Effect Of Bond-Slip On Dynamic Response Of FRP-confined Reinforced Concrete Columns With Non-linear Damping

FRP material has wide application because of the advantages of light weight, high strength, corrosion resistance, convenient construction and so on. The research on FRP-confined concrete mostly focuses on static and dynamic performance. But the study on damping of FRP-confined concrete is insufficient. In seismic analysis, the structure’s dynamic response is greatly influenced by its damping ratio. Due to the complexity in mechanism and too many influence factors of damping, researchers often use constant damping ratio in response calculation. Also, bond slip may occur between concrete and steel when there is a large deformation. However, due to the complicated load transfer mechanism and other reasons, the influence of bond slip of steel bars is often neglected in existed nonlinear analysis of FRP confined concrete column.As mentioned above, this paper will study the effect of bond slip on dynamic response of FRP confined reinforced concrete columns based on the theory of nonlinear damping. In this study, nonlinear finite element analysis software OpenSEES is used to simulate the bond slip between steel bar and concrete with zero length element. The calculated hysteresis curves are then compared with the experimental data to verify the rationality of the model. On the basis of the stress-related damping model proposed by Lazan, the unit volume energy dissipation formula considering bond slip is established. Nonlinear damping ratio is defined by the energy method. Finally, under harmonic load and seismic load, the dynamic response considering bond slip is calculated and compared with the results which does not take into account bond slip. The main work is as follows:(1) The constitutive relation of FRP-confined concrete is established in OpenSEES, and the parameters of bond slip constitutive relation of reinforcement in the zero length element are reasonably valued. Nonlinear beam column element and zero length element are used to construct the model. From the energy point of view, the calculation results and the experimental results are compared.(2) On the basis of the stress-related damping model proposed by Lazan, considering the influence of reinforcement ratio, volume ratio of FRP, concrete strength and axial load ratio, the unit volume energy dissipation formula of FRP-confined RC columns considering bond slip of steel bar is obtained. Relationship between the five factors and the energy consumption of unit volume is analyzed.(3) Considering the bond slip, dynamic response of FRP confined reinforced concrete columns under harmonic load and seismic load is calculated. Comparing with calculations which don’t consider the bond slip, it is found that the result with nonlinear damping is larger than those with constant damping. The dynamic response of FRP confined reinforced concrete columns is larger considering the bond slip. The dynamic response under uniaxial load is greater than under biaxial load.