含流体层的河谷场地对地震波散射的间接边界元法模拟

结合单相介质动力格林函数和流体域格林函数,将间接边界元方法拓展到含流体层河谷对地震波散射的求解,并结合具体算例进行大量参数分析。研究结果表明,含流体层河谷地形对平面P波、SV波入射时的地震响应受控于入射波频率、入射波角度及流体深度等多种因素。总体来看:① 在低频域内,含流体河谷底部及附近地表的频谱特性与不含流体的河谷反应基本一致;② P波入射时在水层体系共振频率处,河谷底部位移缩小效应显著,而此频率处流体表面位移达到最大;③ 流体层具有吸收地震波能量的作用,流体深度越大,河谷表面及附近地表的地震动位移越小。研究成果可在一定程度上为河谷地形附近地震动效应的评估及防震减灾工作提供理论依据。      

Numerical investigation of stochastic response of an elevated water tank to random underground blast loading

This paper presents a stochastic finite element seismic response study of a water tank subjected to random underground blast-induced ground motion. Such tanks contain water and hazardous chemical substances, which implies significant risk to human life, serious environmental pollution, and considerable economic loss. The random blast-induced ground motion is represented by power spectral density function and applied to each support point of the three dimensional finite element model of the elevated water tank–fluid interaction system. A parametric study is conducted to estimate the effects of the blast-induced ground motion on the stochastic response of the elevated water tank system. Therefore, the analyses are carried out for different values of the charge weight and the distance from the charge centre. Additionally, in order to investigate the effect of the fluid on the stochastic response of the elevated water tank, three cases with different water levels are considered in the analyses. Finally, it is observed that underground blast loading considerably changes the stochastic behavior of the elevated water tank system.     

SH波入射下圆弧状沉积盆地地震反应瞬态解析解计算

地震波散射问题的解析解是研究局部场地、地形、盆地等不规则地层结构对地震动参数放大效应影响的重要理论工具.现有解析解大部分在频域内给出,无法直接用于研究不规则地层结构对地震动峰值、反应谱等参数的放大效应.本文基于平面SH波入射下圆弧状沉积盆地动力响应宽频带稳态解析解,通过Fourier变换,获取瞬态响应解析解.基于此,研...     

考虑流固耦合的桥墩地震反应方法

跨海桥梁地震反应中,作用于桥墩上的动水压力具有明显的流固耦合特征。依据张量理论,推导时变区域散度变换关系及微分形式的几何守恒律;基于任意拉格朗日一欧拉描述,从采用欧拉描述的流体运动Navier—Stokes方程出发,推导时变区域的流体运动控制方程;给出流固耦合问题中的结构计算模型、耦合面接触条件、耦合场计算方法以及流场网格运动控制方法。以某跨海大桥为例说明桥墩地震反应方法,重点突出地震动输入、流场初始条件模拟等问题。计算结果表明：流固耦合理论能够模拟桥梁墩台地震反应中的流场和结构特性;流场初始条件的正确模拟可保证计算稳定性,并减少运算量;横向地震动激励下,桥墩基底剪力较大,纵向地震动激励下,结构运动剧烈;流固耦合系统中的线弹性结构在地震反应中具有明显的非线性特征。     

Linear analysis of concrete arch dams including dam–water–foundation rock interaction considering spatially varying ground motions

The available substructure method and computer program for earthquake response analysis of arch dams, including the effects of dam–water–foundation rock interaction and recognizing the semi‐unbounded size of the foundation rock and fluid domains, are extended to consider spatial variations in ground motions around the canyon. The response of Mauvoisin Dam in Switzerland to spatially varying ground motion recorded during a small earthquake is analyzed to illustrate the results from this analysis procedure. Copyright © 2009 John Wiley & Sons, Ltd.     

