Full-scale experimental study of the seismic performance of pretensioned spun high-strength concrete piles

Pretensioned spun high-strength concrete (PHC) piles have been widely used in the pile foundations of buildings in soft soil areas due to their high axial bearing capacity and good economic benefit. However, the behavior of PHC piles under lateral loading is generally poor and this restricts their application in high-intensity seismic regions, especially for high-rise buildings. The existing research on the performance of PHC piles under cyclic lateral loading and with the presence of axial force is scarce. In this paper, the seismic performance of PHC piles is systematically evaluated through full-scale tests and numerical simulations. Lateral cyclic loading tests for two full-scale PHC pile specimens were conducted under different axial force ratios, and their performances were examined in terms of cracking pattern, failure mode, hysteretic characteristics, lateral bearing capacity, ductility, stiffness degradation and energy dissipation capacity. A dedicated finite element (FE) model was then developed using the software DIANA to compute the cyclic behavior of PHC piles, and the model was verified against the experimental results. Using the verified FE model, parametric analyses have been carried out to study the effects of axial force ratio, prestressing level of prestressing tendons, longitudinal reinforcement ratio, concrete wall thickness of the pile body and distributed pattern of prestressing tendons on the seismic performance of the PHC piles. The results show that the axial force ratio has a significant effect on the cyclic behavior and failure mode of PHC piles; an increase in the axial force ratio leads to an increase in the lateral bearing capacity but generally a decrease in the deformation capacity. The failure mode of the PHC piles is controlled by the rupture of prestressing tendons under lower axial force ratios (less than 0.15) but crushing of concrete under higher axial force ratios (greater than 0.15). Increasing the concrete wall thickness tends to improve the overall performance of the PHC piles, especially under higher axial force ratios.