Design Response Spectrum Research Articles

A comparison of IBC with 1997 UBC for modal response spectrum analysis in standard-occupancy buildings

This paper presents a comparison of the seismic forces generated from a Modal Response Spectrum Analysis (MRSA) by applying the provisions of two building codes, the 1997 Uniform Building Code (UBC) and the 2000–2009 International Building Code (IBC), to the most common ordinary residential buildings of standard occupancy. Considering IBC as the state of the art benchmark code, the primary concern is the safety of buildings designed using the UBC as compared to those designed using the IBC. A sample of four buildings with different layouts and heights was used for this comparison. Each of these buildings was assumed to be located at four different geographical sample locations arbitrarily selected to represent various earthquake zones on a seismic map of the USA, and was subjected to code-compliant response spectrum analyses for all sample locations and for five different soil types at each location. Response spectrum analysis was performed using the ETABS software package. For all the cases investigated, the UBC was found to be significantly more conservative than the IBC. The UBC design response spectra have higher spectral accelerations, and as a result, the response spectrum analysis provided a much higher base shear and moment in the structural members as compared to the IBC. The conclusion is that ordinary office and residential buildings designed using UBC 1997 are considered to be overdesigned, and therefore they are quite safe even according to the IBC provisions.

SEISMIC HAZARD ASSESSMENT OF KUALA LUMPUR USING PROBABILISTIC METHOD

This paper presents the seismic hazard assessment which involved spectral hazard for 10 % probability of exceedance in 50 years or correspond to return period of approximately 475 years for bedrock of Kuala Lumpur city. The analysis was performed using the total probability theorm with 2D seismic source model. Time history data for this site was generated synthetically by modifying the existing time history data using spectral matching analysis. In this study, design response spectra were developed by applying the methods proposed by 1997 NEHRP. The final result are the spectral accelaration and the synthetic time histories on the bedrock, and the design response spectra on Kuala Lumpur ground surface for 475 years return periods.

Nonlinear, Effective-Stress Ground Motion Response Analyses following AASHTO Specifications for Load and Resistance Factor Design Seismic Bridge Design

Nonlinear, effective-stress ground motion response analyses were conducted for a bridge site north of Seattle, Washington. This site was characterized by silt and sand layers in the upper 90 ft (27.4 m) of the soil profile that were expected to liquefy during a 975-year seismic event. Procedures described in the 2009 AASHTO Guide Specifications for LRFD Seismic Bridge Design were followed when site-specific analyses of ground motion response were conducted. Two one-dimensional, nonlinear effective-stress computer programs, D-MOD2000 and PSNL, were used to perform the analyses. Field and laboratory tests were conducted to define soil parameters for the nonlinear soil models. Results of the analyses were used to identify soil layers that were likely to liquefy as well as changes in design response spectra that could result from liquefaction. These results demonstrated important differences in site-response prediction from subtle changes in soil modeling, including the potential for shielding of upper liquefiable soil layers and the importance of soil dilation when lower layers liquefy. This paper provides a summary of the analyses and discusses observations made from comparison of the two sets of analyses. The paper also highlights uncertainties that can occur when nonlinear, analyses of effective-stress ground motion response are conducted.

Response of Elasto-Plastic Structure Excited by Artificial Earthquake Ground Motion with Given Non-Stationary Time-Frequency Characteristic

A design basis ground motion is usually defined to be compatible with a given response spectrum which is a useful measure of linear dynamic response of a structure. It has been known that the variance of maximum displacement responses to artificial ground motions in elasto-plasric region is quite large, although every artificial ground motion fits the same design response spectrum. Recently, a new synthesis method was proposed by Masuda, et al. that can generate artificial earthquake ground motions compatible with given time-frequency characteristic as well as a given response spectrum. In this paper, a group of artificial earthquake ground motions are generated, and elasto-plastic response analyses are carried out to examine variance of structural responses in elasto-plastic region. It is revealed that the variance of the structural responses to the earthquake ground motions generated by Masuda's method is less than that to the seismic ground motions by the conventional design method. And it is suggested that the given time-frequency characteristic has an effect on the variance of maximum responses.

