The 14 th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China SEISMIC VULNERABILITY OF ELEVATED WATER TANKS USING PERFORMANCE BASED-DESIGN F. Omidinasab 1 and H. Shakib 2 1 Structures Engineering Ph.D. Candidate, Dept. of Civil Engineering , Tarbiat Modarres Uni.,Tehran, Iran 2 Structure and Earthquake Faculty Professor, Dept. of Civil Engineering , Tarbiat Modarres Uni.,Tehran, Iran Email: omidi@modares.ac.ir, shakib@modares.ac.ir ABSTRACT : Liquid tanks and especially the elevated tanks are structures of high importance which are considered as the main lifeline elements that should be capable of keeping the expected performance. i.e. operation during and after earthquakes. Thus, researchers, in recent years, have focused on studying the seismic behavior of these tanks. Many researches have been done on the behavior, analysis, and design of seismic tanks, particularly ground tanks, while only a few of these researches have concerned with the elevated tanks and even less with the reinforced concrete elevated tanks. In this research, a sample of a reinforced concrete elevated water tank, with 900 cube meters under seven earthquake records have been studied and analyzed in dynamic time history and the tank’s responses including base shear, overturning moment, tank displacement, and sloshing displacement under these seven record have been calculated, and then the results have been compared and contrasted. KEYWORDS: Elevated water tank, Vulnerability, Performance-based design 1. INTRODUCTION Elevated liquid tanks and especially the elevated water tanks are considered as important city services in many cities. Their safety performance during strong earthquakes is of critical concern. They should not fail after earthquake, so that they can be used in meeting essential needs like preparing drinking water and putting out fires. The failure of these structures and the subsiding of water may cause some hazards for the health of city due to the shortage of water or difficulty in putting out fire during critical conditions. Many studies concentrated on the seismic behavior, analysis, and design of tanks, particularly ground tanks. In the past decade most of these studies have focused on the elevated tanks. In the past earthquakes elevated tanks have been of the vulnerable structures and their seismic behavior has not been convenient being damaged. Thus, past earthquakes have shown that due to failure of lifeline structures, such as elevated tanks with insufficient seismic resistance, fire fighting and other emergency response efforts can be hindered (e.g., experiences from Chile 1960, 1978 Izu-Oshima and Miyagi, 1971 San Fernando, and 1987 Whittier earthquakes). There have been numerous studies analyzing and investigating the dynamic behavior of fluid storage tanks, however, most of these studies have focused on the ground level cylindrical tanks. Very few studies have concentrated on the behavior of elevated tanks. Therefore, the attention is generally focused on the dynamic behavior of the fluid and/or the support structure. Most studies investigating the behavior of elevated tanks are summarized below. Haroun and Ellaithy developed a model including an analysis of a variety of elevated rigid tanks undergoing translation and rotation. The model considers fluid sloshing modes and it assesses the effect of tank wall flexibility on the earthquake response of the elevated tanks [1]. Resheidat and Sunna investigated the behavior of a rectangular elevated tank considering the soil-foundation structure interaction during earthquakes. They neglected the sloshing effects on the seismic behavior of the elevated tanks and the radiation damping effect of soil. Haroun and Temraz analyzed models of two-dimensional X-braced elevated tanks supported on the isolated footings to investigate the effects of dynamic interaction between the tower and the supporting soil-foundation system but they also neglected the sloshing effects [2]. Marashi and Shakib carried out an ambient vibration test for the evaluation of the dynamic characteristics of elevated tanks [3]. Dutta et al. studied the supporting system of elevated tanks with reduced torsional vulnerability and they suggested approximate empirical equations for the lateral, horizontal and torsional