扭矩-竖向荷载联合作用下楔形端承摩擦桩承载性能分析

BEARING PERFORMANCE ANALYSIS OF TAPERED END BEARING FRICTION PILE UNDER COMBINED TORQUE-VERTICAL LOADS

  • 摘要: 为了讨论楔形端承摩擦桩在扭矩T-竖向荷载V联合作用下的承载性能,考虑地基土剪切模量在地面处为非零值且随深度呈幂函数的分布形式,根据能量法和变分原理,分别得出基桩在桩顶竖向荷载和扭矩作用下的桩身竖向位移以及扭转角微分控制方程。采用MATLAB编制程序求解楔形端承摩擦桩的极限竖向荷载、极限扭矩,得到相应的承载力包络图。在TV加载顺序下,通过改变初始扭矩值,分析了初始扭矩对楔形端承摩擦桩竖向承载特性的影响。对T-V联合受荷楔形端承摩擦桩进行了参数影响分析。研究结果表明:与等截面桩相比,纯压和纯扭作用下楔形端承摩擦桩的极限竖向荷载和极限扭矩有所提高。在TV加载顺序下,楔形端承摩擦桩承载力包络线相比等截面桩有所外扩。随着桩径变化率的增大,楔形端承摩擦桩的承载力包络线也随之向外扩张。当初始扭矩与极限扭矩之比超过一定值时,楔形端承摩擦桩极限竖向荷载开始显著降低,需注意T-V组合效应。对于大直径长桩而言,需要重视初始扭矩对基桩竖向承载性能的影响。一味提高混凝土标号并不能极大的改善基桩在TV受荷模式下的竖向承载性能。

     

    Abstract: In order to investigate the bearing performance of tapered end bearing friction piles under the combined effect of torque T and vertical load V, the paper obtained separately the differential governing equations of pile vertical displacement and torsion angle under the action of vertical load and torque on pile top based on the energy method and the variational principle, in which the subsoil shear modulus was assumed to be non-zero at the ground surface and have a distribution form of power function with depth. The ultimate vertical load and torque of tapered end bearing friction pile were solved by MATLAB programming, and then the corresponding bearing capacity envelope diagram was obtained. Under TV loading sequence, the influence of initial torque on the vertical bearing characteristics of tapered end bearing friction pile was analyzed by changing the initial torque value. The influence of parameters on tapered end bearing friction pile under combined T-V loads was analyzed. The results show that, compared with equal section pile, the ultimate vertical load and ultimate torque of tapered end bearing friction pile under pure compression and pure torsion are increased. Under TV loading sequence, the bearing capacity envelope of tapered end bearing friction pile is expanded compared with the equal section pile. With the increase of the change rate of pile diameter, the bearing capacity envelope of tapered end bearing friction piles also expands outward. When the ratio of initial torque to ultimate torque exceeds a certain value, the ultimate vertical load of tapered end bearing friction pile begins to decrease significantly, and attention should be paid to T-V combination effect. For large-diameter long piles, it is necessary to pay attention to the effect of initial torque on the vertical bearing capacity of foundation piles. The vertical bearing capacity of single pile under TV loading mode can’t be greatly improved simply by increasing the concrete grade.

     

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