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1.
Wave absorbing-boundary method in seismic centrifuge simulation of vertical free-field ground motion
In this paper, an evaluation of the method of experimental seismic simulation of vertical free-field ground motion by wave-absorbing boundary and centrifuge modeling is presented. By means of a large soil container with Ductseal lining and an in-box shake-table system, a series of seismic tests on a sand stratum model of uniform density and a large width-to-depth ratio was conducted at multiple g-levels. With a focus on the vertical motion produced, the time-domain data was processed using the transfer function approach. By examining the measured resonant regimes for the vertical mode as a function of the g-level or length scale over the frequency spectrum, the capability of the Ductseal boundary approach in simulating vertical free-field motions in one-dimensional inhomogeneous site response theory is highlighted. In seeking a comprehensive basis of synthesis for the modeling methodology, the benefits of using the three-dimensional elastodynamic model in the interpretation of the vertical free-field measurements are demonstrated. 相似文献
2.
While travelling through the subsoil layers, earthquake generated bedrock motions get modified significantly due to local soil and should be quantified using ground response analysis. Present study concentrates on equivalent linear method of site response analysis in SHAKE2000 software. It is a frequency based analysis tool having default frequency set to 15 Hz. While due consideration is given to amplitude, no to very limited information about the frequency content of the input motion to be considered in ground response analysis is available. In the present work, the effect of the maximum frequency of ground motion in site response analysis using SHAKE2000 is examined. Two sets of analyses are carried out in this work based on 30 globally recorded input motions. In the first analyses, input motion up to 15 Hz maximum frequency, which is a default value in SHAKE2000 is considered while second analyses are based on considering each of the 30 input motions up to the Nyquist frequency. Comparing the results from the two sets of analyses highlight that selection of maximum frequency in SHAKE2000 has considerable effect in ground motion amplification at different depths. As a result, even the peak ground acceleration which controls the building behavior and damage scenario, is going to change considerably even in case same input motion is used in the analysis. 相似文献
3.
The effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions 总被引：1，自引：1，他引：0
In this article, the effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions
is investigated. For this purpose, four finite element models of dam–reservoir–foundation interaction system are prepared
by using the Lagrangian approach. In these models, the reservoir length varies from H to 4H (H: the height of dam). The Folsom gravity dam is selected as a numerical application. Two different ground motion records of
1989 Loma Prieta earthquake are used in the analyses. One of ground motions is recorded in near fault; the other is recorded
in far fault. Also, the two records have the same peak ground acceleration. The study mainly consists of three parts to assess
the effects of reservoir length on the seismic performance of the concrete gravity dam. In the first part, the linear time-history
analyses of the four finite element models prepared for the Folsom gravity dam are performed. In the second part, the seismic
performance of the dam is evaluated according to demand–capacity ratio and cumulative inelastic duration. Finally, the nonlinear
time-history analyses of the finite element models of the dam are carried out by using Drucker–Prager yield criteria for dam
concrete. It is seen from the analyses results that the seismic behavior of the concrete gravity dams is considerably affected
from the length of the reservoir. The reservoir length of 3H is adequate for concrete gravity dams. The selection of ground motion is on of the important parts of seismic evaluation
of gravity dams. Also, the frequency characteristics of the ground motion having the same peak ground acceleration affect
the seismic performance of the dam. The near-fault ground motions are generally creates more stress on the dam body than far-fault
ground motions. The used performance approach provides a systematic methodology for assessment of the seismic performance
and necessity of nonlinear analyses for dam systems. 相似文献
4.
SV波入射下河谷地形地震动分布特征分析 总被引：1，自引：1，他引：0
基于显式有限元方法和人工透射边界,对二维河谷地形在3条地震动波以SV波形式垂直入射和30°斜入射下进行了地震反应分析,比较了河谷地表各观测点地震动的差别,探讨了河谷地形地震动空间分布特征。结果表明,河谷地形对地震动分布具有重要影响,沿河谷斜坡顶到谷底的各观测点地震动峰值加速度（PGA）存在显著差异,地震动位移存在差动现象,地震动加速度反应谱在大于1 Hz的高频段差别明显。入射角度是影响场地地震反应的重要因素,斜入射时各观测点PGA和相对位移的离散程度明显大于垂直入射情形。 相似文献
5.
