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以Ⅱ类场地为例,选取了山东地区2个场地的工程地质勘探及剪切波速等资料,通过改变不同深度段波速,分别建立土层模型,计算分析了不同深度段、不同概率水平条件下剪切波速的变化对场地地震动参数的影响。研究结果表明,剪切波速的变化对场地地震动加速度峰值影响在浅层影响最大,基岩输入面处次之,深层最小;对特征周期的影响,在浅层影响最大,深层次之、基岩输入面处最小。研究结果为进一步研究土层剪切波速测试中的不确定性对场地地震动参数的影响及合理确定场地地震动参数提供一定的参考。 相似文献
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Soil amplification characteristics are investigated using data from the Chibaken‐Toho‐Oki earthquake and its aftershocks recorded at Chiba dense array in Japan. The frequency‐dependent amplification function of soil is calculated using uphole‐to‐downhole spectral ratio analysis, considering the horizontal components of shear wave. The identified spectral ratios consistently demonstrate the splitting of peaks in their resonance frequencies and low amplification values in comparison with a 1D model. The torsional behaviour and horizontal ground motion coupling are clarified as the reasons for these phenomena at the site. To prove the hypothesis, the torsional motion is directly evaluated using the data of the horizontal dense array in different depths at the site. The comparison between Fourier spectra of torsional motion and identified transfer functions reveals the peaks at the same frequencies. The wave equation including torsion and horizontal motion coupling is introduced and solved for the layered media by applying wave propagation theory. Using the developed model, the effects of torsional motion with horizontal motion coupling on soil transfer function are numerically examined. Splitting and low amplification at resonance frequencies are confirmed by the results of numerical analysis. Furthermore, the ground motion in two horizontal directions at the site is simulated using site geotechnical specification and optimizing the model parameters. The simulated and recorded motions demonstrate good agreement that is used to validate the hypothesis. In addition, the spectral density of torsional ground motions are compared with the calculated one and found to be well predicted by the model. Finally, the results are used to explain the overestimation of damping in back‐calculation of dynamic soil properties using vertical array data in small strain level. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Non‐linear dynamic time‐history analyses conducted as part of a performance‐based seismic design approach often require that the ground motion records are scaled to a specified level of seismic intensity. Recent research has demonstrated that certain ground motion scaling methods can introduce a large scatter in the estimated seismic demands. The resulting demand estimates may be biased, leading to designs with significant uncertainty and unknown margins of safety, unless a relatively large ensemble of ground motion records is used. This paper investigates the effectiveness of seven ground motion scaling methods in reducing the scatter in estimated peak lateral displacement demands. Non‐linear single‐degree‐of‐freedom systems and non‐linear multi‐degree‐of‐freedom systems are considered with different site conditions (site soil profile and epicentral distance) and structural characteristics (yield strength, period, and hysteretic behavior). It is shown that scaling methods that work well for ground motions representative of stiff soil and far‐field conditions lose their effectiveness for soft soil and near‐field conditions for a wide range of structural characteristics. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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不同类别场地地震动参数的计算分析 总被引：45，自引：2，他引：45
基于188个工程场地计算剖面及场地地震反应分析的等线性化波动分析方法，通过对场地地震反应的计算及计算结果的分析，研究了4类场地条件对场地地震动影响的特点及规律，给出了每一类场地地震动参数变化的经验关系。 相似文献
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Surface wave methods consist of the extraction and inversion of the Rayleigh wave phase-velocity dispersion curve to recover the (usually 1D) shear-wave velocity profile. In the literature, uncertainty due to data error has not received much attention, but the discussion about uncertainty due to model error is even poorer. Even with an unrealistic noise-free dataset and an exact forward model, an inappropriate parameterization can generate solutions very far from the actual soil structure. In general, the model used for the dispersion curve interpretation is 1D. Hence, when the velocity distribution is laterally heterogeneous, model errors can have significant consequences on the reliability of the resulting shear-wave velocity distribution. From a poor velocity reconstruction, an unsatisfactory, and often dangerous site response analysis follows. In fact, shear wave measurements play a relevant role in seismic ground motion amplification estimation. In this paper, we discuss the possibility of processing the seismograms using a multi-offset phase analysis (MOPA), in order to derive soil elastic parameters for weak motion predictions. This technique allows the detection and location of the lateral discontinuities, and a better model parameterization. In fact, once the discontinuities are identified, we can split the profile into several, truly 1D, parts. The use of the standard 1D dispersion curve extraction and inversion for each side of the heterogeneity generates velocity profiles that we can put side by side to get correct 2D reconstructions of the shear-wave distributions. From 2D velocity reconstruction, we can calculate the site response that may be significantly different from the site response generated from a traditional 1D analysis of the same seismograms. In this work, we discuss the site responses of two synthetic examples with lateral heterogeneities. We show how misleading a 1D analysis may be if applied to a truly 2D velocity distribution, particularly in terms of site response prediction. 相似文献