J101012 非定常時間周波数性を与えた模擬地震波による弾塑性系の最大応答量のばらつきに関する研究([J10101]原子力施設の耐震安全性に関する実験的・解析的検討(1))

In this paper, a number of artificial earthquake ground motions compatible with non-stationary time-frequency characteristics as well as the given target response spectrum are generated using wavelet transform. The maximum displacement, velocity and acceleration responses of elasto-plastic structures by excited these artificial earthquake ground motions are calculated numerically. Displacement response, velocity response and cumulative input energy are shown in the case of the ground motion which cause larger displacement response. Under the given design response spectrum, a selection manner of generated artificial earthquake ground motion which causes larger maximum displacement response of elasto-plastic structure are suggested.

Development of PISA4SB for Applications in the Taiwan School Building Seismic Retrofit Program

The National Center for Research on Earthquake Engineering (NCREE) in Taiwan has implemented the static pushover procedures for the detailed seismic evaluation of school buildings. In the pushover analysis, the hinge properties of columns, beams, brick walls and RC walls are carefully calibrated based on the full scale experiments conducted in NCREE in the past ten years. Additionally, auxiliary modules for calculating the hinge properties have been developed by NCREE researchers to enhance user friendliness. This could allow engineers to more accurately apply available commercial software. However, when the auxiliary modules are applied to commercial software, the user must first define then assign the sections to the corresponding columns, beams, brick and RC walls in the text-based files. Without the graphic user interface, errors have commonly been found in cross-platform operations. The Platform of Inelastic Structural Analysis for 3D systems (PISA3D) has been developed since 2002 in NCREE. PISA3D provides a friendly user interface and high computational efficiency for engineers and researchers to simulate the nonlinear systems under various kinds of load effects. In order to resolve these issues noted above in the application to commercial software, NCREE has customized the nonlinear structural analysis program, PISA4SB (Platform for Inelastic Structural Analysis of School Buildings) specifically for the school building structures. PISA4SB allows the user to conveniently construct the analytical models for typical low-rise school buildings. After the gravity load analysis is conducted, PISA4SB automatically incorporates the column axial loads in calculating the parameters for the multilinear fracture material properties of any plastic hinge. PISA4SB evaluates the capacity curve and computes the seismic performance point based on the given design response spectrum provided by the user for the school building site. Engineers can conveniently apply PISA4SB to complete the seismic evaluation of a school building without cross-platform operations. The detailed development and example applications of PISA4SB are illustrated in this paper.

Comparison and Research on Seismic Performance between Guidelines for Seismic Design of Highway Bridges and Eurocode 8 for Seismic Design of Bridges

Earthquake codes have been revised and updated in recent years. The issue and implementation of the guidelines for seismic design of bridges have attracted interests and attentions of many researchs at home and abroad. In this paper, it is compared that the provisions about performance criteria, seismic design categories, response spectrum and earthquake action between guidelines for seismic design of highway bridges and Eurocode 8 for bridges. The main purpose of this study is to investigate the differences caused by the two codes in performance criteria, seismic design categories, response spectrum and earthquake action. The results indicate that it is similar in performance criteria, seismic design categories and response spectrum between guidelines for seismic design of highway bridges and Eurocode 8 for bridges. Based on the lessons learned from significant earthquakes in the last few years, the existing problems of the current code are pointed, and the trends of future study are discussed.

Floor response spectra for seismic design of operational and functional components of concrete buildings in Canada

It has been observed during previous earthquakes that the damage to operational and functional components of buildings often result in more injuries, fatalities and property damage than those inflicted by structural damage. Operational and functional components of a building include architectural components, mechanical and electrical equipment, as well as building contents. A rational approach to designing these elements against seismic excitations involves the use of floor design spectra. The development of such design spectra for buildings in Canada constitutes the objective of the paper. This objective was achieved by conducting comprehensive analyses of selected reinforced concrete buildings, with different lateral force resisting systems and building heights, under code compatible earthquake records for an eastern and a western Canadian city. It was observed that the floor response was significantly amplified, especially for buildings with short periods. Generally, the higher floors showed higher amplifications with differences in spectra between the floors being more pronounced in low-rise buildings and shear wall buildings with short fundamental periods. The results provided a large volume of data to generate floor response spectra for the design of operational and functional components of buildings in Canada. The details of the approach and the design spectra are presented in the paper.

