Abstract: In order to investigate the fatigue failure modes and the fatigue performance of orthotropic steel decks (OSDs) with hot rolled thickened U ribs, a variable amplitude fatigue test was conducted on two full-scale steel deck specimens. The failure mode and stress amplitude of fatigue details in steel decks with hot rolled thickened U ribs and with cold formed U ribs were analyzed, and an assessment of fatigue performance for OSDs was carried out using the structural hot spot stress method. Furthermore, a three-dimensional finite element model of the OSD specimen was developed, and the influence of U rib specifications on the fatigue performance of critical weld details was investigated upon the structural stress method. The test results indicate that fatigue cracks in OSDs with hot rolled thickened U ribs initiate at the rib-diaphragm welded joint, subsequently propagating along both the height and thickness directions of U ribs. The use of hot rolled thickened U ribs significantly reduces the equivalent structural stress at the U rib to deck weld and at the U rib to diaphragm weld, with reductions of 16.8% and 29.6%, respectively. The implementation of hot rolled thickened U ribs effectively improve the fatigue life of the rib-diaphragm weld and of rib-deck weld details. Compared to cold formed U ribs, the average equivalent fatigue strength of the hot rolled thickened U rib-diaphragm joint increase by 43%, reaching 126.9 MPa.