Experimental and Numerical Investigations on Unstiffened Tubular T-Joints of Offshore Platforms

This paper presents the failure pattern, the ultimate strength, and the stress concentration factor of unstiffened T-joints obtained from experimental and numerical investigations conducted on them under axial brace compression loading. The numerical modeling was performed on the whole joint using ANSYS software package. This modeling has predicted the ultimate strength accurately when compared with that of the conventional modeling of only a portion of the joint. The nominal diameter and thickness of the chord of the unstiffened T-joints were 324 mm and 12 mm, respectively, and the corresponding values of the brace were 219 mm and 8 mm, respectively. The T-joint was approximately one-fourth the size of the largest joints in the platforms built in a shallow water depth of 80 m in the Bombay High field. The bending of the whole chord member combined with punching shear failure due to its ovalization was observed to be the predominant behavior of the unstiffened joint. The numerical analysis has simulated the behavior of the joint as was observed in the experiment and has also helped establish its correct failure pattern. It was also observed in these investigations that the unstiffened joint was stiffer in ovalization mode than in flexural deflection. The results obtained from the numerical modeling were observed, in general, to be in good agreement with that obtained from the testing. The stress concentration factor predicted by the numerical analysis is in close agreement with that measured in the experiment as well as that computed using well established parametric equations.