侧阻附加弯矩对桥梁桩基水平承载力影响研究

为研究桩身被动侧竖向摩阻力对大直径桥梁基桩的水平承载特性影响,首先在抗力矩概念基础上分别建立任意桩身横截面竖向侧摩阻力产生的附加弯矩计算公式及其影响下的桩身单元受力微分表达式。基于传递矩阵法及Laplace正逆变换,分别得出考虑侧阻附加弯矩影响时桩身弹性段、塑性段的传递矩阵系数解。结合推导的桩端水平阻力本构模型和给定的迭代求解方法,进而得出考虑桩侧竖向摩阻力影响的桥梁基桩桩身响应解。通过试验对比验证了本文方法的合理性,证明了桩侧竖向侧摩阻力所产生的附加弯矩对桩基水平承载力的影响非常显著。最后开展了附加弯矩参数影响分析,结果表明:不同τ-s曲线作用时桩身最大变形降低幅度变化规律均类似;桩身最大变形降低幅度随着桩侧摩阻力τ-s曲线极限值τu的增加、临界位移su的减小而增加;当长径比Lb/d≥4时,可忽略桩端水平阻力的影响;当Lb/d≥10时,可忽略侧阻附加弯矩效应的影响;长径比相同时,桩径越大,相应的初始阶段最大位移降低幅度也越大。

Additional Moment Effect Induced by Shaft Resistance on Lateral Bearing Capacity of Bridge Pile Foundation

To analyze the effect of skin friction along the passive side on the lateral bearing capacity of large diameter pile foundation of bridge,the calculation formula of the additional moment caused by vertical shaft resistance for each cross-section of pile shaft is established by means of the conception of resisting moment,and the differential expression of pile element stress subjected to the effect is obtained.Furthermore,based on the transfer matrix method and Laplace transformation,this paper deduces the solutions of transfer matrix coefficients for pile in elastic and plastic state and obtains the horizontal responses of bridge pile foundation considering the influence of additional moment induced by vertical shaft resistance on the basis of the derived constitutive model of horizontal resistance at pile end and the given iteration method. The test result verifies the proposed approach and shows that the influence of resisting moment on lateral bearing capacity is significant. Finally,parametric study of additional moment is performed and the results reveal that the decreasing ratio of maximum pile deflection has the same changing patterns with different τ-s curve; the decreasing ratio of maximum pile deflection increases with increasing limit friction τuor decreasing critical displacement su of τ-s curve; the influence of horizontal resistance of pile tip can be neglected when aspect ratio of pile exceeds 4 and the additional moment effect can also be ignored when aspect ratio of pile exceeds 10. Furthermore, the larger the pile diameter is,the bigger the decreasing ratio of the maximum pile deflection at the initial stage will be under the condition of identical aspect ratio of pile.