ABSTRACT
ABSTRACT Fatigue is the problem that constantly bothers the durability and serviceability of orthotropic steel decks. As fatigue cracks always emerge at the welded joints of orthotropic steel decks, the accuracy and feasibility of fatigue assessment of welded details on this type of structure should be further evaluated. The regular way based on S-N curves should be specifically discussed, since it is proven to be inconsistent with experiments and sometimes results in premature fatigue damage on actual bridges. On the other hand, a fatigue assessment method based on the fracture mechanics provides an alternative option, according to reports concerning welded joints in other industries. This study compared the results from both methods, and showed the advantages and disadvantages for each. Firstly, a long-term weigh-in-motion data of the traffic flow on the Runyang Yangtze River Bridge in China was obtained, indicating that the slow lane to the north is the most fatigue-prone one among all lanes. Afterwards, the finite element model of the orthotropic steel deck was built, providing the influence surface of stresses at key positions. Consequently, the stress range histories induced by the traffic flow can be obtained. Hot-spot stress method was employed to evaluate the fatigue damage. Meanwhile, a fracture mechanics method with reasonable assumptions was conducted as well. By comparing the two sets of results, it can be concluded that the hot-spot stress method will not necessarily obtain conservative results, while the fracture mechanic method will be more proper as it considered the initial crack size as a key factor. Additionally, by taking the crack growth process into account, it enables a combination with inspection and maintenance works with respect to the life-cycle cost and performance of this structure.
