深水桥墩地震响应离心振动台试验及数值模拟

Centrifuge shaking table test and numerical simulation on seismic response of deep-water bridge pier

为研究地震作用下深水桥墩的动力特性及动水压力分布规律,分别针对圆形截面桥墩和矩形截面桥墩开展了不同水深条件的离心振动台模型试验。将桥梁上部结构简化为质量块,桥墩固定在层状剪切箱底部,同时设计了侧限挡板,使得在激振过程中,只有桥墩底部发生相对运动,而水体保持相对静止。采用白噪声和4条具有不同频谱成分的地震波进行激振,并在此基础上开展数值模拟,验证动水附加质量方法是否适用于深水桥墩的动力响应分析。研究表明:水深增大后桥墩的模态频率明显减小,而桥墩模态阻尼略微增大;动水压力对桥墩地震响应的影响规律与地震波频率分布特征和深水环境下桥墩模态频率相关;试验测得的动水压力和桥墩表面的加速度呈现高度线性相关,且基本与荷载频率和桥墩的运动形式无关;试验与数值分析结果表明,动水附加质量方法能够较好地模拟地震引起的动水效应。

To investigate the dynamic behavior and hydrodynamic pressure of deep-water bridge piers under earthquake excitation,centrifugal shaking table model tests were carried out for circular bridge piers and rectangular bridge piers with different water depths.The upper structure of the bridge was simplified as a lumped mass,and the piers were fixed at the bottom of the layered shear box.A confining baffle was designed to ensure that during the excitation,only the bottom of the pier would move relatively,while the water remained relatively static.Five waves were adopted for excitation including white noise.On this basis,numerical simulation was carried out to further verify the viability of added mass method for the analysis of deep-water bridge piers.The results indicate that the increase in water depth can lead to a decrease in the modal frequency and a slight increase in the modal damping of the bridge pier;the influence of the hydrodynamic pressure on the seismic response of the bridge pier is related to the spectral contents of the seismic wave and the modal frequency of the bridge pier.The measured hydrodynamic pressure has a highly linear relationship with the acceleration of the bridge pier and is almost independent of the load frequency and the motion form of the bridge pier.The experimental and numerical results show that the added mass method can appropriately simulate the hydrodynamic effect caused by earthquakes.