《Geomechanics and Geoengineering》2013,8(4):247-257
Three dynamic centrifuge models were tested to obtain data for safety evaluation of the Jen-Yi-Tan Dam in Taiwan subject to a strong earthquake. In these tests, recorded 1999 Chi-Chi earthquake ground motions were modified and used on the electro-hydraulic shaking table mounted on the 400 g-ton centrifuge at the University of Colorado at Boulder. All tests were conducted under centrifugal acceleration of 150 g, and the input acceleration was scaled accordingly in order to simulate the given earthquake. A rigid container and water as pore fluid were used in the tests. In both Models 2 and 3, no sign of soil liquefaction was observed in the tests although a noticeable amount of settlements were found from the earth dam cross-section profile after testing. 相似文献
6.
Analytical study of ground motion caused by seismic wave propagation across faulted rock masses 
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下载免费PDF全文 Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Qp and Qs. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions. 相似文献
7.
Recent destructive earthquakes have clearly shown that near-surface geological conditions play a major role in the level of
ground shaking in urban areas. In Canada, Montreal is ranked second for seismic risk after Vancouver considering its population
and regional seismic hazard. The city is largely built on recent unconsolidated marine and river deposits and most of its
infrastructure is old and deteriorated. A seismic risk project that includes a combined methodology for site effects zoning
in large cities, using microtremor measurements (H/V method) coupled with 1D numerical modelling (SHAKE91), has been initiated. The experimental approach gives good estimates
of the fundamental frequency of soft deposits, while the numerical approach provides good estimates of the soil response in
terms of amplification factor related to frequency. Main mechanical properties of soft soils were compiled from various data
available, and a sample of input rock motions from real and synthetic earthquakes was used to compute soil response. The influence
of marine clays on soil response is significant and is well correlated with thickness of these deposits. PGA amplification
factors range from 2 to 4 at frequencies from 2 to 7 Hz, with some occasional larger values. The results demonstrate that
the methodology used for our study is both fast and efficient to determine the influence of soft soils in urban environments.
Such studies are essential for the effective deployment of seismic instrumentation, land-use planning and seismic mitigation. 相似文献
8.
针对基岩明显起伏、土层非均匀分布的典型河口盆地场地,考虑土体非线性特征,采用黏弹性人工边界模拟无限域对地震波动的影响,建立大尺度精细化二维有限元模型,分析了盆地地表地震动幅值、频谱、持时、传递函数特征,探讨了基岩起伏土层的地震动聚集效应及盆地边缘效应。结果表明：（1）盆地近地表土层表现出不同程度的地震动放大效应,且随土层深度增加呈非单调递减特征,基岩突变处地震动聚集效应明显,盆地两侧产生较为显著的边缘效应;场地中、长周期地震动的放大作用显著;（2）多遇地震、偶遇地震和罕遇地震水平时,场地卓越周期依次介于0.35～0.65 s、0.40～0.75 s和0.50～1.05 s之间;给出了盆地地表PGA（地表峰值加速度）、卓越周期均值等值线图及地表加速度反应谱放大因子建议值,地表设计地震动参数amax（地震影响系数）与Tg（特征周期）明显大于现行《建筑抗震设计规范》取值;（3）盆地特殊位置地表地震动持时得到不同幅度增长,且与输入地震动特性相关;（4）该盆地对0.5～2.0 Hz频段基岩地震动的放大效应比较显著,对小于0.2 Hz或大于2.5 Hz的基岩地震动,该盆地地震动放大效应不明显;（5）福州城区及其邻近区域地震动放大效应普遍较大。大尺度二维非线性分析一定程度上能合理反映微地形起伏、土层分布及土体非线性对地震波传播过程的影响。 相似文献
9.
