桥梁-桩-土相互作用三维地震反应分析方法

利用大型有限元通用软件ANSYS/LS-DYNA及其并行运算功能,提出了一种大跨度斜拉桥在地震作用下考虑SSI效应的三维整体时程反应分析方法,比较了考虑桥梁结构线性和非线性两种情形的计算结果,并对其计算效率进行了探讨。     

基于性态的液化场地多跨桥梁桩基地震响应分析

针对液化场地多跨简支桩基桥梁体系,考虑地震随机性的不确定性和认知的不确定性,结合地震危险性曲线自身的不确定性,推导性态指标危险性曲线的解析表达式.利用地震动强度指标PGV/PGA,输入不同幅值的地震动,进行液化场地多跨桩基桥梁体系地震反应有限元分析.基于有限元数值分析结果,选取地震过程中关键位置位移和弯矩的最大值作为性...     

Effect of coupling excess pore pressure and soil deformation on nonlinear SSI in liquefiable soil deposits

The current seismic design philosophy is based on nonlinear behavior of structures where the foundation soil is often simplified by a modification of the input acceleration depending on the expected site effects. The latter are generally limited to depend on the shear-wave velocity profile or a classification of the site. Findings presented in this work illustrate the importance of accounting for both soil nonlinearity due to seismic liquefaction and for soil-structure interaction when dealing with liquefiable soil deposits. This paper concerns the assessment of the effect of excess pore pressure (\(\Delta p_{w}\)) and deformation for the nonlinear response of liquefiable soils on the structure’s performance. For this purpose a coupled \(\Delta p_{w}\) and soil deformation (CPD) analysis is used to represent the soil behavior. A mechanical-equivalent fully drained decoupled (DPD) analysis is also performed. The differences between the analyses on different engineering demand parameters are evaluated. The results allow to identify and to quantify the differences between the analyses. Thus, it is possible to establish the situations for which the fully drained analysis might tend to overestimate or underestimate the structure’s demand.     

Assessment of variability and uncertainties effects on the seismic response of a liquefiable soil profile

The present work deals with the evaluation of the effect of the randomness of both soil parameters and input motion on the seismic response of a sandy soil profile. Special attention is given to estimate the relative contribution of model input parameters on (i) the probability of liquefaction apparition and (ii) the surface seismic response. The Monte Carlo simulations were used for that purpose. This analysis shows that, for the considered case, the choice of the earthquake input signal remains the most subtle parameter in order to define the liquefaction probability. Otherwise, spatial variability of both soil properties and soil model's parameters have a weak impact on the response of the soil profile.     

A microslip model for the seismic response analysis of drained cohesionless soil deposits

Constitutive equations for drained cohesionless soils under triaxial stress states, based on a microslip model with internal friction, are proposed and applied to the analysis of the seismic response of soil deposits. The microslips, assumed localized in the discontinuity surfaces passing through the particle-to-particle contacts, describe the effects of the sliding and rolling between grains of sand. Once the response of the model under cyclic shearing stresses and strains superimposed on the geostatic stress state has been analysed, the constitutive equations are applied to a one-dimensional shear model for the dynamic analysis of the layered deposits. An application to an instrumented soil deposit is then developed, the experimental results of which refer to both strong and weak motion earthquakes; the comparisons between the experimental and theoretical results point out the peculiarities and validity limits of the model. The model here developed may be applied also to the analysis of two- and three-dimensional sites.     

3-D seismic response analysis of long lined tunnels in half-space

The dynamic response of infinitely long lined tunnels with a uniform cross-section buried into an elastic or viscoelastic half-space to body and surface harmonic seismic waves is numerically determined by a special direct boundary element method in the frequency domain. The waves have an arbitrary direction of propagation with respect to the axis of the tunnel and this renders the problem three-dimensional. However, this problem is effectively reduced to a two-dimensional one by a coordinate transformation and appropriate integration of the full-space dynamic fundamental solution along the direction of the tunnel axis. Quadratic isoparametric boundary line elements and advanced numerical integration techniques for the treatment of singular integrals produce results of high accuracy. Numerical results are presented for the case of an infinitely long lined tunnel of circular cross-section and compared against those of a full three-dimensional boundary element analysis, as well as those of other methods. Thus the proposed method is illustrated and its merits demonstrated.     

地震动参数对边坡地震响应的影响规律

选取了具有不同峰值加速度、频谱和持时的6组地震动加速度时程作为输入,基于有限元数值模拟方法建立了二维均质边坡有限元模型,模拟分析了不同地震动作用下边坡模型的加速度和位移响应,揭示了地震动峰值加速度、频谱和持时对土坡地震响应的影响作用及其规律.研究结果显示:地震动峰值加速度、频谱和持时对土坡地震响应均有显著的影响,其中,边坡坡脚处和坡肩处的变形位移随地震动峰值加速度、特征周期和持时的增大而增大,坡体临空面各点的峰值加速度放大系数呈现随输入地震动特征周期的增大而增大、随输入地震动峰值加速度的增大而减小的规律.研究结果可为地震作用下边坡稳定性设计及防治研究提供参考.      

