specimens having a composite floor slab with lateral bracing, or no floor slab and a supplemental lateral brace at the RBS, were found to meet the criteria in Appendix S of the AISC Seismic Provisions for qualifying the connection for seismic resistant design.

In cold-formed thin-walled steel structures the skeleton is usually sheathed with sheets or panels made of different materials. Connections between sheathings and cold-formed profiles are generally made of self-drilling or self-piercing screws. If the panel has adequate strength and stiffness and if it is effectively connected with the skeleton, then the interaction between profiles, sheathings and connections can be advantageously taken into account in the structural analysis ("sheathing-braced design"). This is the case of sheathed cold-formed "stick-built" constructions, in which the presence of the sheathing positively affects the structural response under both vertical and horizontal actions. In this type of structures the most ductile failure mode is exhibited when sheathing-to-wall framing connections local failure governs the global collapse mode. Then the characterization of the mechanical behavior of screw connections between cold-formed steel profiles and panels is necessary. In this paper, the main issues related with an experimental investigation on shear connections between wood or gypsum sheathings and steel studs are discussed.

In today's engineering practice, there is no such thing as a "normal" or "standard" structural analysis: Advanced analysis methods that were regarded as research tools a few years ago have entered some design offices while other practices are still using the same (except bigger and faster) analysis tools they had a generation ago. This is especially true in the area of stability: Direct, rigorous second-order analysis is regarded as routine in some practices but not in others. As will be apparent from this brief outline of its stability-related provision, the 2005 AISC Specification for Structural Steel Buildings recognizes the wide range of analyses in common use. It spells out the general safety - and reliability-based requirements that must be satisfied in all structural designs and then gives designers the freedom to select or devise their own methods of analysis and design within these constraints. The Specification also offers designers specific, simple analysis and design procedures applicable to typical structures.

Basic guidelines are needed to aid engineers and structural analysis software developers in understanding the requirements for capturing member and system strength limit states within advanced analysis models. This paper discusses a current to develop proposed guidelines for the use of direct second-order inelastic analysis for the design of planar steel frames. These guidelines, when completed, will provide the designer with guidance in analysis and modeling requirements, as well as design considerations (e.g. appropriate factors of safety) such that the behavior and strength of the overall system and limit states of individual members are checked concurrently without the need for individual specification member strength checks.

In the past three decades analysis techniques applied in the field of structural engineering have taken a very interesting journey from academia to practice. Linear elastic structural analysis techniques were immediately received favorably by the structural engineering profession when it was realized that computerized structural analysis could remove the tedious application of moment distribution in the analysis of simple framing systems, improve the accuracy of computations when comparing results to portal or cantilever methods, and allow more rational inclusion of three-dimensional behavior in the structural analysis and design. With the development of plastic design procedures of the mid-1960's and mid-1970's, the profession recognized that economy in structural systems may be achieved by implementing analysis procedures that were more reflective of structural behavior near the strength or stability limit state. It was truly unfortunate that thirty years of design experience using plastic design methodologies was lost as a result of a technique being developed at perhaps an inopportune time (i.e. pre-computer age). The migration of structural design methodologies to load and resistance factor design formats in the late 1970's and early 1980's brought renewed interest in developing structural analysis techniques that would more accurately reflect the response of structural systems at the stability and strength limit states. Structural analysis capabilities made significant leaps during the 1980's and early 1990's to the point where distributed plasticity analysis could be implemented on relatively large structural systems. These analysis capabilities were driven by the extraordinarily rapid development of computing power. Recognizing that computing power was going to increase in the coming decade, researchers began to examine ways of performing structural steel design without the use of the design specification equations through application of advanced computing techniques. In the steel research community, this was coined "advanced analysis". The Structural Stability Research Council defined advanced analysis, in a nutshell, to be an analytical methodology for the structural steel system that was capable of quantifying its strength through consideration of member out-of-straightness, story out-of-plumbness, residual stresses, material nonlinearity, and geometric nonlinearity. At the time of its development and initial research efforts, application of advanced analysis in practice was a long way off as a result of a lag in commercial software development capable of considering all these effects. To this point, advanced analysis unfortunately has been relegated to research endeavors. Today, inelastic analysis-based (i.e. advanced analysis-based) design of structural steel framing systems is on the cusp of practicality. The seismic engineering community has pushed development of inelastic analysis capability in commercial software to perform nonlinear pushover analysis; and the risk of progressive collapse in structural systems has also fostered rapid development of commercial software to perform nonlinear geometric and material analysis. The profession is now in a much more desirable position that it was in the 1970's when plastic (mechanism) analysis procedures were first developed. In fact, the level of computerized analysis made available today demands that the profession look back to the future. Computational power is now at the point where the profession can receive plastic analysis methodologies with open arms and specifications for the design of steel structures are on the move toward liberating structural engineers from the constraints imposed by design specifications. The 2005 AISC Specifications include Appendix 7 entitled Direct Analysis. This appendix was formulated upon the preceding decades-worth of work in the area of advanced analysis and stretching back all the way back to the Lehigh Summer Workshops on Plastic Design conducted in the mid 1960's. The fundamental needs and assumptions of the direct analysis methodology are as follows: (1) the designer must carry out accurate geometrically nonlinear analysis, (2) an effective length factor of 1.0 can be used to define the axial compressive capacity of a member when considering the combination of in-plane bending and axial loading, (3) out-of-plane flexural buckling capacity of the members must still be considered, (4) initial imperfections may be instantiated in the computer model, or a notional loading designed to simulate the effect of imperfections must be used in the analysis, and (5) if axial loading is 50% or more of the squash loading of the member cross-section, a reduced effective stiffness for the cross-section is included. Appendix 7 is the first step for the structural steel industry in the direction of including advanced simulation in the arsenal of the structural engineer to better understand structure performance. In the future, the design specifications would simply outline basic requirements of the simulation, and it would be up to the structural engineer to implement an analysis procedure that meets these requirements. The objectives of the presentation are to demonstrate the analysis activity that a structural engineer would likely undertake if he or she were to design a two-dimensional structural steel frame with partially restrained connections using the direct analysis procedure. To achieve these goals, the presentation will consider a planar moment-resisting framework and will: (1) provide an example of how a manual design procedure may be used for preliminary sizing of structural systems and checking the reasonableness of computer-generated solutions, (2) provide an example of how Appendix 7 procedures may be implemented in commercial-grade software, and (3) provide detailed distributed plasticity analysis results outlining the performance of a partially restrained structural system as it approaches the strength limit state.

Several types of floor systems can be integrated with cold-formed steel stud walls to form a suitable hybrid system for mid-rise load bearing construction. Hollow-core concrete planks offer the advantages of high stiffness-to-weight ratio, rapid field installation, and the longest design spans. The recent advances in cold-formed steel load bearing walls to be integrated with the hollow-core plank system include the development of stronger studs and stiffer lateral bracing members. The development of connection details and simplified design tools are also key elements to make this sytem integration a successful process.

Over the past decade, the cold-formed steel industry, both in the US and worldwide, has seen a significant increase in number of practical design guidelines and standards developed to facilitate structural design in residential, commercial and institutional buildings. One of these new standards, the 2004 American Iron and Steel Institute (AISI) Cold-Formed Steel (CFS) Design Standard — Lateral Design, provided designers with the necessary tools to better investigate, understand and engineer structures to comply with the wind and seismic provisions of the local building codes, particularly in regions with high wind and seismic risks. Where design for lateral loads is a concern, one important consideration is the distribution of lateral forces in accordance with the relative stiffness of the diaphragm and the in-plane wall bracing. Additionally, in seismic resistant design because interstory lateral displacements (drifts) are restricted, it is necessary to be able to computed expected inelastic lateral displacements. In this paper, the current provisions for estimating the lateral displacement of conventional CFS shear walls are reviewed and discussed. A comparison of inelastic drifts based on the Lateral Standard equations and inelastic estimates using the provisions of the 2003 International building is also presented and recommendations for future research are suggested.

For more than half a century, cold-formed steel framing (CFSF) has been used in the construction marketplace for light industrial, commercial, residential, and other building construction. CFSF has several advantages over wood framing that has been traditionally used for similar structures and framing. Steel is not-combustible. It is not susceptible to attack by mold, fungi, or other organic materials. It is not susceptible to termites, or other wood-eating or consuming organisms. It does not support mold growth. It is dimensionally stable with changes in moisture content or vapor pressure. It is isotropic, and does not have knots, cracks, splits, or wanes. Other products that have been used in this buildings sector include poured concrete, concrete masonry units (CMUs) tilt-up walls, and to a lesser extent, structural steel. CFSF has both advantages and disadvantages with respect to some of these other, non-combustible materials.

This paper presents the results of a series of uni-axial shake table tests performed at Colorado State University on a one-story woodframe house. The objective of these tests was to determine the correlation between the FEMA 356 suggested drift limits and qualitative damage descriptions. Ground motions having varying levels of seismic hazard were used. The house was repaired between each test and a total of six tests were performed. Correlations at each of these seismic hazard/performance levels are discussed for three versions of the one-story house: (1) the exterior wood shearwalls with only oriented strand board (OSB) and no non-structural finishes, (2) the exterior wood shearwalls with OSB and drywall, and (3) the exterior wood shearwalls with OSB and drywall and a non-structural partition wall. Although the drift limits associated with a particular hazard level were not always reached, relatively good agreement between the qualitative descriptions was found.

This paper compares damage to wood-frame shear walls from two independent sources, one experimental and the other a blind numerical prediction. Incremental dynamic analysis (IDA) was investigated as a possible tool for damage prediction. Qualitative damage descriptions and seismic force demands matched very well while maximum transient drifts did not match experimental results as well.

Hurricane Katrina, the most costly natural disasters in U.S. history, made landfall on August 29, 2005 at 7:10 a.m. local time in Plaquemines Parish, LA. Although Katrina caused widespread damage and loss of life, it also provided an opportunity to evaluate how woodframe construction performed in a naturally occurring high wind speed environment. A team of researches from across the country, sponsored by the National Science Foundation, conducted a three day study that investigated 27 sites containing woodframe structures along the Gulf Coast of Mississippi. Sites included entire subdivisions, light commercial structures, multifamily apartment buildings, and singe family homes. Observed wind induced damage at these sites included the loss of a few shingles, loss roof sheathing, loss of siding or brick veneers, porch collapses, roof loss, and also woodframe building collapse. The goal of this study was to examine wind damage in detail, determine the failure mechanisms when ever possible, and provide recommendations for individuals and organizations involved in the woodframe structure industry. Results of this investigation indicated that woodframe residential and light commercial structures that followed design codes and guidelines performed well during hurricane Katrina's wind loading. It appeared that builders and inspectors were familiar with conventional construction provisions; however, these provisions were used erroneously at times in this high wind region along the Gulf Coast. Where failures occurred, careful attention was not paid to all details, particularly the (correct) use of all straps and ties, to ensure a continuous load path from the roof to the foundation. It was observed that architectural shingles tended to remain intact more often that regular roof shingles and a closer/heavier nailing schedule for roof sheathing would reduce the amount of roof sheathing loss. Seemingly insignificant details such as the proper connection of non-structural siding resulted in the loss of siding followed by the loss of foam board substrate that allowed rain water intrusion and major damage. The information gained from this study will be useful to design engineers, owners, building material manufactures, builders, and building code officials whom are all striving to produce improved woodframe structures.

The vulnerability of wood residential construction to earthquake effects was evident from its performance during the 1994 Northridge earthquake. This paper presents a methodology for seismic reliability assessment of light frame residential construction subjected to various levels of earthquake ground motions. A finite element-based platform and stochastic models are used to simulate the behavior of wood frame structures in which shear walls provide the lateral force-resisting systems. Uncertainties in ground motion are identified and incorporated in the probabilistic analysis of system behavior, leading to fragilities (conditional failure probabilities) of the shear walls for various performance limits as a function of spectral acceleration. Seismic hazard curves that have been determined by U.S. Geological Survey are used to define the probabilities of a spectrum of earthquake hazards. Probabilities of failing to meet stipulated performance goals can be calculated by convolving the structural fragility with these seismic hazard curves. This methodology can serve as a tool for quantitative seismic reliability assessment for residential buildings, and a basis for loss estimation and for improvements to current residential construction practices.

Running a successful airport with projections of increasing passenger demand, the Raleigh Durham Airport Authority is building a replacement for their existing Terminal C. The new Terminal C will feature over 800,000 square feet of processor and concourse space and 30 gates. In addition to creating a first-rate passenger experience, the Authority expects to create a regional gateway and an architectural landmark. Construction began in the fall of 2004, with the phased demolition of portions of the existing Terminal C as required to make room for the first phase of the new terminal. This was followed by construction starts on a new Central Energy Plant and a portion of the terminal building foundations. At the time of this writing, the Authority is evaluating bids for the terminal building itself, with construction expected to begin shortly. The lead architectural firm, Fentress Bradburn Architects, began by developing a design intended to celebrate the character of the region. A rolling roof line was conceived to suggest the Piedmont's hills. The architects also seized on the culture of craftsmanship reflected in the region's textile and furniture making industries. In response, we promoted an exposed timber roof as a natural fit to their design goals. Timber evokes this sense of craftsmanship both by virtue of its material qualities as well as the large scale structural connections. The wood structure also promises to differentiate RDU from other terminals; most of which are constructed from steel trusses.

For many hundreds of years, builders have found needs and applications for timbers bigger than they could readily find within the trees from local forests. An obvious solution lay in bundling smaller timbers to make larger ones. This can work well, and even ease installation, but is generally not as structurally efficient as using solid sections. Builders, even early ones, recognized the value of generating some composite action between the components, with the attendant gains in load capacity and/or reduced member sizes. Modern glue technologies can yield composite action at least on a par with Mother Nature's. Before we had such cheap and reliable glues, however, we relied on mechanically connected — or laminated — composite members. Builders have applied a lot of ingenuity and effort, in developing composite action among grouped timbers. The literature contains many examples of mechanically laminated beams; some nearly breathtaking in their elegance, others in their costliness. Innately, none of them can offer the same degree of composite action as solid or glue-laminated timbers. Even given modern forests of smaller trees and modern gluing techniques, however, there are still some undeniable reasons to mechanically laminate smaller timbers into bigger ones. Most of the reasons revolve around aesthetic impacts in exposed and celebrated timber structures. Some building owners simply have trouble with the "stripiness," and the industrialized appearance, of modern glue laminated timbers. The Greene brothers, famous architect/builders of early twentieth California bungalows, celebrated the fine craftsmanship required in key laminated exposed timbers. Building realities, however, can make mechanically laminating a tempting option even for contemporary builders interested in replacing large timbers that are still available as solid sawn timbers.

A longstanding and excellent client called with a unique problem. The Metropolitan District Commission (MDC) was charged with maintaining the Bernie King Pavilion. Built in the late nineteenth century, the structure is an open pavilion located on Nantasket Beach in Hull, Massachusetts — a town that lies on a peninsula that extends northward to form the southeast protection for Boston Harbor. Originally, the pavilion stood between two hotels, providing a shelter against rain for summer picnics and a shady respite from the bright summer sunshine. With summer winds and thunderstorms generally blowing from west to east, the structure's west wall formed a partial enclosure, with varying low and full-height in-fill panels. A low sloping roof rose from the west eave to a ridge line very close to the structure's east edge. There, a steep pitch brought the roof line back down to the eave. The east side of the pavilion was fully open, with a view of the beach and the Atlantic Ocean beyond. As the MDC architect and project manager examined the condition of the structure, he realized that the timbers and their connections had suffered irreparably from the effects of a century of exposure to the New England weather. Repair would be impractical, so the difficult decision was made to raze the existing building and replace it with a historically faithful reproduction. What follows is my account of the journey taken to support this goal. What started as a response to a simple request for a structural evaluation of the existing timber structure became an assignment to design a structure and all of its connections to meet the demands of current building codes and simultaneously to meet the aesthetic objectives of a passionate historical society.

This paper discusses strengthening and remediation of a roof structure at the Massachusetts Institute of Technology's (MIT) W33 Cage Building. Twenty-four, curved-chord wooden lattice roof trusses comprise the roof structure of this athletic facility that has been in service for over 50 years. The trusses, which span 100 ft and are predominantly constructed of `two-by' (2 x ) dimension lumber, had become a concern due to multiple, local failures of the bottom chord. To avoid future safety concerns and the continuation of costly maintenance associated with repairing the fractures locally, Simpson Gumpertz and Heger (SGH), on behalf of MIT, designed a global remediation and strengthening scheme for the trusses. The main feature of this repair was the installation of post-tensioned steel rods designed to relieve the truss bottom chords of overstress due to code-prescribed snow loads. Custom fabricated, steel brackets were installed at the heel joints to transfer the top-chord loads into the new steel tension rods. Strain gages were employed to monitor the transfer of dead load into the steel rods during initial post-tensioning. The post-tensioned strengthening scheme provided an economic solution for prolonging the service life of the truss structure and efficiently utilizing other existing portions of the roof structure.

A portable real time vibration measurement data acquisition system was assembled with the intention of studying the accuracy of the results provided by the AISC Design Guide 11 design equations. Some experiments were conducted in the field with the interest of refining experimental methods and obtaining preliminary data. Some observations were made regarding the data obtained in these experiments.

This paper addresses the analysis and experimental investigation of PMC panels utilized for seismic and vibration mitigation. The concepts rely on introducing considerable shear deformation at strategically located layers. The layers at which the shear deformation to take place, referred to here as the interface layers, are composed of a combination of solid visco-elastic material combined with honeycomb material. As part of this research, a series of experiments were performed to quantify the energy dissipation characteristics of the interface layer. The effects of thickness, loading rate, and the ratio of the volume fractions of the constituent materials are investigated. Utilizing the results obtained from material testing, three conceptual panel designs were tested to assess the over all energy dissipation in a structural system. The main advantage of these panels is that they can reduce floor response in a structural system. As such for Hospital structures, the concern is to reduce the floor responses to mitigate damage to nonstructural components that are motion sensitive. In this research, the conceptual designs of the panels are employed in a benchmark hospital building-namely, the Multidisciplinary Center for Earthquake Engineering Research (MCEER) demonstration hospital structure. Nonlinear 3D finite element analyses were carried out to evaluate the effective damping of added PMC composite panel with viscoelastic interface layers in the retrofitting of the MCEER's demonstration hospital structure. An equivalent Kelvin model consisting of an elastic spring and a linear viscous damper combined in parallel is proposed to represent the FRP composite panel with viscoelastic interface layers. The retrofitted structure was subjected to MCEER west coast ground motions. Significant increase in the system damping was observed with the added PMC composite panels. Both the modal strain energy method and logarithmic decrement method showed the PMC composite panel contributed 8% damping to the hospital structure. Time history analyses results showed that the peak floor displacement and acceleration response were reduced significantly and the vibration damped out very quickly.

Low-frequency floor and footbridge vibration serviceability problems typically arise when the structure is excited in resonance due to a walking excitation and the resulting accelerations exceed human comfort levels. The measures required to resolve an annoying vibration problem after the structure is constructed can be very difficult and expensive to implement. In most cases, the costs of fixing the problem in-situ are much greater than tackling the problem in the design phase, prior to the structure's construction, considering the potential cost to building owners from possible legal expenses, loss of rental revenue, and consultation fees. Design guidance for composite steel framed floor systems and footbridges is available in the AISC/CISC Steel Design Guide Series 11: Floor Vibrations Due to Human Acitivity. Although the current design guidance is generally acceptable, there is a need to continue characterizing the often-complicated vibration behavior of these structures in an effort to refine current design and analysis techniques, particularly as researchers gain a better understanding of behavior by collecting high-quality experimental data on in-situ floor and footbridge structures. This paper presents observations from such efforts to further characterize behavior through experimental modal testing of a large in-situ composite steel office floor and a laboratory constructed multi-span footbridge. While not entirely inclusive, some general observations are noted on the dynamic behavior, problems encountered, and the consistency/reliability of the applied testing/analysis techniques employed by the researchers.

Forms of vibration criteria for sensitive equipment are discussed. The forcing history parameters associated with walking at various speeds are delineated and quantified. Graphs are presented for estimation of the maximum and root-mean-square velocities and accelerations of floors subject to typical slow, moderate, and rapid walking. Application of these results to practical situations is discussed.

Of mid-1990s use nonprestressed composites (FRP strips) for strengthening structures throughout world as well as Czech Republic. Experiences obtain on strengthening structures and practise experimental test make for result, that for utilize material property composites and for increasing effectiveness strengthening structures have to need use FRP strips, as that of prestressed reinforcement in the form of reinforcement no cohesion (loose cable). By reason of safety so that do need mechanical failure FRP strips, there are bond in the entire area.

Fibre Reinforced Polymer (FRP) strips offer an economic strengthening alternative for steel I-beams. Investigations are currently limited to applying FRP strips to the tension flange of the I-section to increase its flexural strength. However, for thin walled "slender" I-section steel beams, the risk of buckling failure is also a major concern. According to CAN/CSA-S16, I-sections subject to flexure are classified into four classes depending on the width-to-thickness ratios of the web and the flanges. Compact sections of Class 1 and Class 2 can develop the full plastic moment of the cross-section while Class 3 sections are guaranteed only to develop the cross-section yield moment. Failure of Class 4 sections is controlled by local buckling: these sections fail before reaching the yield moment. A numerical investigation is performed to investigate the effect of bonding CFRP strips to the webs of I-section steel beams on the beam's flexural strength. The main advantage of this innovative technique is delaying the local buckling of the beam's web and allowing a slender I-section to reach its yield or plastic flexural capacity. Different details for bonding the CRPR strips to the web are investigated. The study reveals that bonding the CFRP strips to the web of a slender I-section significantly increases the critical load and may allow the beam to reach its yield or plastic capacity.

