Experiment And Calculation Method Research On Reinforced Concrete(Rc) Beams Strengthened With The Composite Of FRP Grid And ECC

Aiming at the problems of using fiber reinforced polymer(FRP)to quickly repair and strengthening the reinforced concrete(RC)structures,a new strengthening technique is proposed in this project by combining the FRP grid and ECC as a composite reinforcement layer,which overcomes the disadvantages of FRP strengthening technique,such as aging problem of epoxy resin,poor resistances of high temperature and fire,and poor durability of the interface subjected to humid or freeze thawing environment.To clarify the feasibility of construction application using the FRP-ECC strengthening technique,the flexural and shear behavior of RC beams strengthened with the composite of FRP grid and ECC were explored based on the requirements of National Natural Science Funds and other projects,the main research work of this paper was carried out as follows:(1)The uniaxial tensile test of forty-two FRP grid strengthening ECC specimens were conducted in this paper.The reinforcement ratios of FRP grid,the mixture proportion of ECC,the type of chopped PVA fiber in the cement-based materials,and the construction method were selected as the main test parameters.The bonding behavior of interface between the FRP grid and ECC substrate,the mechanical behavior and failure modes of the FRP-ECC composite were explored,and the cracking pattern and cracking propagation mode of FRP-ECC composite were clarified in this paper.(2)Based on the tensile test results of FRP-ECC composite and the existing research achievement,the stress-strain relationship model and strength model of FRP-ECC composite were proposed to predicate their tensile behavior.It is highlighted that the proposed stress-strain relationship of FRP-ECC composite had a good consistency with the test curve,the predicted cracking load and the ultimate load of FRP-ECC composite agree well with the test data with low levels of data dispersion,which indicated that the proposed models of FRP-ECC composite can be used to effectively predict the tensile stress-strain relationship and ultimate tensile strength ofFRP-ECC composite.(3)Eleven RC beams strengthened with the composite of basalt FRP grid and ECC were conducted to investigate their flexural behavior.The types and reinforcement ratios of FRP grid,the bonding length of FRP-ECC composite,the fiber volume of chopped PVA in the ECC layer,the strengthening method,and the construction technology were selected as the main test parameters.The experimental results showed that three failure modes of the strengthened beams were observed during the test,including the concrete crushing at the compressive zone,the rupture of FRP grid in the reinforcement layer,and the end debonding failure of FRP-ECC composite.Compared with the non-strengthened beam,the maximum increase of cracking,yielding and ultimate load of the strengthened beams were 32%?97%,10%?40%and 2%?33%,respectively.(4)Based on the flexural test results of FRP-ECC strengthening RC beams and the requirements of specifications,the calculation models of flexural load capacity and deflection theory of FRP-ECC strengthening RC beam were proposed to predicte their flexural behavior.The calculated results indicated that the proposed model had a good consistency with the test data with low levels of data dispersion,which can be used to effectively predict the flexural capacity and displacement of FRP-ECC strengthening RC beams.(5)The flexural behavior of RC beams strengthened with the FRP-ECC composite was analysed using the general finite element software of ABAQUS/Standard,the types of FRP grid,the reinforcement ratio of FRP grid,and the strengthening method of ECC were selected as the main test prameters.Moreover,the bonding behavior of the interface between the FRP-ECC composite and concrete substrate was also modeled in this paper.The analysis results highlighted that the calculation results of finite element analysis had a good consistency with the test data with low levels of data dispersion,which can be used to effectively predict the flexural capacity of FRP-ECC strengthening RC beams.(6)Ten RC beams strengthened with the composite of basalt FRP grid and ECC were conducted to investigate their shear behavior.The strengthening methods,the reinforcement ratios of FRP grid,the shear-span ratios of RC beam,and the fiber volume of chopped PVA in the ECC layer were selected as the main test parameters.The effects of these test parameters on the mechanical property and failure mechanism of FRP-ECC strengthening RC beam was analysised in this paper.The experimental results showed that the failure modes of the strengthened beams were shear-compression failure in the shear moment regions and the concrete crushing failure in the pure bending region.The propagation of diagonal cracks was effectively suppressed due to the good bonding performance of the interface between the FRP-ECC composite and concrete substrate.The maximum increase of shear force capacity of the strengthened beams was 59%compared to the non-strengthened beam.(7)Based on the shear test results of FRP-ECC strengthening RC beams and the requirements of specifications,the design and calculation methods of shear bearing capacity of FRP-ECC strengthening RC beam were proposed to predicte their shear behavior.The calculated results indicated that the proposed model of shear bearing capacity had a good consistency with the test data with low levels of data dispersion,which can be used to effectively predict the shear force capacity of FRP-ECC strengthening RC beams.(8)The shear behavior of RC beams strengthened with the FRP-ECC composite was analysed using the general finite element software of ABAQUS/Standard,the types and reinforcement ratio of FRP grid,the shear-span ratio of RC beam,the strengthening method,the construction technology of ECC,the fiber volume of chopped PVA in the ECC layer were selected as the main test prameters.Moreover,the bonding behavior of the interface between the FRP-ECC composite and concrete substrate was also modeled in this paper.The analysis results highlighted that the calculation results of finite element analysis had a good consistency with the test data with low levels of data dispersion,which can be used to effectively predict the shear force capacity of FRP-ECC strengthening RC beams.