Showing papers on "Earthquake resistant structures published in 2004"

Component Testing, Seismic Evaluation and Characterization of Buckling-Restrained Braces

Abstract: This paper reports on the results from a comprehensive component testing program on a type of buckling-restrained brace known as the Unbonded Brace™. The experimental data are used to: ~1! verify the results of theoretical predictions on the structural stability of the braces; ~2! validate the inelasitc capacity of the braces under severe earthquake demands; and ~3! calibrate a macroscopic hysteretic model that is found to predict, with fidelity, the brace force-displacement behavior. The study concludes that the unbonded brace is a reliable and practical alternative to conventional framing systems to enhance the earthquake resistance of new and existing structures; capable of providing both the rigidity needed to satisfy structural drift limits, while delivering a substantial and repeatable energy absorption capability.

Experimental Evaluation of the Seismic Performance of Reinforced Concrete Bridge Columns

Abstract: A current focus in earthquake engineering research and practice is the development of seismic design procedures whose aim is to achieve a specified performance. To implement such procedures, engineers require methods to define damage in terms of engineering criteria. Previous experimental research on bridge columns has focused on component failure, with relatively little attention to other damage states. A research program was undertaken to assess the seismic performance of well-confined, circular-cross-section, reinforced concrete bridge columns at a range of damage states. The test variables included aspect ratio, longitudinal reinforcement ratio, spiral reinforcement ratio, axial load ratio, and the length of the well-confined region adjacent to the zone where plastic hinging is anticipated. The progression of damage was similar for all columns. Analysis of the experimental results suggest that key damage states of residual cracking, cover spalling, and core crushing can best be related to engineering parameters, such as longitudinal reinforcement tensile strain and concrete compressive strain, using cumulative probability curves.

Wind and Earthquake Resistant Buildings: Structural Analysis and Design

Abstract: WIND LOADS Design Considerations Nature of Wind Characteristics of Wind Code Provisions for Wind Loads Wind-Tunnel Engineering Perception of Building Motions SEISMIC DESIGN Building Behavior Seismic Design Concept Uniform Building Code, 1997 Edition: Seismic Provisions ASCE 7-02,IBC 2003,and NFPA 5000:Seismic Provisions Seismic Design of Structural Elements, Nonstructural Components, and Equipment 1997 UBC Provisions Dynamic Analysis Theory Chapter Summary STEEL BUILDINGS Rigid Frames (Moment Frames) Braced Frames Staggered Truss System Eccentric Braced Frame (EBF) Interacting System of Braced and Rigid Frames Outrigger and Belt Truss Systems Framed Tube System Irregular Tube Trussed Tube Bundled Tube Seismic Design CONCRETE BUILDINGS Structural Systems Seismic Design COMPOSITE BUILDINGS Composite Elements Composite Building Systems Example Projects Super-Tall Buildings: Structural Concept Seismic Composite Systems SEISMIC REHABILITATION OF EXISTING BUILDINGS Code-Sponsored Design Alternate Design Philosophy Code Provisions for Seismic Upgrade Building Deformations Common Deficiencies and Upgrade Methods FEMA 356: Prestandard and Commentary on the Seismic Rehabilitation of Buildings Summary of FEMA 356 Fiber-Reinforced Polymer Systems for Strengthening of Concrete Buildings Seismic Strengthening Details GRAVITY SYSTEMS Structural Steel Concrete Systems Composite Gravity Systems SPECIAL TOPICS Tall Buildings Damping Devices for Reducing Motion Perception Panel Zone Effects Differential Shortening of Columns Floor-Leveling Problems Floor Vibrations Seismic Isolation Passive Energy Dissipation Systems Buckling-Restrained Braced Frame Selected References Appendix A Conversion Factors: U.S.Customary to SI Units Index

Foundation isolation for seismic protection using a smooth synthetic liner

Abstract: Smooth synthetic materials placed underneath foundations of structures can provide seismic protection by absorbing energy through sliding. Cyclic and shaking table tests were conducted on a variety of synthetic interfaces to identify a suitable liner for use as foundation isolation. It was concluded that a high strength, nonwoven geotextile placed over an ultrahigh molecular weight polyethylene, UHMWPE (geotextile/UHMWPE) constitutes a liner that is well suited for this application. The static friction coefficient of the interface (between the geotextile and the UHMWPE) is about 0.1. The dynamic coefficient is about 0.07 and is insensitive to changes in slip rate and normal stress. A single-story structural model with and without foundation isolation was tested using a shaker table. The results demonstrate the role of foundation isolation in substantially reducing the seismic shear forces in the model. Accompanying this reduction in shear forces are slip displacements along the isolation liner. Permanent slip (final location of the structure relative to its initial position) can be reduced through the use of a small restoring force that could be provided through passive soil resistance. Peak-to-peak slip (maximum slip during shaking) needs to be permitted for foundation isolation to be effective. The experimental and analytical research results demonstrate the technical feasibility of using a smooth synthetic liner in earthquake hazard mitigation.