Seattle's Harborview Medical Center is a critical community resource and the only regional Level 1 trauma center in a five-state area. To retain that status, the Harborview Bond Program calls for a seismic upgrade of the hospital's North Wing, which was designed in 1973. The North Wing houses critical emergency services and will serve as a vital physical link between the existing West Hospital and the new Inpatient Expansion Building. The performance of the North Wing in an earthquake therefore has to be consistent with the performance of newer construction, requiring an upgrade to current seismic performance standards for Essential Facilities. When engineers at Magnusson Klemencic Associates (MKA) began the structural design for the seismic upgrade, the following goals were established: (1) the building shall allow for "Immediate Occupancy" following a design-level earthquake (with Immediate Occupancy being defined as minimal post-earthquake damage and disruption, with some repairs and cleanup performed while the building remains occupied and safe), (2) the seismic upgrade must be accomplished without closing off major portions of the building, (3) disruption to the critical functions within the building must be minimized during construction, and (4) an economical design solution—within the current bond budget—must be provided. Seismically upgrading a full-to-capacity trauma center while it remains completely operational presented a significant challenge. The earthquake-resisting system in the North Wing consists of concrete shear walls around the elevator core and perimeter concrete walls. The perimeter walls have 14-inch-thick vertical piers between the windows and 6–1/2-inch-thick concrete panels stacked on top of the windows, spanning between the vertical piers. A computer analysis of the North Wing revealed that the building is very stiff but the thin concrete panels are at risk of cracking, yielding, and losing strength during an earthquake.

Externally bonded FRP has been established as a successful technique for strengthening concrete members. Other techniques, like Near Surface Mounted (NSM) FRP bars, have emerged as viable alternatives. In this study, four composite-based strengthening systems were designed to provide equivalent flexural performance. These systems were externally bonded Carbon Fiber Reinforced Polymer (CFRP) sheets, NSM prefabricated CFRP strips, externally bonded Steel Reinforced Polymer (SRP) sheets known as Hardwire ® and NSM stainless steel bars. The strengthening design was based on achieving approximately 33% increase in flexural capacity over the unstrengthened control beams. The mode of failure by design was concrete crushing using a maximum concrete compressive strain of 0.003. Six beams were tested under three-point bending, two as control specimens and four strengthened with each of the systems mentioned above. The experimental results of the strengthened beams showed that a higher strengthening ratio of 50% can be accurately achieved using these techniques despite the different failure modes involved. Failure of all strengthened specimens was initiated by concrete crushing and top cover spalling. However, the post peak capacity of confined concrete allowed for better utilization of the flexural section that led to significant stresses in the extreme compression and tension fibers that eventually caused rupture or partial delamination of different strengthening systems upon confined core crushing. Comparisons of experimental response and detailed numerical predictions show excellent correlation. The numerical procedure takes into account the compression behavior of confined concrete based on Kent and Park model. Constructability evaluation was achieved based on man-hours of labor and concerns encountered during installation.

In Simple-Span Precast Prestressed Bridge Girders Made Continuous to improve structural efficiency partial and/or full continuity is provided through cast-in-place concrete diaphragm and decks. That is, the bridge behaves as continuous or partially continuous for live loads. The continuity connection is also beneficial from a maintenance point of view by eliminating open joints. However, existing continuity connections also have their own structural, construction, and maintenance shortcomings. Development of positive moments and diaphragm cracking at the internal pier due to time dependent effects is a major structural problem that also affects bridge durability and esthetics. Another issue is that due to reinforcement congestion, joint construction is time consuming and thus expensive. Furthermore, the degree of continuity varies depending on structural and construction conditions. These problems are common to various design details used by many states in the US. This paper discusses the development of a new continuity connection using Carbon Fiber Reinforced Polymer (CFRP) sheet that will address these problems while further enhancing structural effectiveness. To provide continuity, CFRP reinforcement is attached to the top of the girders over the cast in place diaphragm. The negative moment over the supports caused by the deck weight balances the positive restraint moment caused by creep in the prestressed girders. Thus, while increasing structural efficiency the proposed design eliminates positive moment cracking. Furthermore, there is no need for positive moment reinforcement in the diaphragm under gravity loads, thus, reducing reinforcement congestion and facilitating construction. A series of laboratory tests were carried out to validate the new connection. The results support the viability of the proposed connection and that CFRP sheet is an ideal material for continuity connections.

Fiber reinforced polymer (FRP) bridge decks are used in bridge rehabilitation projects, often because of their relatively low self weight and high durability. Related benefits of FRP include rapid construction and advantages in terms of life cycle costs (e.g., corrosion resistance). A case study bridge in Tippecanoe County is the first in Indiana to be rehabilitated with a FRP deck. Among the bridges evaluated, County Road 900E over Wildcat Creek is a three-span continuous steel stringer bridge with two concrete approach spans. The FRP deck replacement would only take place on the three main spans. This bridge rehabilitation project presents a unique challenge in that the deck would be widened with no changes to the superstructure. The resulting overhang would also be the longest seen for this application. Since the properties of FRP are such that serviceability issues govern deck design, requirements for the overhang dominate decisions related to deck type and geometry, and choice of barrier or guardrail. These and other project details will be discussed. The choice of deck is affected by deflection limits of the overhang at the exterior stringer. Based on American Association of State Highway and Transportation Officials (AASHTO) span-to-deflection ratio recommendations, a deck produced by hand lay-up rather than pultrusion is selected. The ability to tailor the deck cross section geometry to satisfy serviceability limits motivated this decision. The FRP deck consists of a honeycomb core sandwiched between two faces, or structural surfaces. This bridge design also involves a trade-off between a deeper section to satisfy deflection criteria and overall cost. Specifically, a deeper section will increase material cost for FRP and the cost of building up the concrete approaches to match the deck height on the main spans. The deck geometry also affects the decision regarding proposed stiffener brackets, which would supply discrete support points to the overhang at each diaphragm location. Finite element analyses show that the deck is significantly more flexible in its transverse direction, affecting distribution of load and resulting in absolutely no reduction in deflection or stress with the bracket supports. The brackets are therefore excluded from the design. Finally, the choice of vehicular rail/ barrier is also affected by the overhang. Both concrete barrier and steel guardrail options are evaluated. AASHTO allows for a reduction in overhang loading for concrete barriers due to the structural continuity provided to the deck. However, finite element analyses demonstrate that this provision is not applicable for this FRP deck application. This and dead load considerations result in the choice of a steel guardrail.

Because of advanced corrosion of the steel reinforcement, a large number of reinforced concrete bridges in the Federal Highway System require rehabilitation. To alleviate this problem, Fiber Reinforced Polymer (FRP) materials are being investigated as an alternative reinforcement to replace the steel. This research was carried out to find out whether FRP-reinforced concrete flexural elements will perform adequately under cyclic loading. This research focuses on investigating the effects of cyclic loading on flexural strength of members reinforced with FRP reinforcing bars. The results indicate that the flexural strength of the FRP reinforced concrete specimens studied remained virtually intact after the cyclic loading.

Behavior of column specimens reinforced with a new reinforcement, termed Prefabricated Cage System (PCS) is investigated. A total of 16 small-scale PCS and rebar reinforced column specimens with normal strength concrete were constructed and tested. The experimental data indicate that the PCS reinforced specimens have better overall performance and are more ductile than the equivalent rebar specimens. The effect of different parameters, such as the tube thickness, number of longitudinal reinforcements, transverse steel spacing, and crossties on the specimens' strength and deformation capacity are also investigated.

The Federal Highway Administration (FHWA) funds programs for State Departments of Transportation (DOTs) to advance new technology and techniques in the design and construction of transportation infrastructure projects. These grant funding programs directly contribute to the goals of cost efficiency and traffic mobility. Maximizing the efficient movement of the public throughout states during the execution of bridge repair or replacement projects creates cost savings to the state, traveling public and commerce. To attain these goals, federal programs have been identified that assist in funding innovative design and construction techniques. This paper summarizes current and upcoming programs that can assist State DOTs in meeting these needs. Examples of the types of innovation that have recently been funded or constructed throughout the United States are discussed, and background information used to apply for federal grant money is highlighted.

Research on structural performance of confined self-consolidating concrete (SCC) tubes as short columns is scarce and there is little data available. Similarly there is little research on use of blended cement containing agricultural waste i.e. rice husk ash as cementitious material in normal/high strength concrete. Limited research has shown better performance of such blended cements with increased strength by up to 30% and improved durability, reduced permeability and shrinkage. It's behaviour under confined conditions is still to be studied. This paper provides valuable research in this area with special focus on the use of blended cement SCC confined in steel tubes applicable for columns of bridges, buildings as well as in deep foundation applications. This paper presents an experimental study on the behaviour of short, SCC, with blended cement containing 75% ordinary Portland cement and 25% rice husk ash, filled steel tubular columns axially loaded in compression to failure and comparing the results with testing on similar hollow tubes and tubes filled with normal concrete. Almost 350 to 460% increase in strength was observed by filling steel tubes with SCC (containing blended cement) in square and circular tubes respectively. Failure strains were also reduced by 40 to 45%. Smaller steel sections and use of blended cement containing rice husk ash increases efficiency, reduces cost of construction along with reducing the disposal problems of this massively produced agricultural waste in the rice growing regions.

Rice husk is an agricultural waste generated in massive quantitites from rice processing units worldwide. With no worthwhile use, it is a waste material which creates disposal problems. It's high silica content makes it suitable for use with cement. Very limited investigations on rice husk ash have suggested improved strength/durability however its performance in high strength SCC has not been investigated to-date. This experimental study aimed at evaluating the properties of high strength SCC made from blended cements using rice husk ash, portland cement, natural aggregates and sand. Wide ranging investigations covering most aspects of mechanical behaviour and permeability were carried out for various mixes for compressive strengths of 60N/mm², 80N/mm² and 100N/mm². Compressive strengths of high strength SCC specimen with blended cements for 60N/mm², 80N/mm² and 100N/mm² were observed to be higher by about 4 to 9% than the control specimen, for concrete with 50% Portland cement blended with 50% rice husk ash. Higher elastic moduli and reduced permeabilities were observed along with better sulphate and acid resistance. Better strengths and improved durability of such high strength SCC make it a more acceptable material for major construction projects.

Ultra-high performance concrete (UHPC) is proposed as an innovative new material for the construction of highway bridge superstructures. UHPC mix designs typically include no aggregates larger than sand, and include steel fibers 0.2 mm in diameter and 13 mm in length. These steel fibers and special mix design increase the strength and toughness of the UHPC significantly relative to more traditional concretes. However, low water to cement ratios typically used result in difficult casting and curing conditions and as a result there is a need to evaluate strength and stiffness parameter of as-cast members. This research reports on the development of ultrasonic methods for monitoring the elastic properties of UHPC under a series of curing scenarios. Ultrasonic velocity measurements are used to estimate the bulk elastic modulus, shear modulus and Poisson's ratio of UHPC and results are compared with traditional, destructive methods. Changes in ultrasonic velocities during curing and relationships to early-age strength of the materials are discussed. The application of ultrasonic testing for the evaluation of early-age material properties and for nondestructive, in-situ materials characterization are explored. The potential for the development of practical quality control techniques for the future implementation of UHPC is also discussed.

In several successful accelerated bridge construction projects in Florida and Texas, pre-fabricated bridge pier components have been utilized, which result in significant reduction of the construction schedule. This paper summarizes major accelerated bridge construction projects through adopting pre-fabricated bridge pier components, which shows its popularity in recent years. In particular, details in geometry, reinforcement, and connections from several projects are compared, focusing on their applicability in seismic regions. Systems in seismic regions investigated recently by several research groups are also summarized and compared. As concluding remarks, issues and recommendations regarding connections and reinforcement detailing are summarized.

Segmental bridge column construction has been proven to be an economic and durable option to accelerate the bridge construction in non-seismic regions in the United States. Examples include Seven Mile Bridge in Florida and Chesapeake and Delaware (C&D) Canal Bridge in Delaware. The lack of knowledge of the seismic behavior of a bridge with segmental columns is one of the important reasons which limit the use of such kind of system in seismic regions. To promote the use of segmental bridge columns into seismic regions, four large scale segmental columns were constructed and tested at National Center for Research on Earthquake Engineering (NCEER) in Taiwan. Recently, some researches on seismic behavior of precast segmental columns have been carried out worldwide. Some studies emphasized the use of bonded tendons to enhance the durability and strength of the column as opposed to unbonded systems. Relevant studies can be found in Mo et al. and Arai et al. In addition to the bonded systems, some other researchers advocated the use of unbonded tendons to reduce the possibility of the yielding of the tendons, thus preserving the necessary clamping force after strong seismic event. Relevant studies can be found in Hewes et al., Chou et al., Billington et al., and Lee et al. The first column specimen tested in NCREE used unbonded post-tensioned tendons and no supplemental energy dissipation devices were provided. The other three specimens used bonded tendons and were provided with mild steel reinforcements that were extended across the joints to enhance the hysteretic energy dissipation.

For accelerated bridge construction, substructures are critical path elements of the schedule in many cases. In order to accelerate the construction of substructures, in particular, piers, precast concrete segmental columns (PCSC) has been used for a number of projects. However, their application in strong seismic regions is very limited because of lack of experience and knowledge. Recently, several analytical and experimental studies investigated the possibilities and the problems of PCSCs. It has been observed that the interface between segments experience opening-closing under cyclic loadings, which prevent the formation of plastic hinges at the intended bottom/top of the column. In this present study, a finite element analysis scheme is developed for analyses of PCSCs. The modeling requires accurate and robust characterization of concrete material, reinforcing steel, post-tensioning tendons, and segmental interfaces. Finite element analysis pushover results compared well with available experimental results. The finite element analysis scheme was extended to determine seismic characteristics of the system. Furthermore, seismic response of the structures subjected to earthquake ground motions is to be investigated based on nonlinear dynamic time-history analysis.

Over the years, precast bent cap systems have been used on a variety of bridges to meet project goals. These systems can accelerate construction, reduce environmental impacts, improve worker safety, and provide more durable and economic structures. Currently, minimal guidance is provided to engineers who design such systems, and this limited guidance has led to a wide variety of systems being used. Traditionally, connections made between precast members are the biggest uncertainty related to their performance. Adequate performance of these connections is essential in order to achieve satisfactory system behavior over time under any loading situation; however, their performance can greatly affect the behavior of precast bent cap systems during seismic events. A better understanding of system and connection behavior during strong ground motion is required in order to ensure good long-term performance and to facilitate the widespread use of these innovative systems. A review of current practice was conducted as a part of the recently funded National Cooperative Highway Research Program (NCHRP) Project 12–74, "Development of Precast Bent Cap Systems for Seismic Regions." Information obtained through these efforts is provided in this paper, as well as a discussion of work which is needed in order to provide design engineers with tools that can be used to confidently design precast bent cap systems in all seismic regions.

In this paper, we present a study conducted on investigating the nature of damping matrix associated with multi degree of freedom simple shear building models. The various conventional methods of creating damping matrices in structures are summarized and numerical examples are used to illustrate the inconsistencies among them. Numerical examples are also used to illustrate the significance of non-zero off diagonal terms in the transformed damping matrix obtained after pre and post multiplication with mode shape matrix, i.e. the significance of non-classical nature of damping matrix in certain cases. The analytical study is followed by the description of a laboratory experiment that is developed to evaluate the validity of analytical results. The results from experimental studies of a simple 2-DOF shear building model are presented to validate the inconsistencies associated with the conventional methods of creating damping matrices in structures. It is also shown that the incorrect formulation of damping matrix results in highly incorrect responses.

In this paper, a damping-enhanced strengthening technique is introduced for seismic retrofitting of reinforced concrete (RC) columns for multiple performance objectives. This technique involves an integrated and compact system of fiber reinforced polymer (FRP) sheets and viscoelastic (VE) layers. The effect of various parameters of VE layers on the dynamic response of a column was studied. Shear strain distribution of VE layers was analyzed to help understand VE material effects on the performance of the column. Numerical results indicated that the proposed technique is very effective in reducing not only the acceleration response but also the displacement response of the column.

The quartz resonator is the most common piezoelectric resonating structure designed to provide a stable frequency source for electronic devices and applications. An important figure of merit for the quartz resonator structure is the quality factor Q which measures the "sharpness" of its frequency response curve and its frequency stability. This quality factor Q is inversely proportional to the energy loss per cycle of oscillation. The Q is hence also inversely proportional to the resonator resistance or impedance. Currently there are no analytical tools for estimating the Q without an apriori assumption of the resonator damping or impedance. In order to get good numerical agreement with the measured data, all the current finite element software requires an assumption of either the resonator resistance or resonator Q value. We propose and present a new analytical tool for estimating the quartz resonator Q and other figures of merit by an energy sink method. Results for the thickness shear mode, AT-cut quartz resonators are presented. Experimentally measured material constants of mechanical dissipation and conductivity of quartz was included in our models. Our energy sink method is more realistic than assuming the crystal impedance or Q. One of the most important factors affecting the Q in the design of a new quartz resonator structure of a given frequency is the loss of energy from the electrode area to the base via the mounting supports. The acoustical characteristics of the plate resonator are changed when the plate is mounted onto a base. This is analogous to a soil-structure interaction problem with a semi-infinite boundary. The substrate base affects the frequency spectra of the plate resonator. A resonator with a high Q may not have a similarly high Q when mounted on a substrate base; hence the base is an energy sink. We present the frequency spectra of the quartz resonator with and without the substrate base. A scaled boundary finite element method is employed to model a semi-infinite base. Since a semi-infinite base will absorb all acoustical energies radiated from the resonator, a forced vibration analysis of such a model will provide the lower bound Q values. The model with a semi infinite base could be used for evaluating resonator and mountings designs. The effect of the mountings, plate and electrode geometries on the resonator Q and other figures of merit are presented. Comparisons of the experimental measurements of the admittance and Q with the simulated results using the semi-infinite energy sink method were performed. The measured admittance compared very well with the simulated results. The measured Q showed the same trend as the simulated Q.

Typical bridges in the state of Alaska are characterized by columns with excessive reinforcing ratios encased in a steel shell that is partially embedded in the bent cap; analysis of existing bridges indicate that the bent caps are inadequately designed for flexure, shear, and joint shear for the feasible moments that would be imposed upon them during a seismic event. This research proposes a method to retrofit such bridges to perform in a ductile manner during a seismic event. Three 80% scale column-bent cap t-connections were built to model such typical as-built bridges in Alaska. They were retrofitted to improve their response to a lateral loading and then tested under a reversed cyclic load. From a moment curvature analysis of a prototype column and bent cap, it was decided to reduce the longitudinal reinforcement ratio of the column at the joint to increase its ductility at lower lateral load levels and subsequently to reduce the moment demand on the adjacent bent caps. As such, the moment ratio of the bent cap over the column was increased thus forcing the plastic hinge to form at the top of the column, as this is the current seismic design practice. Using existing strut and tie models for joint design, additional reinforcement was provided to prevent joint shear failure. The retrofit was applied by enlarging the bent cap in the joint region to allow for proper placement of the additional reinforcement. The specimens were then loaded in a reversed cyclic loading and results from this research program are presented and discussed in this paper.

In this paper, based on vibration measurement and analysis of finite element method (FEM) for RC framed structure, Genetic Algorithm with real number encoding (GARNE) is employed in diagnosing crack damage occurrence, location, and severity for the RC framed structure by means of minimizing the objective function, which directly compares the changes in vibration data (namely, the frequency changes, the mode shape changes and simultaneous changes of both the frequency and the mode shape) measured from the un-cracked and cracked RC framed structure. The GARNE explores the region of the whole solution space and can obtain the global optimum. Numerical results show that the cracked elements can be diagnosed by the GARNE. The effectiveness of the GARNE for such crack damage diagnosis of the RC framed structures is verified through comparison with site measurement.

A new concept for the design of coaxial cables was recently proposed and developed by the research team by introducing the change in topology of the cable structure when the cable is subjected to strain effects. In this study, three implementation issues are discussed to further advance the emerging technology towards its commercialization and implementation for crack monitoring and detection of reinforced concrete (RC) structures. They include plasma sprayed coating of a coaxial cable sensor, correlation between the reflection coefficient and the width of a crack, and interference of steel reinforcing bars with the electromagnetic field used for time-domain reflectometry measurements. Test results have shown that the sprayed coating can significantly enhance the uniformity of coaxial cable sensors and thus the quality of measured data. With controlled cracking tests, the peak reflection coefficient was found linearly related to the width of a crack. Furthermore, the interference by the adjacent steel bars is negligible even when a coaxial sensor is nearly in contact with a reinforcing bar.

Wood has many talents, including, among others, the possession of growth characteristics that provide it with stiffness and strength in key directions, a naturally superior resistance to fatigue loading compared with many other structural materials, and piezoelectric properties that, as we are wont to say, must be there for some reason. A piezoelectric material is one that becomes electrically polarized when mechanical stress is applied, a so-called direct effect. A converse effect is the onset of deformation when the material is placed in an electric field. These are characteristics exhibited by many materials, among them many polymers, and wood is a piezo-active polymer. The most widely accepted reason given for the piezoelectric property in wood comes from the microfibrils that make up part of the cell wall structure. These cylindrically-shaped structures, which have diameters in the 10–30 nm range, consist of regions with both parallel and more amorphous arrangements of chains of cellulose molecules. It is in the more orderly parallel portions of this structure, called crystallites because in the aggregate they have a crystalline structure, that the piezoelectric effect has its origin. Piezoelectric properties of wood are correlated with the degree of crystallinity. Given that piezoelectricity exists in wood, can this electrical property be used in such applications as structural health monitoring since, as reported below, its voltage potential appears to be proportional to the magnitude of applied stress? The results reported herein are from a computational study into the feasibility of using surficial voltage or charge measurements to predict mechanical stress unobtrusively for the purposes of structural health monitoring. The present study is focused on modeling dry wood subjected to static loads; future research will include wood with moisture and cyclic loads.

