Analysis Of Complex Stress State And Ultimate Bearing Capacity Of Steel Wire In Main Saddle Of Suspension Bridge

As the key bearing structure of suspension bridge,the main cable will exert strong extrusion force in the saddle groove while realizing the smooth transition between spans through the cable saddle.With the design span of the suspension bridge exceeding 2000 m,the radial pressure of the upper steel wire on the lower steel wire and the vertical pressure between the lower steel wire and the saddle groove become more and more significant.However,at present,the designers regard the stress state of the steel wire as a one-way tension state,which is inconsistent with the actual stress state of the steel wire in the saddle.Therefore,it is very necessary to explore the influence of complex stress on the ultimate bearing capacity of the steel wire.Based on this,this thesis systematically analyzes the variation law and influencing factors of the ultimate bearing capacity of steel wire in the saddle by using the research method of numerical simulation.The main research work is as follows:(1)Taking the dispersed steel wire and saddle as the research object,the practical problems are simplified from the perspective of geometric structure and mechanical process,the simulation of contact relationship,the definition of material damage and failure and the algorithm process of solution are described,and the numerical model of steel wire ultimate bearing capacity in saddle is established to provide a basic analysis method for subsequent parameter research.The results show that the ductile metal damage constitutive model takes the equivalent plastic strain when the element reaches the material ultimate stress as the starting point of damage accumulation and the damage failure displacement as the judgment criterion of element failure,which can effectively simulate the influence of complex stress state on the ultimate bearing capacity of the structure and realize the whole process analysis of steel wire fracture in the saddle.(2)Based on the analysis of the main cable size of suspension bridges at home and abroad,considering the influence of saddle radius and steel wire position in saddle on the ultimate bearing capacity of steel wire,through the numerical simulation of multiple working conditions,the key problems such as the fracture process,fracture position and the development law of ultimate bearing capacity of steel wire under different stress states are deeply studied,combined with the plastic development trend of saddle and steel wire,the pressing depth of saddle groove and other parameters,Evaluate the damage degree of saddle and steel wire under design load.The results show that under the complex stress state,the contact extrusion between steel wire and steel wire and between steel wire and saddle is enhanced,resulting in the significant increase of the third principal strain of the most unfavorable section of steel wire,resulting in the fracture of steel wire;With the decrease of the arc radius at the bottom of the saddle groove,the degradation ratio of the ultimate bearing capacity of the steel wire in the saddle increases linearly,but the overall change range is small;With the increase of height,the total radial pressure from the upper steel wire gradually decreases,the degradation ratio of the ultimate bearing capacity of the steel wire shows a downward trend,and the plastic deformation distribution of the steel wire changes from centralized distribution to uniform distribution,that is,the stress state of the steel wire changes from complex stress state to unidirectional tensile stress state.(3)Considering the influence of the difference of contact friction between steel wire and saddle under different material properties on the actual stress and deformation state of the structure,the variation laws of steel wire ultimate bearing capacity,plastic area,saddle stress and plastic area under different steel wire and saddle materials are deeply studied,and the judgment basis is provided for the reasonable matching of steel wire and saddle material properties.The results show that the degradation ratio of the ultimate bearing capacity of the bottom steel wire in the saddle increases with the increase of the standard tensile strength of the steel wire,but the overall increase is small;The saddle material has little effect on the ultimate bearing capacity of steel wire.The fundamental reason is that the excessive contact stress leads to the plastic deformation of saddle groove before the steel wire,so that the most unfavorable position of the section controlled by the contact surface between steel wire and steel wire;If the proportion of the plastic area of the saddle groove under the design load is less than 10% as the standard to judge the material matching degree,the materials of ZG200-400 H and ZG230-450 H saddles cannot match the current high-strength steel wire materials of the main cable.(4)Based on the accelerated corrosion test data of 1860 MPa high-strength steel wire,the geometric model of steel wire with random distribution of corrosion pits under different corrosion degrees is established,and the failure mode,ultimate bearing capacity and plastic development law of corroded steel wire in saddle under complex stress state are analyzed,so as to provide basis for the evaluation of working performance of corroded steel wire in saddle.The results show that with the increase of corrosion pits,the cracks germinate in the overlapping corrosion pits near the contact surface between steel wire and steel wire,and expand rapidly along the connecting line of its circle center.The random distribution of corrosion pits has a great influence on the longitudinal fracture position of steel wire;Under the combined action of complex stress state and corrosion,the ultimate bearing capacity of steel wire will be further reduced.When the degree of corrosion is greater than 11.74%,the complex stress state has a great impact on the ultimate bearing capacity of corroded steel wire,making the steel wire brittle failure under the tension far less than the yield strength.