Earthquake analysis of concrete gravity dams including dam-water-foundation rock interaction

A general procedure for analysis of the response of concrete gravity dams, including the dynamic effects of impounded water and flexible foundation rock, to the transverse (horizontal) and vertical components of earthquake ground motion is presented. The problem is reduced to one in two dimensions, considering the transverse vibration of a monolith of the dam. The system is analysed under the assumption of linear behaviour for the concrete, foundation rock and water. The complete system is considered as composed of three substructures—the dam, represented as a finite element system, the fluid domain, as a continuum of infinite length in the upstream direction, and the foundation rock region as a viscoelastic half-plane. The structural displacements of the dam are expressed as a linear combination of Ritz vectors, chosen as normal modes of an associated undamped dam-rock system. The effectiveness of this analytical formulation lies in its being able to produce excellent results by considering only a few Ritz vectors. The generalized displacements due to earthquake motion are computed by synthesizing their complex frequency responses using Fast Fourier Transform procedures. The stress responses are calculated from the displacements. An example analysis is presented to illustrate results obtained from this analytical procedure. Computation times for several analyses are presented to illustrate the effectiveness of the procedure.     

地铁隧道群对地震动的放大作用

本文采用有限元方法在时域内研究了基岩上均匀场地中隧道群对地震动的放大作用,分析了隧道间距、人射地震波频谱等因素对隧道群附近地表地震动反应谱的影响.研究表明,隧道群对地震动具有显著的放大作用,放大作用的大小与隧道间距和人射地震波频谱有着密切关系;隧道之间存在相互作用,加速度峰值的最大值多大于单隧道情况,且水平加速度峰值的...     

The effect of seasonally frozen soil on stochastic response of elevated water tank under random excitation

Significant seismic events have occurred around the world during winter months in regions where cold temperatures cause ground freezing. Current seismic design practice does not address the effects of cold temperatures in the seasonally frozen areas. Since many elevated water tank structures in cold regions are located in seismic active zones, determining the effect of seasonally frozen soil on the stochastic response of elevated water tank structures subjected to random seismic excitation is an important structural consideration. A three dimensional finite element model, which considers viscous boundaries, was built up to obtain the stochastic seismic behavior of an elevated water tank–fluid–soil interaction system for frozen soil condition. For this model, the power spectral density function represents random ground motion applied to each support point of the three dimensional finite element model of the elevated water tank–fluid–soil interaction system. Numerical results show that the soil temperature affects the seismic response of the elevated water tank; whereas the variation in the thickness of the frozen soil causes insignificant changes on the response. In addition, the effect of the variation in water tank’s fullness on the stochastic response of the coupled system is investigated in the study. As a result, the seasonal frost changes the foundation soil stiffness and may impact seismic behavior of the water tank.     

多维地震动各方向相关性对拱坝动应力的影响

本文将随机振动的虚拟激励法与拱坝-地基动力相互作用FE-BE-IBE时域模型结合，发展了一个可以考虑多维随机地震动作用下的拱坝动力响应计算模型，并用Monte Garlo方法对模型进行了验证，计算结果表明，地震动分量的相关性对结构的动力响应存在一定影响，合理考虑地震动各方向分量的相关性可以更好地计算实际地震作用下的拱坝动力响应。     

Response of offshore towers to strong motion earthquakes

Presented is a stochastic method of analysis of offshore towers subjected to strong motion earthquakes. A zero mean ergodic Gaussian process of finite duration is used to characterize horizontal ground acceleration and full fluid structure interaction effects are included. Numerical results for four representative deep water towers having heights of 475, 675, 875 and 1075 ft are compared with corresponding results obtained by the response spectrum method of analysis. Particular emphasis is placed on the maximum or extreme values of total transverse shear and total overturning moment. Comparisons are made with code values and the role of ductility is briefly discussed.     

Stochastic dynamic response of dam–reservoir–foundation systems to spatially varying earthquake ground motions

In this paper, stochastic dynamic responses of dam–reservoir–foundation systems subjected to spatially varying earthquake ground motions are investigated using the displacement-based fluid finite elements. For this purpose, variable-number-node two-dimensional (2D) fluid finite elements based on the Lagrangian approach is programmed in FORTRAN language and incorporated into a computer program SVEM, which is used for stochastic dynamic analysis of solid systems subjected to spatially varying earthquake ground motion. The spatially varying earthquake ground motion model includes incoherence, wave-passage and site-response effects. The incoherence effect is examined by considering the Harichandran and Vanmarcke coherency model. The effect of the wave passage is investigated by using various wave velocities. Homogeneous medium and firm soil types are selected for considering the site-response effect where the foundation supports are constructed. The Sar?yar concrete gravity dam, constructed in Turkey is selected for numerical example. The ground motion is described by filtered white noise and applied to each support point of the 2D finite element model of the dam–reservoir–foundation system. The record of Kocaeli earthquake in 1999 is used in the analyses. Displacements, stresses and hydrodynamic pressures occurring on the upstream face of the dam are calculated for four cases. It is concluded that spatially varying earthquake ground motions have important effects on the stochastic dynamic response of dam–reservoir–foundation systems.     

