Research On Seismic Performance Of High Strength Precast, Prestressed Pile-cap Connection

Precast piles have been widely used with the process of industrialization in civil engineering, but domestic application in area with high anti-seismic fortification grade stays limited due to the lack of relevant local seismic study.Pile to cast-in-place(CIP) concrete pile-cap connection is the key part while evaluating the seismic performance of precast pile foundation. Analytical study, experimental test and numerical simulation arethree common methods for seismic research on the pile-cap connection.Pile end anchor, filling concrete in the hollow section and a shallow embedment consist of the most common precast piles to CIP pile-cap connection conformation design in China. In this design, anchors supply adequate bending capacity and filling concrete enhance the shearing resistance of the connection while a shallow embedment allow considerable connection deformation. In this study, a quasi-static experiment on precasted prestressed hollow square pile with this pile-cap design is first conducted. Six connection with variable axial load, lateral loading direction, embedment depth and pile reinforcement were tested. Test results demonstrated an plastic hingedevastation within twice the pile diameter on the pile end and indicated that the connection performed under an axial load less than half of thevertical loading capacity, and redundance in vertical load is suggested considering the seismic design.This paper also conducteda quasi-static experiment on how the connection design performed on prestressed reinforced high-intensity concrete(PRHC) piles which contain both high-strength prestressed concrete steel bar and ordinary bars without pretension. The experiment contains seven specimens, three of them were tested with different axial load to discuss the influence of considerable vertical loading variance, one specimen with no hollow section filling and one PHC pile were tested to exhibit how filling concrete and complex reinforcement would work, and a typical connection for tension pile was also tested. In addition, a semi-reigid connection with construction convenience was designed and tested in this part. The test results indicated that connection was destructed with pile-cap cracking and embedment failure, and post-failure capacity was mainly supplied by anchoring and hollow section filling. Compared with the square pile, this connection showed superior seismic performance with better ductility and bigger deformation in the destruction mode of cap failure except for the specimen with no axial loading and the tension pile connection which had a brittle decline in bending capacity and stiffness after cap failure. It is proposed to keep enough vertical load and enhance the cap reinforcement in the embedding region. The comparison also indicated that difference between pile and cap material impact the final failure mode most. Both test showed that pile damage increased with the axial load. The semi-rigid connection realized the separating mechanism in the test and indicated excellent ductility and energy dissipation.The study also contains numerical simulation for test on connection in square piles with the FEM software, Abaqus. Predefined stress field and non-linear spring were used to simulate the process of CIP construction and bond slippage between anchoring bar and pile-cap. Comparison with the test results proved the validity of the monotonic simulation, and indicated that hysteretic simulation didn’t match the test because the concrete damage plasticity model lead to incorrect concrete reaction while simulating shearing behavior which was observed in the test. Further simulation on the influence of axial load, hollow section filling and reinforcement were conducted based on the validity of monotonic simulation. The results indicated that axial loading had a major impact on the connection failure mode, friction between pile and the filling concrete had no obvious effect on monotonic loading behavior, and the spiral reinforcement enhancement efficiently improved the monotonic loading performance of pile-cap connection with a plastic hinge in the pile.