水库蓄放水对库底岩石介质弹性波速影响的数值模拟          下载免费PDF全文

周斌  孙峰  薛世峰  蒋海昆  史水平 《地震地质》2014,36(1):39-51

为了解水库水体加、卸载及渗透过程中,库底岩石介质有效应力变化对弹性波速的影响,以及弹性波速变化与孔隙压力、有效应力变化之间的定量关系,以四川省紫坪铺水库为例,在前期已建立库区地质构造与水文地质结构模型,并推导出岩石介质变形与流体渗流耦合数学模型的基础上,进一步建立了有效应力对岩石弹性波速影响的数学模型,利用有限元方法定量计算了库底岩石介质的孔隙压力、附加有效应力和弹性波速的变化。结果表明:在水库水体加、卸载及渗透过程中,地下岩石介质弹性波速增量值的变化并不明显,最大变幅仅为±0.013km/s,变化范围主要集中在库底5km以上的局部区域;弹性波速增量值与附加有效应力变化同步,与水库水位变化形态相似;不同观测点弹性波速变化量的大小与埋藏位置、深度及附加有效应力的变化幅度有关,同一观测点,弹性纵波波速变化幅度大于弹性横波波速。文中数值模拟的结果与一些学者通过环境噪声方法获得的紫坪铺水库附近区域相对波速变化的反演结果在变化形态上大体一致,但变化幅度略有差异。  相似文献   

橡胶水泥土动力特性的试验研究     

王凤池  王庆龙  董明  李庆冰 《地震学刊》2014,(2):253-258

通过动三轴试验,研究了橡胶水泥土复合试样的动强度、动弹性模量和阻尼比等动力参数的变化规律,着重研究了橡胶粉掺量、围压和应变3个主要因素的影响并分析了内在机理。在围压不变的情况下,随着橡胶粉掺量的增大,橡胶水泥土复合试样动强度降低。围压越大,动强度越高,受橡胶粉掺量的影响越小。随着围压的增大,动弹性模量增大而阻尼比减小;随着橡胶粉掺量的增加,动弹性模量减小而阻尼比增大。通过数据拟合,得到了橡胶水泥土动弹性模量和阻尼比的计算公式。橡胶粉可以提高水泥土吸收能量的能力,采用橡胶水泥土作为地基处理材料时,能够起到减震的作用。  相似文献   

龙滩水库诱发地震三维孔隙弹性有限元数值模拟   总被引：5，自引：2，他引：3       下载免费PDF全文

周斌  孙峰  阎春恒  薛世峰  史水平 《地球物理学报》2014,57(9):2846-2868

本文以龙滩水库为例,根据库区地质构造、深部速度结构及数字地面高程,建立了库区三维有限元模型,基于孔隙弹性理论计算了水库蓄水过程中库底断层和围岩体孔隙压力、有效附加正应力、剪应力和库伦应力的动态变化,并结合水库蓄水后库区地震活动时空分布的特征,讨论了RIS时空演化与库水加卸载及渗透过程的动态响应关系及其可能的成因机制.结果表明：（1） 龙滩水库蓄水后地震活动呈现出明显的丛集性,主要分布在罗妥（丛Ⅰ）、八茂（丛Ⅱ）、拉浪（丛Ⅲ）、坝首（丛Ⅳ）和布柳河（丛Ⅴ）5个水库蓄水后淹没的深水区,这些区域也恰恰是库水加卸载及渗透过程中ΔCFS增加最明显的区域,而ΔCFS的影区几乎没有地震发生,表明水库蓄水后库区地震活动与ΔCFS的变化密切相关.（2） 在水库蓄水过程中,与水库有直接水力联系且渗透性较好的断裂成为地表水体附加水头压力向深部扩散的优势通道,沿此通道附加水头压力扩散的最大深度达13 km左右,震旦系-古生界以碳酸盐岩为主的地层成为附加水头压力扩散的主体层位,这与蓄水后库区中、小地震震源深度均小于13 km,且优势分布在5~10 km的特征相吻合,表明由于孔隙压力的存在降低了岩石的抗剪强度,同时部分抵消了围压的影响,致使该层位的岩体易于产生脆性破坏从而诱发地震活动.（3） 无论是深部还是浅部,各丛地震密集发生的时段绝大部分与相应深度ΔCFS加速升高或阶段性高值时段相重叠,可能说明在库水位快速抬升或阶段性高值时段,受外部荷载加载速率快速升高的影响,库底岩体和断层、裂隙等结构面更容易实现失稳扩展;深、浅部地震响应时间、活动频度和强度的差异可能与不同层位岩体力学性质及渗透性能的不均匀性有关.（4） 各丛地震诱发的物理力学机制有所不同.丛Ⅰ、丛Ⅱ、丛Ⅲ地震的诱发可能与库体重力荷载、孔隙压力扩散和库水浸润弱化3种作用都有关;丛Ⅳ地震的诱发主要受控于库体重力荷载作用,孔隙压力扩散和库水浸润弱化不起主导作用;丛Ⅴ地震的诱发主要受孔隙压力扩散和库水浸润弱化作用的影响,库体重力荷载作用一定程度上抑制了地震的发生.  相似文献   

