桩与土非线性耦合扭转振动特性分析

Analysis of Dynamic Behaviors of Pile-soil Nonlinear Coupling Torsional Vibration

在Novak边界层模型基础上,将桩周土分为非线性粘弹性内域和线弹性外域,采用随内域平均应变减小的等效剪切模量和增长的等效材料阻尼比近似考虑桩周土的非线性,并采用等效线性法对桩与土层耦合扭转振动进行了研究,得到了考虑桩-土动力相互作用的单桩桩顶扭转角及其扭转动力阻抗函数,然后通过算例对桩-土体系进行了扭转振动特性的参数分析。结果表明:桩顶激振扭转荷载的频率和幅值、外域土与桩的剪切波速比、内域土非线性范围以及桩长径比等因素对非线性土中单桩扭转动刚度和阻尼具有较大影响,所得结论为进一步研究桩-土-桥梁结构非线性动力相互作用机理提供了理论基础。

Based on the boundary model presented by Novak, the soil around the single pile was divided into two regions： the inner zone on nonlinear viscoelastic field and the outer zone on linear viscoelastic region. The soil nonlinearity can be considered approximately by using a reduced equivalent shear modulus and an increased equivalent material damping ratio with decrease of the average strain in the inner zone. By means of equivalent linearization method, torsional angle and torsional dynamic impedance function of single pile head with consideration of pile-soil interaction were deduced from studying pile-soil coupling torsional vibration. Parameters of dynamic behaviors of pile-soil system under torsional vibration were analyzed through an example. Results show that torsional dynamic stiffness and damping of single pile embedded in nonlinear soil depend on frequency and amplitude of dynamic load on the pile head, shear wave velocity ratio of pile and outer soil, theoretical foundation for inner nonlinear soil area and slenderness ratio of the pile. It provides mechanism of pile-soil-bridge structure nonlinear dynamic interaction.