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1.
《地震工程与结构动力学》2018,47(5):1229-1249
This paper deals with the effect of the foundation mass on the filtering action exerted by embedded foundations. The system under examination comprises a rigid rectangular foundation embedded in a homogeneous isotropic viscoelastic half‐space under harmonic shear waves propagating vertically. The problem is addressed both theoretically and numerically by means of a hybrid approach, where the foundation mass is explicitly included in the kinematic interaction between the foundation and the surrounding soil, thus referring to a “quasi‐kinematic” interaction problem. Based on the results of an extensive parametric study, it is shown that the filtering problem depends essentially on three dimensionless parameters, i.e.: the dimensionless frequency of the input motion, the foundation width‐to‐embedment depth ratio, and the foundation‐to‐soil mass density ratio. In complements to the translational and rotational kinematic interaction factors that are commonly adopted to quantify the filtering effect of rigid massless foundations on the free‐field motion, an additional kinematic interaction factor is introduced, referring to the horizontal motion at the top of a rigid massive foundation. New analytical expressions for the above kinematic interaction factors are proposed and compared with foundation‐to‐free‐field transfer functions computed from available earthquake recordings on two instrumented buildings in LA (California) and Thessaloniki (Greece). Results indicate that the foundation mass can have a strong beneficial effect on the filtering action with increasing foundation‐to‐soil mass density and foundation width‐to‐embedment depth ratios. 相似文献
2.
Equations for the prediction of vertical peak and absolute acceleration spectral ordinates in terms of magnitude, source-distance and site geology are presented. Comparison to similarly derived horizontal equations shows vertical spectral values to be 1/2–1/4 of the horizontal. The influence of site geology on vertical ground motion is reduced with respect to the horizontal. Ratios of peak vertical to peak horizontal ground acceleration in the near-field of thrust faults are magnitude and distance dependent, reaching values in excess of one very near the fault of large magnitude events. For strike-slip faults the ratio exceeds one for moderate events, decreasing for larger events, and is distance independent. Spectral acceleration ratios exceed one at short periods but are less than one at intermediate and long periods, irrespective of the source mechanism. 相似文献
3.
Katta Venkataramana 《地震工程与结构动力学》1994,23(1):63-74
Dynamic response of tethers of tension-leg-platforms to current and horizontal earthquake excitations is investigated. The static deflected shape of tether under a steady current is firstly identified. Next dynamic analysis for earthquake input is carried out for this deflected tether. The fluid loading due to surrounding water is included in the analysis as an added mass term and a hydrodynamic damping term. The tether is discretized by lumping masses at selected nodes. The platform is represented by a mass at the top end of the tether. The effect of pretension in the tether is taken into account in the form of a geometric stiffness term. At each node three degrees of freedom corresponding to surge, heave and pitch motion are considered. As the vibration modes and hence the responses are likely to be affected by the foundation characteristics, the study is extended to include the dynamic soil–structure interaction. The dynamic equations of motion for the tether–pile–soil system are derived using the substructure method. The natural frequencies and the vibration mode shapes of the total system are determined by eigenvalue analysis. The input ground acceleration is represented by Tajimi–Kanai's power spectrum for stationary conditions. The response analysis is carried out using the frequency-domain random-vibration approach. The coupled axial and lateral responses are evaluated for horizontal ground excitations. Numerical results indicate that the horizontal displacements of the tether increase with the input ground acceleration, but are nearly equal for all the cases of current velocities considered in the study; the vertical displacements however increase rapidly with the increase in current velocity. For the model considered in the present study, the responses are reduced when soil–structure interaction is included in the analysis. 相似文献
4.
为研究强震区跨断层桥梁桩基非线性动力相互作用特性,依托海文大桥实体工程,利用MIDAS/GTS有限元软件,建立了桩-土-断层相互作用模型,分析0.20~0.60g地震动强度下断层上下盘桩基加速度响应、桩顶水平位移、桩身弯矩以及桩身剪力响应情况。结果表明:覆盖层土体对桩身加速度放大作用明显,且随着输入地震动强度的增大,放大作用逐渐减弱;覆盖层对地震波的滤波作用显著,随着输入地震动强度的增大,滤波作用逐渐减弱;上盘桩基达到桩顶峰值加速度的时刻滞后于下盘;随着输入地震动强度的增大,上、下盘桩的桩顶产生的永久位移和水平位移峰值逐渐变大,上盘桩顶产生的永久位移和桩顶峰值位移均大于下盘,产生显著的"上盘效应";不同强度地震动作用下,断层上、下盘桩基弯矩均在上部土层界面处达到峰值,剪力均在基岩面处达到峰值,下盘桩基弯矩和剪力峰值大于上盘桩基,呈现出显著的"下盘效应"。在桥梁桩基抗震设计时,应着重考虑断层上、下盘桩基的差异和不同强度地震作用对桩基承载特性的影响。 相似文献
5.
