Analytical and numerical analysis of anchored flexible steel liquid storage tanks subjected to seismic loads considering soil structure interaction

Abstract

The impact of climate change on the natural and built environment is posing a significant threat to potable water supply infrastructure systems. This can result in an increase in the demand for sustainable water storage solutions to avoid service interruption to industries and municipal utilities dependent on water supply. One solution to mitigate the water supply and storage risk is to utilize modular steel water storage tanks designed and manufactured with Zincalume© steel panels. These tanks have a novel design and do not have bottom plates. They are fitted with a synthetic liner, are stiffened with vertical wind girts and are anchored to a concrete ring beam at the bottom of each wind girt using holding down bolts. Due to the high radius to wall thickness ratio (R/t) of these tanks, the structural performance, interaction with the stored fluid and the foundation soil under dynamic loads, have not been well understood. In this research, the effect of seismic loads on the global structural behavior of these tanks such as base shear, overturning moment, circumferential stress as well as the buckling behavior of the thin metal panels was studied using both analytical techniques and numerical Finite Element Method (FEM) analyses. Parametric studies using spring-mounted mass analogy techniques specified by the American Petroleum Institute code (API650) and the New Zealand Society for Earthquake Engineering recommendation (NZSEE) are conducted for three tanks with different fluid height to tank radius ratios (Hw/R). The results are compared with nonlinear time history dynamic analyses performed using the Abaqus 3D finite element software. The results indicate that, due to the flexible nature of the tanks, the method specified by API650, which does not take the flexibility of the tank and soil structure interaction into account, underestimates the global design indicators such as base shear, overturning moment and hoop stress for tanks with higher Hw/R ratios. The method specified in the NZSEE recommendation predicted the global design indicators as well as local buckling phenomena in the panels in good agreement with the FEM results.