Study On Fatigue Properties Of Longitudinal Rib-to-deck Welded Joints At Diaphragm Of Steel Bridge Deck

The orthotropic steel bridge deck structure system consists of structural details with multiple fatigue failure modes.It is affected by multiple factors such as weld joint geometry,initial manufacturing defects and external wheel load.The insufficient fatigue resistance of structural details leads to a series of fatigue cracking phenomena of steel bridge in operation period,which threatens the safety of bridge driving and causes many secondary hazards.In recent years,it has become a chronic disease in the design of steel bridge deck structure.The details of longitudinal rib and roof welding are particularly important.The fatigue deterioration process has a direct negative impact on the stress of the steel bridge deck.As an important structural detail of the steel bridge deck,the fatigue failure mechanism and crack propagation characteristics have been studied in depth.However,at present,domestic and foreign research literature mainly focuses on the welded joints of longitudinal rib and deck(RD welded joints)between the diaphragm joints,while longitudinal rib and deck welded joints(RDF welded joints)lack of in-depth and systematic research.This thesis combines two common forms of RDF welded joints of steel bridge deck,single-side and double-side welding.The main conclusions are as follows:(1)By loading the influence surface of the finite element model of the fatigue segment of orthotropic steel bridge deck with 2 spans and 5 longitudinal ribs,the detail-dominated fatigue failure modes and stress amplitudes of RDF welded joints on one side and double sides are obtained respectively.Considering the self-weight stress,it is shown that the stress characteristics at the initiation point of the two kinds of detail cracks are all compressive-compressive stress cycles,and the necessary condition for fatigue cracking to occur at this point is the existence of welding residual tension stress.(2)Based on Fortran language,ABAQUS-DFLUX heat source subroutine for multi-pass welding with arbitrary path is compiled.Temperature and stress fields of RDF welded joints for single-side and double-side welding are analyzed by thermal-mechanical sequential coupling method.After debugging the parameters of double ellipsoid heat source repeatedly,the accurate distribution of welding temperature field in weld pool is obtained.On this basis,the solution of welding stress field is completed.The variation rules of MISES stress and transverse residual stress are mainly analyzed.(3)A numerical simulation method of fatigue crack growth based on ABAQUS software is established.Taking a four-point bending central cracked beam in the stress state of compound mode cracking as an example,the feasibility of the established numerical simulation method of fatigue crack growth is verified by comparing the numerical simulation path with the experimental results.It provides method support for the subsequent fatigue performance study of single-sided and double-sided RDF welded joints based on fracture mechanics theory.(4)After introducing welding residual stress,there is no obvious stress redistribution phenomenon in the fatigue cracking position of RDF welded joints,and the dissipation effect of welding residual stress can be neglected.Its position stress characteristics are always in the cyclic state of tension-tension stress.On this basis,the fatigue crack propagation simulation method is used to simulate the fatigue crack propagation of RDF detail-dominated fatigue failure modes of single-side and double-side welding respectively.By extracting the amplitude of stress intensity factor at the crack front on the path of concern,two kinds of detail fatigue crack modes and their fatigue life are determined,of which the two kinds of detail fatigue crack modes are all in the form of I-II.Under the two fatigue fracture criteria,the fatigue life of RDF welded joints of double-sided welding is 1.7 times and 1.6 times of that of single-sided welding,respectively.The fatigue performance of RDF welded joints of double-sided welding has outstanding advantages.