Fatigue tests and fatigue assessment approaches for rib-to-diaphragm in steel orthotropic decks

In orthotropic steel decks, a rib-to-diaphragm welded joint was one of the most vulnerable details prone to fatigue. Fatigue resistance and evaluation of the connection are challenges to be dealt with, due to a complicated local stress condition and fatigue cracking mechanism. Fatigue tests of full-scale orthotropic steel decks were carried out focusing on determining actual fatigue resistance and demonstrating the applicability of the fatigue assessment approaches for rib-to-diaphragm joints. Hot spot stress as well as the effective notch stress approaches were introduced to alleviate the difficulties of fatigue resistance assessment, and the evaluation results were compared with consistent nominal stress approach and model tests. Finite element analyses of the test specimen were performed to supplement the laboratory testing and provide additional information on the fatigue behavior of the targeted detail. The evaluation results of hot spot stress and notch stress approaches correlated with model tests better than consistent nominal stress approach. The results indicated that fatigue strength of the rib-to-diaphragm welded joints could be evaluated by hot spot stress or notch stress approaches with a single S-N curve corresponding to fatigue strength design class FAT90 (a stress range of 90 MPa at 2 × 106 cycles with a survival probability Ps = 97.7%) or FAT225. The main reason lying behind the notable divergence in evaluation results was whether local stress condition could be accurately simulated or not. The investigations gave an insight into the fatigue strength of key fatigue details in orthotropic steel decks.