Fatigue Test And Analysis Of Rib-to-Diaphragm Welded Joint Strengthened With CFRP Plate

Orthotropic steel bridge deck is widely used because of its many advantages.However,with the increase of service life,the fatigue problem has become a key problem limiting its development.In orthotropic steel bridge deck,the structure and stress of rib-to-diaphragm welded joint are complex.Under the action of vehicle load,this detail is often one of the main structures prone to fatigue cracks due to welding residual stress and welding defects.Therefore,the effective evaluation of its fatigue performance and effective reinforcement has become the basis for the wide application of the structure.In the field of concrete reinforcement,carbon fiber reinforced polymer(CFRP)has a very significant reinforcement effect,but in the steel structure reinforcement,this method is only limited to the theoretical analysis and experimental research stage.In order to analyze the fatigue performance of the rib-to-diaphragm welded joint of orthotropic steel bridge deck when fatigue cracking occurs,the fatigue test of full-scale specimen and the numerical simulation of the welding details are carried out in parallel,and the propagation law of the fatigue crack length and the change rules of stress with the change of the number of cycles is studied.According to the development of fatigue crack and local stress in the test model,CFRP plates were bonded to the cracked parts of rib-to-diaphragm welded joint,and the strengthening performance was studied.The main conclusions are as follows:(1)During the process of applying fatigue load,fatigue crack appears at the welding end of ribto-diaphragm welded joint,and the fatigue crack gradually expands with the increase of external load cycles.The fatigue crack growth rate has experienced four processes: growth-deceleration-growthdeceleration.The fatigue crack growth rate is approximately 0 until the number of external loading cycles reaches 1.1 million.(2)The results show that the stress amplitude at the end of welding decreases with the increase of fatigue load cycles,and the stress amplitude at the arc notch of diaphragm decreases with the increase of fatigue load cycles.The stress amplitude at the end of the welding of the adjacent details of the two cracked details decreases slightly with the increase of the number of fatigue load cycles.With the increase of fatigue load cycles,the detail cracking has little effect on other details.(3)When the welding details of rib-to-diaphragm welded joint are loaded,out of plane buckling deformation mainly occurs.In view of the deformation and fatigue cracking mode,it is a very effective method to reinforce the cracking details by pasting carbon fiber reinforced polymer(CFRP).(4)The results show that the stress amplitude at the end of welding of cracking details is significantly reduced after strengthening by sticking CFRP plates,which indicates that the stress state at the end of welding of fatigue cracking parts is improved after strengthening,and the collaborative stress performance of CFRP reinforcement and steel deck members is good.The results show that the stress concentration factor near the inner and outer reinforcement area of the crack details almost does not change,which indicates that the new stress concentration phenomenon will not occur near the reinforcement area after the reinforcement of the crack details by pasting CFRP plates.The stress amplitude at the crack tip outside the crack details decreases after reinforcement,and the reduction is large,which indicates that the stress state at the crack tip area is improved after reinforcement.(5)Different reinforcement parameters and reinforcement time have different effects on the reinforcement performance of fatigue cracks in rib-to-diaphragm welded joint.The greater the elastic modulus of structural adhesive layer is,the better the reinforcement performance of fatigue crack in rib-to-diaphragm welded joint of steel bridge deck is;the greater the elastic modulus of CFRP plate is,the better the reinforcement performance of fatigue crack in rib-to-diaphragm welded joint of steel bridge deck is,but the influence is small;the change of reinforcement geometry has little effect on the overall reinforcement performance of crack,and does not show a certain regularity.For the ribto-diaphragm welded joint of steel bridge deck,the crack growth rate is the smallest when the unilateral crack length extends 25 mm,and the reinforcement performance is the best at this time.