| Long-span cable-stayed bridges and suspension bridges have become typical representatives of modern large bridges because of their strong spanning capacity.They are key control projects on the lifeline of the national road network.A lot of researches and engineering practices show that the cable-stayed cable and cross-tie,sling and vibration damping frame are connected to form a coupled cable strut system,and the coupled cable strut system and damper are connected to form a coupled cable strut-damper system,which can achieve the purpose of cable vibration reduction.The study on the vibration mechanism of the coupled cable strut system and the coupled cable strut-damper system is the critical content of the disaster formation and prediction research of cable-stayed bridges and suspension bridges.To deeply understand the actual dynamic behavior of the two systems,grasp the interaction rules of the cross-tie,damping frame and damper,analyze the influence of various parameters on the vibration reduction effect of the system,and further provide a theoretical basis for the vibration reduction design of cable and sling,the linear free vibration characteristics of the coupled multi-layer cable strut system and the coupled multi-layer cable strut-damper system were studied through theoretical derivation,finite element simulation analysis and field experiment.Based on the coupled two-layer cable strut system and the coupled two-layer cable strut-damper system model,an identification method of the unknown parameters of the coupled sling was proposed.The nonlinear free vibration and forced vibration characteristics of coupled two-layer and multi-layer long cable strut systems were studied.The main research contents are as follows:(1)For the free vibration problem of the cable strut structure with cross-tie and damping frame,a linear vibration model of the coupled multi-layer cable strut system considering the influence of bending stiffness of the cable strut was constructed.The characteristic equation of the unequal-length coupled multi-layer cable strut system was established and solved,which was verified by finite element simulation analysis and field experiment.Then taking the slings of the Aizhai Suspension Bridge and the cables of the Jitimen Cable-stayed Bridge as the analysis objects,the effects of the parameters were analyzed from the perspectives of free vibration frequency and mode integrity,and the damping effects of cross-tie and damping frame were intensely studied.(2)The effect of the damper was further considered,and a linear vibration model of the coupled multi-layer cable strut-damper system considering the bending stiffness was constructed.The free vibration characteristics of the system were obtained by solving the complex characteristic equation of the system,and the correctness of the theoretical method was verified by finite element simulation analysis and field experiment.Taking the sling-damper system of the Aizhai Suspension Bridge and the cable-damper system of the Honghe Cable-stayed Bridge as the analysis objects,the effects of the parameters were analyzed from the perspectives of free vibration frequency,damping ratio and mode integrity.The interactional condition of the damper,cross-tie and damping frame were intensely studied.(3)Taking the coupled two-layer cable strut system and the coupled two-layer cable strut-damper system as the research object,an identification algorithm based on optimization theory was proposed to identify the unknown parameters of the system,including cable-strut parameters,coupled parameters and damper parameters.A high-precision and efficient parameter identification program was developed.The feasibility of the identification method was verified by the example of the coupled sling of the Aizhai Suspension Bridge and field experiment,and the process was applied to the parameters identification of the cable force and bending stiffness of the slings of the Shatian Bridge.(4)For the nonlinear free vibration problem of a long cable strut in coupled cable strut system,taking the coupled two-layer long cable strut system as the research object,the nonlinear free vibration differential equations of the coupled system were established based on the Hamilton principle and Galerkin method and solved by using the method of multiple scales.The amplitude time curves of the system with and without damping were obtained by the fourth-order Lundgren-Kutta method according to the actual project.The free vibration characteristics of the cable and cross-tie in the system were studied when 2:1 resonance,sum resonance and difference resonance occurred.(5)The coupled long cable strut system was further expanded from double-layer to multi-layer,which investigated the possible internal resonance types of the system.The free vibration characteristics of the cable,which resonated with different numbers of cross-ties,were studied by analytical and numerical analysis methods.The displacement time curves of the system with and without damping were obtained,which revealed the energy transfer rule between the cable and cross-tie when the cable resonated with different numbers of cross-ties.(6)Taking the coupled multi-layer long cable strut system considering the action of lateral external load as the research object,the nonlinear forced vibration differential equations were established and solved.Combined with engineering examples,the forced vibration characteristics of coupled cable strut system under the occurrence of 2:1 resonance or sum resonance were numerically analyzed.The amplitude-excitation frequency response curves and amplitude-excitation amplitude response curves of the cable and the cross-tie in the system were obtained.The forced vibration characteristics of coupled long cable strut system were studied when the internal resonance occurred and the influence rule of different excitation parameters on the vibration of system components was investigated. |
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