| As the main structural form of long-span bridges,cable load-bearing bridges are widely used in "throat engineering" such as cross-sea engineering,cross-river engineering,and crosscanyon engineering.The parallel steel wire cable is the main structural form of the cable.As the key component of the bridge,its performance degradation during the service period directly affects the overall service performance of the bridge structure.The investigation shows that corrosion and fatigue are the main factors that lead to the degradation of the service performance of such components.Therefore,it is necessary to clarify the performance degradation process of parallel wire cables under corrosion and fatigue,and to establish a scientific evaluation method to ensure the safe operation of the components and structures.To solve this problem,this thesis carried out the research by experimental analysis,literature investigation,theoretical derivation,and numerical simulation.The main work and results are as follows:(1)To meet the needs of the evolution analysis of the corrosion process of parallel steel wire cable,based on the accelerated corrosion test,the macro and micro corrosion evolution processes of the galvanized and the Galfan steel wire were analyzed.The development law of the surface element content of the steel wire during the corrosion process was studied.Moreover,it is verified that there are differences in the corrosion process of the inner and outer layers of the parallel wire cable components.(2)To quantify the corrosion process of parallel steel wire cables,on the basis of the data of the accelerated salt spray test and atmospheric corrosion test,and using the variable of uniform corrosion depth of steel wire as the "medium",a time-varying probability model of pitting depth of cable’s wire in the atmospheric was established.Then the probability model of the difference in the corrosion process of this type of components under different sheath damage patterns was established by calculating the difference in the quality of the steel wire between layers.(3)Facing the need of improving the damage analysis process of high-strength steel wires of cables under corrosion fatigue,based on the existing fracture mechanics cracking theory,by introducing the coupling relationship between corrosion and stress,the shape development model of the pitting pit and the pitting nucleation life model under corrosion fatigue were deduced and improved.By fully considering the influence of crack tip anodic dissolution and hydrogen evolution effect at the crack tip,the calculation model of corrosion fatigue crack propagation was deduced.Additionally,the influence of various factors in the whole process of corrosion fatigue damage development of steel wire was revealed(4)To solve the broken wire problem of parallel steel wire cable under corrosion fatigue,the diffusion and transmission mechanism of radial gripping force form the cable wrapping tape and sheath were analyzed.A model of nonlinear contact force between cable wires was established.A more efficient finite element simulation method for cable broken wires was proposed.Based on the wind-vehicle-bridge coupled vibration analysis,the stress distribution of the components and the response law of the remaining steel wires after the parallel wire cable breaks under the action of wind and vehicle loads were revealed.(5)Facing the need for service performance evaluation of cable members,by improving the traditional machine learning clustering algorithm,a traffic load simulation method considering the linear growth of traffic flow was proposed.A probabilistic model of the joint distribution of long-term wind speed and direction was established.The influence of wind direction was introduced into corrosion fatigue assessment.A service reliability evaluation framework for parallel steel wire cables considering the influences of service environment and sheath damage was proposed,and a case study was carried out. |
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