A Multi-scale Corrosion Fatigue Damage Model Of High-strength Wires And Fatige Analysis Of Bridge Cable

During the service period,bridges are subjected to long-term environmental erosion and alternate loading simultaneously,which cause the fatigue damage of bridge structures to accumulate.Cables are the most sensitive components to damage in cable-supported bridges and the failure of cables is generally caused by the mechanical degradation of wires inside.The corrosive environment would accelerate the evolution of tiny defects in the material,decreasing the fracture toughness of wires and reducing the service lives of cables inevitably.Based on this engineering background,the issues on the trans-scale corrosion fatigue damage evolution process of the bridge cable structure are investigated using multi-scale method.The main research work can be summarized as follows:1.Based on the analysis of the common damage phenomenon of cables during the service period,the failure path of the cable structure is summarized and the research strategy for the damage evolution process of the cable structure is discussed from the theoretical framework.The results show that the failure of the cable structure is caused by the continuous evolution of the tiny defects in the wire material under the combined action environmental erosion and alternate loading,which is the end of the structural damage evolution process.Thus,in order to investigate the issues of the damage evolution process of cables in corrosive environment,the corrosion fatigue damage evolution process of wires must be studied first.2.A multi-scale corrosion fatigue damage model is developed to explain the fatigue failure of wires in corrosive environment,which connects the damage mechanism in microscopic scale and the degradation rule of mechanical properties in macroscopic scale.The accuracy of this damage model is also verified through experimental data.The results show that when the loading frequency is between 1Hz and 10 Hz,the corrosion fatigue life of wire predicted by this damage model is in good agreement with experiment data.However,when the loading frequency is beyond this range,the predicted result will deviate from the experiment data,because the damage evolution mechanism has been changed.The developed damage evolution model reflects the characteristics of corrosion fatigue damage evolution process of wires in different scales and provide a new way to under the transscale damage evolution mechanism during the corrosion fatigue process better.3.Based on the block cycle jump algorithm,a new adaptive time-stepping simulation method is developed to simulate the corrosion fatigue damage evolution process of cables.The results show that the developed method can simulate the fatigue evolution process of cables at lower computational cost and can well reflect the synergistic damage evolution of wires inside,which provides an efficient numerical tool to investigate the damage evolution mechanism of cables in corrosive environment.4.Based on the strength model of fiber bundle,the corrosion fatigue behavior of the cable is simulated to study the fatigue failure mechanism of the cable in corrosive environment.The results show that the degradation process of cable is the result of synergic damage evolution of wires inside.The damage difference between wires will affect the unevenness of stress distribution and the stress redistribution will also reduce the damage difference between wires.These two elements interact and affect each other,jointly promoting the cable damage evolution process.In this process,the unevenness of stress distribution will not only depend on the damage evolution of wire,but also be affected by the change of effective bearing area ratio.Before the cable average damage reaches 0.42,the difference between initial damages is the main factor that makes the difference of damage between wires increase,and the unevenness of stress distribution will also gradually increase in this stage.When the cable average damage develops from 0.42 to 0.68,the stress redistribution is the main factor that makes the difference of damage between wires decrease,but the unevenness of stress distribution will still gradually increase in this stage.After the cable average damage reaches 0.68,the unevenness of stress distribution will drop rapidly.In addition,the wires with greater initial damage have first-mover advantage in the damage evolution process.The stress redistribution can only reduce the damage difference between wires and can not eliminate the first-mover advantage completely.5.Based on the concurrent multi-scale modeling method and the developed simulation method for cable damage evolution process,a multi-scale model of Runyang cable-stayed bridge is developed to study failure process of the cable structure in corrosive environment.The results show that during the deterioration process of cable structure,when one cable loses its bearing capacity gradually,most of its load will be shared by the surrounding cables and the force of nearby cables could increase over 20%.Obviously,the transference of load will accelerate the fatigue damage evolution rate of these surrounding cables,which can cause the effect of breaking one by one in the cable structure and eventually lead to the failure of the whole bridge structure.In addition,when the cable damage reaches the criterion of cable replacement,the decrease of cable force is fairly modest,only about 7.3%.In the cable force inspection,the decrease of cable force caused by damage can be easily covered by the cable force change caused by environment or traffic loads.Thus,it is necessary to develop a new detection method to evaluate the damage condition of cables more accurately and effectively.