Large aboveground oil storage tanks are unanchored and rest freely on flexible foundation. The shell-to-annular joint of unanchored oil storage tanks will uplift due to strong seismic excitation, and a large plastic strain occurs in this joint. This paper presents the elastic-plastic, large deformation behavior of the uplifted shell-to-annular joint using axisymmetric finite element analysis. In the analysis, the uplift behavior is assumed to be axisymmetric. The constitutive equation is based on the J₂ flow theory with the kinematic hardening rule. The ductile fracture strength characteristics of uplifted shell-to-annular joint in a large tank with capacity 90, 000m³ were reported. The following conclusions were obtained. Even if the fillet weld surface in the shell-to-annular joint becomes smooth, the stress and strain does not change except for the toe. The yield stress of a welded metal at the joint does not influence the strength of annular plate. The strength at the joint becomes high when liquid density is high.