A Stochastic Approach for Assessing Imperfection Sensitivity of Liquid Storage Tanks

Abstract eng:
The research described in the present paper is part of a large research effort, aimed at developing rigorous tools for the analysis of liquid storage tanks, towards determining their capacity under strong seismic loading and safeguarding their structural integrity. The present work focuses on the effect of random geometric imperfections in the response of cylindrical shells subjected to meridional compression under hoop tension. This condition simulates the formation of elephant’s foot buckling at the base of liquid storage tanks, a common mode of failure subjected to strong lateral loading due to earthquake excitation. Geometric imperfections, in the form of tank wall wrinkles, are assumed to be nonhomogeneous Gaussian random fields. Samples of these fields, that represent possible initial imperfect geometries, are generated using the spectral representation method with evolutionary power spectra derived from real measurements using the method of separation. The measurements have been obtained from scanning of the tank shell surface, using highperformance digital laser-scanning equipment. A number of samples of these random imperfect geometries are generated and discretized with shell finite elements. The structural response variability is determined using a brute force Monte Carlo simulation in which repeated material and geometrically nonlinear finite element analyses are preformed and the corresponding histograms of bucking loads are derived. Based on the results of the aforementioned stochastic analysis, useful conclusions are obtained regarding imperfection-triggered buckling response and buckling load variability in liquid storage tanks subjected to meridional compression under internal pressure.

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