ANALYSIS OF UPLIFT BEHAVIOR OF THE SHELL-TO-BOTTOM JOINT OF A SEISMICALLY-LOADED OIL STORAGE TANK USING AXISYMMETRIC SOLID FINITE ELEMENT METHOD

摘要

Above-ground cylindrical storage tanks are widely used in the petroleum and chemical industries. Most of these tanks are unanchored and rest freely on flexible foundations. The shell-to-bottom joint of an unanchored oil storage tank will uplift due to strong horizontal seismic excitation, and a large plastic strain occurs cyclically in this joint.Studies into the seismic response of unanchored liquid storage tanks considering the uplift behavior were made by many researchers. These were put forward from a viewpoint of the vibration of the fluid-filled cylindrical tanks due to horizontal seismic excitation, and useful information was derived on the relation between the seismic input and the uplift displacement. However, because of the complexity of the elastic-plastic, large displacement problem of the uplift behavior, there is little research concerning the relationship between the large plastic peak strain at the toe of the fillet weld in the shell-to-bottom joint and the seismic input.This paper presents the elastic-plastic, large displacement behavior of the uplifted shell-to-bottom joint which is analyzed for the uplifted joint model using an axisymmetric finite element method instead of a 3D dynamic analysis model. In this analysis, the complex uplift model is transformed into a simplified axisymmetric model from a viewpoint of the stress and strain in the shell-to-bottom joint. The shell-to-bottom joint is modeled using solid elements in order to consider the effect of the weld metal shape on the stress and strain at the toe, and the foundation is modeled using a Winkler's elastic spring. Relationships between the uplifting force and the uplift displacement at the joint, and between the uplifting force and the peak strain at the toe are presented.