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1.
剪切波速对场地地表地震动参数的影响 总被引：3，自引：2，他引：1
本文以江淮地区典型场地资料为原型,将土层剪切波速实测值按照一定比例进行增减,构造多种场地土层地震反应分析模型,选择Taft、E1centro和Kobe三条强震记录作为地震输入,采用一维频域等效线性化波动方法进行了土层地震反应分析.研究结果表明,剪切波速的变异性与场地地表地震动的影响程度与输入基岩地震动的频谱特性、幅值、土层结构等因素有关.地表峰值加速度随着剪切波速的增大而逐渐增大,地表加速度反应谱的特征周期随着剪切波速的增大而逐渐减小. 相似文献
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场地条件对地震动特性影响显著,在抗震设计反应谱的确定过程中,需根据场地条件对加速度反应谱予以相应的调整。已有场地条件影响调整方案研究成果,均基于数值模拟或局部地区强震动记录统计,多数仅给出了峰值加速度PGA场地条件影响调整系数,对非线性的考虑缺乏观测数据依据。为此在全球强震动记录统计获得的PGA归一化加速度反应谱和日本钻井台阵记录获得的加速度反应谱平台值非线性衰减指数的基础上,结合钻孔模型数值模拟和近期研究成果,建立了考虑场地条件影响非线性的地震动加速度反应谱场地条件影响调整系数方案。 相似文献
4.
本文选取山东地区2个Ⅲ类场地的工程地质勘探及土层剪切波速等资料,将土层厚度按5个深度段,每个分段给出了4个土层剪切波速的改变量,通过改变不同深度段土层剪切波速,建立了19种土层地震反应分析模型,分析了不同深度段,不同概率水平下土层剪切波速的变化对场地地震动参数的影响。研究表明,不同深度段土层剪切波速的变化对场地地震动参数的影响有差异。具体表现为,土层剪切波速的改变在1—10m、11—40m和地震输入界面处三个深度段对地震动加速度峰值影响较大;其中,41—70m和71—100m两个深度段剪切波速的改变对地震动加速度峰值影响小;在土层深度1—10m时,剪切波速降低,峰值变大,剪切波速的改变与峰值的改变呈负相关;在其它深度段,剪切波速降低,峰值变小,剪切波速的改变与峰值的改变呈正相关。剪切波速的改变在1—10m和11—40m两个深度段对地震加速度反应谱影响较大;在41—70m、71—100m和地震输入界面三个深度段对地震加速度反应谱影响很小。 相似文献
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美国阿拉斯加安克雷奇德兰尼公园的土层地震反应观测台阵建有6个井下观测点和1个地表观测点, 每个观测点设置一个三分量加速度传感器, 该台阵建成后记录了多次地震事件. 本文通过反卷积地震干涉法对这些地震记录进行土层反应分析, 根据该分析结果提取土层结构的等效剪切波速和阻尼比. 所有层位的地震记录对地表记录的反卷积波形均反映出在土层中传播的上、 下行波, 其上行与下行至每一层的时间差别明显. 根据每一层的到时差, 确定土层中的等效剪切波速和分层等效剪切波速, 该结果与现场土层等效剪切波速测试结果吻合较好; 根据等效剪切波速计算出的土层卓越频率, 其一致性亦较好; 根据上、 下行波的峰值分析确定该场地土层的等效阻尼比, 也与软土的阻尼比经验值相当. 这些参数为后续的土层反应模拟和土结相互作用研究奠定了良好的数据基础. 结果表明, 反卷积干涉法能够用于土层反应分析和土层地震反应特性的提取. 相似文献
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2020年7月12日发生了唐山古冶5.1级地震,其强震动影响波及京津唐地区,特别是北京城区也出现了强烈的震感。中国强震动观测台网、国家地震烈度速报台网及典型建筑结构地震反应观测台阵获得大量的强震动记录。这次地震震级不大,但为地震科学研究提供了较为丰富的信息。基于获得的地震影响信息,可开展以下方面的研究:①利用地震附近及区域范围内地震烈度速报台网的密集观测记录,开展地震影响烈度快速计算分析及台网功能可靠性检测;②利用北京和天津地区的强震动观测记录,探讨深厚覆盖土层和盆地场地地震动影响;③利用京津唐地区震中距至300 km的强震动观测记录,研究京津唐地区的地震动衰减特性;④利用北京城区的建筑结构地震反应观测台阵记录,分析典型工程结构地震反应特征;⑤其他,如场地土层参数和工程结构参数反演研究等。本文针对以上关注的问题,介绍了相关初步研究工作并开展了进一步探讨性分析研究,展示了唐山古冶5.1级地震影响的丰富信息和对相关研究的潜在推进作用。 相似文献
