Study on the Relationship of Seismic Design Ground Motion at Different Fortification Levels in the Xinjiang Region

The seismic risk analysis results of 79 cities in Xinjiang are presented, and the bedrock peak ground accelerations under three seismic levels and their ratios are discussed. Then, the relationship between earthquake environments and the seismic risk analysis results of different exceeding probabilities are researched. The results show that minor and major earthquake motion parameters calculated from moderate earthquakes do not have a consistent probability and the ratio of bedrock peak accelerations under different exceedance probabilities are dosdy correlated with earthquake environments.

Study on the severest real ground motion for seismic design and analysis

How to select the adequate real strong earthquake ground motion for seismic analysis and design of structures is an essential problem in earthquake engineering research and practice. In the paper the concept of the severest design ground motion is proposed and a method is developed for comparing the severity of the recorded strong ground motions. By using this method the severest earthquake ground motions are selected out as seismic inputs to the structures to be designed from a database that consists of more than five thousand significant strong ground motion records collected over the world. The selected severest ground motions are very likely to be able to drive the structures to their critical response and thereby result in the highest damage potential. It is noted that for different structures with different predominant natural periods and at different sites where structures are located the severest design ground motions are usually different. Finally, two examples are illustrated to demonstrate the rationality of the concept and the reliability of the selected design motion.

Study on Site Specific Design Earthquake Ground Motion of Nuclear Power Plants in China

The main technical backgrounds and requirements are introduced with regard to earthquake ground motion design parameters in several domestic and American standards,codes and guides involved in the seismic analysis and design activities of nuclear power plants in China.Based on the research results from site seismic safety evaluation of domestic nuclear power plant projects in the last years,characteristics and differences of site specific design spectra are analyzed in comparison with standard response spectra,and the suitability of standard response spectra for domestic nuclear power plant projects is discussed.

Determination of horizontal and vertical design spectra based on ground motion records at Lali tunnel, Iran

Most acceleration diagrams show high levels of unpredictability, as a result, it is the best to avoid using diagrams of earthquake acceleration spect~＇a, even if the diagrams recorded at the site in question. In order to design earthquake resistant structures, we, instead, suggest constructing a design spectrum using a set of spectra that have common characteristics to the recorded acceleration diagrams at a particular site and smoothing the associated data. In this study, we conducted a time history analysis and determined a design spectrum for the region near the Lali tunnel in Southwestern Iran. We selected 13 specific ground motion records from the rock site to construct the design spectrum. To process the data, we first applied a base-line correction and then calculated the signal-to-noise ratio （]~SN） for each record. Next, we calculated the Fourier amplitude spectra of the acceleration pertaining to the signal window （1）, and the Fourier amplitude spectra of the associated noise （2）. After dividing each spectra by the square root of the selected window interval, they were divided by each other （1 divided by 2）, in order to obtain the ~SN ratio （filtering was also applied）. In addition, all data were normalized to the peak ground acceleration （PGA）. Next, the normalized vertical and horizontal responses and mean response spectrum （50%） and the mean plus-one standard deviation （84%） were calculated for all the selected ground motion records at 5% damping. Finally, the mean design spectrum and the mean plus-one standard deviation were plotted for the spectrums. The equation of the mean and the above-mean design spectrum at the Lali tunnel site are also provided, along with our observed conclusions.

Correlation study between ground motion intensity measure parameters and deformation demands for bilinear SDOF systems

The correlation between ground motion intensity measures （IM） and single-degree-of-freedom （SDOF） deformation demands is described in this study. Peak ground acceleration （APG）, peak ground velocity （VPG）, peak ground displacement （DPG）, spectral acceleration at the first-mode period of vibration [As（T1）] and ratio of VPG to APG are used as IM parameters, and the correlation is characterized by correlation coefficients p. The numerical results obtained by nonlinear dynamic analyses have shown good correlation between As（T1） or VPG and deformation demands. Furthermore, the effect of As（T1） and VPG as IM on the dispersion of the mean value of deformation demands is also investigated for SDOF systems with three different periods T=0.3 s, 1.0 s, 3.0 s respectively.

