•Employed ITSS method is initially validated for analyzing OBD under combined loading.•A good correlation was obtained from predicted and experimental results.•The effects of shear stress and the ratio of specimen width to length are obtained. This paper investigates the fatigue property of U rib-crossbeam-deck connections in orthotropic steel bridge decks (OBD) under combined loading of bending and torsion by using the improved traction structural stress method. Applicability of the method for analyzing OBD under combined loads is validated by comparing the simulation results with the experimental results from the literature. The fatigue property of OBD in multiaxial stress states is studied by investigating the effects of the ratio of specimen width to length and combined loading amplitude. The trend and amplitude of the improved traction structural stress distribution change with an increase in the ratio of width to length.