新丰江水库大坝强震动监测及其动力特性分析

新丰江水库大坝是世界上第一座经受六级地震考验的超百米高混凝土大坝,并且至今库区周围仍然有地震不断发生,因此对其进行抗震分析十分必要。首先利用大坝强震动台阵的监测数据进行模态分析,然后结合模态分析结果建立大坝典型引水坝段ANSYS有限元模型并对其进行静力和动力分析,探讨坝体的变形和应力分布规律。结果表明:大坝模态频率与水位负相关;大坝在地震作用下,上游坝面突变处出现最大拉应力,这一现象与挡水坝段上游坝面突变处出现贯穿裂缝的破坏结果是一致的,应当引起一定重视,静力作用和地震作用下其他部位均有一定的安全储备;动力时程分析结果与反应谱分析结果相比,前者更加偏于安全。     

液化场地水库土石坝地震动力响应研究

基于有限差分法基本原理,采用FLAC3D软件对水库大坝在地震作用下的动力响应进行分析,研究地震强度、水库蓄水高度等对坝体稳定性的影响。结果表明:随着地震强度增加,坝基液化程度加剧,诱发的坝顶竖向沉陷增大;随着蓄水高度的增加,坝基液化程度和范围增大,坝顶竖向沉陷变形增大。当蓄水高度为10 m,地震峰值加速度为0.4 g时,坝顶沉陷量约为0.13 m,坝体稳定性降低,出现明显的潜在滑动面。因此在水库大坝选址、设计和施工中应注意可液化地基的地震灾害并做好相应的抗液化及加固措施。     

乌拉泊水库大坝的抗震安全性评价

位于北天山地震带中段的乌拉泊水库工程场地，自有历史地震记载以来，影响场区的最大烈度是Ⅶ度。通过参考前人工作成果及数据对大坝及附属建筑进行了动力稳定性计算研究，探讨了造成坝体震害的原因，评价了水库大坝的抗震安全性。     

水库地震安全问题分析

通过分析水库周围社会及大坝安全的地震影响、世界水库的发展情况、目前对水库地震安全的认识及其研究技术,认为水库周围的地震威胁有天然地震和水库诱发地震两类,表现为对水库大坝及其附属工程和库区社会均产生影响,因此水库地震安全主要由大坝地震安全、大坝附属工程地震安全和库区社会安全构成。随着水库大坝建设速度的不断加快和大型水库的不断增加,尤其是复杂地质构造区水库建设的增多,有必要在对大坝地震安全进行研究的基础上,重视水库地震安全的研究。     

乐昌峡大坝地震响应分析

乐昌峡大坝位于广东省韶关市乐昌市境内,建造时按照Ⅴ度区进行抗震设计,随着2016年第五代地震动参数区划图的实施,该区设防烈度提高为Ⅵ度,大坝在Ⅵ度地震影响下是否安全需要进行分析.利用图纸资料建立了大坝的三维有限元模型,计算分析了多水位下特征坝段的频率和大坝的地震响应,结果表明:溢流坝段的频率小于两岸挡水坝段.地震作用下,大坝位移最大值出现在坝顶处,应力最大处出现在闸墩、牛腿及坝踵处,但均处于安全范围,证明大坝抗震性能良好;库水水位会显著影响大坝的频率及地震响应,在抗震设计时,应引起注意.     

不同强度地震作用下的心墙堆石坝三维动力液化分析

东圳水库大坝位于福建省莆田市城厢区,该水利枢纽处于华南沿海地震带北段,由于水库建设时我国尚未有抗震设防烈度标准,因此亟需对其抗震稳定性进行复核。以东圳水库大坝为原型,结合已有的地震资料,选用Byrne液化模型,采用FLAC3D软件,研究了在50年超越概率10%、5%和2%地震作用下坝体填料的液化特征及最终位移情况。结果显示,在地震作用下,坝体上游砂砾石填料会发生局部液化,且液化区随着地震强度的增大而增加,但尚未出现大面积连续液化区;坝体填料发生液化后,产生了有限度的塑性变形,其变形量也随着地震强度的增大而有所增加;除坝顶较小区域外,坝体总位移量相对较小,对大坝整体稳定性不会产生显著影响。研究结论可以为大坝的抗震加固和治理措施的选择提供依据和参考。     

