The Study On Seismic Behavior Of PHC Pipe Pile Under Axial Force

In recent years,people’s demand for quality of life continues to improve.Green,energy saving and high efficiency has become the theme of the development of the construction industry.Pre-stressed high-strength concrete pile is more and more widely used in foundation engineering because of high quality,fast construction speed,low construction cost,construction of green environment protection,convenient pile detection,factory production and so on.However,the research on the seismic performance of pile is not enough,especially the research on the seismic performance of PHC pipe pile under pressure is difficult to become a system,which limited the application of PHC pipe pile.Under this background,the seismic behavior of PHC pipe piles under pressure is studied by finite element simulation,experimental study and other methods,and the existing relevant formulas are evaluated based on the experimental data.The main work is as follows:(1)The finite element software ABAQUS was used to simulate and analyze the six pipe pile specimens.The constitutive relations of the steel bars and concrete were calculated by using the double broken line model and the concrete damage plasticity model respectively.Select the relevant parameters according to the "Code for Design of Concrete Structures"(GB50010-2010),the influence of different axial compression ratio and stress ratio of prestressed steel bars on the bearing capacity of PHC pile was qualitatively analyzed.The results show that the axial load ratio and prestressing steel stress ratio can increase the bearing capacity of the pile and increase the stiffness of the pipe pile within a certain range.(2)The vertical static load test method of the PHC pipe pile with vertical axial force is put forward,and a lot of special experimental devices are designed and made.According to the test requirements,the vertical load distribution beam is designed and a special loading fixture for pipe pile was made.In order to improve the efficiency and save material,the assembled pile foundation was designed.(3)The quasi-static cyclic test of 2 group PHC pipe piles with different axial pressures and different prestressing forces were carried out.According to Observe the experiment phenomenon 、 the experimental data’s statistics,and analyzing the hysteresis curve,skeleton curve,stiffness degradation,the capacity of PHC piles with different axial pressures and different prestresses is evaluated,and the seismic performance of PHC piles under actual conditions is discussed.The experimental results are in good agreement with the results of previous simulation,which is further verified that the increase of axial compression ratio and stress ratio of prestressed steel bars can increase the ultimate bearing capacity and stiffness of PHC pipe pile,but will decrease the ductility of pipe pile specimens within a certain range.At the same time,based on the experimental data,it is shown that the pipe piles with axial compression ratio of 0.15 show better energy dissipation capacity than 0 axial compression and large axial compression.(4)The calculation formula of the ultimate bearing capacity of the pipe piles in the existing National Atlas and the modified formulas proposed by some researchers are compared and evaluated through the experimental data.The result shows that the formulas presented in the existing National Atlas are biased towards safety and the formula has a modified meaning.