S. A. Agafonova N. L. Frolova I. N. Krylenko A. A. Sazonov P. P. Golovlyov 《Natural Hazards》2017,85(1):171-195
The site amplification functions at 48 sites of NCR have been estimated in this study using the waveforms of locally recorded 23 earthquakes. Due to the absence of a suitable reference site in the region, the widely used horizontal-to-vertical spectral ratio (HVSR) technique has been used for this purpose. The maps showing the spatial distribution of predominant frequencies and the site amplifications at different frequencies corresponding to the natural frequencies of the different-storey buildings have been presented. The predominant frequencies in general are found to be in the range 2.5–7.5 Hz with an average of 4.4 Hz for the region having older alluvium sediments and in the range 1.1–6.4 Hz with an average of 3.3 Hz for the region with the younger alluvium deposits. The average value of the site amplifications for the frequency band 3.0–10.0 Hz is in the range 2.0–5.3 for the sites with significant soil cover, while the spectral amplification corresponding to the predominant frequency varies from 2.5 to 7.5 at most of the sites. The spectral amplification level lies in the range 2.0–3.0 for the sites with less or no sediment cover. The spectral amplification levels presented for the different-storey buildings may be used for the mitigation of seismic hazard in the region. The estimated site amplification functions may be used in the simulation of the site-specific strong ground motions and therefore useful for the evaluation of seismic hazard of a region. 相似文献
10.
To study factors that affect reliability of the derived vertical rotational ground motions (about vertical axis) from translational array waveforms, we have conducted a field test using explosion. The dataset was collected on March 4, 2008 from an active source experiment of the Taiwan Geodynamics Research project (TAIGER, 2008), in which 750 kg of explosives were set off about 500 m away from a specially designed seismic array in free field consisting of 8 tri-axial rotational sensors, 13 tri-axial accelerometers, and 12 six-channel, 24-bit dataloggers with GPS receivers. Our results show that the waveform fits were greatly improved when the explosion-induced crustal strains were less than 2 × 10−5 for our station configuration. As a result, our modeling for the large amplitude part of the mainshock was not entirely successful. However, we have successfully recovered the first order features of the later part of the vertical rotational ground motions using translational velocity waveforms in the 0.5–20 Hz bandwidth using the Spudich and Fletcher’s procedure (2009). Moreover, we used a modified Jaeger’s (1969) formula and derived similar rotational synthetics. We found that the best rotational rate waveform fits were derived using a station configuration of a dense, small-aperture, translational array combined with a few large-offset stations. A small-aperture array is needed to fulfill the uniform rotation assumption. However, inverting data from an array of small spatial dimension requires waveforms of high signal to noise ratio and high sampling rates. Surprisingly, large-offset translation stations provided additional constraints in time and space, helping to fit the low frequency waveforms. Using the inverted result, we forward predicted the vertical translational waveforms not used in the inversion and got excellent fits. This suggests that the inverted results are of good quality for predicting the complete translational ground motions, even though only horizontal components were used in the inversion. Array-derived or directly measured rotational ground motions can be used to predict translational ground motions in the near-by region. Lessons learned from this study could be helpful for future studies using translational ground motions to derive dynamic ground strains, tilts, and torsions. 相似文献
11.
F. Bozzano L. Lenti Salvatore Martino A. Paciello G. Scarascia Mugnozza 《International Journal of Earth Sciences》2011,100(4):861-879
The basin-like setting of stiff bedrock combined with pre-existing landslide masses can contribute to seismic amplifications
in a wide frequency range (0–10 Hz) and induce a self-excitation process responsible for earthquake-triggered landsliding.
