Structures 2001: A Structural Engineering Odyssey

The present Dome of the U.S. Capitol Building was designed and built from the 1850s to the 1860s and is a masterpiece of 19^th-century engineering and construction. The majority of the Dome is comprised of cast iron; remaining elements are wrought iron. LZA Technology (LZA), A Division of The Thornton-Tomasetti Group, utilized investigative techniques used in the practice of forensic engineering to perform a comprehensive structural analysis and review of the Dome and concluded the following: (1) The U.S. Capitol Dome was brilliantly designed and well built; (2) The U.S. Capitol Dome is structurally sound, and capable of resisting all reasonably anticipated loadings; and (3) The current undertaking to waterproof the Dome will play an essential role in the longevity of the Dome structure, as it will assist in controlling and minimizing corrosion of the Dome's metal components.

This paper discusses application of Fiber Reinforced Polymer (FRP) composite plates to strengthen a capbeam of a bridge in New York State. Addition of a concrete wearing surface and a median barrier, led to an increase in dead load moment and shear, and resulted in flexural and shear cracking of the concrete capbeam. The capbeam was accordingly strengthened to improve its moment and shear capacities using bonded FRP composite plates. The capbeam was load-tested before and after the plates were installed, to investigate effectiveness of the strengthening system. Some of the results from these tests are presented and compared with those obtained using finite element analysis.

Westfield Pill Bridge was built in 1969 and is a post tensioned seven span continuous bridge with an overall length of approximately 260-m. Parsons Brinckerhoff Ltd was commissioned in 1997 to carry out a Special Inspection of the Post Tensioning System in accordance with UK Highways Agency Standard BA 50/93. As a result of this inspection and due to matters unrelated to the condition of the post tensioning system the bridge was closed to all traffic because of serious structural inadequacies. Following temporary strengthening, the bridge was reopened to limited traffic while permanent strengthening was designed and procured. Innovative Design and Contract Procurement methods have allowed the bridge to be strengthened quickly to allow the bridge to be opened to unrestricted traffic. This paper describes the lifecycle of the project.

Fiber Reinforced Polymer (FRP) plates and wrapping are increasingly becoming very popular retrofit material. These FRP materials have the advantages of being corrosion resistant and having a high strength to weight ratio. The performance of the FRP retrofit is highly dependent on the quality of the bond between the plate or fabric and the surface of the member been retrofitted. The current installation procedures are mainly hand rolling the FRP fabric or plate. Ideally, the rolling should squeeze any air that may have been trapped in the epoxy bond layer. In practical applications, this approach lends itself to the potential of having varying bond thickness and even voids between the FRP and the surface of the structural element. Meanwhile Infrared (IR) imaging technology developments have allowed rapid evaluation of large areas to determine skin temperature variations. These temperature variations are influenced by the presence of anomalies in the bond between the FRP and the member to be retrofitted. In this paper, a case study of such evaluation is presented.

Design and management of important civil structural systems in a multi-hazard environment is investigated. The strategy is based on minimization of expected lifecycle cost. The emphasis is on proper consideration and modeling of the uncertainty in the demands on and capacity of the systems. Costs of construction, maintenance, consequences of structural limit states including damage, revenue loss, death and injury as well as discounting cost over time are considered. The importance of various design parameters is first examined by a parametric study. The method is then applied to design of a multistory office building against winds and earthquakes in Los Angeles, Seattle, and Charleston. The sensitivity of optimal design to important but uncertain design parameters such as structural life, discount rate and death and injury cost is investigated. The question of uniform reliability against different hazards is also examined. It is found that the design is highly dependent on failure consequence and moderately sensitive to assumption of structural life span and discount rate. It may or may not be sensitive to death and injury cost assumption dependent on location and hazard risk characteristics. Uniform reliability against different hazards is not required. The design is often dominated, but not controlled, by the hazard that has large uncertainty and causes large consequences.

In an effort to ensure-public safety, many civil engineering structures undergo various inspections to assess their condition or performance. Comprehensive procedures for using routine inspection data to update reliability assessments have not been developed. This paper illustrates how the Condition Index inspection data from a specific miter gate on a Corps of Engineers navigation lock can be modified and used for this purpose.

This study is focused on the development of a reliability-based methodology for management of aging bridges. The proposed methodology addresses the problems encountered in planning optimal cost-based strategies for bridge maintenance under uncertainties.

In this paper, an attempt is made to develop an integrated maintenance system that can treat various members and elements in a total and practical way by introducing the concept of life cycle cost and using genetic algorithms. In order to improve the convergence and reduce the computation time, a virus evolutionary genetic algorithm is introduced, which is based on the theory of virus evolution. Several numerical examples are presented to illustrate the calculation procedure and to demonstrate the efficiency of the method proposed here.

Cables and other tension members are used as critical structural components for a variety of structures. Suspended and cable-stayed bridges, guyed towers and suspended roofs are among the structures that have extensively utilized cables. In most of these structures, cables and tension members are very suitable for reliable structural health monitoring and adaptation as surrogate sensors for detecting damage and deterioration. Every damage source (at any location) will induce a unique certain force change pattern in cables. Identifying these patterns through measurements and applying damage detection methods can determine the source(s) of damage(s) and signal the location(s). In this paper, new techniques for measurement of forces in tension elements are introduced. These include both experimental techniques to facilitate a rapid and cost-effective vibration-based measurement, and analytical methodology for accurate interpretation of the measured quantities for tension force calculation. Some examples of force measurement in actual cable structures are presented. The tension forces are calculated based on the measured frequencies taking into account all parameters involved. Local and global damage detection methods tailored for the case of cable supported structures are also discussed. These include a new damage detection method, Precursor Transformation Method (PTM), developed specifically for cable structures. This method can determine damage sources and their relative significance with minimum calculation effort and acceptable accuracies. An emphasis is placed in this paper on a newer generation of bridge structures, i.e., cable-stayed bridges, however, the techniques discussed are mostly applicable to other types of cable supported structures.

The procedures used to evaluate seven historic reinforced concrete bridges in different regions of the United States are discussed. Constructed between 1907 and 1938, three of the bridges have soil infill above arched vaults, three are open spandrel arch structures, and the seventh is a continuous span structure in the states of Nevada, Indiana, Rhode Island, Washington and Pennsylvania. A combination of visual inspection, nondestructive methods and coring followed by laboratory testing was used in all cases. Advanced NDT methods were used to maximize information obtained, while minimizing invasive investigation and disruption to bridge operations. Laboratory testing addressed such topics as the extent of deterioration and chloride concentration in the concrete, as well as identification of aggregates and cement constituents, so repair concrete could be developed to match existing. These cost-effective programs provided vital structural and material information necessary for successful rehabilitation.

Prompted by high economic losses from the 1994 Northridge, California, earthquake, the City of Los Angeles has initiated a program to develop, test, and implement standardized procedures for the seismic evaluation and retrofit of single-family wood-frame dwellings (ATC-50 project). The primary products of the project include: (1) a seismic evaluation and grading system; (2) a seismic grading form; and (3) seismic rehabilitation guidelines. The procedures are being tested in a pilot program involving evaluation and grading of approximately 500 detached single-family wood-frame dwellings in the Los Angeles area, and rehabilitation (or retrofit) of approximately 50 dwellings with inadequate earthquake resistance. The ATC-50 project was conceived with input from the banking and insurance industries, is being performed by the Applied Technology Council for the City of Los Angeles, and is being funded by the Federal Emergency Management Agency through a Hazard Mitigation Grant Program award from the California Office of Emergency Services.

The impact-echo method is a technique for flaw detection in concrete. It is based on monitoring the surface motion resulting from a short-duration mechanical impact. The method overcomes many of the barriers associated with flaw detection in concrete based on ultrasonic methods. The purpose of this paper is to provide an overview of the technique and to discuss the important parameters involved in this type of testing. One of the key features of the method is the transformation of the recorded time domain waveform of the surface motion into the frequency domain. The impact gives rise to modes of vibration and the frequency of these modes is related to the geometry of the test object and the presence of flaws. The principles involved in frequency analysis are discussed. The importance of the impact duration in relation to flaw detection and other factors affecting the smallest flaw that can be detected are also reviewed. The paper concludes with a summary of the ASTM standard governing the use of the impact-echo method for measuring the thickness of plate-like structures.

Impact-echo testing has been highly successful in locating and evaluating numerous types of flaws in concrete and masonry structures. While the requisite knowledge and experience for successful testing is not overly difficult to obtain, it is not uncommon to encounter improper application of impact-echo for flaw detection. This paper presents both theory and application of impact-echo for flaw detection, with an emphasis on actual field application of the method. Examples of application of the method for flaw detection are also shown. It has been found that a thorough understanding of the actual testing parameters and variables will result in more accurate and successful flaw detection.

The maturity method is a technique to account for the combined effects of time and temperature on the strength development of concrete. The method provides a relatively simple approach for making reliable estimates of in-place strength during construction. The origin of the method can be traced to work on steam curing of concrete carried out in England in the late 1940s and early 1950s. As a result of technology transfer efforts by the Federal Highway Administration, there is renewed interest in the method within the United States. The purpose of this paper is to review of the basic concepts underlying the method and to explain how the method is applied. The review focuses on work carried out by researchers at the National Institute of Standards and Technology (formerly the National Bureau of Standards).

One of the goals of the Federal Highway Administration (FHWA) Nondestructive Evaluation Validation Center (NDEVC) is to enhance the types of tools available to bridge inspectors. Instrumentation and techniques that provide more information about the condition of a structure are a focus of the center. Systems are currently being developed that greatly increase the amount of data that can presently be gathered with conventional instrumentation and in some cases provide types of data previously impractical to obtain. One of these systems is a laser-based instrument that has been successfully used in a number of applications related to highway bridges. Four of the main projects related to this laser system are presented as an example of the capabilities of the instrumentation. These applications include laboratory testing on a full-sized steel curved girder bridge, measurement of the as-built state of bridge abutments in a full-sized test bridge, load testing of in-service bridges, and tests related to the fabrication of steel bridges.

This paper develops the use of limit-state based reliability analysis techniques for reliability evaluation of aging structures under two major deterioration mechanisms: corrosion and fatigue. Probabilistic models are proposed to simulate the total corrosion fatigue damage process and to estimate the reliability, considering both single site and multiple site damage. Corrosion fatigue damage initiations both at rivet holes and lap sheet surfaces are considered. Numerical examples are developed to illustrate the reliability evaluation of aircraft fuselage lap joints under corrosion and fatigue. In addition to computational reliability predictions, the updating of reliability estimates using non-destructive inspection data and Bayesian analysis is investigated. The proposed methodology is demonstrated with numerical examples related to aging aircraft structures.

Fatigue reliability analysis, in most applications, requires a complete live load history of the structure. This can be achieved through a comprehensive field data compilation. For certain class of fatigue-critical structures (such as airframe systems), a continuous monitoring program is used to periodically compile load data and update the information on fatigue reliability. This process is costly and may not be easily applicable or economically viable for other types of structures. A more reasonable process for such structures will be a limited amount of data that can be assumed to represent the load population. This paper presents several types of fatigue-critical systems for which field data will be necessary for fatigue reliability analysis. Specifically, airframe structures, bridges, structures that support mechanical systems, railroad cars, and offshore structures are considered. The methods used for fatigue reliability analysis of these systems are briefly reviewed. Based on their needs for field data, the paper discusses each structure's requirements for the field data, including the requirements in terms of the number of parameters, data quality assurance and the expected length of a data acquisition session.

To accurately determine the structural integrity of an aging structure requires the assessment of bridge/building components having varying degrees of deterioration. In order to perform this assessment, the condition state of each structural element must be thoroughly known. This however is not practical. Therefore, sample measurements or assumed levels of deterioration are used to quantify the condition state. Once the condition state is determined, the structural integrity can be computed. This method generally underestimates the actual integrity of the aging structure. Case studies which have included load tests on aging structures are presented to demonstrate the accuracy of computational methods, when condition states are determined through sample measurement or by assumption.

The present manuscript proposes a rational concept of description and evaluation of the damage states of structures. All mechanical, chemical or bio-chemical deterioration processes will reduce the originally virgin stiffnesses of a particular structure over its life-time. In the following it shall be outlined, how the consequences of structural damage of real or anticipated deterioration processes can be described and computer-simulated, from the virgin state of the structure up to failure.

The present contribution proposes a rational combination of the full-scale nonlinear structural analysis for reinforced concrete structures including damage effects with efficient probabilistic reliability calculations. A time-variant reliability of a RC bridge deck is studied numerically under fatigue and corrosion conditions.

The prediction of a realistic life cycle of steel bridges is an important task for the owners. The model usually used shows only low reliability. The model is a chain of a load model, a system-transfer model and a damage model. The results of these coupled models are usually unreliable, especially the influence of the unsafe load and damage models controls the reliability of the result. It is shown that monitoring at critical points and time reduced parallel testing leads to highly satisfactory results.

