0022±460X/99/210141  15 $30.00/0 # 1999 Academic Press SEISMIC ANALYSIS OF A LIQUID STORAGE TANK WITH A BAFFLE A. GED _ IKL _ I AND M. E. ERGU È VEN Technical University of Istanbul, Civil Engineering Faculty, Maslak, Istanbul 80626, Turkey (Received 5 September 1998, and in ®nal form 4 January 1999) The eects of a rigid bae on the seismic response of liquid in a rigid cylindrical tank are presented. A bae is an additional structural element which supplies a kind of passive control on the eects of earthquake motion. Fluid motion is assumed to be irrotational, incompressible and inviscid. The method of superposition of modes has been implemented to compute the seismic response. The boundary element method is used to evaluate the natural modes of liquid in a cylindrical tank. Linearized free surface conditions have been taken into consideration. # 1999 Academic Press 1. INTRODUCTION In recent years, the civil engineering community has been concerned with the development and implementation of innovative design concepts for seismic protection of structures, particularly for the control of earthquake effects on buildings [1, 2]. Seismic response reduction systems need not be located only in the base of the structure. Control systems have mainly two categories called active and passive systems. The system is called an active control system if external forces are applied with the base isolation system to the structure to control the earthquake effects. In passive control systems external forces are not required [1]. Attempts have been made to install them in different parts of the structure, either in the form of additional response reduction masses, or dampers, friction devices, etc. One of the passive control systems is based on the known behavior of a braced steel frame when using friction effects of friction dampers. During an earthquake the friction damper mechanism develops additional energy- dissipating sources which can protect the main members from structural damage. In liquid containers, breaking of surface waves, while highly dependent on vibration amplitude, is the main mechanism of energy dissipation. Liquid dampers have been in use in space satellites and marine vessels. The value of additional damping can increase with low viscosity of the liquid, with a smooth bottom of the container, and with an adequate gap between the liquid and the roof of the container. Another approach to the response reduction systems is the Journal of Sound and Vibration (1999) 223(1), 141±155 Article No. jsvi.1999.2091, available online at http://www.idealibrary.com on