Seismic Fragility Analysis for Unanchored Steel Tanks Considering Shell Buckling


Abstract eng:
When unanchored steel liquid storage tanks are subjected to strong ground motions, the contained liquid impulses the tank shell causing uplift of the tank base. As the tank undergoes uplift, sections of the shell that remain in contact with the ground can experience large compressive forces often leading to buckling failure. This phenomenon has been documented in several reconnaissance reports following major earthquakes. In these reports, two types of shell buckling are commonly encountered: 1) elastic buckling (sometimes referred to as diamond bucking from the distinct diamond pattern that often emerges in the tank shell), and 2) plastic buckling (also called elephant foot buckling from the deformed tank shape which resembles an elephants foot bulging out at the bottom). This paper presents a method for determining the buckling vulnerability of unanchored steel tanks using simplified massspring models incorporated into the Open System for Earthquake Engineering Simulation (OpenSEES), and incremental dynamic analysis. The simplified mass-spring models simulate resistance to uplift, tank rocking, and provide an equilibrium-based approach to determining tank shell compressive forces resulting from dynamic earthquake loadings. Four existing tanks (considering both broad and slender geometries) are analyzed under 20 recorded ground motions, scaled at 30 different levels (from 0.05g to 1.5g) for a total of 2,400 dynamic analyses. Results from the incremental dynamic analyses are used to create fragility curves, wherein shell buckling probabilities are related to the level of seismic excitation. Results from the analyses on the four existing tank geometries highlight vulnerabilities for both broad and slender tank geometries under moderate seismic excitation.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 509.:
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