本文根据保定市及周围地区的地震地质环境，在地震危险性分析的基础上，采用等效线性一维波动方程进行土层的地震反应分析。给出50年超越概率63％、10％、2％基岩和地面的水平向峰值加速度、反应谱（场址基本烈度Ⅶ度）和地震影响系数最大值。该结果为抗震设计提供了可靠依据，具有应用价值。 相似文献
6.
Near-field horizontal and vertical earthquake ground motions 总被引：8，自引：0，他引：8
Strong-motion attenuation relationships are presented for peak ground acceleration, spectral acceleration, energy density, maximum absolute input energy for horizontal and vertical directions and for the ratio of vertical to horizontal of these ground motion parameters. These equations were derived using a worldwide dataset of 186 strong-motion records recorded with 15 km of the surface projection of earthquakes between Ms=5.8 and 7.8. The effect of local site conditions and focal mechanism is included in some of these equations. 相似文献
7.
This study is aimed at developing statistical equations to estimate the inelastic displacement ratio of singledegree- of-freedom systems subjected to far fault repeated earthquakes. In the study, peak ground motion parameters are used to define the scatter of the original data. The ratio of peak ground acceleration to peak ground velocity, and peak ground velocity of the ground motion records and structural parameters such as period of vibration and lateral strength ratio are used in the proposed equations. For the development of the equations, nonlinear time history analyses of single-degree-offreedom systems are conducted. Then, the results are used in a multivariate regression procedure. The equations are verified by comparing the estimated results with the calculated results. The average error and coefficient of variation of the proposed equations are presented. The analyses results revealed that the direct use of peak ground motion parameters for the estimation of inelastic displacement ratio significantly reduced the scatter in the original data and yielded accurate results. From the comparative results it is also observed that results obtained using equations specific to peak ground velocity or peak ground acceleration to peak ground velocity ratio are similar. 相似文献
8.
为了解软土自由场地地震反应特性,开展饱和软土自由场地地震反应特性大型振动台模型试验。分别从模型体系自振特性、震陷位移及不同土层深度测点的加速度、动孔压比等动力响应指标方面,较为深入和全面地分析饱和软土自由场地地震反应规律、破坏机理。同时还分析模型箱的"边界效应"以验证试验土箱的合理性、有效性和测试仪器性能,并由此进一步确定模型地基有效工作区域。研究表明:(1)地震动作用下,饱和软土自由场地特征频率降低,阻尼增大;(2)饱和软土自由场地对水平输入地震波具有短周期滤波、长周期放大效应,且强震作用下地基失效并表现为减隔震作用;(3)饱和软土自由场地动孔压比优势区域位于浅埋土层,并随着输入地震动强度的增大,该区域动孔压比优势逐渐减弱。该研究可为非自由软土场地试验研究提供必要的技术经验。 相似文献
9.
强震动记录的使用通常不考虑观测方向对于水平地震动参数计算的影响。文中以2008年汶川Ms8.0级地震中绵竹清平台获取的强震动记录为研究对象,对记录进行水平向旋转以模拟观测方向的变化,分析水平向峰值加速度PGA、峰值速度PGV、相对持时DR、绝对持时DA及谱加速度PSA随观测方向的变化情况。结果表明,PGA、PGV及PSA的计算较大依赖于观测方向,而DR和DA则受观测方向影响较小。为此文中提出了一种与观测方向无关的水平地震动参数计算方法,对于计算诸如PGA、PGV等与周期无关的地震动参数时不考虑周期独立;而对于计算诸如PSA等与周期有关的地震动参数时考虑周期独立。 相似文献
10.
The non‐stationary rocking response of liquid storage tanks under seismic base excitations including soil interaction has been developed based on the wavelet domain random vibration theory. The ground motion has been characterized through statistical functionals of wavelet coefficients of the ground acceleration history. The tank–liquid–foundation system is modelled as a multi‐degree‐of‐freedom (MDOF) system with both lateral and rocking motions of vibration of the foundation. The impulsive and convective modes of vibration of the liquid in the tank have been considered. The wavelet domain coupled dynamic equations are formulated and then solved to get the expressions of instantaneous power spectral density function (PSDF) in terms of functionals of input wavelet coefficients. The moments of the instantaneous PSDF are used to obtain the stochastic responses of the tank in the form of coefficients of hydrodynamic pressure, base shear and overturning base moment for the largest expected peak responses. Parametric variations are carried out to study the effects of various governing parameters like height of liquid in the tank, height–radius ratio of the tank, ratio of total liquid mass to mass of foundation, and shear wave velocity in the soil medium, on the responses of the tank. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
11.