Seismic Response of Multiple Span Steel Bridges in Central and Southeastern United States. II: Retrofitted

Abstract: The seismic response of typical multispan simply supported (MSSS) and multispan continuous steel girder bridges in the central and southeastern United States is evaluated. Nonlinear time history analyses are conducted using synthetic ground motion for three cities for 475 and 2,475-year return period earthquakes (10 and 2% probability of exceedance in 50 years). The results indicate that the seismic response for the 475-year return period earthquake would lead to an essentially linear response in typical bridges. However, the seismic response for a 2,475-year return period earthquake resulted in significant demands on nonductile columns, fixed and expansion bearings, and abutments. In particular, pounding between decks in the MSSS bridge would result in significant damage to steel bearings and would lead to the toppling of rocker bearings, which may result in unseating of the bridge deck.

Experimental and Analytical Study of Masonry Infill Reinforced Concrete Frames Retrofitted with Steel Braces

Abstract: In the present work a seismic retrofitting technique is proposed for masonry infilled reinforced concrete frames based on the replacement of infill panels by K-bracing with vertical shear link. The performance of this technique is evaluated through experimental tests. A simplified numerical model for structural damage evaluation is also formulated according to the notions and principles of continuum damage mechanics. The proposed model is calibrated with the experimental results. The experimental results have shown an excellent energy dissipation capacity with the proposed technique. Likewise, the numerical predictions with the proposed model are in good agreement with experimental results.

Performance evaluation of short span reinforced concrete arch bridges

Abstract: In this paper, the static and seismic performance of some short span reinforced concrete arch bridges, before and after strengthening interventions, are evaluated. To verify whether retrofit strategies for the considered arch bridges, which were designed for resisting under permanent and service actions, were adequate for earthquake resistance, seismic analyses of the as-built model of the structures have been undertaken. To account for multiple input effects on arches, induced by out-of-phase motions at foundation levels as well as different boundary conditions at structural supports, the seismic response of the structures under correlated horizontal and vertical multiple excitations is calculated. The effects on arch bridges of conventionally used uniform input and partially correlated multiple inputs with phase shifts are compared. In all cases, the results are discussed with particular reference to the influence of structural configuration, secondary systems, cross-section thickness of the arch, and retrofit interventions.

Energy Balance Assessment of Base-Isolated Structures

Abstract: This paper explores the use of energy concepts in the analysis of base-isolated structures subject to severe earthquake ground motions. We formulate the energy balance equations in moving- and fixed-base coordinate frames and provide new physical insight into the time-dependent behavior of individual terms. Conventional wisdom in earthquake engineering circles is that systems with base isolation devices should be economically competitive and designed to: (1) minimize input energy, and (2) maximize the percentage of input energy dissipated by damping and inelastic mechanisms. Through the nonlinear time-history analysis of a base-isolated mass-spring system subject to an ensemble of severe ground motion inputs, we demonstrate that improvements in objective (2) often need to be balanced against increases in input energy. Hence, by itself, objective (1) presents an overly simplified view of desirable behavior.

Seismic Design Enhancements and the Reduced Beam Section Detail for Steel Moment Frames

Abstract: An area of heightened interest after the 1994 Northridge earthquake damage was the seismic ductility of steel moment frame connections. Work conducted by the Federal Emergency Management Agency ~FEMA! and the SAC Joint Venture, National Institute of Standards and Technology ~NIST!, the American Institute of Steel Construction Inc. ~AISC!, and many others in academia, industry, and the profession over the last few years has greatly expanded the knowledge base in a number of relevant areas. This resulting information has led to a set of new and modified steel moment connection details and accompanying design criteria for improved seismic performance. One of the more popular seismic connection types that has been prequalified in FEMA 350-353 is the new reduced beam section detail.