The coupling effect of moisture diffusion and drying shrinkage is an important factor in the durability design of concrete structures. The internal damage in concrete due to excessive shrinkage accelerates the diffusion of moisture. On the other hand, the drying shrinkage of concrete occurs due to moisture loss. Thus, drying shrinkage and moisture diffusion are two coupled processes and their interactive effect is very important for the durability of concrete structures. The moisture diffusion is modeled based on Ficks' laws and the drying shrinkage is modeled based on a multiscale method. The effect of drying shrinkage on the moisture diffusion is introduced by the scalar damage model based on the concept of the continuum damage mechanics (CDM). The coupled problem of moisture diffusion and drying shrinkage is solved using a finite difference method. The influential parameters such as water-cement ratio and aggregate volume fraction are analyzed by several numerical applications. In recent years, many researchers have investigated the interactive effect of the mass diffusion and the cracking resulted from moisture gradient, temperature gradient and mechanical loading. All the research work on this area indicated that the microcraking produced during hardening, drying and heating of concrete and the cracking resulted from the mechanical loading could increase the diffusivity and thus, accelerate the mass diffusion process.

A shake table test of a lightly reinforced concrete three story frame building is simulated using the finite element method. To reduce the computational time for an efficient analysis, an approach concentrating nonlinearities into possible failure sections while keeping other portions of the simulation model elastic is proposed. Nonlinear interface elements are used to connect the linear and nonlinear portions of the model. The current effort using the interface element is to partially offset expensive experimental efforts to obtain the phenomenological hysteretic behavior for a frame structure. The constitutive model for the interface element is calibrated by considering energy equivalence during member failure. The simulation from the calibrated constitutive cohesive model predicts the overall seismic behavior of a shaking table test of a reinforced concrete frame structure with reasonable accuracy.

In this study, the experimental results of three shear deficient T-beams strengthened using web-bonded CFRP strips are presented. Non-linear finite element modelling and analyses are also used to investigate the behaviour of these beams assuming plane stress condition and perfect bond between the concrete surface and the web-bonded CFRP strips. Both numerical and experimental results are then compared to assess the viability of using non-linear finite element modelling in predicting the behaviour of CFRP shear strengthened T-beams.

This paper describes the many alternatives studied for the San Francisco-Oakland Bay Bridge replacement from Yerba Buena Island to Oakland and the selection of the final design concepts.

The seismically-vulnerable San Francisco-Oakland Bay Bridge East Spans, which connect Oakland to Yerba Buena Island (YBI), will be replaced with a dual, 3.6-kilometer-long parallel structure. The cost of the replacement bridge is estimated to be $1.6 billion. Performance criteria requires that the bridge, which is situated between the Hayward and the San Andreas faults, must be operational following a 1,500-year return period earthquake from either of these two faults.

A new bridge to replace the eastern half of the San Francisco-Oakland Bay Bridge has been designed for a high level of seismic performance so that it will provide full service almost immediately after a major earthquake. This paper presents the seismic design criteria and the analysis. and design methodologies used to achieve that level of performance.

This paper describes two technologies for reinforcing or strengthening timber bridges with Fiber-Reinforced Polymers (FRP). The first consists of reinforcing the tension side of glulam girders or decks with unidirectional FRP. This technology allows to significantly increase the flexural strength of girders, particularly when low-grade laminating stock is used. The second consists of post-tensioning stress-laminated timber decks with transverse Glass FRP (GFRP) 7-wire strands. The paper briefly describes three demonstration bridges constructed in Maine using different aspects of these technologies: (1) the Medway FRP-glulam girder bridge, (2) the Milbridge FRP-glulam deck vehicular pier and (3) the Milbridge GFRP stress-laminated deck.

For the past three years, the New York State Department of Transportation has been experimenting with Fiber Reinforced Polymer (FRP) materials in bridge applications. These projects include strengthening reinforced concrete bridge beams and capbeams, wrapping concrete columns to arrest deterioration, and replacing heavy, old superstructures components with lightweight FRP components. This paper describes some of these applications and the nondestructive testing techniques that were used to evaluate the in-service performance, and effectiveness of the methods used for the design of these materials.

A continuous, long-term, structural "health" monitoring system has been designed and installed on an all-composite bridge, recently built in Delaware. The system has been designed to automatically record information about the structural behavior of the bridge, due to such factors as live load cycles, sustained load, thermal effects and environmental factors. The data gathered by the system will be used to study the long-term performance of this unique structure.

This paper presents the ongoing research dealing with the design, fabrication and testing of polymer matrix composite (PMC) infill walls to be employed as a seismic energy dissipation strategy. The composite infill wall structure is comprised of two fiber-reinforced polymer laminates with an infill of a vinyl sheet foam. At the interface between the laminates, visco-elastic material which is expected to exhibit maximum shear strain, is used to dissipate energy and improving the damping characteristics of the structure. Analytical and experimental studies were performed to explore the effectiveness of the energy absorbing strategy and the behavior of a PMC infill wall when subjected to monotonic and cyclic loading. A steel frame retrofitted by a PMC infill wall was monitored to assess the enhancements to the seismic resistant capacity. A large-scale steel frame and PMC infill panels are considered in this research to avoid typical uncertainties associated with scaling the dimensions. The design of an optimum infill panel was determined based on performance and material cost using finite element analysis. And, material tests were used to obtain the characteristics of each material used in the infill wall. Finally, the observed behavior of the PMC infilled frame is assessed on the basis of stiffness, strength, modes of failure and energy dissipation output.

High performance steels (HPS) are providing new opportunities to design cost-effective steel bridges by exploiting the high strength, corrosion resistance, fracture toughness, and weldability of HPS. Under certain conditions, however, steel bridge designs may be controlled by design limits that are not influenced by steel strength, and the use of HPS may not be economical. Innovative bridge girders have been proposed to overcome these design limits. This paper focuses on I-shaped girders with corrugated webs and I-shaped girders with tubular flanges. Design criteria for these girders are proposed and limited design studies are presented.

This paper briefly introduces the current FHWA Bridge Seismic Retrofitting Manual's retrofitting philosophies and strategies, and its application to a double decker bridge in Missouri. Superstructure retrofits with restrainers and bridge piers or columns retrofits with steel jackets follow the recommendation of the current retrofitting manual.

This paper reports on the seismic retrofit of two New York City Bridges, the Macombs Dam Bridge and the 145^th Street Bridge. Both span over the Harlem River, a navigable waterway in New York City. Both bridges are owned, operated, and maintained by the New York City Department of Transportation (NYCDOT). The Macombs Dam Bridge, completed in 1905, consists of 78 spans of various types, including a 415m steel viaduct, a 126.5m main swing span, a 67m camelback truss, and other approaches and ramps., The 145^th Street Bridge, completed in 1885, consists of a 94.5m main swing span, steel girder and truss approach viaducts, and earth filled approaches for a total length of 482m. A new superstructure has been designed by NYCDOT for the 145^th Street Bridge. There were several unique challenges of this project. First, site-specific seismic hazard criteria only recently adopted by NYCDOT were applied to the bridges. The criteria were developed by an expert panel of six nationally reputable seismologists. This is the first time that a group of seismological experts was assembled to resolve the long-debated issue on seismic hazard levels in the Northeastern United States. Second, seismic performance of a movable bridge requires some unique considerations, including the behavior of machinery elements and their tolerance for misalignment during earthquakes, and the issue of the requirement for seismic design when the bridge is in the open position. Third, the substructures and foundations of the bridges are complex and in many cases there is a lack of detailed information. Fourth, the subsurface conditions at the site are highly variable, making site-specific response analysis important. A focus of this paper is the development of the seismic retrofit design based on the seismic deficiencies established through the performance evaluation. The retrofit schemes for the substructures and foundations will be discussed.

This paper describes the methods and results of a research project to produce a set of acceleration contour maps to be used in the design of Tennessee Department of Transportation (TDOT) facilities. The investigation is composed of three major tasks: (1) develop procedures to generate horizontal bedrock motions in West Tennessee from a seismologically based model. The model must include the effects of attenuation, characteristics of the source zone, recurrence interval (500 and 2500 years), and seismotectonic setting of the region, (2) perform seismic field investigation to determine the dynamic properties of soil in West Tennessee, and (3) propagate the soft bedrock motion through the layered soil deposits using the computer program SHAKE to determine the earthquake motions at the ground surface of a site. Methods employed and the results are discussed and described in this paper.

This paper presents the seismic assessment and retrofit design for US-40/I-64 double-deck complex in St Louis, Missouri. Analytical model, performance criteria, vulnerabilities, and retrofit measures are discussed. Major design constraints include maintenance of traffic during construction, interface with numerous underground utilities, coordination with multiple property owners, and restricted headroom for installing foundation modifications. Typical pre-1980 details requires major seismic retrofit designs for the foundations, pilecaps, columns, bentcaps, bearings, cross frames, expansion joints, cross girders, and two-girder spans.

This paper presents the results of an analytical study on the seismic response of Multi-Span-Simply-Supported (MSSS) bridges in New Jersey. The investigation includes the detailed nonlinear dynamic analysis of three actual bridges as representatives of typical 2, 3, and 4 span bridges which are common in New Jersey and the East Coast in general. Both 2-D and 3-D models were employed in the analyses. Several parameters prove to have an important effect on the seismic response of MSSS bridges, such as soil-structure interaction, impact between adjacent spans, steel bearings, and plasticity at pier columns. The seismic response of MSSS bridges is evaluated in the light of a comprehensive parametric study based on these factors and quantified through capacity/demand (C/D) ratios for critical elements. Furthermore, the research needs related to the seismic evaluation and design of MSSS bridges are also discussed.

Steel truss bridges have long been a popular design option and come in a wide variety of sizes shapes and forms- from a simple span truss of less than 100ft to a cantilever truss with a total length of thousands of feet. Most of the steel truss bridges built in the Eastern United States were not designed for seismic loads as now specified in the current AASHTO provisions. As a result, many public transportation agencies are now considering seismic retrofit as a component of major rehabilitation projects. The extent of seismic retrofitting is determined by performing a comprehensive seismic analysis and computing capacity-demand ratios for various bridge components. Unfortunately, it is difficult to standardize the seismic analysis, evaluation and retrofit procedure for truss bridges due to their variety in size, shape and form. Many practicing engineers today are faced with the question of selecting an appropriate method for a seismic analysis and evaluation of truss bridges. This is especially the case with the Eastern United States where earthquakes are not common.

There should be no argument that the quality of life and the economic vitality of modern civilizations are dependent on the infrastructures that support them. Of major importance is the transportation system that provides for the transport of goods and services as well as the mobility of the citizens within those civilizations. The enormous investment that Governments have made in highway systems since the 1950's has led the U.S. to be recognized as having the largest and most modern highway system in the world. Within this highway system, bridges are singly the most important link. Without bridges, highway transportation as we know it would cease to exist. In recognition of this, the California Department of Transportation continues to take aggressive actions in the protection of its bridge infrastructure as evidenced by the delivery efforts of the Seismic Retrofit Program and the creation of the Bridge Scour Mitigation Program.

The Aquitaine bridge across the Garonne was open to traffic in 1967. Its central span is 393.75 m long, and its total length is 1,767 m. The first indications of corrosion in the main cables were observed in 1979. In 1998, a detailed inspection showed that 2 % of the wires were broken. The article describes the various investigations conducted (measurement of tension, evaluation of safety coefficient and fatigue risks), the high level monitoring applied (by acoustic monitoring), the choice of the adopted solution among other alternatives in the context of widening the deck and maintaining the traffic during repair, and the anti-corrosion protection of the new cables.

Since opening to traffic in 1903, the Williamsburg bridge across East River has been repeatedly in the center of important New York City development trends. The article summarizes past highlights and current progress of the bridge rehabilitation, estimated to cost roughly 750 million USD. Technical and management decisions defining the bridge future and its impact on the community are briefly described.

Ongoing efforts to develop a comprehensive road structures management system in Switzerland have resulted in a project called KUBA-MS. The paper briefly describes the methodology adopted in the software.

OBMS employs an analyst-in-the-loop process of project evaluation and decision support. The software, written in Visual Basic, is a collection of interacting objects representing network-level concerns, such as budgets and programs, and project-level concerns, such as element-level treatment alternatives and bridge-level projects. Whenever a process such as bridge inspection or budget analysis changes any of the input data of the objects, the objects cooperate with each other to update their status. The overall result may be changes in priorities, performance, or costs. Each of the objects performs a part of a life cycle cost analysis for prioritization and evaluation of projects and policies. Projects, for example, examine their own element-level scope of work to determine the quantities of work items that will be required, and then use the Ministry's tender item cost database to estimate a project cost. Projects contribute this information to Programs, which accumulate systemwide costs and performance measures. The scope and benefit of each Project are determined at the element level. Each element is responsible for a life-cycle cost analysis, using typical benchmark costs and a Markovian deterioration model, to estimate the benefits of bridge element preservation and to select the optimal treatment for a given set of conditions.

Direct displacement-based design requires a simplified procedure to estimate the seismic deformation of an inelastic SDF system, representing the first (elastic) mode of vibration of the structure. This step is usually accomplished by analysis of an "equivalent" linear system using elastic design spectra. In this paper, an equally simple procedure is developed that is based on the well-known concepts of inelastic design spectra. This procedure provides: (1) accurate values of displacement and ductility demands, and (2) a structural design that satisfies the design criteria for allowable plastic rotation. In contrast, the existing procedure using elastic design spectra for equivalent linear systems is shown to underestimate significantly the displacement and ductility demands. The existing procedure is shown to be deficient in yet another sense; the plastic rotation demand on structures designed by this procedure may exceed the acceptable value of the plastic rotation, leaving an erroneous impression that the allowable plastic rotation constraint has been satisfied.

The design of a data center is discussed for both earthquakes and extreme winds. The owner's stated performance objective for the facility was continued operations following selected extreme natural hazards affecting the site. The motives, constraints, and structural solutions developed to meet this performance objective are discussed, along with the impact of enhanced structural design on construction costs and schedule.

