Monitoring And Study On Shear Bahavior Of Concrete Beam Strengthened In Shear

With the aging of bridges in China,the diagonal concrete cracks are generally observed in many prestressed concrete continuous box girder bridges,which leads to the shortage of their shear capacity.The maintenance and reinforcement are becoming increasingly serious and important.The reinforcement method with Polyvinyl Alcohol-Engineered Cementitious Composite(PVA-ECC)is a new technology for concrete structure reinforcement due to its excellent properties.The strengthening with PVA-ECC can greatly improve the shearing load carrying ability and durability of bridges with concrete cracks.Based on the developed longgauge fiber Bragg Grating sensing method,the shear behaviors and strengthening effects were studied for the concrete beams and an actual prestressed concrete continuous box girder bridge.The main contents and conclusions are as follows:(1)A series of experiments with 2 control specimens and 4 strengthened specimens were carried out to study the influences of reinforcing ECC thickness and steel reinforcement ratios on the shear behavior of concrete beams reinforced with the PVA-ECC.Long-gauge FBG strain sensors were applied to monitor the strain distribution in the position of mid-span and diagonal crack;the traditional displacement gauge were used to measure the deflection of the specimens.The ultimate shear capacity and failure models were analyzed.The experimental results indicate that the strengthening method with PVA-ECC can markedly enhance the shear capacity of reinforced concrete beams,which can be even improved by 124%.In addition,it is indicated that the data measured with the long-gauge FBG sensors can reflect the structural condition of the specimens strengthened with PVA-ECC.(2)According to the design parameters of experiments,the nonlinear finite element simulation model was established with ANSYS.The influences of the parameters of PVA-ECC thickness and reinforcement ratios were simulated and analyzed.The simulation results indicate that the finite element analysis can accurately simulate the whole process of the mechanical behaviors of the specimens during the loading,including stress-strain distribution,ultimate shear capacity and so on.The results obtained from finite element simulation are in good agreement with experimental results with a maximum error smaller than 8%.It is revealed that this model can be used for the further study.(3)An actual box girder bridge strengthened with PVA-ECC was taken as an engineering background.The distributed long-gauge FBG sensors were used to monitor the strain in the key position of the bridge.Effect of the reinforcement method was investigated according to the comparison of the measured results before and after the reinforcement.Moreover,the FE model was established to simulate the different stages of bridge reinforcement with PVAECC.Simulation results indicate that the principal stress of middle span and side span reduce by 24.1%,9.5% after strengthening,respectively.And maximum tensile stress of the box girder webs is less than 0.7MPa.The results indicate that the strengthening method with PVA-ECC can significantly decrease the stress amplitude and enhance the shear capacity of the prestressed concrete continuous box girder bridge with concrete cracks.Above all,the validity and reliability of strengthening method and monitoring technique are verified.