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为了认识响嘡真实地震动下土体动力特征，分析场地响应，以及检验和提高工程钻探方法、现场测试及土工试验的精度，通过层转换矩阵永为实矩阵的成层场地地震反应分析， 结合遗传算法-单纯形法这一全局-局部混合优化方法，进行了同时考虑SH、P和SV波型的多分量实际波形的反演拟合. 最后给出了响嘡钻井台阵(2＃)3次中小地震反演结果，并提供了以往研究中没有涉及的纵波波速值、阻尼比值及与频率有关的阻尼频率因子b值. 结果表明，反演的响嘡2＃钻井台阵剪切波速值大于1994年单孔原位波速测试结果， 而更接近于距其200多米的3＃的剪切波速结果；并发现在峰值加速度60times;10-2m/s2量级的地震作用中就存在反演可以察觉的土体非线性. 另外， 该方法亦可用于其它钻井台阵的研究和分析. 相似文献
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浅地表软弱覆盖层对地震动的影响具有强非线性,但因观测记录样本量过小,难以通过参考谱比法等直接方法予以可靠分析。本文基于日本KiK-net台网136个竖向钻井台阵获取的141881 组加速度记录的统计分析,研究了地表/井下反应谱比值随地震动强度变化的非线性变化规律与主要影响因素。利用变窗口尺度的滑动窗口平均法加强数据线性度,并确定了与地震动强度相关的台站最小记录样本量,统计结果表明地表/井下反应谱比值平台值随地震动强度变化的非线性衰减指数为-0.24～-0.08。利用套索（Lasso）算法统计回归发现,本研究12个场地特性表征参数中,30 m平均剪切波速（$ {V}_{\mathrm{s}30} $）、场地卓越频率与地表/井下反应谱比值非线性衰减指数具有较好的正相关性;较弱强度地震动作用下地表/井下傅里叶谱比值峰值、地表/井下反应谱比值峰值与地表/井下反应谱比值非线性衰减指数具有较好的负相关性。 相似文献
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《世界地震工程》2017,(4)
为研究南海地区珊瑚岛礁场地对地震动的放大作用特征,基于南海珊瑚岛礁几个代表性场地钻孔资料和60条近断层脉冲型强震记录,结合强震数据和土层地震反应分析结果讨论了地震动幅值水平和场地条件对场地放大的影响。根据地貌单元特性、地层岩性、成因和分布规律,得到4类工程地质场地,建立了一维土层地震反应分析模型并选取了土体动力参数,讨论了其在脉冲型地震动作用下地震反应特征。结果表明:从土层剪切波速来看珊瑚礁场地属于我国国家《建筑抗震设计规范》中的Ⅱ类场地;珊瑚礁场地对脉冲型地震动的放大倍数在1.6~2.4之间,放大明显的周期在0.2~0.8s之间。另外,对珊瑚礁礁坪区、泻湖区、沙洲区和灰沙岛区4类场地的地震反应分析表明:在脉冲型地震动作用下沙洲区场地放大倍数小于其他区;灰沙岛区在周期为0.3s左右时场地放大倍数明显大于其他区。研究结果整体反映了珊瑚礁场地对脉冲型地震动的场地放大特征,可对珊瑚礁的开发建设提供参考。 相似文献
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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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Centrifuge modeling of seismic response of layered soft clay 总被引：1，自引：0，他引：1
Centrifuge modeling is a valuable tool used to study the response of geotechnical structures to infrequent or extreme events
such as earthquakes. A series of centrifuge model tests was conducted at 80g using an electro-hydraulic earthquake simulator mounted on the C-CORE geotechnical centrifuge to study the dynamic response
of soft soils and seismic soil–structure interaction (SSI). The acceleration records at different locations within the soil
bed and at its surface along with the settlement records at the surface were used to analyze the soft soil seismic response.
