SEISMIC ANALYSIS OF ELEVATED COMPOSITE CONICAL TANKS

Abstract

Truncated Conical vessels are commonly used as liquid containers in elevated tanks. Despite the widespread of this type of structures worldwide, no direct code provisions are currently available covering their seismic analysis and design. During a seismic excita- tion, two components of hydrodynamic pressure develop inside a liquid-filled tank. Those are the impulsive component, which synchronizes with the vibration of the walls of the tank and the convective component associated with the free surface sloshing motion. The current study describes the seismic behaviour of an elevated conical tank having a composite steel/concrete construction. The study is conducted numerically using a coupled finite/boundary element model developed in-house. The walls of the tank are modeled using a degenerated consistent shell element. The impulsive component of the hydrodynamic pressure is formulated taking into account the fluid-structure interaction that occurs between the fluid pressure and the shell vibration. The numerical model also predicts the sloshing motion associated with a seismic excitation. Due to the inclination of the walls, the vertical component of seismic ground motion produces meridional axial stresses in a conical tank. As such, both the hori- zontal and vertical components of the seismic motion are considered in the study. Time histo- ry seismic analyses are conducted under a number of pre-recorded seismic excitations. The bending and membrane stresses obtained from the analyses are evaluated in various location of the structure and are compared to the values associated with hydrostatic pressure in order to assess the importance of seismic stresses in this type of structures. The maximum values for the free surface sloshing motion are also obtained from the seismic analyses. Finally, com- parisons are made between the seismic forces calculated using the equivalent cylinder ap- proach adopted in some of the design codes.