采用承插式桩接头的预制方桩受弯承载性能研究

Study on bending performance of prefabricated square pile with socket and spigot joint

由济南R1线工程的预制方桩受弯承载力试验结果可知,采用承插式桩接头的预制方桩的受弯承载力取决于接头的承载性能,由此提出了该预制方桩受弯承载力极限状态的检验标志为桩身挠度、裂缝宽度达到规范限值或桩接头屈服,以此给出预制方桩的受弯承载力计算式,同时对预制方桩的受力变形过程进行阶段划分。结合数值分析方法,分析了预制方桩各受力阶段的桩接头受力变形特征,建立了桩接头的受力变形模型,验证了以Tresca屈服准则判别桩接头屈服的正确性,并推导了桩接头受弯承载力计算式,并以试验结果验证了该式的正确性。结果表明：当桩接头材料达到屈服强度时,挠度、裂缝宽度均远小于规范限值。桩接头上部受压区初始以销栓传递应力给腹板、上翼板,腹板、上翼板与端板接触后,由腹板、上翼板直接承受压应力;下部受拉区以销栓传递应力给腹板、下翼板,由受压侧腹板、下翼板承受受拉区应力,且受拉区受压侧腹板、下翼板首先屈服,并以此作为计算桩接头受弯承载力的依据。受拉区腹板、下翼板第二主应力比第一、第三主应力小两个数量级。根据桩接头受压区分布情况,桩接头屈服时,受压区应力分布为＂倒三角形＂,并以此确定受压区合力位置。

Based on bearing capacity tests of prefabricated square pile in Jinan rail transit R1 construction,bending capacity of prefabricated square pile with socket and spigot joint was obtained,which was determined by the pile joint.The ultimate bending limit states of prefabricated square pile including the deflection and crack width limits and pile joint yielding were proposed. Formula for computing the bending capacity was deduced and process of deformation was divided. With numerical analysis method,bending performance of prefabricated square piles was studied and model of bending performance was built,the correctness of Tresca yield criterion for judgment of pile joint yield was proved and the explicit expression of bending performance for pile joint was derived,and the correctness of the explicit expression was verified through experimental study. The results show that deflection and crack width are far less than limits when pile joint reaches yield strength. The stress in the upper compression part of the pile joint is transmitted to the web and upper flange by the pin bolt initially,then the web and upper flange directly bear compressive stress when web and upper flange are in contact with end plate. The stress in the lower tension part is transmitted to the web and lower flange by the pin bolt. The compression side web and lower flange bear tensile stress and tend to yield firstly,which is the basis for calculating the bending bearing capacity of the pile joint. The second principal stress is smaller two orders in magnitude than the first and the third principal stress. According to distribution of compression zone of pile joint,stress distribution on compression zone is inverse triangle when pile joint reaches yield strength and can be used to determine the point of resultant force.