Seismic performance of pretensioned centrifugal spun concrete piles with steel strands

Abstract

Pretensioned centrifugal spun concrete piles with steel strands (PSC piles) have been developed to improve the seismic performance of the piles by using higher strength and more ductile prestressing steel strands, instead of the more traditional high strength steel bars. This paper presents a systematic evaluation of the seismic behavior of PSC piles by means of full-scale test and finite element (FE) simulation. Lateral cyclic loading tests have been carried out on three full-scale PSC pile specimens subjected to different axial compressive forces. The performances of test specimens, including cracking pattern, lateral bearing and deformation capacities, stiffness degradation, energy dissipation and failure mode are examined. The performances of PSC piles are subsequently compared with piles reinforced by high strength steel bars (referred as PHC piles) tested in a previous study. A detailed FE model was developed to simulate the hysteretic behavior of PSC piles using DIANA. This model was validated against test results and then used for parametric analyses. The effects of four key design parameters, in terms of axial force ratio, steel strand ratio, prestressing level of steel strands and concrete wall thickness, on the cyclic behavior of PSC piles have been investigated. The results show that all PSC pile specimens are dominated by the bending damage, and their cyclic behavior and failure mode are influenced significantly by the axial force. The lateral bearing capacity increases remarkably while the deformation capacity generally decreases with the increase of the axial force ratio. The PSC pile failure is mainly dominated by the tensile rupture of steel strands under lower axial force ratios, while concrete crushing under higher axial force ratios. Compared with PHC piles, PSC piles with a smaller reinforcement ratio demonstrate better overall seismic performance, especially ductility, under low to medium axial force ratios, as in such cases the high ductility of steel strands can be fully utilized. Further improvement of the seismic performance of PSC piles under higher axial force ratios can generally be achieved by increasing concrete wall thickness.