The U.S. Courthouse Building in Seattle was evaluated using the procedures described in the publication NEHRP Guidelines for the Seismic Rehabilitation of Buildings FEMA 273. A parallel evaluation using "prevailing local practice" was also carried out. For the Seattle area in 1998, prevailing local practice consists of identifying life safety deficiencies using procedures described in the publication NEHRP Handbook for the Seismic Evaluation of Existing Buildings FEMA 178, then designing rehabilitation measures that mitigate these deficiencies. In general, it was found that the FEMA 273 evaluation was much more complicated to perform than the prevailing practice evaluation, and that the resulting retrofit scheme was more extensive and more costly. Based on our experience with other concrete shear wall buildings, and based on the parallel prevailing practice evaluation for this building, it is our opinion that the retrofit scheme resulting from the FEMA 273 evaluation is conservative. We recommend that further effort be devoted to simplifying and calibrating the FEMA 273 procedures.

This paper discusses the seismic retrofit of a building using passive energy-dissipation devices. The design criteria for seismic retrofit was adopted primarily from NEHRP Guidelines for Seismic Rehabilitation of Buildings, FEMA-273/356. A brief building description, site constraints in implementing seismic retrofit, reasons for selecting passive energy-dissipation devices, and pertinent analysis/design parameters are presented in the following sections.

The seismic rehabilitation of the Stacy Park Reservoir located in St. Louis, Missouri using nonlinear viscous dampers according to the NEHRP Guidelines for the Seismic Rehabilitation of Buildings, FEMA-273 is presented. The reservoir is a partially buried concrete structure measuring 183 m (600 ft) by 245 m (800 ft) in plan, and 10.4 m (34 ft) in depth. The reservoir has a concrete post-tensioned roof slab supported by interior columns and beam frames, and on the exterior walls. The walls provide vertical support, but the roof slabs are able to slide freely in both horizontal directions. The reservoir is considered to be a critical link for post-disaster recovery. Thus, the Performance Level selected by the City of St. Louis is "Immediate Occupancy" in accordance with FEMA-273 where the ground motion with a return period of 2500 years (or approximately 2% probability of being exceeded in 50 year) is selected as the Maximum Considered Earthquake (MCE). The intent is to keep reservoir intact as much as possible after such an earthquake so that the water it contains will be immediately usable. For the retrofitting procedure investigated in this study, nonlinear viscous dampers are utilized to link the individual slabs together and then to the exterior walls. Nonlinear time history finite element analysis is conducted. The results indicates that the concrete roof slabs can be restrained effectively by using ninety two 445-kN (100-kip) dampers at the exterior joints of slabs and ninety nine 222-kN (50-kip) dampers in the interior joints, respectively.

This paper presents an experimental study of a hybrid base isolation system consisting of sliding and rubber bearings for seismic retrofit of electric power transformers. Triaxial earthquake simulator testing was performed on a large-scale transformer/bushing model equipped with the isolation system. The effectiveness of the isolation system was demonstrated by the significantly reduced seismic response of transformer model and bushing. Meanwhile, some test results indicated that the vertical component of the earthquake ground motion can stimulate high frequency response of the bushing due to the friction force in the sliding bearings.

The Bonneville Power Administration is a high-voltage electrical transmission system provider in the Pacific Northwest. The seismic hazards in the Pacific Northwest have increased based on new seismological information. The existing high-voltage electrical transmission system has been reviewed for seismic vulnerabilities and a seismic mitigation plan implemented. This paper discusses the process used for identifying critical substation facilities, vulnerable electrical equipment, and mitigation solutions developed by the Bonneville Power Administration.

Substations are critical components in a power system. Performance of substations during past earthquakes has not been satisfactory and many key components such as transformers and bushings have sustained significant damage. Recently several research investigations have been conducted to better evaluate, assess, and qualify seismic performance of critical substation components with emphasis on transformers and bushings. These studies include both analytical and experimental research. This paper discusses the performance of substation transformers and development of an analytical model using finite element method. Due to weight limitation, shaking table tests of transformers are not feasible. Therefore, finite element analysis is the only suitable platform to assess their seismic performance and to evaluate their effect on the response of other important components such as bushings. Furthermore, the use of base-isolation, which appears to be a practical and economical rehabilitation approach, is discussed. In this research study application of friction pendulum system for base isolation of substation transformers has been investigated and some of the results are presented. Finally, a brief discussion of a series of experimental tests on a fixed and isolated transformer model supporting a bushing is also given.

The standard industry procedures for the seismic qualification of substation equipment were assessed by analysis and triaxial experimentation using the earthquake simulator at the Pacific Earthquake Engineering Research Center, which is headquartered at the University of California at Berkeley. Information on the qualification of in-service high-voltage transformer bushings is presented. Two of the three classes of bushings performed substantially better in the laboratory than in the field during modest earthquake shaking. The excellent performance of these two classes of bushings calls into question the standard industry procedures for equipment qualification. Improved procedures that account for equipment interaction, permit uniaxial qualification, better address response amplification due to transformer tank and turret flexibility, and utilize standardized earthquake histories and filtering procedures, are needed.

The present article will give a brief introduction into the shape optimization, design and construction of the 200 m high natural draught cooling tower shell at Niederauβem, which has been completed in the last year. This tower belongs world-wide to the largest and thinnest concrete buildings at present. Because of these dimensions, special care has to be taken to the shape optimization of the shell structure. An optimal design of the shell reduces fatigue, cracking and corrosion of the reinforcement to insure an adequate level of safety and durability.

In this paper, the local-global strategy is extend to column-supported reinforced concrete shell structures and applied to the nonlinear structural analysis of a column- supported reinforced concrete cooling tower shell with imperfections. To solve this problem, a general shell element and a transitional shell element as well as a column element derived earlier have been extended considering the nonlinear behavior of the concrete. First, a perfect reinforced concrete cooling tower supported by columns is selected as the base line numerical model. The stress distribution around the intersection with the columns is analyzed under an axisymmetric loading by the local global strategy and is verified by comparing with a previous analysis. Second, a column-supported R/C cooling tower with an imperfection is considered and the nonlinear behavior is computed under a combination of dead load and static wind pressure. The local-global analysis produces similar results with those obtained by the general finite element analysis and brings considerable reduction of computing effort, so that this method is applicable to verify the safety the local behavior of the cooling tower within the limitation of present design requirements.

Inelastic dynamic time-history analyses of single-degree-of-freedom (SDOF) oscillators with elastic-perfectly plastic (EPP) hysteresis loops were performed to assess the inelastic demands predicted by the Capacity Spectra Method (CSM). The oscillators, which had natural periods from 0.05s to 3s were analyzed with 32 far-field (FF) earthquake records. It was found that the average effective damping decreased as oscillator period increased and it was often smaller than that assumed in the ATC-40 code. Also the displacement reduction factor (SR) due to damping given in the ATC-40 code was usually non-conservative. For structures with periods greater than 1.1s, ATC-40 estimated inelastic displacements generally less than 60% of the actual average displacements.

This paper describes recent progress in modeling and predicting earthquake ground shaking for the cities of Seattle, WA and San Jose, CA, areas of substantial seismic risk situated on deep sedimentary basins. The goal of these efforts is to produce detailed seismic hazard maps for each urban area by quantifying the effects of the sedimentary basins before future damaging earthquakes occur. Arrays of digital seismographs have been deployed in each region to record nearby moderate earthquakes. The finite-difference method has been used to simulate ground motions in three-dimensional (3D) models of these sedimentary basins. This method has been successful at modeling the observed seismograms of earthquakes near Seattle. Ground motions have been simulated for a potential M6.5 earthquake on the Seattle fault, highlighting the effects of rupture directivity and the response of the Seattle Basin. Recordings from a 40-station seismic array in San Jose generally show larger ground motions for locations farther from the eastern edge of the Santa Clara Valley. Three-dimensional simulations show that the large surface waves observed by the San Jose array are likely produced by conversion of incident shear (S) waves at the southeastern edge of the Santa Clara Valley.

The U. S. Geological Survey (USGS) has completed new probabilistic seismic hazard maps for the United States. The maps depict peak horizontal ground acceleration, and 0.2, 0.3, and 1.0 sec response spectral acceleration values for 10%, 5%, and 2% probabilities of exceedance in 50 years (corresponding to approximate return times of 500, 1000, and 2500 years, respectively). The maps for the 0.2 sec and 1.0 sec response spectral acceleration with a 2% probability exceedance in 50 years, modified by engineering judgement, are the basis for seismic design maps developed for the 1997 NEHRP Recommended Provisions for Seismic Regulations for New Buildings. The USGS team preparing the new maps made a concentrated effort to make as much of the data used available via our Internet Website. This includes documentation, input data, output data, and computer code used to calculate the maps. In addition two CDROMs have been prepared - one for the probabilistic maps and one for the seismic design maps. Paper maps are also available.

The extended damage in beam-column connections, particularly during earthquakes, prompted researchers and designers in the 1970's to investigate the behavior of that region, as well as to develop analysis and design criteria. The ACI-ASCE 352 Committee published the first comprehensive technical guideline for the analysis, design and detailing of beam-column joints in 1976. Since then, the report, and its revisions, has been widely used by designers throughout the world, thus leading to better designs or reinforced concrete (RC) frame buildings. Moreover, this document has served as a cornerstone for the development of RC building codes in different countries. The simple, yet conservative, model of joint behavior and the document format are most appealing to the practice. It is the aim of this paper to briefly describe the evolution of ACI-ASCE 352 Committee report on beam-column joints (now referred to connections), and to briefly present main modifications and additions to the most recent revision.

The American Concrete Institute (ACI) Recommendations for Design of Beam-Column Joints in Monolithic Reinforced Concrete Structures (ACI 352R-91) currently recommends that wide beam construction not be used in structures to inelastically dissipate energy from earthquake ground motions, because of concerns about wide beam flexural reinforcement anchored in transverse beams, as well as concerns about the stiffness and energy dissipation of wide beam frames. In the last ten years, much research has been conducted on wide beam construction, and as a result, changes are being introduced for the treatment of wide beam construction in the new revised ACI 352 recommendations. This paper summarizes the research results to date and presents the revised ACI 352 recommendations.

The bombings of the World Trade Center in New York (1993), the Alfred P. Murrah Federal Office Building in Oklahoma City (1995), and U.S. military housing in Dhahran, Saudi Arabia (1996) are recent, well-known incidents that have attracted the attention of structural engineers with regard to special design requirements for abnormal loading, leading to new guidance for building design. Even more recently, U.S. embassy bombings in East Africa (1998) have refocused attention on embassy design. These latest terrorist attacks, as well as those against Department of State overseas buildings over the last two decades, have led to substantial revisions in design requirements for our buildings. The focus of this paper is an examination of the architectural and structural ramifications of designing U.S. embassies.

The prevention of progressive collapse through design requires attention to the abnormal state of loading that may produce a localized failure and the response of the structure in redistributing the loads to the undamaged elements. The design requirements for new structures, where the specification of continuous reinforcement and moment resisting connections are reasonable, are not necessarily the most appropriate for the retrofit of existing structures, for which the adaptation of these beneficial details may be a practical impossibility. Therefore, the design practices required to prevent a progressive collapse must be related, on a case by case basis, to the structural system that must be upgraded and the extent of protection that will be provided. A rational approach is presented for determining the appropriate protective design required to prevent a progressive collapse in both new and existing structures. The paper will also discuss the analytical methods that are needed to accurately assess a structure's response to abnormal loading and provide an assessment of different conditions where the Indirect, Specific Local Resistance and Alternate Path methods are most appropriate.

The paper includes the summary of the Israeli experience in the blast mitigation for non-structural elements. The observed damages to non-structural components from real attacks with various types of weapons and explosive devices as well as from controlled explosive tests are presented. Based on the extensive practical damage data, the failure modes of the non-structural elements and the hazards to people are described. The design criteria for blast mitigation were defined and detailed specifications for the blast resistant non-structural components were compiled and included in the Israeli design manuals for protective structures. Their concise description is included in the paper.

This study investigates some of the special aspects of the response of steel structures to blast loading. The distinctive features of steel systems, including connections, splice, and thin-walled sections and their vulnerabilities to blast loading, are presented and discussed. Also, vulnerabilities of composite and light steel constructions are investigated and simplified examples presented. The needs for special design and construction considerations, as well as additional research studies are concluded.

The protective design of structures to withstand the effects of explosive loading requires analytical analogies and performance criteria that are supported by first principles analyses and explosive test results. In particular, state-of-the-art protective design retrofit solutions require both an analytical evaluation and a full-scale test program to confirm their adequacy and performance standards. However, different government agencies specify different explosive threats and response criteria. In order to provide the desired level of protection these agencies must be able to review the analytical approaches and assess the adequacy of the proposed solutions. Presented is a discussion of the different protective design approaches for minimizing the hazard to debris and structural collapse resulting from both the vehicle and satchel threats that may originate outside the structure or within the pre-screened public spaces.

Exterior wall panels of conventional structures are often constructed of concrete-masonry-units (CMUs), commonly known as concrete blocks. These walls may become a debris hazard to building occupants when high explosives are detonated by terrorists outside of a building. The U.S. Department of Defense, Office of Special Technology, Technical Support Working Group (TSWG) is sponsoring a series of physical experiments and analytical evaluations that will be used to develop methods of predicting the hazard levels associated with CMU walls. Subsequently, retrofitting techniques will be developed to mitigate the hazards. The experiments include non-retrofitted CMU walls, as well as several different types of retrofits. Test data, high-speed video, and post-test inspection of the experiments and dynamic visualizations of the analyses of the experiments are used to assess the parameters that affect the response of CMU walls and how each of the retrofit systems performs.

