DYNAMIC RESPONSE OF A CONCRETE GRAVITY DAM

Abstract

Concrete gravity dams are generally constructed for multipurpose projects like irrigation, water-supply, flood control and hydro-electric Many such river valley projects are located in seismically active zones and dams located in these regions will be subjected to dynamic forces caused by earthquakes. Several dams are being built in highly seismic regions and others may be planned for future. It is, therefore, necessary that these dams should be designed taking into account anticipated earthquake forces so that they can safely withstand future shocks without serious damage, since the failure of a dam is more disastrous to a community than that of other structures. For the earthquake resistant design of a dam, a designer is interested in knowing the forces exerted on the dam due to the probable ground motion expected at the site so that the stresses and the deformations induced in the dam can be estimated. The dynamic response of an actual concrete gravity dam has been analysed due to expected earthquake using mode-superposition method. The effect of reservoir water has been considered as virtual mass. The contribution of first three modes of vibration has been considered. Total stresses have been obtained by combining the dynamic stresses with the static stresses. It is concluded that the dam is unsafe for the earthquake expected at site and requires strengthening. The behaviour of the dam-reservoir system has also been studied using frequency-domain analysis. Responses of dam alone, reservoir alone and dam-reservoir system have been studied due to harmonic ground motion. Further responses due to earthquake excitation can be obtained using standard procedures