DYNAMIC BEHAVIOUR OF PILE- SUPPORTED ELEVATED TANKS DURING EARTHAQUAKES

Abstract

This thesis aimed to investigate the seismic behavior of elevated water tanks supported on piles taking into consideration the effect of the foundation system for different motion characteristics into consideration. Using previous earthquake records, the frequency contents of each record is classified to Low, Medium and High categories. It was assumed that the peak ground acceleration for all records is normalized to 0.15 of ground acceleration which was accepted by many researchers for average seismic activities in Egypt. Deep foundations, such as piles, are used to support heavily loaded structures. Dynamic behavior of elevated water tanks may be affected by its foundation stiffness. Static and dynamic structural analysis of pile• supported structures requires the stiffness and damping constants of piles. Dynamic stiffnesses (impedance functions) of a single pile driven In a layered soil have been presented. The approach makes the computation of pile's impedance functions possible using available structural analysis programs such as Sap2000. The mathematical model is based on soil reactions of individual layers calculated according to any assumption such as the plane strain one, or any soil reactions. The approach compares very well with the finite element approaches and experiments. The analytical model of the whole tank is based on the stiffness matrix method with lumped mass system. The water is simulated by two masses one is the Impulsive mass that is to be attached to the tanks walls, the second mass is the Convective mass that is to be connected to tanks walls by means of imaginary springs. A well designed elevated water tank is used to demonstrate the effects of the frequency content of the earthquake excitations, the foundation system , the height of tank and the height of water in the tank.