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1.
India is prone to earthquake hazard; almost 65 % area falls in high to very high seismic zones, as per the seismic zoning map of the country. The Himalaya and the Indo-Gangetic plains are particularly vulnerable to high seismic hazard. Any major earthquake in Himalaya can cause severe destruction and multiple fatalities in urban centers located in the vicinity. Seismically induced ground motion amplification and soil liquefaction are the two main factors responsible for severe damage to the structures, especially, built on soft sedimentary environment. These are essentially governed by the size of earthquake, epicentral distance and geology of the area. Besides, lithology of the strata, i.e., sediment type, grain size and their distribution, thickness, lateral discontinuity and ground water depth, play an important role in determining the nature and degree of destruction. There has been significant advancement in our understanding and assessment of these two phenomena. However, data from past earthquakes provide valuable information which help in better estimation of ground motion amplification and soil liquefaction for evaluation of seismic risk in future and planning the mitigation strategies. In this paper, we present the case studies of past three large Indian earthquakes, i.e., 1803 Uttaranchal earthquake (Mw 7.5); 1934 Bihar–Nepal earthquake (Mw 8.1) and 2001 Bhuj earthquake (Mw 7.7) and discuss the role of soft sediments particularly, alluvial deposits in relation to the damage pattern due to amplified ground motions and soil liquefaction induced by the events. The results presented in the paper are mainly focused around the sites located on the river banks and experienced major destruction during these events. It is observed that the soft sedimentary sites located even far from earthquake epicenter, with low water saturation, experienced high ground motion amplification; while the sites with high saturation level have undergone soil liquefaction. We also discuss the need of intensifying studies related to ground motion amplification and soil liquefaction in India as these are the important inputs for detailed seismic hazard estimation. 相似文献
2.
The strong ground motion from Athens, Greece 07/09/1999 earthquake has been recorded by eighteen (18) stations, fourteen (14) within the central Athens area and four (4) at the centers of nearby towns. The ground conditions for most of the recording sites were identified, based on previous geotechnical investigations carried out in the wider area of the sites, and consequently correlated to the seismic motion characteristics. Hence, it has been possible to evaluate the accuracy of different seismological methods for site characterization and also estimate soil effects on peak ground acceleration and elastic response spectra. In addition, preliminary estimates are drawn for the seismic motion characteristics at the epicentral area, where no strong motion recordings are available. The detailed soil profiles at the recordingsites are placed in the Appendix. 相似文献
3.
桩板式抗滑挡墙地震响应的振动台试验研究 总被引：2，自引：0，他引：2
汶川地震路基震害调查表明,在顺层或堆积体边坡中的桩板式抗滑挡墙具有良好的抗震性能。为了更好地了解该结构的抗震性能和优化抗震设计方法,以大型振动台模型试验为手段对其进行研究。为明确地震作用下桩板式抗滑挡墙的地震响应特性,试验采用缩尺的卧龙台站实测地震波对模型激励。试验结果揭示了土压力沿桩身分布规律、桩体位移和边坡岩土体加速度的地震响应特征。研究表明,地震土压力沿桩身呈非线性分布,竖向地震荷载对水平加速度有放大效果。所以,双向加载时的地震土压力比水平单向加载时大,但二者差距在地震基本烈度VII、VIII度区域不显著。滑坡推力、滑床对桩的土体抗力和桩身位移均与输入地震动峰值加速度成正比,即随着地震动峰值加速度的增加,加速度放大比增大;滑动面材料剪切强度折减,滑坡推力、土体抗力和抗身位移均增大,且增大速率加快。此外,结合试验成果,建议了桩板式抗滑挡墙设计时地震综合影响系数Cz的合理取值,对应地震基本烈度VII、VIII、IX度区分别为0.2、0.35、0.4。试验结果有助于揭示该结构抗震机制,也为其抗震设计提供了可靠依据。 相似文献
4.