2018年9月12日陕西省宁强县发生5.3级地震,中国数字强震动台网的39个专业台站在此次地震中触发。文章中通过处理捕获的117条三分向加速度记录,给出近场台站的地震动参数,绘制震中附近区域峰值加速度等值线图,其长轴呈西南-东北方向展布。采用实际观测数据与几种常用地震动衰减关系对比,发现霍俊荣衰减预测模型能更好地反映此次地震的影响场。将振幅最大的51GYD台的反应谱与我国抗震设计反应谱比较,采用最小二乘法拟合出不同震中距5个台站各周期谱加速度衰减特性,总结出此次地震的反应谱基本特征。运用H/V谱比法对51GYD土层台和62ZM台阵进行局部场地地震反应分析,研究覆盖土层对地震动的放大作用,及局部地形对峰值加速度和峰值速度的影响过程。 相似文献
12.
13.
A wavelet‐based random vibration theory has been developed for the non‐stationary seismic response of liquid storage tanks including soil interaction. The ground motion process has been characterized via estimates of statistical functionals of wavelet coefficients obtained from a single time history of ground accelerations. The tank–liquid–soil system has been modelled as a two‐degree‐of‐freedom (2‐DOF) system. The wavelet domain equations have been formulated and the wavelet coefficients of the required response state are obtained by solving two linear simultaneous algebraic equations. The explicit expression for the instantaneous power spectral density function (PSDF) in terms of the functionals of the input wavelet coefficients has been obtained. The moments of this PSDF are used to estimate the expected pseudo‐spectral acceleration (PSA) response of the tank. Parametric variations are carried out to study the effects of tank height, foundation natural frequency, shear wave velocity of soil and ratio of the mass of tank (including liquid) to the mass of foundation on the PSA responses of tanks. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
14.
软土具有高灵敏度、低强度等特性,在地震过程中极易产生震陷。基于OpenSees数值模拟方法对软土场地的震陷反应进行非线性动力有限元分析,通过改变地震动峰值加速度、频谱特性、输入方式来研究其对软土震陷的影响。结果表明,地震动峰值加速度对地基土的不均匀震陷有显著影响,地震动峰值加速度越大,震陷量显著增大,震陷影响深度更大,对水平地表造成的破坏范围也更大;地震动频谱特性对软土震陷有重要影响,当地震动卓越频率与场地自振频率相近时,其幅值越大,产生的震陷越严重;水平、竖向同时输入地震动的方式能更好地反映土体的振动及震陷响应。该研究成果对探索软土震陷的机理有一定的指导意义。 相似文献
15.
D. Bindi F. Pacor L. Luzi R. Puglia M. Massa G. Ameri R. Paolucci 《Bulletin of Earthquake Engineering》2011,9(6):1899-1920
We present a set of ground motion prediction equations (GMPEs) derived for the geometrical mean of the horizontal components and the vertical, considering the latest release of the strong motion database for Italy. The regressions are performed over the magnitude range 4?C6.9 and considering distances up to 200?km. The equations are derived for peak ground acceleration (PGA), peak ground velocity (PGV) and 5%-damped spectral acceleration at periods between 0.04 and 2?s. The total standard deviation (sigma) varies between 0.34 and 0.38?log10 unit, confirming the large variability of ground shaking parameters when regional data sets containing small to moderate magnitude events (M?<?6) are used. The between-stations variability provides the largest values for periods shorter than 0.2?s while, for longer periods, the between-events and between-stations distributions of error provide similar contribution to the total variability. 相似文献
16.
本文旨在讨论位于回填土场地上及回填土场地深挖基坑内的强震动观测仪所获得地震动是否是真实自由场地震动,若不是,其影响如何?结合回填土场地的强震动观测台站建设的实际情形,建立了回填土场地和回填土场地深挖基坑的有限元分析模型,基于集中质量显式动力有限元数值模拟方法,分析了回填土的波速和厚度、基坑尺寸对自由场地震动的影响.同时,提出了通过用重塑土置换回填土以降低回填土对自由场地震动影响的措施,并对重塑土置换回填土的效果进行了数值模拟分析.结果表明:回填土上和回填土深挖基坑内的地震动峰值和反应谱值与原始场地的均有明显的差异,随着回填土厚度和基坑深度的增加,其差异越大;通过重塑土置换回填土可以减小回填土对场地地震动的影响.本文所得关于回填土、基坑和重塑土的影响规律可为回填土场地上强震动观测结果的合理利用以及强震动观测台站建设提供依据. 相似文献
17.
