bluuebunny/crossref_metadata_2025 huggingface dataset:
On Seismic Design Implications of the 1994 Northridge Earthquake Records
Authors: Naeim Farzad
Published: July 2003

Significant earthquake resistant design characteristics of selected 1994 Northridge strong motion records are evaluated. Instrumental, spectral, and energy content attributes of the records are examined. Seismic design implications of these data are discussed. The weaknesses of the current seismic design philosophy in dealing with near-field strong ground motions representing significant acceleration pulses is demonstrated and recommendations to improve both the demand side and the capacity side of the current seismic design formulations are provided.
Building Reliability and Code Calibration
Authors: Wen Y. K.
Published: July 2003

Designs of buildings and structures for seismic loads are traditionally based on experience on performance of structures in past earthquakes. The large variability in the earthquake loadings has long been recognized by engineers but not fully accounted for in the code procedures. Although the selection of the design earthquake is based on probability, since it is used in conjunction with a series of factors depending on structural period, site soil conditions, inelastic behavior, importance of the structure e.t.c., the reliability and safety of the final design remains unknown and undefined. The recent sentiment of the research community and design professionals is that there is a need to develop design formats based more on consideration of the physics of the problem and explicit treatment of the variabilities and uncertainties. Such format may be used as the basis for developing future building codes. This paper summarizes some recent developments in this area; in particular, reliability evaluation and comparison of buildings designed in accordance with current code procedures in different countries and development of design procedures and formats based on multi-level, probabilistic structural performance criteria.
Seismic Damage Indices for Concrete Structures: A State-of-the-Art Review
Authors: Williams Martin S. , Sexsmith Robert G.
Published: July 2003

This paper gives a review of seismic damage indices, with particular reference to their use in retrofit decision making. Damage indices aim to provide a means of quantifying numerically the damage in concrete structures sustained under earthquake loading. Indices may be defined locally, for an individual element, or globally, for a whole structure. Most local indices are cumulative in nature, reflecting the dependence of damage on both the amplitude and the number of cycles of loading. The main disadvantages of most local damage indices are the need for tuning of coefficients for a particular structural type and the lack of calibration against varying degrees of damage. Global damage indices may be calculated by taking a weighted average of the local indices throughout a structure, or by comparing the modal properties of the structure before and after (and sometimes during) the earthquake. The weighted-average indices are prone to much the same problems as the local indices. The modal indices vary widely in their level of sophistication, those capable of detecting relatively minor damage requiring the accurate determination of a large number of modes of vibration. The development and application of damage indices has until now concentrated almost exclusively on flexural modes of failure; there is a clear need to investigate the ability of the indices to represent shear damage.
Behavior of Bridge Outrigger Knee Joint Systems
Authors: Thewalt Christopher R. , Stojadinović Božidar
Published: July 2003

The catastrophic collapse of the Cypress Street Viaduct during the 1989 Loma Prieta earthquake emphasized the vulnerability of older elevated freeway bridge structures. One part of a joint Caltrans/University of California at Berkeley research project is the investigation of outrigger knee joints found in elevated freeway bents. This project has two principal goals: to evaluate the behavior of the existing outrigger knee joint systems under a combined transverse and longitudinal loading, and to design and experimentally verify upgrading strategies and repair techniques suitable for application on the existing elevated freeways. The primary focus of this paper will be to present the behavior of the as-built and upgraded systems, but an overview of the design method and the analytical tools used in the upgrade will also be presented.
The Continuing Challenge: Report on the Performance of State Bridges in the Northridge Earthquake
Authors: Housner George W. , Thiel Charles C.
Published: July 2003

Bridges affected by the Northridge earthquake were examined to evaluate the performance of Caltrans bridges, retrofit and peer review programs, and technical procedures. All structures in the region of strong shaking that had been retrofitted since 1989 performed adequately; if the seven bridges that collapsed had been retrofitted, they would be expected to have survived with little damage. The bridges subjected to strong shaking that had been constructed or retrofitted to current Caltrans criteria had, at most, minor damage; all remained in service. The Seismic Advisory Board concluded that the Caltrans seismic design procedures for new bridges and its retrofit procedures for existing hazardous bridges are technically sound. The Board found that the retrofit program is proceeding fairly well, but that the screening methods used to identify hazardous bridges could be improved as could the pace of retrofitting, particularly toll bridges. There were no construction projects underway in the Spring of 1994 for toll bridges, nor had preparation of retrofit designs begun. Twenty-one findings and seventeen recommendations are presented. Although much has been accomplished, much remains to be done. With some improvements, the Caltrans program should be continued with dispatch and determination. The major foreseeable impediments to a successful program are inadequate or fluctuating funding. The Seismic Advisory Board has confidence that the California highway system is progressing in an orderly fashion to one that is significantly more seismically safe.
Effects of Scale and Loading Rate with Tests of Concrete and Masonry Structures
Authors: Abrams Daniel
Published: July 2003