汶川地震中宝珠寺重力坝地震响应的三维有限元模拟

汶川地震中宝珠寺水电站遭受的地震烈度为8°(相当于水平峰值加速度0.2 g),远超过大坝的设计地震水平(0.1 g),震后大坝未见明显震损.为解释大坝在地震中的抗震现象,构建了坝址区三维模型.考虑坝体横缝非线性以及三个方向地震作用的不同组合方式,对汶川地震中大坝的动力响应进行有限元模拟.在此基础上,针对震后提高的抗震设防标准,进一步选取典型坝段,采用二维弹塑性方法对大坝进行抗震复核并分析可能的破坏模式.模拟结果表明:横河向地震分量起主导作用而顺河向地震作用相对较弱是宝珠寺重力坝在汶川地震中免于发生损坏的主要原因.坝顶混凝土发生挤压破碎缘于永久横缝在地震中高频渐开渐合行为引起的剧烈碰撞.宝珠寺重力坝对设计地震0.27 g的强震可以保持整体的安全性,对校核地震0.32 g的强震整体安全性降低,水库正常运行及抵抗余震的能力将受到影响.     

罗江县水库土坝汶川大地震震害调查与分析

5·12汶川8.0级大地震对德阳市罗江县的水库造成了不同程度的破坏,经济损失严重,若水库出现渍坝现象,将会带来更大的损失。对罗江县19座高危以上险情水库的土坝震害进行了调查研究.发现典型的震害现象包括裂缝、渗漏、防浪墙损坏以及泄水建筑物和附属设施的损毁等。根据水库土坝的震前病害调查资料可以看出：水库土坝在地震前多是带病运行,严重影响地震时水库运行的因素主要有土料或填筑质量差、坝基问题、坝体结构设计不当、蚁害、观测设施不全等。依据震后水库土坝的破坏形态,分析了水库大坝的震前病害对大坝震害现象的影响。为今后水库土坝的抗震设计提供基础性的资料。     

去学水电站流动地震监测台网建设及蓄水初期地震活动初步分析

四川去学水电站位于四川省甘孜藏族自治州得荣县境内,金沙江二级支流硕曲河干流上,库区及附近处于青藏高原东南缘地质结构不稳定地区,地震构造背景复杂。介绍了该水库地震监测台网及监测能力情况,并利用记录的蓄水后近10个月地震数据,对库区及附近的地震活动时空特征进行了初步分析。分析认为水库监测区域内地震主要集中分布在两个区域,一个位于在大坝及以东且延硕曲河展布,另一个则是大坝以南28～30 km处,沿德钦—中甸—大具断裂分布;利用最小完整性震级ML0.3级以上地震分区进行了时间进程分析,两个区域地震活动强度均较弱,但频度和深度上有明显的差异,表明大坝附近地震活动水平在时间趋势变化上受水库蓄水有一定影响,需加强跟踪监测库区及附近地震活动。     

河源新丰江地区地震烈度、地震影响场与新丰江水库大坝设防烈度

简述了1950年以来新丰江水库地区和水库大坝地震烈度的变化,并对新旧大坝设防烈度进行了对比,认为按现今的国家标准,新丰江水库大坝的设防烈度为Ⅶ度强。对库区6次4级以上地震的烈度宏观调查数据进行了分析,拟合了河源地区的地震烈度衰减关系,并与华南地区的地震烈度关系进行了比较．最后计算了新丰江水库地区的在5-6级地震情况下的宏观烈度影响场。     