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本文设计独立基础框架和整体箱型基础框架结构模型,基于试验数据的对比分析,探讨基础类型与地震动特性对场地土以及结构自身地震响应的影响。试验结果及分析表明:地表结构的存在总体上是放大了地表加速度响应,放大最大幅度达到了40%,影响范围可达3倍的结构跨度,且具有一定埋深的箱型基础的影响大于浅埋独立基础。由于土体对独立基础的约束相对较弱,导致独立基础结构模型的加速度响应总体上大于箱型基础的;独立基础结构模型可能发生摇摆运动导致结构基础竖向响应的频谱特性含有较多的高频成分。另外,地震动特性对结构响应也较显著,其中脉冲地震动NR波的影响最为显著。 相似文献
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System identification (SI) methods are used to determine empirical Green's functions (EGF) for soil intervals at the Port Island Site in Kobe, Japan and in shake table model tests performed by the Port and Harbor Research Institute (PHRI) to emulate the site during the 17 January 1995 Hyogo‐ken Nanbu earthquake. The model form for the EGFs is a parametric auto‐regressive moving average (ARMA) model mapping the ground motions recorded at the base of a soil interval to the top of that interval, hence capturing the effect of the soil on the through‐passing wave. The consistency of site response at Port Island before, during, and after the mainshock is examined by application of small motion foreshock EGFs to incoming ground motions over these time intervals. The prediction errors (or misfits) for the foreshocks, the mainshock, and the aftershocks, are assessed to determine the extent of altered soil response as a result of liquefaction of the ground during the mainshock. In addition, the consistency of soil response between field and model test is verified by application of EGFs calculated from the shake table test to the 17 January input data. The prediction error is then used to assess the consistency of behaviour between the two cases. By using EGFs developed for small‐amplitude foreshock ground motions, ground motions were predicted for all intervals of the vertical array except those that liquefied with small error. Analysis of the post‐liquefied ground conditions implies that the site response gradually returns to a pre‐earthquake state. Site behaviour is found to be consistent between foreshocks and the mainshock for the native ground (below 16 m in the field) with a normalized mean square error (NMSE) of 0.080 and a peak ground acceleration (PGA) of 0.5g. When the soil actually liquefies (change of state), recursive models are needed to track the variable soil behaviour for the remainder of the shaking. The recursive models are shown to demonstrate consistency between the shake table tests and the field with a NMSE of 0.102 for the 16 m to surface interval that liquefied. The aftershock ground response was not modelled well with the foreshock EGF immediately after the mainshock (NMSE ranging from 0.37 to 0.92). One month after the mainshock, the prediction error from the foreshock modeled was back to the foreshock error level. Copyright © 2001 John Wiley Sons, Ltd. 相似文献
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D Raptakis F.J Chvez-Garc&#x;&#x;a K Makra K Pitilakis 《Soil Dynamics and Earthquake Engineering》2000,19(1):411
This paper describes the process of construction of the 2D model of Volvi's geological structure and results of empirical and theoretical approaches to the evaluation of site response at Euroseistest. The construction of the 2D model is based on a re-interpretation of the available geophysical and geotechnical data in an effort to improve the definition of the subsoil structure at Euroseistest in terms of the most important parameters needed to model site response. The results of this re-interpretation are compared with a previous published 2D model of the same alluvial valley. Different analysis of the measurements and different criteria in the synthesis of data have led to a different model, even if both studies had access to the same field measurements. This underscores the fact that a model results of an interpretation and is not uniquely determined by the data, no matter how detailed they are. The well known subsoil structure opened the possibility to correlate the geometry and the dynamic properties of the 2D model with the results of site response determined from a detailed analysis of two events in frequency and time domains and 1D numerical modeling. The study of site response shows the important effect of the lateral variations on the ground motion and suggests that the contribution of locally generated surface waves to the resonant peak may be important. In the case of Volvi's graben, the limitations of the 1D approximation to simulate ground motion under complex soil conditions in both frequency and time domains are also shown. This paper lays the ground for a companion article dealing with 2D site effects in this basin. 相似文献
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An integrated probabilistic seismic hazard analysis procedure that incorporates nonlinear site effects, PSHA-NL, is developed and used to characterize the influence of thick deposits of the upper Mississippi Embayment (ME) on seismic site coefficients. PSHA-NL follows the methodology of the 2002 USGS hazard maps and generates a compatible set of ground motion records. The motions are propagated using nonlinear and equivalent linear site response analyses and ME properties developed in a companion paper and used to derive surface uniform hazard response spectra. A set of generic site coefficients are derived and summarized in a format similar to NEHRP site coefficients, with an added dimension of ME deposits thickness to the Paleozoic rock, a physically meaningful impedance boundary. These coefficients compare well with NEHRP site coefficients for 30 m profiles. For thicker soil profiles, developed site coefficients are lower at short periods and higher at long periods than NEHRP site coefficients. 相似文献
