Fatigue Performance Strengthening And Residual Life Assessment Of Rib-to-Deck Welded Joints Of Orthotropic Steel Bridge Deck

The orthotropic steel deck has complex geometric structure and large number of welds,it is easy to cause fatigue cracking problems under the action of wheel loads.Among them,the fatigue cracks in the welding details of longitudinal rib and deck plate can easily cause leakage,corrosion and other disasters.In order to prolong the service life of in-service bridge structures,many scholars at home and abroad have proposed different reinforcement schemes.In actual engineering,with the increasing traffic volume and heavy load ratio,fatigue cracking will occur again after the bridge structure is reinforced.Based on this actual engineering problem,this thesis studies the fatigue deterioration characteristics of the welding details of the longitudinal rib and the deck and the influence of different parameters of internal welding reinforcement,and further analyzes the dominant fatigue cracking mode after reinforcement.On this basis,a secondary reinforcement scheme is proposed and its reinforcement effect is evaluated.The main research contents and conclusions are as follows:(1)Review the evaluation methods of fatigue performance of orthotropic steel decks at home and abroad and the research status of fatigue cracking mode reinforcement methods for welding details of longitudinal ribs and deck.In view of the relevant problems that need to be solved urgently at present,formulate research objectives,clarify the technical route,and carry out relevant research.(2)Combined with linear elastic fracture mechanics and equivalent structural stress method,a reinforcement evaluation method based on residual fatigue life of welding details is established.The correctness of the crack numerical simulation is verified by the relevant experiments of our team.The equivalent stress intensity factor in the depth direction of the fatigue crack front is greater than the equivalent stress intensity factor in the surface direction,and the shape of the fatigue crack tends to be flattened.(3)Based on the fatigue cracking mode of the welding root of the welding details of the longitudinal rib and the deck,the key parameters of the internal welding reinforcement are analyzed.Different penetration rates of the internal welding reinforcement can have the effect of arresting cracks and prolonging the fatigue life of the structure.Although the crack arrest effect is better after reinforcement,the fatigue life is reduced.When the fatigue crack does not penetrate the deck,internal welding reinforcement measures can be used to achieve the reinforcement effect.Once the crack breaks through the deck,the fatigue crack growth cannot be inhibited.Selecting the typical internal welding leg size for reinforcement can achieve the effect of crack arrest.With the increase of the internal welding leg size,the crack arrest effect becomes better and the fatigue life is slightly reduced,so the welding leg size should be within the Under the premise of crack arrest,choose a smaller fillet size.(4)The fatigue performance of the structural system reinforced by internal welding is analyzed,combined with the accumulation of fatigue damage in each concerned part during the fatigue crack propagation process and the change of the stress state of the structural system after reinforcement,it can be seen that the dominant fatigue cracking mode of the structure is the migration of the welding root.to the outside weld toe.The use of steel plate for secondary reinforcement can only delay the crack propagation,but cannot achieve the effect of crack arrest.The use of angle steel,U-shaped steel and UHPC for secondary reinforcement can achieve the effect of crack arrest and prolongation of structural fatigue life,and the reinforcement effect of U-shaped steel is better than that of angle steel,and UHPC has the best reinforcement effect.