Study On Bond Behavior Between FRP Bar And ECC Based On Beam Tests

Fiber Reinforced Polymer(FRP)bar shows remarkable superiority in weight,tensile strength,durability,fatigue resistance and corrosion resistance,and has been used as reinforcement material in concrete structures.Engineered Cementitiuos Composites(ECC)is a new type of cement-based material with excellent tensile ductility and crack control ability.When FRP bars and ECC are combined together,the composite structural members would exhibit good ductility,durability and energy consumption.A good bonding action is the basic precondition for conjunct work of FRP bars and ECC.Therefore,research on bond mechanism between FRP bars and ECC is of great significance in the design of the corresponding structural members.To this purpose,this paper studied the bond-slip performence between FRP bars and ECC by beam specimens.The main research contents are divided into the following four aspects:(1)Based on the experimental investigation of the beam specimens,the influence of the matrix materials(concrete and ECC),the types of FRP bars,the diameters of FRP bars,the surface treatment methods of FRP bars,the bond length of FRP bars,the thickness of ECC cover,and the testing methods(pullout and beam tests)on the bond performance between FRP bars and ECC were discussed.Test results indicated that the surface geometry of FRP rebar has a significant effect on the interface bond strength,and the FRP bars of sand blasting surface could obviously improve the mechanical interaction and the frictional action between the FRP bars and ECC.The bonding strength was increased 67%,after the surface geometry changed into sand blasting surface.The increasing of ECC cover thickness improve the bond strength between the FRP bars and ECC.When the cover thickness increased from 20mm to 40mm,the average bond strength was increased by 34%.However,the bond strength of interface between FRP rebar and ECC gradually decreased with the increase of FRP diameter and bond length.When the diameter of FRP bars increased from 6mm to 13mm,the average bond strength was decreased by 22.2%.When the bond length increased from 5d to 10d,the average bond strength was decreased by 23.5%.The type of FRP rebar and the matrix material had a great influence on the shape of the bond slip curve,but little effect on the bond strength.Due to the difference in bearing mechanism,the test method showed great influence on the bond performance between FRP bars and ECC.Finally,a calculation formula was proposed for ultimate bond strength through the numerical regression analysis of the test results.(2)The strain distribution of FRP bars under different loads were measured by the beam tests.Based on the test results,the distribution of bond stress,the relative slip and FRP bars stress along the bond length of embedded bars were obtained through theoretical analysis.Finally,the position function,?(x),reflecting the relationship between the bond strength and the position was proposed.(3)According to the test results,a segmented bond-slip constitutive model between FRP bars and ECC was proposed.Based on the segmented model,the mathematical expressions of bond stress on the surface of FRP bars,relative slip between the FRP bars and ECC,and the stress distribution of FRP bar along the bond length were obtained by theoretical analysis.Finally,the calculation formula of the basic bond length of FRP bars was established.(4)The finite element software ABAQUS was used to simulate the flexural performance of FRP bars reinforced ECC beam considering the influence of bond slip effect.In the calculated model,the element Spring2 was applied to simulate the interface between FRP bars and ECC.Good agreement was attained between the simulated and experimental results,which certificated the accuracy of the proposed bond-slip constitutive model in this paper.Finally,the influence of the number of FRP bars and the size of the beam on the bending performance of FRP-ECC beams was analyzed in this paper.