Study On Welding Thermal Effect And Fatigue Performance Of Orthotropic Steel Deck Of Weather Steel Bridge

Weathering steel has been gradually used in bridge structures such as orthotropic steel deck(OSD)because of its good corrosion resistance,green environmental protection and low life cycle cost.There are many welds in the OSD structure of the weathering steel bridge.The thermal effect of arc welding is very significant,resulting in high residual stress in the welded joint and the influence of high welding temperature on the steel microstructure,which aggravates the complexity and vulnerability of fatigue cracking.At present,there are few studies on the welding residual stress distribution of welded joint of OSD made of weathering steel and the fatigue performance of weathering steel considering the influence of welding high temperature.In order to more accurately evaluate the fatigue life of OSD made of weathering steel,it is necessary to establish a fatigue life analysis framework considering the influence of welding residual stress and welding high temperature(collectively referred to as welding thermal effect).Based on this,the main work of this thesis is as follows:(1)The welding process of rib-to-deck joints of OSD made of weathering steel is simulated by the thermal-structure sequential coupling analysis method,and the variation law of welding temperature field and the distribution characteristics of welding residual stress field are analyzed.The results show that the transverse residual stress of the top plate on the weld side reaches the peak at the weld toe and heel,which are 180 MPa and 184 MPa respectively.(2)The high-cycle fatigue test of Q370 q ENH steel considering the influence of welding high temperature is carried out.The specimens with similar microstructure of fine grain heat affected zone(FGHAZ)and coarse grain heat affected zone(CGHAZ)are prepared by welding thermal simulation test.The metallographic structure of the heat-treated specimens and the actual welded joint is compared and analyzed to verify the accuracy of microstructure simulation.The high-cycle fatigue tests of heat-treated specimens and base metal specimens are carried out,and their fatigue performance is analyzed and P-S-N curves are established.The test results show that compared with base metal,the fatigue life of FGHAZ and CGHAZ is significantly reduced,and the fatigue strength of 2 million cycles is reduced by 19.68% and 20.98% respectively.(3)Combining with the research results of welding residual stress distribution and S-N curve considering the influence of welding high temperature,a fatigue life analysis framework of OSD welded joints considering welding thermal effect is proposed based on the effective notch stress method.The fatigue damage analysis and fatigue life prediction of rib-to-deck joints of OSD in heavy haul railway are carried out using this frame,and the results are compared with those of effective notch stress method and nominal stress method.