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1.
场地条件对地震动相干函数的影响 总被引：3，自引：1，他引：3
本通过弹性半空间内位错源的数值解法研究了曲岩地震动相干函数，采用有限元方法分析了一些典型场地的地表地震动相干函数，两的对比结果表明：复杂场地对地震动相干函数的影响强烈。 相似文献
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Djilali Berkane Hakima Harichane Zamila Çelebi Erkan Elachachi Sidi Mohammed 《地震工程与工程振动(英文版)》2019,18(3):497-509
The goal of this study is to provide a stochastic method to investigate the effects of the randomness of soil properties due to their natural spatial variability on the response spectra spatial variation at sites with varying conditions. For this purpose, Monte Carlo Simulations are used to include the variability of both incident ground motion and soil parameters in the response spectra by mean of an appropriate coherency loss function and a site-dependent transfer function, respectively. The approach is built on the assumption of vertical propagation of SH type waves in soil strata with uncertain parameters. The response spectra are obtained by numerical integration of the governing equation of a single-degree-of-freedom(SDOF) system under non-stationary site-dependent and spatially varying ground motion accelerations simulated with non-uniform spectral densities and coherency loss functions. Numerical examples showed that randomness of soil properties significantly affects the amplitudes of the response spectra, indicating that as the heterogeneity induced by the randomness of the parameters of the medium increases, the spectral ordinates attenuate. 相似文献
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H. HAO 《地震工程与结构动力学》1996,25(6):599-610
Due to the inherent difficulty in directly recording the rotational ground motions, torsional ground motions have to be estimated from the recorded spatially varying translational motions. In this paper, an empirical coherency function, which is based on the recorded motions at the SMART-1 array, is suggested to model the spatial variation of translational motions. Then, the torsional ground motion power spectral density function is derived. It depends on the translational motion power spectral density function and the coherency function. Both the empirical coherency function and the torsional motion power spectral density function are verified by the recorded motions at the SMART-1 array. The response spectra of the torsional motions are also estimated. Discussion on the relations between the torsional motion response spectrum and the corresponding translational motion response spectrum is made. Numerical results presented can be used to estimate the torsional ground motion power spectral density function and response spectrum. 相似文献
6.
Coherency functions are used to describe the spatial variation of seismic ground motions at multiple supports of long span structures. Many coherency function models have been proposed based on theoretical derivation or measured spatial ground motion time histories at dense seismographic arrays. Most of them are suitable for modelling spatial ground motions on flat‐lying alluvial sites. It has been found that these coherency functions are not appropriate for modelling spatial variations of ground motions at sites with irregular topography (Struct. Saf. 1991; 10 (1):1–13). This paper investigates the influence of layered irregular sites and random soil properties on coherency functions of spatial ground motions on ground surface. Ground motion time histories at different locations on ground surface of the irregular site are generated based on the combined spectral representation method and one‐dimensional wave propagation theory. Random soil properties, including shear modulus, density and damping ratio of each layer, are assumed to follow normal distributions, and are modelled by the independent one‐dimensional random fields in the vertical direction. Monte‐Carlo simulations are employed to model the effect of random variations of soil properties on the simulated surface ground motion time histories. The coherency function is estimated from the simulated ground motion time histories. Numerical examples are presented to illustrate the proposed method. Numerical results show that coherency function directly relates to the spectral ratio of two local sites, and the influence of randomly varying soil properties at a canyon site on coherency functions of spatial surface ground motions cannot be neglected. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
7.
Many studies have focused on horizontal ground motion, resulting in many coherency functions for horizontal ground motion while neglecting related problems arising from vertical ground motion. However, seismic events have demonstrated that the vertical components of ground motion sometimes govern the ultimate failure of structures. In this paper, a vertical coherency function model of spatial ground motion is proposed based on the Hao model and SMART 1 array records, and the validity of the model is demonstrated. The vertical coherency function model of spatial ground motion is also compared with the horizontal coherency function model, indicating that neither model exhibits isotropic characteristics. The value of the vertical coherency function has little correlation with that of the horizontal coherency function. However, the coherence of the vertical ground motion between a pair of stations decreases with their projection distance and the frequency of the ground motion. When the projection distance in the wave direction is greater than 800 meters, the coherency between the two points can be neglected. 相似文献
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K. AfifChaouch B. Tiliouine M. Hammoutene R. Sigbjörnsson R. Rupakhety 《Bulletin of Earthquake Engineering》2016,14(4):1195-1217
