Experimental and Numerical Investigation of Constant-Amplitude Fatigue Performance in Welded Joints of Steel Tubular Flange Connections for Steel Structures

Welded joints of tubular flange connections (TFCs) for steel structures are prone to cumulative fatigue breakdown under oscillatory loading regimes. This study investigates the constant-amplitude fatigue performance of these welded connections through combined experimental testing and finite element analysis. Seven tubular flange connection specimens were subjected to constant-amplitude fatigue tests, and the nominal stress range approach was employed to establish S-N curves for the TFC welds, which were then compared with existing design codes. Stress concentration behavior at the weld toe was analyzed using ABAQUS finite element software. Macro- and micro-scale examinations of fatigue fracture surfaces were conducted to elucidate the fatigue crack mechanisms. The results demonstrate an allowable stress range of 82.41 MPa at a 2-million-cycle fatigue strength, exceeding the specifications of current fatigue design codes. The finite element analysis shows that there is a significant stress concentration at the weld toe of the steel tube–flange weld, and the uneven stress distribution in the circumferential direction of the weld makes this position more prone to fatigue failure, which is consistent with the experimental phenomena. The derived fatigue design method for TFCs provides practical guidance for engineering applications.