Study On Flexural Behavior Of FRP Rebar Reinforced ECC Beams

Fiber Reinforced Polymer(FRP)rebar has the characteristics of light weight,high strength,and corrosion resistance.Using it instead of steel rebar in concrete structures could solve the corrosion problem of the reinforcement.However,FRP rebar has same disadvantages,such as low elastic modulus and elastic brittleness under loading.Therefore,when FRP rebars are applied with concrete,it will be easy to cause same problems for the structures,such as wide cracks and poor ductility.Engineered Cementitious Composites(ECC)is a new type of cement-based material with excellent tensile ductility and crack control ability.Combining with FRP bars and ECC together,the composite structural members would exhibit good ductility,durability and energy consumption.In order to establish the theoretical system and research method suitable for FRP rebar reinforced ECC structures,this paper studied the flexural performance of FRP rebar reinforced ECC beam through four-point bending test.Based on the test results,a theoretical analysis method of FRP reinforced ECC beam was proposed.The applicability of the test and the feasibility of theoretical analysis were verified by finite element.The specific research content includes the following aspects:(1)The mechanical properties of ECC under uniaxial tension and uniaxial compression were studied through experimental investigation in this paper.Based on the test results,the constitutive models suitable for ECC under uniaxial compression and tension were proposed.Meanwhile,the tensile properties of FRP rebars were measured,and the constitutive model for FRP rebars was established.(2)Based on four-point bending test,the influences of matrix type,reinforcement type and reinforcement ratio on the mechanical response of FRP reinforced ECC beams were discussed.It could be found from the test results that the failure modes of FRP reinforced ECC beams could be divided into over-reinforced failure(ECC was failed in compressive zone)and under-reinforced failure(FRP rebars were broken in the tensile zone).The ultimate bearing capacity and ultimate deflection of FRP rebar reinforced ECC beam are determined by section stiffness.The ultimate bearing capacities of the beams could be improved by the increasing of reinforcement ratio and elastic modulus of longitudinal reinforcement.The neutral axis moved up with the load increasing.The tested FRP reinforced concrete beams also failed by over-reinforcement,while the ECC beams showed better integrity at failure.When using the same reinforcement ratio and the same compressive strength,the bearing capacity of FRP reinforced ECC beams showed 19.62% to 31.35% higher than FRP reinforced concrete beams.The utilization rate of FRP rebars increased 10% due to the combination of FRP bars and ECC.Fine cracks appeared at the failure of FRP reinforced ECC beams,while the number of cracks and the crack width of the tested concrete beams were small and wide.Under the same load level,the maximun crack width of FRP reinforced ECC beams was 30% smaller than that of concrete beams,which indicated that ECC beams with FRP rebars have good crack control capabilities.Through contact measurement and non-contact measurement results,the mid-span section strains of all beams were linearly distributed along the beam height,which satisfied the assumption of flat section.Compared with the conventional measurement result,the digital image correlation measurement method showed higher accuracy and better integrity which was helpful to understand the damage failure mechanism of beams.(3)Based on the flexural experimental results and the constitutive model established of ECC,the calculation methods for the bearing capacity,deformation and maximun crack width of FRP rebar reinforced ECC beams were proposed.The calculation results showed good agreement with the experimental results.On the basis of the existing methods,the method for evaluating the ductility of FRP reinforced ECC beams was proposed to analyzed the ductility of FRP reinforced ECC beams.(4)The finite element software ABAQUS was used to simulate the flexural behavior of FRP reinforced ECC beams without considering the bond-slip between FRP rebars and ECC.The simulation results showed good agreement with the experimental results,which verified the correctness and applicability of the constitutive model proposed in this paper.This provided a reference for the design analysis and engineering application of FRP reinforced ECC beams.