Analysis,Evaluation,and Identification Of Cable Bridge Structure Based On Long-term Monitoring

The development of long-span bridges is very fast.At the same time,the safety and durability problems of structures in operation period are also increasingly prominent and received unprecedented attention.Besides the technical measures for design and construction stage,the operation health monitoring system has been implemented on most new large bridges.The long-term monitoring system provides abundant operational environment and structural response data for structural safety and durability evaluation.It is an important prerequisite for the purpose of health monitoring to analyze and make full use of the monitoring data of the bridge,to reveal the internal relationship between the working state of the structure and the monitoring response,and to establish an accurate and efficient evaluation system.By deeply analyzing and making full use of bridge monitoring data,the internal relationship between structural working state and monitoring response was revealed,then an accurate and efficient evaluation system was established.It has important engineering significance and scientific research value for bridge health diagnosis,and safety and durability evaluation of bridges.Cable-stayed bridge and suspension bridge are the main types of modern large-scale bridges.Cables(stayed-cable,hanger,main cable)are the most important structures of the bearing system in bridges.The cables and hangers have wide spatial distribution on the whole bridge structure.Cable tension directly reflects the stress and working state of the whole bridge structure.Therefore,cable tension monitoring is an important object of long-term monitoring system for bridge structure.This paper is based on the actual project,combined with the main characteristics of bridge structure.By means of real bridge monitoring,numerical simulation and model test,evaluation and identification problems of long-term monitoring of bridge structure are discussed.The innovative results have been obtained in cable tension evaluation with statistical model based on monitoring data,the double-direction vibration control of the cable,and the vehicle load identification based on the monitoring cable tension.The main contents are as follows:(1)The FE-model was optimized according to the measured static and dynamic characteristics of the bridge.For the natural frequency and the cable force of the bridge,response surface method and iterative optimization method are adopted to correct the main parameters of the model.The accuracy of the correction model is verified by comparing target with the measured results.(2)Based on long-term temperature monitoring data,a statistical analysis model of bridge site and structure temperature is first established.Then the extreme value analysis is applied to establish the extreme temperature distribution model.On this basis,the basic temperature values in the bridge operation period are analyzed and evaluated.After that,the spatial and temporal distribution characteristics and extreme value characteristics of temperature difference of steel box girder are discussed.Through finite element simulation,the cross-section stress of steel box girder under the effect of temperature difference between the measured standard value and the existing design value is compared.(3)Firstly,the main components of monitoring operation cable tension data are analyzed.The influence of temperature,vehicle and other factors on operation cable tension is separated.Based on statistical analysis,the relationship between static cable tension and temperature correlation model is established,and a standard cable tension independent of temperature is built.A statistical analysis model of standard cable force is established.And evaluation method for cable tension based on standard cable tension distribution is also proposed.Subsequently,taking the measured data as an example,the cable tension evaluation experiment is carried out.On this basis,the static cable tension under damage condition is simulated by the finite element model.The cable tension sampling inspection and the evaluation method based on the standard cable tension distribution characteristic inspection are adopted respectively.The feasibility of damage warning method based on monitoring cable tension is discussed.(4)The effect of wind and other dynamic loads will cause large vibration of cables,reducing the safety and durability of cables.In view of the shortcomings of the existing methods of vibration reduction for stay cables,two vibration control schemes are put forward in this paper:the cable space layout vibration reduction design and the sleeve vibration reduction scheme.For the cable space layout vibration reduction design,vibration characteristic equation of unequal length parallel cables with inter cable connections is derived.The efficiency ratio of energy dissipation is proposed as the evaluation index of cable space layout vibration reduction.The influence of main parameters in vibration reduction design on vibration damping performance is studied by numerical simulation.On this basis,the zero-order optimization algorithm is used to optimize the special cables.The response surface method is used to optimize the main design parameters for the sleeve vibration reduction scheme.Through the finite element simulation,the effect of two kinds of vibration reduction schemes on the in-plane and out-plane vibration reduction of cable is verified.(5)Automatic identification method of vehicle speed and weight based on monitoring cable tension is discussed.Firstly,a vehicle-bridge coupling dynamic analysis model is established.The influence of vehicle parameters and road roughness on the dynamic response of cables is studied.A vehicle-bridge coupled dynamic analysis method for random traffic flow based on the joint distribution of measured vehicle and weight is developed.On this basis,the cable tension response characteristics of vehicles are extracted through EMD and wavelet analysis.Load identification method of cable-stayed bridge based on monitoring cable force and neural network technology is discussed.Vehicle identification tests are carried out with actual monitoring cable forces,and the actual monitoring cable tension is tested.(6)Based on the structural characteristics of the suspension bridge,the damage identification method of suspension bridge according to cable tension,deflection and vibration frequency is discussed.Oriented to the practical conditions of damage identification,a network learning sample with different damage conditions is built by numerical simulation.The damage identification test is carried out by using model data,and the damage identification method of suspension bridge based on BP network is discussed.