Seismic fragility analysis of retrofitted steel tanks considering corrosion

Abstract

Several types of steel tank are used in industrial plants to store hazardous chemical products. Most of these are unanchored tanks that are not designed to withstand seismic loads. Many of the old process industries in high seismic hazard areas have launched retrofitting programmes for their components, especially cylindrical tanks. Providing mechanical anchors is a common strategy for the seismic retrofitting of cylindrical tanks and there are thus several existing pre-code tanks that have been retrofitted by the provision of anchor bolts. In this work, fragility analyses of pre-code and retrofitted tanks were conducted for existing broad tanks. The effects of steel corrosion were considered in the fragility analyses and 250 tank–earthquake non-linear analysis cases were considered. The results of the study revealed that shell corrosion is an important source of uncertainty in the seismic fragility analysis of tanks. Moreover, it was found that providing mechanical anchors is a suitable technique for preventing moderate to major damage states in broad tanks, but is not efficient at preventing minor damage, especially for small peak ground accelerations.