시간영역 인공지진파 생성

국내에서 내진설계의 중요성이 점차적으로 부각되고 있으며 이에 따라 설계 시 동적 지진해석의 수행빈도가 높아지고 있다. 동적 지진해석을 수행하기 위한 가장 중요한 입력변수 중 한가지는 입력지진파이다. 그러나 현재 국내에서는 지진학적 검토 없이 미국, 일본 등에서 계측된 강진 기록을 입력지진파로 사용하거나 주파수영역에서 생성된 인공지진파를 사용하고 있다. 국외 계측 지진기록은 지진 규모에 따라 변화하는 지속시간과 에너지를 고려할 수 없어서 국내 지진환경에는 적합하지 않으며, 주파수 영역에서 생성되는 설계응답스펙트럼에 맞춤형 인공지진파는 실제 지진기록과 주파수 특성이 상이한 문제가 있다. 본 연구에서는 이와 같은 입력지진파의 문제점을 극복하기 위하여 시간영역에서 수행되는 응답스펙트럼 맞춤형 인공지진파 알고리즘을 적용하여 입력 지진파를 생성하였다. 생성된 지진파는 계측 지진기록의 고유한 성질인 Non-stationary 특성을 보존하며 동시에 설계 응답스펙트럼과 거의 완벽한 일치성을 보이는 것으로 나타났다. The importance of seismic design is greatly emphasized recently in Korea, resulting in an increase in the number of dynamic analysis being performed. One of the most important input parameters for the dynamic seismic analysis is input ground motion. However, it is common practice to use recorded motions from U.S. or Japan without considering the seismic environment of Korea or synthetic motions generated in the frequency domain. The recorded motions are not suitable for the seismic environment of Korea since the variation in the duration and energy with the earthquake magnitude cannot be considered. The artificial motions generated in frequency domain used to generated design response spectrum compatible ground motion has the problem of generating motions that have different frequency characteristics compared to real recordings. In this study, an algorithm that generates target response spectrum compatible ground motions in time domain is used to generate a suite of input ground motions. The generated motions are shown to preserve the non-stationary characteristics of the real ground motion and at the same, almost perfectly match the design response spectrum.

Performance-goal based (risk informed) approach for establishing the SSE site specific response spectrum for future nuclear power plants

This paper provides the technical basis for the performance-goal based approach presented in the American Society of Civil Engineering Standard ASCE/SEI 43-05 for establishing the safe shutdown earthquake (SSE) site specific design response spectrum (SSRS) for future nuclear power plants. This approach has been adopted by the U.S. Nuclear Regulatory Commission (NRC) in their Regulatory Guide 1.208. This approach has now been followed at more than 20 sites.In addition to more thoroughly documenting the basis for the ASCE 43-05 performance-goal based approach, the paper also summarizes the minimum seismic core damage frequency (SCDF) achieved at 28 Central and Eastern U.S. sites when the SSRS is defined by this approach coupled with other NRC requirements. The minimum SCDF lies in the range of less than 6×10−6/yr to 0.6×10−6/yr with a median ratio of about 3×10−6/yr.

A Ground Motion Scaling Method considering Higher-Mode Effects and Structural Characteristics

As nonlinear response history analysis (NLRHA) becomes a frequently used procedure for the seismic demand evaluation of multistory buildings, it becomes increasingly important to develop a ground motion scaling method which properly includes the dominating modes in the seismic demand estimates. This paper proposes a multimode ground motion scaling (MMS) method, which applies the square root of the sum of the squares (SRSS) or complete quadratic combination (CQC) rule in computing peak seismic demands. The aim is to minimize the weighted sum of the square differences between the spectral responses of a given ground motion and the design response spectrum for the first few modes. Using four case studies, this paper compares the effectiveness of the MMS method with the other common scaling procedures. It is illustrated that the MMS method is effective in reducing the scatter in the peak seismic demands computed from both the response spectral analysis (RSA) and the NLRHA. Recommendations for selecting the ground motion records for the application of MMS method are also provided.