Over the last two decades, computer programs have been written for the modeling glazing response to explosive blast. Initially these programs addressed first-crack of the glazing only. Over the last 2 years, the U.S. Technical Support Working Group (TSWG) has funded the development of software to extend the early first-crack methodologies to predict post-crack window blast response to include glass fragment fly-out. This work is funded as a subtask to TSWG's Blast Mitigation for Structures Program which supports anti-terrorism and force protection needs of the Department of Defense (DoD). This paper briefly describes the newly developed engineering models and presents results from preliminary validation exercises. The validation work not only helps validate the newer models but also serves as additional validation of the early first-crack models.

The development of performance codes is a becoming a common occurrence internationally. Countries such as the United Kingdom, New Zealand, Australia and Japan have developed and are using performance-based building codes. Other countries such as Canada and Spain are in the process of developing performance-building codes. It should be noted that Canada is actually developing what is called an "objective-based code" which is similar to a performance-based code. The common structure of these codes is to provide a document that contains qualitative statements of intent and to also provide at least one set of prescriptive solutions. ICC saw this trend and felt it was necessary to explore this concept as an ICC document. This paper is intended to provide a background into the development of the ICC Performance Code for Buildings and Facilities and highlight how structural fire protection is addressed within the document. It should be noted that structural fire protection being the protection of structural members from the effects of fire in order to prevent and reduce the likelihood of unacceptable structural damage. Part of this discussion will touch upon the variation in the levels of performance design that can occur and how that affects structural fire protection design.

This paper describes a prestandard that documents analysis methods for performance-based fire resistance analyses that has recently been provided to a joint ASCE and SFPE committee. The prestandard includes engineering tools to assess the impact of a prescribed fire exposure on the ability of a structural member to continue to function structurally or as a barrier to fire spread. A brief overview of the type of heat transfer and structural analysis methods for steel, concrete and masonry assemblies is provided in this paper. These methods include moment analyses for beams and slabs and stability analyses for columns and walls. Existing computational methods range from algebraic equations to finite difference or finite element models for the needed analyses. For this paper, the applicability of the algebraic-equation based methods will be emphasized for the various assemblies and exposure conditions, with only a brief overview provided of the capabilities of computer-based models.

As jurisdictions throughout the world progress toward performance based building codes, it is important that the proper tools be made available to the engineering profession in order that they may take full advantage of these new codes. There is currently a large body of work written on the subject of performance based or engineered structural fire safety. Unfortunately, most of this information is scattered throughout technical journals from different countries and organizations, and not easily accessible for the practicing engineer without considerable effort. Under the current prescriptive code regime there is generally no requirement to undertake an engineering approach to structural fire safety, since the required fire resistance ratings are prescribed and the fire resistance ratings of materials/assemblies are determined through standard tests. However, these methods have been shown to be both unnecessary and expensive in some cases. A method will be developed that can be used to determine required fire resistance ratings for fire exposed structural steel based on a realistic engineering approach.

Traditionally fire resistance requirements for the structure and separating elements of buildings have been derived from tabulated values, based on building use and height above ground level. There are many factors that influence the fire resistance requirements other than occupancy and height, which are generally `built into' the values presented in the tables. The influence of all these other factors is difficult to identify and virtually impossible to quantify within the present grading system. In keeping with the trend towards performance based fire engineering design, there is a need for a more rational and transparent method for determining the fire resistance requirements for buildings. This paper presents a performance-based method for calculating fire resistance requirements, based on the time equivalent concept. The t-equivalent calculation is a function of fire load, compartment linings and ventilation conditions. The fire resistance period is calculated and then adjusted to take account of the probability of occurrence of a fire, the consequences of structural failure and the effects of an automatic suppression system.

The design of structure during fire is developing at a significant pace in line with fire safety engineering (performance based design) as a whole. New advanced analytical methods and improved risk assessment techniques enable the performance-based design of structures during fire. It is certainly starting to have a growing impact on the way structures are designed, procured and specified in many countries throughout the world. Many clients are also able to identify the value that can be achieved. The extent to which the structural engineer is involved with these new developments when compared to the fire consultant is still developing. Appendix 1 is a consultation statement, which is representative of the approach being adopted by the Institution of Structural Engineers in the UK, who are now producing a design guide on fire safety engineering on behalf of the structural engineering community, government, industry bodies and architects.

A computer program VULCAN has been progressively developed for some years at the University of Sheffield, with the objective of enabling three-dimensional modelling of the behaviour of composite buildings in fire. In this paper the theoretical basis of the non-linear layered procedure used to model the reinforced concrete floor slabs, which includes both geometric and material non-linearity, is briefly outlined. Several of the full-scale fire tests carried out in 1995–96 on the composite frame at Cardington, representing cases in which different degrees of in-plane restraint are provided by the adjacent structure, are modelled to evaluate the influence of tensile membrane action in the concrete slabs on the structural behaviour in fire. In order to illustrate the influence of membrane action and its relationship with boundary restraint, all cases have been analysed using both geometrically linear and non-linear slab elements. A series of parametric studies has been carried out as an initial investigation into the characteristics of steel reinforcement which allow this action to take place. It is clear that the influence of tensile membrane action of concrete slabs on the behaviour of such composite structures in fire is very important, and should be accounted for in later additions and amendments to structural fire engineering design codes.

This paper describes a case study where performance based design has been used for the design of a water cooled roof at a large cargo handling facility at Superterminal 1 Chek Lap Kok Airport, Hong Kong. The Superterminal is some 200m x 200m in plan area and six stories high. This paper includes details of the calculation methodology that was used to assess the adequacy of the design, and of the full-scale fire tests that were performed to back-up the theoretical analysis.

The intent of this analysis was to evaluate the fire performance of unprotected structural steel beams serving as part of the floor/ceiling assembly between two gymnasiums in a large new university recreation complex. The objective of this analysis was to evaluate whether structural fire protection is required for these beams. The floor/ceiling assembly between the 3^rd and 4^th floor gymnasiums consists of 11.5 cm (4½ inches) thick normal weight concrete over a 7.6 cm (3 inch) composite metal deck, all supported by 137 cm (54 inch) deep steel beams having a weight of 872 kilograms per linear meter (586 pounds per linear foot). The 3^rd floor Gymnasium also includes an elevated running track around the perimeter. Conditions within the space were evaluated using computer fire models to estimate the performance of the beams when exposed to design fire scenarios. The primary goal of this analysis was to evaluate the design of the large structural floor beams that support the floor (137 cm (54 inch) deep beams) without fire protection.

When fire occurs in buildings, depending on the relative severity of the fire, there might be fire-induced damage which affect the performance of building elements. While collapse of buildings, in fires, may be rare events it is not uncommon to have damage or distortion in various structural elements. The extent of damage to a structure is dependent on the fire intensity, duration of fire, geometry, materials used in construction and the load intensity. In many cases the structural members might have substantial strength and often can be restored to its original shape through repairs. Before undertaking such repairs an assessment of the building has to be carried out to determine the extent of damage and the residual load-bearing capacity of structural members. In this paper, the application of computer program SAFIR for determining the residual load bearing capacity is illustrated though three case studies; a simply supported beam, a column and a restrained beam. The three elements were modeled in two configurations, steel and reinforced concrete, and were designed to have the same fire resistance ratings. The analysis was carried out in a scenario that includes heating under a natural fire, cooling down to ambient temperature and then loading to failure. Results from three case show that the load bearing capacity was hardly modified, by the fire damage, in a simply supported beam, was increased by the effect of an axial restraint, especially in the concrete beam, and was reduced in the column, especially in the concrete column.

This paper summarizes the current movement towards a more logical, considered approach to designing structures for fire conditions. The increasing reliability and understanding of fire engineering analysis, coupled with recent large scale fire tests is encouraging the greater use of performance based standards both nationally and internationally. The available techniques for a performance-based design are described in this paper along with some ArupFire projects, where these design techniques have been applied.

For structures within or near significant amounts of complex natural terrain the influence of that terrain on the design wind loads can be significant. Prior to physically modelling flows at typically useful scales of 1:300 to 1:500 in a boundary-layer wind tunnel one must first assess the approach conditions with a smaller scale terrain model in the range 1:2000 to 1:6000. Work presented by researchers such as Meroney and Cermak indicate that scales smaller than 1:6000 have serious modeling limitations, and so the focus of this discussion will be on terrain models larger than this nominal scale.

Wind pressures on buildings and other structures, pedestrian level winds, wind-induced dispersion of pollutants in urban locations depend, among other factors, on the velocity profile and turbulence characteristics of the upcoming wind. These, in turn, depend on the roughness and general configuration of the upstream terrain. Consequently, wind standards and codes of practice typically assume upstream terrain of homogeneous roughness or provide explicit corrections for specific topographies such as hills or escarpments; for more complex situations they refer the practitioner to physical simulation in a boundary layer wind tunnel. The evolution of computational wind engineering makes the evaluation of wind velocities over complex terrain very attractive. In fact, significant progress has been made in the application of Computational Fluid Dynamics (CFD) for specific cases of escarpments, single and multiple hills, as well as valleys. Numerical modelling of wind flow consists of utilizing a set of differential equations (Navier-Stokes) describing the flow in a particular domain, say near an obstruction. The Reynolds-Averaged Navier-Stokes equations have been used in most of the studies dealing with wind flow over complex terrain such as that corresponding to a mountain-valley system. Turbulence of the flow is represented by a particular model, such as the well known k-ε model which is appropriate for the case of homogeneous isotropic turbulence. Descretization of the flow equations leads to a set of solvable algebraic equations. The simplification inherent in the use of algebraic equations is what makes the numerical approach so powerful and attractive. The following sections present and summarize the progress made in the numerical evaluation of wind flow over complex topographies.

The study of surface wind field may provide the primary input for decision-making in extreme wind simulation, structural design improvement, the understanding of wind induced structural vibration, and many other applications. The numerical model used in the study is a three-dimensional mass-consistent kinematic flow model. The major elements considered in the surface wind field modeling are topography and surface roughness. The purpose of this paper is to demonstrate that surface wind field with a complex terrain can be successfully modeled by a Geographic Information System (GIS) assisted solution of the kinematic flow model. From the simulated wind field, extreme winds at specified sites may be obtained.

While numerous approaches for simulating turbulent flows around structures have been published, most exhibit weaknesses and have fairly limited fields of application. This paper will present a relatively new approach which has been successfully employed in the hydraulics field for several years to model water flow around bridge substructures. Adaptation of this model for simulation of wind flow around bridge superstructures will also be discussed.

This paper describes the numerical simulation of wind flow around bridges using the Finite Element Method (FEM) and the principles of Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD). Since, the suspension bridges are prone to the aerodynamic instabilities caused by wind this becomes a prime criterion to be checked during the design. If the wind velocity exceeds the critical velocity for flutter that the bridge can withstand, then the bridge fails due to the phenomenon of flutter. Tacoma's narrows bridge failure in Washington, USA is a classical example of this failure. Larsen and Walther used the Discrete Vortex Method (DVM) similar to the wind tunnel procedures. In this work, the computations are carried out for both the fixed and the moving bridge conditions. A Large Eddy Simulation (LES) turbulence model is used and the rigid body grid movement technique is adopted. The critical velocity for flutter is calculated directly using the free oscillation procedure similar to the approaches reported by Selvam et. al. The influence of grid on critical velocity is also studied. The computed critical velocity for flutter is in good agreement with the wind tunnel measurements. The conditions of flutter and no flutter are demonstrated clearly using the response of the bridge in time.

A general overview is given of a modeling effort to simulate the fate and transport of a tracer within the downtown core of Salt Lake City and beyond into the Salt Lake Basin. The problem crosses three significant scales where different physics are predominant: atmospheric mesoscale, city scale, and building scale. Three different computational fluid dynamics models were used, each with strengths at particular spatial and temporal scales. We show preliminary results and discuss what we believe to be the relevant phenomenon one must model as one crosses from atmospheric scale to engineering scale flow problems. We also describe our model validation efforts, including wind-tunnel and tow-tank experiments and a recently completed urban field experiment.

The internal and external effects of fluid flow on structures and equipment has always been a concern of designers. Since the 1970s efforts have been made to create reliable numerical methods to compute fluid flow around or through a body to supplement information gained from scale model testing. The traditional numerical approach involved solving a highly non-linear set of partial differential equations know as Navier-Stokes equations. However, an alternative approach emerged during the 1990s based on the lattice Boltzmann method. This method of modeling fluid flow has shown promising results over a broad range of fluid flow applications. This paper presents the results of simulation runs on a jack-up leg of an offshore drilling rig using the lattice Boltzmann method. The results are then compared to values obtained from wind tunnel testing. An important advantage of this alternative CFD approach is that it can simulate the actual wind velocity under full-scale conditions, thus eliminating concerns associated with Reynolds number effects in a wind tunnel.