Evaluating Earthquake Safety in Mid-American Communities

Abstract: This paper reports on research being conducted at the Mid-America Earthquake Center to explore the characteristics of seismic risk for communities in the vicinity of the New Madrid seismic zone. By risk, the product of seismic hazards and community vulnerability is meant. The research focused on two communities, Carbondale, Illinois and Sikeston, Missouri, to estimate potential earthquake effects to specific buildings and to identify potential mitigation actions. Buildings were evaluated using ATC-21 rapid visual screening and HAZUS99 was used to estimate earthquake losses for a range of plausible earthquake threats to each community. Vulnerable structure types in the two study areas included reinforced masonry, unreinforced masonry and concrete frame, which are common among important educational, governmental, residential and commercial buildings in the two communities. Annualized direct economic losses to buildings are approximately $500,000 per year for each study area. Serious injuries from earthquakes appear to be relatively unlikely for those communities under most earthquake scenarios, but may severely stain the capabilities of earthquake-damaged hospitals to provide adequate services. The study underscores the need for a prudent level of mitigation and preparedness in mid-America.

Seismic vulnerability of post-islamic monumental structures in Iran: Review of historical sources

Abstract: This paper reports on a study undertaken to investigate the earthquake performance and assess the seismic vulnerability of post-Islamic monumental structures in Iran. These structures are primarily of brick masonry construction, though some notable stone and mud-brick structures also exist. The structures are first classified according to their structural forms. A review of the available historical and recent sources on the earthquake behavior of different structural forms is then conducted. A second classification of the structures is subsequently made according to their seismic vulnerability. By estimating the location intensity for a large number of past and present structures, subjected to earthquakes in the last millennium, “damage” and “survival” intensity levels are calculated for different structural groups. Based on the estimated damage and survival intensity levels, an intensity scale is proposed for the post-Islamic historical structures in Iran.

Design of pile foundations for liquefaction-induced lateral spread displacements

Abstract: A two-story building was proposed within the Port of Los Angeles (POLA) Pier 400 site, which was created by hydraulically placing dredged materials contained by perimeter dikes. The close proximity of the building to the dike could result in significant vertical and lateral movements of the ground surface during a design earthquake due to lateral spreading of the dike. A dynamic, two-dimensional, finite-element analysis performed near the site indicated that the lateral spread at the ground surface could be large near the edge of the building footprint during the design seismic event. The use of shallow foundations on improved ground was not permitted as the reviewing agency for the building design, the City of Los Angeles Department of Building and Safety (LADBS), would not allow large movements of the shallow foundations or a floating mat foundation. The design team selected pile foundations and lateral pile analyses were performed to determine the bending moments and shear forces within the piles due to varying lateral speed of the liquefied hydraulic fill surrounding the. The lateral spread estimates were made using simplified Newmark analysis, and an iterative scheme developed whereby shear forces developed in the pile were used to estimate the "pinning" effects of the pile, which were in turn added to the residual shear strength of the hydraulic fill. The total number of piles needed to reduce the lateral spread was determined so that the maximum moment within a pile would remain within the elastic limit, as required by the LADBS. The design procedure took advantage of pile pinning effects through the use of a simple analytical approach to achieve the project goals and gain acceptance by the LADBS.

Assessment of Steel and Fiber Reinforced Plastic Jackets for Seismic Retrofit of Reinforced Concrete Columns with Structural Flares

Abstract: An analytical and experimental study of reinforced concrete flared bridge columns was conducted to determine an appropriate retrofit method for columns with inadequate shear capacity under earthquake loads. Four 0.3-scale models were tested on a shake table to failure, one representing as-built columns and the other three retrofitted with jackets, one with steel, one with a glass fiber reinforced plastic ~FRP!, and the third with a carbon FRP jacket. The jackets were designed to keep the plastic hinge away from the column end. A new lay up method was developed for FRP fabrics used on nonprismatic members. The results showed that all jackets improved the seismic performance. The effectiveness of the jackets was nearly the same for all materials. The method to estimate shear capacity based on the guidelines of the California Department of Transportation and a modified version of that method were found to closely estimate the shear capacity. However, the method in the Federal Highway Administration seismic retrofit manual overestimated the shear capacity and was unconservative.

