Study On Long-term Performance Degradation Of Long-span Weathering Steel-concrete Composite Stiffening Girder Suspension Bridge

With the rapid development of highway transportation in our country,the construction of long-span highway bridges is in the upsurge.Suspension bridges are widely used in long-span bridges because of their small self weight,outstanding span capacity and beautiful shape.In the suspension bridge,the use of weather resistant steelconcrete composite stiffening beam can make better use of the material characteristics of weather resistant steel and concrete,improve the durability and reduce the project cost.As the main load-bearing components of suspension bridge,stiffening beam and main cable always bear the role of environmental erosion in the service process,so the bearing capacity decreases,threatening the operation safety of the bridge.Therefore,it is particularly important to evaluate the decline of bearing capacity of the bridge during the operation period.In view of this,this paper takes a weather resistant steel-concrete composite stiffening beam suspension bridge as an example to study the change rule of its bearing capacity under the joint action of environment and vehicle.The main work includes:(1)based on Fick’s second law,the calculation method of chloride ion in unsaturated concrete under the combined action of dry and wet cycle,ambient temperature,vehicle load and concrete damage is deduced.A subroutine of chloride ion transport in unsaturated concrete is compiled,which considers the comprehensive influence of environmental temperature,precipitation,concrete damage,vehicle load and other factors.The general finite element software ABAQUS is used for long-term chloride ion transport analysis.(2)based on the test data of weathering steel hanging piece reported in the literature,the corrosion dynamic curve parameters of weathering steel suitable for different corrosion grades of atmospheric environment are determined.The double parameter Weibull distribution is used to describe the distribution of corrosion pit depth.According to the simulation results of corrosion pit depth in the earlier stage of the research group,the corrosion pit depth classification of different corrosion grades of atmospheric environment at different corrosion times is proposed Cloth simplification algorithm.The maximum corrosion pit depth on the surface of weathering steel is described by the extreme value distribution.The section corrosion degradation of the steel stiffening beam of a long-span suspension bridge is calculated as an example.The average corrosion depth,maximum corrosion pit depth and section loss of each steel plate that make up the steel stiffening beam are obtained.(3)summarize the current detection method and calculation process of main cable strength for suspension bridge.The plastic model is used to calculate the residual strength of the main cable.The main factors affecting the corrosion of the main cable steel wire are determined as the internal temperature,relative humidity,p H value and chloride ion concentration of the main cable,and the methods for calculating the internal temperature,relative humidity,p H value and chloride ion concentration of the main cable are derived.According to the local climate of the suspension bridge,the distribution of the internal corrosion factors of the main cable is calculated,and then the corrosion degree of the main cable steel wire and the time-varying law of the residual strength of the main cable are calculated.(4)considering the time-varying law of corrosion degradation of reinforced concrete deck,weathering steel beam and main cable of suspension bridge,the time-varying law of mechanical properties of the whole suspension bridge is calculated.Under the action of no-load,the most unfavorable live load and vehicle load,the changes of midspan displacement,main tower displacement along the bridge direction and main tower root stress are compared under different service time.