| Cable is the key component of bridge,and its service environment is harsh.It is of great significance to accurately detect and evaluate its safety state.Key technologies of detection and evaluation for cable state were focused on.Studies were mainly carried out from four aspects,including accurate detection method for tension of short cable,nondestructive detection method for broken wire of cable,climbing technology and equipment for unmanned cable detection,safety evaluation method and system for cable state.Main study work,results and conclusions were as follows:(1)Aiming at the problems of low efficiency,high cost and low accuracy of cable force measurement by conventional frequency method and Jack method,a cable force calculation method based on effective calculation length was proposed.In view of large influence of shock absorber on boundary conditions of short cable and large error of short cable force measured by conventional methods,a calculation method of equivalent length for short cable considering influence of shock absorber was proposed.Additional mass block was arranged in cable,first-order natural frequency of cable before and after additional mass block was considered,calculation formula of effective length for short cable with additional mass block was deduced,and accurate calculation method for cable force of short cable was established.Actual bridge test results show that,compared with frequency method specified in code,deviation between cable force calculation results and theoretical value of the proposed method was small,which can effectively improve the accuracy of short cable force test.(2)Aiming at the problem that conventional windowing detection method has great damage to cable structure,a nondestructive detection method of cable broken wire based on vibration parameters was proposed.Finite element model of intact simply supported beam with 6 degrees of freedom nodes was simulated as the finite element model of intact cable,and finite element model of space cable element with crack which has 12 degrees of freedom was established.Quantitative method of cable body damage based on change of natural frequency was proposed,calculation formula of cable cross-sectional area reduction rate was deduced,and damage location method of cable body based on vibration mode curvature was established.Laboratory test results show that the proposed damage degree quantitative method and damage location method can get the results which were consistent with real damage situation,and the damage quantitative identification error was less than 1%.(3)Aiming at the problems of high risk,low efficiency and high cost for manual detection of cable safety state,cable unmanned detection technology and equipment equipped with climbing technology were studied.The problem of autonomous improvement of unmanned bridge cable state detection robot was solved,and the autonomous ability of robot in control,perception and detection was improved.The specific design schemes of power management module,position measurement system,motor drive system,control strategy and redundant control system in cable detection robot system were proposed,and the apparent image acquisition system and vibration test system of cable were developed.Prototype of cable unmanned detection robot was developed and applied to cable detection of actual cable bridges,which can accurately identify apparent diseases and vibration frequencies of cable.(4)Considering that there were many index factors influencing the overall safety state of cable,a cable safety state evaluation method considering multiple indexes was proposed.A single-level cable state evaluation system with cable force state,damaged protective layer,broken wire or corrosion of cable body and corrosion of anchor head as indexes was established,and weight of each index was determined according to uncertainty analytic hierarchy process.Aiming at the main influencing factors of each index in a single level,an index system considering multilevel and multi factors was established,and the evaluation criteria of each index in evaluation system were put forward.According to the established single-level and multi-level cable safety state evaluation system,calculation formula of cable safety state and classification standard of cable safety grade were put forward.(5)In order to monitor the safety status and damage of cables in real time,design function and system framework of cable bridge safety status evaluation system were proposed.Steel box suspender arch bridge Dafengjiang bridge with a clear span of 120 m was taken as an engineering background,its health monitoring system was developed,which integrates the key technologies of high-precision detection and evaluation of cables proposed in this paper.Based on suspender monitoring sub module and suspender evaluation sub module established in health monitoring system,automatic monitoring for suspender cable force and damage state of Dafengjiang bridge and automatic evaluation of cable safety state were realized.Practical application results show that suspender and cable of Dafengjiang bridge were in normal condition and have certain safety reserves,timeliness of cable safety condition monitoring and evaluation was improved by the developed monitoring system effectively,and it is conducive to the management of bridge life cycle data. |