Monitoring of civil engineering structures is a new area that has gained significant attention recently and became a topic of extreme national interest. This area is being driven by the need to develop efficient condition assessment procedures for structural performance in response to societal and economic needs. The main goal of monitoring is to detect accurately and efficiently structural damage either due to long-term deterioration processes or due to extreme events (e.g. earthquakes, blasts). With the emergence of new technologies, structures can now be monitored remotely from a central monitoring station located several miles away from the field. Sensors are placed at several critical locations along the structure, and send structural information to a central station. The structure is thus thought of as an intelligent or smart system that is capable of sending information and providing warnings before any major failure. This remote capability allows immediate damage detection, so that necessary actions that ensure public safety are taken. The research work concerns the development, construction, and testing of the first smart bridge structure in Florida, the East Bay bridge over Bullfrog Creek in Gibsonton, Hillsborough County. Fiber Optic Fabry-Perot smart sensors were both surface-mounted to the concrete, and bonded to the deck reinforcing bars during the construction phase of the bridge. Static and Dynamic testing of the bridge were performed using loaded SU-4 trucks. A 3-dimensional analytical finite element model of the bridge was developed and its results were compared to the test data. The study confirmed the accuracy of the sensors in estimating the bridge behavior under heavy truck loads. In addition to the tests described above, the smart sensors are currently being connected to a data acquisition system permanently installed on-site. The acquisition system could be accessed through remote communication with DSL lines, which permits the evaluation of the bridge behavior under live traffic loads. Currently, live structural data under traffic loading is being transmitted continuously to the county maintenance office. The technology developed under this work will enable practical, cost-effective, and reliable maintenance of bridge structures, and the study will provide a unique opportunity for future growth of this technology within the state of Florida.

Fuzzy logic control (FLC) systems have been applied as an effective control system in various fields, including vibration control of structures. The advantage of this approach is its inherent robustness and ability to handle non-linearities and uncertainties in structural behavior and loading. The study evaluates the three-dimensional benchmark control problem for a seismically excited highway bridge using an ANFIS driven hydraulic actuators. An ANN based training strategy that considers both velocity and acceleration feedback together with a fuzzy logic rule base is developed. Present study needs only 4 accelerometers and 4 fuzzy rule bases to determine the control force, instead of 8 accelerometers and 4 displacement transducers used in the benchmark study problem. The results obtained are better than that obtained from the benchmark control algorithm.

The seismically excited benchmark problem is based on the newly constructed 91/5 highway over-crossing in Southern California. The goal of this effort is to develop a standardized model of a highway bridge using which competing control strategies, including devices, algorithms and sensors, can be evaluated comparatively. To achieve this goal, a 3-D finite-element model is developed in MATLAB to represent the complex behavior of the full-scale highway crossing. The nonlinear behavior of center columns and isolation bearings are considered in formulating the bilinear force-deformation relationship. The effect of soil-structure interaction is considered by modeling the interaction by equivalent spring and dashpot. The ground motions are considered to be applied simultaneously in two directions. A MATLAB based nonlinear structural analysis tool has been developed and made available for nonlinear dynamic analysis. Passive, semi-active and active control devices are assumed to be installed between the deck and the end-abutments of the bridge. Evaluation criteria and control constraints are specified for the design of controllers.

Recently, a benchmark problem has been developed to study seismically excited highway bridges. In the second phase of the aforementioned study, the bridge is isolated both at the abutments and at the central pier location. The isolation, though effective in reducing the superstructure responses such as mid-span accelerations, results in increased mid-span and isolator displacements. The performance of a newly developed Lyapunov semiactive controller in reducing the isolator and mid-span displacements is investigated analytically on this newly developed phase II full-scale three-dimensional seismically excited highway bridge. The bridge is isolated using nonlinear hysteretic bearings with a lead core on the inside and an elastomer surrounding the lead core. Magneto-rheological (MR) dampers are used to control the seismic responses of the bridge semiactively. The semiactive control devices are installed at the isolation level between the deck and the isolators on bridge piers and center column at ten locations, each location consisting of a single orthogonal pair to control the responses in both directions. The outputs allowed in the benchmark problem definition are used to design the controller and where velocity measurements are required, the accelerations are integrated using a filter that simulates integration. The performance of the controller is analyzed in terms of the performance indices defined in the benchmark problem definition. The results of the Lyapunov controller are compared with the results of the sample controller presented in the benchmark problem.

Active and semi-active control methods for reduction of the dynamic response of structures are emerging and some are being implemented in buildings and bridges. This vast growing technology ows to recent developments of sensing and digital control techniques. Semi-active control is a promising approach for the seismic response reduction in which the control offers the adaptability of active control without requiring the associated large power sources, since the external energy is only used to modify the dynamic properties (e.g., stiffness, damping, and friction level) of semi-active device during an earthquake attack. Therefore, the semi-active control devices can be considered as controllable passive devices. The problem lies on what algorithm should control this device so that the structural response is favorable under earthquake excitation. Earthquake input energy absorption capability of structural components described by hysteretic loops plays the key role in ensuring proper seismic performance of structures. Members that have stable and large hysteretic loops are considered as ductile have been proved successful in reducing seismic responses. For very important structures, energy-absorbing devices are added to structures so that the hysteretic loops are localized only at the devices. For seismic isolation techniques, for example, hysteretic loops are also employed at the isolation devices to reduce excessive displacement. In this study, passive and semi-active control devices combined with base isolation bearings are used to generate desirable hysteretic loops. The control algorithm is designed so that the combination of the variable damper and isolation bearings yields the desirable hysteretic loops.

This paper presents an application of fuzzy logic for response modification of the seismically excited highway bridge benchmark problem. The benchmark problem consists of a three-dimensional, nonlinear model of an isolated two-span continuous prestressed concrete box-girder bridge. The isolation system consists of lead-core rubber seismic isolation bearings combined with semi-active viscous fluid dampers positioned between the bridge deck and end abutments. The dynamics of the semi-active dampers are accounted for via neuro-fuzzy models developed as part of a recent experimental study. The degree of seismic response modification is evaluated via numerical simulations using a supervisory fuzzy logic controller and comparisons are made with respect to sample controllers provided in the benchmark problem statement. The results of this study demonstrate that the supervisory fuzzy logic control algorithm combined with semi-active dampers can offer an effective approach to response modification of seismically isolated highway bridge structures.

In this study, the reduction factors for FRP (Fiber Reinforced Polymers) proposed by various guidelines from countries including the USA, Japan, Canada, Great Britain, Norway and Europe were obtained to assemble a database of current environmental reduction factors and review their appropriateness. A literature review was also conducted that summarizes recent durability investigations conducted worldwide on various FRP materials under different exposure conditions. These FRP materials include carbon, aramid, glass, and hybrid FRP's. The reduction factors obtained from the results of the recent laboratory studies are compared with those provided by various codes on FRPs around the world. Some of the values obtained from reported experimental work were similar to the values proposed by various guidelines; however, none of the experimental results obtained provided the strength degradation due to the synergistic effect for the different exposures presented.

Service-life prediction models provide a useful and practical approach to estimate the durability that may be expected in concrete structures. For reliable performance predictions, these life-cycle models require accurate material property inputs that describe the quality of the placed concrete. Insitu sensing and monitoring has been suggested as an effective way to measure the properties of the in-place concrete. In this regard, the use of different types of sensors that measure fundamentally different material responses (e.g., stress/strain, acoustic/ultrasonic, electrical, and temperature) can be useful. This paper focuses on utilizing electrical conductivity measurements. It is discussed that while the sole measurement of concrete conductivity might not be able to accurately quantify material properties, a combination of three conductivity-based sensors plus a temperature measurement can provide valuable information for durability performance predictions. The proposed sensing system enables insitu measurement of properties such as porosity, pore connectivity, water permeability, and ion diffusivity. In addition, the sensors provide a means for life-cycle monitoring of moisture movement and ion (e.g., chloride) penetration inside the material. This paper discusses the applications of the sensing system and describes the role of each sensor, parameters measured, and principles of how each sensor operates.

This research study investigated the shrinkage behavior of High Strength Concrete (HSC) subjected to accelerated curing. In addition, the effects of accelerated curing temperature, water-cementitious (w/cm) ratio, fly ash replacement up to 50% of cement content by weight and surface sealant were also studied. In the research study, shrinkage measurements were taken from 252 HSC specimens. These specimens were subjected to various accelerated curing temperatures, laboratory and moist cured conditions. Two w/cm ratios and three different fly ash replacement of cement levels were considered in this research study. Half of the specimens were sealed with a waterproofing concrete sealer to study the effect of sealer on the shrinkage behavior of HSC. Quality control (QC) cylinders of size 4-in. x 8-in. (100 x 200 mm) were also prepared along with the shrinkage specimens to verify the compressive strength and modulus of elasticity (MOE) of concrete. Early-age (1-day) and later-ages (56-day) compressive strength and MOE were measured from the QC cylinders for all mix designs studied. Results from the study were compared to five commonly used shrinkage models in the United States and Europe and conclusions were cited in terms of the models and variables investigated.

Wind loads for use in structural design are based in part on extreme value analysis of historical wind speed data for the location of interest. In some cases wind direction data are also required to characterize the directionality of the local wind climate. The Automated Surface Observing System (ASOS), a network of about 1000 standardized weather stations throughout the United States, is a good source of such local wind speed and direction data. In order to facilitate more widespread use of ASOS wind data for structural engineering purposes, this paper presents procedures and software for (1) extraction of peak gust wind data from archived ASOS reports, (2) extraction of thunderstorm observations from archived ASOS reports, (3) classification of wind data as thunderstorm or non-thunderstorm to enable separate statistical analysis of these distinct types of winds, and (4) construction of data sets separated by specified minimum time intervals to ensure statistical independence. These procedures are illustrated using ASOS data from three stations near New York City over a period of about 20 years.

Structures subjected to wind loads experience torsional moments due to the eccentricity of the time-dependent resultant aerodynamic load with respect to the structure's elastic center. We refer to such moments as aerodynamic torsional moments. In structures with significant dynamic response additional torsional moments arise if the center of mass does not coincide with the elastic center. Empirical information on aerodynamic torsional moments was developed from wind tunnel tests on building models by, among others, Greig, Lythe and Surry, Isyumov and Poole (for results obtained by Isyumov see also. Such moments appear to have been a main contributor to the serious damage experienced under strong winds by the 15-story Realty building and the 17-story Meyer-Kyser building in Miami. It appears that the John Hancock Building in Boston has also performed poorly under aerodynamic torsional moments. To our knowledge, the first attempts to develop design criteria on aerodynamic torsional moments were reported in 1939; however, it was not until 1995 that provisions for such effects were included in a U.S. standard. The dynamics associated with aerodynamic torsional moments on tall buildings was studied by Patrickson and Friedmann, Foutch and Safak, Hart et al. However, unlike in earthquake engineering, to our knowledge no methods have been developed for calculating wind-induced effects on tall buildings, including effects associated with torsional moments due to the distance between the mass and elastic centers, in a manner that can be used confidently in structural design. Ad-hoc wind tunnel studies are therefore routinely being conducted, but to our knowledge they do not account for distance between centers of mass and elastic centers. For the majority of buildings, including very tall buildings, wind tunnel studies are performed on rigid models. Two approaches to performing such studies are available. In the first approach, called the High Frequency Force Balance (HFFB) approach, the wind tunnel operator records the time histories of the base shears and moments for two orthogonal horizontal directions, and the base torsional moment. In the second approach, the quantities recorded in the wind tunnel are the simultaneous time histories of aerodynamic pressures at a large number — up to the order of 1000 — of pressure taps on the external faces of the building. The direct use of such measured pressures in design is called is called the Database-Assisted Design (DAD) approach. The distribution of the wind forces with height is therefore known (this is not the case for the HFFB approach) and can be accounted for in the calculations. DAD also makes it possible to account, if necessary, for the contributions of higher modes of vibration to the wind-induced response. The sets of time histories recorded simultaneously for each of a sufficiently large number of mean wind directions are used to obtain generalized forces and torsional moments for the dynamic analysis of the structure. The first step in the analysis consists of using the equation of motion of the freely vibrating system to obtain the system's natural frequencies of vibration and the corresponding mode shapes. The second step consists of using the equations of motion of the system forced by the external wind loads to obtain the wind-induced displacements, accelerations, and inertial forces and torsional moments acting on the building. Once the inertial forces and moments are known, they are used, in conjunction with the aerodynamic forces and torsional moments, to calculate the wind effects of interest induced by wind blowing from direction θ. These wind effects include internal forces in structural members. The last step is the use of directional dynamic and climatological information for all directions θ to obtain the requisite wind effects with specified mean recurrence intervals. The non-zero distance between the elastic center and the mass center causes coupling of responses in the x and y directions and in torsion. The sections that follow are concerned with the following issues: first, the modal analysis of the freely vibrating system, which takes that distance into account. Second, the dynamic analysis of the system excited by the wind loading calculated from simultaneously recorded pressures obtained in the wind tunnel at a large number of taps over the building surface. The analysis yields the requisite wind-induced deflections, velocities, and accelerations of the system. This type of information is used by the structural engineer for serviceability design purposes. For safety design the information needed consists of internal forces in the structure's members. Third, the calculation of the internal forces as sums of contributions due to the applied wind loads and the wind-induced inertial forces is discussed. Fourth, the combination of internal forces in individual members via interaction equations and specified load combinations is presented. The combinations cannot be performed globally for the entire structure. Rather, sets of influence coefficients must be used to rigorously reflect the interaction equations and load combinations as used for each individual member being designed. Fifth is the estimation of mean recurrence intervals of wind effects specified for structural design. A numerical example is then presented. The paper ends with a set of conclusions.

Passive auxiliary dynamic vibration absorbers (DVA), in particular the tuned mass damper (TMD) and tuned liquid damper (TLD), have become accepted devices for reducing the resonant motions of lively tall structures. A TLD is comprised of a rigid tank partially filled with liquid (usually water) and fitted with energy dissipating mechanisms such as screens. Despite the simplicity of a TLD's physical components, its nonlinear dynamic characteristics complicate the prediction of its performance as a DVA. This paper focuses on the application side of tuned liquid dampers fitted with internal damping screens. Experimental data are presented from a research program conducted to provide insight into the performance of a TLD in terms of its efficiency and robustness. The efficiency of a TLD is measured by comparing the effectiveness of a particular TLD to that of an equivalent optimal linear TMD with the same mass ratio. The entire water mass often does not participate in the sloshing motion resulting in an efficiency level that is less than that of an equivalent optimal linear TMD. Robustness of a damper is the measure of insensitivity of its performance to changes in the parameters of the damper and the main structure from their proposed values. In this study, robustness is determined by examining the effectiveness of a TLD under various response amplitudes, the limiting of the sloshing motion by restricting the available freeboard, and varying the natural frequency of the structure itself. Two directional TLDs, which operate simultaneously in two orthogonal directions, are also briefly discussed.

Estimates of the World Trade Center (WTC) towers' response to wind by two North American wind engineering laboratories differed from each other by almost 40%. A recent investigation by the National Institute of Standards and Technology determined that those differences were mainly due to discrepancies between the respective estimates of the wind speeds. In this paper we present a procedure for estimating extreme wind speeds near the WTC site that corresponds to a sector-by-sector approach to the estimation of extreme wind effects. We provide details of the data sets and their treatment, as well as details of the estimates themselves, in a manner intended to be thorough, clear, and transparent. Efforts in the direction of clarity and transparency are in our view necessary if estimates of extreme winds and their effects are to meet the need for effective scrutiny by users and building authorities, and if a solid technical basis for a consensus that remains to be developed among standard and professional organizations is to be created in the near future. Our analyses indicate that sectorial extreme wind speeds, and their counterparts in methods based on the up-crossing technique, are sensitive to sampling errors of a type that does not affect estimates of extreme wind speeds considered without regard for their direction. For this reason, estimates based on overly refined schemes for taking wind directionality into account and that disregard the possibility of such sampling errors are in our opinion prone to being significantly in error.

This paper presents an improved method to design buildings to resist high wind. The method consists of using databases of pressures measured in wind tunnel tests and applying these pressures in nonlinear structural analyses, hence the name nonlinear database-assisted design (NLDAD). Available databases of experimental measurements provide structural designers with an envelope of peak loads for all critical sections of a structure, and thus greater confidence in the safety of the design than if a few idealized pressure distributions specified by building codes were used. Unlike earlier approaches, the approach used in this paper targets all potentially critical cross sections of the structure being designed. Precise knowledge of the load cases required enables optimization of the structure, thus leading to more efficient use of materials, which translates into lower cost and less demand on the environment, as well as improvement in safety. NLDAD is not proposed for routine office calculations, but rather for calculations intended to develop standards provisions that reflect more correctly than current methods based on linear response do, the capacity of structures to withstand wind and gravity loads. To illustrate the method, one frame of a steel warehouse originally designed to satisfy ASCE 7-93 wind loads, was investigated. Updated ASCE 7-02 loads were used in this investigation, as well as wind tunnel measurements. The paper describes the selection of load cases from the experimental database using a linear beam model. Next, a much more detailed finite-element model was analyzed under the selected load cases into the large displacement, post-yielding range, with account taken of local plate buckling and initial imperfections. By using NLDAD, improvement in wind resistance of 30% was achieved, at the cost of 3.6% increase in weight. Most of the performance improvement was attributable to structural modifications that were partly enabled by nonlinear analysis. Conversely, for the same wind resistance, a decrease in weight of 10% or so is possible with NLDAD. The governing load case from the wind tunnel pressure database confirms the validity of ASCE 7-02 pressures. When initial deformations are accounted for, the structure still passes ASCE 7-02 Standards only to the extent that wind load factors specified in the Standards may be construed to be associated with ultimate strength rather than allowable stress design. The margin of safety mentioned in ASCE 7-02 Commentary is overly optimistic.

There are many different types of structural condition assessments of buildings, depending on the circumstances and the objective of the client. The assessments can vary widely in terms of their scope, the level of detail and their comprehensiveness. However, some types of inspections are reoccurring. This paper presents the most common types of structural condition assessments that are performed on buildings or on portions of buildings. It includes the purposes of the assessments, common problems, methodologies, and strategies for performing a high quality assessment. The principles presented apply to all types of buildings, including steel construction, reinforced concrete, high-rises, and industrial facilities. As a case study, the application of these principles to the buildings surrounding the World Trade Center following the 9/11 attack are presented. This paper is an abridgment of Chapter 6, "Buildings," in Ratay, Robert T., ed. (2005). Structural Condition Assessment, John Wiley & Sons, Inc., Hoboken, NJ.

Although they are classified and constructed as buildings, parking structures are unique because they are loaded primarily by moving vehicles and are exposed directly to the environment. In cold climates, they are often exposed to snow, ice and water, and to the corrosive action of deicing salts. Since they are frequently very large in plan, they experience greater volume changes (temperature, shrinkage and creep) than enclosed structures. Functional and traffic requirements requirements dictate open floor spans, lateral barriers, and consideration of ramp slopes and turning radii. All these factors make the parking structures different from the other types of building structures, and the assessment of the condition of parking structures has to take these factors into account. This paper is an abridgment of Chapter 9, "Parking Structures," in Ratay, Robert T., ed. (2005). Structural Condition Assessment, John Wiley & Sons, Inc., Hoboken, NJ.

Structures, like people, never get younger. Structures, like people, can maintain their good health with age, if properly cared for, examined, and treated when needed. Structures, like people, need periodic check-ups as part of their preventive care to ensure their fitness; and need examination when exhibiting signs of illness. Interestingly, structural condition is often referred to as fitness-for-service. This paper is an introduction to a series of eight papers on structural condition assessment, delivered at the 2006 Structures Congress in St. Louis, Missouri, and published in the Proceedings of the Congress. It is based heavily on the Preface written by the author in the book, Structural Condition Assessment, Robert T. Ratay, Editor, John Wiley & Son, 2005. The authors of these papers are the authors and co-authors of the corresponding eight of twenty-one chapters in the book. The seven topics were selected for this series of papers because they represent the most frequently assessed building-type structures and construction materials. It may be said that a structure that has withstood the combined effects of use, abuse, loads and environmental conditions over time has, in effect, proven itself. However, buildings, bridges, parking structures, stadiums, and all other structures do deteriorate with time as the result of repeated loadings, exposure to the elements, aging of materials, wear-and-tear from normal use, abuse, inadequate maintenance, and other factors. We design structures for strength, stability and deformation, but the most common problems that occur are those of deteriorations, durability and serviceability. The deterioration may progress to the point, or one or more individual debilitating events may have the consequence, of compromising the structure's strength, stability or serviceability. Evaluating the condition of structures is an area of professional practice within the field of structural engineering. It is an increasingly active business driven in part by the need for maintenance, repair and rehabilitation of buildings, bridges and other deteriorating infrastructure; by change in ownership; by the choice of adaptive reuse of facilities; by the necessity of retrofitting for ever-changing code compliance; by damage sustained as the result of natural hazard; and, particularly for corporate and public buildings, by the need for increased physical security. In simplified terms, structural condition assessment consists of activities of visual observation, measuring, photographing, probing and sampling, field and laboratory testing, engineering analyses, record keeping, documentation, and report preparation. Appropriateness and accuracy of field measurements, testing and analyses notwithstanding, the reliability of the condition assessment lies in the interpretation of the collected and generated data and in the judgments converting them to accurate conclusions and recommendations. Condition assessment may be made of apparently "healthy" as well of visibly "damaged" structures. It is not to be confused with forensic investigation of structures, which is the determination of the causes and modes of failure (where failure is not only collapse but also the unacceptable difference between intended and actual performance). A very important part of the evaluation and reporting, particularly if the structure will be repaired and/or restored, is the recognition of the adverse condition as being a "defect" or "deterioration". Defects are usually errors in design or shortcomings in construction or imperfections in materials; deterioration is the gradual loss of original properties; and defects often enhance deterioration. Both the predicted consequences and the recommended remediation are influenced by whether the condition is the result of a defect or deterioration. While "a structure is a structure", each is unique in the combination of its design, construction, history of use and abuse, and quality of its maintenance. Therefore, while there are "typical" signs that indicate "obvious" conditions, some unrecognized details may distort one's conclusions. There is the need in the structural engineering profession to instruct the novice and guide the experienced engineer in performing the condition assessment of structures and their materials: how to conduct the assessment; how to inspect the structure; how to recognize various conditions; what to look for; what methods of field examination, laboratory testing, and analytical evaluations are available; how to report the findings; and what to recommend. This series of presentations and papers are intended to fill at least part of that need. They include description of assessment strategies, methodologies, techniques and equipment.

Conventional building assessment techniques, points of interest and areas of focus are applicable to sports facilities, but covered in other papers in this conference proceedings. This paper highlights some building aspects unique to sports facilities to understand design intent, critical elements, locations likely to exhibit distress, and observed behaviors. Discussion proceeds from roof down to show how loads are imposed, collected and delivered to supports.