Influence of Batter Piles on the Dynamic Behavior of Pile-Supported Wharf Structures

Abstract: Recent experience has demonstrated that waterfront structures are highly susceptible to earthquake-induced damage. In the western United States, port waterfront structures are commonly constructed using pile-supported wharves in combination with rock dike structures retaining hydraulically placed fills. Many ports use batter piles to limit deflections from lateral loads, such as ship berthing and seismic loads. Extensive earthquake-induced damage to batter piles has been observed at several ports worldwide. Consequently, batter piles are now used cautiously in the design of new wharves in seismically active regions even though many wharves with batter piles have performed adequately. They have also been used as part of the unique “structural fuse” concept that has been adopted on major projects in the western United States. The continued use of batter piles combined with the significant number of existing wharves supported with batter piles creates the need for a better understanding of their seismic performance. In order to augment the limited number of instrumented earthquake case studies for modern wharves and evaluate the performance of the soil-foundation-structure system, a series of large-scale centrifuge models have been constructed and tested with typical pile-supported wharf configurations. This paper presents the results of the final two models where batter piles were incorporated. Tests were carried out with and without the batter piles attached for each model at identical input accelerations. To the authors’ knowledge, the tests provide the first recording and quantification of seismic force distribution for pile-supported wharf structures with batter piles. This paper summarizes 1) quantification of seismic lateral loads on vertical and batter piles, 2) pile shear and moment data with emphasis on the wharf deck connection, 3) embankment displacements with comments regarding their influence on pile loading.

Reaching for the Sky

Abstract: Tapei 101—soon to open its doors as the world’s tallest building—will resist devastating typhoons, earthquakes, and sway with an ingenious system of outrigger trusses, supercolumns, and tuned-mass dampers.

Overview of international cooperative research on seismic performance of composite and hybrid structures

Abstract: Innovative combinations of two or more materials can result in very efficient and high performing structural systems to resist severe forces due to events such as earthquakes. During the past two decades or so, significant gains in the knowledge base regarding the seismic behavior of composite and hybrid structural components and systems have been made. Much of this has been accomplished through international cooperative res earch programs. This paper presents an overview of two such major programs: The US-Japan Research Program which spanned over a period approximately seven years from 1993-2000, followed by the US-Taiwan Cooperative Research Program which started in 2001 and is currently in progress. While the US -Japan Program was significantly broader in scope and magnitude, greater emphasis was placed on component and sub-assemblage studies and testing of f ull scale structures could not be undertaken due to time and budget limitations. The US -Taiwan Program was designed to fill this gap, by undertaking testing of two full size three story, three bay frames at the National Center for Research in Earthquake Engineering (NCREE), Taiwan, accompanied by related sub-assemblage tests at participating research institutions in Taiwan and analytical and design implication studies in the US. The two structural systems selected for the US -Taiwan program are: RC column- steel beam (RCS) moment frames, and concrete-filled tubular columns-steel beams-buckling restrained composite braced frames (CFT-BRBF). A five-year research program on Composite and Hybrid Structures as Phase 5 of the U.S. -Japan Cooperative Earthquake Research Program was recommended to be initiated in 1993 in both countries. The research work in Japan started in fiscal year 1993. However, fuller participation of researchers on both sides started in early summer 1995. The sponsorship of the program was by the National Science Foundation in the U.S. and by the Ministry of Construction along with a number of industry groups in Japan. This paper presents a brief overview of the program and accomplishments made on both sides. Because of diverse and broad scope of the subject area, the research program was organized into the following four groups: Concrete Filled Tube Column Systems (CFT); Reinforced Concrete (RC) and Steel Reinforced Concrete (SRC) Column Systems (RCS); RC/SRC Hybrid Wall Systems (HWS); and New Materials, Elements and Systems (RFI). A theme structure with well selected layout, geometry and design loads provided a common focus for various systems that were studied, and also a common prototype structure from which the components and sub-assemblages were drawn. U.S.-Japan Program The U.S.-Japan Cooperative Earthquake Research Program began in 1979 under the auspices of the UJNR Panel on Wind and Seismic Effects. The overall objective of the total program was to improve seismic safety practices in bot h countries through cooperative studies to determine the

Seismic retrofit of bridge foundations

Abstract: The Richmond-San Rafael Bridge in California is located in an area know for its high seismicity. This paper describes the recent seismic retrofit of the bridge foundation. The project presented tremendous engineering challenges due to the varying geotechnical conditions, high seismic load demands, and an adverse construction environment with swift and deep water. The retrofit incorporated an innovative concrete-steel composite design in order to achieve the seismic performance and constructability required for the bridge. Prefabricated steel elements were used in combination with cast-in-place concrete or grout throughout the foundation. The existing bracings of the bridges' 38 towers were retrofit with new eccentrically braced frames and special moment-resisting frames. Piers founded on mud were retrofit by installing large-diameter, concrete-steel cylinder piles to reduce the potential lateral drift of the pier. Piers founded on rock required the installation of micropiles between the existing H-piles in order to supplement the overturning resistance of the as-built foundation and to prevent the pullout failure of the H-piles by limiting the rocking motion of their piers. The design criteria for the micropiles include both specific tension load capacity and allowable vertical deflection for a specified design load. The project demonstrates how confinement and composite action can result in high strength, stiffness and ductility of the retrofitted bridge foundations.