Seismic design and analysis of nuclear power plant structures

The seismic design and analysis of nuclear power plant (NPP) begin with the seismic hazard assessment and design ground motion development for the site. The following steps are needed for the seismic hazard assessment and design ground motion development:a. the development of regional seismo-tectonic model with seismic source areas within 500 km radius centered to the site;b. the development of strong motion prediction equations; c. logic three development for taking into account uncertainties and seismic hazard quantification;d. the development of uniform hazard response spectra for ground motion at the site;e. simulation of acceleration time histories compatible with uniform hazard response spectra. The following phase two in seismic design of NPP structures is the analysis of structural response for the design ground motion. This second phase of the process consists of the following steps:a. development of structural models of the plant buildings;b. development of the soil model underneath the plant buildings for soilstructure interaction response analysis;c. determination of instructure response spectra for the plant buildings for the equipment response analysis. In the third phase of the seismic design and analysis the equipment is analyzed on the basis of in-structure response spectra. For this purpose the structural models of the mechanical components and piping in the plant are set up. In large 3D-structural models used today the heaviest equipment of the primary coolant circuit is included in the structural model of the reactor building. In the fourth phase the electrical equipment and automation and control equipment are seismically qualified with the aid of the in-structure spectra developed in the phase two using large three-axial shaking tables. For this purpose the smoothed envelope spectra for calculated in-structure spectra are constructed and acceleration time is fitted to these smoothed envelope spectra.

Highway bridge seismic design:summary of FHWA/MCEER project on seismic vulnerability of new highway construction

The Federal Highway Administration (FHWA) sponsored a large,multi-year project conducted by the Multidisciplinary Center for Earthquake Engineering Research (MCEER) titled'Seismic Vulnerability of New Highway Construction'(MCEER Project 112),which was completed in 1998.MCEER coordinated the work of many researchers,who performed studies on the seismic design and vulnerability analysis of highway bridges,tunnels,and retaining structures. Extensive research was conducted to provide revisions and improvements to current design and detailing approaches and national design specifications for highway bridges.The program included both analytical and experimental studies,and addressed seismic hazard exposure and ground motion input for the U.S.highway system;foundation design and soil behavior: structural importance,analysis,and response:structural design issues and details;and structural design criteria.

Acomparative study between China and U.S.on seismic design philosophy and practice of a long span arch bridge

This paper presents the first of a series of case studies on the seismic design of long span bridges （cable-stayed bridges, suspension bridges and arch bridges） under a cooperative research project on seismic behavior and design of highway bridges between the State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University and the Multidisciplinary Center for Earthquake Engineering Research, University at Buffalo. The objective of this series of case studies is to examine the differences and similarities on the seismic design practice of long span bridges in China and the U.S., to identify research needs and to develop design guidelines beneficial to bridge engineers in both countries. Unlike short to medium span bridges, long span bridges are not included in most seismic design specifications, mainly because they are location dependent and structurally unique. In this paper, an available model of a steel tied half through arch bridge with a main span of 550m in China is discussed. Analysis is focused on comparisons of the seismic responses due to different ground motions. Seismic design criteria and seismic performance requirements for long span bridges in both countries were first introduced and compared, and then three near field earthquake records with large vertical components were selected as the excitations to examine the seismic behavior and seismic vulnerability of the bridge. Results show that （1） the selected near field ground motions cause larger responses to key components （critical sections） of the bridge （such as arch rib ends） with a maximum increase of more than twice those caused by the site specific ground motions; （2） piers, longitudinal girders and arch crowns are more vulnerable to vertical motions, especially their axial forces; and （3） large vertical components of near field ground motions may not significantly affect the bridge＇s internal forces provided that their peak acceleration spectra ordinates only appear at periods of less than 0.2s. However, they may have more influence on the longitudinal displacements of sliding bearings due to their large displacement spectra ordinates at the fundamental period of the bridge.

