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Seismic safety assessment of gravity dams has become a major concern in many regions of the world while the effects of vertical seismic accelerations on the response of structures remain poorly understood. This paper first investigates the effect of including vertical accelerations in the sliding response analysis of gravity dams subjected to a range of historical ground motion records separated in two groups according to their source-to-site distance. Analyses showed that the incidence of vertical accelerations on the sliding response of gravity dams is significantly higher for near-source records than for farsource records. The pseudo-static 30% load combination rule, commonly used in practice to account for the non-simultaneous occurrence of the peak horizontal and vertical accelerations, yielded good approximations of the minimum safety factors against sliding computed from time-history analyses. A method for empirically estimating the vertical response spectra based on horizontal spectra, accounting for the difference in frequency content and amplitudes between the two components is investigated. Results from analyses using spectrum compatible horizontal and vertical synthetic records also approximated well the sliding response of a gravity dam subjected to series of simultaneous horizontal and vertical historical earthquake records. 相似文献
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An experimental study of a seismically isolated and a comparable non-isolated bridge is presented. The bridge model featured flexible piers, weighed 158kN and was tested on a shake table with an array of real and simulated seismic motions with peak acceleration in the range 0⋅1–1⋅1g. When isolated, the bridge deck was supported by four spherically shaped sliding bearings (known as Friction Pendulum System or FPS bearings) with friction coefficient under dynamic conditions in the range 0⋅07–0⋅12. The experimental results demonstrated a substantial improvement in the ability of the isolated bridge to sustain all levels of seismic excitation under elastic conditions. 相似文献
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A series of full‐scale shaking table tests were conducted at E‐Defense for a four‐story base‐isolated hospital. The operation room in the specimen was chosen for detailed examination of its disorder and damage during large ground motions. It was arranged with various medical appliances in as a realistic manner as possible, and the appliances were characterized by casters installed at the bottom to ensure mobility. Two types of ground motion, the near‐fault ground motion and long‐period ground motion, were adopted, and the responses of the appliances were recorded using the motion capture technique. Thanks to the base isolation, the floor response was greatly reduced, and no disorder or damage was observed in the operation room except for the case when subjected to a long‐period ground motion. In this case, the unlocked appliances moved seriously (by more than 3 m), and collisions occurred between the appliances and between appliances and the surrounding wall. The force of collision reached 36 kN, which is sufficient to injure a person. The acceleration due to collision was as high as 10 g, which is far beyond what can be tolerated by acceleration‐sensitive appliances. It is notable that such large motion was not observed once the appliances were locked. The test was also carried out for the corresponding fixed‐base structure. Among all cases in the experiment, by far the most serious damage occurred in the fixed‐base structure when subjected to the near‐fault ground motion, clearly because the floor response was significantly amplified from the ground motion. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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After the occurrence of various destructive earthquakes in Japan, extensive efforts have been made to improve the seismic performance of bridges. Although improvements to the ductile capacities of reinforced concrete (RC) bridge piers have been developed over the past few decades, seismic resilience has not been adequately ensured. Simple ductile structures are not robust and exhibit a certain level of damage under extremely strong earthquakes, leading to large residual displacements and higher repair costs, which incur in societies with less-effective disaster response and recovery measures. To ensure the seismic resilience of bridges, it is necessary to continue developing the seismic design methodology of RC bridges by exploring new concepts while avoiding the use of expensive materials. Therefore, to maximize the postevent operability, a novel RC bridge pier with a low-cost sliding pendulum system is proposed. The seismic force is reduced as the upper component moves along a concave sliding surface atop the lower component of the RC bridge pier. No replaceable seismic devices are included to lengthen the natural period; only conventional concrete and steel are used to achieve low-cost design solutions. The seismic performance was evaluated through unidirectional shaking table tests. The experimental results demonstrated a reduction in the shear force transmitted to the substructure, and the residual displacement decreased by establishing an adequate radius of the sliding surface. Finally, a nonlinear dynamic analysis was performed to estimate the seismic response of the proposed RC bridge pier. 相似文献
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本文对一基础隔震模型进行了软着陆保护振动台模拟地震动试验,展示了该隔震体系在发生水平向大变形条件下,在不同后备支座以及滑移面摩擦系数不同情况下,轴压力从承载支座向后备支座转移的情况。结果表明:软着陆隔震保护体系不仅保护了承载支座免遭大变形失稳破坏,同时还能提供摩擦阻尼,将隔震层位移和上部结构层间位移控制在允许范围内。文中对隔震层位移、上部结构最大层间位移及绝对加速度等进行了分析,所得理论曲线与试验拟合曲线吻合较好。具有很大的应用前景。 相似文献
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Shaking tables are suitable facilities to assess and validate the behavior of structures and nonstructural components under actual seismic actions. Because of the size and weight limitations of the tables, some approaches, like testing reduced‐scale models or testing only the main structural components, are deemed necessary. In these cases, to comply with modeling requirements, large amount of extra‐mass should be added to the specimen. Therefore, to avoid the risk of lateral instability of models, to maintain the weight of test specimens within table payload, while maintaining the amount of mass needed, an external device for transmitting the inertia forces to the models using an improved sliding system is proposed. Although friction devices for similar purposes have been developed using sliding bearings (Teflon pads or rollers), the measured coefficient of dynamic friction and the energy dissipated by friction have been very high. In order to drastically diminish the damping added to the specimen response when a friction device is used, the improved device employs a linear motion guide system (LMGS) with very low friction. Shaking table tests to collapse of reinforced concrete walls were used to evaluate the effectiveness of the proposed device. Measured dynamic friction coefficients, spectral accelerations and hysteresis loops show that friction developed in the LMGS did not add any significant amount of damping into the specimen response. Thus, the proposed device is a reliable and suitable mass‐carrying sliding system (MCSS) for dynamic testing using medium‐size shaking tables. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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近年来我国振动台设备发展迅猛,相关试验技术也随之提升,渐成研究热点,然而目前对利用振动台设备开展结构抗震试验的精度如何仍关注较少.本文结合中南大学所建设的振动台台阵试验系统,介绍台阵的具体组成和技术,并综合已开展试验工作,探讨振动台模型试验的精度,明确了重力失真效应、模型材料和制作水平、强地震复现等重要误差因素,并给出了现有实验室技术水平下的误差范围,表明需减小不必要误差以提升试验精度,避免错误试验结论. 相似文献
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本文归纳了桥梁结构采用隔震技术时存在的主要问题，指出了模型桥梁进行模拟地震振动台试验研究的意义，简要介绍了模型试验设计情况及三种隔震体系模型桥梁动力特性测试结果。 相似文献