Modification in the semi-empirical technique for the simulation of strong ground motion has been introduced to incorporate the strong motion generation areas (SMGA) in the modeled rupture plane. Strong motion generation areas identified within the rupture plane of the Tohoku earthquake of March 11, 2011 (M w = 9.0), have been modeled using this modified technique. Two different source models having four and five SMGAs, respectively, are considered for modeling purpose. Strong motion records using modified semi-empirical technique have been simulated at two near-field stations located at epicentral distance of 137 and 140 km, respectively, using two different source models. Comparison of the observed and simulated acceleration waveforms is made in terms of root mean square error (RMSE) at both stations. Minimum root mean square error of the waveform comparison has been obtained at both the stations for source model having five SMGAs. Simulations from same rupture model have been made at other four stations lying at epicentral distance between 154 and 249 km. Comparison of observed and simulated records has been made in terms of RMSE in acceleration records, velocity records and response spectra at each six station. Simulations have been made at six other stations to obtain distribution of peak ground acceleration and peak ground velocity with hypocentral distance. Peak ground acceleration and velocity from simulated and observed records are compared at twelve stations surrounding the source of Tohoku earthquake. Comparison of waveforms and parameters extracted from observed and simulated strong motion records confirms the efficacy of the developed modified technique to model earthquake characterized by SMGAs. 相似文献
5.
开展了近远场地震动作用下盾构扩挖地铁车站结构的振动台试验,分析了砂土模型地基的水平位移、地表变形、加速度、土压力反应及模型结构的加速度、应变等。结果表明：模型地基-结构体系的地震响应对中低频成分发育的地震波反应更为强烈;强震作用下地铁车站结构具有明显的空间效应,地下结构的存在将会改变模型地基表面变形的分布模式。小震时模型结构中柱的加速度反应自下而上逐渐增加,而大震时其反应规律变成先增大后减小;车站结构中板的加速度反应最大、底板次之、顶板最小;小震时,同等深度处模型结构的加速度反应与模型地基土的加速度反应大小相当,侧墙的动土压力自下而上逐渐增大;大震时,模型结构的加速度反应明显大于同深度处模型地基土的加速度反应,动土压力的最大值发生在扩挖隧道的拱肩和中间部位。基于震后模型结构的宏观现象和拉应变幅值,给出了砂土地基中盾构扩挖车站结构的地震损伤演化机制。 相似文献
6.
液化自由场地震响应大型振动台模型试验分析 总被引：1，自引：0，他引：1
开展了含上部黏土层、饱和砂土层、密实砂土层的可液化自由场地在水平地震动激励下的大型振动台模型试验研究,分析了地震动激励时饱和砂土液化后场地加速度、位移、孔压比时空响应等动力响应。试验结果表明：在小震激励时,场地动力反应较小,加速度反应自下而上不断放大,各深度处孔压比均较小,模型地基整体处于弹性反应阶段;0.3g汶川地震卧龙台地震记录输入时,孔压积累迅速,可液化土体最上部土层孔压比达到1,饱和土体液化,模型地基表现出明显的非线性反应特征,加速度反应在饱和砂土层中未有明显放大,土体卓越周期对应的反应加速度自下而上有不断增大趋势。该研究是土-群桩-上部结构体系大型振动台系列试验中可液化自由场动力反应部分,可供今后做对比分析和验证数值模拟参考。 相似文献
7.
Surface wave methods are increasingly being used for geotechnical site characterization. The methodology is based on the dispersive characteristic of Rayleigh waves in vertically heterogeneous medium. Experimental dispersion curve is inverted to obtain one-dimensional shear-wave velocity profile by inverse problem solution. Uncertainty associated with this surface wave inversion has drawn much attention. Inverse problem solution can provide different equivalent shear-wave velocity profiles, which may lead to different seismic site response analysis. In this study, a neighborhood algorithm has been used for inversion of dispersion curve to get a set of equivalent shear-wave velocity profiles. These equivalent velocity profiles are then used for 1D ground response analysis for different input motion record of the same earthquake at different epicentral distances. Results show significant variation in amplification spectrum in terms of maximum amplification as well as peak frequency. The extent of this uncertainty largely depends on the characteristics of the ground motion records at different epicentral distances. A linear variation is observed between mean coefficients of variation of amplification spectrum and epicentral distance of ground motion records. A gradual increase in mean value of peak frequency and peak amplification with the epicentral distance is also observed. 相似文献
8.