Geotechnical and seismic hazard study for a Type F site development

This paper presents practical approaches for developing design response spectra in a liquefiable site and for evaluating liquefaction-induced ground settlement and lateral deformation for a site development consisting of four main structures, which are up to 12-story high over a two- to three-level parking structure in Marina Del Ray, CA, USA. The site encompasses approximately 6.5-acre (2.63-hectare) area bounded by two channels and is underlain by typical marine soils including soft clay and liquefiable sand. Extensive field exploration and laboratory testing were performed to investigate site-specific geotechnical conditions. After developing site-specific design ground motion parameters, liquefaction potential, liquefaction-induced settlements and lateral spreading were evaluated using the methodologies of the current state of practice. Several site retrofit measures to mitigate liquefaction-induced ground deformations were discussed and recommendations were made.

Probabilistic seismic and tsunami hazard analysis for design criteria development of a coastal area in the city of Banda Aceh

Both seismic and tsunami hazards design criteria are essential input to the rehabilitation and long-term development of city of Banda Aceh Post Sumatra 2004 (M w=9.3) disaster. A case study to develop design criteria for future disaster mitigation of the area is presented. The pilot study consists of probabilistic seismic and tsunami hazard analysis. Results of the probabilistic seismic hazard analysis indicates that peak ground acceleration at baserock for 10 and 2% probability of exceedance in 50 years is 0.3 and 0.55 g, respectively. The analysis also provides spectral values at short (T=0.2 s) and long period (T=1.0 s) motions. Some non-linear time-domain earthquake response analyses for soft, medium, and hard site-class were conducted to recommend design response spectra for each site-class. In addition, tsunami inundation maps generated from probabilistic tsunami hazard analysis were developed through tsunami wave propagation analysis and run-up numerical modeling associated with its probability of tsunamigenic earthquake source potential. Both the seismic and tsunami hazard curve and design criteria are recommended as contribution of this study for design criteria, as part of the disaster mitigation effort in the development process of the city. The methodology developed herein could be applied to other seismic and tsunami disaster potential areas.

Acceleration Response Estimation of a Structure on a Supportive Structure for Seismic Design

A number of structures in industrial facilities are installed on supports, and there have been cases in which damage to such structures has been caused by coupled vibration. In seismic design procedure, the response magnification is obtained from the natural frequency and the modal damping ratio of the coupled system between the structure and the supportive structure. Therefore, the simplified estimation method for calculating the natural frequency and the modal damping ratio of the coupled system is required in the seismic design. In the past study, an equation to calculate the modal damping ratio of a coupled system was presented. The proposed equation was useful for obtaining the modal damping ratio without performing an eigenvalue analysis or a shaking test. In current seismic design procedure, for simplicity, the design response spectrum is used to estimate the acceleration response magnification of a system having one degree of freedom (1-DOF). Though the response magnification of a coupled system can be calculated based on the response magnifications of the 1st mode and the 2nd mode, the participation factor and modal matrix of the coupled system are required. In order to obtain the response magnification, a simpler method that does not involve the participation factor or the modal matrix is proposed, and the characteristics of the proposed method are examined.

DESIGN RESPONSE SPECTRA FOR PULSE-LIKE GROUND MOTIONS

In recent inland shallow earthquakes, pulse-like ground motions have been observed which subsequently caused severe damage to buildings. However, the response of buildings to pulse-like ground motions has not been sufficiently characterized yet. In this study, we investigate the effect of pulse-like ground motions on the design of structures and define the maximum response of an undamped singledegree-of-freedom (SDOF) system subjected to a sinusoidal pulse as a function of natural period. In addition, design response spectra for pulse-like ground motions are proposed.

Evaluation of equivalent linear methods for estimating target displacements of existing structures

This paper presents a statistical study that evaluates the accuracy of four equivalent linear methods which allow the maximum deformation demands of nonlinear structures to be estimated from the maximum deformation demands of the equivalent linear ones. Three of them are defined by displacement ductility ratios, and the other is defined by lateral strength ratios. It is shown from the study that conclusions for the approximate displacements derived from structures with known displacement ductility ratios (new structures) such as the work done by Miranda and Ruiz-Garcia in 2002 [16] are not applicable to structures with known strength ratios (existing structures). The equivalent damping of the equivalent linear systems is usually greater than 5% and the design response spectra specified in codes have a viscous damping ratio of 5% only. Therefore, the highly damped maximum displacement responses of the equivalent linear systems in this study are derived from both damping reduction factors and linear response-history analyses to discuss the effect of different damping reduction factors. Elastoplastic single-degree-of-freedom systems with periods between 0.1 and 3.0 s are considered when subjected to 72 earthquake ground motions recorded on firm sites in California. Mean ratios and the dispersion of approximate to exact maximum inelastic displacements for each method are computed as functions of periods of vibration and strength ratios. This study focuses on existing structures, which already have known vibrating periods and strength ratios.