Static and dynamic response of large-scale and reduced-scale test structures are correlated to discern effects attributable to scale and loading rate. Three case studies are presented where reduced-scale models were subjected to dynamic excitation using a shaking table. The test structures were: (a) multi-story reinforced masonry building systems, (b) two-story unreinforced masonry bearing and shear wall systems, and (c) ten-story reinforced concrete frame-wall systems. For each study, static testing of either critical components, or of the complete structural system, was done at a large scale to examine differences attributable to the modeling method, or to the loading procedure.
Application of Pseudodynamic Test Method to Structural Research
Authors: Shing P. Benson , Nakashima Masayoshi , Bursi Oreste S.
Published: July 2003

The pseudodynamic test method is intended as an efficient and powerful alternative to the shaking table test method. Since its inception, a variety of new testing techniques and numerical schemes have been developed to improve the efficiency and accuracy of the method. The main objective of this paper is to present the pseudodynamic test method from a user's perspective. With this objective in mind, an overview of the pseudodynamic test method is provided. Some of the most up-to-date developments, including substructure testing techniques, are illustrated with test examples. It is shown that while the method is definitely more complicated than conventional quasi-static tests, it can be implemented and applied to structural research with a small incremental cost.
Simulated Seismic Laboratory Load Testing of Full-Scale Buildings
Authors: Seible Frieder , Hegemier Gilbert , Igarashi Akira
Published: July 2003

Full-scale building systems have been tested to-date in Japan, the United States, and Europe under controlled laboratory conditions with simulated seismic loads, to determine behavior and design limit states and to calibrate predictive analytical and design models. Seismic load simulation for these tests consisted of increasing cyclic load/deformation patterns with predetermined load distribution or, where possible, of loading patterns derived experimentally from the measured building response in conjunction with updated displacement time-histories through pseudo-dynamic testing. Difficulties in the pseudo-dynamic testing of stiff multi-story buildings due to the tight coupling between individual actuators, stability problems with the numerical integration alorithms, measurement errors and error growth, as well as the control of undesirable torsional modes, were addressed with innovations in the testing hardware and in the actuator control alorithms in the first US full-scale building test of a 5-story reinforced masonry building.
Considerations for the Use of Quasi-Static Testing
Authors: Leon Robert T. , Deierlein Gregory G.
Published: July 2003

While advances in servo-hydraulic technology and computer simulation are making real-time pseudo-dynamic and shake table testing more feasible for research in earthquake engineering, quasi-static testing will remain the most prevalent form of testing for the foreseeable future. This paper describes the evolution of quasi-static testing, discusses by means of an example the main issues involved in developing a quasi-static testing program, and describes some of the advantages and limitations of this mode of testing.
Testing of Masonry Structures for Seismic Assessment
Authors: Calvi G. Michele , Kingsley Gregory R. , Magenes Guido
Published: July 2003

The experimental evaluation of strength, deformability, and energy dissipation capacity of unreinforced masonry buildings subjected to seismic loadings presents unique and complex problems, both for laboratory and field evaluations. The paper addresses these problems, focusing on the relative merits and roles of several experimental techniques, including quasistatic, dynamic, and pseudodynamic loadings at full and reduced scale.
Dynamic Properties of a Circuit Breaker with Friction-Based Seismic Dampers
Authors: Kar R. , Rainer J. H. , Lefrançois A. C.
Published: July 2003

The design parameter of 1.05 g peak seismic ground acceleration for a 300 kV SF6 circuit breaker necessitated the provision of supplemental friction-based dampers. This paper describes the dampers and the dynamic properties of the circuit breaker as obtained from a series of pull-release tests with increasing force amplitudes. These tests permitted a determination of a wide range of damping ratios and natural frequencies as a function of displacements. A comparison is also presented between the measured and the calculated damping ratios and frequencies, using common engineering approximation of the energy dissipated per cycle for damping, and a discrete parameter and linearized stiffness approach for the calculation of natural frequency. Reasonable comparisons were achieved between the measured and calculated values.
Site Response Studies for Purpose of Revising NEHRP Seismic Provisions
Authors: Crouse C. B. , McGuire J. W.
Published: July 2003

A strong motion database was compiled for California earthquakes of surfacewave magnitudes, Ms ≥ 6, occurring from 1933 through 1992. The database consisted of horizontal peak ground acceleration and 5 percent damped response spectra of accelerograms recorded on four different local geologies: rock (class A), soft rock or stiff soil (class B), medium stiff soil (class C), and soft soil (class D). The results of analyses of the database within each of these site classes were used to derive a set of site-dependent spectral amplification factors for oscillator periods between 0.1 and 4.0 sec and ground acceleration levels between 0.1 and 0.4 g. The amplification factors at 0.3 and 1.0 sec periods (designated as Fa and Fv, respectively) are generally within 20 percent of those recommended during the 1992 Site Response Workshop conducted by the National Center for Earthquake Engineering Research (NCEER). The Fa and Fv values recommended from our study and those from the NCEER workshop are intended for use by code committees making future revisions to the National Earthquake Hazard Reduction Program (NEHRP) seismic provisions and the Uniform Building Code.
Retrofit of Non-Ductile Moment-Resisting Frames Using Precast Infill Wall Panels
Authors: Frosch Robert J. , Li Wanzhi , Jirsa James O. , Kreger Michael E.
Published: July 2003