Here, the self-excitation process is proposed to justify the far-field seismic trigger of the Cerda landslide (Sicily, Italy)
which was reactivated by the 6th September 2002 Palermo earthquake (M
s = 5.4), about 50 km far from the epicentre. The landslide caused damage to farm houses, roads and aqueducts, close to the
village of Cerda, and involved about 40 × 106 m3 of clay shales; the first ground cracks due to the landslide movement formed about 30 min after the main shock. A stress–strain
dynamic numerical modelling, performed by FDM code FLAC 5.0, supports the notion that the combination of local geological
setting and earthquake frequency content played a fundamental role in the landslide reactivation. Since accelerometric records
of the triggering event are not available, dynamic equivalent inputs have been used for the numerical modelling. These inputs
can be regarded as representative for the local ground shaking, having a PGA value up to 0.2 m/s2, which is the maximum expected in 475 years, according to the Italian seismic hazard maps. A 2D numerical modelling of the
seismic wave propagation in the Cerda landslide area was also performed; it pointed out amplification effects due to both
the structural setting of the stiff bedrock (at about 1 Hz) and the pre-existing landslide mass (in the range 3–6 Hz). The
frequency peaks of the resulting amplification functions (A(f)) fit well the H/V spectral ratios from ambient noise and the H/H spectral ratios to a reference station from earthquake records, obtained by in situ velocimetric measurements. Moreover,
the Fourier spectra of earthquake accelerometric records, whose source and magnitude are consistent with the triggering event,
show a main peak at about 1 Hz. This frequency value well fits the one amplified by the geological setting of the bedrock
in correspondence with the landslide area, which is constituted of marly limestones and characterised by a basin-like geometry. 相似文献
12.
福建沿海地区地微动的谱结构特征 总被引：7，自引：0，他引：7
在福建沿海地区的福州、泉州、莆田等地进行了场地地微动的测试 ,利用快速富里叶变换 (FFT)方法对观测到的地微动信号进行频谱分析。结果表明 ,覆盖层厚度大、有厚层的软弱夹层淤泥的场地 ,其整体刚度小 ,地微动谱能量相当分散 ,频带宽 ,峰值频率低 ,卓越频率一般为 1～ 5Hz ;覆盖层薄、土层刚度 (Vs)大的场地 ,地微动的峰值频率也大 ,卓越频率一般为8～ 11Hz,且常呈单峰形态。软土对高频地微动信号有滤波作用 ,对低频信号起放大作用 ,而硬土层则相反. 相似文献
13.
Ground motion records obtained in recent major strong earthquakes have provided evidence that ground motions recorded near the near-fault regions differ in many cases from those observed further away from the seismic source. As the forward directivity and fling effect characteristics of the near-fault ground motions, they have the potential to cause more considerable damage to structures during an earthquake. Therefore, understanding the influence of near-fault ground motions on the performance of structures is critical to mitigate damage and perform effective response. This paper presents results of a study aimed at evaluating the effects of near-fault and far-fault ground motions on seismic performance of concrete gravity dams including dam-reservoir-foundation interaction. Koyna gravity dam is selected as a numerical application. Four different near-fault ground motion records with an apparent velocity pulse are used in the analyses. 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 seismic performance evaluation method based on the demand-capacity ratio, the cumulative overstress duration and the spatial extent of overstressed regions is presented. The concrete damaged plasticity model including the strain hardening or softening behavior is employed in nonlinear analyses. Nonlinear seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. The results obtained from the analyses show the effects of near-fault ground motions on seismic performance of concrete gravity dams and demonstrate the importance of considering the near-fault ground excitations. 相似文献
14.
