Research On Mechanical Characteristics Of Long Span Cable-Stayed Bridges Under Cable Damage Conditions

The cable-stayed cable is subjected to complex environment and repeated load for a long time,and often appears fatigue,corrosion,fracture and other damage problems,which reduces the safety performance of the bridge,causes safety risks,and increases the probability of accidents.Based on the engineering background of a double-tower and double-cable-plane cable-stayed bridge,this paper studies the mechanical properties of the bridge structure under cable damage from the aspects of single cable damage and multi-cable damage,and analyzes the vulnerability under local cable fracture,which provides certain theoretical basis and technical support for the subsequent identification,monitoring,maintenance and reinforcement of cable damage of bridge structures.(1)On the background of practical engineering,this paper establishes the overall structure model of long-span cable-stayed bridge,adopts the minimum bending energy method to adjust the cable to make the bridge reach a reasonable bridge state,and obtains the maximum vertical deflection of the main span in the span of 102 mm.By comparing the numerical simulation with the main beam deflection monitored in the field,the relative error of the two main spans in the mid-span area is within 5%.The relative error of the main tower area is within 10%,which verifies the accuracy of the model.The natural vibration characteristics of bridge structure are analyzed so that the dynamic characteristics under the condition of cable damage can be studied later.(2)Analyze the mechanical properties of the bridge structure with cable damage at different positions and the linearity of the main beam,cable force,deformation of the main tower and the whole bridge frequency under the different degree of damage of the long and short cables.Simulate cable damage by reducing the section area of the cable,summarize the variation law of the mechanical properties of the bridge structure under the damage of a single cable,and find out the damage conditions that have more adverse effects on the bridge structure.It is found that when a single cable is damaged,the mechanical properties of the bridge structure increase with the increase of the damage degree,the damaged cable’s own cable force decreases obviously,and the other cable’s cable force increases slightly.The damage of the long cable has a greater effect on the linearity of the main beam and the deformation of the main tower,and the short cable has a greater effect on the frequency of the whole bridge.(3)The mechanical properties of the bridge structure with multiple cable damage were studied,the damage of multiple cable was simulated by reducing the elastic modulus of the cable,and the variation law of the mechanical properties of the bridge structure was analyzed when the whole bridge cable was uniformly damaged.It was concluded that the uniform damage of the whole bridge had a significant influence on the linearity of the main beam,the displacement of the main tower and the frequency of partial mode shapes.(4)Analyze the mechanical characteristics of the bridge structure under local cable fracture.By setting the two sides of the main tower to compare the working conditions,the change law of the mechanical properties of the structure under the local cable fracture conditions of the side span and the main span,obtain the safety factor of the bridge structure under local cable fracture.Analyze the vulnerability of the local cable fracture by using the Palo to boundary,and find out the damage conditions in many.The damage scenario is as serious as possible,which provides a certain reference value for the monitoring of key areas and the evaluation of structural safety performance of in-service cable-stayed Bridges.