Many existing reinforced concrete moment-resisting frames located in seismic zones lack strength and ductility. One approach for correcting these deficiencies is the construction of infill walls to strengthen and stiffen the structure. Cast-in-place construction is often used; however, there are conditions where cost, time constraints, or limiting disruptions to building operations may dictate other solutions. One possible modification is the use of infill walls constructed of precast concrete panels. A precast infill wall system eliminates the need for large formwork during construction. Elimination or reduction of connection hardware between precast panels or between panels and the existing frame element can provide additional efficiency. Problems associated with casting large quantities of concrete in an existing building are eliminated. Construction time and inconvenience to occupants may be reduced along with the costs. The precast system has the potential of reducing the overall costs of rehabilitating existing structures.
Out-of-Plane Strength of Unreinforced Masonry Infill Panels
Authors: Abrams Daniel P. , Angel Richard , Uzarski Joseph
Published: July 2003

Simple procedures are presented for estimating out-of-plane strength of unreinforced masonry infill panels. The procedures are based on an experimental study and subsequent development of an analytical model, which are described as a preface to derivation of a simple and approximate expression for estimating out-of-plane strength of a general class of infill panels. An example is given illustrating application of the proposed guideline.
Stochastic Response Comparison between Base Isolated and Fixed-Base Structures
Authors: Palazzo Bruno , Petti Luigi
Published: July 2003

Random response of linear Base Isolated Systems, mounted on elastomeric bearings, subject to horizontal random excitations, is analyzed in comparison with the one of the fixed-base structures. Considering the superstructure motion described by its first modal contribution, a two-degree-of-freedom equivalent linear model, under stationary Gaussian excitations modelled by the modified Kanai-Tajimi power density spectrum, has been used in the analysis. The response sensitivity to design parameters for the superstructure and the isolators have been evaluated for a wide range of parameters. Optimum viscous damping and isolation degree values which minimize structural response are also obtained. Some implications of these results for the design and code requirements are discussed.
Models and Methods to Characterize Site Amplification from a Pair of Records
Authors: Şafak Erdal
Published: July 2003

The paper presents a tutorial review of the models and methods that are used to characterize site amplification from the pairs of rock- and soil-site records, and introduces some new techniques with better theoretical foundations. The models and methods discussed include spectral and cross-spectral ratios, spectral ratios for downhole records, response spectral ratios, constant amplification factors, parametric models, physical models, and time-varying filters. An extensive analytical and numerical error analysis of spectral and cross-spectral ratios shows that probabilistically cross-spectral ratios give more reliable estimates of site amplification. Spectral ratios should not be used to determine site amplification from downhole-surface recording pairs because of the feedback in the downhole sensor. Response spectral ratios are appropriate for low frequencies, but overestimate the amplification at high frequencies. The best method to be used depends on how much precision is required in the estimates.
Seismic Response of an Instrumented 13-Story Steel Frame Building Damaged in the 1994 Northridge Earthquake
Authors: Uang Chia-Ming , Yu Qi-Song , Sadre Ali , Bonowitz David , Youssef Nabih , Vinkler Jacqueline
Published: July 2003

This paper summarizes a case study of a 13-story welded steel moment frame (WSMF) building affected by the 1994 Northridge earthquake. The building, which was instrumented, sustained extensive damage to its welded connections. Ground motion records from the basement and response records from the sixth and twelfth floors were available. Damage data was collected with post-earthquake inspection and testing of each joint. The primary objective of the study was to compare modeled behavior with recorded response in order to assess the value of present analytical tools and modeling techniques for predicting the distribution and severity of connection failures. Calculated elastic time-history displacements matched well with recorded displacements in the E-W direction, less so in the heavily-damaged N-S direction where the elastic model was unable to simulate fractured moment connections. In the elastic analyses, joint demand was represented by beam demand-capacity ratios (DCRs). The highest beam DCRs were concentrated between the second and seventh floors; these locations correlated strongly with observed damage. Inelastic time-history analyses improved the displacement match in the N-S direction. They also indicated that panel zone yielding would have controlled the intended ductile response. This study suggests that for a regular structure, current modeling and analysis tools for both elastic and inelastic analysis, while unable to simulate premature brittle fractures, can be useful for predicting in a probabilistic way the intensity and distribution of damage expected in moderate seismic events.
EERI Annual Student Paper Award a Multidisciplinary Urban Earthquake Disaster Risk Index
Authors: Davidson Rachel
Published: July 2003

