Residual Stress Analysis And Fatigue Properties Estimation On Welding Joints Steel Bridges

The Construction of steel bridges is on an increasing trend with bridge construction development of China, with welding joints being an important component of design. There is no complete design standards for welding joint since the development of welding fatigue standard starts relatively late. The fatigue crack of welding details on steel bridge may cause accident due to the lack of design on the welding joints.Welding is a complicated physicochemical and mechanics process. The residual stress is generated by the heating and cooling process of welding. The direct reason for decreased fatigue performance of welding joints is stress concentration during the stress transmission process, welding defects and the tensile welding residual. Under the cyclic loading, in order to define the actual stress field, the residual stress should be numerical simulated at first and then superpose actual to the stress amplitude caused by different external loads. The accurate simulation of residual stress is of great significance for the research for fatigue performance of welding joints.In this thesis, the residual stress of butt joint, T-joint, roof and U rib joint are simulated by ANS YS software and the fatigue properties of dangerous position is analyzed. This thesis mainly included following aspects:1The welding heat source model, welding parameters is determined based on thermo-physical parameters and mechanical parameters of Q345. The ANSYS process APDL documents of3different joints is compiled for numerical simulation.2The stress distribution is calculated by indirect coupling of temperature and stress through calling the temperature results. The equivalent residual stress of roof and U rib joints increased with the roof thick. Residual stress of welding arc striking or arc extinguishing positing is slightly higher than yielding stress.3The actual stress of3joints is calculated based on the nominal stress of BS EN standard,and define the dangerous points which has serious stress concentration. After superposing the actual stress and residual stress of dangerous points, new S-N curve is drew based on Goodman relationship and the material S-N curve. Comparing the calculated S-N curve with BS standard, the reason of difference between them is analyzed and lead into two correction coefficient.