Spatial variability of ground motions has significant influence on dynamic response of extended structures such as bridges and tunnels. In this study, the widely used finite-source ground motion simulation approach, the so-called Empirical Green’s Function (EGF) method, is extended to synthesize seismic motions across an array of stations located at bedrock in the epicentral region of the 1980 El-Asnam region (North-West Algeria). The target event being simulated is the October 10 1980 \( M_{s} = 7.2 \) Earthquake, and the EGF is obtained from the ground motion recorded at Sogedia Factory station during the 8 November 1980 \( M_{L} = 5.6 \) aftershock. Coherency functions are then estimated from the simulated ground accelerations. A parametric study investigating the influence of shear wave velocity, earthquake magnitude, and epicentral distance is conducted by simulating ground acceleration for different scenarios using the Hybrid Green’s Function method. The main finding of the study is that finite source effects can cause significant loss in coherency at bedrock in the near-field. In the far-field, the source effect alone does not seem to produce incoherent motion, which implies that scattering and local site effects could be dominating there. Furthermore, coherency functions are found to be more sensitive to inter-station separation in the near-field than in the far-field. Increasing shear wave velocity seems to increase coherency functions, and larger earthquakes seem to produce more incoherent motion than smaller ones. The simulation method presented here produces incoherent motion mainly due to the finite source effect, while path effects are partially accounted for through the EGF, and local site effects are not considered. In this sense, the estimated coherency functions represent that of plane waves. A parametric model of plane wave coherency is calibrated and presented based on the simulation results. The results indicate that the parametric model can be used as a first approximation, and at least an upper bound of lagged coherency in the near-field region of the El-Asnam Earthquake scenario. This model could be useful in random vibration analysis or generation of spatially variable ground motion for time history analysis of lifeline structures in the study area. 相似文献
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《地震工程与工程振动(英文版)》2015,(3)
This paper addresses the analytical evaluation of soil lateral heterogeneity effects,especially the random fluctuations of the soil layer's predominant frequency,on the spatial coherency of ground motion and the seismic response of multi-support structures.A coherency probabilistic model is proposed.In this model,the spatial variation of motion is attributed to wave passage effects,effects of loss of coherence in the bedrock motion and particularly site response effects(based on the assumption of vertically propagating shear-waves through a horizontal layer with random characteristics).The results indicate that soil lateral heterogeneity effects tend to cause diminution of the values of the total coherency function.This diminution is not limited to the vicinity of the mean resonant frequency of the layer,but reaches considerably high frequencies even for relatively low values of coefficient of variation(CV of 5 to 15%).Therefore,the trend of the total coherency function(exponential decay) can be influenced significantly by site effects.Finally,the proposed coherency model is applied for two different support seismic excitations.Study results indicate that the greater the soil heterogeneity,the larger are the dynamic displacements and shear forces in the columns of the oscillator(i.e.,support structure).Furthermore,these two components of the response are influenced differently by soil heterogeneity effects. 相似文献
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将土非线性分析的等效线性化方法与随机工程波动散射问题的求解方法相结合，建立了开放系统中非一致激励条件下考虑岩土介质非线性的工程场地地震动随机场数值模拟方法并研究了介质非线性对场地地震动相干性的影响。分析结果表明：与不考虑非线性相比，在地震过程中，场地土介质的非线性改变了复杂场地的局部特性从而导致场地地震动空间相干性的变化，因此有必要在场地地震动相干函数的分析中考虑场地介质非线性特性对地震动相干性的影响。 相似文献
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Response spectrum analysis for non-classically damped linear system with multiple-support excitations 总被引：1，自引：0，他引：1
A new response spectrum method, which is named complex multiple-support response spectrum (CMSRS) method in this article,
is developed for seismic analysis of non-classically damped linear system subjected to spatially varying multiple-supported
ground motion. The CMSRS method is based on fundamental principles of random vibration theory and properly accounts for the
effect of correlation between the support motions as well as between the modal displacement and velocity responses of structure,
and provides an reasonable and acceptable estimate of the peak response in term of peak seismic ground motions and response
spectra at the support points and the coherency function. Meanwhile, three new cross-correlation coefficients or cross covariance
especially for the non-classically damped linear structures with multiple-supports excitations are derived under the same
assumptions of the MSRS method of classically damped system. The CMSRS method is examined and compared to the results of time
history analyses in two numerical examples of non-classically damped structures in consideration of the coherences of spatially
variable ground motion. The results show that for non-classically damped structure, the cross terms representing the cross
covariance between the pseudo-static and dynamic component are also quite small just as same as classically damped system.
