Influence of welding residual stresses on stable crack growth in tubular K-joints under compressive fatigue loadings

Tubular bridge design has to deal with fatigue issues. The fatigue susceptibility of these bridges, composed of circular hollow section profiles welded together in K-joints, is mainly due to stress concentrations, to welding imperfections and to tensile residual stresses induced by the welding process. Since these residual stresses are unknown for K-joints, measurements were carried out in vicinity of weld toes using the incremental hole-drilling method, X-ray diffraction and neutron diffraction in particular. Re-sults from these techniques show that on the first millimeters from the surface, the most important tensile re-sidual stresses are oriented perpendicular to the weld and reach the yield strength. According to experimental investigations on two large scale specimens, it is established that tensile residual stresses have a strong influ-ence down to a depth of 2-3 mm from the surface, allowing cracks to propagate in compressive joints. Prelim-inary Finite Element Analyses are presented in this paper.