The computational wind engineering problems such as flow around bridges is computationally expensive. For these unsteady computations, adaptive finite element technique may reduce the computer time and storage while keeping a desired accuracy. In this paper, the p-version as well as the h-version adaptive finite element techniques are implemented into the computational wind flow respectively. In these techniques, the error distribution of vorticity is first estimated. Then, the finite element grid and the order of interpolation polynomials are, respectively, changed continuously for h-version and p-version methods in accordance with the change of the error distribution. One through four levels of h-refinement and the 2nd through 5th orders of polynomial are considered for the two versions of adaptive techniques respectively. Unequal orders of interpolations are used for the velocity and pressure. A numerical simulation, the flow around a circular cylinder with Reynolds number of 1000, is also included. The computed results are in good agreement with other reported ones. The h-version works very well if it is started with an equal spacing mesh at this time.

This paper presents the overall application of a recently proposed simulation method, capable of representing Gaussian and non-Gaussian local roof pressure characteristics using the Fast Fourier Transform (FFT) algorithm, for codification purposes. The proposed approach is capable of providing peak pressure coefficients corresponding to specific roof geometries and according to risk levels; this can generate risk consistent and more economical design loads for specific roof configurations taking into account, for instance, directional design conditions and upstream roughnesses.

While limited data have been collected on the wind effects on low-rise construction, few have been in high winds. Not only is there a general lack of structural load and resistance data in these storms, but also there is a paucity of detailed meteorological data. Although the most recent revision of the wind load provisions of the ASCE Standard (ASCE 7-98) includes updated information for use in hurricane-prone regions, questions still remain about the suitability of these provisions in high-wind regions. An ongoing full-scale field measurement program begun in 1997, in Southern Shores, North Carolina offers an opportunity to collect and analyze data in hurricanes and other high wind events and contribute to some of the existing data gaps in this area. To date the system has collected measurements of the wind environment, pressure loading and structural resistance during the passage of frontal systems, in several northeasters, arid during three hurricanes making landfall in North Carolina (Hurricane Bonnie (1998) and Hurricanes Dennis and Floyd (1999)). One of the main goals of this measurement program is to compare the loads measured during these high wind events to the loads predicted by the ASCE standard in similar meteorological conditions. An additional goal is to compare properties of winds from different storm types (e.g., hurricanes, tropical storms, northeasters, thunderstorms) and to compare measurements with various widely accepted models (e.g., Durst relationship for time averaging effects, spectral content). The main goal of this paper is to present summary results from the meteorological data collected in the three hurricanes. In addition, analyses of the gust structure (including turbulence intensity and effects of averaging time on reported gusts) and a preliminary attempt to quantitatively describe the surrounding terrain will be presented.

Overall loads on a structure typically are established in model-scale in a wind tunnel. Most of these model scale studies focus on high-rise structures. Overall loads on a low-rise building have been measured on the full-scale test structure in the natural wind environment at Texas Tech University's Wind Engineering Research Field Laboratory (WERFL). This facility consists of a 49 m (160 ft) high meteorological tower instrumented at six heights to measure wind flow characteristics, a rotatable 9.1 x 13.7 x 4.0 m (30 x 45 x 13 ft) high test building, and a data acquisition system housed in a 3.0 x 3.0 x 2.4 m (10 x 10 x 8 ft) data acquisition room. The fundamental features of the field site are described in Levitan and Mehta. To measure the overall loads a triaxial load cell was installed at each corner of the building. These four load cells supported the entire weight of the building and measured two orthogonal horizontal shear forces and one vertical force. The triaxial load cells were custom designed for this experiment under a cooperative agreement with ISI in Round Rock, Texas. Each load cell was positioned under a wide flange section that was welded to the existing undercarriage adjacent each corner of the building. The top and bottom bearing surfaces consisted of machined plates (one embedded in the concrete foundation and one attached to the steel wide flange) to insure that the building was level during the experiments. The wheels of the building's rotation system were disengaged from the foundation to insure that the load cells measure all the wind-induced shear and vertical loads.

This paper describes the techniques used to determine design wind loads for the roofs of four large venues used for the 2000 Olympics in Sydney, Australia, including Stadium Australia. The techniques used for all four structures involved the measurement of correlation coefficients for panel pressures from rigid wind-tunnel models, the determination of structural influence coefficients by the designers, and the determination of effective static load distributions.

PowerLight Corporation has developed the PowerGuard Roofing System for installation of photovoltaic panels on flat and moderately sloped roofs. The system has been optimized for wind resistance as a result of comprehensive wind tunnel studies carried out at the Wind Engineering and Fluids Laboratory, Colorado State University. The system and steps involved in its development are briefly described in this paper.

This paper presents the results of a study performed to assess human comfort in the naturally ventilated Ticket Lobbies of the Overseas Terminal (OST) of Honolulu International Airport (HIA) The location and operational constraints of the ventilation openings in the OST in conjunction with the seasonal wind flow patterns on the Hawaiian Islands can occasionally create uncomfortable situations for passengers and tenants in the ticket lobbies. Hawaii DOT officials wanted to preserve the naturally ventilated environment at HIA. A set of enhancements was thus considered to improve the natural ventilation in the ticket lobbies to provide increased comfort to users of the facility. The study involved modeling of the OST in a boundary layer atmospheric wind tunnel followed by statistical analysis of the measured wind flow rates inside the ticket lobbies and wind speed data recorded at the weather station at HIA.

State-of-the-art wind-tunnel techniques are applied to evaluate wind loads on a case-study building, consisting of two tower structures sharing a common substantial podium. All three substructures are complex and asymmetric, resulting in dynamic motion components which are coupled both within and between towers. Two techniques were used to determine wind loads, to meet the engineer's demands for early approximate results on a preliminary design, followed by a more complex and detailed method upon fixation of the architectural shape.

Recently published AISC guidelines allow comprehensive evaluation of dynamic floor response in multiple bending modes, and provide a significant improvement over the heel drop procedures which they supercede. Vibration transmission is a phenomenon identified as potentially problematic, but not explicitly addressed. This phenomenon arises when a long floor slab exists, free of irregularities or openings, and the framing system is regular. Floor vibrations can then be transmitted perpendicular to the supporting members, causing unacceptable vibration serviceability behavior. This paper presents a preliminary analysis of this problem, modeling the long floor slab and framing system as a beam on a visco-elastic foundation. Examination of the response of the "Winkler beam" model yields a first estimate of floor accelerations caused by walking. The beam model is then used to evaluate the response to walking excitation of a floor in the Seattle-Tacoma International Airport.

Genetic Algorithm (GA), with its evolutionary optimization power, has become an attractive artificial intelligence tool in the field of earthquake engineering. After Northridge (1994) and Kobe (1995) earthquakes, development of robust and reliable control systems to encounter large velocity and displacement ground pulses seemed necessary. Based on that, a computer program is developed to simulate a GA-based open-closed loop control system. The Program is able to find the optimum off-line modal control gain of an active or hybrid system for a predefined allowable structural response. As a proof of concept, behavior of the control system is simulated on the mathematical model of a benchmark problem. Minimum active mass damper acceleration time histories were obtained for different limitations on response quantities under near source strong ground motions. It was shown that the proposed system is able to encounter long time delays between velocity sense and control force act. Also it was observed that the presence of large input pulses could strongly affect the behavior of the open-closed loop control system in terms of gain value.

Elastomeric isolation bearings are required to be stable at high shear strains, which occur during strong earthquakes. Hence, rigorous determination of the critical axial load during design is important. Currently the critical load is determined using small displacement Haringx theory and modified to account for large shear strains by an approximate correction factor. The objective of this study is to experimentally determine the effect of horizontal displacement or shear strain on critical load and to study the validity of the approximate correction factor. Experiments were conducted on a series of elastomeric bearings with low shape factors. Test procedure and test results are presented in detail. It is shown that the critical load decreases with increasing horizontal displacement or shear strain. It is also shown that substantial critical load capacity exists at a horizontal displacement equal to the width of the bearing and is not zero, as predicted by the correction factor. It is further shown that the approximate formula is not conservative at smaller displacements and overly conservative at larger displacements. The critical loads obtained from experiments are compared with results from finite element analyses and nonlinear analytical solutions; the comparisons indicate that the effect of large horizontal displacements on the critical load can be reliably predicted.

As a consequence of the recent Izmit Earthquake (August 1999), the builder/operator of the International Terminal at the Ataturk International Airport desired to increase the performance level for operation of the terminal after seismic activity. The LZA Technology, a division of the Thornton-Tomasetti Group Inc., provided a solution that incorporated a unique blend of column jacketing and roof isolation. This paper presents the upgrade.

The new three-story reinforced concrete terminal building at the Ataturk International Airport was damaged during the 1999 Izmit earthquake. Conventional and innovative retrofit strategies were developed for the building to meet higher levels of performance than that specified for such construction by the Turkish seismic code. The retrofit scheme selected by the owner included seismic isolation of the space-frame roof, jacketing and strengthening of existing reinforced concrete columns, and elimination of expansion joints between the pods that formed the building. The existing and retrofitted buildings were evaluated using the nonlinear static procedures of FEMA 273. The performance of the retrofitted building was further evaluated by nonlinear dynamic analysis.

After the magnitude 7.4 August 17, 1999, Koceli Earthquake rocked the eastern part of Turkey, the owners of the new International Terminal at Atatürk Airport in Istanbul, opted for a voluntary upgrade for improved seismic performance, beyond the requirements of the local seismic design codes. The location of the Terminal was more than 100 km away from the earthquake's epicenter, and the observed damage was not life-threatening. The voluntary upgrade included strengthening of existing columns above the Arrivals Level and installation of the Friction Pendulum seismic isolation bearings between the roof and its supporting columns. This paper briefly describes the Terminal's structure, identification of potential structural vulnerabilities through various analytical studies and the resulting final upgrade solution. Implementation of the Friction Pendulum seismic isolators as part of the final upgrade solution is presented.

Response of sliding isolated buildings with smart dampers subjected to near fault earthquake ground motions is studied. The smart damper used is a Magnetorheological (MR) damper. A 1:5 scale two-story sliding isolated building model with four sliding bearings, restoring springs, and a MR damper is studied. A new Lyapunov controller is developed and implemented in real time. Several near fault ground motions recorded in the Northridge earthquake are used in the testing. Experimental and analytical results of the scaled sliding isolated building model with MR damper are presented to demonstrate the effectiveness of the dampers. It is shown that the smart MR dampers can reduce displacements further than the passive dampers, with forces comparable to the passive case. While these displacement reductions can be achieved by increasing the passive damping further, it can only be done at the expense of greater forces.

Since the energy cost of active vibration control is an important problem and the performance of the passive devices is limited, semi-active control devices have received much attention in recent years. In this paper, we compare the performance of two pseudo-skyhook control methods; a bang-bang control and a continuous control to passive viscous control and the optimal semi-active control. Numerical results show that the proposed control rules perform almost as well as the optimal semi-active control and can overcome the deficiency of the passive viscous control at high frequency range.

The dynamic behaviors of piezoelectric friction dampers are studied in this paper. The friction dampers utilize their sliding mode to accommodate large deformations in civil engineering structures and use piezoelectric actuators to regulate their clamped force. An efficient control logic is proposed to determine the friction force for increased energy dissipation capacity. It combines the hysteretic and viscous damping mechanisms. The damper is first used to mitigate the dynamic responses of a single-story frame structure subjected to harmonic loads. Analytical results obtained in this case have shown the superiority of the proposed algorithm over others in terms of structural response reduction and energy dissipation. Such friction dampers are then placed on a 20-story benchmark structure for control of seismic responses. The simulation results show that the proposed control strategy is very efficient in reducing peak responses under earthquake excitations.

Chicago's downtown theater district has seen a stunning revival during the past decade. Led by Mayor Richard M. Daley, the city has invested $300 million in the reconstruction of Grant Park to feature two performance venues: an outdoor pavilion designed by Frank Gehry and the Music and Dance Theater Chicago, a 1,500-seat performing arts center designed by Thomas Beeby. In the North Loop area, major houses such as the Chicago Theater, the Oriental Theater/Ford Center for the Performing Arts and the Cadillac Palace Theatre have undergone significant renovations to enable them to stage modern Broadway shows, concerts and special events. A major anchor of this revitalized district is the new home for a longtime cultural institution, the Goodman Theatre.

We have developed a continuously variable semi-active hydraulic damper that generates the control force up to a maximum of 1000 kN with an external power supply of only 70 watts. This damper was applied to an actual five-story building in 1998. This is the world's first application of the continuously variable semi-active structural control system for large earthquakes. The semi-active structural control system controls a building's response by changing the damping factor of the variable damping components. This paper outlines the developed semi-active damper system and the building to which it was applied. It also describes the control performance of the system based on an evaluation of forced vibration tests conducted after the system was installed, and the seismic observation records.

The friction type base isolation systems have been found to be very effective in reducing the structural response, and several effective isolators have been proposed in the recent past. These isolators need to integrate base isolation, energy dissipation and restoring mechanism from practical considerations. In this paper, the effectiveness of a recently developed isolation system known as Variable Frequency Pendulum Isolator (VFPI) in controlling response of a torsionally coupled structure has been examined. The VFPI exhibits progressive period shift and softening mechanism of restoring force, and is found to be more effective isolation in comparison with some other friction-type isolation systems.

