STRENGTH AND DUCTILITY EVALUATION OF ELEVATED WATER STORAGE TANK

Abstract

Large capacity elevated intze tanks are used to store a variety of liquids, e.g. water for drinking and fire fighting, petroleum, chemicals, and liquefied natural gas. The liquid storage tanks are particularly subjected to the risk of damage due to earthquake-induced vibrations. A large number of overhead water tanks damaged during past earthquake. Majority of them were shaft staging while a few were on frame staging. Recently the Muzaffarabad earthquake 2005 and Bhuj earthquake 2001 also represented similar damage. Most of the damage was caused because of the tanks were either designed without considering the earthquake forces or inadequate seismic design considerations. To cope with this need the seismic design codes for over head water tanks have been revised and upgraded. The objective of this dissertation is to shed light on the difference in the design parameters of (a) over head water tanks without having earthquake forces, (b) over head water tanks constructed with a consideration of earthquake forces following two approaches; firstly based on Indian standard code 1893, (1984) i.e. adopting single mass method and second is based on draft code 1893-Part 2, (2005) considering two mass modal i.e. convective and impulsive mode method. Two types of elevated water tanks namely Intze tank supported by frame staging and shaft staging have been considered in this study. These elevated water tanks are first conventionally designed and then seismic analyzed and again redesigned considering earthquake forces. Their strength and ductility have also been evaluated and compared. It has been observed that time period in frame staging is higher then the shaft staging since the lateral stiffness of shaft staging is much larger. The tank supported on shaft staging has higher strength as compare to tank supported on frame staging but the ductility is low that may be the return of frequent failure of elevated water tank supported on shaft staging. iii