近、远场地震下深水桥墩动力响应特性对比研究

Comparative study on the dynamic response feature of bridge pier in deep-water excited by near-fault and far-field earthquake ground motions

以某典型铁路深水桥梁等效单墩模型为对象,采用基于流固耦合理论的势流体计算方法,首次对近、远场地震作用下等效单墩结构振动特性及动力响应进行对比分析。结果表明,动水环境的存在会改变桥墩振动特性,随水深增加桥墩自振周期不断增大,30 m水深时第一阶周期增长率达10.4%。墩周动水压力呈抛物线型分布,近场地震下大于远场地震,二者差别随水深增加而增大。近、远场地震下桥墩结构的动力响应存在明显差别,较无水环境,近场地震下墩顶位移、墩底弯矩及剪力峰值分别增大34.5%、37.8%及51.3%;远场地震下三项指标分别增大17.0%、21.8%及40.0%,具有明显速度脉冲的近场地震下结构动力响应显著大于远场地震。具有速度脉冲的近场地震破坏能力更强,在近断层区深水桥梁抗震设计中应特别重视。

Taking the equivalent pier of a typical railway bridge built in deep-water as an example,the vibration characteristics and dynamic responses under near-fault and far-field earthquakes were contrasted by using the potential-based fluid method based on fluid-structure interaction theory.The results show that,the vibration characteristic of pier is changed due to the water around it.With the increase of the depth of water,the natural vibration period of pier becomes larger and the first period increases by 10.4% when the water depth is 30 m.The distribution of hydrodynamic pressure along the pier is in parabolic form,the pressure is larger by the near-fault earthquake than by the far-field and the difference becomes more obvious with the addition of water depth.There is also significant difference between the dynamic responses under near-fault and far-field earthquakes,in addition,the dynamic response under near-fault ground motions is greater than that under far-field earthquake.The diplacement at the top of pier,the moment and the shear force at the bottom of pier increase by 34.5%,37.8% and 51.3% respectively under near-fault earthquake;while these three indicators are 17.0%,21.8% and 40.0% for far-field earthquake.In summary,the destructive capacity of near-fault ground motions with obvious velocity pulse is far greater than that of far-field earthquake,so special attention should be paid to those bridges with piers surrounded by deep-water in near-fault zone.