High‐mode buckling responses of buckling‐restrained brace core plates          下载免费PDF全文

An‐Chien Wu  Pao‐Chun Lin  Keh‐Chyuan Tsai 《地震工程与结构动力学》2014,43(3):375-393

Cyclic loading tests and finite element analyses on six novel all‐steel buckling‐restrained braces (BRBs) are conducted using different loading patterns to investigate the core plate high‐mode buckling phenomenon. The proposed BRB is composed of a core member and a pair of identical restraining members, which restrains the core member by using bolted shim spacers. The design of the proposed BRB allows the core plate to be visually inspected immediately following a major earthquake. If necessary, the pair of restraining members can be conveniently disassembled, and the damaged core plate can be replaced. Test results indicate that the proposed BRBs can sustain large cyclic strain reversals and cumulative plastic deformations in excess of 400 times the yield strain. Experimental and analytical results confirm that the high‐mode buckling wavelength is related to the core plate thickness and the applied loading patterns. The larger the axial compressive strain is applied, the shorter the high‐mode buckling wavelength would be developed. The buckling wavelength is about 12 times the core plate thickness when the high‐mode buckling shape is fully developed. However, it reduces to about 10 times the core plate thickness when a compressive core strain reaches greater than 0.03. The high‐mode bucking wavelength can be satisfactorily predicted using the proposed method or from the finite element analysis. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Seismic design and test of gusset connections for buckling‐restrained braced frames          下载免费PDF全文

Pao‐Chun Lin  Keh‐Chyuan Tsai  An‐Chien Wu  Ming‐Chieh Chuang 《地震工程与结构动力学》2014,43(4):565-587

The corner gusset plates in a steel braced frame can be subjected to forces not only from the brace but also from the effects of the frame actions. In this study, several finite element models are constructed to analyze the gusset‐to‐beam and gusset‐to‐column interface forces. It is found that the frame actions affect the gusset interface force distributions significantly. A simplified strut model to represent the gusset plate is adopted to evaluate the frame action forces. In addition, the generalized uniform force method is adopted as it provides more freedom for designers to configure the gusset plate shapes than using the uniform force method. In this paper, a performance‐based design method is proposed. The gusset interface force demands take into account the combined effect of the brace maximum axial force capacity and the peak beam shear possibly developed in the frame. The specimen design and key results of a series of full‐scale three‐story buckling‐restrained braced frame (BRBF) hybrid tests are discussed. The gusset interface cracks observed at inter‐story drift greater than 0.03 radians can be well predicted by using the proposed design method. The BRBF tests and analyses confirm that the proposed design method is reasonable. The effectiveness of varying the width of gusset edge stiffeners in reducing the gusset tip stress concentrations is also investigated. This paper concludes with recommendations for the seismic design of BRBF corner gusset plates. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Welded end‐slot connection and debonding layers for buckling‐restrained braces          下载免费PDF全文

Keh‐Chyuan Tsai  An‐Chien Wu  Chih‐Yu Wei  Pao‐Chun Lin  Ming‐Chieh Chuang  Yi‐Jer Yu 《地震工程与结构动力学》2014,43(12):1785-1807

The debonding mechanism has a significant effect on the performance of a buckling‐restrained brace (BRB). In this paper, a method for estimating the compression strength adjustment factor for any given BRB core strain is presented. Experimental investigations were conducted on four BRBs to examine the efficiency of four different debonding materials in reducing the difference between the cyclic peak compression and tension. Test results indicate that chloroprene rubber is very easy to install and very effective in minimizing the difference between the compressive and tensile capacities. The excellent performance of 13 full‐scale welded end‐slot BRBs (WES‐BRBs) is illustrated through experiments. Cyclic loading test results of a 12.5‐m long jumbo WES‐BRB reveal that its peak compressive strength exceeds 16,800 kN and its maximum core strain reaches 0.035. All WES‐BRBs show satisfactory performance with a very stable hysteresis response, modest peak compressive to tensile strength ratio, and very predictable axial stiffness. These specimens sustain a cumulative plastic deformation of greater than 400 times the yield deformation. The hysteresis responses can be satisfactorily predicted by using a two‐surface plasticity analytical model. Advantages of the welded end‐slot connections are also presented through a discussion on the effects of the BRB yield region length ratio on the effective stiffness, the yield story drift, and the core strain level. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Bidirectional substructure pseudo‐dynamic tests and analysis of a full‐scale two‐story buckling‐restrained braced frame          下载免费PDF全文

Hsen‐Han Khoo  Keh‐Chyuan Tsai  Ching‐Yi Tsai  Cheng‐Yu Tsai  Kung‐Juin Wang 《地震工程与结构动力学》2016,45(7):1085-1107

