DYNAMIC ANALYSIS OF GRAVITY DAMS BY BEAM MODELS

Abstract

Aseismic design of dams based on detailed finite element dynamic analysis is a time consuming and expensive procedure. At the preliminary design stage it is often considered sufficient to use beam models for dynamic analysis or employ a simplified method. Several simplified procedures are available for dynamic analysis of dams such as the method in IS o 1893 1975, simpli-fied procedures by Saini and Vishwanath and Chopra. Bending-shear analysis using beam model is another procedure for dynamic analysis which can be employed at the preliminary design stage. In this thesis, each procedure adopted for dynamic analysis is compared with the response obtained from bending-shear analysis taking it as the procedure of dynamic analysis for comparison. Each of these methods are based on certain assumptions and have some limitations. The purpose of this thesis is to make a critical study of these methods. Using these different simpli-f led methods, the dynamic analysis of seven gravity dams ranging from low height dams (6o m) to tall height dams (225 m) are analysed.. The comparison of force distributions obtained by the simplified methods and bending-shear analysis has been made. IS e Code method has been found to underestimate the time period and forces for reservoir empty conditions for most dams as compared to bending-shear analysis. a study has also been made to generate design curves similar to those given in IS o 1893-1975 considering hydro dynamic pressure effect as added mass of water. The modification in time period formulae in the code because of added mass of water is also presented.