When attempting to evaluate the structural condition of a concrete structure to develop an appropriate plan for future use, a thorough understanding of the concrete is mandatory. The first phase of any evaluation is to identify a qualified team of investigators. The person in charge should be a structural engineer who has passed his or her professional engineers examination and is in good standing within his or her profession. The lead engineer first should perform an extensive review of all existing information about the structure, which, among other materials, includes the design documents, construction records and the service history of the structure. This paper is an abridgment of Chapter 16, "Concrete," in Ratay, Robert T., ed. (2005). Structural Condition Assessment, John Wiley & Sons, Inc., Hoboken, NJ.

The safe and reliable operation of structures has always been a major engineering priority. Condition assessment or fitness-for-service evaluation, therefore, plays a fundamental role in ensuring the integrity of such structures. Fitness-for-service (FFS) is a methodology, which accounts for actual service stresses, flaw or damage zone sizes, as-built material properties, and operating environment in determining the actual safety or reliability of a structure in its present condition or expected future state. That is, FFS is a common sense engineering approach to evaluating the suitability of a structure for its intended service. Moreover, a fitness-for-service assessment can provide the foundation for establishing the remaining life of a structure and, thereby, provide a basis for making capital based decisions for repair or replacement. Steel, in particular, because of its extensive use in a wide assortment of structures (e.g., bridges, buildings, power plants, etc.) and its ability to be easily fabricated by welding, has become the most widely evaluated material with respect to fitness-for-service. Welded joints inherently contain flaws or discontinuities such as cracks, incomplete penetration, slag and/or porosity, as well as exhibiting altered base metal mechanical and metallurgical properties. Traditional design of steel structures accounts for weld joint discontinuities and altered metallurgical properties of the base metal by conservatively limiting the size of discontinuities permitted in fabricated joints and applying cautious factors of safety to joint stresses. In effect, traditional design assumes that no significant flaws or service-induced damage (i.e., fatigue cracking, corrosion, fire-induced distortion) exists in the structure. In contrast, the fitness-for-service approach acknowledges the presence of flaws, damage, and/or degraded material properties and assesses a structure in its existing or anticipated condition. Thus, the FFS approach is a quantitative assessment, which is based on rational evaluation of stresses, material properties, nondestructive examination, and fracture mechanics. This paper is an abridgment of Chapter 17, "Steel," in Ratay, Robert T., ed. (2005). Structural Condition Assessment, John Wiley & Sons, Inc., Hoboken, NJ.

An overall understanding of durability and service life (design life) of both structural and non-structural materials can assist the engineer in making informed, economical decisions on whether undesirable existing conditions are still acceptable or whether rehabilitation is required. Durability is defined here as the relationship between the expected service life and the actual service life of building components, in the absence of uncontrolled defects and deterioration. Understanding the normal (expected) service life of a material or system is essential in determining whether it is suffering expected levels of deterioration, or whether defects are present that may be shortening the service life. This paper will discuss classification and estimation of the design life of structural materials and the standards and publications that address these issues. It will also discuss the issues involved in accepting undesirable existing conditions: is the public served by remedying an existing condition to strict compliance with design standards and building codes? This paper presents a synthesis of the information presented by the authors in Chapter One, "Defects, Deterioration and Durability" of the recently published book Structural Condition Assessment; for more depth of coverage on the subject matter, readers are referred to this book.

Many engineering projects require evaluation of masonry materials for determination of structural capacity, specification of restoration and repair materials, and for resolution of building contract disputes. Evaluation includes field and laboratory investigation of the units, mortar, and the masonry assemblage. Nondestructive and semi-destructive test methods are available for the determination of properties of in-place masonry materials, and some of these are standardized. Building codes provide requirements and guidance for the use of testing to determine engineering properties for structural evaluation and for quality assurance. In lieu of testing, guidelines are available for the estimation of material properties. Preservation of masonry buildings involves selecting replacement materials that are compatible in both performance characteristics and appearance. There are a wide variety of methods available for mortar analysis, ranging from simple color and particle gradation matching of aggregates to thorough chemical and petrographic analyses. Recent standardization work has provided useful guidelines for the design of restoration mortars. Determination of the properties of in-use masonry units allows the selection of compatible salvaged units, fabrication of replacement units, and assists in the design of restoration mortars and other materials such as grout. This paper is an abridgment of Chapter 18, "Masonry," in Ratay, Robert T., ed. (2005). Structural Condition Assessment, John Wiley & Sons, Inc., Hoboken, NJ.

As part of the New York City's redevelopment of the far west side of the mid-town Manhattan, the No. 7 Subway Line Extension project will add 1.5 miles of twin bored tunnels to the existing subway line and two new subway stations. The underground construction has two major components: (1) Running Tunnel & 34^th Street Station Cavern and (2) Tenth Avenue Station & Times Square Connection. The running tunnel contract will have a TBM launching shaft (Shaft A), an Adit connecting Shaft A to the running tunnels, and TBM Assembly Chamber at the southern end of the project, i.e., near 25th Street at Eleventh Avenue, where tunnel excavation begins. This paper will discuss challenges of the design and construction of Shaft A where it meets the Adit.

Deep excavations require bracing along the wall height to resist lateral earth pressures. Design of a typical straight strut is influenced by self-weight bending stresses acting simultaneously with axial stresses. As length increases beam-column actions and second order effects (P-δ) can significantly reduce the axial load carrying capacity of the strut. Long struts therefore need to be supported intermittently, using "pin-piles", resulting in additional cost and inefficiencies associated with congestion in the excavation trench. Additionally there can be problems associated with leakage of water in the invert slabs due to penetration in the waterproofing system around the "pin-piles". Weidlinger Associates has proposed the use of a cambered, or "tuned", strut. In this design a long span twin I-girder strut is cambered upwards, such that the P-δ effects partially offset the gravity induced bending stresses. This could result in minimized bending stresses and optimal strut axial capacity, minimizing the need for intermediate supports. This paper describes an experimental and analytical research program in which scaled strut models were tested. The deflection and strain of axially loaded struts of varying length and camber were compared to a finite element analysis to verify concept and establish design recommendations.

The subtitle of this paper should be, "Building a Perfect Building in 7,362,854.3 Easy Steps, None of Which Could be Out of Order." The Pulitzer Foundation for the Arts building was the proverbial "Swiss Watch," in which everyone, from the Owner to the design team to the builders, had to anticipate and participate in an array of issues far beyond what the design and construction process usually presents. The final team was established partway through the design process, when the Contractor, Owner's Representative, and Construction Superintendent were brought on board to help guide the design of the building toward construction. The team was as unique as the project: (1) a remarkably brave, patient, Owner with the vision to build a building with as much architectural and artistic significance as the collection of important Modern works it was to house, (2) a Pritzker Award-winning Design Architect, (3) two major American artists, who designed works for the building that informed its design, even as the design informed the works themselves, (4) a Structural Engineer who understood that the structure of the building, in a very real sense, was the building, even though Ando's work is about the architecture, not the structure, (5) an internationally-renowned Mechanical and Electrical Design Engineer, (6) an Owner's Representative and a Construction Superintendent who knew firsthand the complexity and craftsmanship involved in constructing an Ando building, (7) a Contractor with the commitment, people, and resources to do the job right, (8) an Engineer of Record with experience in designing complex mechanical and electrical systems in visually demanding environments, and (9) an Architect of Record who was fortunate enough to be surrounded by such an incredible team. Very early in the design process, it became clear that the design and construction of the building would develop hand-in-hand. At every stage of design, the construction implications of every detail had to be understood. And all the way throughout construction, the design intent of every detail also had to be understood. That the building was so successful is a tribute to the art and skill of listening: (1) the craftsmen (the usual words, "journeyman," "apprentice," "foreman," etc., don't even begin to do justice to the levels of skill and commitment of the men and women who actually built this building) listened, learning what was important about the design and the details, and then went well beyond the best work they had ever done, and (2) the design team listened, learning from these same craftsmen how to improve and execute every detail of the building, including the ones that "couldn't be done." So, we set out together on a journey into an unknown realm, where intent became design became means became methods became results. What follows are some thoughts on that journey, for the information of those who may have wondered how it was done, and for a fond look back for those of us lucky enough to have taken that journey.

Constructing buildings designed by architect, Tadao Ando, is fascinating, exhausting, challenging, demanding and very rewarding. The buildings look deceptively simple but require a tremendous amount of effort to build correctly. Ando is a minimalist architect. His work does not have baseboard, window trim, door casings, moldings or other details that can hide any imperfections in the construction. If you make a mistake with an Ando building you have two choices — either live with the mistake or tear it out and reconstruct. Ando uses "silky smooth concrete" as his signature material. The concrete is cast in place and requires perfect planning and execution. It is an unforgiving material and the "smooth as-cast" finish is the most difficult concrete finish to achieve. The finished product should be virtually free of bug holes (air bubbles trapped at the formwork surfaces), with clear pattern lines and crisp, sharp corners and edges. When I was asked in 1996 to become the Construction Manager/Owner's Representative for the Pulitzer, I was already working on Tadao Ando's first building in the USA - the Eychaner House in Chicago, a 10,500 square foot residence in the Lincoln Park neighborhood. This was a demanding building. It is concrete both inside and out — no plaster on the walls and ceilings but finished architectural concrete. Because of the constraints of the Chicago winters, insulation had to be sandwiched between the inner and outer concrete wall pours. I had learnt much from working on the fantastic Eychaner House but knew that with the Pulitzer I could improve upon what had been done. Ando's design module for the Pulitzer Foundation for The Arts and Eychaner House was based on sheets of plywood (4 x 8 foot) which make up the liners for the formwork. His design called for the wall surfaces to display the panel lines between each individual 4 x 8 foot plywood liner as well as show the individual screw heads and form ties that make up the formwork. Everything had to be perfectly aligned and the panel lines had to be exactly parallel with the one above, below and to either side. These panel lines ran completely around the exterior and continued in the interior of the structure. Window heads, sills, door heads, ceilings, floor finishes, millwork, light fixtures, security devices all aligned with the panel lines. Since the panel lines were less than a pencil line in width there was no room for error. Ando also typically detailed a 1/8^th inch margin around door frames, light fixtures, electrical outlets, smoke detectors etc. This margin had to be perfect because if it was a mere 1/16^th inch out then you have lost or gained 50% of the margin. In constructing an Ando building the concrete is the key. If the concrete were not perfect then the other elements of the building would not be accurate. When I first saw Tadao Ando's concept sketches of the Pulitzer I was impressed by the linearity of the building. It is essentially two long boxes of differing heights separated by a water court. A roof slab extends from the taller box over the lower and is supported by a single column. I loved the purity of the design but I realized from these sketches that because of the accent on length, particularly in the main gallery and water court, that all the lines in the walls, ceilings and floors have to be perfectly straight and parallel. If a line was wavy or not aligned then it would be very obvious to the eye.

The first time I experienced "Ando Concrete" was at the Eychaner Residence in Chicago. Our team was brought in to complete a project that had been under construction for approximately 18 months. I had previously worked in all phases of concrete construction from residential to commercial, spanning some 25 years, but had never seen such exacting details, and the expectation of such high levels of wall quality was amazing. In the fall of 1997, with the concrete work on the Eychaner Residence complete, I came to St. Louis to join a group of extremely talented craftsmen to construct a private building to house The Pulitzer Foundation for the Arts. This building was also designed by Tadao Ando, with the initial goal to construct a poured-in-place concrete structure of such quality to surpass anything that had been done to date. From the beginning there were many decisions to be made concerning both design and logistics. One of these was the selection of the construction team and the individuals who would do the concrete work. A local construction company, BSI Constructors, was chosen to be the general contractor for the project, and they were to supply the carpenters, laborers, and ironworkers required to construct the architectural concrete walls. This decision proved to be one of the most important, because with BSI, we received the personal commitment and dedication that would be required to successfully complete such an extremely challenging project.

The initial impression to a structural engineer is that the box-like cast-in-place concrete structures of Tadao Ando's designs are relatively simple to engineer and detail. Upon learning of the high performance expectations for the project, the limited space allowed for the structural elements, and the precision of the concrete details, this project was anything but ordinary. The success of the Pulizer Foundation for Arts facility required dedication, communication, and collaboration by all team members.

The Creve Coeur Lake Memorial Park (CCLMP) Bridge is the first major concrete segmental bridge constructed in Missouri, and is part of the Page Avenue Extension (Missouri Route 364) near St. Louis, Missouri. The Missouri Department of Transportation (MoDOT) built the extension to provide an additional route for commuters between St. Louis County and St. Charles County to the northwest of the city, relieving heavy congestion from the current corridors of I-70, to the north, and Highway 40 to the south. The CCLMP Bridge is a 2,675 ft. long, cast-in-place, post-tensioned, concrete segmental box girder structure with sloping, variable depth web walls, built by the balanced cantilever method. It includes nine spans from 185 ft. to 469 ft., and carries five lanes of traffic with full width shoulders in each direction on twin structures, built 4 inches apart at the deck. The deck of each directional structure is composed of two, single-cell box girders joined at the top for a total deck width of 86 ft. Each box is supported by a single, normally reinforced, concrete column to the pile cap, drilled shaft cap, or spread footing foundation, bearing directly on sound rock. This paper will briefly outline the technique of segmental construction by the balanced cantilever method. It continues by describing the use of the "maturity method" for concrete strength assessment, and its function as part of a cold weather concrete plan. The paper also describes the application of a silica-fume concrete deck overlay, and some of the problems encountered. These two specific aspects of the endeavor have applications to many other transportation projects.

The practice of structural engineering in the U.S. today for many licensed professionals includes involvement with reviews, by others, of projects they have designed as well as the review of designs developed by other engineers. These project reviews take many forms and can occur at any phase of the project preplanning, design, construction or completion. Reviews are sometimes conducted for internal purposes only while others occur as a result of requirements outside of the individual's company. External project peer reviews can include those mandated by state and local codes and statutes or voluntary reviews conducted independently at the request of a client, owner or other interested party. Anecdotal experiences of many design professionals indicates that most of the mandatory project reviews are conducted in a professional manner and involve specific guidelines and check lists to assure a thorough and orderly review process. On the other hand, it appears that voluntary reviews and reviews conducted by non-licensed individuals are very often conducted in a haphazard and unprofessional manner. In order to bring some uniformity and control to all peer reviews conducted in the U.S., particularly voluntary reviews, it is recommended that a guideline be developed to establish an industry standard for the structural engineering community.

Facing the escalating demands in both technical competence and financial accountability, practicing structural engineers are being forced into an ever-intensified fast-pace working environment. With more and more structural design codes becoming lengthy and cumbersome and, meanwhile, the time allocated for structural engineering design being drastically reduced, the quality assurance of the structural engineering design has been becoming more critical than ever for practicing structural engineers to succeed. Structural engineering design errors and failures have been observed in a variety of design phases and categories. Among them, there are several typical problems needed to be discussed and a systematical procedure of quality assurance of the structural engineering design shall be studied and developed. As a part of our collective professional effort to assure the quality of the structural engineering design, this paper will discuss following eight typical aspects related to quality control and assurance of structural engineering design and a number of real world practical examples will be presented to assist in illustrating the importance of the quality control and assurance for real world structural engineering design projects.

The benchmark of quality for a design professional's services is referred to in the law as "the standard of care." The word "quality" in this context refers to qualitative concerns in performing a quantified scope of services. Such qualitative concerns include: code compliance, originality or ingenuity, balancing utility versus cost, the absence of ambiguities and errors, constructability and the like. Stated another way, this "quality" is reflective of a professional's competence and judgment when performing a quantified scope of services. Try to describe to an inexperienced engineer or architect how to know when his or her services have reached a legally acceptable level of quality. The exercise may generate more questions than answers. For example: (1) acceptable to whom, (2) acceptable enough to avoid a contract claim by the client, and/or (3) acceptable enough to avoid a non-contract claim (such as negligence) by a member of the general public? The short, easy and correct answer is when his or her services and deliverables meet the applicable standard of care. Then what "standard of care" applies? The answer is presented in two parts. Part One explains the distinct body of law governing professional services, of which the standard of care is an integral part, and ways in which this benchmark can be modified. Part Two explains the role of the standard of care when a claim is made against the design professional and how compliance with the applicable standard of care is proven. Understanding the role in the law and the practical applications of the standard of care should assist the design professional in defining and recognizing the benchmark of quality for the scope of services he or she will provide, testing the services in practice against the applicable benchmark and seeing how these services will be judged according to the benchmark when a claim is brought.

Jon Schmidt represents the Structural Engineers Association of Kansas & Missouri (SEAKM), the sponsor of this session, as a member of its Professional Practice Committee. Ten states currently have specific provisions in place that distinguish structural engineers from professional engineers in other disciplines. However, there is considerable variation among these jurisdictions in the qualifications that are required for structural engineering (S.E.) licensure. There are also important differences in the significance of S.E. licensure within each jurisdiction. This inhibits the mobility of those who already have the S.E. license in one state and seek to obtain it in another. Recognizing this, NCEES added a definition for a Model Law Structural Engineer (MLSE) to its Model Law in 2003 and its Council Records Program in 2005. Separately, the Member Organizations of NCSEA voted in 2003 to establish an independent body, SECB, to administer a national board certification program for structural engineers. The MLSE and SECB criteria are intended eventually to serve as the basis for national uniformity in the qualifications required for S.E. licensure.

This paper will examine the differences between the as-modeled structure and the as-built structure and evaluate the assumptions made during the design process as it relates to main member and connection design. It will also explore the effects connection configuration can have on the behavior of the structure, and how connections can be configured to accommodate unanticipated or extreme loadings.

Generally, steel design courses contain very little information on connections, but the basic principles learned in statics and strength of materials provide the basis for most connection design. This paper will review some topics in connection design that are not commonly included in steel design courses.

An Internet-based teaching aid for undergraduate steel design was developed and enhanced at the University of Kansas with the support of the American Institute of Steel Construction. The teaching aid consists of a case study of the design of a fictitious three-story steel braced-frame office building. The main goal of this teaching aid is to provide instructors with a tool to expose students to design of steel building elements in a realistic building context. This tool bridges the gap between typical book text element design examples and the design situation students will encounter in a realistic professional environment. To facilitate the distribution of the material through the use of the Internet, the drawings are in AutoCAD electronic files and the calculations use Microsoft Excel spreadsheets. Animations are in Microsoft .avi format with smaller versions in .mpg format. This project was developed as a package that can be passed on to professors at other universities, for use in steel design courses. The project package includes member design and load calculation spreadsheets, floor plans, elevations, and drawings that display the application of vertical and lateral loads. This package is delivered as a web document, with links to all included drawings and spreadsheets. This web document is built in HTML, so that it can be easily viewed and edited. All aspects of this package are compatible with PC and Macintosh formats. This package is broken into and arranged by topic in order to allow it to be easily implemented into a lecture or lab session. To ease the use of the material in varying learning/teaching environments, the following range of formats has been used: Microsoft Excel (.xls); Microsoft Word (.doc); Adobe Acrobat (.pdf); AutoCAD (.dwg); Encapsulated Postscript (.eps) and simple text files (.txt). The use of the Web is not required for class delivery. The use of hardcopy can be used as a choice for class delivery.

The Olmsted Navigation Lock and Dam currently under construction near Olmsted, Illinois is on a stretch of the Lower Ohio River that is a major intersection of the inland water system involving the Mississippi, Tennessee, Cumberland and Ohio Rivers. The new Lock and Dam replaces L & D 52 and 53 that were built in the late 1920' s and, as repair and maintenance costs escalate, are operating beyond their useful life. The US Army Corps of Engineers predicts that the new Olmsted Dam will reduce transit time from five hours through L&D 52/53 to only one hour. The estimated average annual economic benefit is more than $700 million. The purpose of the lock and dam are to help maintain a navigable depth of water along this stretch of the river. The dam consists of a Tainter Gated Section (550'), a Wicket Gated Section (1400') and a Fixed Weir Section tying to the Kentucky shore. During periods of low water flow (about 40 % of the year) the Wicket gates are raised to block river flow, the Tainter Gates set to regulate flow, and barge tows must pass through the Locks. During periods of normal or higher flows the Wicket gates are lowered and lay along the bottom of the river, the Tainter Gates are fully raised and tows navigate through this section of the River unimpeded. Construction of the Dam is still in its early stages, while construction of the Lock is complete. There are five Tainter Gates which sit between concrete piers with a 110 foot face to face spacing. The dam face of the gate is a circular segment with a 54 ft radius from downstream face of the skin plate to the center line of gate trunnion and a 44.33 ft circular segment length giving a height above the sill of 37 ft. An unusual feature of these gates is operation utilizing hydraulic cylinders over the more traditional wire rope hoists. They will be stored in the fully raised position during periods of normal or higher river flows and thus are designed to rest on retractable gate stops that are extended from the supporting concrete piers. The weight of each gate is approximately 650 kips.

The Olmsted Lock and Dam on the Ohio River replaces Lock and Dam #52 and #53 and is described in more detail by others. A Lock Operating Bulkhead (LOB closes the lock canal to restore miter gate control after annual high water periods. The LOB design was completed in 2001. Fabrication, related construction, installation and testing were completed in 2005. There are two lock operating bulkheads. The following discusses features of the LOB that may be of interest.

New York State Department of Transportation maintains an inventory of over 20,000 bridges across the state. These bridges are inspected biannually based on rating criteria of 1 to 7, 7 being new and 1 being failed. Bridge inspection ratings can be used to calculate deterioration rates of bridge elements by considering effects of environmental (climate, ice, salt), geographical (highways below or above bridges), ownership, material types, design types, and other factors. This paper presents deterioration rates using Markov Chain and Weibull Distribution based approaches. Further investigation is ongoing to generate deterioration rates of different bridge elements affected by factors such as climate, bridge element materials, average daily truck traffic, ice, salts, etc.