In addition, the records of acceleration at the surface of a foundation model partially embedded in the soil were used to
investigate the seismic SSI. Centrifuge data was used to evaluate the variation of shear modulus and damping ratio with shear
strain amplitude and confining pressure, and to assess their effects on site response. Site response analysis using the measured
shear wave velocity, estimated modulus reduction and damping ratio as input parameters produced good agreement with the measured
site response. A spectral analysis of the results showed that the stiffness of the soil deposits had a significant effect
on the characteristics of the input motions and the overall behavior of the structure. The peak surface acceleration measured
in the centrifuge was significantly amplified, especially for low amplitude base acceleration. The amplification of the earthquake
shaking as well as the frequency of the response spectra decreased with increasing earthquake intensity. The results clearly
demonstrate that the layering system has to be considered, and not just the average shear wave velocity, when evaluating the
local site effects. 相似文献
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Mourad Zeghal Ahmed-W. Elgamal Ender Parra 《Soil Dynamics and Earthquake Engineering》1996,15(8):523-547
Downhole records of seismically-induced soil liquefaction are a valuable source of information on the associated mechanisms of stiffness degradation and lateral spreading. In this paper, free-field downhole array seismic records are employed to identify and model the recorded response at Wildlife Refuge (California, USA) and Port Island (Kobe, Japan) sites. The Wildlife Refuge site was instrumented in 1982 with a two-accelerometer array and six piezometers that recorded a case of seismically induced site liquefaction. At Port Island, a four-accelerometer down-hole array recorded strong motion during the recent 1995 Hyogoken-Nanbu earthquake. This earthquake resulted in widespread liquefaction and major ground deformations at Port Island. Using the recorded downhole accelerations at these two sites, the actual seismic shear stress-strain histories are directly evaluated. These histories provide valuable insight into the mechanisms of site liquefaction and associated loss of stiffness and strength. Based on the identified dynamic soil behaviors, computational simulations of the observed seismic response are performed. Optimization techniques are employed to estimate the necessary computational modeling parameters. This document constitutes the second part of a set of two companion papers about site amplification and liquefaction. 相似文献
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As the forward directivity and fling effect characteristics of the near-fault ground motions, seismic response of structures in the near field of a rupturing fault can be significantly different from those observed in the far field. The unique characteristics of the near-fault ground motions can cause considerable damage during an earthquake. This paper presents results of a study aimed at evaluating the near-fault and far-fault ground motion effects on nonlinear dynamic response and seismic damage of concrete gravity dams including dam-reservoir-foundation interaction. For this purpose, 10 as-recorded earthquake records which display ground motions with an apparent velocity pulse are selected to represent the near-fault ground motion characteristics. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The Koyna gravity dam, which is selected as a numerical application, is subjected to a set of as-recorded near-fault and far-fault strong ground motion records. The Concrete Damaged Plasticity (CDP) model including the strain hardening or softening behavior is employed in nonlinear analysis. Nonlinear dynamic response and seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. Both local and global damage indices are established as the response parameters. The results obtained from the analyses of the dam subjected to each fault effect are compared with each other. It is seen from the analysis results that the near-fault ground motions, which have significant influence on the dynamic response of dam–reservoir–foundation systems, have the potential to cause more severe damage to the dam body than far-fault ground motions. 相似文献
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Earthquake-induced hazards are profoundly affected by site effects related to the amplification of ground motions, which are strongly influenced by local geologic conditions such as soil thickness or bedrock depth and soil stiffness. In this study, an integrated geographic information system (GIS)-based system for geotechnical data, called the geotechnical information system (GTIS), was developed to establish a regional counterplan against earthquake ground motions in the Seoul metropolitan area. In particular, to reliably predict spatial geotechnical information, a procedural methodology for building the GTIS within a GIS framework was developed and applied to the Seoul area in Korea. To build the GTIS, pre-existing geotechnical data were collected in and around the study area, and then a walk-over site survey was conducted to acquire surface geo-knowledge data. In addition, the representative shear wave velocities for geotechnical layers were derived by statistically analyzing many seismic test data in Korea. The GTIS was used in a practical application to estimate site effects in the study area; seismic zoning maps of geotechnical earthquake parameters, such as the depth to bedrock and the site period, were created and presented as a regional synthetic strategy for earthquake risk assessment. Furthermore, seismic zonation of site classification was also performed to determine the site amplification coefficients for seismic design and seismic performance evaluation at any site and administrative sub-unit in the study area. The methodology and results of the case study of seismic zonations in the Seoul area verified that the GIS-based GTIS can be very useful for the regional estimation of seismic risk and also to support decisions regarding seismic hazard mitigation, particularly in the metropolitan area. 相似文献
15.
