Fatigue Performance Study Of Rib-to-diaphragm Connection Details On Orthotropic Steel Bridge Deck

Orthotropic steel bridge deck is widely used in bridge engineering because of its high strength-to-weight ratio, convenient construction and so on. However, the internal forces in the orthotropic bridge deck is complex under vehicle loading, coupled with serious traffic overloading.Various welding details are prone to fatigue cracking. The structural behavior is studied under live load, the cracking mechanism of structure details are analyzed and reasonable structure details of orthotropic steel bridge deck are provided, which are very important for safe service and durability of bridges. Starting from the assessment method and experiments analysis, the paper discusses rib-to-diaphragm connection details on orthotropic steel bridge deck on a real bridge.The main research contents and achievements are introduced as follows:(1) The current situations and fatigue problem of orthotropic steel bridge deck are introduced. Then, the method of fatigue studies is reviewed and the main work of the thesis is outlined.(2) The principles, the using condition, the calculation method and the corresponding specifications of nominal stress method, hot spot stress method, zero structural stress method, notch strain method and linear elastic fracture mechanics are introduced, respectively. In addition, it analyzes the advantages and disadvantages of these methods.(3) The effective notch stress method is employed for fatigue assessment, and element type, mesh size and weld root area for meshing way are analyzed in fillet welded cruciform joint. The results show that the calculation of effective notch stress should use high order element in consideration of lock phenomenon. The mesh size must satisfy the IIW regulations, and excessive mesh is not suggested because of an increased CPU time. When the load is applied parallel to the notch, key-hole and U-hole are suitable to be used, when the load is vertical to the notch, key-hole is preferable.(4) In order to verify the present method, the fatigue stress is calculated by hot spot stress method and effective notch stress method, respectively. The result shows that effective notch stress method is a suitable method for assessing fatigue performance of orthotropic steel bridge deck, and it is more appropriate than hot spot stress method. The effective notch stresses are compared in two different diagram transition forms, resulting to suggested sutiable transition forms. The effective notch stress in weld toe of the rib-to-diaphragm is significantly higher than the value in weld root, so weld toe is more easy to crack. The crack initiation in the rib-to-diaphragm connection seems to be easier with the increase in rib thickness.(5) The stress-time curve of a real bridge is obtained by field measurement. The equivalent stress amplitudes are calculated by rainflow counting method and Miner criteria in typical weld of orthotropic bridge deck, and the fatigue life is evaluated per AASHTO fatigue specification. The result shows that the fatigue life does not meet the AASHTO requirements in the sturucture details of rib-to-diaphragm welding, and the reduced fatigue strength may be due to cause of no welding treatment.