The Earthquake Disaster Risk Index (EDRI) is a composite index that will allow direct comparison of the relative overall earthquake disaster risk of cities worldwide, and will describe the relative contributions of various factors to that overall risk. The basic development of the EDRI involves (1) creating a conceptual framework of all the factors that contribute to earthquake disaster risk—geological, engineering, economic, social, political, and cultural factors; (2) identifying simple, measurable indicators to represent each of the factors in the framework; (3) combining the indicators mathematically into the composite EDRI; and (4) presenting the results in an easily understandable form. The index is being created using a holistic, multidisciplinary approach that aims to synthesize knowledge of urban earthquake disaster risk into a concise, easily accessible summary that is currently unavailable from any other source.
Are Existing Seismic Torsion Provisions Achieving the Design Aims?
Authors: Paulay Thomas
Published: July 2003

A simple approach to the consideration of torsional effects on the ductile seismic response of buildings is suggested. Instead of increasing torsional strength, the control of twist, which may amplify local inelastic translational deformations, is emphasised. This may be achieved when assuring in the design that some residual stiffness in ductile systems is available. To this end a classification in terms of torsional restraint is suggested. It is postulated that traditional codified techniques, based on the evaluation of torsional effects on elastic systems, are largely irrelevant to ductile structural response. The primary consideration of inelastic deformation demands rather than strength is advocated. The presentation addresses foremost concepts of torsional behaviour and their relevance to routine seismic design, rather than advancement in analytical techniques.
Design of Soft Stories—A Simplified Energy Approach
Authors: Scarlat Adrian S.
Published: July 2003

Most specialists dealing with earthquake engineering agree that soft stories represent a major reason for buildings collapses during major earthquakes, but seismic forces acting upon soft stories have not yet been quantified. The author proposes an energy approach yielding equivalent static forces to be taken into account in the design of resisting elements of soft stories. It is based on interpolation between two extreme situations: uniform structures and rigid structures supported by a soft story. Although the solution is based on quantifying the plastic energy absorbed during the seismic motion, it is shown that the effective computations can be performed in the elastic range.
Evaluation of a Four-Story Reinforccd Concrete Building Damaged during the Northridge Earthquake
Authors: Hueste Mary Beth D. , Wight James K.
Published: July 2003

A four-story reinforced concrete (RC) frame structure damaged during the Northridge Earthquake was evaluated to determine if punching shear failures that occurred at interior slab-column connections could be post-calculated using analytical methods. The building was evaluated using: 1) a code level strength analysis, 2) a static nonlinear (“pushover”) analysis, and 3) a dynamic nonlinear response analysis using ground motions recorded within 1 km (0.6 mi.) of the building. Based on design material properties and field observations, both the static and dynamic nonlinear analyses were able to successfully post-calculate the observed punching shear failures.
Stability of Isolators at Large Horizontal Displacements
Authors: Imbimbo Maura , Kelly James M.
Published: July 2003

Elastomeric bearings used as seismic isolators are susceptible to a buckling type of instability similar to that of structural columns. The buckling load and buckling behaviour can be determined from an elastic analysis of the isolator modelled as a continuous composite column with bending and shear flexibility; this analysis cannot be used, however, to assess the post-buckling behaviour or the stability of the isolator at large horizontal displacements. By using a two-spring rigid link model that considers large angles without using linear approximations, it is possible to predict the post-buckling behaviour of an isolator. Using the simple closed form expression, this paper will model three aspects of post-buckled isolator behaviour: the dependence of horizontal stiffness on vertical load, the stability at large horizontal displacements, and the increase of horizontal displacement with respect to axial load and vertical displacement.
Earthquake Damage and Loss Estimation Methodology and Data for Salt Lake County, Utah (ATC-36)
Authors: Rojahn Christopher , King Stephanie A. , Scholl Roger E. , Kiremidjian Anne S. , Reaveley Lawrence D. , Wilson Robert R.
Published: July 2003

As a follow on to the Applied Technology Council (ATC) project to develop earthquake damage evaluation data for California (ATC-13 project), ATC has conducted a project to update and translate the ATC-13 data and methodology for use in Salt Lake County, Utah (ATC-36 project). Methodology has been developed and/or updated for: (1) estimation of damage due to ground shaking, (2) estimation of damage due to collateral loss causes such as fault rupture, ground failure, inundation, and fire following earthquake, (3) estimation of time to restore damaged facilities to pre-earthquake usability, and (4) estimation of deaths and injuries. In addition, an electronic inventory of approximately 200,000 structures (buildings and lifeline systems) within Salt Lake County has been developed. The data and methodology have been developed for implementation in a geographic information system (GIS) application, or in a non-GIS software application, such as a relational database management system or spreadsheet.
Development of Building Damage Functions for Earthquake Loss Estimation
Authors: Kircher Charles A. , Nassar Aladdin A. , Kustu Onder , Holmes William T.
Published: July 2003

