Effects of driving forces and bending fatigue on the structural performance of a novel concrete-filled fibre -reinforced-polymer tube pile

摘要

The effects of driving forces and high-cycle fatigue on the flexural performance of a novel pile consisting of a concrete-filled glass-fibre-reinforced polymer (GFRP) tube (CFFT) are investigated. A 367 mm diameter CFFT pile was driven and then extracted from the ground. Two 6 m segments cut from the upper and lower ends of the pile were tested to failure under monotonic bending and compared with a similar undriven CFFT pile. In addition, a 625 mm diameter CFFT and a conventional 508 mm square prestressed concrete pile of similar moment capacities, both 13.1 m long, were driven, tested in the field under lateral loads, and compared. It was found that driving forces have a marginal effect (about 5 percent reduction) on the flexural strength of CFFT piles. Also, CFFT piles have larger deflections than prestressed piles do. Because the GFRP tube is the sole reinforcement for the CFFT system, a comprehensive fatigue test program was conducted: coupons cut from the tube were tested under cyclic loading at various stress levels (20 percent-60 percent of ultimate) to establish the S-N curve and stiffness-degradation characteristics of the tube. A full-scale 367 mm diameter and 6 m long CFFT pile was tested under reversed cyclic bending at 60 percent of ultimate moment to validate the coupon test results. It is recommended that the service moment be limited to 20 percent-30 percent of ultimate moment to achieve at least 1 million cycles.