| The rib-to-diaphragm welded joints are most prone to fatigue cracking of orthotropic steel bridge deck(OSD),developing new type of rib-to-diaphragm welded joints with good fatigue resistance,clarifying their fatigue faliue mechanism and determining their fatigue resistance has important significance both in theory and engineering.Taking a new type of rib-todiaphragm welded joints with the floor of U-rib and diaphragm is connected by welding as research object,a fatigue test of the full-scale segmental model was carried out,the result showed fatigue cracks in the compression zone under fatigue load,it is difficult to explain this phenomenon without considering the welding residual stress.The influence of welding residual stress on the fatigue resistance of structural details remains to be further studied.In this paper,for the cracking phenomenon in compression zone of the new structural details,a simulation method for fatigue crack growth which can consider the welding residual stress as well as corresponding calculation method of fatigue life was established.On this basis,the fatigue faliue mechanism and actual fatigue resistance of the new structural details were studied combined with fatigue test.The main conclusions are as follows:(1)By modeling FEM of the full-scale fatigue test model with 2 spans and 4 longitudinal ribs,the mechanical characteristics of fatigue prone parts of the new structual details were analyzed,the results indicated fatigue cracks will appear under both tensile-tensile and compressive-compressive stress circulation,welding vestige stress was the important factor of cracks in compression zone.(2)ABAQUS-DFLUX soubroutine of heat source for Multi-pass welding was written in Fortran language,and based on the thermal-mechanical sequential coupling method,the residual stress of traditional and innovative rib-to-diaphragm welded joints were calcated,at the same time,the accuracy of welding simulation method was verified by the experimental measurement results.The variation of von Mises stress and key lateral stress were analyzed from the above calculated results,and the reasonable welding sequence of the innovative structural details was studied as well.(3)Taking the welding residual stress as initial stress,condering the combined effect of welding residual stress and fatigue load by superimposed method,then tensile-tensile stress circulation appeared in the fatigue cracking area under compressive stress of the rib floor.On this basis,condering the coupling effect of welding residual stress and initial micro-cracks,the features of fatigue crack growth were quantitative studied by fracture mechanics,the results showed that after superimposing the welding residual stress,the equivalent stress intensity factor(SIF)amplitude of crack front all exceeded the expansion threshold,the welding residual tensile stress was the key factor of fatigue cracking in compression zone under fatigue load.(4)Based on interaction integral and mesh reconstruction method,a numerical simulation method of fatigue crack growth was established by ABAQUS,and then,the calculation method of fatigue life in tensile zone and compression zone was presented by numerical calculation theory separately when considering welding residual stress and fatigue load together.Through the above simulation method of fatigue crack growth and ABAQUS-SIGINI subroutine which was used to construct the initial residual stress field,the key fatigue cracks of test model were simulated under both fatigue load and residual stress,and then,the crack propagation characteristics and crack life were discussed by the stress intensity factor(SIF)amplitude. |
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