| The rib-to-deck welded joint is one of the most frequent parts of fatigue cracking in orthotropic steel bridge deck.Clarifying its fatigue failure mechanism and determining its fatigue resistance is of great significance.In relevant tests,it was observed that when the weld is originating from the weld root and extending along the deck thickness direction,the rib-to-deck-details-at-midspan(i.e.RD details)and the rib-to-deck-details-at-floorbeam(i.e.RDF details)shows different cracking location.At present,there has no unified methodology or interpretive theory to explain the difference.Based on typical fatigue test of orthotropic steel bridge deck,adopting Chaboche cyclic elastoplastic constitutive model and considering the residual stress relaxation effect,this thesis carries out welding finite element simulation to explain the difference in cracking of two types of rib-to-deck details with stress amplitude theory.On this basis,this thesis simulate the fatigue crack propagation of the two details with the theory of fracture mechanics and clarify the the influence of weld residual stress on the whole process of crack propagation.The relevant results and conclusions are as follows:(1)Use ABAQUS finite element analysis software to establish the RD details segment model with single span and RDF details with double spans based on typical fatigue test of orthotropic steel bridge deck,and verify the grid correctness by the results under static load.The results show: the stress cycle law of cracking position of RDF details under static load is compression-to-compression cycle,the stress cycle law of cracking position of RD details under static load is tention-to-tention cycle.Only take static load into consideration cannot explain the different cracking phenomena of two types of details.(2)ABAQUS-DFLUX heating subroutine is written based on FORTRAN language,and simulate the temperature field and stress field of single side welding RD detail and RDF detail under the thermal mechanical sequential coupling method,after which the distribution of transverse residual stress along the weld is obtained.Then we can reveal the stress cycle characteristics under the combination of residual stress and static load of two details,which shows: The maximum stress amplitude of RD details and RDF details are both located directly below the loading position,and their stress cyclic characteristics are both tension-to-tension cycle.Take initial stress welding field into consideration also cannot explain the different cracking phenomena of two types of details.(3)The residual stress and residual strain after welding simulation are taken as the initial stress field and strain field,and the same cyclic load as the test is applied.The residual stress relaxation simulation is carried out based on Chaboche cyclic plastic constitutive model to obtain the relaxation law of weld residual stress around weld roof of RD detail and RDF detail.After that the distribution of transverse residual stress along the weld is obtained,from which we can reveal the stress cycle characteristics under the combination of residual stress considering stress relaxation and static load of two details.Then we can find that it’s residual stress relaxation lead to the migration of RD details’ crack location.(4)Under the theory of fracture mechanics,we establish a simulation method of fatigue crack growth considering residual stress to simulate the fatigue crack propagation of RD details’ and RDF details’ dominating fatigue failure modes and determining two kinds of detail fatigue cracking modes and their fatigue life.At last,clarify the influence of weld residual stress on the whole process of crack propagation. |
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