The devastating earthquakes in California, Japan, Turkey, Greece and Taiwan, and the resulting loss of lives and property, have made it apparent that it is necessary to protect bridges from earthquake damage. The uninterrupted operation of bridges immediately after an earthquake is vital for rescue operations, as well as to limit the economic losses of a region. Design methods that rely on structure ductility to absorb earthquake movements do so at the expense of damage to the bridge structure. These damaged bridges may not be usable after an earthquake, and the time and costs to implement repairs can be extensive. In contrast, seismic isolation design relies on the ductility of the isolation devices to absorb or reduce the earthquake energy transmitted to the structure, and thereby protects the structure from damage and preserves its functionality. The application of Friction Pendulum seismic isolation for the seismic retrofit of the Benicia-Martinez Toll Bridge located near San Francisco, California is presented. It is one of the largest bridges to date to undertake a seismic isolation retrofit, and uses the largest seismic isolation bearings ever manufactured. Results of tests of full-size prototype bearings at the new Seismic Response Modification Device Test Facility at the University of California in San Diego are also presented.

Prestressed masonry has become more popular in the U.S. in recent years. In particular, post-tensioned concrete masonry is likely to be the form of prestressed masonry that is the most cost-effective alternative to conventionally reinforced masonry and other forms of wall construction. Post-tensioned masonry involves the construction of hollow-unit concrete masonry walls with little or no reinforcing and grout. Prestressing tendons are placed vertically in the unit cells during construction as would reinforcing bars in conventional systems. The tendons can be prestressing wire, strand or bar, but bar is likely the most convenient and competitive form currently available in the U.S. The tendons are anchored at the bottom and top of the wall section with steel-hardware anchored against a grouted bond beam or special concrete unit designed to evenly distribute the force from the tendon to the wall. The tendons can then be tensioned with a hydraulic jack or impact wrench. Prestress is checked by hydraulic pressure or DTI (direct-tension indicating) washers and verified by measuring elongation.

The performance of post-tensioned prestressed masonry under bending moment and shear force at both serviceability and ultimate limit states is now well established. Performance under axial load, however, is not fully understood. This paper puts forward a theoretical model, which describes the behaviour of post-tensioned masonry columns and compares this with the results of tests on brick masonry columns post-tensioned with high tensile steel bar tendons. The paper considers the action of laterally restrained and laterally unrestrained tendons placed both concentrically and eccentrically and with different levels of prestress.

To allow the more widespread use of prestressed masonry, design provisions were included in the 1998 edition of the Australian Masonry Code. These were based predominately on previous British research complemented by Australian research carried out at the University of Newcastle. The Australian research addressed local materials and building practice particularly related to flexural performance and the mechanisms of transfer of prestress. The main features of this Australian research are presented together with an overview of the Australian code provisions.

An approach for the in-plane design of post-tensioned concrete masonry (PCM) walls with unbonded tendons is proposed. The concept of PCM walls is briefly presented, followed by a discussion of a method for prediction of the wall in-plane force-displacement response. A dynamic analysis procedure is proposed for deriving the seismic demand, notably in terms of structural displacement demand for given wall dimensions and post-tensioning layout. The seismic demand on a 5 storey PCM cantilever wall is derived by time-history analysis, and is compared with seismic demands imposed on ductile and nominally elastic reinforced concrete masonry walls of similar dimensions.

While building code requirements are important, designers need further guidance as to their practical use. This paper is intended to provide ideas for planning masonry projects to use this new technology efficiently. There are two forms of prestressed masonry, post-tensioning and pre-tensioning. The primary use of prestressed masonry is post-tensioning and will not be discussed; pre-tensioning is more suited to prefabricated masonry elements and is not discussed here. This paper will address general recommendations which the designers should consider, as well as specific criteria for cavity walls, single-wythe walls, partitions, and veneers.

With financial support from the Council for Masonry Research, the Research Committee of The Masonry Society has been involved in a strategic planning project known as "Planning for Enhanced Research in Masonry (PERM)." Through these efforts, an outcomes assessment report has been written on advances in masonry construction resulting from past research needs workshops, and a position paper summarizing the present state of masonry research and directions for the future. Based on these two documents, a strategic plan is being formulated for a coordinated plan of masonry research in this country. Whereas the stakeholders have yet to be identified to fund such a major research program, elements of the plan as presented herein should be of interest to individuals and groups involved in masonry research and its implementation. This extended abstract summarizes work under the PERM project and presents basic vision, mission and goal statements as defined at a recent planning workshop.

Masonry falls from a building facade some where in the US about every three weeks. People are frequently killed or injured. The causes are improper materials, design, construction, and maintenance. Every city should require periodic inspection of high-rise building facades. Definitions are necessary for facade conditioning methods. New and improved methods for testing materials and for technology transfer are required.

Unreinforced masonry (URM) walls are prone to failure when subjected to out-of-plane and in-plane loads. The development of effective and affordable strengthening strategies is a need. In this context fiber reinforced polymer (FRP) materials offer viable solutions to solve or lessen the effects of overloading. This paper describes FRP systems proposed for use in the strengthening of masonry elements as well as the impact of such systems on the building being retrofitted. Also, field applications, some potential and others already implemented applications, are described. Field applications include strengthening for natural hazards (i.e. earthquakes and high wind pressures) as well as man-caused hazards (i.e. blasting). The potential of FRP systems for retrofitting of historic structures is also illustrated. Finally, research needs in this area are discussed.

This paper presents the development of a simplified equation for floor vibration assessment of steel office floors for walking excitations. Using a database of over 2000 floor system evaluations, multivariate statistical methods were employed in the formulation. The research was undertaken to provide building design professionals with an "easier" means of checking floor system properties early in the design process, hopefully resulting in the most economical system, while maintaining serviceability. Presently, the simplified equation is limited to non-composite, grade 50 steel beams and girders selected using the LRFD method.

During the erection of structural steel, occasionally steel members will have connections that require field repairs due to mis-fits of the parts. Structural engineers are required to review and approve the "field work" details for these corrections. The field work details must be both structurally adequate and cost effective. Generally the field work details are proposed by the steel fabricator or steel erector. Sometimes the proposal may address the "cost" criteria without fully addressing structural adequacy. The proposal may be one that has been used in the past by the fabricator/erector but is not appropriate for the loading conditions where the problem occurs on your project.

There are several circumstances that can contribute to misalignment of structural steel during the construction process. Typically, it is not economically feasible to refabricate misaligned steel; Therefore, the misalignments need to be repaired with a field retrofit. The challenge is to keep these retrofits simple so that they do not have a great impact on the construction cost. The retrofit of misaligned steel can be very costly to the engineer, because of the time that it takes to resolve each occurrence. Often these conditions are not apparent until the steel is being set, and an immediate response is necessary so that the construction sequence can go on. There isn't a great deal of information available on the design procedures required for retrofit of misaligned steel; However, there are several procedures listed in the AISC manuals that can be utilized to provide fast efficient solutions. It would be advantageous to have some generally accepted solutions available to the design engineer for typical misalignments. To that end, below is a list of several different types of typical misalignments found in actual field conditions. A brief description of the field fix that was provided is listed with each one, in order to help suggest/share some solutions for application in similar circumstances of various projects.

For large structures such as stadiums, aquariums, or convention centers, architectural requirements frequently dictate the structural system that will be used by the structural engineer. These complex projects often have heavy loadings and long spans that create challenging engineering issues. Foremost among these issues is ability of the structure to safely and efficiently transfer the design loads through the structure to the foundation system. This presentation will focus on the constructibility of connections that allow the structure to transfer these loads.

In this paper the design procedures for tension, compression, shear, and bending governed by yielding or rupture, with no instability, as presented in three design codes for aluminum structures, are compared. Other papers in this series deal with "Material Properties and Connections" and "Buckling". The codes reviewed are. CSA: Canadian Standards Association, S157 "Strength Design in Aluminum", EC9: Eurocode 9 "Design of Aluminum Alloy Structures- Part 1-1: General Rules and Rules for Building", ENV 1999-1-1, and SAS: Aluminum Association "Specification for Aluminum Structures: Load and Resistance Factor Design".

This paper is one of three which compare the rules in three aluminum codes of practice for the design of aluminum components subjected to static loads. The subject here is buckling and the design of members in compression. (Other papers deal with Material Properties and Connections, and Tension Members). By reviewing the various treatments it is intended to provide assistance in drafting a Guide which will cover all the pertinent cases using the most suitable procedures and presenting them in a uniform and coherent fashion acceptable to the widest possible audience.

In recent years, in Colombia, there were designed and built many structures using aluminum shapes. Some reasons to explain this development are presented. Also some examples of this kind of structures, that were imagined, designed and erected using this material are presented. The structures are grouped accordingly the use of the buildings they are installed: Swimming pools, Malls, Coliseums, other Buildings. Most of these projects were developed by TECMO LTDA.

Three aluminum structural design codes - the US, Canadian, and European - include most of the world's rules for designing aluminum structures. This paper and two others in this session compare the provisions of these codes that address statically loaded, building type structures. This paper introduces the codes and compares the treatment of material properties and connections in the codes.

The concept of using truss (strut and tie) models to analyze and design reinforced concrete members has existed since the early part of the twentieth century. The procedure for designing shear reinforcement in the current ACI Building Code is based on a plane truss theory that assumes a principal compression angle of 45 degrees. A key advantage of a truss model is that the designer can visualize the flow of stresses in the member. The flows of compression stress are idealized by compression member called "struts" and the flows of tension stresses are modeled by tension members called "ties". More than one strut and tie model may be required to find the lower-bound strength of a member, or region within a member. Strut and tie models may be used to analyze and design whole members, but the more common application is to use them in "disturbed" regions, known as D-regions. Disturbed regions are assumed to occur at concentrated loads and reactions, and at geometric discontinuities where the flow of stresses cannot be predicted by normal "beam theory". Following St. Venant's principle, these regions are assumed to extend one member depth away from the source of the load or geometric disturbance. Portions of members not included in these D-regions are referred to as B-regions, i.e., regions where nomal beam theory accurately predicts stresses due to axial load and bending. For some members, for instance deep beams and corbels, the whole member may be classified as a D-region.

Strut-and-tie models are an especially valuable tool for designing discontinuity regions (D-regions) of structures with irregular geometry where the flow of forces is not well known, like at points where high forces are applied to a beam, for shear walls with openings or for connections of members. The latter is especially important for highly stressed members like in concrete offshore platforms. The different modeling techniques are not presented here, since they were explained by Schlaich et al as well as Reineck, like the orientation of the model by the results of linear elastic analyses, adjusting standard models or using the load-path method.

The Strut-and-Tie Method (STM) is an emerging procedure for the design of D- (Discontinuity) Regions. D-Regions are those parts of a structure in which there is a complex variation in strain, such as corbels, deep beams, joints, and walls with openings. The STM design process involves idealizing that an internal truss carries the load through the discontinuity region to its boundaries, providing sufficient reinforcement to serve as the tension ties, and then checking that the compressive struts and nodal zones (joints) are sufficiently large enough to support the applied forces. While the STM is conceptually simple, calculating and modifying the dimensions of the truss and its members can be prohibitively time consuming. This paper describes a graphical design tool that enables the user to draw the D-Region to be designed, draw an internal supporting truss, select member dimensions, and select tension tie reinforcement. The program continuously recalculates the truss and nodal zone forces (and stresses), and thereby creates an efficient interactive STM design tool.

The paper provides a review on the development of tubed concrete columns, in which the steel tube is used as the transverse reinforcement for the column. The tubed column concept was first introduced by Tomii, Sakino and the author in 1985, and proved to be very effective in preventing column shear failure and developing significant ductility. The concept was then expanded to retrofit of existing reinforced concrete columns using both welded steel tubes and FRP tubular shells. Research on new column design using FRP tubes is also discussed.

Retrofitting of concrete structures with fiber reinforced polymers is a relatively new technique. In an extensive research program underway at the University of Toronto, effectiveness of FRP in enhancing structural performance both in terms of strength and ductility is being investigated. The structural components tested include columns, beams, slabs and bridge culverts. Research on columns has focussed on improving their seismic resistance by confining with FRP. Results from a select group of eight circular and four square columns are presented here. All the columns were subjected to simulated seismic loads. Based on a comparison of the moment-curvature responses of the critical sections of FRP-retrofitted specimens with those of similar companion specimens with FRP, it can be concluded that FRP wraps significantly improved the seismic resistance of columns.

The increasing uses of FRP materials for the strengthening and upgrade of buildings has motivated the international engineering community to produce guidelines for the proper design, handling and installation of the externally bonded FRP systems. Thus, independent efforts coordinated by different organizations such as the Japan Building Disaster Prevention Association (JBDPA) and the American Concrete Institute (ACI) have led to implementing appropriate provisions. The JBDPA guidelines mainly focus on seismic retrofitting of structural elements, which implies the strengthening for shear of deficient structural elements. This paper describes and comments on some of the design approaches provided by the JBDPA guidelines for the strengthening of reinforced concrete (RC) columns. This was one of the main targets of the Japanese experience on infrastructure strengthening, which became an imperative task after the post-earthquake observations of the damage caused by the Kobe earthquake in 1995. Finally, comparisons with the ACI guidelines for the strengthening of RC members with FRP systems are also formulated.

This paper summarizes recent research developments on a structural concept that combines filament wound Carbon Fiber Reinforced Polymer (CFRP) shells/tubes filled on-site with concrete for composite columns. The CFRP shell provides the functions of formwork and external reinforcement, while the concrete core supplies the main compression force mechanism and allows for the anchorage of connection elements. A ductile design concept has resulted in a very ductile overall system, while a strength connection design concepts with essentially elastic response have also been characterized. Analytical and design models were developed together with parallel research efforts on the use of concrete filled CFRP shells for bridge girders. The structural behavior of the two column design concepts was experimentally validated through large-scale lateral load tests.

