风和车流作用下悬索桥纵向减振及阻尼器参数优化

Longitudinal vibration mitigation of a suspension bridge under wind and traffic loads and optimization of fluid viscous damper

为了对运营阶段风和车流作用下大跨公路悬索桥进行纵向减振并对阻尼器进行参数优化,通过在已有的风‑车‑桥耦合振动分析系统中引入液体黏滞阻尼器单元,建立了随机风‑车流‑悬索桥分析系统。以一座典型山区大跨悬索桥为工程背景,采用建立的分析系统对比分析了布置阻尼器前后加劲梁在随机风和车流作用下纵向振动的时频特性。在此基础上,进行了阻尼器的参数敏感性分析,研究了阻尼器参数的不同取值对加劲梁位移和塔底内力的影响规律。以优化全桥结构受力、降低纵向振动响应为目标,采用响应面法对阻尼器的参数进行了优化分析。研究表明:对于风、车流荷载单独以及联合作用下的加劲梁纵向振动,阻尼器均能有效降低纵向振动的幅值;但能否降低纵向振动的频率取决于纵向振动中主频的成分。设置液体黏滞阻尼器后,风、车流荷载单独或者联合作用下,加劲梁纵向位移极值和纵向累积位移均随着阻尼系数的增大和速度指数的减小呈减小趋势。此外,不同荷载工况下液体黏滞阻尼器对塔底纵向弯矩的影响规律不同:在风荷载单独作用下,阻尼器会增加塔底纵向弯矩。优化后的液体黏滞阻尼器参数建议取值区间为:阻尼系数宜取500-700 kN/(m/s)^(α),速度指数宜取0.3-0.5。

In order to mitigate the longitudinal vibration of the long-span highway suspension bridge under combined wind and traffic loads during normal operation,an analytical platform of wind-traffic-suspension was established by introducing the fluid viscous damper(FVD)into the existing wind-vehicle-bridge coupled dynamic system.Using a typical long-span suspension bridge in mountain area as an engineering background,the established analytical platform was applied to investigate the time-frequency characteristics of the longitudinal vibration of the stiffening girder under stochastic wind and traffic loads.The time-frequency characteristics in the cases with and without implementing the FVD was compared.Subsequently,sensitivity analysis was carried out to study the influence of the FVD on the displacement response of the stiffening girder and the tower bending moment.The response surface method was employed to seek the optimum FVD parameters with the goal to optimize the structural mechanical behaviors and reduce the girder’s longitudinal vibration under stochastic wind and traffic loads.The results indicate that after implementing the FVD,the amplitude of the longitudinal vibration of the stiffening girder under various loading scenarios can be mitigated,while whether the vibration frequency can be reduced depends on the dominant frequencies of the longitudinal vibration.In addition,both the maximum longitudinal displacement and the longitudinal cumulative displacement of the stiffening girder under wind only,traffic only or the combined wind and traffic loading scenarios can be reduced effectively after the implementation of the FVD,and the performance of the FVD in mitigating the longitudinal vibration increases with larger damping coefficient and smaller velocity exponent.Furthermore,the influence of the FVD on the tower bending moment depends on the loading type and the use of the FVD could enlarge the tower bending moment under wind-only loading scenario.The optimization result shows that the optimum damping coefficient ranges from 500 to 700 kN/(m/s)^(α),and the optimum velocity exponent ranges from 0.3 to 0.5.