Conversion factors are useful for attenuation and damage estimation relationships. These factors among different definitions of peaks (i.e. larger, average and resultant) for peak ground motion indices and acceleration response spectrum were investigated. A large number of horizontal acceleration records recorded at 76 free-field sites of the Japan Meteorological Agency were used in this study. Two orthogonal horizontal components were combined in the time domain to get the maximum resultant peak ground motion indices and acceleration response spectrum in the horizontal plane. From the analysis, the means of the larger/resultant ratio were found to be 0·934 for acceleration, 0·926 for velocity, and 0·913 for displacement. A similar decreasing trend was observed for the means of the average/resultant ratio of the ground motion indices and acceleration response spectrum. The directivity of peak ground motion indices was also examined. It was found that the peak ground motion is more likely to occur in the transverse direction than in other directions. This trend is more prominent in the long-period contents of ground motion. 相似文献
18.
The validity of the response spectrum concept for determining loads in structures excited by differential earthquake ground motion is examined. It is shown that the common definition of response spectrum for synchronous ground motion can be reconciled to remain valid in cases when the columns of extended structures experience different motions. Then, a relative displacement response spectrum for design of first-storey columns, SDC(T, δ, ζ, τ), is defined. In addition to natural period, T, and fraction of critical damping, ζ, this spectrum depends also on the ‘travel time’, τ (of the waves in the soil over distances about one half width, or length of the structure), and on a factor, δ, specifying the relative displacement of the first floor. It is shown how this spectrum can be determined using existing empirical scaling equations for relative displacement spectra SD(T, ζ) and for peak velocity and peak acceleration of strong ground motion. These new spectra are illustrated for a horizontal component of a record in the near field of the 1994 Northridge earthquake. The results show that differential motions are more important for short period (stiff) than for longer period (flexible) structures, and for structures founded on softer ground (small shear wave velocity). © 1997 by John Wiley & Sons, Ltd. 相似文献
19.
It is commonly understood that earthquake ground excitations at multiple supports of large dimensional structures are not the same. These ground motion spatial variations may significantly influence the structural responses. Similarly, the interaction between the foundation and the surrounding soil during earthquake shaking also affects the dynamic response of the structure. Most previous studies on ground motion spatial variation effects on structural responses neglected soil–structure interaction (SSI) effect. This paper studies the combined effects of ground motion spatial variation, local site amplification and SSI on bridge responses, and estimates the required separation distances that modular expansion joints must provide to avoid seismic pounding. It is an extension of a previous study (Earthquake Engng Struct. Dyn. 2010; 39 (3):303–323), in which combined ground motion spatial variation and local site amplification effects on bridge responses were investigated. The present paper focuses on the simultaneous effect of SSI and ground motion spatial variation on structural responses. The soil surrounding the pile foundation is modelled by frequency‐dependent springs and dashpots in the horizontal and rotational directions. The peak structural responses are estimated by using the standard random vibration method. The minimum total gap between two adjacent bridge decks or between bridge deck and adjacent abutment to prevent seismic pounding is estimated. Numerical results show that SSI significantly affects the structural responses, and cannot be neglected. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
20.
An evaluation of the wave passage effects on the relevant dynamic properties of structures with flexible foundation is presented. A simple soil–structure system similar to that used in practice to take into account the inertial interaction effects by the soil flexibility is studied. The kinematic interaction effects due to non‐vertically incident P, SV and Rayleigh waves are accounted for in this model. The effective period and damping of the system are obtained by establishing an equivalence between the interacting system excited by the foundation input motion and a replacement oscillator excited by the free‐field ground motion. In this way, the maximum structural response could be estimated from standard free‐field response spectra using the period and damping of the building modified by both the soil flexibility and the travelling wave effects. Also, an approximate solution for the travelling wave problem is examined over wide ranges of the main parameters involved. Numerical results are computed for a number of soil–structure systems to identify under which conditions the effects of wave passage are important. It comes out that these effects are generally negligible for the system period, but they may significantly change the system damping since the energy dissipation within the soil depends on both the wave radiation and the diffraction and scattering of the incident waves by the foundation. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献