Probabilistic Seismic Design of Pile Foundations in Non Liquefiable Soil by Response Spectrum Approach

The behavior of pile foundations in non liquefiable soil under seismic loading is considerably influenced by the variability in the soil and seismic design parameters. Hence, probabilistic models for the assessment of seismic pile design are necessary. Deformation of pile foundation in non liquefiable soil is dominated by inertial force from superstructure. The present study considers a pseudo-static approach based on code specified design response spectra. The response of the pile is determined by equivalent cantilever approach. The soil medium is modeled as a one-dimensional random field along the depth. The variability associated with undrained shear strength, design response spectrum ordinate, and superstructure mass is taken into consideration. Monte Carlo simulation technique is adopted to determine the probability of failure and reliability indices based on pile failure modes, namely exceedance of lateral displacement limit and moment capacity. A reliability-based design approach for the free head pile under seismic force is suggested that enables a rational choice of pile design parameters.

Sensitivity of Predicted Maximum Bending Moment to IBC Design Response Spectrum Parameters

The parameters used to generate IBC (International Building Code) compliant design response spectra are specified only approximately for a given site in most cases and values may even be erroneous. S o, the question arises about the effect of approximation or error in the values of these parameters on the predicted internal forces in the structural elements of a building calculated on the basis of the provisions of IBC. This paper explores this issue and presents the sensitivities of design response spectra and maximum moments induced in the structure to these IBC parameters. Within the critical range of short time periods, the variation in peak acceleration of design response spectra for various site classes is found non-uniform. Only peak acceleration is affected by varying SS. Thus, for buildings with the fundamental time period of around 0.6 sec and greater, the parameter SS of IBC is immaterial. Also, for a given site class, the design response spectra are almost identical in the peak acceleration region for all values of S1. The maximum moment is insensitive to SS except for the site class E. This implies that any error in the evaluation of this parameter will not affect the design of the structure.

Seismic Response Analysis of Wind Turbine Tower Systems Considering Soil-structure Interaction

A multi-body and integrated model of wind turbine system consisting of rotor blade, nacelle, tower and foundation is established. The wind turbine system with the consideration of soil-structure interaction (SSI) is proposed to investigate their dynamic behavior to seismic excitations in time domain. With the multi-body system method, the wind turbine system is approximated with a number of so-called superelements. Besides, spring and damping elements are introduced into the interface between foundation and surrounding soil to investigate the effects of SSI. In the multi-body system method, the hard-to-determine superelement parameters are worked out by mechanics of materials and the governing motion equations are derived by using Lagrange method. To investigate the characteristic behavior of wind turbine systems under dynamic loads, the seismic analysis is carried out with artificial earthquake records from acceleration design response spectrum of Eurocode8. The results show that apparent difference exists between the dynamic responses from the model considering SSI effect and from the model not considering SSI effect. Generally speaking, the SSI effect attributes to the flexible connection of the tower foot with ground. The SSI plays different roles in different free vibrations. It has much more effects on the tower bending vibrations, especially on vibrations of high orders.

Performance-based seismic design of a continuous bridge

Performance-based design (PBD) provides an insight into the expected performance of a designed structure during an earthquake. Over recent decades, considerable development on the PBD of buildings has taken place, but studies regarding the PBD of bridges are limited. This paper examines the estimated performance of a three-span continuous bridge designed using a codal procedure for the site-specific design response spectrum. A three-dimensional model of the bridge was developed using non-linear modelling of the piers. The response of the bridge was estimated using non-linear static and dynamic procedures. The effect of loading patterns and the accuracy of different pushover analysis methods were examined, and Fema-356 performance levels compared with limit states defined by Kowalsky. The performance of the bridge was studied for different values of the response reduction factor used in the design. The paper also discusses the advantages of PBD and pushover analysis.