P.G. Silva F. Borja C. Zazo J.L. Goy T. Bardají L. De Luque J. Lario C.J. Dabrio 《Tectonophysics》2005,408(1-4):129
This study represents the first paleoseismic approach in Spain in which archaeological remains are considered. The ancient Roman city of Baelo Claudia (1st–4th centuries AD), located at the axial zone of the Gibraltar Strait (Cadiz, south Spain), contains abundant disrupted architectural relics and ground collapses (i.e. landsliding, liquefacion) probably related to historic earthquake damage of intensity IX–X MSK. The archaeological stratigraphy of the city evidence two major episodes of abrupt city destruction bracketed in AD 40–60 and AD 350–395 separated by an intervening horizon of demolition for city rebuilding, otherwise characteristic for many earthquake-damaged archaeological sites in the Mediterranean. The second episode led the eventual city abandonment, and it is evidenced by good examples of column collapse, distortion, failure and breakdown of house and city walls, and pavement warping and disruptions documented during different archaeological excavations, which can be catalogued as secondary coseismic effects. Main damaged relicts observable today are the set of pop-up like arrays and warping developed in the ancient Roman pavement. Their analysis indicate an anomalous westwards ground displacement oblique to the main gentle southward slope of the topography, as also evidence failures, collapses and breakdown of walls and columns, suggesting that stress acted in a broad SW–NE/WSW–ENE orientation consistent whit the expectable motion along the largest NE–SW strike-slip faults of the zone, which in turn can be catalogued as seismic sources of moderate events (ca. 5 mb). Major disruptions and city abandonment were hesitantly related to relatively far strong earthquakes occurred during the late 4th century AD in the Mediterranean or western coast of Iberia by Menanteau et al. [Menanteau, L., Vanney, J.R., Zazo, C., 1983. Belo II : Belo et son environment (Detroit de Gibraltar), Etude physique d'un site antique. Pub. Casa de Velazquez, Serie Archeologie 4., Ed. Broccard, París.]. However, this study indicates that the occurrence of close moderate earthquakes jointly with the unstable character of the ground at the zone (site effect) is a more reliable hypothesis to explain the observed deformations. 相似文献
15.
V. S. Phanikanth Deepankar Choudhury G. Rami Reddy 《Geotechnical and Geological Engineering》2011,29(6):1109-1126
Any earthquake event is associated with a rupture mechanism at the source, propagation of seismic waves through underlying
rock and finally these waves travel through the soil layers to the particular site of interest. The bedrock motion is significantly
modified at the ground surface due to the presence of local soil layers above the bedrock beneath the site of interest. The
estimation of the amplifications in ground response due to the local soil sites is a complex problem to the designers and
the problem is more important for mega cities like Mumbai in India, where huge population may get affected due to devastations
of earthquake. In the present study, the effect of local soil sites in modifying ground response is studied by performing
one dimensional equivalent-linear ground response analysis for some of the typical Mumbai soil sites. Field borelog data of
some typical sites in Mumbai city viz. Mangalwadi site, Walkeswar site, BJ Marg near Pandhari Chawl site are considered in
this study. The ground responses are observed for range of input motions and the results are presented in terms of surface
acceleration time history, ratio of shear stress to vertical effective stress versus time, acceleration response spectrum,
Fourier amplitude ratio versus frequency etc. The typical amplifications of ground accelerations considering four strong ground
motions with wide variation of low to high MHA, frequency contents and durations are obtained. Results show that MHA, bracketed
duration, frequency content have significant effects on the amplification of seismic accelerations for typical 2001 Bhuj motion.
The peak ground acceleration amplification factors are found to be about 2.50 for Mangalwadi site, 2.60 for Walkeswar site
and 3.45 for BJ Marg site using 2001 Bhuj input motion. The response spectrum along various soil layers are obtained which
will be useful for designers for earthquake resistant design of geotechnical structures in Mumbai for similar sites in the
absence of site specific data. 相似文献
16.
作为地铁车站结构地震破坏机制大型振动台系列模型试验之一,开展了近、远场强地震动作用下软弱粉质黏土场地框架式地铁车站结构体系的大型振动台模型试验。测试分析了模型地基的加速度、孔压、地表震陷和模型结构的加速度、应变、水平位移反应等。结果表明：地震波在模型地基的传播过程中呈现出自下而上低频增大、高频减小的现象;强地震动作用下模型地基的基频明显降低,呈现出明显的低频聚集（放大）、高频滤波效应;模型地基的孔压比增长较小,在不同特性地震动作用下模型地基孔压比的发展过程存在较大的差异,并显示出显著的空间效应;近、远场地震动作用下模型地下结构的加速度反应存在明显差异,模型地下结构对软土地基地震动加速度反应的影响具有显著的空间效应;模型地下结构相对变形小、未出现明显上浮现象,地震动频谱特性对其侧墙的变形模式和大小存在显著的影响;模型结构中柱为地震损伤最严重部位;模型结构整体损伤情况较轻、处于非破坏状态。 相似文献
17.
