地基刚度和不均匀性对混凝土大坝地震响应的影响

应用比例边界有限元方法进行了坝-水库-无限地基的动力相互作用分析。深入研究了无限地基刚度变化以及地基非均匀性对大坝地震响应的影响。计算了不同的均匀地基刚度和地基刚度随深度变化情况下Koyna大坝的频响曲线以及地震作用下大坝的时程响应。计算结果表明,地基刚度和不均匀性对大坝地震响应产生重要影响。对于均质地基刚度增加时,坝的地震响应随之增加;对于地基刚度随深度增加的不均匀地基,坝的地震响应增加迅速。此外还讨论了工程中广泛应用的无质量地基模型对于相互作用分析的适用性问题。     

无限地基辐射阻尼对溪洛渡拱坝地震响应的影响

用有限元、边界元和无限边界元(FE-BE-IBE)在时域内的耦合模型分析了溪洛渡拱坝的动力响应,在分析中考虑了无限地基辐射阻尼,结果表明辐射阻尼对拱坝的动力响应有显著的影响。又研究了辐射阻尼的不同影响因素,如水位、地基弹性模量和不同地震输入等。     

复杂非均质场地条件下核岛厂房结构地震响应分析研究

考虑结构-地基动力相互作用是各国核电抗震规范的一致要求,其中,非均质地基动力特性的合理模拟是 当前重要的关注之一。提出基于施加高阻尼并逐步移频抽取思想的阻尼溶剂逐步抽取法,最大限度地降低了阻尼 溶剂抽取法数值实现中人工高阻尼与地基区域大小的相互制约性,进而耦合上部核岛厂房子结构,在有限元框架 内建立了复杂非均质场地条件下核岛厂房结构地震响应分析模型,并给出了具体的实现公式,以便在通用有限元 程序中的开发。以三维半无限空间方形地基以及非均匀分层地基的动力分析为例,针对上述计算模型进行具体验 证,并就地基局部非均质对核岛厂房结构响应的影响进行探讨。计算结果表明,实测地基中所含捕虏体对核岛厂 房结构的地震响应影响较小,而该模型表现出良好的精度和计算效率,以及更好地适用于地基非均质性以及表面 几何结构复杂多变的情况。     

双塔楼大底盘高层建筑-基础-地基地震动力相互作用分析

采用三维有限元方法建立了双塔楼大底盘高层建筑-厚筏基础-地基相互作用体系的动力分析模型,通过同比例增减某一参数的取值,分析了结构抗侧刚度、混凝土强度、楼板厚度和地基土刚度对双塔楼结构振动特性和地震响应的影响。结构抗侧刚度对结构动力响应的影响较大,地基土刚度和楼板厚度变化的影响次之。同时,通过与刚性基底假定的分析结果进行对比可知,土-结构之间的动力相互作用对结构动力响应的影响不容忽视。     

粘弹性人工边界在重力坝地震分析中的应用

介绍了粘弹性人工边界以及粘弹性人工边界单元的推导过程,在此基础上对某重力坝的坝体—地基结构系统进行有限元三维地震响应分析,结果表明无限地基辐射阻尼的粘弹性人工边界能够显著减小坝体地震响应。     

混凝土坝-基岩地震动力相互作用时域有限元分析

混凝土坝地震响应分析是坝工安全评估的关键一步。坝与基岩动力相互作用对混凝土坝地震响应具有重要影响。因此,建立一个可考虑坝与基岩动力相互作用影响的数值分析方法是十分必要的。给出了分析混凝土坝–基岩系统地震响应的时域有限元法。在时域有限元分析中,地震波的输入以及地基辐射阻尼的模拟常常是2个十分重要的课题。基于柱面波动方程提出了能同时实现地震动输入和模拟地基辐射阻尼的方法,这种方法非常简单有效,几个数值算例验证了方法的精度和有效性。最后,对混凝土重力坝地震响应进行了数值分析,结果表明无限地基辐射阻尼的影响是显著的。     

混凝土坝–基岩地震动力相互作用时域有限元分析

混凝土坝地震响应分析是坝工安全评估的关键一步。坝与基岩动力相互作用对混凝土坝地震响应具有重要影响。因此，建立一个可考虑坝与基岩动力相互作用影响的数值分析方法是十分必要的。给出了分析混凝土坝–基岩系统地震响应的时域有限元法。在时域有限元分析中，地震波的输入以及地基辐射阻尼的模拟常常是2个十分重要的课题。基于柱面波动方程提出了能同时实现地震动输入和模拟地基辐射阻尼的方法，这种方法非常简单有效，几个数值算例验证了方法的精度和有效性。最后，对混凝土重力坝地震响应进行了数值分析，结果表明无限地基辐射阻尼的影响是显著的。     