This paper describes building damage functions that were developed for the FEMA/NIBS earthquake loss estimation methodology (Whitman et al., 1997). These functions estimate the probability of discrete states of structural and nonstructural building damage that are used as inputs to the estimation of building losses, including economic loss, casualties and loss of function (Kircher et al., 1997). These functions are of a new form and represent a significant step forward in the prediction of earthquake impacts. Unlike previous building damage models that are based on Modified Mercalli Intensity, the new functions use quantitative measures of ground shaking (and ground failure) and analyze model building types in a similar manner to the engineering analysis of a single structure.
The Role of Earthquake Hazard Maps in Loss Estimation: A Study of the Northridge Earthquake
Authors: Olshansky Robert B.
Published: July 2003

Local-scale seismic hazard maps are an important component of loss estimation because they provide information on possible site effects. This paper evaluates how well seismic hazard maps predicted damage in the Northridge earthquake. Normalizing for residential density, the research found that structures built on several geologic map units shown on pre-1994 hazard maps had significantly more damage than the area-wide average. Specifically, buildings on fine-grained Holocene alluvium, hillside bedrock, and “moderate” and “very high” liquefaction susceptibility zones were 1.5 to 2.5 times more likely to be damaged than the area average. Pipes were four times more likely to break in “very high” liquefaction susceptibility zones than in the area as a whole. The use of hazard maps in loss estimation can help state and local governments to set priorities in managing land use, enforcing building codes, conducting seismic strengthening programs for existing structures, and planning for emergency response and longterm recovery.
Advances in Earthquake Loss Estimation and Application to Memphis, Tennessee
Authors: Shinozuka Masanobu , Chang Stephanie E. , Eguchi Ronald T. , Abrams Daniel P. , Hwang Howard H. M. , Rose Adam
Published: July 2003

In recent years, a number of research efforts conducted through the National Center for Earthquake Engineering Research (NCEER) have focused on assessing seismic hazard and vulnerability in the Central United States. These multi-year, coordinated multi-investigator research efforts culminated in two loss estimation demonstration projects for Memphis (Shelby County), Tennessee, that evaluate losses associated with buildings and lifelines, respectively. While conducted independently, these two loss estimation studies share similar approaches, such as the emphasis on using detailed local data. Furthermore, the significance of the projects derives not only from the advances made by individual investigators, but also from the innovations developed in synthesizing the various studies into a coordinated loss estimation effort. This paper discusses the NCEER buildings and lifelines loss estimation projects with emphasis on methodological advances and insights from the loss estimation results.
Seismic Performance Evaluation of Fire Stations in Shelby County, Tennessee
Authors: Hwang Howard H. M. , Lin Huijie , Huo Jun-Rong
Published: July 2003

This paper presents an evaluation of the seismic performance of fire stations in Shelby County, Tennessee. Data relevant to 71 fire stations were collected and implemented as a database using Professional MapInfo. The peak ground accelerations resulting from two scenario earthquakes with moment magnitudes of 6.5 and 7.0 at Marked Tree, Arkansas, were estimated at these fire stations. Furthermore, the fragility curves for various types of buildings in the Memphis area were established based on the fragility data available in the literature. Using these fragility curves, the expected damage to all the fire stations caused by both scenario earthquakes was determined. The results indicate that most of the fire stations will suffer moderate to heavy damage and are expected to be out of operation after the earthquakes. Thus, the authorities need to take appropriate action to mitigate the risks posed by the loss of fire stations.
Seismic Microzonation and Estimation of Earthquake Loss Scenarios: Integrated Risk Mitigation Project of Bogotá, Colombia
Authors: Cardona Omar D. , Yamín Luis E.
Published: July 2003

The Universidad de los Andes and the National Institute of Geosciences INGEOMINAS, with the financial support of the national and the municipal governments, have been executing studies to evaluate the seismic hazard and the urban seismic risk for three hypothetical earthquakes that could strike Bogotá, the capital city of Colombia. After having obtained results related to soil amplification using soil dynamic lab studies, analysis of strong-motion records of recent earthquakes and microtremor measurements in a wide area of Bogotá, the study of different scenarios of losses were estimated for different types of buildings and lifelines systems. These earthquake loss estimations have been used by national and local disaster preparedness authorities to design emergency response plans for public information and for educational activities. New requirements are being studied for urban planning, updating the earthquake resistance construction code and for the reinforcement of the seismic rehabilitation of key buildings.
The Spectral Source Model: A Tool for Deterministic and Probabilistic Seismic Hazard Assessment
Authors: Berge Catherine , Herrero André , Bernard Pascal , Bour Myriam , Dominique Pascal
Published: July 2003

Seismic-hazard assessment at small scales requires the computation of realistic broad-band accelerograms near the sources. Methods that use only natural records are often limited because of the limited data set. Among recently developed methods for source modelling, the spectral-source model, based on the k−2 dislocation distribution seems particularly promising as it enables computation of synthetics for any source-receiver distance and directivity configuration. The spectral model takes into account important source characteristics, such as stress drop and directivity effects predicting acceptable high-frequency levels, whatever the station location (Bernard et al., 1996b). Firstly, some tests to explain the directivity properties of the model are presented, followed by the main results of a deterministic study carried out for the 1992 Erzincan earthquake, Turkey. Finally, results of a probabilistic study in the Moyenne-Durance region (France) are used to demonstrate the ability of this method to produce seismic-hazard maps and spectra linked to a specific return period.
Effects of Isolation Damping on Stochastic Response of Structures with Nonlinear Base Isolators
Authors: Jangid R. S. , Banerji P.
Published: July 2003