Summary Pseudo-static and dynamic non-linear finite element analyses have been performed to assess the dynamic behaviour of gravity retaining walls subjected to horizontal earthquake loading. In the pseudo-static analysis, the peak ground acceleration is converted into a pseudo-static inertia force and applied as a horizontal incremental gravity load. In the dynamic analysis, an actual measured earthquake acceleration time history has been scaled to provide peak ground acceleration values of 0.1 g and 0.3 g. Good agreement is obtained between the pseudo-static analysis and analytical methods for the calculation of the active coefficient of earth pressure. However, the results from the dynamic analysis require careful interpretation. In the pseudo-static analysis, the increase in the point of application of the resultant active force with the horizontal earthquake coefficient k
h from the one-third point to the mid-height of the wall is clearly observed. In the dynamic analysis, the variation in the point of application is shown to be a function of the type of wall deformation. Both finite element analyses indicate the importance of determining the magnitude of the predicted displacements when assessing the behaviour of the wall to seismic loading. 相似文献
18.
针对现行水工抗震规范中对近断层地震缺乏考虑这一实际问题,首先讨论了近断层、远场地震动的差别,对比了近断层、远场地震动对地下洞室地震响应的影响,继而提出一种新的人工合成近断层地震动时程的方法,并采用合成的近断层地震动时程对某水电站地下洞室群进行了近断层地震稳定性专门研究。结果表明：与常规地震分析中考虑的远场地震动相比,近断层脉冲型地震动的主要特征为Vmax/Amax和Dmax/Amax（Vmax、Dmax、Amax分别为速度峰值、位移峰值、加速度峰值）指标更大,且近断层脉冲型地震动的主要能量集中在1 Hz以下的频段;在相同峰值加速度幅值、相同反应谱的前提下,近断层地震动对高边墙、大跨度地下工程的破坏程度远比远场地震动大;较之前人的研究方法,文中提出的近断层脉冲型地震动合成方法考虑了[1/Tp, 1] Hz这一频段内的地震波信息,更具合理性;在设定的计算条件下,地下厂房洞室群有在近断层地震动作用下发生失稳的危险性,需要进一步针对近断层地震动进行专项风险性评价,以讨论是否需要增设针对性的抗震支护措施。 相似文献
19.
A modified three‐dimensional discontinuous deformation analysis (3D‐DDA) method is derived using four‐noded tetrahedral elements to improve the accuracy of current 3D‐DDA algorithm in practical applications. The analysis program for the modified 3D‐DDA method is developed in a C++ environment and its accuracy is illustrated through comparisons with several analytical solutions that are available for selected problems. The predicted solutions for these problems using the modified 3D‐DDA approach all show satisfactory agreement with the corresponding analytical results. Results presented in this paper demonstrate that the modified 3D‐DDA method with discontinuous modeling capabilities offers a useful computational tool to determine stresses and deformations in practical problems involving fissured elastic media with reasonable accuracy. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
20.
This paper presents probabilistic assessment of seismically-induced slope displacements considering uncertainties of seismic ground motions and soil properties.A stochastic ground motion model representing both the temporal and spectral non-stationarity of earthquake shakings and a three-dimensional rotational failure mechanism are integrated to assess Newmark-type slope displacements.A new probabilistic approach that incorporates machine learning in metamodeling technique is proposed,by combining relevance vector machine with polynomial chaos expansions(RVM-PCE).Compared with other PCE methods,the proposed RVM-PCE is shown to be more effective in estimating failure probabilities.The sensitivity and relative influence of each random input parameter to the slope displacements are discussed.Finally,the fragility curves for slope displacements are established for sitespecific soil conditions and earthquake hazard levels.The results indicate that the slope displacement is more sensitive to the intensities and strong shaking durations of seismic ground motions than the frequency contents,and a critical Arias intensity that leads to the maximum annual failure probabilities can be identified by the proposed approach. 相似文献