三维台阶地形地震动效应研究

运用谱元法模拟了不同类型三维台阶地形对点源地震动的影响, 发现在中小地震中, 大型山系边缘的三维台阶地形对地表地震波具有一定的影响. 台阶斜坡与上水平地层交线和下水平地层交线的影响作用各不相同. 通过地表接收到的地震动描述了各种不同地形的波形快照特点, 并且通过绘制的台阶斜坡与上水平地层交线及下水平地层交线的测线图, 发现波形相对于水平地形有明显的后续波. 同时发现, 台阶地形上下测线相对于水平地形具有放大作用.下测线波形放大倍数基本在1.1—1.5, 上测线放大倍数在0.9—1之间. 通过描述山体边缘台阶结构在点源地震中产生的影响, 定量计算了三维台阶不同角度各个位置相对于水平地形的放大倍数, 为以后工程研究提供一个依据.     

承台型式对可液化场地桥梁桩-柱墩地震响应影响振动台试验

基于相同土层结构地基条件下,分别采用低承台群桩-独柱墩与高承台群桩-独柱墩结构,完成了两次可液化场地群桩-土-桥梁结构地震反应振动台试验,据此研究了承台型式对桥梁桩-柱墩地震反应的影响。研究表明,与高承台桩相比,可液化场地中低承台桩的抗震性能更优;地震中砂层尚未液化或液化不充分时,低承台更多表现出减弱桩尤其桩上段的加速度反应的作用,相反高承台更多起到放大桩的加速度作用,而高承台桩与低承台桩的峰值应变自下而上更多表现出逐渐增大趋势;即使砂层完全液化时,低承台桩的峰值应变自下而上仍以渐增为主;与低承台桩相比,高承台桩更有助于放大墩顶加速度、位移反应,对结构体系整体稳定性产生了不良影响;虽然低承台桩未出现严重破坏,但砂层中部桩的应变却很大,液化砂土-桩运动相互作用对桩的抗震性能影响不容忽视。     

土层动力参数变化对地表地震反应影响的研究

通过模拟土层剖面,采用等效线性化程序,对土体的非线性动力参数～动剪切模量比与阻尼比分别使用实测值、行业推荐值和规范值来计算地表的反应谱,比较地表的地震动峰值与反应谱的特征周期大小以及反应谱的形状,以评价土层参数变化对地表地震反应的影响.     

Shaking table test on the seismic failure characteristics of a subway station structure on liquefiable ground

In order to investigate the seismic failure characteristics of a structure on the liquefiable ground, a series of shaking table tests were conducted based on a plaster model of a three‐story and three‐span subway station. The dynamic responses of the structure and ground soil under main shock and aftershock ground motions were studied. The sand boils and waterspouts phenomena, ground surface cracks, and earthquake‐induced ground surface settlements were observed in the testing. For the structure, the upward movement, local damage and member cracking were obtained. Under the main shock, there appeared longer liquefaction duration for the ground soil while the pore pressure dissipated slowly. The acceleration amplification effect of the liquefied soil was weakened, and the soil showed a remarkable shock absorption and concentration effect with low frequency component of ground motion. However, under the aftershock, the dissipation of pore pressure in the ground soil became obvious. The peak acceleration of the structure reduced with the buried depth. Dynamic soil pressure on the side wall was smaller in the middle and larger at both ends. The interior column of the model structure was the weakest member. The peak strain and damage degree for both sides of the interior column exhibited an ‘S’ type distribution along the height. Moreover, the seismic response of both ground soil and subway station structure exhibited a remarkable spatial effect. The seismic damage development process and failure mechanism of the structure illustrated in this study can provide references for the engineers and researcher. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of soil depth on inelastic seismic response of structures

Effect of depth of soil stratum on estimated inelastic displacement of three typical structures, viz. a four storey building, a continuous bridge, and a tower, is studied and adequacy of the site amplification models of the current design codes and available empirical relationships is examined. The structures are assumed to be located on well-defined sites with varying bedrock depths, and effect of depth on elastic response spectrum, site amplification factor, displacement modification factor and inelastic displacement is studied, numerically, for two values of PGA. It is observed that soil depth has a significant effect on elastic as well as inelastic response of the structures; however, the effect of soil amplification on inelastic response is not as pronounced as in case of elastic response. Therefore, use of empirical site amplification models based on elastic response may be too conservative, for estimating inelastic response.     