A two‐story buckling‐restrained brace (BRB) frame was tested under bidirectional in‐plane and out‐of‐plane loading to evaluate the BRB stability and gusset plate design. The test comprised pseudo‐dynamic loadings using the 1999 Chi‐Chi earthquake scaled to the 50%, 10%, and 2% probability of exceedance in 50 years and a cyclic regime of increasing amplitudes of up to 3.0% story drift ratio (SDR). The specimen had a unique configuration where the beams were connected to the columns through shear tabs welded to the column flanges and bolted to the beam webs. Stable hysteretic behavior with only minor cracking at the gusset‐to‐column welds was observed under the pseudo‐dynamic tests, with maximum in‐plane and out‐of‐plane SDRs of 2.24% and 1.47% respectively. Stable behavior continued into the cyclic test where fracture of the gusset‐to‐column welds occurred in the first cycle to simultaneous bidirectional SDR of 3.0%. The observed BRB stability is consistent with a methodology developed for BRB frames under simultaneous in‐plane and out‐of‐plane drifts. The specimen behavior was studied using a finite element model. It was shown that gusset plates are subjected to a combination of BRB force and frame action demands, with the latter increasing the gusset‐to‐beam and gusset‐to‐column interface demands by an average of 69% and 83% respectively. Consistent with the test results, failure at the gusset‐to‐column interfaces is computed when frame action demands are included, thus confirming that not considering frame action demands may results in unconservative gusset plate designs. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Influence of time‐varying frequency content in earthquake ground motions on seismic response of linear elastic systems          下载免费PDF全文

Yong Li  Joel P. Conte  Michele Barbato 《地震工程与结构动力学》2016,45(8):1271-1291

Earthquake ground motion records are nonstationary in both amplitude and frequency content. However, the latter nonstationarity is typically neglected mainly for the sake of mathematical simplicity. To study the stochastic effects of the time‐varying frequency content of earthquake ground motions on the seismic response of structural systems, a pair of closely related stochastic ground motion models is adopted here. The first model (referred to as ground motion model I) corresponds to a fully nonstationary stochastic earthquake ground motion model previously developed by the authors. The second model (referred to as ground motion model II) is nonstationary in amplitude only and is derived from the first model. Ground motion models I and II have the same mean‐square function and global frequency content but different features of time variation in the frequency content, in that no time variation of the frequency content exists in ground motion model II. New explicit closed‐form solutions are derived for the response of linear elastic SDOF and MDOF systems subjected to stochastic ground motion model II. New analytical solutions for the evolutionary cross‐correlation and cross‐PSD functions between the ground motion input and the structural response are also derived for linear systems subjected to ground motion model I. Comparative analytical results are presented to quantify the effects of the time‐varying frequency content of earthquake ground motions on the structural response of linear elastic systems. It is found that the time‐varying frequency content in the seismic input can have significant effects on the stochastic properties of system response. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

多波多分量高斯束叠前深度偏移   总被引：2，自引：2，他引：0       下载免费PDF全文

栗学磊  毛伟建 《地球物理学报》2016,59(8):2989-3005

本文对基于弹性波动理论的多波多分量高斯束偏移进行了完整且详细的分析和公式推导,实现了3D空间多分量(矢量)波场的直接成像.由于当前多数基于弹性波动方程的偏移方法只是假设应力边界条件为自由地表边界条件,这种假设不符合垂直地震剖面(VSP)和海底电缆(OBC)等地震数据.为此本文详细分析了实际应用中常见的三种弹性各向同性介质模型的应力边界条件:自由空间、海底和自由地表模型.在上行传播假设情况下,获得了应力边界条件与位移边界条件的关系式.在此基础上,准确推导了3D多波多分量高斯束波场延拓和偏移成像公式,并在偏移过程中实现了完整的多波型自动分离.由于常规的互相关成像条件不适用于矢量波场成像,本文引用了散度/旋度互相关成像条件.通过约定PS转换波的正向旋转方向解决了3D空间PS成像极性翻转问题.利用2D和3D模型数据偏移成像验证了我们所提出的多波多分量高斯束偏移方法的可行性.  相似文献   

Nonlinear rooftop tuned mass damper frame for the seismic retrofit of buildings          下载免费PDF全文

Jerod G. Johnson  Chris P. Pantelides  Lawrence D. Reaveley 《地震工程与结构动力学》2015,44(2):299-316

Numerical studies of existing buildings demonstrate the effectiveness of nonlinear/inelastic rooftop tuned mass damper frames (NRTMDF) used as a retrofit for reducing seismic response. The technique utilizes a rooftop penthouse as a tuned mass damper with mass incorporated as the roof deck of the penthouse while targeted nonlinearity and energy dissipation are introduced through buckling restrained braces (BRBs) linking the penthouse mass to the structure below. The writers summarize numerical studies of ten existing buildings modified with a specifically tuned NRTMDF. The studies demonstrate the effectiveness of the technique that stems from elastic and transient inelastic period shifts enabled by the damper coupled with targeted energy dissipation in the penthouse BRBs. Numerical simulations using response nonlinear time‐history analysis techniques show that for many structures and sites, the NRTMDF decreases peak transient response and overall seismic demand of the original structure. The technique also reduces seismic demand on nonstructural elements and components, manifested as reductions in floor acceleration spectra. Energy methods show that the approach enables significant reductions in energy demand on the original structure through the complete earthquake acceleration history. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献