Fluid-Structure-Soil Interaction Effects on Seismic Behaviour of Elevated Water Tanks

Abstract

Abstract The multiple base motion effect on hydrodynamic pressure, acceleration of tank and fluid surface elevation problem in Elevated water tank is understood as a Fluid-Structure-Soil Interaction problem. Where, Soil-Structure interaction causes rocking motion and Fluid Structure interaction causes the hydrodynamic behaviour of water tank. According to the available literature, substantial amount of study has been done on behaviour of elevated steel water tank under pure rocking, but no study is done on water tanks with horizontal and vertical earthquake excitation, along with rocking motion. An experimental investigation for a 1:4 scale model of cylindrical steel elevated water tank has been carried out on shake table facility at CSIR-SERC, Chennai. Test program on elevated steel water tank consisted of combined horizontal, vertical and rocking motions, for a synthetic earthquake excitation for 0.1 g and 0.2 g accelerations, with increasing angle of rocking motion. The impulsive base shear and impulsive base moment values increase with increase in earthquake acceleration. Whereas, the convective base shear and base moment values increase for increase in earthquake acceleration, but decrease with increasing angular motion. Hence, there is no considerable effect of rocking motion on sloshing of water. The non-linearity in structure is observed, when the impulsive pressure of tank decreases with increase in tank acceleration. The pressure variation along tank height due to vertical excitation increased with increasing acceleration, and increased furthermore with added rocking. Using various codes available on water tanks, the recorded experimental results were used to calculate and compare the base shear, base moment, pressure variation in the tank.