Pseudo‐dynamic testing of a concrete gravity dam

Inspired from the simplified single degree of freedom modeling approach used in the preliminary design of concrete gravity dams, a pseudo‐dynamic testing method was devised for the seismic testing of a concrete gravity dam section. The test specimen was a 1/75 scaled section of the 120‐m‐high monolith of the Melen Dam, one of the highest concrete gravity dams to be built in Turkey. The single degree of freedom idealization of the dam section was validated in the first stage of the study using numerical simulations including the dam–reservoir interaction. Afterwards, pseudo‐dynamic testing was conducted on the specimen using three ground motions corresponding to different hazard levels. Lateral displacement and base shear demands were measured. The crack propagation at the base of the dam was monitored with the measurement of the crack widths and the base sliding displacements. After the pseudo‐dynamic loading, a static pushover test was conducted to determine the reserve capacity of the test specimen. Despite major cracking at the base of the monolith, neither significant sliding nor a stability problem that might jeopardize the stability of the dam was observed. Copyright © 2015 John Wiley & Sons, Ltd.     

An experimental evaluation of ice cover effects on the dynamic behaviour of a concrete gravity dam

An extensive forced‐vibration testing programme has been carried out on an 84‐m concrete gravity dam located in northeastern Québec, Canada. The dam was subjected to a harmonic load on the crest in summer and severe winter conditions with temperatures ranging from ?10°C to ?15°C and a 1.0–1.5m ice cover. Acceleration and hydrodynamic frequency responses were obtained in different locations on the dam and in the reservoir. The main objective of the repeated tests was to investigate the effects of the ice cover on the dynamic behaviour of the dam–reservoir–foundation system, by comparing summer and winter results. Modifications in damping and resonance frequencies were observed, as well as an additional resonance that was attributed to an interaction of the dam with the ice cover. These findings provided a reliable and unique database for the investigations of dam–reservoir–foundation interaction and, in particular, the ice‐cover effects for dams located in northern regions. Copyright © 2002 John Wiley & Sons, Ltd.     

An experimental investigation of water level effects on the dynamic behaviour of a large arch dam

The need for full‐scale dynamic tests, which are recognized as the most reliable method to evaluate a structure's vibration properties, is increasing as new analysis techniques are developed that take into account the complex interaction phenomenons that occur in dam–reservoir–foundation systems. They are extremely useful to obtain reliable data for the calibration of newly developed numerical methods. The Earthquake Engineering and Structural Dynamics Research Center (CRGP) at the University of Sherbrooke has been developing and applying dynamic testing methods for large structures in the past 10 years. This paper presents the experimental evaluation of the effects of the varying water level on the dynamic response of the 180 m Emosson arch dam in Switzerland. Repeated forced‐vibration tests were carried out on the dam during four different periods of the reservoir's filling cycle during a one‐year span. Acceleration and hydrodynamic pressure frequency responses were obtained at several locations while the dam was subjected to horizontal harmonic loading. The variation of the resonant frequencies as a function of the reservoir level is investigated. A summary of the ongoing numerical correlation phase with a three‐dimensional finite element model for the dam–reservoir–foundation system is also presented. Copyright © 2001 John Wiley & Sons, Ltd.     

考虑流固耦合效应的辽宁葠窝水库溢流坝段抗震性能分析

针对辽宁葠窝水库混凝土重力坝抗震问题,采用耦合的拉格朗日-欧拉有限元分析技术,建立了可考虑库水-坝体-基岩动力耦合效应的典型溢流坝段抗震分析数值模型。模型中,采用等效一致粘弹性边界模拟基岩的人工截断边界;采用混凝土弥散裂缝本构模型模拟混凝土的动力特性。根据烈度与地震动之间的关系,确定了水库坝体抗震设计的输入加速度峰值。据此,分析了在不同季节水位变化条件下坝体地震反应的基本特性。研究表明：完好的辽宁葠窝水库混凝土重力坝溢流坝段能满足8度的抗震设防烈度要求。地震下溢流坝段峰值位移出现在胖坝和瘦坝的坝顶迎水面位置处,胖坝的动位移较瘦坝动位移大。胖坝在闸墩与溢流堰交接处出现了拉应力最大值。有库水条件下,瘦坝峰值拉应力出现在坝趾处,无库水条件下,瘦坝最大拉应力出现在溢流堰与闸墩交接处。     

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.     

