Abstract:The U-rib, top plate and diaphragm of the orthotropic steel bridge deck are complicated in structure at the junction of the three, and the welds are staggered, which is likely to cause fatigue cracking under the action of the local wheel load of the automobile. It is an improved method to replace the traditional U-rib with a new type of hot-rolled U-rib with variable thickness, and to increase the weld size between the U-rib and the top plate to reduce the stress concentration. Through the modelling of a refined finite element model of the beam, the fatigue vulnerable parts and the corresponding most dangerous loading positions under the action of the automobile are analyzed, and the new U-rib structure details are compared parametrically. With reference to the local stress and the deformation trend of the vulnerable parts, the structural optimization suggestions for the new U-rib are given. After research, the following conclusions are obtained: (1) The new variable-thickness hot-rolled U-rib is beneficial to abate the stress concentration of the U-rib top and the opening of the diaphragm, and can also reduce the local deflection of the top plate under the wheel load; (2) It is recommended that the new U rib adopts h=40mm, Δt1=4mm, Δt2=4 design parameters to achieve the better mechanical behavior(The basic thickness of the rib is 8mm).