Evaluation of the seismic response of conical steel tanks using the equivalent model technique

Abstract eng:
A typical elevated tank consists of two main components, the containment vessel and the supporting shaft. Vessels are commonly constructed in a truncated conical-shape. This paper focuses on pedestal-type tanks where the steel conical vessels are supported by reinforced concrete shafts with hollow circular cross-sections. Current design standards do not provide direct procedure to estimate the forces acting on conical vessels when the tanks are subjected to earthquake excitation. Most of the codes of practice account for the seismic forces only in the design of the shaft assuming a full participation of the fluid mass which is not usually the case. The current study aims at assessing the effect of the above mentioned limitation on the seismic analysis and design of elevated conical tanks. A coupled finite-boundary element formulation is adopted to develop a simplified equivalent model for the evaluation of seismically-induced forces in liquidfilled conical vessels. The proposed model is utilized to assess seismic forces induced in the main structural components of several elevated conical tanks. Analyzed structures are assumed to be located at three different sites to account for different seismic activities in Canada. The dynamicbased stresses are evaluated for both the containment conical vessel and the supporting shaft. Seismically-induced stresses are then compared to the equivalent static stresses induced in the shaft showing a conservative design. Seismic stresses developed at the base of the conical vessel are found to significantly increase those stresses associated with the hydrostatic pressure of the contained fluid. In general, the study highlights the significance of considering the seismic forces for the analysis and design of liquid-filled conical steel tanks.

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