Experimental study on fatigue performance of double welded orthotropic steel bridge deck

Fatigue cracks which develop at multiple locations of orthotropic steel bridge decks (OSD) seriously deteriorate the safety and durability of steel bridges. U-rib fabricated using the double-sided penetration welding technique have been practically applied in bridges, but the fatigue performance of this type of U-rib has not been systematically studied. This study conducts fatigue tests on large-scale models of various fatigue details in the diaphragm area of orthotropic steel bridge decks with double-sided welds, obtaining the fatigue vulnerable locations and dominant cracking modes in the diaphragm area. The evolution law of out-of-plane deformation of diaphragm is clarified. The distribution characteristics of residual stress at the arched opening region and fatigue failure modes are acquired. Experimental results show that the interior weld toe of the U-rib-to-top-plate joint is the most fatigue-vulnerable zone, with a fatigue strength of 53.6 MPa. New fatigue cracks initiated from the weld toe of the top plate of the inner side of the U-rib or the weld toe of the U-rib perpendicularly or obliquely intersecting the longitudinal weld along 45° were found. After 10 million loading cycles, the residual stress in the arc-shaped opening area of the diaphragm reached 90–145 MPa, and the residual stress was higher where curvature of the opening was larger. The arc-shaped incision was in a circling state of tension and compression. It was also found that fatigue cracks that initiated from the weld toe of the diaphragm extended along the weld toe for some length before propagating into the diaphragm.