Buckling behavior of floating-roof steel tanks under measured differential settlement

Abstract

Large vertical cylindrical steel tanks constructed on soft foundations may bring forth various types of settlement, which is well known as the uniform settlement, the planar tilt and the differential settlement. Measured settlements of steel tanks in several practical projects are first summarized according to the in-site surveying data, and two kinds of settlement patterns are clearly defined, which are referred to as the global differential settlement and the localized differential settlement. Two practical floating-roof steel tanks are taken as the illustrative examples of large steel tanks, which are marked TK-2020 with the height-to-radius ratio of 0.35 as the representatives of large volume tanks and TK-2090 with the height-to-radius ratio of 0.7 as representatives of smaller volume tanks in this paper. Buckling behaviors of the two illustrative tanks under the global and localized differential settlement are investigated using the general-purpose finite element computer package ABAQUS by means of the geometrical nonlinearity algorithm. It is shown that for tanks under global differential settlement, local buckling occurs first at the eave wind girder, followed by a stable post-buckling behavior, so that the local buckling of the wind girder can be taken as the serviceability limit state and the post-buckling strength can be utilized in structural design of tanks. Moreover, the behavior of tanks under localized differential settlement is related to the degree of localization. The buckling behavior in the case of a large circumferential central angle for localized settlement is similar to that under global differential settlement, while the effect of the localized settlement with a relatively small central angle is more obvious than that of the global differential settlement, and the snap-through buckling induced by localized settlement would govern the design.