Optimum isolator damping required to minimize absolute acceleration responses to stochastic ground motions in buildings with non-linear resilient-friction base isolation (R-FBI) devices is studied. Using a stochastic equivalent linearization technique, an analytical expression is developed for estimating optimum material damping values in an R-FBI system for a rigid superstructure. This optimum damping value depends on the effective time period and friction coefficient of the R-FBI system and the design earthquake intensity. The fixed base structural time period, damping, and the number of stories also affect the optimum isolator damping values, if the superstructure is flexible. However, the analytical expression mentioned above provides an upper-bound optimum isolator damping value for any superstructure with an R-FBI system subjected to a given earthquake intensity. Comparison of optimum damping values for a linear isolator and the R-FBI system, with identical lateral stiffness properties, illustrates the beneficial effect of sliding friction in reducing the optimum damping in the latter type of isolator, for a given earthquake intensity.
Observed Variation of Earthquake Motion across a Basin—Taipei City
Authors: Loh Chin-Hsiung , Hwang Jeng-Yaw , Shin Tzay-Chyn
Published: July 2003

Local site amplification of sedimentary deposit during earthquakes is an important issue in strong ground motion analysis. The phenomenon is more obvious for sediment basin. From the strong-motion instrumentation network of Taipei basin, the ground motion characteristics of the basin effects are studied from two seismic events: the June 5, 1994 earthquake with ML = 6.57 and the June 25, 1995 earthquake with ML = 6.50. The objective is to investigate the effects of the basin structure on the patterns of the recorded ground motions. The analyses include: (1) response spectrum and spectral ratio analyses; (2) correlation of seismic source, PGA distribution and strong-motion duration with site amplification, (3) principal direction analysis of seismic waves in the basin. The observed variations of ground motion across the basin are different from each other because of the basin effect. It means that for the Taipei basin, the basin effects for shallow sources are going to be much more significant than for the deep sources.
Scaling Procedure for Natural Accelerograms Based on a System of Spectrum Intensity Scales
Authors: Martínez-Rueda Juan Enrique
Published: July 2003

A parametric study on the scaling of natural accelerograms using spectrum intensity scales is presented. A series of nonlinear time-history analyses for a SDOF system is conducted using an ensemble of world-wide damaging earthquake records for a wide range of seismic conditions. Structural parameters considered in the study include: yield seismic coefficient, yield natural period and postyield stiffness. The effectiveness of several spectrum intensity scales is evaluated in terms of their correlation with displacement ductility demand. Results indicate that there is not a unique scale with best performance over the entire range of strength and stiffness. An alternative combined criterion to define spectrum intensity is proposed in terms of a system of spectrum intensity scales. The system optimises the correlation between spectrum intensity and displacement ductility demand. This is achieved by defining regions in the space of structural parameters for which it is possible to identify a spectrum intensity scale of best performance.
Effect of Site Amplification and Basin Response on Strong Motion in Las Vegas, Nevada
Authors: Su Feng , Anderson John G. , Der Ni Shean , Zeng Yuehua
Published: July 2003

The June 29, 1992, Little Skull Mountain earthquake (M=5.6) was recorded at nine strong-motion stations in Las Vegas, Nevada. Ground motion on alluvial sites is much greater than on rock sites, especially at low frequencies, and had a longer duration than expected. Five of the seven stations on sediment have Fourier spectral amplifications that average at least a factor of five greater than the rock reference sites from 0.5 to 2 Hz. Thus, large earthquakes at moderate distances, that would excite strong long-period waves, are a concern. We generated synthetic seismograms, including the site amplification, for magnitude 7.4 earthquakes on the Death Valley fault system 150km from Las Vegas. The synthetics have average peak accelerations ranging from 0.058 to 0.13g at the rock and from 0.051 to 0.22g at the sediment sites. The average peak velocity and displacement is 49 cm/sec and 33 cm, respectively, on the larger component of a sediment site.
EERI Annual Student Paper Award Confinement of Rectangular Bridge Columns in Moderate Seismic Areas
Authors: Wehbe Nadim
Published: July 2003

The work presented in this paper examines the ductility and behavior of rectangular reinforced concrete bridge columns with moderate confinement. Four half-scaled rectangular columns were built and tested. The transverse reinforcement ratios provided in the strong direction of the column specimens corresponded to 46 percent and 60 percent of the minimum lateral reinforcement required by AASHTO for seismic detailing. Each specimen was tested under constant axial load while subjected to quasi-static cyclic lateral loading in the column strong direction. The axial load indexes were 10 percent and 25 percent. The specimens exhibited displacement ductilities ranging between 5 and 7. Based on analytical and experimental results, a simple design equation relating the amount of confinement steel to attainable displacement ductility was developed.
The NSF Earthquake Disaster Mitigation Research Program
Authors: Liu S. C. , Anderson W. , Astill C. , Weber L.
Published: July 2003

