Experimental Study On Flexural Behavior Of FRPC Composite Piles

The traditional pile(steel pipe composite pile,reinforced concrete pile)is easy to be corroded.FRPC composite pile(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 FRP materials,the characteristics of FRPC composite pile are quite different from traditional piles.This paper discusses the flexural properties of FRPC composite pile by laboratory test,theoretical analysis and numerical simulation,main contents and research results are as follows:Based on the pure bending test of 7 FRPC piles,the paper analyzes the characteristics of FRPC composite piles in three stages(the whole working stage,the normal working stage and the ultimate bearing stage).The plane section assumption is verified through the strain distribution disciplinarian;In addition,variation of the bending stiffness and stiffness superposition principle is discussed.The impact of various factors(wall thickness of FRP tube bonded form,concrete strength)is focused on FRPC composite pile's bending performance,receiving following conclusions:(1)FRP tube thickness has large impact on the bearing capacity,increasing the wall thickness can both improve the stiffness of the specimen,and the hooping effect.(2)The strength of concrete has great influence on the initial stiffness.(3)The relative slip of FRP tube and concrete will make the moment of inertia of cross section and stiffness smaller,thus affecting the flexural capacity.The similarities and differences between the FRPC composite pile and the traditional material pile are analyzed and compared.FRPC commposite pile has better ductility and large safety stock.Safety coefficient is put forward to determine the design load(normal critical state)of FRPC composite piles,and to serve as the unified safety storage.Through the ultimate equilibrium method to derive calculation formula of flexural bearing capacity of FRPC commposite pile.The calculation method of concrete equivalent rectangular circular stress pattern of cross section coefficient ?c is given,which is relevant with the height of compression zone ? but independent of radius of cross section.Refer to the general theory of steel pipe composite pile,the FRP tube and the concrete is considered as a whole.The ultimate bending bearing capacity calculation formula of the general theory of FRPC composite pile is put forward based on the formula of compressive strength of concrete in the constrained condition.The calculated values of the ultimate equilibrium method and the unified method are compared with the experimental values.The results show that the limit equilibrium method is safe,and the unified method is closer to the experimental values.The modeling results are in good agreement with the experimental results by using ABAQUS.With the increase of wall thickness and concrete strength,the ultimate bearing capacity of FRPC composite pile increases linearly.The ultimate compressive strength exceeds the maximum stress of concrete compression zone,shows that the hooping effect in pure bending under the action of FRP tube can improve the strength of concrete.