Design spectra including effect of rupture directivity in near-fault region

In order to propose a seismic design spectrum that includes the effect of rupture directivity in the near-fault region, this study investigates the application of equivalent pulses to the parameter attenuation relationships developed for near-fault, forward-directivity motions. Near-fault ground motions are represented by equivalent pulses with different waveforms defined by a small number of parameters （peak acceleration, A, and velocity V; and pulse period, Tv）. Dimensionless ratios between these parameters （e.g., ATv/V, VTv/D） and response spectral shapes and amplitudes are examined for different pulses to gain insight on their dependence on basic pulse waveforms. Ratios of ATv/V, VTv/D, and the ratio of pulse period to the period for peak spectral velocity （Tv-p） are utilized to quantify the difference between rock and soil sites for near-fault forward-directivity ground motions. The ATv/Vratio of recorded near-fault motions is substantially larger for rock sites than that for soil sites, while Tvp/Tv ratios are smaller at rock sites than at soil sites. Furthermore, using simple pulses and available predictive relationships for the pulse parameters, a preliminary model for the design acceleration response spectra for the near-fault region that includes the dependence on magnitude, rupture distance, and local site conditions are developed.

Study on strength reduction factors consid-ering the effect of classification of design earthquake

The strength reduction factors are not only the key factors in determining seismic action for force-based seismic design, but also the key parameters to derive the inelastic response spectra for performance-based seismic design. In this paper, with a high quality ground motion database that includes a reasonable-sized set of records from China, a statistical study on the strength reduction factors is conducted and a new expression of strength reduction factors involving classification of design earthquake, which is an important concept to determine design spectra in Chinese seismic design code, is proposed. The expression of strength reduction factors can reflect the ground motion characteristics of China to a certain extent and is particularly suitable for Chinese seismic design. Then, the influence effects of site condition, classification of design earthquake, period of vibration, ductility level, earthquake magnitude and distance to fault on strength reduction factors are investigated. It is concluded that the effect of site condition on the strength reduction factors cannot be neglected, especially for the short-period structures of higher ductility. The classification of design earthquake also has an important effect on strength reduction factors and it may be unsuitable to use the existing expressions of strength reduction factors to the design spectra of current Chinese seismic code. The earthquake magnitude has no practical effect on strength reduction factors and if the near-fault records with forward directivity effect are not taken into consideration, the effect of distance to fault on strength reduction factors can also be neglected.

An alternative construction of normalized seismic design spectra for near-fault regions

This paper presents a methodology for constructing seismic design spectra in near-fault regions. By analyzing the characteristics of near-fault pulse-type ground motions, an equivalent pulse model is proposed, which can well represent the characteristics of the near-fault forward-directivity and fling-step pulse-type ground motions. The normalized horizontal seismic design spectra for near-fault regions are presented using recorded near-fault pulse-type ground motions and equivalent pulse-type ground motions, which are derived based on the equivalent pulse model coupled with ground motion parameter attenuation relations. The normalized vertical seismic design spectra for near-fault regions are obtained by scaling the corresponding horizontal spectra with the vertical-to-horizontal acceleration spectral ratios of near-fault pulse-type ground motions. The proposed seismic design spectra appear to have relatively small dispersion in a statistical sense. The seismic design spectra for both horizontal and vertical directions can provide alternative spectral shapes for seismic design codes.

长持时地震动对建筑结构抗震影响的研究进展

该文综述了长持时地震动作用下建筑结构抗震性能的研究进展。介绍了长持时地震动的定义和特性;梳理了长持时地震动作用下建筑结构数值模拟、试验研究和理论分析的研究进展;详细综述了长持时地震动作用下建筑结构的延性性能、耗能能力、易损性和抗倒塌性能的研究进展。此外,介绍了考虑长持时地震作用影响的建筑结构抗震设计方法,梳理了国内外建筑结构抗震设计规范对长持时地震作用的考虑方法,并对长持时地震动作用下建筑结构抗震性能的研究进行了展望。建议关注长持时地震动作用下建筑结构的抗震性能,进一步研究长持时地震动的定义和特性,改进长持时地震动作用下建筑结构的数值模拟、理论分析和试验研究方法,深入探讨长持时地震动作用下各类建筑结构的地震响应、易损性和抗倒塌性能,为未来结构抗震设计及评估中考虑长持时地震作用的影响和规范修订提供参考。