In the late 1990's, after decades of little investment in its transportation infrastructure, Ireland's National Roads Authority (NRA) began to implement a bridge management system, EIRSPAN, with funds generated by the booming economy of the Ireland's Celtic Tiger, and from participation in the European Union. The EIRSPAN bridge management system was developed after studying systems used throughout the world, and it has some significant differences from systems used in the United States. Ireland has an estimated 20,000 bridges, and previously had no comprehensive inventory, no established procedures for bridge inspection, no universally accepted methods for rating their approximately 16,000 masonry arch bridges, many of which are more than 200 years old, and no system for prioritizing maintenance on a national level. The NRA, conceived an overall approach to bridge management, which met their special needs, expanded their staff to manage the system, established system guidelines, and, in 2001, retained Irish, United Kingdom and American consulting engineers to implement an inspection and evaluation program. The NRA program is especially interesting because it was necessary to start the program from virtually nothing, with thousands of structures already in place. The initial inventory data gathering and initial inspections were completed from 2001 to 2005. Currently, structural assessments and special inspections are progressing, as well as limited repair and improvement work.

Construction of Delaware's new Indian River Inlet Bridge is being planned. An innovative 305 m single-rib concrete arch bridge was designed by the Figg Engineering Group. In an effect to help the Delaware Department of Transportation (DelDOT) better maintain and operate the bridge, the Center for Innovative Bridge Engineering (CIBrE) at the University of Delaware has proposed to install a permanent long-term Structural Health Monitoring (SHM) system on this unique bridge. Working closely with DelDOT and Figg from the initiation of the project, the CIBrE research team designed a comprehensive SHM system for the bridge, which will enable monitoring of critical behaviors during construction, and continuous monitoring during normal operation. The SHM system will be used to verify the innovative design, to monitor the structure during construction, and to monitor the long-term performance of the bridge. Data from the system will become part of the bridge maintenance and inspection records for the bridge, which will enable the DOT to better maintain and operate the bridge throughout its life. The SHM system includes numerous embedded and surface mounted sensors distributed throughout the bridge, a networked data acquisition system, power and communications conduits, and a central processing system. The SHM includes structural as well as geotechnical monitoring. Critical to the success of the design was the close coordination maintained with the design team, reviewers and owner throughout the entire design process. Presented in the paper is a description of the bridge and details of the monitoring system.

Bridge management main tenets are ensuring safety while minimizing costs. Some of the procedures that are used to achieve these tenets are inspection, maintenance, and repair. There are numerous qualitative and quantitative tools that aid management of bridges. Structural health monitoring can aid in several aspects of bridge management, such as reducing inspection costs while improving quality, prioritizing repair/maintenance schedules, and increasing accuracy of both deterioration estimations and the decision-making process. This paper briefly describes the possible role structural health monitoring can play in bridge maintenance and management aspects.

The Eads Bridge, the first bridge to span the Mississippi River at St. Louis, was dedicated on July 4, 1874. The double deck structure is a National Historic Landmark that has carried countless horse drawn wagons, locomotives, automobiles, trucks and pedestrians. For most of its history, the Eads Bridge was owned by various railroads. The Terminal Railroad Association of St. Louis operated the upper highway deck as toll bridge even after the lower rail deck was closed in 1974. The City of St. Louis acquired the bridge in 1989 and donated the lower level to be used by the community's light rail system, MetroLink. The lower rail deck was rehabilitated and re-opened in 1993 when MetroLink debuted. The upper roadway deck became structurally deficient and the bridge was closed to highway traffic in 1991 during the construction of MetroLink. The most recognizable feature of the bridge is the portion over the river, which consists of three long steel arch truss spans, as seen in Figure 1. Besides the main river spans, the historic structure consists of the West Approach, the West Arcade and the East Arcade. The Eads Bridge also includes two East Approach ramps that had been entirely replaced before the bridge was 50 years old. The historic structure is approximately 3000 feet in length while the ramps are each approximately 1000 feet long. The demolition portion of the project included removal of the existing deck and toll facilities on the historic structure and removal of the entire East Aproach ramps. After an extensive rehabilitation that began in late 1998, the highway deck was re-opened in a ceremony held July 4, 2003, 129 years after its original debut.

The bridge over Lake Pomme de Terre was originally designed and built by the Corps of Engineers in 1962. The bridge roadway is 22'–0" wide and carries two 11' lanes. The superstructure consists of four composite continuous steel stringers (W36 x 150). There are seventeen 90'–0" spans and end spans of 76'–10". The superstructure comprises five units (a typical unit is 360' long) that are joined by a pin and hanger connection located 18'–0" from the pier. The grade of the bridge is level (0% grade). The substructure consists of two column bents with spread footings. Because of the tall pier heights, the superstructure girders are post-tensioned to the pier capbeams. Although the stringers and substructure were in good condition, the six inch composite deck was rated deficient by the owner, Missouri Department of Transportation (MoDOT), because of advanced deterioration brought on by deicing salts. Because the bridge connects the towns of Pittsburg and Nemo, and the length of the nearest detour route was 28 miles, MoDOT deemed it essential that the bridge remain in service during construction. Additionally, the local economy of these towns is very reliant on the tourism industry and most of their income is generated during the summer months.

This article describes the inspection philosophy for the McKinley Bridge and the methodology used for its rehabilitation, both of which kept public safety as the highest priority while maximizing the limited funding available. The bridge was owned and operated by the City of Venice, IL, and is now under the jurisdictional control of the State of Illinois, Department of Transportation. The inspection methodology followed the National Bridge Inspection Standards (NBIS) requirements; however, the inspection philosophy emphasized concentrating inspection time and resources into those portions of the bridge that were most likely to fail or most likely to become a hazard to the traveling public. The existing bridge includes a variety of common construction materials and methods, including the use of steel girders, steel trusses, timber trestles, reinforced concrete viaducts, reinforced concrete decks, wooden decks, and concrete-filled steel grid deck, which were open and closed to the traveling public at various times. The inspection resources given to each portion of the bridge were weighted based upon their structural importance, usage, and degree of deterioration. Due to the targeted use of resources, the bridge was kept operational for many years past its normal useful life. Eventually, with limited maintenance funding, it could no longer be kept in operating service, and the State of Illinois closed it to public use. Realizing that the McKinley Bridge was needed as a vital link in the St. Louis Metropolitan area, especially until the new downtown bridge is built, the State of Illinois decided to fund the rehabilitation of the bridge. All of the approach spans and deck trusses are being replaced; however, the main through trusses will remain, with the exception of the cantilever roadways. This was all based on keeping public safety as the highest priority while still making the best use of the funds available for rehabilitation.

Located in Hardin, Illinois, the Joe Page Bridge carries Illinois Routes 100 and 16 over the Illinois River. By connecting Calhoun County, on the west side, to Greene County, on the east side, the structure provides a vital transportation link for access into Hardin and central Calhoun County. The closest, alternate crossings of the Illinois River are the Kampsville ferry, approximately 10 miles upstream, and the Brussels ferry, approximately 17 miles downstream. Many challenging engineering aspects were encountered and addressed during this multi-million dollar rehabilitation project. The Joe Page Bridge rehabilitation began in March 2003 and was essentially complete by December 2004. The structure remained open to one lane of vehicular traffic throughout the project. Due to the wire rope and trunnion replacements, the structure remained in the closed position for approximately 23 days in August/September of 2003. During this time, marine traffic was required to pass barges under the structure or utilize tow boats with retractable helms. Partnering meetings between IDOT, Modjeski and Masters, and the Contractor were essential to keeping the project on-track. Coordination between the Contractor and their Sub-Contractors was key to performing the work in a manner which did not inhibit one another. Today, the Joe Page Bridge remains a reliable source for both vehicular and marine traffic, and a historical landmark for the City of Hardin, Illinois. The rehabilitated structural, mechanical and electrical systems will serve the transportation industry well into the future.

The Merchants Bridge is a two-track railroad structure that crosses the upper Mississippi River at Mile 183.2, just north of downtown St. Louis, Missouri. It is owned and operated by the Terminal Railroad Association (TRRA) of St. Louis, a local railroad with a history that dates back to 1889. The bridge itself was completed and opened to traffic in 1890. The Merchants Bridge is a key route for TRRA and its tenant lines. It is a critical link in the transcontinental railroad system. It affords access to industrial districts on both sides of the river and serves as a connection for numerous rail lines. Currently, the structure carries traffic consisting of approximately 35 trains a day and 40 million gross tons each year.

The 1989 Loma Prieta Earthquake collapsed part of the Interstate 880 Freeway (Cypress Street Viaduct) taking the largest human toll exacted on a highway system. As a result, the Federal Highway Administration began a program requiring immediate evaluation of all double deck highway bridges in the United States. This paper presents the evaluation of one such structure in St. Louis, Missouri highlighting seismic retrofitting techniques designed to improve the performance of concrete elements and overall bridge performance in an urban setting. The Daniel Boone Expressway in downtown St. Louis, Missouri, is one such multi-level bridge providing a major east-west transportation link for Interstate 64 in this Midwestern city. Built in the mid 1960s, the bridge complex is about 1.5 miles in length comprised of equal part side by side elevated structure and over-under elevated structure. The mainline bridge is typically concrete slab on steel I-girder with reinforced concrete substructure units. The substructure units vary from single column bents to multi-frame column bents. The elevated ramps leading to or from the bridge complex vary from concrete slab on steel I-girder to continuous voided slab or box-girder spans. Given the variety of structural elements, this project, now in its tenth year, has provided a wealth of experience in seismic retrofit for the Central United States.

A new publication entitled Structural Wood Design Using ASD and LRFD has been developed as a companion design tool to the 2005 National Design Specification® (NDS®) for Wood Construction and will be available beginning in the Spring of 2006 through the American Forest & Paper Association (AF&PA). The book, authored by Dr. Dan L. Wheat, P.E. of the University of Texas at Austin and Dr. Steven M. Cramer, P.E. of the University of Wisconsin-Madison is intended to aid instruction on structural design of wood structures using both allowable stress design (ASD) and load and resistance factor design (LRFD). It will allow direct comparison of ASD and LRFD for wood structures on a problem by problem basis.

Most timber bridges are currently designed in accordance with the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges, 17th Edition (SSHB), which follows an allowable stress design (ASD) approach. However, the Federal Highway Administration (FHWA) will be requiring all highway bridges designed after October 1, 2007, to follow the AASHTO LRFD (Load & Resistance Factor Design) Bridge Design Specifications, 3rd Edition. As the transition from ASD to LRFD nears, engineers need to be aware of the differences. Information will be presented about more recent changes to the design codes and differences between AASHTO's Manual for Condition Evaluation and Load Resistance Factor Rating (LRFR) of Highway Bridges, which uses the LRFD method, and AASHTO's Manual for Condition Evaluation of Bridges, 2nd Edition (MCEB), which uses the ASD method. This paper will provide an overview of the pertinent issues related to wood bridge load ratings. Examples are included that illustrate the dramatic reduction in rated load capacity when sawn wood and glued-laminated timber stringers are load rated by the LRFD method compared to the ASD method.

The 2005 Edition of the National Design Specification for Wood Construction was approved as an American National Standard on January 6, 2005, with a designation ANSI/AF&PA NDS-2005. The 2005 NDS was developed as a dual format specification incorporating design provisions for both allowable stress design (ASD) and load and resistance factor design (LRFD). AF&PA's Wood Design Standards Committee (WDSC) guided it through the consensus process over the course of 2 1/2 years. The primary change in the 2005 NDS is the introduction of LRFD methods to the Specification. Several format changes to the NDS to accommodate addition of LRFD are summarized in this paper and include: (1) revised terminology (2) expanded applicability of adjustment factor tables, (3) re-format of radial tension design values, (4) revised format of beam and column stability provisions (addition of E_min property), and (5) addition of NDS Appendix N - Load and Resistance Factor Design. A number of other changes introduced in the 2005 Edition include: (1) removal of form factor, (2) revision of repetitive member factor for I-joists, (3) revision of full-design value terminlogy, and (4) clarification of built-up column provision. The NDS Supplement, Design Values for Wood Construction has also been updated to provide the latest design values for sawn lumber and glued laminated timber.

In 1993 AASHTO adopted a new load and resistance factor design (LRFD) code for highway bridges. The new code provides a rational basis for the design of steel and concrete structures. Although wood bridge design was also included in LRFD format, the calibration was not carried out for these structures. Therefore, there was a concern about the consistency of the reliability level for wood structures. Previous studies have shown that the reliability index for wood bridge components can be significantly different from those for steel or concrete structures. The degree of variation for wood properties is a function of dimensions, load duration, moisture content and other parameters. There is particular concern for plank decks, for which section aspect ratio also significantly affects results. The objective of this study is to summarize the load and resistance criteria for highway bridge plank decks, and to estimate the reliability of plank decks designed by AASHTO Code. A typical plank deck consists of planks placed on stringers that run either transversely to or parallel to the direction of traffic. The span length of stringers is usually 16–20 ft (5–6m), while stringers are typically spaced from 12–24 in (300–600mm). Stringers are commonly made of Southern Pine or Douglas-Fir sawn lumber, often nominally 6 in x 18 in (150 x 450mm), or larger. The planks are typically 4 in x 10 in (100 x 250mm) or 4 in x 12 in (100 x 300 mm).

In the current bridge design methodology, beam line analysis and girder distribution factors are often used to compute the maximum live load demands on the girders. However, this method does not predict the response of all girders under live load. Furthermore, it has been found to be conservative compared to 3-D analysis results and load tests of bridges. With the proposed simple method, it can be possible to closely approximate the 3-D live load response of bridges with accuracy comparable to that from a detailed finite element analysis. For a given truck position, the bending moment resisted by each girder and individual girder deflections can be computed easily. The live load demand imposed on the secondary members, such as diaphragms or cross-frames, can also be predicted using the proposed analysis.

I-shaped flexural members can be subjected to significant lateral forces or torsion combined with major axis bending. This condition commonly occurs with bridge girders that are skewed or curved in plan. Within an elastic range of loading, vector addition of minor axis bending stress or warping normal stress with major axis bending normal stresses results in a linearly varying stress gradient across the flange, which causes a reduction in major axis bending moment at which a slender flange plate buckles. Under combined major axis bending and lateral flange bending, yielding initiates from one edge of the flange and propagates towards the web, which results in the need for compactness and strength definitions that consider the interaction of major-axis and lateral-flange moments. This paper presents a definition of flange strength and slenderness based upon theoretical and analytical models that consider the effect of lateral bending or warping stresses. The effect of stress gradient on elastic flange buckling is quantified using a Galerkin series solution that considers the full width of the flange plate with a variable rotational stiffness along the center of the plate. The coupling of stress gradient and centerline rotation resistance is demonstrated and it is shown that the full flange width must be considered for evaluating buckling capacity of flanges in which the stress varies across the plate. The solution is then used to define the transition point between non-compact and slender flanges subjected to stress gradient. The strength of compact flanges is defined by considering the portion of the plastic flange that is available to resist the vertical moment. Finite element analyses are used to demonstrate the accuracy and applicability of the solution.

The AASHTO-LRFD live 2load distribution factors for highway bridges show significant change compared to the standard AASHTO that have been used for the last 50 years. This paper presents a comparison between the moments distribution factors of concrete bridges due to live load calculated in accordance with the current AASHTO-LRFD (2004) formulas and finite-element analysis. Several three-dimensional linear elastic models were built using the structural analysis program SAP2000 to obtain the most accurate method to model the bridge superstructure. The bridge deck was modeled as quadrilateral shell elements and the girders as space frame elements. The live load used in the analysis is the vehicular load plus the standard uniform lane load as specified by AASHTO-LRFD. The live load is positioned at the longitudinal location that produces the maximum moments, then the load is moved transversely across the bridge width in order to investigate all possibilities of bridge loading (one, two and three lanes loaded). In this comparison the range of applicability specified by the AASHTO-LRFD is fully covered in terms of span length, slab thickness, girder spacing and longitudinal stiffness. One parameter is considered at a time while the remaining parameters are fixed. All the AASHTO-PCI girders (Type I to VI) are considered to cover the complete range of longitudinal stiffness specified in the AASHTO-LRFD specifications. The results of this study are presented in format of graphs and some recommendations for specific bridge geometries are presented.

Current bridge design codes do not clearly specify the girder distribution factors for continuous bridges. The objective of the paper is to validate the use of code-specified girder distribution factors for the continuous steel girder bridges, and to provide a basis for recommended girder distribution factors (GDF) for interior girders, suitable for evaluation of existing continuous steel girder bridges. This paper presents the procedure and results of 3-dimensional finite element analysis that were performed on five continuous two-lane steel girder bridges to verify girder distribution factors. In the numerical models, the selected bridges were analyzed under fully loaded 11 -axle trucks available in Michigan. The analysis results showed that the live load moment distribution is very similar for negative moment region compared with positive moment region in continuous steel girder bridges. It was also found that the GDF's based on the strain values are similar to those based on the deflection. GDF's based on the deflection show marginally better distribution. The analysis results confirmed that the code specified GDF's for continuous steel girder bridges are very conservative, for both AASHTO LRFD and AASHTO Standard. AASHTO Standard provides more conservative GDF's.

This paper describes a finite element model that has been developed to calculate the live load response of a major steel trussed-arch bridge in Idaho. Any truck configuration (axle loads and spacing) can be modeled as a moving load along one of several predefined load paths. The finite element model calculates the envelope of maximum and minimum live load effects (shear, bending moment or axial force) in the bridge members. Live load tests were conducted to verify the accuracy of the finite element model. A preliminary examination of the results of these tests indicate that the finite element model provides reasonably accurate predictions of live load effects in principal members subjected to direct loads. Live load calculations for indirectly-loaded secondary members were less accurate. Further calibration of the model is expected improve the accuracy of forces and moments predicted in both cases, providing a reliable and flexible bridge rating procedure.

In the fall of 2004, a series of field tests were conducted on the steel truss bridge that carries Route 896 over the C&D Canal near Glasgow, Delaware. Owned and maintained by the U.S. Army Corp of Engineers, the bridge is more commonly referred to as the Summit Bridge. Previous inspections of the bridge had identified small cracks in some of the tack welds placed on the bridge when it was originally built. A theoretical fatigue life calculation showed that some of the members had little or no remaining fatigue life. As a result, a field test was conducted to measure strains (stresses) in selected truss members under controlled loads and ambient traffic, in order to get a more accurate estimate of the effective stress range in the members for fatigue life calculations.

In an attempt to improve the safety and reliability of highway structures, the Federal Highway Administration has requested that every department of transportation begin using the AASHTO-LRFD Bridge Design Specification to design new highway structures by 2007. It is estimated that the design shears computed using the LRFD Specifications could be up to 40% larger than those calculated using the LFD Specifications. The design shears are larger because of increased design loads and modified shear distribution factors. In an attempt to evaluate the more conservative design recommended by the LRFD Specifications, the Illinois Department of Transportation (IDOT) has funded a research project conducted by Southern Illinois University Edwardsville and Modjeski and Masters. The project investigates the conservativeness of the modified shear distribution factors, especially near the bearing. This research uses field testing and finite element analysis to evaluate the LRFD Specifications related to shear distribution factors. Twelve typical interstate highway bridges in Illinois were selected for instrumentation. The twelve bridges represent a wide range of typical parameters including skew, span length, girder spacing, and girder material (concrete or steel girders). Three strain gauge rosettes were affixed to each girder near the bearing to record the shear force during static load tests. Static load tests were performed using a truck loaded with aggregate provided by IDOT. The truck was statically positioned in several predetermined locations and data was recorded. The accuracy of the field test data was evaluated using finite element models of each bridge deck. The axle weights, obtained from a local weigh station, were applied to the finite element model for each static load position. Shear distribution factors calculated from finite element analysis and field-testing could be compared to those predicted by the LFD and LRFD Specifications. The preliminary data results for the determination of the shear distribution factors are complete for six of the twelve bridges. The following research paper will give a summary of the methods used to analyze the field data and finite element models for the bridges using Structure Number (SN) 059-0041 as an example. This structure is a noncomposite, six girder, three-span, steel bridge. The other structures were modeled and tested in a similar manner.

This paper summarizes measured versus computed results from a field test with heavy live load conducted on a multi-span, horizontally curved steel I-girder bridge. Eight 72,000 lbs trucks were placed on the bridge in several static and dynamic loading configurations, and results were compared to those obtained from grillage analyses. Through comparison with other field and experimental tests in the literature, load rating procedures both with and without the use of load testing were then investigated for horizontally curved steel I-girder bridges based upon use of the AASHTO Load and Resistance Factor Rating procedures.

On July 21, 1853, the New York State Legislature passed an act setting aside land for a public park. In 1857, a public competition was held for the design of the park. The winning entry was the "Greensward Plan" by Frederic Law Olmsted and Calvert Vaux. Construction of the 843-acre Central Park was started in 1857 and completed some 20 years later. Bounded by Central Park South (59^th Street), Central Park North (110^th Street), 5^th Avenue, and Central Park West (8^th Avenue), the park has roads, paths, bodies ofwater (a lake, ponds, a reservoir), lawns, and meadows, over 26,000 trees, the Metropolitan Museum of Art and other buildings. Central Park has East, West, Center, and Terrace drives for highway traffic with pedestrian sidewalks; pedestrian paths; and bridle paths — for horses and pedestrians. The total length of pedestrian walkways is 58 miles. There are four submerged transverse roads, to carry cross-town traffic, in the shape of bathtubs at 65^th/66^th; 79^th to 81^st; 84^th/85^th; and at 96^th/97^th streets. These roads divide the park into five zones which are accessible only by the bridges over these roads. At present there are 39 bridges in Central Park. These bridges use a variety of structural materials including stone, brick, wood, cast iron, and reinforced concrete. Only five bridges use cast iron. Two cast iron bridges and one stone bridge were demolished in the 1930s to make way for improvements in the park.

The objective of this paper is to describe the experimental and computational research performed on two covered wooden bridges that were selected as part of the National Covered Bridges Recording Project, sponsored by the Historic American Engineering Record and the Federal Highway Administration between 2002 and 2004. Our work highlights the importance of tension splice joints, or scarf joints, common in the lower chords of covered wooden bridges. The first part of the paper discusses the use of full-scale field measurements of the bridges under live load and the subsequent comparison of those results with two-dimensional computational models of the bridges. An outcome of the full-scale field measurements was the experimental and computational work performed on individual, replicated scarf joints from the bridges, which is discussed in the second part of the paper. It was found that details of the scarf joints, particularly grain orientation, play a key role in their behavior.

