Theoretical analysis and design method of CFRP-strengthened inclined welded steel plates with initial cracks under fatigue loadings

CFRP strengthening can effectively enhance fatigue lives of welded steel structures. However, due to the complex multi-axial stress states at the welds and cracks, an effective fatigue life estimation and a strengthening designing method are yet established. Based on fatigue tests and associated finite element simulations from the current research group, a fatigue life calculation model and a design method for CFRP-strengthened inclined welded steel plates with initial cracks were proposed. Firstly, a residual stress distribution model along the critical paths of the inclined weld steel plate was established, considering the effects of weld angle, weld reinforcement, and weld width. The distribution of residual stress, which exhibits a quadratic shape, closely aligns with that in numerical models. Secondly, an analytical model, which is suitable for engineering design, was established to estimate the stress intensity at the welds and cracks of the CFRP strengthened steel plates in the initial and crack propagation states. It involves the influences of weld reinforcement, CFRP strengthening, residual stress, and crack mode mixity. Furthermore, based on the NASGRO model, a fatigue life estimation program was established. Thirdly, a parametric study was conducted to quantify the influences of key parameters, including weld geometry, initial damage, loading condition, and CFRP stiffness. Finally, a strengthening design method was proposed, and design examples were given, providing a valuable reference for engineering practice.