Research On Corrosion Fatigue Crack Propagation Life Assessment Of Arch Bridge Hangers

Because the hanger used in arch bridge is eroded by atmosphere,rain water and corrosive environment,the high tensile steel wire in the hanger will generally corrode and generate corrosion pits.At the same time,under the increasing vehicle load,the hanger is usually in a complex stress cycle state.Under the simultaneous action of corrosion and external loads,the hanger is prone to corrosion fatigue,which will cause the hanger to fail and even the collapse of bridges.Therefore,it is necessary to study the remaining life of the arch bridge hanger after corrosion,and propose the simulation method of crack propagation path of high tensile steel wire and corrosion fatigue life assessment method,which will provide important theoretical help for determining the remaining service life of the hanger and ensuring the safe of the arch bridge.In this paper,an arch bridge in actual engineering is used as the research background.The crack propagation path simulation and corrosion fatigue life assessment of high tensile steel wires with corrosion pits in side hangers are performed.The following aspects of research work have been completed:(1)A non-corroded pit and a steel wire finite element model containing corroded pits were established.Loads were applied to them and the stress distribution in the corroded pit area was compared.It was found that there was a serious stress concentration at the bottom of the corroded pit.The results are compared with a reference to verify that the adverse effects of corrosion pits on steel wire forces need to be considered.(2)The crack active propagation program was written to simulate the crack propagation path of the high tensile steel wire with corrosion pits and calculate the stress intensity factor at the crack tip using the interaction integral method.The results show that the high tensile steel wire has a semicircular crack growth shape.Based on the Paris crack growth rate model,a corrosion fatigue life assessment program was written for corrosion fatigue crack growth life assessment of high tensile steel wires,the results show that the crack growth life of high tensile steel wires is onle 420000 load cycles.(3)The overall finite element model of the arch bridge and the fine finite element model of the side hanger with corroison pits were established.Based on the vehicle load spectrum,a random vehicle flow load program was written and a random vehicle flow load file was obtained.Loading the arch bridge obtained the dynamic response of the overall model and the stress time history curve of each hanger.Through the boundary condition processing method and appropriate assumptions,the time history of the hanger stress obtained in the full bridge dynamic response analysis is applied to the fine finite element model of the side hanger with corrosion pits for dynamic analysis.The results show that through multi-scale modeling and processing methods based on certain boundary conditions,the accuracy of the calculation results can be guaranteed,and the inefficient calculation can be avoided.(4)Equivalent treatment of the stress time history of the side hanger by the rain flow counting method and the equivalent damage method,to obtain the equivalent stress amplitude and apply it to the fine finite element model of the side hanger with corrosion pits,In this way,the crack propagation path is simulated.The interaction integral method was used to calculate the stress intensity factor at the crack tip,and the fatigue life of the side hanger was evaluated by using the corrosion fatigue life assessment program.The results show that the initial crack at the bottom of the side hanger corrosion pit will maintain a uniform growth rate in the early stage.It will grow exponentially in the later period.In summary,the crack propagation path simulation and corrosion fatigue life assessment method of the steel wire containing corrosion pits in the hangers of the arch bridge proposed in this paper have certain engineering application value.After the corroded pits of the arch bridge have initiated corrosion pits,this method can be used to evaluate the remaining life of the hanger.This prediction of the remaining life of the hanger guarantees the safe operation of the arch bridge,and prevents the collapse of bridge caused by failure is of great significance.