Three master builders created signature creations. Although none were professionally trained, they showed an understanding of how their bridges worked that has allowed them to stand to this day. All three crafted fine arches connected with sophisticated, long lasting joinery. The Kennedys built aesthetically refined portals that are works of art, while Daniels and Britton preferred more of a "neat, clean finish." They all showed a sophistication in the types and variety of fishplates they employed in the lower chord, one of the most critical parts of the bridge. Daniels and Britton also demonstrated an ability to artfully incorporate new materials like iron in creating long lasting structures. However, as these builders were completed their careers, threats to their structures were ever present due to the new demands of the automobile. As bridges across the Midwest and across the nation were replaced or allowed to decay, new forces urged their preservation. HABS began documenting these structures in the 1930s, even as they were literally collapsing in front of their eyes. The Parke County Covered Bridge Festival was established in 1957 to help preserve and promote its Daniels and Britton legacy. Indiana tourism. HAER NCB Program. Ongoing threats continue such as the collapse of the Bell Ford Bridge in Indiana and arson of the Hunterdon Bridge in Iowa in 2005. But it is hoped that the success of the National Covered Bridges Preservation Act, which included funding for preservation and protection as well as the research of the HAER National Covered Bridges Program, will insure that this important engineering legacy continues for generations to come.

Binzhou Yellow River Bridge is a four-span cable-stayed bridge with prestressed concrete girders. To ensure the integrity of the girder and resist transverse bending due to dead load and service load, transverse prestressing tendons were disposed in the diaphragms. During the in-situ experiment for full-scale segmental model of the girder, stresses and cracks on one oblique web of the side-boxes were measured. Through mechanical analysis for segmental model of the girder by spatial finite element method (FEM), the mechanism of the two oblique webs under transverse prestressing was obtained. Further analysis showed that improving methods such as adding prestressed strands and reinforced bars were available to distribute high stress concentration and avoid cracking of concrete.

In order to better assess the condition of existing and new bridge systems it is necessary to understand how they would behave under loadings beyond elastic ranges. With about 30% of the 600,000 bridges in the country classified as structurally deficient or functionally obsolete, finding an accurate predictive method becomes a must. The main objectives of this study are (1) to demonstrate how the load distribution affects the behavior of each girder as the live load is increased up to the bridge's ultimate capacity, (2) to understand bridge systems performance in inelastic stages, and (3) to predict the bridge's ultimate capacity. A bridge was analyzed up to its failure under various loading conditions using a 3D finite element model. It was found that the only accurate method to determine load distribution at ultimate stages is through section moments. It was also found that the current bridge rating method underestimates considerably the analyzed bridge's strength. These findings can potentially result in saving millions of dollars annually by avoiding unnecessary weight-limiting postings, rehabilitation or decommissioning and replacement.

The paper describes an innovative precast pavement system located on I-57 near Sikeston, MO. Overview of precast pavement technology and associated merits are presented in addition to instrumentation and monitoring plans and preliminary results from the investigation. Early age response and stress transfer measurements are reported. Plans for monitoring in-service performance data are also discussed. Analysis of preliminary results from the investigation follow, and include: (1) the early age behavior of the panels during and immediately after fabrication (effects due to hydration and differential thermal stresses during curing), (2) material characteristics such as unrestrained creep and shrinkage, chloride permeability, and freeze thaw resistance, (3) transfer of transverse pre-tensioning, (4) frictional stress losses during post-tensioning operations, and (5) plans for the future monitoring of long-term in-service performance of central anchor panels, base panels, and joint panels.

Prestressing of steel girders is an attractive technique to increase their load capacity. For new construction, prestressing will result in reduction in the overall steel weight of the structure, which will result in cost saving. Prestressing can also be used to minimize the deflections when the construction depth is restricted or when a high span to depth ratio is mandated. Prestressing technique is also an effective and practical method to strengthen existing structures when an increase in permissible live loads is needed. Numerous experimental and analytical investigations have been conducted to study the behavior of externally prestressed simply supported composite steel girders under positive moment. However, very few studies have been performed to investigate the effect of continuity on the behavior of prestressed steel girders. Such studies mainly used test specimens that only simulated the negative moment region. Therefore, the behavior under all aspects of continuity was not fully investigated. In this research, a comprehensive experimental investigation was conducted to more thoroughly understand the behavior of externally prestressed continues composite steel girders under negative moment. Three half-scale test specimens consisting of continuous (two-span) composite girders were load tested to their ultimate capacity. The girders were prestressed using 7-wire –1/2 in. low relaxation strands. Among the parameters tested were shored versus unshored construction, and application of prestress to the steel section only or to the composite section. The results showed an increase in the ultimate load capacity by about 15%, a decrease in deflection, as well as an increase in the elastic limit compared to a non-prestressed girder. The results also showed that prestressing continuous composite girders reduces stresses in steel beam and increase the load level where the beams start to buckle. The use of strands to prestress steel girders provided flexibility of performing the required profile to optimize the strength of the steel girder.

Torsion can be a significant action in many structural members that are part of civil engineering infrastructure. Curved bridges and spandrel beams under gravity loads exhibit torsional forces. During an earthquake event, members of other structures such as single column connectors, as well as beams and columns of bridges with outriggers are subject to seismic loads that cause cyclic torsion combined with other actions such as bending and shear. Whether the occurrence of torsional stresses in a member are due to gravity loads or seismic loads, their existence necessitates reliable models to predict their effect on a member's capacity and load-deformation response. Under static loads, it is difficult to precisely characterize the state of internal stress in a member whether the torsion occurs alone or combined with other actions. Early models for predicting the capacity of members under static torsional loads were based on the skew-bending approach. Later, rotating angle truss models were developed that could predict the entire load-deformation history of members under pure torsion or combined actions including torsion. A more recent model was developed for members under combined shear and torsion, however it is inconsistent in its application of Bredt's thin tube theory and is based on Modified Compression Field Theory which has several deficiencies. This paper will describe a proposed model of an RC member under torsion combined with other actions such as shear and bending. The model is based on the softened truss model (STM) developed at the University of Houston. The first part of the paper will explain how the STM has been expanded to account for combined loads and the second part will compare the predicted load-deformation response with some experimental studies.

A detailed instrumentation system has been developed to examine the behavior of different components of a bridge structure under the effect of temperature variations. A 3-span steel girder continuous girder bridge with integral abutment at the ends was selected for this study. The bridge is located in Evansville, West Virginia and the construction was completed in June 2003. The instrumentation plan is based on continuous monitoring of the triaxial state of strain, temperature gradient, crack opening, and relative movement between the substructure elements. The relative motion between the abutment and the pier at the edge span and between the two piers at the middle span its effect on the thermal strains and stresses induced in the steel girders as well as concrete bridge deck has been examined. The results indicates that motion of the substructure due to the expansion or contraction of the bridge superstructures is partially restrained, which generates thermal stresses in the girders and the deck that are not currently accounted for in the design. The instrumentation approach used in this study has shown that it could be used as an alert system for the deterioration of bridge structures.

This paper presents a study on the effect of bridge skewness on live load reactions at piers of continuous skewed bridges. Finite element modeling and analysis are performed on selected steel I-beam bridges with varied skew angles. The bridges are analyzed for the live load reactions at piers and live load shears at beam end. A comparison study is performed for the difference between the distribution factors of reactions and shears. The comparison reveals that the distribution factor of reaction at support is higher than that of shear at beam end near the same support. The increase in reaction distribution factor is more significant, compared to shear, when skew angle is greater than 30°. It is recommended that more research be performed for the distribution factor of live load reaction to quantify the responses.

The research focused on the effects of low velocity impact loading on high strength concrete confined by a prefabricated polypropylene jacket and comparing the results with similar specimens confined by carbon fiber. In order to accomplish this, both static and dynamic load tests were performed. Concrete cylinders were used for static loading. Twelve concrete cylinders were prepared for static load testing: three were plain concrete and used as control specimens, three were wrapped with one layer of unidirectional carbon fiber, and six were confined by the polypropylene pipe. The thickness of the polypropylene wrap was machined to different thicknesses; three 3 mm and three 6 mm. The cylinders were standard 152 mm x 305 mm. Cylinders were loaded to failure in uniaxial compression using a Tinius-Olsen Universal Testing Machine. Impact testing was performed using four 152 mm x 914 mm columns. The columns consisted of one control sample; one carbon fiber wrapped, and two (one of each thickness) wrapped with polypropylene. Impact testing was conducted using an Instron drop-tower testing machine.

Over the past twenty years, regulatory changes, identified problems, and continued growth of our population and commerce have resulted in a greater need to perform structural inspections of transportation facilities on a regular basis. A problem of growing damages to bridges identified over time has resulted in increasing the minimum design stress for H-20 loading. Older bridges were not designed to meet the new criterion. More and heavier trucks are using our roads every day, increasing the rates of deterioration of bridges and pavements. Growing traffic on our waterways is increasing the probabilities of a barge — bridge collision that can result in a disaster. Aging highway signage and high mast lighting (luminaries) are becoming structurally unsound, usually due to failing connections, and are dropping to the roadway with large potential for damages and risk of loss of life. Concerning bridges, the Federal Highway Administration established mandatory guidelines for periodic inspections, both above and below water. This has resulted in steady, if slow, improvement over the years. The number of structurally deficient bridges has dropped from 93,359 in 1998 to 81,582 in 2003. That's a reduction of 11,777 deficient bridges. During the same period, 5,540 new bridges were constructed. The actual percentage of structurally deficient bridges went down from 0.153% to 0.132%. Some states are deterring their responsibility for bridge maintenance by soliciting bids from private companies to be fully responsible for inspections and repairs, quite possibly lowering the standards for qualifications of the people performing the inspections. This is a low bid system; meaning that the least qualified people will be performing the inspections. While the Federal government did establish minimum guidelines and requirements for bridge inspections, it has not established similar requirements for signs or luminaries. As a result, some states do not inspect signs or luminaries. The value of regular inspections of bridges being required, not optional, has been proven in the past. Similar requirements for bridge pier protection, highway signs, and luminaries should be in place. Without regular inspections, the first sign of a problem is a failure and collapse, quite possibly injuring or killing a number of people.

By 1956, the Chesapeake Bay Ferry District and predecessor to the current Chesapeake Bay Bridge and Tunnel District, a political subdivision of the State of Virginia, operated the largest ferry system in the world. It was an 85-minute crossing of the mouth of Chesapeake Bay from the southern shore in the Norfolk-Virginia Beach area to the Eastern Shore of Virginia peninsula, with up to 90 one-way daily crossings. However, capacity was could not keep up with increasing traffic demands. Consequently, Virginia gave legislative approval for the District to construct, maintain and operate a bridge and tunnel project. This would close the last gap along U.S. Route 13, one of the principal north-south highways between New England and Mid-Atlantic States and the southeastern sections of the country. Planning and design began almost immediately. Construction followed in late 1960 and was completed on April 15, 1964. The crossing was widely regarded as one of the world's modern engineering marvels, receiving many awards, including the Outstanding Civil Engineering Achievement Award from the American Society of Civil Engineers. Total cost of studies, engineering and construction was approximately $200 million. The project was financed without tax money through revenue bonds. Tolls were used to pay the bond debt and cover operation and maintenance costs for the facility.

Fabrication facilities serving integrated circuit (IC) and FPD (flat panel display) manufacturing have evolved through the years. These "fab" facilities are unique in many aspects. One of their unique features is the fact that they are cleanroom environments designed to control particle, temperature, humidity, vibration, and noise contaminants. The current-generation high-end IC manufacturing is dedicated to handling 300mm silicon wafers using 0.090 micron (90 nanometers) feature size. This paper discusses the structural concepts of these fabs. The fab structure is controlled by micro-vibration performance. The paper blends discussion on the unique structural features of the state-of-the-art fabs with their vibration design fundamentals. Construction techniques and materials are also covered. On one hand, member sizing of fab floors, columns, foundations, lateral systems are dictated by the vibration design. On the other hand, other facility needs such as fire code issues, space utilization, functionality and production tool layout impose other constraints on the fab structures.

The suspender rope-to-suspended superstructure link is a substantial connection in suspension bridge engineering that has to be detailed to function properly during the entire bridge service life. For the New Tacoma Narrows Bridge, this connection incorporates an open socket with its pin in bearing contact with a suspender bracket assembly through a pin plate and doubling plates. The weld between the suspender pin plate and doubling plates was detailed to have an effective weld throat size of 8 mm. During fabrication of this connection, ultra sonic tests demonstrated some shortcomings in the form of undersized effective weld throat size. The present study was consequently conducted to investigate the impact of this reduction on the connection performance under maximum design loads. A three dimensional finite element model was developed that included non-linear boundaries at the pin-to-pin plate interface to investigate whether or not this modification could conform to performance needs. The study illustrated that despite the weld size the connection can withstand the maximum design loads and that the base metal controlled the performance down to a 3mm effective throat weld size.

Main water resource of SW projects of KWPA will be supplied using the pipeline under the Karun River that is located in the North of the Persian Gulf region. Fresh water should be transferred through PE (Steel pipe) siphon pipeline under the river bed in project area. Great problems have been occurred when the extra deflection produce in low soil resistance at Bed River and settlement criterion can not be satisfied by rotation at joints in pipeline. Bed and Bank of River are nonsymmetrical deflection through pipe line installation. Intersection point of pipeline will be needed a knee connection and will be damaged by external twist at sides of knee connection. Intelligence behavior could be solved the settlements and rotation problems through reptile motion on soil to make new artificial intelligence designing. Therefore, desired pipeline could be divided into segmental members with rotating connections. Members can be rotated around the connections using the two degree freedom of rotation and the one degree at longitudinal axes. Spherical balls should be installed to satisfy the three degree freedom at knee connection. Movements and twist is produced by the spherical balls and steel link to move through the guide slotting in load direction.

Saint Louis University is an integral participant in the USGS Advanced National Seismic System along with the University of Memphis, the University of Kentucky, University of South Carolina and Virginia Tech. The Saint Louis University Component consists of two complementary elements: broadband monitoring of the earthquake process in a large area surrounding the New Madrid seismic zone, and the recently installed ANSS urban monitoring stations. Figures 1 and 2 show the stations monitoring the region. The few analog stations near St. Louis and Cape Girardeau, Missouri, are not shown. Also the most distant station, Piqua, Ohio is not plotted. The distribution of the broadband stations was chosen to provide a backbone coverage of the earthquake within this active region of the mid-west. The ANSS Urban stations were sited realizing that an occurrence of a large earthquake during the lifetime of these installation is small, and that it is necessary to put instruments where significant earthquakes have occurred in the past. This is the reason for an emphasis at a number of non-urban sites in the Wabash Valley of southeastern Illinois and southwestern Indiana. The Harrisburg, Illinois site (HAIL) is near the location of the November 9, 1968 earthquake, which was the largest in the region during the last 50–60 years. In general the ANSS strong motion stations are working well. However, the 4g instruments installed provide little information on smaller earthquakes for location or ground motion studies.

We present a comprehensive set of computational tools, hereinafter called JAMA-ADA, recently developed for the analysis of strong motion data of instrumented buildings and damage detection implications. By using the system, structural engineers have a legion of advanced analytical tools at their disposal to (1) identify the possibility of damage, (2) to recognize the extend of damage, and (3) to some degree find the location of damage within a structure virtually minutes in the aftermath of an earthquake. The methods have been applied to more than 80 instrumented buildings which have recordings from more than one earthquake. The results indicate that the proposed methods, when used in combination, can provide very useful information regarding the status of a building immediately after an earthquake by simple and rapid analysis of sensor data and prior to any building inspections. JAMA-ADA utilizes a single-input multiple-output identification procedure of time-variant and time-invariant systems for estimation of modal properties of the instrumented buildings as they respond to ground shaking. The system identification procedure uses a novel solution of dynamic response of multistory buildings in an evolutionary algorithm. Most structural identification procedures proposed to date only provide some estimates of the modal quantities from which any inference to the commencement of damage may not be trivially available. However in our proposed method, besides modal properties such as mode shapes and periods, an overall estimate of the participation of shear to flexural deformations in the lateral response of a building structure can be obtained. As a result, any changes in the mode of response to and from flexural and shear dominant can be monitored in a time-varying fashion. The method is fully automated such that it can be used virtually without any delay in the aftermath of an urban earthquake.

The Bill Emerson Memorial Bridge is a new cable-stayed Mississippi River crossing in Cape Girardeau, Missouri that opened on December 13, 2003. The site is known for its proximity to the New Madrid Fault, necessitating a design for a M7.5 event. It is the first major bridge structure in the Central and Eastern United States (CEUS) where seismic (and wind) monitoring was considered from the early stages of design. A multi-agency team effort was used to design a system, acquire the sensors and other instrumentation, provide for installation and performance testing, and establish a suitable protocol for operation and data dissemination. The instrumentation of the bridge including two free-field arrays with downholes was completed in March 2005. Data is now being streamed in real-time and transmitted via the internet to the user community for analyses and conducting structural health monitoring. The purpose of this paper is to describe the entire process so the experience can be studied and used as a guide for future bridge projects, especially those in the CEUS. The Bill Emerson Memorial Bridge consists of a three span cable-stay river crossing and an eleven span steel plate girder Illinois approach. The total bridge length is 3,965 feet (1210 m) with a 1,150-foot (350 m) main river span. Cape Girardeau is approximately 50 miles due north of the New Madrid Seismic Zone (NMSZ), the location of three large (M > 7.5) and numerous smaller earthquakes during the winter of 1811–1812. A Federal Highway Administration (FHWA) geotechnical engineer, Chris Dumas, originally conceived seismic instrumentation of the Bill Emerson Memorial Bridge in 1996. Several meetings were conducted in 1996 and 1997 between various stakeholders associated with the bridge and seismic instrumentation networks. As an outcome of this series of meetings, a seismic instrumentation plan for the structure was developed by the United States Geological Survey (USGS) and authored by Mehmet Çelebi. However, at the time no funding source for the project existed so acquisition of the system did not proceed. In the subsequent Transportation Efficiency for the 21st Century (TEA-21) Federal Highway Bill, the FHWA sponsored a 6-year seismic research program with the Multidisciplinary Center for Earthquake Engineering Research (MCEER) at the State University of New York - Buffalo. The program included funding for the final design and hardware acquisition of the seismic instrumentation system for the Bill Emerson Memorial Bridge. Total funding set aside for the purchase of the hardware including 84 channels of accelerometers and data acquisition and transmission systems, as part of this program, was $375,000.

This paper introduces the state of the art, real-time and broad-band seismic monitoring network implemented for the 1206 m [3956 ft] long, cable-stayed Bill Emerson Memorial Bridge in Cape Girardeau (MO), a new Mississippi River crossing, approximately 80 km from the epicentral region of the 1811–1812 New Madrid earthquakes. The bridge was designed for a strong earthquake (magnitude 7.5 or greater) during the design life of the bridge. The monitoring network comprises a total of 84 channels of accelerometers deployed on the superstructure, pier foundations and at surface and downhole free-field arrays of the bridge. The paper also presents the high quality response data obtained from the network. Such data is aimed to be used by the owner, researchers and engineers to assess the performance of the bridge, to check design parameters, including the comparison of dynamic characteristics with actual response, and to better design future similar bridges. Preliminary analyses of ambient and low amplitude small earthquake data reveal specific response characteristics of the bridge and the free-field. There is evidence of coherent tower, cable, deck interaction that sometimes results in amplified ambient motions. Motions at the lowest tri-axial downhole accelerometers on both MO and IL sides are practically free from any feedback from the bridge. Motions at the mid-level and surface downhole accelerometers are influenced significantly by feedback due to amplified ambient motions of the bridge.

Over the past several years, The Hernando Desoto Bridge carrying I-40 across the Mississippi river at Memphis has been the scene of an intensive strong motion monitoring project, involving the installation of numerous traditional and several non-traditional forms of instrumentation designed to characterize the response of the structure to shaking from seismic and induced sources. This bridge is being retrofitted to withstand a magnitude (mb) 7 event at 65 km distance from the site at a depth of 20 km. The goal of the retrofit is to have this bridge fully operational following the maximum probable earthquake (2500 year return period). As part of the I-40 bridge retrofit, Friction Pendulum TM Isolation Bearings have been used to insure the integrity of the main spans of the bridge. The Tennessee Department of Transportations (TDOT) in conjunction with the Federal Highway Administration (FHWA) have provided funding to install strong-motion instrumentation with 108 data channels at 36 different locations on the bridge. The United State Geological Survey (USGS) in 2002 funded the installation of sensors at the foundation levels. In addition, two free field monitoring stations were installed by Center for Earthquake Research and Information (CERI), at the University of Memphis, through funding from the Advanced National Seismic System (ANSS). Currently, in the United States and elsewhere in the world, there are very little data available on the response of long-span bridges during seismic events. Since such data are scarce, our ability to understand the behavior of such structures and to verify dynamic analyses performed on such structures during design/analyses/retrofit phases is limited. In the NMSZ, there are no long-span suspension bridge structures instrumented. Therefore, data collected from instrumentation of the I-40 bridge in Memphis will be an invaluable asset in evaluating the structure. The data will be used to assess the performance of the bridge following the retrofit and in particular for the assessment of the performance of the base-isolation system. In addition, data collected on the behavior of the base-isolation system will be applicable to any structure incorporating the system. Furthermore, lessons that will be learned from instrumentation of a bridge such as the I-40 bridge will provide important and needed information that will be applicable to structures built on similar seismological and geological settings as the 1-40 bridge. One of the goals of the instrumentation system is to develop a rapid warning system. The rapid warning system will be developed in partnership with TDOT, FHWA, the United States Geological Survey (USGS) and the Mid-America Earthquake Center (MAEC) researchers. The system will be triggered when certain acceleration thresholds, at free fields, are exceeded. Key officials at TDOT will be automatically notified of the exceedance of threshold acceleration within minutes over standard communication devices. This information will help determine the forces that the bridge underwent in a large earthquake, or other threatening events such a barge collision, and should allow quick determination whether it should be closed or/and what precautions rescuers and engineers should take. This type of monitoring and the associated rapid response may save lives.

