脉动风和车辆荷载联合作用下中央扣对悬索桥吊索疲劳损伤的影响

Effect of central clamps on fatigue damage of suspenders of suspension bridge under joint action of fluctuating wind and vehicle loads

以杭瑞洞庭大桥为研究对象,建立设置中央扣和无中央扣的大跨度悬索桥有限元模型,研究中央扣对悬索桥跨中短吊索疲劳损伤的影响。首先,采用谐波合成法生成大桥桥址处的脉动风场,采用Monte Carlo法模拟随机车流样本,基于ANSYS软件建立风-车-桥耦合振动分析模型,分析桥梁结构在脉动风和车辆荷载单独与联合作用下的动力响应;其次,采用雨流计数法统计跨中短吊索的应力时程,得到吊索的应力幅值、应力均值和循环次数;最后,基于Miner损伤线性累计理论分析中央扣对跨中短吊索的等效总应力幅值和疲劳损伤度的影响。研究结果表明:中央扣对悬索桥竖弯刚度影响较小,但会提高悬索桥的纵飘刚度和反对称扭转刚度,显著减小荷载作用下缆梁相对位移和跨中短吊索的弯曲应力;中央扣不会改变脉动风荷载作用下跨中短吊索的缆梁相对运动特性,但会改变车辆荷载作用下跨中短吊索的缆梁相对运动特性,并显著降低缆梁相对位移对车速的敏感性;在脉动风和车辆荷载联合作用下,跨中短吊索的等效总应力幅值小于脉动风和车辆荷载单独作用下等效应力幅值的叠加值;在脉动风和车辆荷载联合作用下,中央扣会显著减小跨中短吊索尤其是靠近中央扣位置处吊索的等效总应力幅值和疲劳损伤度。因此,中央扣可以有效提高悬索桥跨中短吊索的疲劳寿命。

The Hangrui Dongting Bridge was taken as study object to investigate the effect of the central clamp on the fatigue damage of short suspenders at the midspan of a suspension bridge via two finite element models with and without central clamps.Firstly,the fluctuating wind speed at the bridge site was simulated using the weighted amplitude wave superposition method.The sample of random traffic flow was simulated using the Monte Carlo approach.The analysis model of wind−vehicle−bridge coupling vibration was established based on ANSYS software to obtain the dynamic responses of the bridge under the action of fluctuating wind and vehicle loads which were alone and combined.Secondly,the program of the rain-flow counting procedure was used to get the equivalent total stress amplitude,the mean stress and the cycle times of short suspenders.Finally,the effect of the central clamp on the equivalent total stress amplitude and fatigue damage of short suspenders was finally quantitatively studied based on the Miner linear cumulative damage theory.The results show that the central clamp has little effect on the vertical stiffness of the suspension bridge,but improves its longitudinal and anti-symmetrical torsional stiffness.Meanwhile,the central clamp significantly reduces the cable-girder relative movement and the bending stress of short suspenders at the midspan under loads.The central clamp does not change the cable-girder relative movement characteristic under fluctuating wind load,but it changes this characteristic under vehicle load and significantly reduces the sensitivity of cable-girder relative movement to the vehicle speed.The equivalent total stress amplitude of short suspenders at the midspan under the action of fluctuating wind and vehicle loads is smaller than the superposition value of the equivalent stress amplitudes caused by fluctuating wind load and vehicle load alone.The central clamp dramatically reduces the equivalent total stress amplitude and fatigue damage of short suspenders at the midspan under fluctuating wind and vehicle loads,particularly for short suspenders near the central clamp.Therefore,the central clamp can effectively improve the fatigue life of short suspenders at the midspan of the suspension bridge.