Crack propagation analysis of out-of-plane gusset subjected to bending moment

This study presents a numerical approach to accurately predict fatigue crack propagation in out-of-plane gusset-welded joints subjected to out-of-plane bending. Fatigue tests were conducted on structural steel specimens to investigate crack behavior in both surface and depth directions. Cracks initiated at the boxing weld and propagated in a three-dimensional meandering path through the plate thickness. While the surface crack growth rate remained relatively constant, the depth-wise growth rate decreased as the crack penetrated deeper. To replicate this behavior, a three-dimensional numerical model was developed using the extended finite element method (XFEM), which enables crack growth simulation without remeshing. The model was validated by comparing crack growth rate, shape, and aspect ratio with experimental results. The stress intensity factor estimated by XFEM differed by less than 12 % from that based on actual crack geometries, whereas assuming a semi-elliptical crack led to up to 25 % underestimation, highlighting the importance of realistic crack modeling. To evaluate applicability to practical structures, the proposed model was applied to vertical stiffener-to-deck welded joints commonly found in steel bridges. Additionally, the effectiveness of an installation of a σ-shaped notch at the top of the stiffener was assessed. The model successfully captured the crack growth retardation effect induced by the notch geometry, which reduces local constraint and stress concentration. • Bending fatigue tests provide crack path of out-of-plane gusset under bending moment. • Proposed XFEM framework reproduces crack shape and propagation rate accurately. • Stress intensity factor induced by residual stress is considered as mean stress. • Assumption of semi-elliptical crack underestimate stress intensity factor.