Over 50 bridges in Georgia have been elevated using steel pedestals as a cost-effective means to increase the clearance height and to reduce the likelihood of impact damage from over-height vehicles. Steel pedestals are W-shape members that resemble stub columns and transfer loads from the bridge deck to the substructure. While steel pedestals perform similar in function as bearings which have been vulnerable components in past earthquakes due to lack of deformation capacity and potential instability, steel pedestals may also prove to be vulnerable components for similar reasons. To evaluate the behavior of steel pedestals, an experimental study is conducted and the results from 33 1/2" tall steel pedestals are compared to past experimental studies that showed the results of cyclic quasi-static loading on 19" short steel pedestals. The experimental test setup consists of a full-scale two-beam 40' span bridge system with steel pedestals subjected to low level (cyclic quasi-static) and high level (peak) loads. Results from the experimental testing are presented in terms of load-deflection hysteretic behavior and effective stiffness exhibited by the system. Different configurations for the post-installed anchor bolt connection elements to the reinforced concrete pier cap are tested and compared. Future analytical studies will use a bridge model to reveal the most vulnerable aspects of steel pedestals and provide recommendations for appropriate connection details for ensuring adequate seismic performance.

In this paper, the effect of SSI is examined and a fundamental re-evaluation of the features of SSI that influence both supply and demand is undertaken. A procedure is proposed to evaluate effective soil strains as a function of surface peak ground acceleration. Uncertainties in soil properties are included in the vulnerability assessment framework. The results show that SSI elongate system periods significantly, variably and unpredictably. The total displacement demand on a structure with SSI may increase depending on the frequency content and duration of ground motion, but most displacement demand is consumed in soil deformations. Finally, uncertainties in soil properties affect derived vulnerability curves in a significant manner that cannot be ignored.

Many states in the Central and Southeastern United States (CSUS) are in the early phases of evaluating potential bridge vulnerability and assessing viable retrofit strategies for deficient bridges. While there are a host of potential retrofit strategies that exist for bridge types common to the CSUS, such as seat extenders, restrainer cables, isolation bearings, or steel jackets, each retrofit is generally targeted on the improving a particular deficiency. This paper evaluates the impact of retrofit measures on the response of various components including the columns, abutments, fixed and expansion bearings, as well as the impact of the retrofit on overall bridge system performance. The performance of the retrofitted bridge system is evaluated through a fragility curve, which offers the probability of the bridge being damaged beyond a given state for various levels of ground motion intensity. The analytical methodology for developing these retrofitted bridge fragility curves is presented, along with preliminary results for an example bridge class.

Bridge fragility curves, which express the probability of a bridge reaching a certain damage state for a given ground motion parameter, play an important role in the overall seismic risk assessment of a transportation network. For various reasons, analytical methodologies for developing these fragility curves have experienced an increase in demand and popularity. However, these methodologies have yet to adequately account for all major contributing bridge components in the generation of analytical bridge fragility curves. There have been some studies which have shown that for certain bridge types, neglecting to account for all of these components can lead to a misrepresentation of the bridges' overall fragilities. In this study, an expanded methodology for the generation of analytical fragility curves for highway bridges is presented. This methodology considers the contribution of the major components of the bridge, such as the columns, bearings and abutments, to its overall system fragility. In particular, this methodology utilizes some probability tools to directly estimate the bridge system fragility from the individual component fragilities. It is illustrated using a bridge whose construction and configuration are typical to the Central and Southeastern part of the United States and the results are presented and discussed herein. As these analytical methodologies are improved, the fragility information they generate will be more reliable and more likely to be implemented into transportation network loss estimation models and retrofit prioritization strategies.

The American Association of State Highway and Transportation Officials (AASHTO), in conjunction with the National Cooperative Highway Research Program (NCHRP) are currently in the process of formulating new guidelines for the seismic design of highway bridges. As a member of the AASHTO Seismic Technical Committee (T-3), Illinois is playing an advisory role in this process. A key aspect of the new guidelines will be design accelerations which are significantly greater than those specified in the current AASHTO LRFD Bridge Design Specifications as well as the Standard Specifications for Highway Bridges. Partly because of anticipated heightened accelerations, Illinois has embarked on a project to simplify as well standardize the seismic design of new bridges along with the retrofitting of existing structures. Improved economy and a measure of accessibility for average Illinois bridge designers to methods of seismic design which are still somewhat unfamiliar to them are other primary impetuses for this effort.

The design of bridges to resist blast loads has become a national concern in recent years. Data from the State Department indicates that violent attacks against transportation targets have increased worldwide over the last decade and that highway infrastructure has been the most frequent target. Since September 11^th, 2001, increased emphasis on bridge security has raised awareness in the engineering community that bridges and other transportation structures be designed to better respond to potential terrorist attacks. This paper presents the results of ongoing research at the University of Texas for the design of different types of bridges to withstand blast loads. Based on the results of these analyses, performance-based design recommendations are provided so that engineers can improve bridge response to blast loads to a level that is appropriate for a given threat scenario. Structural configurations considered in this research include prestressed girder bridges, post-tensioned segmental boxes, steel girder bridges, trusses, and cable-stayed bridges.

The United States has a huge, open and accessible transportation infrastructure making it vulnerable to physical, biological, chemical and radiological attack in addition to natural hazards. As such this presents a tremendous challenge for developing systems and technologies to keep the system safe and operational under all circumstances. There is a need to develop systems and technologies to prevent, detect, respond to and remediate any attacks. Bridges and tunnels are an integral part of the overall transportation system providing vital links for the Nation's economy, defense, and quality of life. This paper summarizes FHWA's vision for a long term, long range research, development and deployment program in support of the next generation of bridges and tunnels that are redundant and resilient to withstand unforeseen events.

The Federal Highway Administration initiated a national pooled fund study in 2003 to synthesize technologies for bridge and tunnel surveillance and security. In the months following the September 11, 2001 terrorist attack, the American Association of State Highway and Transportation Officials (AASHTO) and the Transportation Research Board (TRB) jointly conducted a security and emergency response survey of all State DOTs to help them assess vulnerability and preparedness. The results of this survey indicated that 59% of the respondents had some surveillance capabilities on their bridges. The State transportation agencies and other private bridge owners were seeking options for increasing surveillance and security of vulnerable structures. Yet, they were being overwhelmed by new technologies, and the lack of guidelines to choose between these technologies. The State highway agencies needed better information on cost, effectiveness, design and applicability of state-of-the-art technologies for protecting bridges and tunnels. This paper presents a summary of the completed work soon to be published by the FHWA as Report No. FHWA-HRT-05-082, `Bridge and Tunnel Security and Surveillance Technologies.

Most major long span bridges in the United States are vulnerable to terrorism and are inviting targets due to their symbolism and the potential loss of life. To begin addressing this concern, the Federal Highway Administration (FHWA) has initiated a State Pooled Fund Program entitled "Validation of Numerical Modeling and Analysis of Steel Bridge Towers Subjected to Blast Loading". The research program includes a combination of blast testing against scaled steel tower components and parallel numerical computations using a variety of analytical tools. The original objective of this paper was to provide an overview of the research plan and an update of the testing and analytical results to date. Unfortunately, testing schedules have slipped and there are no results to report at the time of this paper preparation. Therefore, this paper will only provide an overview of the research plan.

For many years both guyed masts and self-supporting towers have been used for supporting antennas for mobile communications etc. The choice between guyed masts and self-supporting towers has often been determined by the tradition. However, guyed masts are clearly superior in the country side, whereas the self-supporting towers are more likely to be chosen in the urban areas. From a production point of view guyed masts should be chosen rather than self-supporting towers, since the number of different elements are significantly reduced, which leads to easier production and logistics. Looking at the few disadvantages of guyed masts the size of the site area is one of them, since a significant larger site area is needed for guyed masts than for self-supporting towers. Another of the few disadvantages with guyed masts has been the foundation. This is due to the number of foundations for the guy ropes as well as for the mast base, where solutions often have been chosen with a short lifetime. However, the development of prefabricated foundations has provided an opportunity of having cost-effective foundations also in terms of shorter erection time. This paper gives an overview of the advantages and disadvantages of guyed mast versus self-supporting towers, including the erection time and maintenance costs of both structures. The economical aspect is discussed as well, taking the costs of the production, foundation works and the erection of the structures into considerations. Furthermore an example from Sweden provides the opportunity for a direct comparison of the economics based on experiences from two different series of guyed masts and self-supporting towers, which were designed on the same design basis, though with slightly different height ranges.

The number of collapses of guyed masts is relatively bigger than for other types of structures. Many collapses of guyed masts are related to failure of a guy rope or the terminations of the guy ropes. Guyed masts have often not been analyzed for guy failures in the design phase. But a design requirement for guy rupture has in the recent codes for analysis and design of guyed masts been introduced for structures of high reliability, see for instance the Eurocode EC3: Part 3.1 and the American Code TIA/EIA 222-G. The most important load effect to the shaft of guyed masts is normally the wind load and the forces from the guy ropes, whereas the dead load of the structure itself has little impact. The rupture of guy ropes leads to a significant different stress scenario in the members of a guyed mast, compared to what wind and other loads initiates: the tensile forces in the leg members in the upper part of the guyed masts are normally increased significantly compared to what originates from the wind load. The forces in the guy rupture situation are determined by the initial tension of the guy rope, and a lower initial tension will lead to lower forces during guy rupture but also larger deflections during normal load conditions. This paper describes different methods for analyzing of guy rupture and the results from an analysis of influences of guy failures using a full dynamic method in the time domain and compares it with different static approaches. The simplified methods adopted in the codes are also briefly discussed.

Beginning in 2006, the tower industry will begin using the new revision of the Structural Standard for Antenna Supporting Structures and Antennas, TIA/EIA-222-G. Revision G incorporates several significant changes from previous revisions. It moves form allowable stress design to limit state design, and incorporates the wind and ice provisions of ASCE 7. However, the most significant change is the addition of seismic provisions for communication towers. This is the first time the Standard has seismic loading requirements for tower in regions of high seismicity. Because towers are special structures, current seismic provisions in building codes do not always adequately predict their behavior in earthquakes. Revision G provides methods that better estimate the performance of communication structures subjected to ground motion. Revision G provides: methods for determining (1) when earthquake loads need to be considered in the design of communication towers, (2) the fundamental period of various classes of towers, (3) seismic forces. In general, communication structures can be classed as self-supporting and guyed. For design purposes, the response of self-supporting towers can be predicted using linear elastic methods of analysis. Pole structures fall under this category. However, guyed towers are intrinsically nonlinear. Despite their nonlinear behavior, studies at the University of Windsor and McGill University show that the equivalent lateral force method provides an adequate estimate of the seismic forces in guyed towers when using the equations for the fundamental frequency defined in Revision G. As a precaution, the writers of Revision G put a limit on the use of the equivalent lateral force method on guyed towers with mass or stiffness irregularities taller than 450 m (1500 ft) and when any guy radius exceeds 300 m (1000 ft). Under these conditions, the Revision G requires that a time history analysis be performed. Furthermore, when any guy radius exceeds 300 m, out-of-phase motion of the anchor points needs to be considered. This paper presents a nonlinear analysis of a 2000 ft guyed tower with and without mass irregularities. The analysis considers both in-phase and out-of-phase base motion for comparison. The results of the nonlinear analyses are compared to the results obtained using the equivalent lateral force method.

Every high-rise building creates unique demands on its structural system. This results in unique system design solutions. A review of three recent buildings, a residential tower in Hong Kong, an office tower in Chicago, and a courthouse in Seattle, clearly demonstrate the spectrum of possible solutions. Each project utilizes steel and concrete in different ways, from a perimeter concrete tube to a concrete core with exterior steel framing to a steel building with a steel plate shear wall core.

Design aspects of high rise buildings, including shape and structural framing, can be driven by wind performance considerations. Strength must be sufficient to resist shear and overturning forces from downwind (drag) and crosswind (lift) loads of severe storms. Stiffness should limit interstory drift to avoid damage to cladding and partitions in frequently-occurring storms. Lateral accelerations should be limited to provide occupant comfort in windy conditions. Early 20^th Century skyscraper wind design focused on strength: the structural frame was sized to resist the full wind load. While not explicitly accounted for, the heavy masonry cladding and partitions of the time contributed considerable stiffness and damping. As a result, building drifts and accelerations were acceptably small. In the mid-20th Century, lightweight curtain wall cladding systems, gypsum board partitions and high strength steels were introduced. Structures sized for strength would be more flexible and less damped than before. So framing would often be up-sized to control interstory and overall building drift. This design approach provided generally acceptable occupant comfort in windy conditions for the buildings and uses of the time. Recent designs with different building proportions, framing systems and occupancies make satisfactory wind performance more challenging. Mixed-use towers may have steel framing and concrete framing systems on different levels of the same building to suit different occupancies. Non-rectangular floor plates alter wind load conditions on that building and those nearby. Occupant comfort critera are also better understood. Petronas Towers, Taipei 101, Bloomberg Building and Random House illustrate challenges posed by nontraditional building shapes, structural systems and wind environments, and solutions used to meet wind performance criteria. Features include long, slender elements subject to vortex shedding, articulated facades and stepped corners, concrete-over-steel framing, and unusual local wind climates. Solutions include stiffness, inherent damping and several types of supplementary damping.

This paper expresses the opinions of the authors based on their experience in looking at hurricane damage and also studying the research of their colleagues since the start on the area of study called Wind Engineering in the 1960's.

The "Postcards" Memorial by Masayuki Sono, honoring Staten Islanders who died in the World Trade Center terrorist attacks, won a design competition sponsored by the borough's president that attracted 179 entries from 19 countries. Sono consulted with Weidlinger Associates on the concept and, upon being selected, asked Weidlinger to lead the project and be the structural and civil engineer. The client was the NYC Economic Development Corporation (EDC), who had jurisdiction over the site. Weidlinger was instrumental in realization of the design from concept to final drawings, engineered the foundations and anchorage, and supervised installation.

In 2000, the State of Florida Capital Center Planning Commission gave approval to the artist Hugh Nicholson to produce a sculpture of 12 leaping dolphins for the front of the State Capitol Building. The sculpture and its structural elements were constructed of stainless steel and took three years to complete. The funds were provided by private donations in addition to a large grant from the Anheuser-Busch Foundation. Problems were encountered when the foundry made errors in fabricating the dolphins which had to be corrected by the sculptor and the structural engineer. On-site erection in a reflecting pool took almost a month but went quite smoothly. The completed sculpture is a noteworthy tourist attraction in the City of Tallahassee.

Sculptors have a long history of pushing the limits of what is physically possible. Originality is a central concern of artistic expression, and the drive to create innovative work pushes not only conceptual and aesthetic boundaries, but also physical engineering and material limits. Material and structural constraints can be sources of both inspiration and limitation to the engineer and artist alike. Designer James Carpenter and James Carpenter Design Associates are pioneers in discovering and designing ground-breaking architectural applications for glass. Having trained as an architect and sculptor at the Rhode Island School of Design and gone on to work for Corning Glass to develop new glass technologies, James Carpenter's philosophy bridges the worlds of science, art, architecture and engineering. A recent project in Nevada consists of fifty free-standing cantilevered "Cast Art Glass Water Walls" that together comprise a sculptural garden of waterfalls, exploring the interplay of light, water, and transparency. The rise in popularity of architecture that emphasizes minimal structure, lightness, and transparency has helped to break down the boundaries between art, architecture, and structure, and is increasingly pushing the limits of engineering and structural analysis. Ambitious works of art and sculpture are often ambitious engineering projects in their own right—Leonardo da Vinci's unfinished monumental 24ft high Gran Cavallo horse statue, Gustave Eiffel's tower and the stature of liberty, Picaso's 50 steel sculpture in Chicago, to name but a few—and demand unconventional and innovative structural solutions.

The past few years has seen a significant increase in construction of cable-stayed bridges. As it is often the case, when designing bridges, engineers are usually so focused on solving the intricate problems and issues related to design and construction that they inadvertently tend to overlook potential effects of their design and detailing choices on the durability, maintenance needs, and long-term behavior of structural elements and details. The specialized and detailed inspection of many cable stayed bridges over the past decade has led to discovery of problem conditions that seem to be consistent across many types of cable-stayed bridges and stay cable designs. This necessitated development and implementation of new approaches and methods applicable to stay cable systems. This paper discusses advances in evaluation and health monitoring of cable-stayed bridges and available methods, and introduces a unified evaluation approach. Global and local damage detection methods are used in this approach to complement each other. The paper also summarizes the findings of several investigations conducted to date.

The assessment of the condition of the main cables of suspension bridges requires specialized techniques that have been developed over the last few decades. In the United States, the Federal Highways Administration ("FHWA") has introduced guidelines for visual inspection of fracture-critical bridge members, including suspension bridge cables. Recently, the NCHRP has published more detailed guidelines focused on the inspection and evaluation of parallel wire suspension cables. Also, over the past ten years, new acoustic monitoring technologies have been introduced that permit long-term monitoring of cables to detect breaking wires.

This paper presents an overview of existing theoretical methods for the analysis of motion-induced and parametric excitations of stay-cables. Application of the methods is illustrated with a practical example of assessment of stay vibrations due to wind buffeting on the proposed Ironton-Russell Bridge, in Ohio. The results obtained from this analysis are compared against direct numerical (finite element) simulations. The selected scheme for cable vibration mitigation is presented, together with a discussion of its effectiveness.

A common configuration of decks on long span cable stayed bridges is to have local stiffness provided by plate girders located near the two edges. However, these sections are susceptible to vortex-induced oscillations that can be disturbing to bridge users and may potentially lead to other problems such as fatigue damage. A recent wind-tunnel investigation was conducted using a generic edge girder section model with a variable edge girder depth. This was done to capture the response characteristics of a range of practical cross-section geometries. The paper outlines the characteristics of both vertical and torsional vortex-induced responses observed in this investigation. Incorporating these response characteristics with the results of various wind tunnel studies, the effectiveness of baffle plates as possible mitigation measures is discussed. The characteristics of the responses, specifically the differences between the vertical and torsional vortex-induced oscillations, are important when optimizing the design of mitigation measures. Approximate prediction methods using Strouhal number estimates of basic sections, which allow specific mitigation measures to be incorporated early in the design process, are discussed. Guidelines for conducting detailed wind tunnel investigations on these sections are also proposed.

For many people, a home is the most significant investment they will make in their lifetime. As such, the homeowner expects their investment to remain aesthetically pleasing and perform acceptably for many years. Although various building codes specify a minimum quantity of roof ventilation in residential structures, these requirements are frequently overlooked during the design and/or construction of one- and two-story dwellings. While numerous studies identifying the pros and cons of attic ventilation have been performed, this paper will provide case studies illustrating how inadequate ventilation affects the long-term structural capacity of roof framing members, as well as the over-all appearance of the home. From these case studies, an argument can be made requiring the designer to adequately detail the quantity and location of the ventilation components required to meet the prescribed code minimums rather than leave this critical decision to the builder.

The design and construction of wind-force resisting elements in detached modern single- family residences frequently is under-appreciated, and, more alarmingly, completely ignored by design professionals. Both architects and engineers must acknowledge and design for lateral forces with the appropriate force resisting systems. Architects must program into the building physical space adjacent, or near to, both corners and penetrations such as windows and doors. Engineers must then analyze and if necessary strengthen these spaces surrounding the openings and corners. Additionally, connections to both the roof and floor diaphragms must be considered along with the strength and stiffness of these lateral force-resisting elements. In general terms, it has been this engineer's experience that adequate consideration of these critical design elements is frequently overlooked in the design of residential structures.

Special requirements are contained with two of the most commonly adopted model building codes, the 1997 Uniform Building Code (UBC) and the 2003 International Building Code (IBC), that are related to repairs to existing structures. These building codes contain provisions for existing structures that require additions, alterations and repairs to conform to the Code requirements for new construction. Additionally, each model building code states that continued use of existing structural elements is allowed as long as such use is not dangerous to life. Unfortunately, the model building codes do not contain a quantitative definition of "dangerous", which has led to differing views regarding the extent of repairs necessary in damaged structures. However, "dangerous" is quantitatively defined in publications that are referenced by the UBC and IBC; specifically, the 1997 Uniform Code for the Abatement of Dangerous Buildings (UCADB) and the 2003 International Existing Building Code (IEBC). Case studies contained in this paper compare repair recommendations of structures that are considered "dangerous" by these referenced publications and those that are not. Unfortunately, in each case, confusion regarding the extent of repairs was found because the provisions of the UCADB and IEBC were not addressed.

Preservation of historic bridges has led to renewed interest in understanding the response of pin-connected truss bridges to lateral loads. While numerous examples of full-scale gravity load testing on truss bridges can be found in the literature lateral load tests on truss bridges of ordinary span lengths are another matter. A low-cost instrumentation system was developed to obtain data from lateral loads on pin-connected truss bridges. The results provide insight into actual performance of pin-connected truss bridges under lateral loads. Both the stiffening effect of different deck types and the actual flexural response of portal frames are examined. The actual responses are compared to results from analyses. These findings are offered as a first step toward experimental investigations of lateral load response on ordinary truss bridges, the type of bridges now of interest for historic preservation. The testing was conducted as verification for a new application of structural modeling for historic truss bridges. The goal of this project was to aid preservation efforts for one of the cradles of civil engineering heritage: the pin-connected truss bridge.

Development of a strain transducer device for use on structural steel members was developed. The inexpensive, reusable transducer can be conveniently and nondestructively clamped to a structural member. It can be reused. Prototype devices have been tested in the laboratory to verify reliability and repeatability of results and have been compared to analytical results. The device has been successfully used in the field on full-scale members. Each device cost approximately $50 USD. Experimental strain measurement of a weathered structural member using strain gauges usually involves the surface preparation work of grinding to remove paint and corrosion, sanding to create a smooth uniform surface, member polishing, bonding, and clamping of the strain gage. This is in addition to other miscellaneous field installation preparation tasks. Access can sometimes be hazardous and the task is always inconvenient. The device presented in this paper has been developed through a combination of laboratory research and finite element modeling.

