Study On FRPC Pile Under Low Cycle Reserved Loading

The traditional pile(steel pipe composite pile,reinforced concrete pile)is easy to be corroded in the hostile environment such as sea,bittern and saline soil.Continuous basalt fiber(CBF)is a new fiber material of lower density,high strength and corrosion resistance and FRPC composite pile made of it(Fiber Reinforced Polymer Composite Piles Filled with Concrete),which is a new kind of pile foundation formed by the FRP shell and its internal filling concrete,can resist the corrosion of external environment,improve the durability of the structure.Because of the high strength and low elastic modulus of CBF materials and the difference of conditional FRP materials,the characteristics of FRPC composite pile are quite different from traditional piles.This paper discusses the flexural properties,seismic behavior and bearing capacity of FRPC composite pile by laboratory test and theoretical analysis,main contents and research results are as follows:(i)One FRPC pile,two PRC piles and two PHC piles were tested under low cycle reserved loading to study the seismic behavior such as failure mechanism,hysteresis curve,skeleton curve,strength and stiffness degradation,ductility performance and energy dissipation.The experimental results indicate that FRPC pile shows better ductility performance,energy dissipation and ultimate bearing capacity than traditional piles.But because of the lower elastic modulus,limit displacement of FRPC pile is also higher than PHC and PRC pile.The damage of CBF pile and the decrease of bearing capacity happen suddenly and there is no plane and downward part of skeleton curve,but the deflection of CBF pile is obvious,so the failure of CBF pile under cycle reserved loading is ductile failure without obvious yield point.(ii)Based on the pure bending test of one FRPC pile and uniaxial compression test of CBF pipe,stiffness degradation curve and load-deflection curve were drew.The difference of mechanical properties between CBF pipe and basalt fiber was studying by analyzing above curve,testing phenomenon,microstructure and cracking behavior.The experimental results indicate the characteristics of FRPC composite piles in three stages(the whole working stage,the normal working stage and the ultimate bearing stage).Elastic modulus of CBF pipe needed to multiply a factor of 0.4 by analzying the bending stiffness,stiffness superposition principle and experiemental result of uniaxial compression test.This conclusion was verified primarily through comparing experimental value and theoretical value of stiffness.(iii)This paper analyzes the derivation process and theoretical significance of ultimate balance theory and unified theory to calculate ultimate shear capacity and bending moment.Possibility of shear failure of FPRC pile is very low and elastic modulus of CBF pipe needed to multiply a factor of 0.4 was verified futher.Ratio of FRP was required more than 17.8% to avoid brittle faiure of FPRC pile.