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弯曲破坏是地震中桩基失效的一类常见模式,其破坏的一个重要原因就是桩体的抗弯刚度不足。对于一定长度的桩体,桩的抗弯刚度与桩的长径比直接相关,但桩基规范中对摩擦桩的长径比并没有像端承桩那样作出限制。在构建的结构性饱和黄土动力本构模型的基础上,针对黄土地区的单桩基础,结合大型有限元程序建立了摩擦桩-土-结构体系、端承桩-土-结构体系的有限元-无限元模型,探讨了不同桩体长径比对两者动力反应特性的影响,得出如下规律:(1)其他条件相同时,不管是端承桩还是摩擦桩,长径比对桩身截面剪应力和水平加速度的分布形态没有影响。但随着长径比的增大,桩身各截面对应的的剪应力值减小,而加速度值反而增大;(2)随着长径比的增大,桩身变形形态从正弯型逐渐过渡到反弯型,桩体的破坏模式也相应由剪切破坏过渡到弯曲破坏;(3)端承桩体系比摩擦桩体系更容易出现反弯型,但当长径比增大到一定程度时,摩擦桩也会呈现反弯型。从抗震角度来说,对摩擦桩长径比的限制应以桩体变形模式表现为正弯型为宜。所得结论对工程实践具有一定的指导意义。
Bending failure is a common mode of failure of pile foundations in earthquakes. An important reason for its failure is the insufficient flexural rigidity of the pile. For a certain length of pile, the bending stiffness of the pile is directly related to the aspect ratio of the pile, but the aspect ratio of the pile in the pile foundation is not limited as the pile. Based on the constitutive model of saturated saturated loess, aiming at the single pile foundation in loess area, the finite element method of finite element method is established for the pile-soil-structure system, end-bearing pile-soil- The finite element model is used to investigate the effect of different aspect ratios on the dynamic response characteristics of the two piles. The following laws are obtained: (1) When the other conditions are the same, either the end bearing pile or the frictional pile, The distribution of shear stress and horizontal acceleration has no effect. However, with the increase of the aspect ratio, the shear stress corresponding to each section of the pile decreases and the acceleration value increases instead. (2) As the aspect ratio increases, And the failure mode of pile body also transitions from shear failure to bending failure. (3) The end bearing pile system is more prone to buckling than the friction pile system, but when the aspect ratio increases to a certain extent When the degree of friction piles will also show the anti-bending type. From the point of view of anti-seismic, the limit of the aspect ratio of the friction pile should be based on the deformation mode of the pile as the positive bending type. The conclusions obtained are of guiding significance to engineering practice.