Читать книгу Earthquake Engineering for Concrete Dams - Anil K. Chopra - Страница 26

The motions of a dam during an earthquake cause dynamic pressures in the impounded water that act on the upstream face of the dam to modify the dam motions, which in turn influence the hydrodynamic pressures. It is this interaction between the dam and water that is the subject of this chapter. Considering only the fundamental mode of vibration of the dam, we first develop a procedure for analysis of dam response including dam–water interaction. Thereafter, results for dam response are presented for a wide range of parameters that characterize the dam–water system. These results provide a basis to identify the effects of dam–water interaction and their influence on the vibration properties – natural vibration period and damping ratio – and on the response of concrete gravity dams to earthquake ground motion. Also investigated are the implications of neglecting compressibility of water, an approximation that enables representation of hydrodynamic effects by inertia forces associated with an added mass of water moving with the dam. Finally, we develop an equivalent single‐degree‐of‐freedom (SDF) system to model the response of dams including dam–water interaction that enables estimation of peak response directly from the earthquake response (or design) spectrum. Such an analysis is intended for preliminary design and safety evaluation of dams.