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

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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.