地震波斜入射地下隧道地震响应：2.5维FE-BE耦合模拟

针对地震波斜入射导致的非一致地震激励结构地震响应问题,提出了地下隧道三维地震响应分析的一个2.5维有限元–边界元（FE-BE）耦合分析方法,该耦合方法具有分析效率高和计算精度高的优势。利用有限元模拟隧道结构,并引入弹簧单元考虑衬砌管片接头的影响;半无限土域利用基于场地三维动力刚度矩阵和移动斜线荷载格林函数的边界元方法模拟。通过与文献结果比较验证了耦合方法的正确性。利用该2.5维FE-BE方法,以某盾构隧道为例,研究了斜入射地震波作用下隧道结构的三维地震响应,着重分析了管片接头对隧道衬砌地震变形和内力的影响,并讨论了通过对隧道衬砌整体刚度进行折减（等效均质圆环模型）来考虑管片接头影响的方法的适用性。研究表明,管片接头对隧道地震响应有重要影响,随接头刚度减小隧道衬砌变形呈增大趋势,但衬砌内力显著减小;而且,对于管片接头刚度较大的情况,等效均质圆环模型可以在一定程度上反映管片接头对隧道结构地震响应的影响,但可能导致隧道纵向弯矩的低估。     

深厚软土场地道路隧道结构横向地震响应分析

确定场地范围和地震输入方式是道路隧道地震响应分析的前提。以上海深厚多层软土场地的自由场解析为基础,验证2D有限元模型的场地基岩和侧向边界假定的合理性;进而选取典型盾构法和明挖法隧道为研究对象,建立有限元2D地层-隧道地震动力响应分析模型,分析评价合理的基岩面深度与侧向边界宽度。结果表明:深厚软土场地的隧道地震响应分析应采用黏弹性人工边界以合理实现自由场边界;侧向边界的选取范围对隧道的动力响应影响较小,计算模型的底部边界深度对响应影响较大;取70 m深度为基岩面得到隧道结构地震动力响应是偏于安全的,但场地的基频有所变化。     

框架结构和半无限地基系统的动力相互作用问题研究

采用梁单元－有限元－映射动力无穷元耦合的方法,建立了频域中框架结构与半无限地基系统动力相互作用问题的分析模型,探讨了结构与地基动力相互作用对该系统的动力特性和地震响应的影响及影响参数．得到了一些规律性的结果和有益的结论,可为工程抗震设计提供参考．     

Earthquake analysis of arch and gravity dams including the effects of foundation inhomogeneity

Dam-foundation interaction plays an important role in the design of earthquake-resistant concrete arch and gravity dams. Geological conditions of the dam canyon are usually very complicated; however, in the literature, the damfoundation interaction analysis is often carried out based on the premise of a homogeneous unbounded foundation. In this paper, the effect of foundation inhomogeneity on the seismic response of arch and gravity dams was studied by means of scaled boundary finite element method (SBFEM). In order to satisfy the similarity requirement of SBFEM and simplify the computational effort, a subdomain approach and a conical representation of an unbounded foundation were proposed. The way of partitioning the domain and the selection of open angle and bottom radius of the cone model on the accuracy of the result were examined. Numerical examples show that the proposed approach is rational and efficient. Cases of foundation inhomogeneity with stiffness varying in accordance with an exponential function along the radial direction, and cases of foundation inhomogeneity with stiffness discontinuity and with weak interlayer strata on the earthquake response of concrete arch dams as well as gravity dams were analyzed. It was found that a homogeneous idealization of the unbounded foundation may sometimes greatly underestimate the maximum earthquake stress response of the dam. Therefore, taking into account the effect of foundation inhomogeneity for the earthquake safety assessment of concrete arch and gravity dams has great significance.     

汶川8.0级地震对典型高坝结构安全的影响分析

 汶川8.0级地震具有震级高、震源浅、破坏性强和次生地质灾害严重等特点。在对震区高坝灾情归类分析的基础上,选择典型的不同坝型高坝,包括宝珠寺重力坝、沙牌碾压混凝土拱坝、紫坪铺面板堆石坝等工程,从大坝距发震断裂距离、大坝基础处理及大坝结构类型的抗震性等因素对大坝结构安全的影响展开分析研究。结合在建的一批300 m级高坝,对抗震设防标准、水库诱发地震等问题进行讨论。结果表明：(1) 现行大坝抗震设计是可行的,300 m级高坝工程抗震能力仍需深化研究;(2) 大坝工程基础、抗力体经合理加固后,增强了岩体结构的整体性,可有效提高大坝及基础的抗震能力;(3) 高坝应急预案的设计与管理,流域性统一公共水电工程灾害应急平台建设有待加强;(4) 对水库诱发地震的研究需加强。     

Reliability and variance-based sensitivity analysis of arch dams during construction and reservoir impoundment

