强震下深水桥梁群桩基础非线性动力特性与设计方法研究

Pile group foundations as the supporting system of the bridge in deep water have been widely used in practice. However, the working behavior and seismic safety of the bridge pile groups in deep water during strong earthquakes have not been fully validated. In response to the present situation that investigations on the dynamic behavior of bridge pile groups in deep water during strong earthquakes are obviously insufficient, the following studies will be systematically carried out. A nonlinear dynamic constitutive model of soil-pile that can consider the degradation of pile-surrounding soil strength and stiffness during strong earthquakes is proposed. And then, based on this improved model, considering the inertial and kinematic response and the hydrodynamic effect, the dynamic BNWF coupling method for the bridge pile groups in deep water is further established. Based on the elasto-plastic bounding surface model of the clay, a three-dimensional numerical method for structure-pile-soil-water dynamic interaction is established. Furtherly, centrifuge shaking table tests for the nonlinear dynamic response of the bridge pile groups in deep water during strong earthquakes are conducted as well. The influences of seismic input parameters, hydrodynamic, superstructure and foundation types on the dynamic internal force and deformation behavior of pile group foundations are therefore comprehensively investigated. On this basis, the engineering practical pseudo-static design method for the bridge pile groups in deep water is further proposed, and thus provides the theoretical basis for the seismic design of deep-water bridge across river and ocean, which is also instructive for improving the feasibility and safety of the bridge pile group foundations in deep water.

群桩基础作为深水桥梁的支承体系已在工程实践中得到了广泛应用，然而，强震下深水桥梁群桩基础的工作性状以及地震安全性尚未得到充分检验。针对强震下深水桥梁群桩基础动力特性的研究存在明显不足的现状，系统地开展以下几个方面的研究。提出一种能够考虑强震下桩周土强度和刚度退化的桩土动力非线性本构模型；基于该改进模型，考虑惯性和运动响应以及动水力的影响，建立起深水桥梁群桩基础的动力BNWF耦合分析方法；基于弹塑性边界面模型，建立桥梁结构–群桩–土体–水体动力相互作用的三维数值分析方法；结合强震下深水桥梁群桩基础动力特性的离心振动台试验结果，全面揭示地震动输入、动水力、上部结构以及基础型式等对群桩基础动内力和变形特性的影响规律。并在此基础上进一步提出适合于工程实用的群桩基础拟静力设计方法，为跨江海深水桥梁的抗震设计提供充实的理论基础，对于提高深水桥梁群桩基础的可行性和安全性具有指导意义。

群桩基础作为深水桥梁的支承体系已在工程实践中得到了广泛应用，然而，强震下深水桥梁群桩基础的工作性状以及地震安全性尚未得到充分检验。针对强震下深水桥梁群桩基础动力特性的研究存在明显不足的现状，结合我国重大工程的实际需求开展相关研究工作，取得的重要成果如下。.（1）基于双曲线型p-y骨干曲线，引入土体刚度随桩周土体平均剪应变退化的假定，提出了描述桩土水平荷载-变形关系的非线性p-y滞回圈模型，用于模拟桩侧土的非线性、桩土分离和土体刚度退化等问题。（2）建立了桩-土-结构动力相互作用耦合分析方法，将上述的动力非线性p-y滞回圈整合至OpenSees软件，实现了强震下桩-土-结构的动力非线性分析，显著提高了计算效率。（3）针对桥墩-水体相互作用三维数值模拟计算量大，效率低的问题，针对矩形空心桥墩，推导了其在地震作用下的动水力精确解，给出了动水附加质量的简化公式，建立了桥墩-水体-群桩-土体相互作用三维数值模方法。（4）开展了冲刷条件下桥梁群桩基础地震响应的离心振动台试验，揭示了地震动输入、冲刷深度、上部结构以及群桩效应等对群桩动内力和变形特性的影响规律，发现冲刷改变了桥梁和场地周期特征，并导致桥梁破坏模式可能由设计时的墩底转移到桩身。（5）基于被动群桩模型提出了适合于工程实用的群桩基础拟静力设计方法，考虑了惯性力和运动响应，在水平荷载和土体最大位移共同作用下，采用拟静力方法分析群桩的内力和变形特性，通过动力离心模型试验验证了所提出的拟静力方法的合理性。.上述研究成果有助于深入认识强震下深水桥梁群桩基础的非线性动力特性，可为桥梁抗震设计提供重要的理论基础，对于提高深水桥梁群桩基础的可行性和安全性具有指导意义，所提出的工程实用简化计算方法也可为桥梁抗震规范的修订提供参考依据。