A critical review of comparative seismic behaviour of RC shaft supported elevated water tanks and chimney

Abstract

In event of severe earthquakes RC structures are subjected to lateral jolts. The behaviour of the structures towards seismic forces is dependent on the structural composition and lateral stiffness. Elevated water tanks supported on shafts are inverted pendulums with heavy mass suspended at the top. While chimneys are stack like structure whose structural composition is like a slender cantilever fixed at the base. In this paper an attempt shall be made to critically compare the lateral seismic behaviour of these two different structures using equivalent static and dynamic analysis procedure. The selection of the two classes of structures has been done from the logic that the RC shaft of an elevated water tank resembles a chimney of low height loaded with heavy load at the top. Whereas chimney being a more slender structure, both these structures falls in different natural period ranges of the design spectra and hence they attract different levels of seismic forces. The paper proposes to compare critically the variation in seismic behaviour of these two classes of structures, which is elevated water tank on shaft a relatively rigid period system and chimney a rather longer period system.