Time-dependent behavior of hybrid systems made of concrete and fiber reinforced polymer tubes (FRP) is affected by the interaction between the two materials as well as their interface bond. A number of creep tests were carried out to predict the behavior of such hybrid systems under sustained axial or flexural loads. Results indicate that current ACI models grossly overestimate the creep of concrete-filled tubes. A nonlinear creep model was developed to account for the different creep properties of concrete and FRP, and the stress re-distribution that takes place between the two materials over time. The model can also be used for concrete-filled steel tubes. Based on the experimental and analytical investigations, changes are proposed to the current ACI creep coefficients for concrete-filled tubes.

The Northridge earthquake of 1994 clearly indicated an urgent need to find efficient and economical means of repairing welded moment connections that experienced cracking and upgrading similar connections in older, existing buildings. One of the more promising and unique procedures for accomplishing this is the use of weld overlays. Using this procedure, an overlay weld of a tough and ductile weld material that is resistant to crack initiation and propagation is deposited over an existing weld that is less resistant and may contain small cracks and other defects. This paper summarizes the results of experimental tests on exterior connections modified with weld overlays and describes some of the analytical studies that were conducted in support of the experimental program.

FEMA 350, Recommend Seismic Design Criteria for New Steel Moment Frame Buildings, contains design recommendations for new steel frame buildings developed during a six-year research effort. Key findings include configuration of new moment frame connections, recommended design procedures, requirements for notch tough welding electrodes, and detailed requirements for quality assurance and quality control.

Post-Northridge earthquake inspection of the steel moment frame connections in the Los Angeles County Public Work Headquarters revealed many original weld defects. As a result, the Federal Emergency Management Agency (FEMA) and the County have provided funding for a seismic hazard mitigation program to upgrade the structure. Using welded haunches to retrofit the connections was considered as one of the possible rehabilitation schemes. Full-scale cyclic testing of two pre-Northridge connections with simulated defects was conducted and used as a benchmark for the design of retrofit schemes. Additional four full-scale retrofitted moment connections were then tested to validate the proposed retrofit design. Test results indicated poor performance of the pre-Northridge connections and excellent performance of the retrofitted specimens. The testing program also showed that the welded haunch design procedure is applicable for haunches with an inclination angle up to 52 degrees.

This paper presents a computer-based computational procedure for cost-revenue conceptual design of office buildings using adaptive search. The conceptual design of an example office building is conducted to illustrate the capability of the computational procedure to generate graphical cost-revenue trade-off relationships taking into account architectural, structural, mechanical and electrical systems.

Stability of long span suspension bridges under wind forces is a very important concern. Sensitivity analysis of the wind speed leading to flutter with regards to the mecanical parameters of the bridge deck can be very helpful for the designer. In this paper this methodology is presented and numerical values for two bridges are enclosed.

Methods for Conceptual (topology) design of linearly elastic structures using the concepts of Transferred Force and Potential Transferred Force are investigated. Since the methods do not use any formal optimization techniques, they are quite easy to use and implement into a computer program. The methods are demonstrated on truss and 2-D plate structures. Improved conceptual designs are obtained from the viewpoint of force transfer. It is concluded that Transferred and Potential Transferred Forces offer viable approaches for conceptual design of structures that need to be developed further for practical applications.

The purpose of this article is to present a new continuum structural topology optimization formulation, and to then investigate its feasibility/utility in obtaining design concepts for long-span bridges. After identifying the instability of continuum structural topology optimization methods based on element level design variables, a novel formulation based on nodal design variables is presented. The proposed node-based formulation is immune to checkerboarding instabilities and can thus be used without spatial filtering with low order (C⁰ continuous) finite elements. The new stabilized formulation is exercised on the topological design of different long-span (1000 – 2000m) bridge forms subjected to both traffic and self-weight loadings. In two dimensions, sparse, efficient concept designs are obtained with only modest computational effort. However since the long-span designs obtained use primarily extensional compression, it is concluded that accounting for geometric stiffening/softening would increase the utility of continuum topology optimization methods in the design of large-scale structures.

This paper provides an overview of contemporary methods of nonlinear analysis, including analytic formulations and application examples. The basic objective is to encourage engineers to consider the merits of using more advanced methods of analysis to design and investigate the behavior of steel structures.

This paper presents a beam-column model, based upon fiber-type, beam-column elements, for inelastic and large deformation analysis of planar steel structural systems. Derivations of the different stiffness matrices that are used in the model are presented. The model has the capacity to account for residual stress consideration. This model satisfies the rigid-body test while some of the other models do not. The accuracy of the model is compared to bench-mark problems via an example. The results indicate that the new model is more robust and has a faster rate of convergence for problems involving inelastic behavior, high stress, and large deflections.

This paper is concerned with nonlinear analysis of planar frames emphasizing how to model the effects of spread of inelasticity accurately and efficiently. A flexibility formulation is used first to derive the incremental flexibility matrix on the basis of the sectional moment-curvature-axial load relationship. The derived flexibility coefficients are explicit and have very simple expressions; therefore computer implementations are easy to perform. Then, the incremental inelastic stiffness matrix is determined from the incremental flexibility matrix using the congruent transformation. If the effects of geometric nonlinearity are important, the conventional geometric stiffness matrix needs to be added to the incremental inelastic stiffness matrix to result in the tangent stiffness matrix. The use of the tangent stiffness matrix in nonlinear analysis of structures follows the standard procedures. Since the presented formulation is based solely on the sectional moment-curvature-axial load relationship, the proposed stiffness and flexibility matrices are applicable to framed structures of various materials. Due to space limitation, only one numerical example on steel frames is provided.

The past several decades have seen tremendous advances in many areas of structural engineering including optimal structural design and inelastic analysis. Researchers in optimal design have made significant progress in applying mathematical programming, optimality criteria, and evolutionary search methods. These algorithms have generally relied upon design specifications (AISC, ACI, etc.) to assess the adequacy of structural members and frames. The development of advanced analytical models (e.g. refined plastic hinge, bounding yield surfaces, distributed plasticity) for steel frames has evolved in parallel with advances in structural optimization. These models do not require specifications or codes to assess the adequacy of a member or frame and the inelastic analysis carried out as part of the design is considered to satisfy the spirit of the member specification or code checks. A relatively new and powerful tool for discrete variable optimization is the genetic or evolutionary algorithm. Evolutionary computation has the potential to fully automate design using advanced analysis. This paper provides an overview of a study presently underway to apply evolutionary computation to the optimized design of steel frames with partially and fully restrained connections using advanced analysis. An overview of the inelastic analysis algorithm is provided, as well as, discussion of the object-oriented evolutionary algorithm. A case study is presented illustrating evolved designs for FR and PR frames using two grades of structural steel. It is shown that the evolutionary algorithm developed is capable of providing optimized frame designs using advanced analysis.

In this paper, a design procedure is presented to determine the optimal thickness of FRP jackets, for enhancing the ductility of existing reinforced concrete bridge piers, having circular cross-section. The procedure stems from the definition of an upgrading index, given as the ratio of the target-to-available ductility at the pier base section, to be attained through FRP jacketing. The available ductility is that identified through the usual assessment procedures on the r.c. member to upgrade, while the target ductility is evaluated based on the expected actions on the bridge. A parametric study on old-code-designed bridge piers sections, upgraded with either glass or carbon fiber jackets, is performed, based on a fiber-section model, equipped with a recently proposed FRP-confined concrete model. The results of the parametric study has been used to developed a design equation that allows to design the optimal thickness of FRP jackets in terms of: the desired upgrading index, the mechanical characteristics of the selected composite material, and the quantities defining the initial state of the pier section.

The flexural behaviour of reinforced beams strengthened by externally bonded steel and carbon fibre reinforced plastic (CFRP) is compared using the experimentally obtained data. Two types of strengthened beams of different span to depth aspect ratio have been tested. The FEM computational method have been used in analysis of failure mechanism and failure limit state. The FEM model gives a promissing results, but further development is needed before its introduction in design practice.

This paper discusses the problem of predicting the stiffness, the load capacity and the failure modes of RC members strengthened in bending with bonded steel or C-FRP thin plates. A critical issue of this strengthening technique is that when the plate debonds, the load capacity suddenly drops and the failure mode is typically brittle. Due to both the concrete cracking diffusion and the yielding of the steel rebars, a significant amplification of the bond stresses takes place at the beam-plate interface. Debonding occurs when the bond strength is reached locally. In order to properly describe and realistically predict the behaviour of the strengthened beams, a displacement-based fiber beam model including bond slip is used. The proposed model is used to confirm and investigate distinct failure modes observed in experimental investigations.

Movable bridges may present a major seismic hazard due to the potential of interrupting both land and marine traffic after an earthquake. This paper presents the analysis, findings and retrofit design of a seismic evaluation performed on a 60-year old vertical lift highway bridge located in the eastern Untied States. This paper also summarizes the structural, mechanical and electrical rehabilitation of the bridge.

The Manhattan Bridge, spanning the East River between lower Manhattan and Brooklyn, is undergoing retrofit to correct deficiencies caused by corrosion and unsymmetrical loading. Simultaneously, the bridge is being evaluated for seismic performance to determine if this should be a factor in the overall rehabilitation program. This paper describes the assumptions and analytical modeling for seismic effects and discusses some of the findings and recommendations.

This paper presents an accessible and cost effective seismic retrofit strategy for a four continuous span bridge in New York City. Due to its importance, the bridge has been classified as "critical" from a seismic point of view. Seismic motion input is based on site response spectra for 500-year and 2500-year earthquakes. A new system of elastomeric bearings is incorporated into the structure. This system is designed to yield at a certain threshold of seismic movement providing a fuse-type action, thus softening the system and reducing the seismic forces transmitted to the substructure. After the seismic event, the yielded part is replaced without need for jacking or replacement of the bearing system.

The Ironton-Russell truss bridge spanning the Ohio River between the cities of Ironton, Ohio and Russell, Kentucky was opened to traffic in April 1922. Although this bridge spans the Ohio River between Ohio and Kentucky, it is owned and operated by the state of Ohio and is considered a landmark by both the residents of Ironton and Russell. The main spans of this truss consist of a 3-span cantilever through truss, with a suspended truss in the center span, and a simple span through truss. Visual inspections of these main spans revealed that recent repairs and modifications to various truss members, floorbeams, and stringers utilized weld techniques that violated the ANSI/AASHTO/AWS Bridge Welding Code. Furthermore, these welded repairs reduced the fatigue classification of primary load carrying truss members to Category E and E', modified design and construction details used in the original bridge construction, and did very little to contribute to truss member section. When the visual inspection team identified these details as well as section loss at certain truss verticals and diagonals, it was their recommendation to reduce the allowable load on the bridge's through truss spans from HS14.3 (23.4 tons) to 3 tons. However, enforcing a 3-ton load limit would severely impact the economy of the region — the transportation of heavy goods and materials across the bridge would be restricted, thus effecting local industries. Recognizing this, the Ohio Department of Transportation contracted University of Cincinnati researchers to organize and perform field tests on the bridge to provide a better assessment of load capacity and in-situ structural health. As a result, controlled truck-load tests involving high-speed (resistance based) strain gages were performed on the bridge and an instrumented monitor utilizing low-speed (vibrating wire) strain gages was installed at the site. In this manner, both the live load and environmental responses of various instrumented truss members and floorbeams were recorded. The respective data recorded during these field efforts was used not only to evaluate environmental effects on the bridge, but also to compute the load rating for each of the instrumented members. These ratings and their corresponding allowable live loads were subsequently compared to the recommended 3-ton load limit. The results of this comparison, as well as how they were utilized by the Ohio Department of Transportation, are presented within this paper.

The primary objective of this paper and its affiliated research is to rigorously demonstrate that modal analysis and the measure of flexibility extracted from modal test data are effective tools for the condition assessment of civil-engineered structures. The use of flexibility as a condition assessment/damage identification index is the fundamental concept, therefore two basic questions need to be resolved scientifically through the analysis and synthesis of modal test data. These are (1) Is a linear parameter such as modal flexibility reliable as an index for infrastructure condition and damage identification?; and, (2) What are the attributes of modal flexibility when obtained through modal test methods? The investigation of these fundamental questions is intended to reveal and characterize behavioral tendencies of modal flexibility (such as stationarity and accuracy). This involves determining how severely flexibility is influenced, or affected, by not only damage, but also by variations in ambient conditions and experimental errors. Consequently, a typical reinforced-concrete deck on steel girder bridge (steel-stringer bridge) will be subjected to a series of deliberately induced damages that simulate typical steel-stringer bridge deterioration and damage scenarios. Throughout this paper, the authors will summarize not only their field test efforts on this bridge, but also the results of the field tests and, in particular, the reliability, practicality, and usefulness of modal testing and flexibility as condition assessment/damage identification tools for typical steel-stringer bridges.

Out-of-plane distortion-induced fatigue cracking is caused by relative rotation and displacement between longitudinal girders and transverse members framing into these girders. This paper describes distortion-induced cracking observed in Kansas Department of Transportation bridges, reviews the current design details used for connecting transverse and longitudinal members, summarizes different approaches that have been used during former repair practice, and presents case studies of three representative bridges that are under current investigation.

