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

魁北克的混凝土大坝平均已有70年的历史。这些大坝的初始设计可能无法满足现代地震安全标准。自2002年4月以来，《大坝安全法》及其相关法规（于2002年4月11日生效）要求大容量水坝的所有者定期评估和监测其结构在各种荷载（包括可能遭受的地震）影响下的行为。评估混凝土坝的地震反应有不同的方法。它们各不相同：(i)考虑各种参数的复杂数值方法，如大坝可变形性、水压缩性、水库底部的波吸收或大坝-岩石和混凝土接缝非线性；（ii）简化技术，其中引入简化假设以促进这些方法在日常工程实践中的应用。世界范围内的经验表明，混凝土坝在地震荷载作用下的破坏是相当罕见的，但已经观察到或多或少广泛的裂缝。这种裂缝可能会改变混凝土坝在震动过程中的动力特性，同时表明其耗散更多地震能量并相应地重新分配地震力的能力。有限的裂缝可以有利于混凝土坝的地震稳定性，因此可以避免不必要的修复干预。然而，基于重力方法的传统裂缝分析无法解释这种潜在的有益行为，而由于建模方法的复杂性，在日常工程实践中很少进行更充分的裂缝数值模拟。在这种情况下，本CRD项目的主要目标是：(i)开发可靠的简化方法，以有效和严格地评估混凝土大坝的地震反应，包括非线性效应；（ii）使用已开发的简化方法评估线性和非线性地震需求及其对水坝附属结构和设备的影响，以及（iii）对选定的混凝土水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.