基于公路与城市桥梁抗震设计规范反应谱的全非平稳地震动过程模拟

【目的】生成拟合公路与城市桥梁抗震设计规范反应谱的全非平稳地震动过程代表性时程集合。【方法】首先,结合非平稳地震动过程的强度-频率调制函数和平稳地震动过程的Clough-Penzien功率谱模型,建立全非平稳地震动过程的演变功率谱模型;其次,依据相关规范确定演变功率谱模型参数取值;然后,根据全非平稳地震动过程模拟的谱表示方法,编写MATLAB程序,生成全非平稳地震动过程代表性时程集合,计算其均值反应谱和规范反应谱拟合误差,并进行迭代修正。【结果】依据公路与城市桥梁抗震设计规范给出了不同场地类别和设计地震分组的演变功率谱模型参数取值;生成的代表性时程集合具有全非平稳地震动的典型特征,其均值反应谱和规范反应谱整体拟合程度较好,平均相对误差均在5%以内。【结论】基于演变功率谱模型,通过编写全非平稳地震动过程模拟谱表示方法的MATLAB程序,可生成满足公路与城市桥梁抗震设计规范要求的全非平稳地震动过程代表性时程集合,其均值反应谱与规范反应谱拟合一致,验证了所给方法和MATLAB程序的有效性,可为桥梁结构抗震性能评估提供可靠的地震动输入。

考虑脉冲效应的近断层地震动能量谱研究

基于能量的设计方法被广泛应用于结构抗震设计与性能评估,而确定结构能量耗散需求是设计过程中需解决的首要问题。目前针对近断层脉冲型地震动能量谱特征的研究仍然不够充分,很可能低估其对结构的破坏作用。为此,从PEER(Pacific Earthquake Engineering Research Center)强震数据库中选取了789条近断层地震动作为输入,并从中识别出192条脉冲型地震动,重点分析了近断层脉冲型地震动与无脉冲地震动的能量谱差异,研究了地震动特征参数及恢复力模型参数对能量谱的影响,并建立了考虑脉冲效应的近断层地震动实用设计能量谱。结果表明:(1)场地越软,近断层地震动能量谱谱值越大,且各类场地下脉冲型地震动能量谱平均谱的谱值明显大于无脉冲地震动;(2)阻尼比ξ增大对输入能量谱具有削峰作用,并减缓其长周期段的衰减速度,延性比μ增大会提高输入能量谱及阻尼耗能谱峰值,并降低滞回耗能谱峰值,屈服后刚度比α对能量谱影响较小,可近似忽略其影响;(3)脉冲型地震动的输入能量设计谱平台段长度远大于无脉冲地震动,所建立的设计能量谱可为近断层区域基于能量的抗震设计提供参考。

近远场地震下RC大跨轻柔拱桥减隔震支座方案优化

为探明不同地震动输入对某大跨轻柔拱桥减隔震的影响,通过非线性有限元模型分析近远场地震下桥梁结构的响应规律,得到大桥支座的优化布置方案.首先,基于模态分析,对比该桥与传统钢筋混凝土(RC)拱桥动力特性差异;其次,选取不同脉冲周期的近场地震动、近场无脉冲及远场长周期地震动记录;最后,研究近远场地震下拱桥的响应行为和损伤演化路径,得到优化桥梁的减隔震支座设计方案.研究结果表明:近场脉冲及远场长周期地震下的桥梁结构响应大于无脉冲地震响应;纵竖向地震下高墩柱剪力及弯矩包络曲线呈“S”形,墩身中部易形成塑性铰,高阶振型影响显著;桥梁纵桥向先于横向震损,损伤路径依次为矮柱、高墩柱及拱肋实心-空心截面段;摩擦摆支座减震效果最佳但位移较大,高阻尼支座方案在近场中长脉冲周期及远场长周期地震下仍会发生损伤,板式橡胶支座方案因无法保证支座同步滑移而不能形成准隔震体系;“高阻尼+摩擦摆”混合方案的支座位移小,拱肋及墩柱均处于弹性,是近断层大跨轻柔RC拱桥的优选减隔震方案.

