拱坝横缝影响及有效抗震措施的研究

大量研究结果和某些拱坝的地震震害表明，横缝对拱坝的地震响应有很大的影响。通过采用非光滑方程组方法以及考虑碰撞时刻动量、动能守恒来模拟横缝所引起的动接触问题，同时为了提高计算效率，采用隐-显式积分方法对坝-基系统的动力平衡方程进行求解。针对在拱坝中上部配筋这一抗震措施，也作了探讨。通过对小湾拱坝的分析，为高拱坝工程抗震措施的选择提供技术依据。     

基于不同设计反应谱的溪洛渡拱坝动力响应分析

合理的设计反应谱是保证高拱坝动力分析和安全评价结果可靠的前提。为研究不同反应谱时程对拱坝非线性响应的影响,分别基于GB 51247—2018《水工建筑物抗震设计标准》设计反应谱、DL 5073—2000《水工建筑物抗震设计规范》设计反应谱、以及溪洛渡场地相关反应谱,拟合出地震动时程,采用溪洛渡拱坝-库水-地基系统非线性损伤开裂模型进行拱坝的非线性地震响应分析。结果表明：反应谱的选择对溪洛渡拱坝地震响应影响显著,相比于2000年标准反应谱,2018年标准反应谱使溪洛渡拱坝坝顶最大动相对位移增加、坝顶上游面横缝开度增大、孔口和坝踵位置损伤加深。并且,2018年标准下的坝体动力响应整体高于基于场地谱的计算结果,而2000年规范下的坝体动力响应低于场地谱的计算结果,说明2000年规范理应更新,2018年标准更符合当下的抗震设计需求。     

拱坝动力特性的试验研究与有限元分析

本文提出两座拱坝的动力特性的研究结果。对一座进行了原型振动试验,对另一座完成了原型与模型的振动试验以及动力有限元分析。试验的主要目的是确定坝的自振频率、振型和阻尼。有限元分析考虑了刚性地基与弹性地基两种情况,采用SAP程序计算了振型、坝率与地震反应。弹性基础模型的计算结果同原型和模型试验结果很接近。     

高拱坝伸缩横缝间布设阻尼器对坝体地震反应影响的研究

对设置伸缩横缝的小湾高拱坝结构，应用子结构理论，分别就正常高水位与常遇低水位两种水位工况，考虑坝体伸缩横缝在地震交变荷载作用下反复开合引起的缝面间滑移、接触等效应的影响，坝体-库水的相互作用而产生的动水压力的影响，对坝体的抗震性能进行了地震反应分析。对伸缩缝间设置阻尼器这新的设计思想进行了可行性的研究，论证推导了阻尼器的计算模型，探讨了阻尼器对坝体抗震性能的影响。     

考虑横缝键槽咬合的拱坝地震响应分析

基于非线性指数型动接触本构模型,对实际键槽模型进行简化处理。采用的本构模型可以考虑缝面的开合非线性以及横缝键槽的咬合作用。采用点-面接触模型模拟横缝的非线性动接触行为,精细研究了缝面开度、径向位移的变化及其对坝体应力状态的影响,并与平缝结果进行了比较。以一座拟建的混凝土重力拱坝,探讨了横缝及其诱导缝对大坝工作性态的影响,并对横缝键槽的影响进行了综合分析。研究表明,横缝的径向滑移量要远大于开度,当考虑诱导缝时,由于大坝整体性受到削弱,横缝开度变大;考虑键槽效应后,径向滑移效应大幅减小,而法向开度增大,坝踵处的主拉应力以及拱冠梁顶处的拱向拉应力的最大值均变大。     

随机地震动场激励下拱坝多点输入的抗震可靠度分析

本文首次将空间随机地震场输入用于拱坝随机振动分析之中，与拱坝三维动力学有限元法结合，完成了三维拱坝在空间随机地震动场作用下的随机振动分析方法及算法的研究，另外考虑动力和静力的叠加，提出了三维空间随机地震动场的拱坝抗震可靠度分析方法，最后编制了相应的程序，对小湾拱坝进行了抗震可靠度分析，并与随机变量的结果进行了比较。     

考虑横缝影响的拱坝动力分析

本文在求解三维弹性静力摩擦接触问题的有效方法-非光滑方程组方法的基础上,通过能够近似满足动量、动能守恒条件的速度、加速度的修正方法,将该方法推广到动力接触问题的求解中,以考虑地震时拱坝中横缝的开合、错动对坝体动力响应的影响。同时文中采用由多次透射公式表示的人工边界条件来考虑坝-基动力相互作用的影响。数值算例中分析了横缝的数目和布置位置对拱坝动力响应的影响。     

考虑坝体材料非线性的混凝土拱坝地震反应分析

本文基于可信概率水准的破坏性强震作用,针对小湾高拱坝进行了考虑坝体材料非线性的拱坝地震反应分析。在分析模型中,同时考虑了无约束域地震能量辐射效应和近域地基材料非均匀性的影响。为了实现非线性条件下的静、动力组合分析,利用显式有限元结合修正的黏弹性人工边界的开放系统时域静、动力统一分析方法进行了求解,对在自重作用下的初始静力解计算采用了动力松弛技术。     

不同模型对足尺钢框架振动台试验模拟的影响

本文分别采用纤维单元模型和塑性铰单元模型对一个四层足尺钢框架振动台试验进行模拟分析,在三维空间非线性分析程序Perform-3D中进行动力非线性分析,比较分析结果,并与试验结果对比,以研究两种模型应用于钢框架整体结构非线性分析的计算精度。文中并讨论了纤维单元模型截面纤维的划分、塑性区长度的取值等问题。最后对采用组合梁的整体结构模型进行了动力非线性分析。结果表明,纤维模型的建模速度比塑性铰模型快,但塑性铰模型能模拟结构的倒塌时间。Perform-3D程序的纤维单元模型和塑性铰单元模型用于计算我国规范规定的7度和8度地震作用的多层钢框架结构,其结果是真实可靠的,而且计算结果偏于安全。     

