泰州大桥北塔群桩基础三维动力非线性抗震计算研究

RESEARCH ON 3D DYNAMIC NONLINEAR ASEISMIC CALCULATION OF PILE GROUP FOUNDATION OF NORTH TOWER OF TAIZHOU BRIDGE

采用三维八节点等参单元与无限元相组合的数值方法进行土和大桥桩基的地震反应分析。基于ABAQUS软件,建立"承台-群桩-土体系统"的大型三维非线性时域地震动力反应分析的弹塑性模型与相应的计算方法。承台和桩采用混凝土损伤塑性模型,土体采用传统莫尔-库仑屈服准则的弹塑性模型。考虑承台和大直径超长钻孔灌注桩的天然自重、江床浅部松散砂性土层部分振动液化等不利因素对桩基础承载能力的影响。提出静、动力统一的黏弹性无限元边界概念,采用四CPU并行计算得到"承台-群桩-土体系统"同时承受竖向静载荷和水平动载联合作用时,群桩的动轴力、动剪力和动弯矩,桩周摩阻力和桩侧与桩周土体的接触压强等对设计和施工具有参考价值的成果,进而对大桥桩基的抗震性能有比较全面和深入的认识。

The coupling numerical method, 8-node three-dimensional isoparametric element with infinite element, was applied to the seismic response analysis of soil and bridge pile foundation. Based on the software of ABAQUS, the study sets up the corresponding calculation method and the great elastoplastic model of threedimensional nonlinear time-history seismic dynamic response analysis concerning pile cap-pile group-soil system. The concrete damaged plasticity model was used for pile cap and pile, and the elastoplastic model of traditional Mohr-Coulomb yield criterion for soil. The unfavorable factors, which influence the bearing capacity of pile foundation, are taken into account, such as the natural self-weight of pile cap and large-diameter super-long bored pile, and the seismic liquefaction of saturated loose sand layer of shallow-buried river-bed around the bridge-pile construction site. The study puts forward the conception of unified static and dynamic viscoelastic infinite boundary. Under the static and horizontal vibration loads applied to pile cap-pile group-soil system at the same time, what have been obtained by 4 CPUS＂ parallel calculation are the dynamic axial force, shear force and moment of pile group, the side friction and the contact pressure between pile shaft and the soil around pile, and so on. These are valuable results for the design and calculation. Furthermore, the calculation results give out anoverall and deep understanding about the aseismic performance of bridge pile foundation.