The static performance of arch dams during construction and reservoir impoundment is assessed taking into account the effects of uncertainties presented in the model properties as well as the loading conditions. Dez arch dam is chosen as the case study; it is modeled along with its rock foundation using the finite element method considering the stage construction. Since previous studies concentrated on simplified models and approaches, comprehensive study of the arch dam model along with efficient and state-of-the-art uncertainty methods are incorporated in this investigation. The reliability method is performed to assess the safety level and the sensitivity analyses for identifying critical input factors and their interaction effects on the response of the dam. Global sensitivity analysis based on improved Latin hypercube sampling is employed in this study to indicate the influence of each random variable and their interaction on variance of the responses. Four levels of model advancement are considered for the dam-foundation system: 1) Monolithic dam without any joint founded on the homogeneous rock foundation, 2) monolithic dam founded on the inhomogeneous foundation including soft rock layers, 3) jointed dam including the peripheral and contraction joints founded on the homogeneous foundation, and 4) jointed dam founded on the inhomogeneous foundation. For each model, proper performance indices are defined through limit-state functions. In this manner, the effects of input parameters in each performance level of the dam are investigated. The outcome of this study is defining the importance of input factors in each stage and model based on the variance of the dam response. Moreover, the results of sampling are computed in order to assess the safety level of the dam in miscellaneous loading and modeling conditions.     

Challenges of high dam construction to computational mechanics

The current situations and growing prospects of China’s hydro-power development and high dam construction are reviewed, giving emphasis to key issues for safety evaluation of large dams and hydro-power plants, especially those associated with application of state-of-the-art computational mechanics. These include but are not limited to: stress and stability analysis of dam foundations under external loads; earthquake behavior of dam-foundation-reservoir systems, mechanical properties of mass concrete for dams, high velocity flow and energy dissipation for high dams, scientific and technical problems of hydro-power plants and underground structures, and newly developed types of dam-Roll Compacted Concrete (RCC) dams and Concrete Face Rock-fill (CFR) dams. Some examples demonstrating successful utilizations of computational mechanics in high dam engineering are given, including seismic nonlinear analysis for arch dam foundations, nonlinear fracture analysis of arch dams under reservoir loads, and failure analysis of arch dam-foundations. To make more use of the computational mechanics in high dam engineering, it is pointed out that much research including different computational methods, numerical models and solution schemes, and verifications through experimental tests and filed measurements is necessary in the future. Selected from Computational Mechanics, Proceedings of the Sixth World Congress on Computational Mechanics in Conjunction with the Second Asian-Pacific Congress on Computational Mechanics, Tsinghua University Press & Springer, 2004, 154–166     

关于高拱坝坝基可利用岩体质量要求的探讨

拱坝作为高次超静定的空间壳体结构,具有自适应能力强、超载安全系数大的显著特点,一般说来,拱坝是经济性和安全性都较优的一种坝型。然而,随着一大批高拱坝工程的相继建成,我国拱坝设计标准中对于高拱坝坝基可利用岩体质量要求过严,导致拱坝适应性和经济性降低的问题也逐渐显现。本文在对中、美拱坝坝基可利用岩体质量要求及中、外代表性拱坝工程坝基可利用岩体情况的对比分析的基础上,系统阐述了高拱坝坝基岩体质量要求过严所带来的不利影响,并列举了我国在特高拱坝及高拱坝设计中突破建基面岩体质量要求限制、取得显著经济效益的工程实例,希望能为类似工作提供参考。     

基于工程体与地质体相互作用的两体力学模型初探

针对大坝和坝基、坝肩和库岸相互作用传统的一体两介质模型,提出了两体力学模型的基本概念、研究思路以及应用范围;阐述了一体两介质力学模型与两体力学模型之间的差异,并用单轴压缩实验进行了验证;建立了重力坝和坝基相互作用的两体力学模型,为大坝与坝基的整体稳定性研究与评判提供了一条新的途径。     

Evaluation of seismic reliability of gravity dam-reservoir-inhomogeneous foundation coupled system

The seismic performance of gravity dam-reservoir-foundation coupled system is investigated utilizing probabilistic approach. In this research, the uncertainties associated with modeling parameters are incorporated in nonlinear response history simulations to realistically quantify their effects on the seismic performance of the system. The methodology is applied to Pine Flat gravity dam and the foundation is considered to be inhomogeneous assuming a constant spatial geometry but with various rock material properties. The sources of uncertainty are taken into account in the reliability analysis using Latin Hypercube Sampling procedure. The effects of the deconvolution process, number of samples, and foundation inhomogeneity are investigated.     

A simplified approach to assess seismic stability of tailings dams

In the zones of high seismic activity, tailings dam should be assessed for the stability against earthquake forces. In the present paper, a simplified method is proposed to compute the factor of safety of tailings dams. The strain-dependent dynamic properties are used to assess the stability of tailings dams under seismic conditions. The effect of foundation soil properties on the seismic stability of tailings dams is studied using the proposed method. For the given input parameters, the factor of safety for low-frequency input motions is nearly 26% lower than that for high-frequency input excitations. The impedance ratio and the depth of foundation have significant effect on the seismic factor of safety of tailings dams. The results from the proposed method are well compared with the existing pseudo-static method of analysis. Tailings dams are vulnerable to damage for low-frequency input motions.