地下综合管廊属于浅埋狭长型结构，变形缝存在较为普遍，而在地震荷载作用下，其会对地下结构的振动响应产生一定影响，但是目前针对该问题的研究却十分有限。基于振动台模型试验并考虑接缝的影响，开展了不同波形、不同峰值加速度地震波激励下的综合管廊地震响应特征研究，对场地加速度、动土压力以及管廊结构加速度、位移、动应变和弯矩等响应进行了测试和分析。试验结果表明：管廊振动主要受周边土体影响，接缝截面边墙在地震过程中与土体发生脱离，但管廊结构整体性保持良好；管廊接缝在强震下位移较小，不会发生大变形破坏；强震作用下动土压力分布呈非线性特征；接缝截面在地震中受到的弯矩作用小于中部截面，对抗震性能有利。 相似文献
9.
10.
叠交隧道是涉及隧道之间、隧道与土体相互作用的复杂体系,其安全性将严重影响城市轨道交通建设。目前,对于叠交隧道振动台试验的研究集中在水平平行和交叉叠交隧道、单向和双向地震动输入。鉴于此,利用自行设计的层状三向剪切模型箱,对竖直平行叠交隧道开展三向地震作用下的振动台模型试验,研究地基土−叠交隧道模型体系动力特性、地基土加速度、叠交隧道加速度、地表沉降、地基土孔压、叠交隧道动土压力及叠交隧道应变等地震响应。结果表明：随着震波峰值加速度（peak ground acceleration,简称PGA）依次增加,地基土−叠交隧道模型体系的自振频率随之减小,而阻尼比随之增大;叠交隧道周围地基土加速度和孔压的梯度差随着地震波PGA的增大而增大,且上隧道周围梯度差比下隧道更大;地基土对加速度的放大效应随着地震波PGA的增大而减弱;相同地震波作用下,相同位置处的叠交隧道加速度傅里叶谱形状相似,但幅值随着地震波PGA的增大而增大。此外,与顶部和底部位置相比,腰部位置加速度傅里叶谱频段范围变宽,幅值峰值有所降低;地表沉降峰值随着地震波PGA的增大而减小,相比地基土两侧位置,中心位置的沉降峰值明显较小;地震波的类型对叠交隧道动土压力峰值和应变峰值影响较小;对于动土压力峰值,两隧道的最大值均为腰部,而上、下隧道的最小值分别为底部、顶部;对于应变峰值,上隧道在腰部明显大于顶部和底部,而下隧道在4个位置相差不大。 相似文献
11.
首先,介绍了基于OpenSees独立开发的一套用于挡土墙-土地震反应相互作用有限元分析计算软件RW_2DPS.据此建立了俯斜式混凝土重力挡土墙-土强震相互作用有限元模型.模型中,引入非线性有限元计算方法,选用多屈服面弹塑性本构模型模拟砂土的动力属性,应用零长度接触单元模拟墙与土体之间的接触特性,且采用一致耗能阻尼边界与速度边界条件.最后,输入随机地震动,进行挡土墙-土强震反应分析,并重点探讨墙背地震土压力和水平地震惯性力沿挡土墙高度分布规律.结果表明,墙背动土压力峰值出现在距挡土墙底约1/3墙高处;挡土墙背加速度具有放大效应,加速度峰值出现在挡土墙顶部;不同地震动作用下,加速度放大系数沿墙高分布规律不同,动土压力沿墙高变化规律基本一致. 相似文献
12.