This paper presents several major developments and research initiatives of NSF's program in earthquake hazard mitigation. These activities include (1) establishment of three new earthquake engineering research centers in the U.S., (2) initiation of a major five-year cooperative research program on urban earthquake disaster mitigation between the U.S. and Japan, (3) initiation of two joint center-to-center projects between the U.S. and Japan, and (4) planning for a high-performance earthquake simulation facility network in the U.S. These activities highlight the ever-increasing importance of research innovations for earthquake disaster mitigation and the continuing challenges for cooperation between the U.S. and Japan.
A Parametric Approach to Performance-Based Numerical Seismic Design
Authors: Teran-Gilmore Amador
Published: July 2003

The economic losses during recent seismic events, partially a product of the inadequate performance of modern buildings, have outlined the need to improve our current seismic design procedures. Current procedures lay out the design problem considering explicitly the demand-supply pairs of strength and stiffness. These two mechanical characteristics are estimated from the same design parameter: the base shear. That is, current procedures are based on a parametric approach, and in particular, on a one-parameter approach. Although it may be desirable to keep the parametric approach, it is necessary to establish design procedures that contemplate the use of more than one design parameter, in such a way that all relevant mechanical characteristics (e.g., strength, stiffness and deformation) can be designed rationally. Although currently it is possible to formulate a parametric approach to performance-based seismic design, ambitious educational and research programs should be undertaken to make possible its practical implementation.
Roof Isolation System to Reduce the Seismic Response of Buildings: A Preliminary Assessment
Authors: Villaverde Roberto
Published: July 2003

A roof isolation system is proposed as a means to reduce the detrimental effect of earthquakes in buildings. This roof isolation system entails the insertion of flexible laminated rubber bearings between a building's roof and the columns that support it, and the addition of viscous dampers connected between the roof and the rest of the building. The properties and dimensions of the rubber bearings and viscous dampers are selected in a way that makes the roof, bearings, and dampers form a highly damped vibration absorber. Presented also is a comparative study with a simple five-story steel building under a strong earthquake ground motion that is carried out to assess the effectiveness of the proposed system. In this comparative study, it is found that the roof isolation scheme reduces the floor displacements and interstory drifts of the analyzed building by as much as 83 percent. On the basis of these results and in view of its simplicity, it is concluded that the proposed roof isolation system has the potential to become a practical and effective way to reduce earthquake damage in buildings.
Shear-Wave Velocity Characteristics of Geologic Units in California
Authors: Wills Christopher J. , Silva Walter
Published: July 2003

Site conditions can be classified by the average shear-wave velocity to 30 meters (Vs30) and used for estimating site effects in seismic hazard calculations. Large scale seismic hazard maps, which include site effects, may be produced, providing Vs30 can be well correlated with geologic units. Vs30 values for several geologic units can be easily classified into soil profile types of the UBC (ICBO 1997). Most geologic units have wide variations in Vs30 and some extensive geologic units, such as older alluvium, the Franciscan Complex or the Puente Formation cannot be easily classified.
Post-Northridge Earthquake Seismic Steel Moment Connections
Authors: Popov Egor P. , Balan Toader A. , Yang Tzong-Shuoh
Published: July 2003

After the 1994 Northridge earthquake a tremendous amount of research activity was generated in the United States. In this paper on introducing the basic concepts of seismic design, and illustrating a typical pre-Northridge earthquake steel connection, the fundamental reasons of the poor behavior of the connections are discussed. Then the development of the so-called Dog Bone connection is brought in. Experimental results on two connections of this type are discussed in detail. The reasons for good behavior of Dog Bone connections are then explained using three-dimensional von Mises yield criterion. This new analytical demonstration provides solid evidence as to why the Dog Bone connections behave well. The problem of torsional instability of these connections is not considered.
On the Correlation of Seismic Intensity with Fourier Amplitude Spectra
Authors: Sokolov V. Yu , Chernov Yu K.
Published: July 2003

This paper presents a method for estimating the seismic intensity (MMI or MSK scale) using Fourier amplitude spectra of ground acceleration. The method implies that the severity of earthquake ground motion is determined by spectral amplitudes in a relatively narrow frequency band: so-called “representative frequencies”, at decreasing frequencies (from 7-8 Hz for small intensities to 0.7-1.0 Hz for MMI=VIII-IX) with increasing intensity level. It is examined through estimation of probable intensity at a site using recordings of recent earthquakes in several seismic regions, and prediction of intensity distribution patterns for the Coalinga, California earthquake of May 2, 1983, and the Spitak, Armenia earthquake of December 7, 1988. Seismic hazard maps, in terms of intensity levels based upon the proposed approach, should describe regional features of seismic waves excitation and propagation, as well as local ground conditions.
Effects of Prior Earthquake Damage on Response of Simple Stiffness-Degrading Structures
Authors: Aschheim Mark , Black Edgar
Published: July 2003

