Test And Theoretical Study On Prestressed And Reinforced Concrete Compounded Pipe Pile For Pit Supporting

Due to the complexity of the foundation conditions,the conventional prestressed concrete piles are always used as compression piles.In areas of high seismic intensity,when the depth of the foundation is shallow,such prestressed concrete piles are use as the retaining piles.Ordinary prestressed piles are restricted in this utilization as the anti-horizontal load capacity is weak.The flexural capacity and ductility of the ordinary prestressed piles are poor,based on this problem.Improvements on ordinary pre-tensioned prestressed concrete pipe piles(PHC)are developed.Prestressed steel bars and non-prestressed reinforcement are interval symmetrical arranged in the piles,which forms a-prestressed and reinforced concrete compounded pipe pile(PRC),this kind of piles are researched with experimental and the oretical approaches in this study.The main content is as follows:10 PRC piles with diameter of 500mm and 600mm and 2 conventional prestressed pipe piles(PC)are prepared and put under flexural capacity test.According to test,the strain graphics and cross-load-deflection(F,f)curves are drawn.The cracking moment,ultimate moment and deflection of PRC and PC piles are compared.The results show that not only is the bearing capacity of the PRC piles higher,but also the ductility and durability is improved.Based on the《Code for design of concrete structures》and《Pretensioned spun concrete pipe piles》,the role of non-prestressed reinforcement is taken into consideration.The calculation formula of cracking moment,ultimate moment,and diagonal cracking carrying capacity as well as the vertical bearing capacity are developed.The calculation results are in good agreement with experimental results,and meet the requirements of reliability.This provides a basis for the structural design of PRC pile.Finally,a computational analysis of the stiffness of the prestressed and reinforced concrete compounded pipe pile using finite element software are introduced,by comparing the before-cracking stiffness and after-cracking stiffness of the finite element calculated values,experimental values and calculated values according to the existing concrete specification formula,a theoretical formula is proposed to calculate the before-cracking and after cracking flexural rigidity.The results of this formula is compared with the numerical simulation results,Showing that the proposed formula can be used to calculate the diameter of 700mm mixed steel pipe pile type.