沙牌坝址基岩场地地震动输入参数研究 总被引：2，自引：0，他引：2
重大水利水电工程地震动输入参数必须根据专门的地震危险性分析结果来确定。目前由地震危险性分析得到的一致概率反应谱具有包络的意义,不能反映实际地震的频谱特性,输入“一致概率反应谱”可能导致地震作用偏大;拟合设计反应谱人工生成地震动加速度时程的频率非平稳性也没有得到很好解决。为了解决这些问题,得到与坝址地震危险性一致、具体地震的输入参数,结合沙牌大坝提出了一套适用于重大水利水电工程基岩场地地震动输入参数确定方法：通过以有效峰值加速度为参数的概率地震危险性计算分析,确定坝址不同超越概率下的有效峰值加速度及对坝址贡献最大的潜在震源区;在最大贡献潜在震源内利用震级空间联合分布概率最大法确定坝址设定地震,依据加速度反应谱衰减关系确定与坝址设定地震对应的设计反应谱;根据设定地震结果和时变功率谱模型参数衰减关系确定时变功率谱,将时变功率谱和最小相位谱按三角级数叠加法进行强度和频率非平稳地震加速度时程合成。在对沙牌坝址区域的地震活动性及地震构造环境分析评价的基础上,采用上述方法,得到了坝址基岩场地不同超越概率下的有效峰值加速度、设计反应谱、强度和频率非平稳地震加速度时程等地震动输入参数。 相似文献
13.
合理地估计汶川破坏区域的地震动有助于地震灾害的研究.通过利用芦山地震记录建立的加速度包络衰减关系和汶川地震近场30个台站的加速度包络,基于线源模型,采用差分进化方法反演了汶川地震断层面上高频 (＞1 Hz) 辐射区域分布.结果表明:断层面上高频辐射分布很不均匀,辐射较强的区域主要位于:(1) 产生较大地表破裂的映秀、北川和南坝区域;(2) 映秀和北川等凹凸体的周边区域,包括震中东北侧60~90 km区域、北川和南坝东北侧30 km处;(3) 断层破裂停止的东北端约30 km长的区域.其中,破裂贯穿到地表的映秀、北川和南坝是低频和高频辐射都很强的区域.对于无观测记录场点,选择其临近且场地条件类似的台站加速度提取平稳随机过程,结合高频辐射分布和衰减关系得到的包络,合成了加速度时程,可为汶川地震结构震害分析提供地震动输入. 相似文献
14.
开展了近场和远场地震动作用下3跨3层地铁车站结构地基液化效应的振动台模型试验,测试了地铁车站结构的加速度、应变、水平位移反应和地基土孔隙水压力、加速度、震陷及其作用于模型结构侧墙的动土压力反应。分析和总结了地铁车站结构地基液化效应特征,结果表明：模型结构对其周围地基土孔隙水压力场的分布有明显影响,结构两侧和底部地基土中的孔压峰值小于相同深度离结构较远地基土中的孔压峰值;地基土中孔压的消散速度自下而上呈逐渐减慢的趋势;地震动作用过程中,模型结构产生向上的相对运动,强地震动作用时模型结构上浮现象明显;模型结构侧墙受到的动土压力随深度增大而减小,输入地震动特性对动土压力的大小有显著影响。 相似文献
15.
P. Marinos G. Bouckovalas G. Tsiambaos N. Sabatakakis A. Antoniou 《Engineering Geology》2001,62(4):343-356
The 1999, Ms=5.9, Athens earthquake caused serious structural damage to buildings in the western part of Athens, Greece. This paper presents the ground zoning against seismic hazard proposed shortly after the earthquake in order to aid reconstruction of the area. Existing engineering geological and geotechnical data were combined with local observations to provide a unified set of classification criteria, consistent with provisions of the Greek Seismic Code EAK. The accuracy and the possible limitations of this zoning procedure are addressed through comparison with observed damage distribution as well as results from seismic ground response analyses performed at sites with well established soil profiles. There is clear evidence that the proposed zones correspond to geological formations exhibiting grossly different seismic response with regard to the design of common engineering structures. However, the mostly qualitative nature of the guidelines for ground categorisation provided by EAK and the general lack of systematic, site-specific geotechnical data for the whole area induce uncertainties in the definition of the seismic design actions for the different zones. These objective uncertainties certainly demand increased conservatism but do not limit application of the proposed methodology for first aid, preliminary planning in the event of destructive earthquakes. 相似文献
16.
