地震区跨活动断层桥梁桩基动力时程响应分析

为了研究强震区桥梁跨活动断层时，桩基在地震中的动力响应，以海文大桥为工程背景，利用Midas GTS有限元软件建立其强震区桩-海床岩土体-断层耦合作用的数值模型，研究不同强度(0.20g～0.60g)的50年超越概率为10%的地震波(后文简称5010地震波)作用下，桥梁桩基加速度、位移、弯矩及剪力的动力时程响应特性。结果表明：上部大厚度松散土体对桩身加速度有放大及滤波作用，而基岩对桩身加速度几乎不产生作用；断层上、下盘桩基础的桩顶水平位移随输入地震动强度的增大而增大，但达到振幅的时刻一致；上、下盘桩基础桩顶竖向位移时程响应都在50 s以后产生永久沉降；桩身最大弯矩截面处时程响应均在40 s以后产生永久弯矩；应重点考虑上部覆盖层软硬土体界面和基岩界面的抗弯承载力设计，及桩顶和基岩面附近的抗剪承载力设计；上盘桩基础按桩身加速度、弯矩、桩顶水平位移等动参数控制设计，下盘桩基础按动剪应力控制设计。

Dynamic time\|history response of bridge pile foundations crossing active faults in seismic regions

Taking the Haven Bridge as the engineering background, we studied the dynamic response of pile foundations during earthquakes in the case where bridges cross active faults in strong seismic zones. The finite element software Midas GTS was applied to establish a numerical model of the pile-seabed rock-fault coupling action in areas characterized by strong earthquakes. The dynamic time-history response characteristics of the acceleration, displacement, bending moment, and shear force of the bridge pile foundation under the action of 5010 seismic wave with different intensities (0.20g-0.60g) were investigated. The results showed that the upper loose soil with a large thickness had an amplifying and filtering effect on the acceleration of the pile body, while the bedrock had a largely negligible effect. The horizontal displacement at the top of the pile foundation in the hanging and foot walls of the fault increased with the increase in the input seismic intensity, while the moment of reaching amplitude was consistent. The permanent settlement appeared 50 s after the vertical displacement time-history response at the top of the pile foundation in the hanging and foot walls, and the permanent bending moment appeared 40 s after the time-history response at the maximum bending moment section of the pile. Emphasis must be on appropriately designing the flexural capacity at the bedrock interface and at the interface between the soft and hard soils of the upper overburden as well as on designing the shear capacity near the pile top and the bedrock face. The pile foundation of the hanging wall should be designed on the basis of the dynamic parameters, such as the pile acceleration, bending moment, and horizontal displacement at the pile top, while the pile foundation of the foot wall should be designed on the basis of the dynamic shear stress.