A.-W. Elgamal M. Zeghal E. Parra R. Gunturi H.T. Tang J.C. Stepp 《Soil Dynamics and Earthquake Engineering》1996,15(8):499-522
Seismic downhole-array data provide a unique source of information on actual soil (and overall site) behavior over a wide range of loading conditions that are not readily covered by in-situ or laboratory experimentation procedures. In this paper, free-field downhole-array seismic records are employed to identify and model the recorded response at the Lotung (Taiwan) and Treasure Island (California) sites. At Lotung, a five-accelerometer array recorded the site response during 18 earthquakes (1985–1986). The Treasure Island site was instrumented in 1992 with an array of six accelerometers that recorded a low amplitude earthquake in 1993. Using this downhole data, correlation and spectral analyses are performed to evaluate shear wave propagation characteristics, variation of shear wave velocity with depth and site resonant frequencies and model configurations. In addition, the actual seismic shear stress-strain histories are directly evaluated from the recorded downhole accelerations. These histories provide valuable insight into the mechanisms of site amplification, damping and pore-pressure build-up. Computational simulations of these case histories are performed based on the identified mechanisms of site response. In a companion paper, two additional case histories of site liquefaction are analyzed using records of downhole seismic response. 相似文献
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The objective of this study is to investigate the effects of local site conditions in the Adapazarı plain crossing the severely damaged central part of Sakarya during the 17th August earthquake. A two-dimensional model has been used to obtain the free-field motions in the valley and on surface formations. A preliminary geotechnical profile model developed from available but limited soil data was checked using recordings of some specific locations where a strong ground motion accelerometer array was in operation after the main earthquake. The range of validity of the model was assessed and modifications were made to compare with the actual recorded motions. The purpose of building such a model, which was used to study the aftershocks in Adapazarı, is to provide an improved database to be used for the design of structures in the city. This study also attempts to provide greater insight into the local site response phenomena through the use of a two-dimensional nonlinear analysis. Simulated site responses are in global agreement with the recorded data. In general agreement between the amplification functions of the computed and recorded data is satisfactory for the frequencies of engineering interest. Alluvial sites show amplification factors in the range of 4–6 in the frequencies between 0.6 and 2 Hz. A relatively shallow alluvial station, HASTAHANE, experienced considerable amplification for small aftershocks and deamplification for the strongest aftershock in frequencies between 0.5 and 2 Hz. Another station, TOYOTA, with significant deamplification characteristics and a clearly observed peak response frequency shift at the soil resonant frequency may have experienced soil shear failure during the strongest aftershock. Other alluvial stations, SEKER and GENC, show deamplification characteristics at 0.55 and at around 1 Hz. with the peak frequency shifts during the magnitude 5.8 aftershock. In general, site responses are larger in the alluvial basin for all aftershocks except the magnitude 5.8 event. 相似文献
17.
The seismic response of the Mexico City Cathedral built of very soft soil deposits is evaluated by using motions recorded in various parts of the structure during several moderate earthquakes. This unique set of records provides significant insight into the seismic response of this and other similar historic stone masonry structures. Free‐field ground motions are carefully compared in time and frequency domains with motions recorded at building basement. The dynamic characteristics of the structure are inferred from the earthquake records by using system identification techniques. Variation of seismic response for different seismic intensities is discussed. It is shown that, due to the soil–structure interaction, due to large differences between dominant frequencies of earthquake ground motions at the site and modal frequencies of vibration of the structure, and due to a particularly high viscous damping, seismic amplifications of ground motion in this and similar historic buildings erected on soft soil deposits are much smaller than that induced in most modern constructions. Nevertheless, earthquake records and analytical results show that several components of the structure such as its central dome and the bell towers may be subjected to local vibrations that significantly amplify ground motions. Overall, results indicate that in its present state the structure has an acceptable level of seismic safety. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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19.
A method for generating a suite of synthetic ground motion time‐histories for specified earthquake and site characteristics defining a design scenario is presented. The method employs a parameterized stochastic model that is based on a modulated, filtered white‐noise process. The model parameters characterize the evolving intensity, predominant frequency, and bandwidth of the acceleration time‐history, and can be identified by matching the statistics of the model to the statistics of a target‐recorded accelerogram. Sample ‘observations’ of the parameters are obtained by fitting the model to a subset of the NGA database for far‐field strong ground motion records on firm ground. Using this sample, predictive equations are developed for the model parameters in terms of the faulting mechanism, earthquake magnitude, source‐to‐site distance, and the site shear‐wave velocity. For any specified set of these earthquake and site characteristics, sets of the model parameters are generated, which are in turn used in the stochastic model to generate the ensemble of synthetic ground motions. The resulting synthetic acceleration as well as corresponding velocity and displacement time‐histories capture the main features of real earthquake ground motions, including the intensity, duration, spectral content, and peak values. Furthermore, the statistics of their resulting elastic response spectra closely agree with both the median and the variability of response spectra of recorded ground motions, as reflected in the existing prediction equations based on the NGA database. The proposed method can be used in seismic design and analysis in conjunction with or instead of recorded ground motions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
20.
砂土自由场地震响应的离心机试验研究 总被引：2，自引：1，他引：2
离心机模型试验是研究岩土地震工程问题的有效手段。本文使用层状剪切箱,通过干落法制备了均匀的砂土模型,进行了离心机振动试验;观测了振动过程中孔隙水压力的发展,土体的加速度响应、侧向变形以及竖向沉降。结果表明,土体的运动和变形与孔隙水压力的发展密切相关,但离心机中的试验现象和现场观测的现象存在显著区别。研究结果增强了对振动过程中土-水之间相互作用机理的理解,同时为自由场地震响应分析方法的验证提供了基础数据。 相似文献