俯冲带地震动特征及其衰减规律探讨

随着我国南海不断开发建设,海洋工程的抗震问题日益受到重视.我国南海东部区域位于大陆板块与海洋板块共同作用的俯冲带地区,地震活动频繁,震级较大,潜在地震对南海开发建设有重要影响.为了研究俯冲带地震的地震动特征及其衰减规律,本文基于实际俯冲带地震数据,并结合数值模拟方法,分析和探讨了俯冲带板内、板缘地震与浅地壳地震的地震动特征和衰减规律的差异.研究结果表明:俯冲带地震动存在区域性差异,在地震动衰减特征方面,同一区域的俯冲带板缘地震要比浅地壳地震衰减慢,俯冲带板内地震要比浅地壳地震衰减得快;数值模拟分析不同深度海水对海底地震动的影响表明,海底地震动水平分量几乎不受海水介质的影响,但是竖向分量随海水深度的增加有减小的趋势.最终,基于数值模拟和经验关系的混合方法建立了南海俯冲带地震动衰减关系模型,其结果可为海域区划等相关研究和海域工程建设提供参考.     

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅰ)

Amplification of in-plane seismic ground motion by underground group cavities in layered half-space is studied both in frequency domain and time domain by using indirect boundary element method (IBEM), and the effect of cavity interval and spectrum of incident waves on the amplification are studied by numerical examples. It is shown that there may be large interaction between cavities, and group cavities with certain intervals may have significant amplification to seismic ground motion. The amplification of PGA (peak ground acceleration) and its PRS (peak response spectrum) can be increased up to 45.2% and 84.4%, for an example site in Tianjin, under the excitation of Taft wave and El Centro wave; and group cavities may also affect the spectra of the seismic ground motion. It is suggested that the effect of underground group cavities on design seismic ground motion should be considered.     

Nonlinear dynamic response of concrete gravity dams: cavitation effect

A finite element method for the dynamic analysis of concrete gravity dams is presented. Displacement based formulation is used for both fluid and structural domains. During severe ground motion, the impounding fluid in the reservoir may separate from the dam and cause forming of micro bubbles. As a result, the compressibility of water is reduced. This nonlinear phenomenon of the reservoir is termed cavitation. When the direction of the ground motion is changed, the micro bubble's region of fluid collapses, and an impact will occur. By using different damping ratios in the fluid and solid domains the spurious oscillations which were caused by the impact are removed. The cavitation is confined to the upper part of the reservoir, where it has an effect of paramount importance on the tensile stresses. To illustrate the cavitation effect, the response of the non-overflow monolith of the Pine Flat dam subjected to the first 6.5 s of the May 1940 El-Centro, California earthquake, is considered. In order that the cavitation phenomenon take place more widely, maximum acceleration was scaled to give an amplitude of 1 g.     

清水地震台地下流体观测资料的分析应用

清水地震台目前有3个测点,有流量、水氡、水位、水温4种手段（5个测项）,是数字和模拟观测同时进行的地下流体综合观测台。通过对该台各种资料的分析发现,流量观测资料在甘肃及邻区多次中强震之前出现明显的高值异常;水氡观测资料也有异常出现。自1999年之后,水氡测点附近地区由于大量开采热水,对观测资料造成明显干扰;水位观测资料除记录到较明显的固体潮现象外,还记录到大震的同震效应;水温观测资料也记录到某些大震的同震效应。     

Three-dimensional simulation of track on poroelastic half-space vibrations due to a moving point load

An analytical approach is used to investigate dynamic responses of a track system and the poroelastic half-space soil medium subjected to a moving point load under three-dimensional condition. The whole system is divided into two separately formulated substructures, the track sub-system and the ground. The ballast supporting rails and sleepers is placed on the surface of the ground. The rail is modeled by introducing the Green function for an infinitely long Euler beam subjected to the action of the moving point load and the reaction of sleepers represented by a continuous mass. Using the double Fourier transform, the governing equations of motion are then solved analytically in the frequency–wave-number domain. The time domain responses are evaluated by the inverse Fourier transform computation for a certain load velocities. Computed results show that dynamic responses of the soil medium are considerably affected by the fluid phase as well as the load velocity.     

