Seismic analysis of liquid storage composite conical tanks

Abstract

Composite tanks with truncated cone vessels, consisting of an outer thin steel shell and an inner concrete wall, are becoming common. Such composite conical tanks benefit from the high buckling resistance to compressive meridional forces of the concrete walls and the efficiency of the steel shells in resisting tensile hoop stresses. Motivated by the lack of information in the literature and the codes of practice about the seismic behaviour and design of such structures, this paper represents the first comprehensive study focusing on the seismic analysis of composite conical tanks. The study is conducted numerically using an in-house developed model that accounts for the hydrodynamic pressure resulting from the vibration of the contained fluid. The model also accounts for the interaction between the fluid and the structure vibrations. In this model, both the steel and concrete walls are modelled separately using shell elements and a special interface element is included to account for the connecting shear studs. The model is capable of conducting both free vibration and seismic analyses for the composite tank-liquid system taking into account the sloshing effect. The model is used to assess the adequacy of using a simplified technique in the seismic analysis and design of such structures. In order to examine the seismic behaviour of those structures, a real composite conical tank is considered as a case study. Time histories and maximum values for stresses at the concrete and steel walls, forces at the base, and forces in the studs under different earthquake excitations are reported. Those values are compared to their counterparts resulting from the hydrostatic pressure to assess the importance of including the seismic loads in the analysis of such structures.