SEISMIC ANALYSIS OF A DAM RESERVOIR FOUNDATION 4 SYSTEM

Abstract

The safety and stability of concrete gravity dams under strong earthquake shaking has long been an issue of great practical importance, and has attracted and continues to attract considerable research interest. The evaluation of their response to earthquakes requires special attention due to their unique characteristics. The proposed scheme is illustrated with the Rihand Dam in India. In the present dam geometry the height of the vertical portion of the upstream face of the dam is more than one-half height of the dam and hence it is analyzed as vertical throughout for frequency extraction. The present study applies the recorded free-field earthquake acceleration directly at the foundation ground surface. Three different acceleration time histories have been adopted for seismic analysis. The fluid-structure interaction is modeled via added mass approach. Due to horizontal acceleration of ground motion at the base of the dam there is an instantaneous hydrodynamic pressure or suction exerted on the dam. The direction of hydrodynamic force is opposite to the direction of earthquake motion. Based on the assumption that the water is incompressible, the hydrodynamic pressure below the reservoir surface has been determined as per IS 1893:1984. The foundation material is considered to be of rock in nature. To simulate the stress vs. strain behavior of foundation a linear elastic constitutive model has been adopted. The dam-foundation interface is simulated by a contact surface with an elastic foundation interaction condition. Lysmer boundaries has been used to eliminate waves propagating outward from the structure by simply connecting dashpots to all degrees of freedom of the boundary nodes and fixing them on the other end. The computational evaluation is performed with the commercial finite element software package Abaqus. The dam and the foundation are modeled using a 4-node bilinear plane stress quadrilateral, structured, reduced integration, hourglass control finite elements (Element Type: CPS411; Abaqus).