Seismic fragility analysis of liquid storage steel tanks considering shell buckling and anchor failure by added-mass method

![CDATA[Liquid storage tanks are vulnerable to a wide variety of failures under severe seismic excitation. Among all failure modes shell buckling and anchor bolt failures are the most critical forms of damage. Sometimes combination of different modes intensifies or accelerates liquid storage tank’s damage. Although the effect of each different failure modes has been studied separately by a number of researchers, few studies may have considered combination of main failure modes concurrently. Hence, in this paper, a cylindrical steel tank has been selected in order to study multiple damages due to dynamic loadings on the tank. All anchor bolts and steel thin wall and reinforced concrete pedestal have been modeled counting material and geometric non-linearity. The methodology for finite element modeling of fluid-structure interaction has included applying the added-mass strategy, followed by performing the numerical analyses. A suite of ground motions has been selected and matched to the target spectrum. Afterwards, incremental dynamic analyses have been conducted to obtain fragility curve according to simultaneous modes of failure. The results have indicated that anchor bolt failures along with shell buckling significantly have contributed to more flexible behavior of the thin-walled steel tank and distribution of buckling to uppermiddle part of tank which might increase seismic effects on the tank. Also, the design of steel tanks needs more considerations beyond current codes in major earthquake prone zones.]]