有缝拱坝-地基系统非线性地震波动反应分析方法

拱坝坝体中缝界面在地震作用下的开、合模拟对拱坝地震反应有重要影响。目前在拱坝地震反应分析中应用的一些模型,如Ｆｅｎｖｅｓ模型、Ｄｏｗｌｉｎｇ的三参数模型,存在对缝界面的接触状态模拟精度不高的问题,这对于准确评价工程上关心的缝界面最大张开率是不足的。此外,坝基中存在的断层、节理、裂隙待软弱夹层的非线性力学特性和无限地基能量辐射作用对拱坝地震反应也有重要影响。在拱坝地震反应分析中同时考虑这三种影响因素     

Non‐linear seismic response of arch dams with contraction joint opening and joint reinforcements

A comprehensive study of non‐linear seismic response of arch dams with contraction joint opening and joint reinforcements has been conducted. A numerical model of contraction joint reinforcements is presented for optimization control of the joint opening. The objective of this control is to reduce the joint opening and expectantly to balance the sustained loads between the horizontal and the vertical components of the dam, thus avoiding an overstress in the cantilever while retaining the release of arch tensile stresses to some extent. Several parameter studies such as critical element size and required number of joints to be simulated for convergence are also performed. As an engineering application, a 292‐m high arch dam (the Xiaowan arch dam) and the Big Tujunga dam are analysed in detail. The results demonstrate that the joint opening and the corresponding load transfer from the arch to cantilever components of the dam during strong earthquakes are substantial. It is also evident that by providing sufficient strength and reinforcement flexibility, the joint opening can be controlled to some extent. However, the stress redistribution due to reinforcement control is not sufficient to avoid the overstress in the cantilever for the Xiaowan arch dam. Thus, alternative measures are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

Experimental study of seismic overloading of large arch dam

A dynamic overloading model test has been carried out on a shaking table for an arch dam of 278 m in height to investigate its behaviours under strong earthquake. The model system included the arch dam with contraction joints, part of reservoir, partial foundation rock with topographic feature near the dam. A damping boundary consisting of viscous liquid has been used to simulate the effect of dynamic energy emission to far field, which made the dynamic interaction between dam and foundation in model arch dam system be represented properly. Three sets of different seismic waves of design level have been used as the input to investigate the difference in the responses of arch dam. Artificial waves of different levels have been used to verify the behaviours of arch dam under seismic overloading. Since the opening of joints during strong earthquake reduced the response acceleration and tensile arch stress, cantilever stress on downstream face exceeded the tensile strength first for the model dam. And the arch dam responded in a non‐linear way when input seismic load increased. Some cracks appeared near abutments, and the damage made the natural frequency of arch dam to drop obviously, but the static function did not seem to change for the model tested. Copyright © 2005 John Wiley & Sons, Ltd.     

Nonlinear earthquake analysis of high arch dam–water–foundation rock systems

A nonlinear finite element model for earthquake response analysis of arch dam–water–foundation rock systems is proposed in this paper. The model includes dynamic dam–water and dam–foundation rock interactions, the opening of contraction joints, the radiation damping of semi‐unbounded foundation rock, the compressibility of impounded water, and the upstream energy propagating along the semi‐unbounded reservoir. Meanwhile, a new equivalent force scheme is suggested to achieve free‐field input in the model. The effects of the earthquake input mechanism, joint opening, water compressibility, and radiation damping on the earthquake response of the Ertan arch dam (240 m high) in China are investigated using the proposed model. The results show that these factors significantly affect the earthquake response of the Ertan arch dam. Such factors should therefore be considered in the earthquake response analysis and earthquake safety evaluation of high arch dams. Copyright © 2011 John Wiley & Sons, Ltd.     

Nonlinear seismic response analysis of arch dam-foundation systems- part II opening and closing contact joints

A time-domain method for the analysis of arch dam-foundation rock dynamic interaction during earthquake was proposed, and the dynamic relaxation technique was adopted to obtain the initial static response for dynamic analysis by [Du et al. (2005). The paper has been contributed to Bulletin of earthquake engineering]. In this paper, a nonlinear explicit method in time domain considering the opening and closing effect of contact joints on arch dam during earthquake is further proposed by introducing the dynamic contact force model into the method. The simulation accuracy of dynamic contact force model is verified by comparing its calculation result and test result of scale model on shaking table. Finally, the influence of joints on the seismic response of Xiaowan arch dam is studied by the proposed method and some conclusions are given.     

Response of jointed arches to earthquake excitation

An efficient method for accurately modelling the gradual opening and closing of joints in two-dimensional slabs and arches has been devised. The method is used in computing the earthquake response of an arch which is a representative horizontal cross-section of a concrete arch dam. Responses of the arch with and without joints are compared to assess the effect of joint opening. An extension to three-dimensional arch dams is proposed.     

A method for coupled arch dam‐foundation‐reservoir seismic behaviour analysis

This paper presents a method for coupled arch dam–foundation–reservoir seismic behaviour analysis. The dam is discretized by finite elements (FE) and the foundation and reservoir are discretized by boundary elements (BE). The opening of contraction joints and the spatial variability of the seismic action is taken into account. The study of Pacoima dam by this method is also presented. The computed results show that no cracks were to be expected due to the vibrations induced during the Feb. 9, 1971 San Fernando earthquake. Copyright © 2000 John Wiley & Sons, Ltd.