近断层地震动对上承式拱桥动力响应的影响

为了揭示近断层地震作用下上承式钢筋混凝土拱桥的动力响应特点,以西南山区某上承式拱桥为背景,用OpenSEES平台建立了全桥非线性动力分析模型,探讨了近断层地震动的输入方式、脉冲效应和竖向地震动等三个关键因素对桥梁动力响应的影响规律。研究结果表明:地震输入方式对拱圈地震响应的影响较小,但对拱上立柱地震响应的影响很大,尤其是拱顶附近的短立柱,在抗震分析中,建议偏安全地采用三向地震输入方式;脉冲效应对拱桥地震响应的影响非常大,会导致拱圈、拱上立柱和桥面板地震响应大幅增加,桥面板残余平面转角甚至增大6倍以上;竖向地震动对拱圈轴力和面内弯矩、拱上立柱纵向弯矩和剪力的影响很大,拱顶处的面内弯矩放大倍数最大可达2.95,总体来说,采用规范所建议的方法考虑竖向地震是偏保守的。     

Implications of surface wave data measurement uncertainty on seismic ground response analysis

The extent of data uncertainty of surface-wave measurements may have significant consequences on 1D seismic response analysis and it may lead to inaccurate estimate of design ground motion. In this paper, an attempt has been made to quantify the data measurement uncertainty from a large repetition of the field data at two test sites and to determine bounds of data uncertainty. In the inversion with neighborhood algorithm, we generated profiles below the misfit value calculated from the uncertainty bound. Equivalent profiles have been selected covering the whole misfit value range and these profiles are subjected to equivalent linear 1D ground response analysis. The results of seismic response analysis are presented in the form of amplification spectra and response spectra which show remarkable variations. Significant variation is observed in peak frequency and peak amplification and it differs from one site to the other based on their measured data uncertainty bound. Peak Ground Acceleration (PGA) and peak spectral acceleration at both the sites reflect very high Coefficient of Variation (COV).     

3D SEM-based seismic ground response analysis of Kathmandu Valley in 2015 Gorkha Nepal earthquake

Journal of Seismology - The aftershocks of the 2015 Mw7.8 Gorkha Nepal earthquake extend up to 130km to the east of the epicenter. The distribution suggests that the rupture has propagated from...     

地震动峰值特征参数对土坡地震响应的规律研究

本文随机选取了100条具有不同地震动峰值特征参数的地震动记录,通过基线校正、积分等方法获取每条地震动的峰值加速度（PGA）、峰值速度（PGV）和峰值位移（PGD）三个参数,进而基于有限元数值模拟,通过对比同一个观测点不同峰值特征参数的特性与不同观测点同一峰值特征参数的特性来研究土坡的地震响应规律,分析各地震动峰值特征参数与土坡地震响应的相关性。计算结果表明:PGA,PGV和PGD与土坡地震响应都具有良好的正相关性,其相关性系数平均值分别为0.868,0.981,0.926;PGV的相关性优于PGA和PGD,而PGD的相关性要稍好于PGA。因此在关于土坡稳定性评价中,建议采用PGV作为参数指标。      

Soil–structure interaction effects on seismic inelastic analysis of 3-D tunnels

This paper investigates the importance of seismic soil–structure interaction in three-dimensional lined tunnels, assuming inelastic material behaviour for both the concrete liner and the soft rock type of soil. The seismic response of the soil–structure system is determined by the finite element method (FEM) in the time domain. Viscous absorbing boundaries are used in conjunction with the discretization of the rock medium. Both the rock medium and the concrete liner are assumed to behave inelastically on the basis of the continuum damage mechanics theory. The seismic waves are assumed to have any arbitrary time variation and direction of propagation. The system is analysed with and without soil–structure interaction in order to assess its importance on the response of the system. Through parametric studies, the influence of the most critical parameters affecting the structural response is determined and critically discussed.     

Orthogonal expansion of ground motion and PDEM-based seismic response analysis of nonlinear structures

This paper introduces an orthogonal expansion method for general stochastic processes.In the method,a normalized orthogonal function of time variable t is first introduced to carry out the decomposition of a stochastic process and then a correlated matrix decomposition technique,which transforms a correlated random vector into a vector of standard uncorrelated random variables,is used to complete a double orthogonal decomposition of the stochastic processes. Considering the relationship between the Hartl...     

Effect of train dynamics on seismic response of steel monorail bridges under moderate ground motion

This study is intended to investigate the seismic response of steel monorail bridges using three‐dimensional dynamic response analysis. We particularly consider monorail bridge–train interaction when subjected to ground motion that occurs with high probability. A monorail train car with two bogies with pneumatic tires for running, steering and stabilizing wheels is assumed to be represented sufficiently by a discrete rigid multi‐body system with 15 degrees of freedom (DOFs). Bridges are considered as an assemblage of beam elements with 6 DOFs at each node. Modal analysis is used for dynamic response analysis under moderate earthquakes. The seismic response of an advanced monorail bridge that adopts a simplified structural system and composite girders is investigated through comparison with seismic responses of a conventional bridge. The acceleration response of a monorail train is also calculated to investigate the effect of structural types of bridges on the train's dynamic response during earthquakes. Results show that the seismic responses of the advanced bridges are greater than those of the conventional monorail bridge because of the simplified structural system and increased girder weight that is attributable to composite girders of the advanced bridge. Moreover, the train on the advanced bridge shows greater dynamic response than that on the conventional bridge. Observations reveal that the dynamic monorail train system acts as a damper on the monorail bridge. That fact shows that the existing design, which considers a train as additional mass, yields a conservative result. Copyright © 2006 John Wiley & Sons, Ltd.