Study On Tensile And Bond Performance Of GFRP Bar Reinforced UHPC Members

In this paper,the GFRP reinforced UHPC structure is taken as the research object,and the bond-slip performance and uniaxial tensile performance test of GFRP reinforced UHPC structure are carried out.The failure mode,bond-slip,load-displacement curve and cracking characteristics are studied.The finite element model of the axial tension specimen is established by ABAQUS finite element software,and the calculation formulas of tensile bearing capacity,cracking stiffness and crack width are proposed.The main research work and conclusions of this thesis are as follows :(1)The bond-slip performance test of 10 GFRP reinforced UHPC specimens was carried out.The bond-slip characteristics such as failure mode and bond-slip curve of pull-out specimens were obtained by taking bond length,surface treatment of reinforcement and diameter of reinforcement as test parameters.The results show that most of the pull-out specimens fail in the pull-out failure mode of GFRP bars.Ribbed treatment on the surface of GFRP bars can obtain better bonding performance than sandblasting,and the more significant the rib pattern,the more obvious the fluctuation of the bond slip curve after the peak load.Based on the existing research,the bond strength fitting estimation formula is proposed.(2)The uniaxial tensile tests of three unreinforced UHPC and six GFRP reinforced UHPC dog bone specimens were carried out.The failure modes,load-displacement curves and cracking properties of reinforced specimens were analyzed with different reinforcement types,reinforcement diameters and reinforcement ratios.The visible cracks of UHPC material appear when the strain reaches the ultimate tensile strain.For reinforced UHPC axial tensile specimens,the configuration of reinforcement does not affect the initial cracking performance of the specimens.The embedding effect of GFRP bars in UHPC will bring favorable ductility to the axial tensile specimens.(3)The finite element model of UHPC axial tension members with GFRP bars was established by ABAQUS software.The failure mode and load-displacement curve of the specimen are accurately predicted by selecting reasonable material constitutive parameters and bond-slip model parameters.Based on this,the finite element parameter analysis was carried out,and the calculation formula of ultimate bearing capacity of GFRP-UHPC axial tensile members and the prediction formula of stiffness after cracking of members under the fracture failure mode of reinforcement were established.The concept of minimum reinforcement ratio required for tensile hardening of GFRP-UHPC tensile members and the corresponding calculation formula were proposed.(4)By referring to the crack width calculation method commonly used in ordinary reinforced concrete members,a crack width calculation method based on the strain field and damage field of UHPC element and a crack width calculation method based on the deformation difference between GFRP bar element and UHPC element are proposed.By comparing with the existing axial tension and bending test results,it is shown that the proposed method can better predict the crack width change process of GFRP-UHPC members.