竖向地震作用下桥梁结构的瞬态波响应分析

Transient wave response analysis of a bridge under vertical earthquakes

竖向地震引起的剧烈地面运动可能导致桥梁结构的损坏。针对竖向地震作用下双跨连续梁桥的瞬态动力学问题,考虑波动效应,应用瞬态波特征函数法求解了地震过程中桥梁结构的瞬态波响应理论解。通过实例分析,描述了桥墩中轴向波和桥跨结构中弯曲波的传播、反射、相互作用和波碰撞等现象。计算结果表明,不同的竖向地震动与水平地震动的比值会引起桥梁响应特征的明显改变。随着比值的增大,桥梁响应特征的改变主要表现为:①接触力的变化幅度增大,出现更大的接触力,加剧支座的损坏可能性;②出现了更低的接触力,甚至零接触力,大大增加了桥跨结构与桥墩相对滑动的可能性;③使原本整体处于受压状态的桥墩中出现了拉应力,拉应力有可能超过混凝土的抗拉强度,并使桥墩出现了拉-压交变应力,使得桥墩底部处于恶劣的应力状态;④桥跨中部向上的最大动挠度超过了两端,也就是桥跨结构被抛起的可能性增大。

Under the strong ground motion excited by vertical earthquakes, structural damage may occur in bridges. Based on the model of a single-pier and two-span continuous bridge under vertical earthquakes, the transient wave effect approach was presented to solve the transient responses of the bridge . The numerical results showed that the propagations of stress wave including reflection, interaction and wave impacts throughout the pier and the girders can be depicted. By comparison of the seismic responses of the bridge with different vertical-to-horizontal peak acceleration ratio, it was shown that the responses characteristics change obviously with increase in vertical-to-horizontal peak acceleration ratio; four main variations of response characteristics may occur; firstly, the fluctuating of contact force between the superstructure and the pier increases and the larger contact force may damage bridge bearing; secondly, the smaller contact force and even the zero contact force may largely increase the possibility of the sliding between the superstructure and the pier; thirdly, the tensile stress even exceeding the tensile strength of concrete takes place in the pier originally being in whole compressed stress state with the small ratio, and the alternating tensile-compression stress makes the pier bottom in a dangerous stress state; finally, the maximum dynamic deflection at the middle of the superstructure exceeds ones at both ends, the possibility of superstructure＇s jumping up increases.