有横缝拱坝的非线性动力模型试验和计算分析研究

本文通过在大型三向地震模拟振动台上进行的设置伸缩横缝的某拱坝非线性动力模型试验，应用非线性有限元动力分析程序同时进行计算分析，全面系统地研究了拱坝横缝对坝体动力特性和地震反应的影响，并对计算程序进行了改进。试验与计算结果相互印证，验证了试验成果的可靠性和计算分析模型、计算程序与计算结果的合理性。     

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。     

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。     

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。     

双向地震波输入时振动方向对拱坝地震响应的影响

拱坝-地基三维地震响应分析中大多只分析入射地震波在拱坝-地基系统坐标系方向输入时的地震响应,而事实上,垂直入射的剪切波其振动方向是不确定的,地震波动的合理输入对拱坝-地基系统的地震响应分析起着决定性的作用.本文研究了拱坝-地基系统在双向地震波输入时不同振动方向对拱坝-地基系统地震响应的影响.计算结果表明:在双向地震波输入情形时,拱坝位移及应力响应最大值均不是发生在传统方法的横河向或者顺河向,而是与输入地震波相关,所以在研究拱坝-地基三维地震响应时有必要考虑入射地震波振动方向的影响.     

墩-水耦合计算模式及深水桥墩动力响应研究

为了研究地震作用下动水压力对深水桥墩的影响,以声波动理论为基础,通过对流体域边界条件的简化和流体域范围的探讨,建立了一种改进的墩-水耦合有限元模型,并提出了常用深水桥墩的理想流体域范围图。分别讨论了深水桥墩在简谐荷载、地震荷载作用下的动力响应,结果表明:动水压力增大了桥墩的动力响应,增幅在20%到50%之间,不可忽视;当桥墩基频越接近简谐荷载激励频率或地震波主频有效带宽区间时,动水压力的影响越大。     

水深对跨库区桥梁地震响应的影响分析

随着我国西南地区梯级水电站的建设,跨库区桥梁抗震设计和地震安全性评价是桥梁抗震领域面临的重要问题。研究了一套考虑峡谷场地-库水-桥梁相互作用的跨库区桥梁地震响应分析方法,采用分区并行方法分析环境介质(含场地、库水)与桥梁的相互作用,库水、场地和水下结构采用广义饱和介质理论统一框架描述,通过集中质量显式有限元进行分析;水面以上结构采用隐式有限元进行分析;显式和隐式计算区之间通过设置一层显-隐式重叠单元实现分区耦合;无限域通过透射人工边界来模拟。以一跨峡谷连续刚构桥为例,在不同水深情况下,输入2条地震波,研究峡谷地形下水深对桥梁地震响应的影响。研究结果表明,库水总体上对桥梁有减震作用,随水深增加,桥梁整体反应减小,但局部反应有增大现象;随着水深增加,水体对桥墩的约束增加,使得其有效刚度增加,改变桥梁的刚度分布,引起桥梁内力的重分布;水体具有弱化地形效应的作用,随着水深增加,由峡谷地形和墩高差异引起的桥梁反应差异逐渐减小。     

库水-淤砂层-坝体-坝基体系地震响应分析

针对我国西部水利工程结构面临的地震安全问题，特别是混凝土高拱坝的抗震安全设计，以小湾水电站混凝土高拱坝为研究对象，进行了库水-淤砂层-坝体-坝基体系的耦合动力分析，同时考虑了复杂的坝基地形、正常蓄水位的库水以及常年运行而堆积的淤沙层的影响。主要内容有：(1)基于传递矩阵法及二维有限元，实现了复杂峡谷地形的自由场计算；(2)基于水-饱和多孔介质-固体的统一计算框架，实现了库水-淤沙层-坝体-坝基体系的三维地震响应分析算法。最后，分别以脉冲波和地震波作为输入，探讨了小湾拱坝的地震响应规律及库水淤沙层对拱坝地震响应的影响。结果表明：坝体顶部中心区域会承受较大的拉、压应力；而库水底部淤砂层对坝体的位移及应力影响并不显著。     

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.     

CFRP composite retrofitting effect on the dynamic characteristics of arch dams

The purpose of this study is to investigate the effect of retrofitting dynamic characteristics of a damaged laboratory arch dam model, subsequently repaired with high-strength structural mortar and strengthened with composite carbon fiber reinforced polymer. This study constructed in laboratory conditions is a prototype arch dam–reservoir–foundation model. Five test cases of ambient vibration on the arch dam model illustrate the changes in dynamic characteristics: natural frequency, mode shape, and damping ratio, before and after retrofitting. The ambient vibration tests collected data from the dam body during vibrations by natural excitations which provided small impacts and response signals from sensitivity accelerometers placed at crest points. Enhanced Frequency Domain Decomposition Method in the frequency domain extracts the experimental dynamic characteristics. At the end of the study, experimentally identified dynamic characteristics obtained from all test cases have been compared with each other. Apparently, after the retrofitting, the natural frequencies of the dam body increased considerably, demonstrating that the retrofitting, including repairing and strengthening is very effective on the flashback of initial dynamic characteristics.     