合成地震动方法用于研究强地震动长周期特性的探讨

合成地震动一直是地震学研究中一个非常跃的领域。针对２长周期结构物抗震设计缺少宽频带强震记录的现状,利用“反射率法”和“围道积分法”等合成地震动方法对地震动长周期特性进行了探讨。结果表明：合成地震动方法是研究地震动长周特性的一个有效方法;在地震动长周期成份中,面波起着重要作用。因此长周期结构物的抗震设计必须考虑面波的影响。     

Hydrodynamic effects in a reservoir with semicircular cross-section and absorptive bottom

A three-dimensional dam-reservoir system under seismic load is analysed. The dam is assumed to be rigid. The reservoir is an infinite channel with semi-circular cross-section. The exact analytical solution, based on the assumption of potential fluid motion is presented, as well as numerical results for selected parameters.The most significant parameters are: the direction and frequency content of the seismic input; the radiation damping at the reservoir bottom; and the compressibility of the fluid. The response of the system depends strongly on the direction of the input ground motion. This is shown by the transfer functions as well as by the pressure time histories due to two earthquakes with different frequency content. The energy absorption at the reservoir bottom is important. A simple plane-wave model shows, that even for a rock foundation, the amount of transmitted energy can reach up to 80%. For comparison the case without bottom absorption is also shown. Compressbility has to be included to capture the resonance effects. The exact analytical solution is also used to verify numerical results obtained by a new method that combines a finite element model with a rigorous radiation boundary for the infinite channel in the time domain.     

A new approach for estimating seismic damage of buried water supply pipelines

Conventional damage prediction methods for lifeline structures are primarily based on peak ground motion measurements. However, line structures such as lifelines suffer damage that is mainly induced by the strain of the ground and therefore are likely to be vulnerable to sharp spatial changes in the ground motion. In this study, we propose a measure for evaluating the damage incurred by underground water supply pipelines based on the spatial gradient of the peak ground velocity (PGV), in an attempt to quantify the effects of the geospatial variabilities in the ground motion on pipeline damage. We investigated the spatial distribution of the damage caused to water pipelines during the Niigata‐ken Chuetsu earthquake on October 10, 2004 (Japan Meteorological Agency magnitude (M_JMA) of 6.8) and the Kobe earthquake on January 17, 1995 (M_JMA7.3) and compared the surveyed damage with the PGV distribution as well as with the gradients of the PGV calculated around the damage areas. For the Kobe earthquake, we used the PGV distribution obtained by the strong‐motion simulation performed by Matsushima and Kawase 1 . In case of the Chuetsu earthquake, we estimated the ground motion using a broadband‐frequency‐based strong‐ground‐motion simulation method based on a multiasperity source model. In both cases, we calculated the gradients of the PGV along the geographical coordinates, with the amplitude of the PGV gradient vector being employed as the damage estimator. Our results show that the distribution of damage to underground water supply pipelines exhibits a greater correlation with the gradients of the PGV than with the PGV itself. Thus, the gradient of the PGV is a useful index for preparing initial‐screening hazard maps of underground facilities. Copyright © 2017 John Wiley & Sons, Ltd.     

Complex Site Effects in Thessaloniki (Greece): II. 2D SH Modelling and Engineering Insights

This paper presents results of numerical modelling of site response for Thessaloniki, obtained with two different 2D methods; a finite difference and a finite element method. Ground motion across a 2D model of the subsoil of the city has been simulated for vertically incident SH waves. The predominance of locally generated surface waves is very clear in the synthetic seismograms of a weak event and of stronger ones. These results are then compared with the observations in time domain and frequency domain. The role of the soil formations with high attenuation in the lateral propagation and the effect of the differential motion close to the lateral variations are also pinpointed. The stronger events were finally used to compute strong ground motion in order to reveal and to discuss practical engineering aspects such as peak ground acceleration value, the most familiar indicator in seismic norms, the soil to rock spectral coefficients for the period bandwidth of interest, and the aggravation factor in terms of 2D to 1D response spectra as a useful ruler to account for complex site effects.