Earthquake Behavior of Reservoir-Dam Systems

Most work, to date, on analysis of earthquake effects on dams treats a dam and a reservoir as two uncoupled systems. The importance of interaction between the two systems is investigated. The analysis is restricted to dams with a vertical upstream face. This idealization is considered to be appropriate for concrete gravity dams. It is assumed that the response of the dam can be satisfactorily represented by the fundamental mode effects. Expressions are derived for the complex frequency responses of the coupled system. For the coupled system, the complex frequency responses, the fundamental period of vibration, and responses to stationary white noise excitation are numerically evaluated for a wide range of the basic parameters: (1) normalized excitation frequency; and (2) the ratio of the fundamental natural frequencies of reservoir and dam separately. The results demonstrate that the interaction effects have considerable influence on the behavior of the system. The analysis of the coupled system is greatly simplified if compressibility of water is neglected. The earthquake response can then be determined as the response of a modified one-degree of freedom system. It is demonstrated that the compressibility of water can be ignored if the dam is flexible enough compared to the reservoir.