Computation of stress concentration factor of tubular joints for the fatigue analysis of steel structures

Abstract

The offshore structures are welded tubular structures which are continuously subjected to cyclic environmental loads like waves, winds, currents, earthquakes etc. These cyclic environmental loads (predominantly wave loads) will induce time varying cyclic stresses on the offshore structures causing fatigue damages even at very low nominal stress levels. Fatigue failure is defined as the tendency of a material to fracture by means of progressive brittle cracking under repeated alternating or cyclic stresses of intensity considerably below the normal strength. Fatigue is very critical at the welded joints, because the stresses at the welded regions are several times higher than the nominal stress. Stress Concentration Factors (SCFs) converts the nominal stress into higher stresses known as hot spot stresses. These SCFs are very sensitive in the computation of fatigue life of steel structures. A small difference in SCFs can cause a huge difference in fatigue life of steel structures. Different empirical methods give different values of SCFs for the same element, hence different fatigue life. This study aims to investigate the stress concentration factor of different configurations of tubular joints numerically using Finite Element Analysis (ANSYS) under certain boundary conditions and compare the result with the SCF obtained from empirical method (using parametric equations).