Research On Axial Compression Of Reinforced Concrete Columns Strengthened With BFRP And CFRP

As the main load-bearing component in the concrete structures,the reinforced concrete columns are always repaired and reinforced to ensure safety caused by the environmental corrosion and natural damage.Fiber Reinforced Polymer（FRP）has become a common reinforcement material for concrete structures due to its advantages of light weight,high strength and corrosion resistance.Among them,Carbon Fiber Reinforced Polymer（CFRP）has been studied and applied widely.In recent years,Basalt Fiber Reinforced Polymer（BFRP）has attracted attention because of its better mechanical properties and lower price.However,there are few studies on the reinforced concrete structures confined by BFRP.The majority of relevant theoretical calculation models are based on CFRP test data,and the accuracy is relatively low when applied to BFRP.Therefore,it is of great theoretical and practical significance to compare the mechanical properties of reinforced concrete structures strengthened by BFRP and CFRP.In this paper,the axial compressive behavior and stress-strain model calculation of reinforced concrete columns strengthened by BFRP and CFRP are systematically studied by experimental,numerical simulated and theoretical analysis.The main research contents are as follows.Firstly,six full-scale reinforced concrete columns confined with BFRP and CFRP were tested under axial compression.The effects of the FRP distribution and concrete strength on the axial compression performance of the columns were studied.The ultimate bearing capacity and strain of the confined columns under the same lateral confinement strength were compared emphatically.The test results show that the failure mode of the confined column changed significantly.The ultimate bearing capacities of C25 grade concrete columns reinforced with CFRP and BFRP were 66% and 61%higher than those of unreinforced columns.The ultimate bearing capacities of C50 grade concrete columns were 51% and 34% higher than those of unreinforced columns,indicating that the capacities of CFRP-confined columns were larger than those of BFRP-confined columns.The transverse ultimate strains of C25 grade concrete columns reinforced by CFRP and BFRP were increased by 682% and 1683% compared with those of unreinforced columns.The axial ultimate strains of C25 grade concrete columns reinforced by CFRP and BFRP were increased by 562% and 882%,respectively.The data indicated that the increasing effect of ultimate strain in BFRP was better than that in CFRP,but the increasing effect of ultimate strain on high-strength concrete reinforced columns was limited.Then,the three-dimensional finite element models of reinforced concrete columns confined by BFRP and CFRP were established by using the software ABAQUS.The axial stress-strain curves of the specimens,the circular strain distributions of FRP,Mises stresses of reinforcements and axial stresses of concrete at the ultimate load were analyzed,respectively.The results show that the simulated axial stress-strain curves were generally close to the experimental curves.The relative errors of peak stresses of the columns between the simulated and the experimental values were between 5.09%and 14.28%,which indicated the simulated results were in good agreement with the experimental results.The longitudinal reinforcement and the circumferential stirrups both reach the yield state,and the reinforcement skeleton take maximum advantage.The effective confinement rates of FRP cloth were 54.53%～70.67%,which shows FRP confined effectively.Finally,the confinement mechanism of FRP reinforced concrete columns is analyzed deeply.Three stress-strain relationship models of FRP confined concrete columns considering strong and weak constraints and of FRP reinforced concrete columns are selected for calculation.Based on the test and simulation results,six models were evaluated in terms of stress-strain curves,compressive strength and ultimate strain of FRP confined columns,and a stress-strain relationship model for both reinforced concrete columns confined by BFRP and CFRP was proposed.