Fatigue strength improvement of gusset end detail with welding techniques

Gusset end details are usually welded-around with fillet welds leading to high structural and notch stress concentrations. Under cyclic loads, these structural details are usually prone to fatigue failures. This study investigates an extended welding technique and post-weld treatment to enhance the fatigue strength of welded-around gusset end details. Experimental fatigue tests are carried out on welded coupon specimens made of S420 structural steel to screen the applicability of different welding techniques and post-weld treatment techniques. A novel multi-pass welding technique – featuring weld stop locations extended further away from the joint region, along with TIG dressing weld stop location notches – was found to substantially enhance fatigue strength compared to welded-around gussets. This configuration was selected for further experimental testing, and characteristic S – N curves were determined using uniaxial constant amplitude fatigue testing with the applied stress ratio of R = 0.1. The characteristic fatigue strength of Δ σ c,97.7% = 127 MPa (slope parameter of m = 5) was obtained based on experimental testing. Further validation of the applicability of the obtained fatigue strength for the in-service variable amplitude loading was carried out by fatigue testing similar joints with variable amplitude block loading at the high-cycle fatigue regime. The results highlight the potential of such extended welding techniques for increasing the fatigue performance of gusset end details. When transforming the results to high mean stress conditions ( R = 0.5), and accounting for typical structural stress concentration of the studied gusset end detail, FAT90 ( m = 5) could be utilized for design purposes based on preliminary finite-element analysis.