In addition, it is found that the usual way of neglecting all the off-diagonal elements in transformed damping matrix in modal
coordinates in order to make the concerned non-classically damped structure to become remaining proportional damping property
will bring some errors in the case of subjected to spatially excited inhomogeneous ground motion. 相似文献
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In this paper, seismic records of Taiwan LSST array and SMART-1 array were selected to calculate the S-wave and surface wave coherence coefficients at different station distances. And then the coherence function model proposed by Loh was used to fit the calculation results. After comparison and analysis, we found that when the distance d < 50 m, the coherency coefficients of surface wave and S-waves are basically the same; when the distance d = 50 m , the coherency coefficients of surface wave is smaller than that of S-wave, and as the distance increases, the differences gradually increase. When the distance d > 500 m, the spatial coherency of the surface wave hardly exists, so no further consideration is needed. Finally, the surface wave coherency model parameters were given in this paper, which can be used as a reference for the synthetic ground motion field in the seismic analysis for long and large structures in large basins. 相似文献
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本文将随机振动的虚拟激励原理与工程波动理论散射问题的求解方法相结合,建立了开放系统中非一致激励条件下工程场地地震动随机场的数值模拟方法。该方法将随机输入下的波动分析问题转换为多个虚拟激励下的确定性波动分析组合问题,从而可以方便地获得场地波动观测量之间的谱密度矩阵,进而计算给出工程场地的地震动相干函数。本文还用数值模拟的办法对所提出方法的合理性和稳定性进行了探讨。 相似文献
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将随机结构正交展开理论和随机振动分析的虚拟激励原理运用于场地波动有限元分析，形成了一种可以考虑岩土介质随机特性对工程场地地震动相干函数影响的分析方法。实例分析表明，非严格均匀分布的随机介质场地对场地表面的迟滞相干函数值有重要影响，这种影响可由场地的随机影响因子来衡量，在进行工程场地地震动随机场研究时应当考虑场地介质随机特性的影响。 相似文献
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目前人们在进行地震动相干函数模型参数的拟合时,选取的频段范围存在很大差异,而确定有效的频段范围对相干函数模型拟合结果的合理性很重要。本文利用AR模型(Autoregressive Model,自回归模型)计算地震动的功率谱,提出了根据功率谱"信噪比(SNR)"确定相干函数有效频段范围的方法。本文的信噪比中的"噪",专指AR模型中的激励白噪声,用于衡量AR模型中某一频率地震动功率谱与激励白噪声功率谱之间的比例。定义信噪比SNR=0时对应的频率为有效频段的最高频率,大于最高频率的频率成分,被当作是地震波中的随机成分,可以不考虑地震动的相关性。采用这一方法,对SMART-1第45次地震记录的不同台站间距下的地震波进行了功率谱估计,根据信噪比确定出了有效频段范围,并计算了相应的相干函数,结果表明此方法是可行的。 相似文献
18.
Hong Hao 《地震工程与结构动力学》1991,20(9):821-838
The ground motions produced by an earthquake at the multiple support points of large structures can differ considerably. In this study, the quasi-static, the dynamic and the total structural responses of a multiply supported rigid plate to spatially varying multiple ground motion inputs are analysed. The results, together with those obtained by neglecting ground motion phase shifts and those by neglecting ground motion coherency losses, are compared with the corresponding structural responses to a single input. The comparisons show that the single input method overestimates translational responses and underestimates rotational responses. They also show that the responses are sometimes overestimated and sometimes underestimated by neglecting the coherency loss effects between the multiple ground motion excitations. 相似文献
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《地震工程与工程振动(英文版)》2021,20(3)
We present examples of a controlled numerical experiment that contribute towards understanding of the physical phenomena that lead to the reduction of coherency of strong earthquake ground motion. We show examples for separation distance of 100 m between the two points on the ground surface, which is in the range of engineering interest. Our examples illustrate the consequences of:(a) standing waves that result from interference of the incident and reflected waves from a near vertical contrast in material properties,(b) standing waves within a concave inhomogeneity(a semi-circular valley in our examples), and(c) smaller motions in the diffraction zone, behind the inhomogeneity. We show that it is possible to reduce coherency, to the extent observed for recorded strong earthquake ground motion, even by a single inclusion in a half space, for incident ground motion that is coherent. We also illustrate the combined effects of geometric spreading and finite fault width, superimposed on the otherwise dominating effects caused by interference. Our examples show reduction of coherence for specific angles of incident waves, while, for other angles of incidence, the coherence remains essentially equal to one. 相似文献
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Spatially varying ground motion (SVGM) may have influence on certain civil engineering structures with spatially extended superstructure and/or substructures. Conditional simulation of spatially varying ground motion (CSSVGM) may be viewed from two different perspectives. Most procedures available in the literature neglect the spatial variability in auto-spectral density (ASD) and estimate the SVGM through cross-spectral density (CSD) which was computed using the empirical coherency models. This paper proposes a coherency model that accounts for the spatial variability of ASD. A framework has been developed for the CSSVGM, through the mapping of both proposed coherency model and ASD over the footprint of an array. Current framework (existing in the literature) accounts for only the phase variability of SVGM while proposed framework accounts for both phase and amplitude variability. Ground motion generated from both perspectives is then assessed with the data recorded over SMART1 and LSST arrays. For the purpose of assessment, a definition of target spectrum based on the direction of arrival is explored. The effect of choice of coherency model on the simulated spatially varying ground motion is investigated first. Spectra resulting from both the perspectives are assessed against the target spectrum. An attempt has been made to predict the SVGM for a future event using a coherency model calibrated against a past event and an estimate of ASD of the seed ground motion. Finally, the effect of form of ASD (of a seed ground motion) on SVGM simulated is investigated by considering the ASD in different forms. Simulating SVGM through the mapping of both coherency model and ASD seems to be more appropriate than through CSD. 相似文献