Experimental Research On Seismic Performance Of Improved PHC Pile

Prestressed high strength concrete piles(PHC piles) are widely used in project due to many advantages such as the higher bearing capacity of a single pile and the faster speed of construction. Several earthquake disaster investigations indicate that PHC pile often damage under seismic loading because of the poor flexural capacity. The failure mode and seismic performance of PHC piles are studied in this paper by means of the low-cycle loading tests. A series of measures are proposed on the basis of this study to improve the mechanical performance of traditional pipe piles and the cyclic loading tests are conducted to investigate the improved effects on the seismic performance of PHC piles provided by these measures.The failure characteristic, hysteretic performance, accumulated damage and ductility of PHC piles are analyzed under cyclic loading tests. It is shown that failure mode of PHC pile is brittle from the test results. The hysteretic curves of PHC piles have a distinctive pinched shape and the dissipation capacity is poor. The displacement ductility coefficient increased by 29% when the volume stirrup ratio increased by 0.08%.The seismic performance tests on the prestressed high strength steel fiber concrete piles(SFPHC piles) by mixing steel fiber in pile concrete, the prestressed high strength concrete piles reinforced with non-prestressed steel bars(PRC piles) and the pipe piles filled in the hollow are carried out. The results of the test indicate that the ductility coefficient increased by 38% when adding the shear-resistance steel fiber with volume fraction of 1.5% into the pile concrete. The ultimate bearing capacity of PRC pile increased by 30%~60% compared with PHC pile, and the failure mode is ductile. The ultimate bearing capacity of PRC pile increases with increasing strength ratio of non-prestressed reinforcements to prestressed reinforcements. The displacement ductility coefficient of PRC pile increases more than 60% compared with PHC pile as the strength ratio ranged from 0.9 to 1.2, and the ductility is excellent. The displacement ductility coefficient of PHC pile, SFPHC pile and PRC pile increased by 23%, 12% and 13% respectively by filling concrete in the hollow. The ductility of pipe pile is improved by filling concrete in the hollow.The finite element analysis is carried out to evaluate the performance of pipe pile under cyclic loading, and the analytical results are verified by the test results. The parameter analysis is done to study the seismic performance of PRC pile. It is shown that the ultimate bearing capacity of PRC pile increases with increasing prestressed reinforcement ratio and non-prestressed reinforcement ratio. The displacement ductility coefficient of PHC pile decreases significantly with increasing prestressed stress.