Seismic Performance Analysis Of FRP-confined RC Rectangular Columns Under Flexural Failure Mode Based On Drift Ratio

Reinforced concrete（RC）columns are the main seismic components of the frame structure.The use of fiber reinforced polymer（FRP）restraint reinforcement for existing RC columns in cities and towns can meet the seismic requirements and safety performance requirements.This paper studies the drift ratio performance of FRP-confined RC columns under axial load and horizontal load from three aspects of data regression analysis,numerical simulation and theoretical research.This article mainly carries out the following work:Firstly,the experimental database of FRP-confined columns under axial load and horizontal load controlled by flexure were established.The influence of different calculation parameters on the drift ratio was studied,and it was found that axial compression ratio n,hoop eigenvaluesλ_svand FRP fiber characteristic valueλ_fwere the significant factors.They were introduced into the quantization of drift ratio,and the linear drift ratio equation of yield drift ratioθ_y and ultimate drift ratioθ_u were established through regression analysis,which verified the rationality of the equation.Then,the seismic performance of FRP-confined columns was divided into 6 stages by comparing the domestic and foreign specifications and the literature in the database.The failure states under each performance state were summarized,and the drift ratio of five characteristic points of the column skeleton curve were determined.Using the axial compression ratio of 0.35,the hoop eigenvalue of 0.06 and the FRP fiber characteristic value of 0.5 as the boundary to divide the range,and the drift ratio limits of performance state of FRP-confined RC columns controlled by flexure was established.Afterwards,using the"seismic code 89"as the design background,three key parameters:axial compression ratio,hoop eigenvalues and FRP fiber characteristic value were used as changing parameters,and ABAQUS finite element software was used to build the column model of low concrete strength grade and low reinforcement grade.The rationality of the limit table of deformation performance index was verified by numerical simulation results,and the maximum strain value of the fiber sheet during"serious failure"was about 30%of the ultimate tensile strain value,and it showed that the FRP-confined RC columns were not damaged due to the breakage of carbon fiber.It was found that the increase of axial compression ratio would lead the decrease of drift ratio,however,the increase of hoop eigenvalues and FRP fiber characteristic value had little influence onθ_y,but greatly improvedθ_u.Finally,a load-drift ratio skeleton model of FRP-confined columns which were bending failure was proposed and verified.Combining with the drift ratio formula of FRP-confined columns under different performance state and taking FRP fiber characteristic valueλ_f as the index of FRP consumption,the seismic design method of FRP constrained strengthening of existing RC column was given.