场地条件对地震动和震害有重要影响。本文简要回顾了场地条件对地震动和震害影响的研究历史,总结和评述了这一领域的研究进展。重点对地形地貌、岩土类型、覆盖层厚度、土层结构、地下水、岩土动力性质及物理地质现象等对地震动和震害的影响进行了总结和评述。提炼和概括了目前场地条件对地震动和震害影响研究中比较一致的几点认识。在此基础上,提出了这一领域当前应进一步研究的问题,主要包括地震现场资料调查、局部地形几何尺度、场地分类、覆盖层安全厚度界限、近断层地震动参数分布规律、活断层避让距离,以及强震资料积累等关键问题。 相似文献
17.
场地土对基岩峰值加速度放大效应分析 总被引：1，自引：2，他引：1
通过实际土层地震反应结果的统计分析和强震加速度观测结果的对比, 讨论了不同场地条件对基岩峰值加速度的放大效应及其特点。该分析可为地震动参数区划图编制和地震安全性评价中场地效应的估计、由基岩地震动估算场地地面地震动提供参考。 相似文献
18.
Intermediate-depth earthquakes in the Vrancea region occur in response to stress generation due to descending lithosphere
beneath the southeastern Carpathians. In this article, tectonic stress and seismicity are analyzed in the region on the basis
of a vast body of observations. We show a correlation between the location of intermediate-depth earthquakes and the predicted
localization of maximum shear stress in the lithosphere. A probabilistic seismic hazard assessment (PSHA) for the region is
presented in terms of various ground motion parameters on the utilization of Fourier amplitude spectra used in engineering
practice and risk assessment (peak ground acceleration, response spectra amplitude, and seismic intensity). We review the
PSHA carried out in the region, and present new PSHA results for the eastern and southern parts of Romania. Our seismic hazard
assessment is based on the information about the features of earthquake ground motion excitation, seismic wave propagation
(attenuation), and site effect in the region. Spectral models and characteristics of site-response on earthquake ground motions
are obtained from the regional ground motion data including several hundred records of small and large earthquakes. Results
of the probabilistic seismic hazard assessment are consistent with the features of observed earthquake effects in the southeastern
Carpathians and show that geological factors play an important part in the distribution of the earthquake ground motion parameters. 相似文献
19.
Evaluating inelastic displacement demand of structures exposed to seismic hazard is required for the design of new buildings as well as for seismic risk assessment of existing structures. Most of the buildings are designed to withstand strong earthquakes by responding in the nonlinear range. Having special parts of the structure designed to develop a stable hysteretic behaviour allows the structure to deform in order to accommodate the displacement demand imposed by strong ground motions. This paper is centred on finding a correspondence between the maximum elastic and inelastic displacement responses of the single degree of freedom (SDOF) systems subjected to earthquakes generated by Vrancea seismic source. Vrancea intermediate-depth earthquakes are responsible for the seismic hazard throughout Romanian territory. They have distinctive features, such as large displacement demand and large predominant periods, which makes Romania a special seismic environment. Using a database of Romanian and Japanese strong ground motions generated by intermediate-depth earthquakes and performing nonlinear dynamic analysis on the SDOF oscillators following the Takeda model, this study estimates the inelastic to elastic displacement ratio of reinforced concrete systems. Soil conditions, epicentral distance and magnitude influence on inelastic response is analysed using constant ductility response spectra. The main findings of the study are: the local increase of the inelastic to elastic displacement ratio for type C soil (Eurocode 8 classification) for large magnitude earthquakes and the significant effect of soil conditions on the inelastic response of the SDOF systems. The inelastic amplification was evaluated using a functional form depending on system ductility, soil conditions and earthquake magnitude.
相似文献20.
In the present study, distribution of the seismic acceleration at base rock level has been computed for the Zakynthos (Western Greece) Ms = 6.6 earthquake of 18 November 1997, using a semi-empirical approach, taking into consideration the shape and dimension of the fault as well as the direction of the rupture propagation. Considering the geological conditions of the region under investigation and a simplifiedamplification factor, the distribution of peak ground acceleration is obtained. The results derived in this study are based on the amplification factors and velocity response spectra observed in Japan. To get more realistic results we also incorporated in our model attenuation factors obtained by using data from earthquakes in Greece. Different sets of results are compared with peak ground acceleration values recorded by instruments installed in the investigated area and the validity of the applied method is discussed. 相似文献