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During an earthquake, the amplitudes of seismic wave may amplify significantly as it propagates through the soil layers near the ground surface. Analysis of site amplification potential is strongly influenced by the uncertainty associated to the definition of soil thickness and its properties. In this paper, the non-recursive algorithm is used in linear and nonlinear Hybrid Frequency Time Domain (HFTD) approaches for stochastic analysis of site amplification. The non-recursive algorithm causes time reduction of analysis that is the essential base of stochastic analysis. The selected soil stochastic parameters are shear wave velocity, density, damping and thickness. The results of sensitivity analysis also show that the damping ratio is the most effective parameter in PGA at ground surface. The stochastic peak ground acceleration, response spectrum and amplification factor at the ground surface are determined by the two approaches for four sites with different average shear wave velocities. Comparison of the results shows that the nonlinear HFTD approach predicts closer response to real recorded data with respect to linear HFTD. 相似文献
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利用天津滨海地区丰富的地震地质钻孔资料及测试数据,建立了相应的地震反应模型.选取美国加州1992年Landers地震的远场记录P0841作为基底输入,采用工程上常用的等效线性化方法进行了土层地震反应分析,以期对天津滨海软土场地的大震远场作用得到一些定性的认识．结果显示,天津滨海软土场地对远场大震地震动峰值加速度的放大作用比较显著,但不同场地条件放大作用有明显差异,Ⅳ类场地的放大效应明显减弱.对基岩与地表反应谱比的分析显示, 滨海场地对基岩地震动的不同频率分量的放大作用具有明显的不同,对短周期分量甚至出现了缩减,但当滨海软土场地受到与场地卓越周期相吻合的地震动影响时,可能会产生很可观的放大作用,这对建在其上的高层、超高层建筑可能会构成较大的威胁． 相似文献
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本文概述了一维土层地震反应分析等效线性化方法评价结果不确定性研究的进展,比较了中美两国核设施土层地震反应分析中参数不确定性的处理方法。基于实测数据,令参数随机变化,建立土层剖面模型,采用随机振动理论方法,分析了土层动力特性、剪切波速、基岩地震动输入界面对评价结果的影响。结果表明,土层剪切波速的不确定性对评价结果影响最大,主要表现为加速度反应谱平台段的延长。对比参数随机变化模型和最佳估计模型的计算结果可知,随机振动理论反映了土层对基岩地震动的影响,将随机模型分析结果的中值加减1倍标准差基本可以包络最佳估计模型的分析结果。 相似文献
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This paper presents a series of analyses for the evaluation of the ground response of two NEHRP class D sites, subjected to shaking by a large number of strong ground-motion records. The two investigated sites have very distinct profiles, but they are characterised by almost identical Vs30 values. The site response analyses are performed using various methods of analysis and input parameters in order to explore the sensitivity of the ground response estimates and to identify the dominating parameters. Equivalent linear analysis is performed using different sets of dynamic soil properties curves, while nonlinear analysis is performed using different target dynamic soil curves, viscous damping formulations and fitting procedures for the constitutive model parameters. Particular focus is given to the sensitivity of the response when soil sites are subjected to high-intensity shaking, a subject of particular interest when the prediction of surface ground motions with low annual probabilities of exceedance is the target of probabilistic seismic hazard analyses (PSHA). The site response analysis results of this paper are incorporated into the probabilistic framework of Bazzurro and Cornell [1] in our companion paper in order to assess their impact on the final soil surface hazard calculation. 相似文献
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Site effects characterize the filtering mechanisms within the soil sedimentary layers overlying bedrock. In regions of high seismicity such as California where strong motion records are relatively abundant, site coefficients can be developed by regression of recorded ground shaking parameters. In regions of low‐to‐moderate seismicity or of high seismicity but with a paucity of recorded strong motion data, such empirical models cannot be obtained in the same way. This study describes the theoretical development of a simple, rational manual procedure to calculate site coefficients, based on a single period approximation (SPA), and to construct displacement response spectra (RSD) for soil sites. The proposed simplified model, which takes into account the non‐linear behaviour of soil that is dependent on the level of shaking, impedance contrast at the soil–bedrock interface and the plasticity of soil material, has been verified by comparison with results obtained from non‐linear shear wave analyses and data recorded during the 1994 Northridge earthquake. The proposed model is believed to be a convenient tool for calculating non‐linear site responses and constructing site‐specific response spectra, which has the potential of being incorporated into code provisions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Introduction The estimation of damage probability distribution among different damage states of rein-forced concrete buildings is a key component of earthquake loss estimation for modern city or a group of cities. With the development of city, the reinforced concrete buildings are major compo-nent parts of modern cities. Vulnerability estimates for these kinds of buildings are of importance to those responsible for civil protection, relief, and emergency services to enable adequate contin-genc… 相似文献