Study On Numerical Simulation And Reinforcement For Fatigue Crack Of Rib-to-diaphragm Welded Joints In Orthotropic Steel Deck

Orthotropic steel bridge decks are widely used in domestic and international highway bridges and railway bridges because of their advantages of light weight,high strength,and convenient construction.The orthotropic steel bridge deck has many advantages,at the same time,the structure is complex,there are many welds,the stress concentration is more prominent,the structure is partially affected by the repeated effects of the car wheel load,and the fatigue problem is very significant.The fatigue problem of orthotropic steel bridge deck is a worldwide problem in the application field of orthotropic steel bridge deck,which seriously affects the service life and safety of the structure.Therefore,to study the maintenance and reinforcement of orthotropic steel bridge decks is imperative.In this thesis,the rib-to-diaphragm are used as the research object.Based on the finite element model,the fatigue crack propagation simulation at this detail is performed,and the fatigue crack propagation characteristics and failure mechanism are studied in depth.On the basis of this,reinforcement is applied to the fatigue cracking at the connection details of longitudinal ribs and diaphragms of steel bridge decks.The main research contents and results are listed as follows:(1)Based on the research results of domestic and foreign scholars on fatigue cracking of steel bridge decks,research and analysis of techniques for fatigue crack propagation simulation and repair and reinforcement of fatigue cracks in steel decks.Based on this,the study about crack propagation simulation of the rib-to-diaphragm welded joints and the related research on its reinforcement are carried out.(2)The numerical model corresponding to the full-scale specimens of the fatigue test of orthotropic steel bridge decks was established by the universal finite element software ANSYS,and through the comparison of measured and theoretical values under test conditions,the accuracy of the finite element model was determined.On this basis,a finite element model for the fatigue cracks at the intersection details of longitudinal ribs and diaphragms was established.On this basis,a finite element model of the fatigue cracks at the rib-to-diaphragm welded joints,analyze the variation law of stress intensity factor in the fatigue crack from the initial crack to the crack through the longitudinal rib web.The basic conclusions are: fatigue cracking at the connection of longitudinal ribs and diaphragms of steel bridge panels with fracture mode I as the main cracking mode,however,with the increase of the length of fatigue cracks,the cracks tend to develop towards the composite cracking mode.(3)For the fatigue cracks at the rib-to-diaphragm welded joints in the orthotropic steel bridge deck,the reinforcement method of the assembled bolted angle steel is used for reinforcement.The analysis and discussion of the reinforcement effect on this technique about two aspects of experimental research and fracture mechanics.From the actual reinforcement effect in the fatigue test,the engineering feasibility of the bolted angle steel reinforcement method was verified,and it was also demonstrated that the bolted angle steel can effectively suppress the expansion of short cracks.From the point of view of the equivalent stress intensity factor of fracture mechanics,the influence of reinforcement timing and the size of the steel sheet on the strengthening effect is analyzed.The results show that the reinforcement should be carried out before the crack is extended to a long length so that the reinforcement effect can be guaranteed,fatigue crack propagation is effectively suppressed.In addition,the thickness of the angle steel used for reinforcement has the greatest effect on the reinforcement effect.(4)The propagation characteristics of penetrating fatigue cracks at the connection details of rib-to-diaphragm were studied.The analysis shows that the fatigue crack propagation through the longitudinal rib will be show in the composite cracking mode.At the same time,the reinforcement method of bolted angle steel is used to reinforce the fatigue cracks.The calculation results show that this reinforcement method mainly suppresses mode I fatigue cracking,and is not ideal for the reinforcement effect of composite fatigue cracks.Therefore,the steel bridge deck fatigue cracking reinforcement must be targeted,a reinforcement measure can not play a good effect on all fatigue cracking.(5)For the penetrating fatigue cracks appearing at the connection details of rib-todiaphragm,a finite element numerical model with the reinforcement of half U-rib steel plate was established on the outside of the longitudinal ribs.On this basis,linear elastic fracture mechanics was used to perform the strengthening effect.The analysis results show that when using single sided steel plate for reinforcement,the further expansion of the fatigue crack tip on the reinforcement side can be effectively suppressed,but the inhibition effect on the fatigue crack propagation on the other side is limited.Double sided half U-rib steel plates for reinforcement on both sides can effectively suppress the further expansion of the crack tip on both sides of the penetrating fatigue crack.