装配式圆形桥墩海啸冲击力试验

Experiment of Tsunami Impact Force on Prefabricated Circular Pier

为研究海啸涌波下装配式圆形桥墩冲击力的特点以得到海啸冲击力的简化计算方法,在水槽中利用溃坝波模拟海啸涌波,开展不同来流波高和初始水深的模型试验。分析溃坝波的波前形态、波前坡度以及波前上游波动状况随来流波高和初始水深的变化规律,对比不同来流波高、初始水深下圆形桥墩的剪力和弯矩时程曲线,讨论来流波高和初始水深对似平稳段剪力均值和弯矩均值,以及冲击全过程剪力和弯矩最大值的影响,得到圆形桥墩似平稳段的剪力系数和弯矩系数,以及剪力和弯矩冲击系数随来流波高和初始水深的变化规律。研究结果表明:除临界破碎波外,溃坝波的波前坡度随着来流波高与初始水深之比的增大而减小;来流波高与初始水深之比不小于1时,波前上游液面无上下波动,力和弯矩的时程曲线无振荡段,且剪力和弯矩的最大值位于似平稳段,对应的量纲一的系数C_r和M_r较小,分别为0.75～1.40和1.12～2.50;来流波高与初始水深之比小于1时,波前上游液面有上下波动,力和弯矩的时程曲线有振荡段,且剪力和弯矩的最大值位于冲击段,对应的C_r和M_r较大,分别为1.46～5.87和1.88～9.86;对相同来流波高而言,随初始水深的增加,似平稳段自由液面效应逐渐减小,力臂量纲一的系数K_r逐渐减小,初始水深由2 cm增加到8 cm和14 cm时,K_r降幅均值分别为21.8%和29.7%;基于试验结果提出了装配式圆形桥墩海啸波作用下剪力和弯矩最大值的计算方法,并给出了各项参数的取值,可为其快速计算提供参考。

A series of model tests with different tsunami wave heights and initial water depths, which were simulated using dam-break waves, were conducted in a flume to study the characteristics of the impact force acting on prefabricated circular piers and to obtain a convenient method for calculating tsunami impact forces. First, the variation of wavefront profile and wavefront slope and the fluctuation of upstream water surface with different wave heights and initial water depths were analyzed;subsequently, the time-history curves of the shear force and bending moment acting on circular piers were compared among cases with different wave heights and initial water depths. Moreover, the influences of the wave height and initial water depth on the averaged shear forces and bending moments in quasi-stable stage and on the maximal values of shear forces and bending moments during the entire impacting process were discussed. Accordingly, the laws of shear force coefficient and bending moment coefficient in quasi-stable stage and the variation of shear force impact coefficient and the corresponding bending moment coefficient with wave height and initial water depth were obtained. The results obtained are as follows. Excluding critical breaking wave, the slope of the wavefront decreases with the ratio of the wave height to the initial water depth;When the ratio of the wave height to the initial water depth is not less than 1, the upstream water surface does not fluctuate, and the shear force and bending moment time-history curves also do not fluctuate. The maximal values of the shear force and bending moment are observed at the quasi-stable stage;accordingly, their dimensionless coefficients C_r and M_r have relatively smaller values, i.e., 0.75-1.40 and 1.12-2.50, respectively. When the ratio of the wave height to the initial water depth is lesser than 1, the upstream water surface fluctuates, and the shear force and bending moment time-history curves also fluctuate. The maximal values of the shear force and bending moment are observed at the impulsive stage;accordingly, their dimensionless coefficients C_r and M_r have relatively larger values, i.e., 1.46-5.87 and 1.88-9.86, respectively;With the increase in the initial water depth, the free surface effect and the dimensionless coefficient of the arm of force Kr decrease gradually, i.e., when the initial water depth increases to 8 cm and 14 cm from 2 cm, the average decrements of K_r are 21.8% and 29.7%, respectively;The calculation methods of the shear force and bending moment, including the suggested values of related parameters, are recommended to facilitate the rapid calculation of tsunami impact forces on the prefabricated circular piers.