The University of Colorado at Denver (UCD) has been involved in cooperative research efforts with the City and County of Denver (CCD) since 1997. The CCD public works department owns, inspects, and maintains 531 bridges in its inventory of which 264 are considered major structures spanning over 6.1 m (20 ft) in length. In this paper, a comprehensive nondestructive analysis of a major structure, the Lawrence Street Bridge, will be presented. The Lawrence Street Bridge is a two-span (each span 23.2 m (76 ft) in length), prestressed concrete girder bridge that spans over Cherry Creek and an adjacent bike path, in downtown Denver. The total bridge width is 19.1 m (62.5) ft. The current structure was built in 1958 and replaced an existing bridge at the site. The original abutments remain, however, and consist of masonry abutment walls founded on concrete footings with timber piles. The pier was comprised of cast-in-place concrete cap and columns. There were five 710-mm (28-in) diameter columns spaced at approximately 5.8 m (19 ft) on center. The pier cap was 27.6 m (90.5 ft) long, 1.07 m (3.5 ft) in height, and varied from 0.76 m (2.5 ft) at the bottom, to 1.07 m (3.5 ft) wide at the top The primary focus of the condition assessment was the existing pier cap and columns. Each span of the two-span superstructure was simply supported with an expansion joint over the pier. Over the years, water had leaked through this expansion joint and directly onto the supporting pier and foundation system. Water penetration and cyclical climatic changes of freezing and thawing had resulted in the deterioration of the supporting substructure system below. The cap suffered from spalling, cracking and exposed steel reinforcement that was corroding. The supporting columns exhibited cracking, from the top downward. In the spring of 2003, a team of UCD researchers began an in-depth nondestructive inspection analysis of the bridge substructure. The objective of the pier analysis was twofold: the first was to provide an assessment of the existing structural condition in order to determine rehabilitative design options. The second was to provide a case study comparing the data from different types of nondestructive and destructive testing. The testing methods performed were as follows: (1) Nondestructive Testing is (a) Visual Inspection, (b) Hammer Sounding, (c) Surface Hardness, (d) Ultrasonic Pulse Velocity, (UPV) (e) Acoustic Tomography, and (f) Ground Penetrating Radar (GPR) Scan; (2) Destructive Testing is (a) Coring and (b) Partial Concrete Removal for Rehabilitation. This particular project was unique in that it provided an opportunity to apply a succession of nondestructive testing methods that ultimately allowed the researchers to identify areas to be further examined using more intensive nondestructive testing as well as destructive testing. Because portions of the concrete cap and columns were removed during rehabilitation, the data from the nondestructive analysis was compared with actual visual inspection of what was found beneath the surface. This paper describes how the nondestructive testing methods were implemented at the bridge site, provides data analysis of the nondestructive test results, and lastly, compares the structural assessments made from nondestructive testing data with observations made during destructive testing and partial concrete removal of the substructure.

Various nondestructive testing (NDT) techniques are available to evaluate the condition of existing concrete structures. These NDT techniques can help to determine in-situ load carrying capabilities and in turn be used to help develop a cost effective rehabilitation solution. In this project, the four pier caps of Denver Colorado' Quebec Street Bridge over Air Lawn Road were inspected using several different NDT techniques. These tests included: carpenter hammer sounding, Schmidt hammer, and ultrasonic pulse velocity (UPV) testing including tomography. In addition visual testing was used to identify crack patterns and spalling conditions. Contour plotting of the NDT data was completed on individual and combined NDT techniques to better determine the condition of the piers. Equal weighted percentages were assumed in combining the hammer sounding, Schmidt, and direct ultrasonic transmission data. Although hammer sounding and Schmidt rebound techniques were used to determine the condition of the exterior layers of the piers, ultrasound and tomography were used to determine the condition of the interior. Various tomographic slices were completed between adjacent sides and from face to face. After the NDT tests were completed, the data were analyzed, interpreted and recommendations were given to further destructively examine local areas of the piers. Destructive tests included compressive strength, chloride, and petrographic testing. The specific detail of all testing methodologies used in this study will be discussed further along with the specific results for the northwest pier cap.

The New Madrid seismic hazard area with a high consequence, low probability earthquake risk presents a new challenge for cost effective designs that are code compliant to the new generation of building codes. Performance-Based Seismic Engineering (PBSE) is one tool that holds the promise of meeting such a challenge that increases the probability of meeting the owners post event performance expectations at minimum cost. PBSE is based on the principal that the client decides on acceptable facility earthquake performance with a careful consideration of informed life cycle trade- offs rather than construction cost alone. In other words, the fully integrated performance design objectives of the facility and its nonstructural components would be assimilated by standard engineering practice such that it will conform to the owner's expectations for the site specific earthquake risk at minimum cost. The challenge for today's research is to deliver an engineering foundation from which a recommended practical methodology for PBSE can be easily implemented into performance based codes. While ongoing research efforts have accomplished much, there is still significant work remaining with some unanswered questions as to whether it can deliver on its promises. Until then, practitioners are left with current state building codes and other tools to deliver seismic engineering solutions for their customers. While not obvious, building codes have been on an evolutionary path towards PBSE and therefore offer the practitioner some tools to implement solutions that have performance based intent. This paper will focus on the use of PBSE types of evolutionary concepts, behind the intent of the building codes prescriptive requirements for designing and specifying electrical equipment in the Mid Western United States. Also discussed will be other newly available tools and standards that are available to manufactures, practitioners and owners to improve seismic mitigation for the total facility life cycle.

A variety of seismic hazard issues may be addressed by a qualified Geotechnical Engineer beyond mere seismic site soils' classification. Understanding and addressing the implications of local geology and soil conditions on the seismic design of even conventional structures can provide cost and time savings throughout all phases of a project, from initial site selection through design, construction, and operations and maintenance of the facility. In addition, it is understood that variability of soil and rock conditions beneath two sites, as little as a few hundred feet laterally from one another, strongly influences the ground motion and base-shear design for structures at the respective sites. However, several codes, such as the Uniform Building Code and Building Officials Code Administration, do not account for important variability in geology and foundation soils.

Memphis Light, Gas and Water (MLGW) required a new facility with an enhanced earthquake performance objective to contain its data center and other business operations. The primary goal was to ensure that the new building — James L. Netters Business Center, dedicated in the spring of 2004, would be available for Immediate Occupancy shortly following a major earthquake occurring on the southern end of the New Madrid Seismic Zone, which would affect the Memphis and Shelby County region of western Tennessee. Several options were evaluated including 1) seismically retrofitting the existing Administration Building that previously contained these operations, 2) constructing a new facility from the ground up, and 3) purchasing and seismically retrofitting an existing building. The decision to select the last option included the consideration of business continuity, disruption to existing operations, location, property acquisition, time to occupancy, cost, and other issues. Interestingly, the structural retrofit cost was not among the top issues affecting the decision to select a spec 94,000 square foot two-story steel frame office building with exterior concrete tilt-up bearing walls. This paper briefly presents the seismic retrofit for the James L. Netters Business Center building structure and non-structural equipment and systems, but more importantly looks at the implications of trying to achieve enhanced earthquake performance in the Midwest where the environment (owner, architect, engineer and construction disciplines), and the perceived risk to earthquakes is not embraced to the degree that it is in other parts of the country where earthquakes are more frequent making it difficult to achieve the desired performance objectives.

This study was aimed at developing an economical seismic retrofit solution for steel-girder highway bridges in low occurrence seismic zones such as in the Central and Eastern United States. To this endeavor, low-carbon tapered steel rods provided by a local vendor were tested for their ductile behavior, material strength, energy dissipation capacity, and fatigue strength under harmonic and earthquake loads. A full-scale damper made of five tapered rods was then designed for the seismic retrofit of a three-span continuous steel-girder bridge in southeast Missouri; its performance was validated with laboratory tests. The energy dissipated by tapered rods in one cycle was shown nearly independent of loading frequency and specimen size; the corresponding damping ratio rapidly increased at small displacements and approached a value of 0.35∼0.40 in the range of over 1.8". Even at a displacement of 2.4", the steel rods survived over 100 cycles of loading with little degradation of their damping property. The five-rod damper fractured in a progressive manner as expected.

Currently under construction, the new I-280 Maumee River Crossing Bridge Project in Toledo, Ohio, at a cost of $220 million, is the largest single project ever undertaken by the Ohio Department of Transportation. The new bridge will bypass one of the last lift bridges on the Interstate system allowing the existing bascule lift span structure to be used for local and pedestrian traffic. This bascule bridge opens in excess of 900 times a year causing major disruption to interstate traffic. Interstate 280 runs north and south through eastern Toledo in a narrow corridor surrounded by residential areas. The City of Toledo and northwest Ohio sit at the crossroads of land and water-based commerce in the Great Lakes area, and Interstate 280 provides a vital link between northwest Ohio and southern Michigan The new bridge consists of approximately 27,000 linear feet of precast concrete segmental construction including a unique cable-stayed main span unit for a total of 1.2 million square feet of bridge deck. The construction contract was awarded in January of 2002 to Fru-Con Construction Corporation of Ballwin, Missouri. Work on the bridge began in the spring of 2002 and has a scheduled completion date of 2006.

Whether an old bridge needs to be brought up-to-date on the seismic design provision, or it deteriorates below the seismic resistant demand it requires a seismic retrofit. A bridge seismic retrofit project often costs a lot and yet the price and the effect of the retrofit are not always proportional. Bridge owners are less likely to experience obvious cases such as described in the Federal Highway Administration Report that once the rehabilitation cost for a given structure begins to exceed 60 percent of the cost of a new structure, the economics begin to favor a replacement. Most of the time, it is ambiguous to owners as to what extend does the retrofit become less cost-effective if the cost of the retrofit does not exceed 60 percent of the cost of a new structure The aim of this paper is to present a generic decision support system for selecting a cost-effective bridge seismic retrofit strategy implementing analytical fragility curves. The seismic vulnerability of bridges is usually expressed in form of fragility curves, which display the conditional probability that the structural demand caused by various levels of ground shaking exceeds the structural capacity defined by a damage state. Empirical fragility curves are usually developed based on the damage reports from past earthquakes, while analytical fragility curves are developed from seismic response analysis of bridge structures. An Economic Index (EI) is proposed to identify the most cost-effective solution when decision-makers face multiple alternatives. Bridge fragility curves corresponding to various cost levels of retrofit are constructed to compare their effectiveness. The proposed methodology provides engineers and owners with a quantifiable solution for selecting retrofit alternatives.

The present study analyzes the bridge-vehicle interaction based on a three dimensional vehicle-bridge coupled model. Vehicles are idealized as a combination of a number of rigid bodies connected by a series of springs and dampers. The study is focused on a slab bridge that is modeled using finite element method to predict the modal characteristics. The bridge and vehicle systems are then integrated into a bridge-vehicle system based on deformation compatibility. Due to the complexity of the FRP sandwich panel, the finite element analysis is based on an equivalent solid plate developed by the authors. The response of the bridge is obtained in the time domain by using an iterative procedure employed at each time step, considering the roughness of the deck as a vertical excitation to the vehicles. The results of bridge dynamic response and the calculated impact factors of vehicle loads are compared between the FRP and concrete slab bridges. Finally, the applicability of the AASHTO impact factors (or called dynamic allowance) to FRP bridges is discussed.

Current seismic maps found in the International Building Code used to design buildings in South Carolina include seismic hazard from a characteristic earthquake assigned a moment magnitude of M7.3. This magnitude represents an estimated magnitude of the 1886 Charleston, SC Earthquake. Although it is well established in South Carolina historical records that the 1886 Charleston, SC Earthquake caused significant damage to coastal South Carolina and was felt as far away as Wisconsin, previous research regarding magnitude estimates has focused on MMI assignments that contain large margins of uncertainty. As a result, current estimates vary from M6.8 to M7.3. The methodology for magnitude estimation presented in this paper includes an approach for estimating the magnitude of historic earthquakes that considers the pseudo dynamic analysis of significant buildings in Charleston, SC that survived the 1886 earthquake with well recorded damage, and using these results to back calculate the probable earthquake magnitude that would have caused such damage. Specifically, the finite element programs RISA-3D are used to perform linear and nonlinear pseudo dynamic analyses of two historic structures with upper and lower bounds placed on material properties and localized soil effects. Because the presented magnitude estimates are developed using an independent approach, they are valuable in terms of providing additional constraints for the MMI-based procedures. This paper presents upper and lower bound magnitude estimates for the 1886 Charleston, SC Earthquake based on pseudo dynamic structural analysis of the Miles Brewton House and Charleston City Hall. These two famous historic structures are both located in the historic district of Charleston, SC.

Section 1808.2.9 of the International Building Code states that certain types of soils called fluid soils (e.g., liquefied sands and bay mud) are not capable of resisting pile buckling and piles used in such soils should be designed as unbraced columns. This paper presents a unified approach for designing steel H-Piles in areas of high seismicity where soil liquefaction and/or loss of lateral support are design considerations. A general procedure for pile design is formulated based on governing codes, accepted practice, and relevant literature. The procedure is in compliance with the International Building Code, the AISC Seismic Provisions for Structural Steel Buildings, and the AISC LRFD Specification for Structural Steel Buildings. Using beam-column design provisions, interaction diagrams (φP_n vs. φM_n) are developed for several hot-rolled H-Pile Sections that are permitted in areas of high seismic risk. The exclusion in this paper of some standard H-Pile sections is a result of local buckling instability as determined by limiting width-thickness ratios presented in the AISC Seismic Provisions for Structural Steel Buildings. Numerous interaction diagrams are developed for each pile size so that practical unbraced lengths resulting from nominal soil support afforded by marine clay and liquefied soil layers can be directly accounted for in the proposed design procedure. This paper provides a simplified approach for designing steel H-Piles to include the effects of pile buckling, the development of interaction diagrams needed for the simplified procedure, an overview of other code requirements for steel H-Piles in high seismic zones, and a practical application example.

Controlling the width and pattern of concrete cracks are important for two primary reasons: durability and aesthetic appearance. Due to rebar corrosion accelerating the deterioration of concrete bridge decks, emphasis has been placed on conserving the service life of structures through adequate crack control. Volume changes due to shrinkage and temperature alone can produce tensile stresses large enough to produce cracks if subjected to sufficient restraint. Reinforcement can not prevent cracks, yet with proper design crack widths are smaller and less likely to contribute to durability problems. Limitations and problems associated with epoxy-coated rebar have led to efforts of trying nonmetallic rebar, such as glass fiber-reinforced polymers (GFRP). This paper examines the cracking behavior of panels subjected to early-age conditioning.

Among common human productive activities, the building industry has been and continues to be one of those generating most serious accidents. Within the industry, the nature of the construction processes of certain public works and buildings lead to the appearance of the risk of falls from considerable height for those working on them at certain stages. In too many cases this has led to the death or serious injury. As a result, certain countries have developed protection systems aimed at preventing falls (edge protection systems: railings) or intercepting them by limiting the scope of the fall and the consequences of serious or fatal impact (safety nets). The latter, in turn, can be sub-divided as follows: (1) horizontal safety nets (approximately), protecting gaps and directly attached either to the structure or by other means (cables, ropes, metal supports, etc.), and (2) vertical safety nets, either directly attached to the structure or by ropes and metal supports. The European vertical safety net system (gallow type) used on building facades is defined in the general European standard on safety nets EN 1263-1, EN 1263-2, which combines previous standards implanted by different member states.

The use of Fiber Reinforced Polymer (FRP) reinforcement is a practical alternative to conventional steel rebars in concrete structures subjected to aggressive environments. The solution is attractive for bridge deck and rail applications, as it eliminates corrosion of the steel reinforcement, which is the major instrument of degradation. Due to the peculiar physical and mechanical characteristics of advanced composite materials, the design philosophy of FRP reinforced concrete (RC) structures differs from that of traditional RC. This paper introduces a systematic approach adopted for the structural and functional design of an open-post bridge railing reinforced with Glass FRP bars (GFRP) as compared to steel RC counterparts, according to the AASHTO LRFD Bridge Design Specifications. Design examples, accounting for different gap opening length and rail beam reinforcement, and based on the experimental static response of full-scale post/deck connections, are finally presented and discussed.

A common problem that is encountered in the design of low-rise base-isolated buildings is the resistance to uplift. Rubber isolators have low tension stiffness and strength and traditional spherical friction pendulum (FP) isolators operate based on contact and thus, have no tension resistance. As a result, most base-isolated buildings require a substantial number of braced frames bays to limit tension demands on the isolators. An innovative new tension-restraint FP isolator has been developed that allows tension and shear to be transferred through the isolator simultaneously. This paper describes the design of an 82,000 square-foot 2-story essential facility that utilizes both tension-restraint FP isolators and traditional spherical FP isolators. A performance-based design approach was utilized for this project in order to satisfy the enhanced seismic performance objectives dictated by the nature of the mission critical functions served by the building. A three-dimensional computer model of the building was developed utilizing nonlinear elements for the FP isolators. Time history analyses were performed using seven sets of ground motion records for each level of seismic hazard and the sensitivity of the building response to several modeling parameters was investigated. The use of the tension-restraint FP isolators was beneficial to the project because it minimized the number of the braces required in the superstructure and thus provided a cost-effective means for meeting the seismic performance objectives of the essential facility. The reduction in braces.also afforded considerable architectural flexibility and minimized the impact on the functional layout of the building.

This paper investigates the cyclic behavior of reinforced concrete circular bridge columns confined using a new confinement technique. The new confinement technique uses two opposing spirals (cross spirals) to confine circular bridge columns in order to enhance their strength and ductility or to increase the spiral spacing (pitch) to facilitate construction. Twelve reduced scale reinforced concrete columns with two different lengths and several spiral spacings were tested. The columns were subjected to constant axial load (bridge self weight) and reversed cyclic lateral displacement (seismic load) to study the influence of the new confinement technique on the lateral strength and ductility of reinforced concrete columns compared to conventional single spiral confinement. Six of the columns were designed to study the flexural behavior, and the other six columns were designed to study the shear behavior. This paper reveals the effect of the new confinement technique on the cyclic behavior of reinforced concrete circular bridge columns.

A novel concept of hybrid fiber-reinforced polymer (FRP) — Autoclaved Aerated Concrete (AAC) sandwich panels have proven to be a structurally efficient combination for lightweight structural components. The FRP composite material was made of carbon reinforcing fabrics embedded in an epoxy resin matrix. The carbon fiber reinforced polymer (CFRP) reinforcement was applied on the top and bottom faces of the AAC panel and several innovative processing techniques were used including hand lay up as well as vacuum assisted resin transfer molding (VARTM). Beside the need to have adequate flexural properties, the AAC-FRP sandwich structures need to be evaluated in their ability to withstand localized damage. During service, the structural members in the building structures are subjected to impact loading that varies from object-caused impact, blast due to explosions, to high velocity impact of debris during tornados, hurricanes, or storms. The objective of this paper is to evaluate the response of AAC-FRP sandwich structures to low velocity impact and to assess the damage performance of the panels. Low velocity impact (LVI) testing serves as a mean to quantify the allowable impact energy that the structure is able to withstand and to assess the typical failure modes encountered during this type of loading. Impact testing was conducted using an Instron drop-tower testing machine.

A number of authors have previously used genetic algorithms to optimize structural systems. This paper illustrates use of simple genetic algorithms for optimum design of large scale steel truss bridge superstructure for railway loadings. Object-Oriented Methodology is used to simplify' the design software development process. Optimal design of practical structures is illustrated, considering system topology, configuration and member sizes represented by mixed design variables (continuous and discrete). Complex design domain requirements conforming to Indian Railways design standard consisting of constraints corresponding to material strength, buckling strength as well as fatigue strength limit have been considered and the objective function to be minimized represents the total cost of the superstructure including cost of fabrication. The paper also demonstrates the efficient integration of genetic algorithms for optimization with the design software, both implemented in an object-oriented environment.

Structural performances of two historic high-rise buildings, constructed in the early 1920s and located in seismic zone 3 in downtown Sacramento, CA were investigated. The objectives of this evaluation were to determine whether these structures met the current seismic criteria and to propose strategies to upgrade such performance to an acceptable level. Both structures, have fourteen main floors, are 200 ft tall, have an approximate floor area of 90,000-ft². Performance-based procedures based on the Life Safety (LS) provisions of FEMA 356 for the Deign Basis earthquake (DBE). Detailed three-dimensional mathematical models of the structures were prepared. Both structures performed better than expected when subject to seismic loading. A voluntary seismic upgrade using fluid viscous dampers (FVDs) and steel struts was utilized for one structure, whereas, for the second structure, structural modifications were undertaken to address some of the occupancy needs.

This paper describes a sensitivity study of the potentially significant parameters which influence seismic response of L-shape concrete moment resisting frame (LCMF) structures in Memphis, TN located in the Central United States. The sensitivity study is necessary to efficiently perform regional seismic assessments of LCMF structures using fragility curves which are conditional cumulative distribution functions that define the exceedance probability of a damage state for a given ground motion intensity level. For the sensitivity study, the main predictors for assessment of the seismic structural response of LCMF structures must be defined. Predictor variables of potential significance include both macro- and micro-parameters. The macro-parameters consist of geometric parameters (e.g., number of stories, eccentricity) and building design provisions (based on building construction date), while the micro-parameters include structural parameters (e.g., damping) and material properties (e.g., concrete compressive strength). This will be accomplished using a combination of Design of Experiments (DOE) and statistical tools. The two different seismic intensities, peak ground acceleration (PGA) and peak ground velocity (PGV), are used in the sensitivity analyses.

In the field of non-destructive evaluation and damage detection, there is continued interest in the utilization of vibrational techniques. Structural damage will result in permanent changes in structural stiffness, distribution of stiffness, and relevant material properties. These changes may be detected by monitoring dynamic behavior of the structure. Because of the direct relationship of mass, damping, and stiffness of a multi-degree-of-freedom system to the natural frequencies, mode shapes, and modal damping values, many studies have been directed at using these properties for the purpose of structural health monitoring. This paper compares the dynamic properties of a precast, prestressed concrete girder bridge determined from forced vibration testing with those of a three dimensional finite element model. The comparison showed that a finite-element model comprised of frame elements could accurately replicate the first seven modal frequencies to within an average difference of 6.5 percent.