Numerical simulation of reservoir sediment and effects on hydro‐dynamic response of arch dams

Based on the dynamic theory for saturated porous media by Biot (Journal of the Acoustical Society of America 1956; 28 : 168–178), a numerical model is presented to analyse the reflection behaviours of reservoir sediment and compared with those from the visco‐elastic model. It is concluded that the two models give very similar results of reflection coefficient α within the frequency range of interest. Then, using the two models, the change of the reflection coefficients α with various sedimentation parameters and excitation frequencies are studied in detail. The results are further used in the analysis of response functions of hydro‐dynamic pressures on, and structural displacements of the Xiang Hong Dian arch dam, for which some results from a field vibration test are available. It appears that effects of water compressibility with sediment reflection on hydro‐dynamic pressures and structural response are not significant for this specific case. Copyright © 2001 John Wiley & Sons, Ltd.     

Earthquake response of concrete arch dams: a plastic–damage approach

There are several alternatives to evaluate seismic damage‐cracking behavior of concrete arch dams, among which damage theory is the most popular. A more recent option introduced for this purpose is plastic–damage (PD) approach. In this study, a special finite element program coded in 3‐D space is developed on the basis of a well‐established PD model successfully applied to gravity dams in 2‐D plane stress state. The model originally proposed by Lee and Fenves in 1998 relies on isotropic damaged elasticity in combination with isotropic tensile and compressive plasticity to capture inelastic behaviors of concrete in cyclic or dynamic loadings. The present implementation is based on the rate‐dependent version of the model, including large crack opening/closing possibilities. Moreover, with utilizing the Hilber–Hughes–Taylor time integration scheme, an incremental–iterative solution strategy is detailed for the coupled dam–reservoir equations while the damage–dependent damping stress is included. The program is initially validated, and then, it is employed for the main analyses of the Koyna gravity dam in a 3‐D modeling as well as a typical concrete arch dam. The former is a major verification for the further examination on the arch dam. The application of the PD model to an arch dam is more challenging because the governing stress condition is multiaxial, causing shear damage to become more important than uniaxial states dominated in gravity dams. In fact, the softening and strength loss in compression for the damaged regions under multiaxial cyclic loadings affect its seismic safety. Copyright © 2013 John Wiley & Sons, Ltd.     

拱坝非线性地震反应分析

以乌东德拱坝为对象,进行了拱坝非线性地震反应分析。结果表明:坝体损伤区域明显大于坝体混凝土按线弹性材料计算时最大主应力超过抗拉强度的区域,说明传统方法低估了拱坝的开裂范围,偏于危险;考虑基岩的非线性后,坝体损伤总体上要有所减小;坝基岩体剪胀角对坝基岩体的屈服和坝体混凝土的损伤都有影响,但是规律不明确,因此应该进行基岩剪胀角的敏感性分析。     

Three‐dimensional models of reservoir sediment and effects on the seismic response of arch dams

The important effects of bottom sediments on the seismic response of arch dams are studied in this paper. To do so, a three‐dimensional boundary element model is used. It includes the water reservoir as a compressible fluid, the dam and unbounded foundation rock as viscoelastic solids, and the bottom sediment as a two‐phase poroelastic domain with dynamic behaviour described by Biot's equations. Dynamic interaction among all those regions, local topography and travelling wave effects are taken into account. The results obtained show the important influence of sediment compressibility and permeability on the seismic response. The former is associated with a general change of the system response whereas the permeability has a significant influence on damping at resonance peaks. The analysis is carried out in the frequency domain considering time harmonic excitation due to P and S plane waves. The time‐domain results obtained by using the Fourier transform for a given earthquake accelerogram are also shown. The possibility of using simplified models to represent the bottom sediment effects is discussed in the paper. Two alternative models for porous sediment are tested. Simplified models are shown to be able to reproduce the effects of porous sediments except for very high permeability values. Copyright © 2004 John Wiley & Sons, Ltd.     

拱坝非线性地震反应分析

本文根据一致粘弹性模型的概念，引入应变率的影响，将混凝土静态William-Warnke三参数模型改造成一致粘塑性William-Warnke三参数本构模型，并用这个模型对某高拱坝进行了非线性地震响应分析，与线弹性模型和应变率无关的William-Warnke三参数模型的结果进行了比较，初步探讨了应变率对拱坝地震反应的影响。     

高拱坝体系整体抗震安全评价方法研究

采用非线性地震波动反应分析方法，将坝体、地基、库水的强震反应本质上作为满足体系中接触面边界约束条件的波传播问题，在时域内以显式有限元方法求解。在不同概率水平的地震波作用下进行高拱坝与地基体系的有限元时程分析，并建议了以坝体位移反应发生突变为依据的拱坝体系整体失稳判断准则，从而建立了进行高拱坝体系整体抗震安全评价的方法，并以小湾拱坝为算例，对其抗震安全度作出初步评价。