Practical methods for the seismic analysis of concrete dams and their appurtenant structures

魁北克的混凝土大坝平均有70年的历史。这些大坝的初始设计可能无法满足现代的地震安全标准。自2002年4月起，《大坝安全法》及其附属法规于2002年4月11日生效，要求大容量大坝的所有者定期评估和监测其在各种荷载作用下的结构行为，包括可能遭受的地震。混凝土坝的地震反应有不同的评估方法。它们从(I)考虑各种参数的复杂的数值方法，如大坝的变形性、水的可压缩性、水库底部的波浪吸收，或大坝-岩石和混凝土接缝的非线性，到(Ii)简化的技术，其中引入了简化的假设，以便于在日常工程实践中应用这些方法。世界各地的经验表明，混凝土坝在地震荷载作用下的破坏相当罕见，但或多或少都观察到了广泛的裂缝。这种裂缝可能会改变混凝土坝在震动过程中的动力特性，同时表明它有能力耗散更多的地震能量，并相应地重新分配地震力。因此，有限的裂缝可以有利于混凝土大坝的地震稳定性，因此可以避免不必要的修复干预。然而，基于重力法的常规开裂分析无法解释这种潜在的有益行为，而在日常工程实践中，由于所涉及的建模方法的复杂性，很少对开裂进行更充分的数值模拟。在这种背景下，CRD项目的主要目标是：(I)开发可靠的简化方法来有效和严格地评估考虑非线性效应的混凝土坝的地震反应；(Ii)使用所开发的简化方法来评估线性和非线性地震需求及其对大坝附属结构和设备的影响；以及(Iii)对选定的混凝土大坝进行概率风险评估和使用简化模型进行地震易损性分析。

Concrete dams in Quebec are 70 years old on average. The initial design of these dams may fail to meet modern seismic safety criteria. Since April 2002, the Dam Safety Act and its attendant regulation, which came into effect on April 11, 2002, requires owners of high-capacity dams to regularly assess and monitor their structural behaviour under the effect of various loads including earthquakes to which they may be subjected. Different approaches are available to assess the seismic response of concrete dams. They vary from: (i) sophisticated numerical methods accounting for various parameters such as dam deformability, water compressibility, wave absorption at reservoir bottom, or dam-rock and concrete joints nonlinearities, to (ii) simplified techniques where simplifying assumptions are introduced to facilitate the application of these methods in day-to-day engineering practice. World-wide experience shows that concrete dam failures under seismic loads are rather rare, but more or less extensive cracking has been observed. Such cracking might modify the dynamic properties of a concrete dam during the shaking, while indicating its capacity to dissipate more seismic energy and to redistribute seismic forces ccordingly. Limited cracking can then be beneficial to the seismic stability of concrete dams and might therefore avoid unnecessary rehabilitation interventions. However, conventional cracking analyses based on the gravity method are unable to account for this potentially beneficial behaviour while more adequate numerical simulation of cracking is rarely conducted in day-to-day engineering practice due to the complexity of the modeling approaches involved. In this context, the main objectives of this CRD project are: (i) to develop reliable simplified methods to effectively and rigorously assess the seismic response of concrete dams including nonlinear effects; (ii) to use the developed simplified methods to assess the linear and nonlinear seismic demands and their effects on dam-appurtenant structures and equipments, and (iii) to carry-out probabilistic risk assessment of selected concrete dams and seismic fragility analyses using simplified models.