减隔震技术对9度近断层区框架结构抗震性能影响与经济性分析

为研究减隔震技术对9度近断层区框架结构抗震性能影响及其经济性,以某多层框架结构为研究对象,在保证结构力学指标为85%的规范限值的原则下,对其分别进行抗震、减震、隔震设计,采用ETABS软件建立结构的抗震、减震、隔震模型并对其进行近断层和非近断层地震动作用下的抗震性能对比分析,以及工程量和经济性分析。结果表明,各模型在近断层地震动下的反应大于非近断层地震动下的。在近断层罕遇地震下,相较于抗震模型,隔震模型最大层间位移角减小6898%,楼面峰值加速度减小7677%,楼层剪力减小8367%;相较于抗震、减震模型,隔震模型在近断层多遇地震和设防地震下的响应及填充墙破坏程度最小,隔震结构抗震性能最优。相较于抗震模型,减震、隔震模型造价分别降低857%、554%,所以减震设计的工程造价最低。

远海岛礁与场地地震反应研究现状

本文从岛礁地质构造、岛礁地震反应数值模拟方法和岛礁场地效应等方面总结了海域岛礁地震反应的研究现状,对比并且分析了海域岛礁数值模拟方法中的流固耦合模拟方法、固体边界模拟方法和地震动输入方法;总结了现有海域岛礁地震反应的场地效应相关的研究成果。相关研究表明:海水对岛礁场地的放大系数有明显影响,岛礁表面砂层对水平向地震动加速度峰值放大显著,随着输入地震动峰值的增大,岛礁场地的PGA放大效应趋于减小;海域岛礁场地对中低频段的地震动反应较为显著,加速度峰值放大系数一般介于1.5到4.0之间。为满足岛礁工程的抗震设计,需要进一步解决岛礁工程合理地震动输入、岛礁场地地震反应规律与岛礁工程的设计地震动参数等关键科学问题。

拟合楼层反应谱的三向地震动时程生成方法研究

为获得满足规范要求的拟合楼层反应谱的三向地震动时程,采用六阶常微分方程的本征函数为基函数,分解并重构天然地震动时程;通过构建影响矩阵,迭代计算逐步调整本征函数的幅值系数,最终实现预设拟合精度;引入正交化方法保证三向地震动时程两两之间的统计独立性,并通过两组算例提供验证。研究结果表明,迭代所得时程反应谱与目标楼层反应谱的拟合精度较高,迭代过程中时程反应谱均匀一致地向目标谱逼近,迭代过程收敛,所得三向地震动时程均无零飘现象,满足规范要求。

与桥梁抗震规范设计反应谱一致的地震动合成

工程上在对结构进行动力响应分析时,大多是在实测强震数据库中筛选出与规范设计反应谱相一致的实测强震记录作为地震动输入依据,然而,实测强震记录数量有限,需要系统地处理才可投入工程应用,且在对大型工程结构进行动力反应分析时无法体现地震动的空间变异性,因此,本文以《公路桥梁抗震设计规范》(JTG/T 2231-01-2020)中的设计反应谱为例,详细梳理了地震动向量过程的本征正交分解方法(POD)和复相干函数模型,并将反应谱转化功率谱法和调幅功率谱迭代法相结合,基于降维模拟方法,在概率层面上高效地生成了与设计反应谱相一致且具有空间变异性和非平稳性的人工地震动向量过程。数值算例表明,根据目标反应谱转化为调幅功率谱后,再根据功率谱迭代法迭代一次生成的地震动样本与目标反应谱对应良好,同时,降维方法生成的地震动样本具有显著的非平稳性和空间变异性,且统计特征与目标值对应良好。可以认为,本文为桥梁结构在地震作用下的地震激励输入提供了新的途径。