Study On Cable Force Evaluation Of Suspension Bridges In Service Based On Main Cable Geometry

With the continuous promotion of traffic infrastructure construction in our country,on the one hand,the application scenes of bridges crossing river valleys and connecting land and sea are gradually increasing,and suspension bridges have become the first choice for long and long bridges because of their superior spanning ability,on the other hand,with the increase of service life,the performance degradation of long-span suspension bridges has become increasingly prominent,and more and more in-service suspension bridges have entered the sling replacement cycle.The cable of the suspension bridge is also regarded as the ‘life cable’.Once the force of the cable exceeds the ultimate bearing capacity of the material,the cable will be broken,which will cause great risk to the safety of the bridge operation.Therefore,the accurate evaluation of cable stress state of in-service suspension bridge is very important for the safe operation,maintenance and reinforcement of the bridge.However,the existing cable force identification methods based on frequency method still face many challenges in suspension bridges.Based on the highly sensitive characteristics of cable shape and stress of suspension bridge,this thesis studies the evaluation method of cable stress state based on the geometry of main cable.The main contents are as follows:(1)A suspender force calculation method based on the geometric parameters of main cable of in-service suspension bridge is proposed.The relationship between geometric shape and cable force of piecewise parabola and piecewise catenary theory is deduced respectively,and the suspender force calculation formula of suspension bridge suspender force based on measured main cable geometry parameters is obtained according to the stress state of joints.The calculation method of suspender force is compared with the finite element method,and the sensitivity of linear error and suspender force deviation is analyzed,and the accuracy and robustness of the proposed method are verified.(2)The reverse calculation method of main cable force of in-service suspension bridge is put forward.For the main cable with suspender area,the calculation method of horizontal force of main cable based on the measured shape of main cable and the fast iterative strategy are put forward,and the calculation formula of cable force at any position of main cable with suspender area is given.taking the sum of square deviation between the measured and theoretical shape of the main cable as the goal,an optimization algorithm based on the golden section method is developed to solve the problem of nonlinear parameter estimation of the main cable force.Numerical simulation experiments are carried out to verify the convergence,accuracy and robustness of the proposed calculation method of main cable force.(3)The fast measurement method of cable geometry of suspension bridge based on ground laser scanning is studied.The point cloud filtering,noise reduction and registration methods suitable for long-span suspension bridges in service are studied,and based on the geometric characteristics of suspension bridges,fast algorithms for extracting geometric parameters of main cable with suspender area and main cable geometry without suspender area are proposed respectively.(4)Based on the Osmanthus Bridge in Wushan County,the cable force calculation method and the main cable geometry acquisition method proposed in this thesis are applied in the real bridge test.The data acquisition results of the real bridge show that the ground laser scanning can capture the geometric parameters of the cable quickly and accurately,and the data acquisition efficiency is 4 times higher than that of the frequency method.The proposed cable force calculation method can accurately and reliably evaluate the cable force and cable force changes of the main cable and suspender of the in-service suspension bridge.