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滑动摩擦隔震支座具有良好的耗能能力、较大水平位移能力和较好的耐久性能,为桥梁减隔震设计提供了一种新方法.本文针对分别安装有单球面摩擦摆支座、双凹面摩擦摆支座、多球面滑动摩擦支座的3种隔震桥梁模型开展了振动台试验研究.通过观察和量测模型桥梁位移、加速度等反应,得出采用3种滑动摩擦支座的隔震桥梁反应特性和隔震效果.由此可知,滑动摩擦隔震支座能有效减小地震对桥梁上部结构的影响,滑动摩擦隔震支座的自振周期与桥梁上部结构无关,只与支座摩擦系数和等效曲率半径相关. 相似文献
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研究速度脉冲地震和结构质量偏心综合不利条件下新型重力柱-核心筒结构体系的弹塑性反应规律。选取速度脉冲和非速度脉冲地震加速度记录各10条,进行地震动双向输入,采用结构非线性分析软件CANNY进行有限元数值分析,研究脉冲型地震和结构质量偏心对新型体系弹塑性地震反应的影响。分析结果表明,速度脉冲型地震作用下各结构的层间位移角、层间剪力和层间扭转角显著高于非速度脉冲地震下的相应值。质量偏心对结构弹塑性抗震需求影响显著,层间位移角和层间扭转角都随着偏心率的增大而增大,而层间剪力则随偏心率的增大呈减小趋势。建议在重力柱-核心筒结构设计中应重视速度脉冲地震和结构偏心的耦合不利影响。 相似文献
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均匀土-桩基-结构相互作用体系的计算分析 总被引：18，自引：4，他引：14
本文以结构-地基动力相互作用振动台模型试验为基础,结合通用有限元软件ANSYS,对均匀土-桩基-结构动力相互作用体系进行了三维有限元分析.计算中土体采用等效线性模型,利用面-面接触单元考虑土体与结构交界面的状态非线性,计算与试验得出的规律基本一致.桩基与土体间发生了脱开再闭合和滑移现象.桩身应变幅值分布呈桩顶大、桩尖小的倒三角分布,角桩的应变幅值较大,边排中桩和中桩的应变幅值较小.桩土接触压力幅值呈桩顶小、桩尖大的三角形分布.在沿振动方向的三排桩中,边排桩的滑移比中排桩的滑移量大.通过计算分析与试验的对照研究,验证了采用的计算模型与分析方法的合理性,为结构-地基相互作用的进一步研究奠定了基础. 相似文献
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大型模拟地震振动台的特殊控制 总被引：4，自引：0，他引：4
阐述了多自由度大型地震模拟振动台由于试件重心高,偏心以及几何等原因在一个轴线方向上振动时,造成对其他轴线方向运动的干扰,同时介绍了克服这些干扰的控制原理. 相似文献
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岩石场地重力式挡土墙地震土压力振动台实验研究 总被引：5，自引：0，他引：5
结合汶川震区调查资料,利用大型振动台模型试验,分析了碎石土填料的岩石场地重力式挡土墙的地震土压力及其分布规律,并以此对我国现行铁路、公路抗震规范做合理性讨论和细化。研究发现,地震作用下,挡土墙的动土压力沿墙高呈单峰曲线状分布,且60%～80%集中作用于挡墙中部;随着地震峰值加速度的增加,地震土压力分布逐渐偏离现行振震设计规范所认为的三角形线性状,而呈现非线性状;合力作用点高于1/3墙高,0.4g地震加速度作用下,接近0.4倍墙高,对岩石场地下粗粒径墙背填料的地震土压力作用点高度,建议取0.35倍墙高。对比计算表明,现行规范能基本满足工程抗震设计需要,但建议对柔性挡土墙的抗震设计作出必要规定。 相似文献
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人工质量在砖混结构振动台试验中的作用 总被引：5，自引：0，他引：5
通过组合墙片的拟静力试验和模型房屋的振动台试验,分析研究了人工质量模拟对砖混结构振动台试验的作用和影响.研究表明,重力对结构的弯曲刚度有较大影响,但不影响结构的剪切刚度.在主拉应力破坏的条件下,结构的破坏荷载随重力的增加而增大.提出了不完全模拟的人工质量模型应满足的相似条件及如何根据模型试验结果估计原型结构的抗震能力. 相似文献
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饱和粉土液化特性的大型振动台模型试验研究 总被引：3，自引：0，他引：3
京沪高速铁路徐沪段路基的粉土粘粒含量少于1.5%、粉粒含量约为80%,在强烈地震作用下存在着液化可能性.为充分研究这一饱和粉土地层的液化特性,本文作者利用大型地震模拟振动台,进行了模拟自由场地饱和粉土的地震液化模型试验,试验结果再现了自然地震触发的粉土液化的各种宏观震害现象,揭示了饱和粉土的地震液化规律和特征.试验结果为京沪高速铁路徐沪段路基的抗震设计提供了参考依据. 相似文献
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Rockfill buttressing resting on the downstream face of masonry or concrete gravity dam is often considered as a strengthening method to improve the stability of existing dam for hydrostatic and seismic loads. Simplified methods for seismic stability analysis of composite concrete-rockfill dams are discussed. Numerical analyses are performed using a nonlinear rockfill model and nonlinear dam-rockfill interface behavior to investigate the effects of backfill on dynamic response of composite dams. A typical 35 m concrete gravity dam, strengthened by rockfill buttressing is considered. The results of analyses confirm that backfill can improve the seismic stability of gravity dams by exerting pressure on the dam in opposition to hydrostatic loads. According to numerical analyses results, the backfill pressures vary during earthquake base excitations and the inertia forces of the backfill are the main source for those variations. It is also shown that significant passive (or active) pressure cannot develop in composite dams with a finite backfill width. A simplified model is also proposed for dynamic analysis of composite dam by replacing the backfill with by a series of vertical cantilever shear beams connected to each other and to the dam by flexible links. 相似文献
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The paper presents the results of a large experimental programme carried out on models, scaled 1:2, of two-storey masonry buildings. After suffering damage, the models were repaired and strengthened and tested again. A total of 24 buildings were subjected to 119 shaking-table tests, by ISMES (Italy) and LEE (Greece) facilities. The results allow to assess the efficiency of the various strengthening techniques employed and to describe the change of dynamic properties of the systems at the increase of damage. © 1998 John Wiley & Sons, Ltd. 相似文献