Nonlinear Finite Element Analysis On Reinforced Concrete Members Strengthened With Carbon-Fiber-Reinforced-Plastic Sheets

The basic research on the technique of strengthening concrete with carbon fiber reinforced plastic(CFRP) sheets is undeveloped in China; and its application has some problems that haven't been solved, especially the bilateral shear behaviors and the bilateral seismic properties of reinforced concrete columns strengthened with CFRP sheets under the obliquely and horizontally cyclic loading haven't been studied by researchers. The research on them has an important significance because the concrete members strengthened with CFRP sheets are subjected to the actions in the two axial directions under the earthquake in the seismic areas in fact. The paper studied the crack development, the deformation, the hysteretic behavior, the failure mode and the damage mechanism, etc. with the method of the nonlinear finite element on the base of analysis of the existing relevant research on the concrete structures strengthened with CFRP sheets, which is finished through a series of damage tests of concrete members strengthened with CFRP sheets under the obliquely and horizontally cyclic loadings. The aim of the paper is to provide a base to study, design in the future. The influences of the placement and amount of CFRP sheets and the direction of loadings on the shear strength(of beams), the deformation(of beams and columns), the hysteretic behavior and the ductility(of columns) were discussed through the shear failure test of three reinforced concrete beams strengthened with CFRP sheets under the monotonic vertical loadings and the flexural failure test of twelve reinforced concrete columns strengthened with CFRP sheets under the obliquely and horizontally cyclic loadings in the paper. The results of the research stated that the shear strengths of reinforced members are enlarged obviously and the stiffness of the concrete members is expanded and the deformation behaviors of the concrete members are amplified obviously and the ductility of them is magnified by bonding the CFRP sheets exteriorly, so the failure mode of the members change from the shear failure to the flexural failure. Moreover, it is discovered that the direction of the horizontally lateral loading has few influences on the loading-carrying capacity, the deformation, the hysteretic behavior and the ductility of reinforced concrete columns strengthened with CFRP sheets.The solid elements of eight-joint of the bond-slip mode between reinforcing bars, CFRP sheets and concrete were adopted firstly according to the different element sizes of the mesh in the analysis of three-dimensional nonlinear finite element, so the sizes of the bond-slip elements were defined due to the sizes of the elements of CFRP sheets, reinforcing bars and concrete. More accurate relationship of bond-slip between CFRP sheets, reinforcing bars and concrete was obtained through the adoption of the displacement functions of surrounding elements of CFRP sheets, reinforcing bars and concrete as the displacement functions of bond-slip elements.The new nonlinear finite element for anchored reinforcing bar model was developed; and the model is based on the flexibility method of analysis with force rather thandisplacement functions forming the starting point of the formulation. This choice is motivated by the fact that anchored reinforcing bars subjected to large deformation reversals exhibit a smooth distribution of steel stress, while the strain and relative displacement between reinforcing steel and surrounding concrete are characterized by steep gradients in the inelastic portion of the anchored bar. With this approach, the hysteretic behaviors of anchored reinforcing bars were analyzed in the reinforced concrete columns strengthened with CFRP sheets. The result of analysis stated that the numerical approach is robust and stable. So the accurate estimates were obtained with only a few elements of mesh.The transverse stirrups and shear CFRP sheets were homogenized in the concrete and the composite material was regarded as the transverse homogenized continuum by adopting as th...