A systematic study involving over 20,000 single-degree-of-freedom (SDOF) analyses was made to assess the effects of prior earthquake damage on the peak displacement response of simple oscillators. Principal variables were oscillator strength, period of vibration, degree of prior damage, and load-deformation relation. Base input was provided by 18 recorded ground motions, representing different frequency content, duration, and the presence or absence of near-field forward directivity effects. Prior damage was modeled as a reduction in initial stiffness under the assumption that residual displacements are negligible. The study is restricted to cases in which prior demands are less than those that would result if the structure were initially undamaged. For these conditions, prior damage usually has a minor effect on peak displacement response. This was observed for SDOF oscillators having the Takeda load-deformation relation with positive post-yield stiffness and for a modified Takeda relation incorporating pinched hysteresis and strength degradation. Takeda oscillators with negative post-yield stiffness were prone to collapse, whether or not they had experienced prior damage.
The Dynamic Response of Wood-Frame Shear Walls with Viscoelastic Dampers
Authors: Dinehart David W. , Shenton Harry W. , Elliott Timothy E.
Published: July 2003

Results are presented of an experimental investigation, the objectives of which were to evaluate and compare the performance of conventional plywood shear walls with walls that include viscoelastic (VE) dampers. Cyclic tests were conducted on conventional walls and walls with VE dampers; five different damper configurations were tested. The walls with the VE dampers showed an increase in the total energy dissipation and an increase in the effective stiffness, relative to the conventional wall, with increases in energy dissipation as high as 59 percent. Tests demonstrated that the sheathing-to-stud and corner dampers can easily be installed within the confines of the wall and can be utilized without impacting the design, construction, or finishing of the shear wall. The results demonstrate that addition of the viscoelastic dampers significantly enhanced the dynamic performance of the walls by increasing the energy dissipation capacity and providing a constant source of energy dissipation.
Spectral Ratios for Mexico City from Free-Field Recordings
Authors: Reinoso Eduardo , Ordaz Mario
Published: July 2003

Spectral ratios obtained for lakebed sites with respect to the average Fourier spectra of the Southwest hill-zone sites in the Mexico City Valley are presented. The amount and quality of data used allowed us to measure relevant amplification characteristics. For all earthquakes, the ratios are relatively constant regardless the magnitude, epicentral distance and azimuth of subduction and normal faulting earthquakes. With data recorded at Station Central de Abastos, it is shown that these ratios are a much better approach than horizontal to vertical ratios, which yield only a rough estimation of site amplification. Also for Central de Abastos, where little nonlinear behavior has been observed, an empirical approximation is used to account for these effects. We also built maps of equal amplification that exhibit those zones that have experienced damage during earthquakes and those at the highest risk. The ratios presented here are useful and reliable to accurately predict the amplification of motion.
The Aqaba Earthquake of November 22, 1995
Authors: Malkawi Abdallah I. Husein , Numayr Karim S. , Barakat Samer A.
Published: July 2003

This study concentrates on the assessment of the structural damages caused by the Aqaba earthquake and attempts to give a better understanding of the geological, geotechnical and structural response following an earthquake event, through focusing on the understanding of the dynamic response of local site conditions to strong shaking and assessing structural performance. Furthermore, this paper calls for future efforts toward enforcing the seismic code provisions for all structures and improving the construction practices in a seismic prone region.
Push-over Analysis Procedure in Earthquake Engineering
Authors: Kim Simon , D'Amore Enzo
Published: July 2003

There has been an increasing trend toward the use of “push-over” analysis as a tool for evaluation of the safety of structures during earthquakes. A variety of existing push-over analysis procedures are currently being consolidated under programs such as ATC40 and FEMA273. This paper is a critical review of the currently proposed push-over analysis procedure, and a case study in which the proposed methodology is evaluated.
RC Building Damage Statistics and SDF Response with Design Seismic Forces
Authors: Otani Shunsuke
Published: July 2003

This paper introduces the damage statistics of reinforced concrete buildings after the 1985 Mexico earthquake, the 1990 Ruzon (Philippines) earthquake, the 1992 Erzincan (Turkey) earthquake, and the 1995 Hyogo-ken Nanbu (Kobe) earthquake. These data were obtained in severely damaged areas in each earthquake through the inventory damage investigation of the Architectural Institute of Japan teams. The damage statistics indicated severer damage in taller buildings and significantly less damage in low-rise buildings. A series of nonlinear single-degree-of-freedom systems having minimum code required lateral resistance were analyzed using the earthquake motions recorded near the area of damage survey. Contrary to the statistics, the nonlinear response analysis results showed higher ductility demand (damage) in lower buildings.