Exploring the use of three-dimensional dispersion to damp building vibrations

Abstract: This paper explores the use of mass/stiffness eccentricity in simple buildings to damp the response to excitation due to base motion. Examples include one- and two-story buildings when discussing low-rise structures and shear beams when discussing taller structures. Base motions include a simple step function and earthquake input. A broad range of efficiencies is achieved depending upon the system eccentricity and the available viscous damping. Asymptotic efficiencies of 50% are indicated in some cases. Optimal parameters are discussed.

Seismic Versus Blast Loading

Abstract: Both seismic and blast loading are unpredictable and can produce large magnitude forces that may be difficult to accommodate in structural design. However there are important differences. Because earthquakes are always unpredictable, the only way to prevent damage and casualties is through structural engineering. Earthquakes also tend to engage the whole building by flexing it back and forth in repeated cyclic-type motion. Blast loads, in contrast, can be either accidental or deliberate, and so can be mitigated through nonengineering methods. Unlike an earthquake, a blast may affect a structure locally, and the impulse nature sometimes evokes a rather limited ductile response of reinforced concrete members. This paper presents a series of tables that compare the forces/loading, analysis, material behavior, structural response, design and detailing of reinforced concrete buildings subjected to earthquakes with those affected by blasts.

IDEERS - An international competition to design earthquake resistant model buildings.

Abstract: Since 2000, members of the Earthquake Engineering Research Centre (EERC) at Bristol University have been running an international competition to design earthquake resistant model buildings. The competition was originally developed to educate UK school students about the effects of earthquakes on structures and to help them investigate and develop solutions to a simple design problem. However, the competition is now also being used in Taiwan and Japan to help enthuse and educate High School students, University students and the general public about the principles of good engineering design for earthquake resistant structures. Many different, and often innovative, structural solutions to the problem have been developed by students over the last four years and some of the more unusual solutions are presented here. This paper also compares the different styles of design created by students from the different countries. It is hoped that use of the competition in countries at a higher risk from earthquakes will increase general awareness of the importance of good design and help reduce the likelihood that inappropriate structures are built where there is a risk of earthquakes.

Recent advancement in tall earthquake resistant structures

Abstract: After extensive development and testing, the world’s tallest precast concrete building has been constructed using proprietary Welded Reinforcement Grid (WRG) reinforcement that saves cost, time and labor. Also recently completed with construction time reduced by 40%+ is a 42-story building. A 47-story building is planned at a rate of a floor every three days, using tall WRG reinforcement cages that connect easily on site to rapidly construct elevator shear cores, that resist gravity, earthquake and blast forces very efficiently. Fatigue testing is underway in preparation for its possible use in segmental bridges, where the dimensional accuracy of ±3mm allows automation of the reinforcing cage assembly.

Seismic Code Developments For Nonbuilding Structures Similar To Buildings

Abstract: Structures are generally regarded as having many attributes, including: 1) are self-supporting, 2) have the capacity to support gravity loads, and 3) have the capacity to resist seismic forces imposed at their base. Building codes historically are most interested in life safety and have historically concentrated on prescribing requirements for buildings occupied by the general public. Over time, the existence of nonbuilding structures has been acknowledged by building codes, with prescription requirements gradually being incorporated based on the performance of building structures. They have also recognized that some nonbuilding structures have building like systems (industrial frame structures, pipe racks) and some don't (tanks, vessels, silos, chimneys, cooling towers, etc.). This paper will show how nonbuilding structures similar to buildings have been handled in past building codes and summarize proposed changes for future building codes.

Seismic Design Considerations for Single Plate Shear Connections

Abstract: Single plate shear connections are commonly used in many types of structural frames. Currently these connections are d esigned to resist gravity loads and little consideration is given during the design process to their performance under seismic loading. The lateral displacements experienced by structures responding to seismic loads place significant local deformation dem ands at these “pinned end” shear connections. In certain instances these demands exceed the ability of the connection to respond and maintain structure continuity. This paper investigates the nature of the deformation demand placed on single plate shear connections, develops an analysis method, and recommends a deformation limit state for the connections to be used during their design and evalu ation.