The Swiftwater Covered Bridge is a 48.158 m (158-foot) long, asymmetrical, two-span timber covered bridge that spans the Wild Ammonoosuc River in Bath, New Hampshire. The bridge was built in 1849 utilizing Paddleford trusses; the oldest of only twenty-two (22) bridges of this unique truss type remaining in the country (6). After nearly 150 years with minimal maintenance, the bridge was in very poor condition and required a complete rehabilitation so that it could continue to serve the residents of Bath, NH. This paper details the inspection, analysis, design of repairs and rehabilitation of this historic bridge.

Composite steel deck does not rely on the use of shear studs for its installation — there are other attachment methods of the deck that can be, and are, used and the composite deck still performs as it should. The most common method of installing the deck is with arc puddle welds. Screws and pneumatically and powder driven pins have also been used with success. Indeed, there are particular job applications when the less frequently used methods are required.

Concrete placed inside hollow steel tubular columns, which are part of braced frame structures, can significantly increase the axial strength and stiffness of these columns. However, in order for the contribution of the concrete in the columns to be taken advantage of, forces applied to the columns through the braces must be effectively distributed to the concrete. The connection details between the brace and column are the key aspects of ensuring that this distribution occurs. Past connection designs vary widely, and their seismic behavior is uncertain. An analytical and experimental study is being carried out at the University of Washington to describe the behavior of these connections and their impact on global performance. As part of this study, an analytical study of the joint is carried out which is described in this paper. It is shown that for connections which involve a through-plate, the majority of the force is transferred into the concrete from the steel by bearing, rather than by friction. Also, slip deformations between the steel and concrete are too small to mobilize the strength of shear studs which may be used in the connection.

Hybrid coupled walls consist of reinforced concrete shear walls coupled together in-plane with structural steel coupling beams, forming an efficient structural system that is particularly suited for seismic applications. Although more economical than isolated shear walls because of the coupling action inherent in the system, little research has been done towards developing performance measures and a practical design method for such a system. Existing seismic provisions, including FEMA 302 and AISC 1997 Seismic Provisions, give little guidance for system design and the amount of coupling necessary for optimum performance.

The CUREE-Caltech Woodframe Project is currently underway in California as a combined research and implementation effort to improve the seismic performance of woodframe buildings, a need which was brought to light by the January 17, 1994 Northridge, California Earthquake in the Los Angeles metropolitan region. The objective of this paper is to briefly present the results of shake table tests on a full-scale two-story woodframe house conducted within the CUREE-Caltech Woodframe Project.

The MIDPLY Shearwall System has been developed by Forintek. The system is designed to provide superior resistance to earthquake and wind loads. The improved performance is achieved by rearrangement of wall framing components and sheathing used in standard nailed wood shearwalls. Possible applications of the system are a) platform-frame construction where additional lateral load capacity is needed (e.g., narrow shearwalls next to garage and large window openings); b) post and beam construction (e.g., as an insert between post and beams); c) seismic upgrading of existing structures; and d) manufactured housing systems directed at areas with high risk of earthquakes and hurricanes. The proof-of-concept for the MIDPLY wall system design and construction method was established through testing and analysis of full-scale test specimens subjected to monotonic (ramp), cyclic and dynamic displacement schedules. The MIDPLY wall system is currently being considered by a large construction company in the design of several multi-storey wood-frame buildings.

The Northridge earthquake demonstrated the susceptibility of wood-frame structures to seismic events. Approximately one half of the 40 billion dollars of damage was attributed to wood-frame construction, with a majority of the financial losses associated with non-structural damage. One consequence of the Northridge event has been a focus on the development and implementation of innovative techniques to reduce the damage of wood-frame structures subjected to earthquakes. The objective of this study is to present recent innovative applications of viscoelastic (VE) material to wood.

In the recent past, a large number of steel-flamed buildings have been constructed or retrofitted with supplemental energy dissipation systems for the purpose of seismic protection. However, the application of such systems to woodframe structures has been essentially non-existent except for a limited number of experimental laboratory studies. This paper presents a numerical study of the application of fluid dampers for seismic protection of wood-framed structures. Such dampers dissipate energy via orificing of a fluid. The seismic response of a wood-framed shear wall with and without dampers is evaluated via nonlinear finite element analyses. The results of the analyses demonstrate that the dampers are capable of dissipating a large portion of the seismic input energy while simultaneously relieving the inelastic energy dissipation demand on the shear wall.

Available hysteretic dampers can offer large and stable energy dissipation, but are not suitable for wood frame shear wall construction. A new type of hysteretic damper, called a kinematically expanding hysteretic damper (KE-HD), can dissipate significant energy through controlled tension-only yielding of the device. The damper employs a special anchorage that permits the yielding-element to slide on compression cycles without buckling and then load in tension at any arbitrary displacement amplitude. This feature has the apparent effect of expanding the kinematic surface of the element. The device has been installed in a wood frame shear wall and results shown significant improvement in response with no pinching, stiffness, or strength degradation. Eventual failure of the yielding elements occurs through fracture of the gross section at large elongations. Time-history analysis of single-degree-of-freedom structures with KE-HDs indicates the dampers can provide significant response reduction.

A compound Poisson process damage model is suggested for modeling the cumulative damage (CD) behavior associated with the load-duration effect. Two specific versions of that model were fit to time to failure data for steel doweled wood connections. Both versions of the model fit the data fairly well and so did a deterministic CD model. Application to a wider range of data is required before final judgements can be made about the efficacy of the proposed model.

The developers of early specifications for load and resistance factor design (LRFD) based many of their initial judgments on analyses of specific data sets representing structural elements of various types of materials. Because the specification committees based their final recommendations not only on analytical results, but also on calibration judgments, the resulting documents provided an excellent incremental step in the evolution of structural design. More recently, as reliability analysis procedures have become widely available, an increasing number of technical papers are discussing their results in terms of the reliability index of a given design. While some of the authors of these papers take particular care to disclose all of their underlying assumptions (some even conduct sensitivity studies on specific parameters), many authors do not. Specifically in the field of engineered wood products, some authors characterize their resistance data completely in terms of a single limited test program. Others do no testing at all, and rely on data from the historical literature as the basis of their analyses. This paper discusses reasons why specific "answers" in terms of specific reliability indices are difficult to obtain. It focuses on the magnitude of error that would occur if one mistakenly assumes that resistance data are static. The analysis in this paper focuses on the most stable calculation method — the format conversion option in ASTM D5457. Future work will explore the additional instability introduced when more advanced reliability calculation techniques are used. The paper concludes by recommending several techniques for dealing with resistance data variations for various classes of structural wood materials.

Analysis of wood assemblies must consider both mechanistic and statistical principles to quantify the differences between the response of the assembly and that assumed in single-member design. These differences are presented in this paper for metal-plate connected trusses that are geometrically similar and dissimilar within an assembly. The results suggest that for the truss assemblies studied that load distribution occurring through structural sheathing provides a strengthening effect in the range of 5 to 20 percent.

Recently published test data for bolted and nailed connections was evaluated to assess the structural reliability inherent in current allowable stress design procedures for connections in wood structures. Reliability indices were determined for timber connections using standard first-order, second moment (FOSM) procedures. For the connections considered in this study, reliability indices range from 2.6 to 5.1, generally providing higher levels of safety than the structural members in timber structures.

Solid-sawn wood or wood composite beams may be reinforced with Fiber Reinforced Polymers (FRPs) on the tension side to increase their bending strength, stiffness and ductility. This paper describes results of an extensive full-scale physical testing program designed to verify the accuracy of a probabilistic model of reinforced glued laminated (glulam) beams. The testing program evaluated 90 glulam beams 130 mm wide x 305 mm deep x 6.7 m long reinforced in tension with E-glass FRP (GFRP). The beams were made using a random layup of L2 and better grade of Douglas Fir and Western Hemlock lamstock and were tested in four-point bending according to ASTM D198. The numerical model, called ReLAM (for Reinforced LAMinated beams), predicts the probability density functions (PDFs) of the Modulus of Rupture (MOR) and Modulus of Elasticity (MOE) for a selected layup of reinforced glulam beams. The model utilizes a moment-curvature mechanics approach, Monte Carlo simulations, and internally calculates the volume effect in reinforced glulam beams from basic statistical mechanics principles. Both the laboratory testing and ReLAM showed that for the Douglas Fir layup tested, a GFRP tension reinforcement ratio of 3.3% increased the allowable bending strength F_b by 119%. ReLAM was found to be an accurate tool for predicting the bending strength and stiffness PDFs of reinforced glulams. These PDFs can be used in reliability-based design of FRP-glulams.

In 1997, the National Science Foundation (NSF) funded three Earthquake Engineering Research Centers (EERCs) to focus on earthquake hazard mitigation through systems-oriented research, education and outreach, and industrial/practitioner/end user collaboration and technology transfer. Collectively receiving about one third of the total annual funding in NSF's earthquake engineering research portfolio, the three EERCs enable cross-disciplinary, cross-institutional teams of faculty and students to work collaboratively, in partnership with industry, practitioners and other end users, over a long-term period, on science, engineering, and societal research issues related to earthquake hazard mitigation. This paper presents an overview of the key features of the EERCs and their individual and collaborative efforts.

The Multidisciplinary Center for Earthquake Engineering Research (MCEER) was established by the National Science Foundation (NSF) in 1986 as the National Center for Earthquake Engineering Research (NCEER). In 1997, NCEER became MCEER as one of the three NSF sponsored earthquake engineering research centers. The other two centers are: Mid America Earthquake Center and Pacific Earthquake Engineering Research Center. Since 1989 MCEER has been fostering systems integrated research by multidisciplinary team efforts with special emphasis given to the application of emerging technologies in earthquake hazard mitigation and emergency response. A selected number of civil infrastructure systems (CIS) and critical facilities (which should function during and after earthquakes) have been targeted for which seismic retrofit strategies are being developed by MCEER research teams. The targeted CIS are electric power, water and gas networks, bridges and highway systems. The critical facilities are hospitals. MCEER researchers working in teams include the following areas of expertise: structural engineering, geotechnical engineering, engineering seismology, risk and reliability, high performance structural materials, structural control, electrical engineering, mechanical engineering, computer engineering, public policy, economics, urban and regional sciences, architecture and sociology.

Research projects of the Mid-America Earthquake Center are planned and managed about cross-disciplinary themes including vulnerability of transportation networks and performance of essential facilities. To extract from these coordinated programs just the structural engineering research projects and list them out of their program context does not reflect the attractive systems-integration focus of these programs. However, for the purpose of this session and the mono-disciplinary audience of a Structures Congress, Center structural engineering projects are listed as a point of reference. This extended abstract is intended to inform a potential research collaborator, or end-user of the research, to the structural engineering research activities of the MAE Center in the hope that further detailed information will be sought. Each one of these projects is described in more detail on project task statements given on the MAE Center website (http://mae.ce.uiuc.edu) as well as with research reports.

Earthquake engineering research at NSF is authorized by Congress through the National Earthquake Hazard Reduction Program (NEHRP). NEHRP supports earthquake related programs at FEMA, USGS, NIST, and NSF. NSF's annual budget for NEHRP-related research is approximately $29 million, of which $11 million is invested through the Geoscience Directorate (GEO), and $18 million through the Civil and Mechanical (CMS) Systems Division of the Directorate for Engineering (ENG). In addition to these funds, monies are appropriated separately to fund the Major Research Equipment project - the George E. Brown, Jr. Network for Earthquake Engineering Simulation, NEES. The NEES project is also administered through the Civil and Mechanical (CMS) Systems Division.

This paper presents an overview of the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES), a Major Research Equipment project for the National Science Foundation, which has been authorized by the Congress of the United States for a total funding of $81.9 million between October 1, 1999 and September 30, 2004.

The U.S. Geological Survey (USGS) is the lead federal agency of the National Earthquake Hazards Research Program (NEHRP) to conduct research related to earth sciences. Therefore, whether it is research on structures or other civil engineering disciplines, the subject matter of such research at USGS must meet NEHRP objectives. The most recent charges for USGS are outlined in the Draft of the NEHRP Strategic Plan (August 2000) which details several research issues on the effects of ground motions on built environment.

This paper summarizes the current FHWA seismic research program in highway constructions. This research program consists of two phases. The first phase, entitled "Seismic Vulnerability Studies of New and Existing Highway Construction", was briefly introduced by group areas: Seismic Hazards and Ground Motion, Geotechnical Engineering, Intelligent and Protective Systems, Structures and Systems, Earthquake Reconnaissance, Demonstration Projects and Workshops and Conferences. The research studies of the second phase, Seismic Vulnerability Studies of Highway Systems, is introduced with the topical areas: Loss Estimation Methods for Highway Systems, Seismic Design and Retrofit Manual for Long Span Bridges, Earthquake Protective Systems, Foundation and geotechnical Studies, Special Studies, Technology Exchange and Transfer. This program will result in the development of an improved understanding of the seismic hazard in the eastern and central United States, the behavior and response of foundations and soils under seismic excitation, and the overall response of highway structures and systems during earthquakes. This program is also developing retrofitting technologies appropriate for bridges and other highway structures in low-to-moderate seismic zones and design criteria and philosophies intended to reduce the vulnerability of future highway construction nationally.

Amendment X to the United States Constitution is a masterful simple one-sentence statement that has produced several lengthy books attempting to interpret its meaning. In researching this topic, 68 Supreme Court cases were found concerning the meaning of this single sentence. Often these cases were decided by a 5 to 4 vote. However, it is the primary basis for state jurisdictional regulation of the professions. Many individuals have proposed that engineers attempt to get this changed in order to allow for a national license. There are many arguments both pro and con but the likelihood of change in the next several decades is very small.