AbstractThe fatigue of orthotropic steel bridge decks (OSBDs) is a bottleneck for its application, especially the fatigue of rib-to-floor beam (RF) junction. Thus, it is necessary to optimize the RF junction to improve its fatigue performance. In this study, the effect of equipping a separate inner stiffener (SIS) on the fatigue performance of an RF junction was investigated. The growth of fatigue cracks in the weld toe of the rib at the RF junction tip (RT) was examined through static and fatigue tests of a full-scale OSBD. Moreover, the influence of crack growth on other details was also studied. Subsequently, the fatigue strengths of two cracked details and the minimum fatigue strengths of four uncracked details were evaluated considering the results of a finite-element analysis. Finally, the verified finite-element model was used to analyze the influence of the form and size of the inner stiffener on the fatigue performance of RF junction. The SIS was found to be the most optimal inner stiffener, and its recommended size was obtained. When the recommended RF junction was adopted, the most unfavorable stress of the RT detail most prone to fatigue cracking could be reduced by 51.3%.