Influence of time-domain dam–reservoir interaction on cracking of concrete gravity DAMS

Based on a non-linear dam-reservoir interaction model, a study investigating the earthquake response of concrete gravity dams is presented. For the propagation of cracks in unreinforced mass concrete, a discrete crack approach formulation based on the finite element method is applied. A special crack element is used to follow a fictitious crack in order to account for a zone of microcracks developing at the crack tip. The reservoir is modelled using the boundary element method. At a fictitious boundary dividing the irregular finite part of the reservoir from the regular infinite part, the loss of energy due to pressure waves moving away towards infinity is taken into account rigorously. Analyses are performed on the tallest non-overflow monolith of the Pine Flat Dam located in Kern County, California. The interaction of a dam, which may exhibit cracks in mass concrete, with a reservoir domain of arbitrary geometry extending to infinity is studied. Some main parameters are investigated. The importance of tools capable of handling the non-linear dam-reservoir interaction is emphasized.     

Overturning of top profile of the Koyna Dam during severe ground motion

The Koyna Dam in India was subjected to a severe earthquake on 11 December 1967 with its epicentre very close to the dam site. During this earthquake, higher non-overflow monoliths of the dam suffered significant damage. In the highest non-overflow monolith, a horizontal crack occurred at the level where there was an abrupt change in the downstream slope. The dynamic behaviour of the top profile of this monolith of the dam above the crack has been investigated treating it as a rigid body. The study shows that the overturning of the cracked portion of the dam will not occur due to the severest anticipated ground motion at the site. However, to prevent the seepage of water and as a permanent remedial measure, strengthening of the dam is necessary but no emergency measures need be taken.     

Application of perfectly matched layers in the transient analysis of dam–reservoir systems

The transient analysis of dam–reservoir systems by employing perfectly matched layers has been investigated. In previous studies, boundary conditions of the PML region in the reservoir have been neglected. In this paper, they are incorporated completely in the formulation. Moreover, a technique is introduced to involve the effect of incident waves caused by vertical ground motions at the reservoir bottom in the analysis. Performing several numerical experiments indicates that applying boundary conditions of the PML domain and utilizing the proposed method for vertical excitation cases reduce the computational cost significantly and make the PML method a very efficient approach for the transient analysis of dam–reservoir systems.     

Coupled hydrodynamic response of concrete gravity dams using finite and infinite elements

This paper presents the application of the finite element method for analysing the two-dimensional response of reservoir-dam systems subjected to horizontal ground motion. The interaction between the dam and the reservoir as well as the compressibility of water has been taken into account. The complete system has been considered to be composed of two substructures, namely the reservoir and the dam. To take into account the large extent of the reservoir, it has been idealized using specially developed infinite elements coupled with standard finite elements while the dam is represented using finite elements alone. Structural damping of the dam and radiation damping in the fluid phase have been accounted for in the analysis. It is concluded that the effect of radiation damping is considerable at high frequencies of excitation. The coupled response of the system is significantly large at and near the fundamental natural frequency of the system in comparison to the uncoupled responses. The method is computationally quite economical, capable of taking into account the arbitrary geometry of the system and is recommended for practical application. Further applications and extensions of the approach to three dimensional analyses are possible.     

Seismic fracture analysis of concrete gravity dams

A numerical procedure for evaluation of the fracture process of gravity dams during strong earthquakes is presented. The BEM is used to discretize the dam reservoir system including the crack surfaces, and stress intensity factors at the crack tip are employed in a stage by stage procedure which simulates the crack extension. For each stage of constant crack length the mode superposition technique is applied; this is made possible by simulating the impact process of crack closing by a load pulse applied at the contact points which permits the structural stiffness to be assumed unchanged. To verify the proposed procedure, a cantilever beam model structure made of gypsum was tested on a shaking table. Good correlation with the numerical results was obtained, from which it is concluded that the procedure can be employed for evaluation of the crack propagation process in concrete structures subjected to dynamic loadings.