Compressive Behavior Of Predamaged Reinforced Concrete Columns Confined With Basalt Fiber-reinforced Polymers

In recent years,due to frequent earthquakes and the aging of building structures,the reinforcement and maintenance of existing building structures has gradually become a hot spot in the field of structural engineering.Fiber Reinforced Polymer(FRP)has become a common material in the field of building reinforcement because of its good properties such as light weight,high strength,and corrosion resistance.However,Basalt Fiber Reinforced Polymer(BFRP)has become the research object of many scholars in the world not only because of its excellent mechanical properties similar to those of FRP,but also the features of environmental protection,and wide source of materials,etc.The main supporting components of the building structure will suffer different degrees of damage under the action of accidental loads such as earthquakes.Among the damaged structural components,except for those that need to be demolished and rebuilt due to large damages and large lateral residual displacements,a large number of building structures with moderate to minor damages and small lateral residual displacements still have the necessity of use after reinforcement.At present,there are many experimental studies on FRP-reinforced concrete columns,but most of the existing experimental studies are mainly focused on FRP-constrained intact concrete columns.While among those studies about the FRP-constrained damaged reinforced concrete columns,the initial damage levels of reinforced concrete columns are relatively low,so there is still a large gap in the research field of axial compressive performance of FRP-constrained reinforced concrete columns with large damages.Therefore,the axial compression test and theoretical study of the BFRP-constrained reinforced concrete columns were carried out.The main research contents were as follows:(1)In this paper,the axial compression test was carried out on 22 concrete circular columns with a diameter of 242 mm and a height of 726 mm(including 20 reinforced concrete circular columns and 2 plain concrete circular columns)to study the effect of reinforcing steel bars,the number of BFRP layers,and pre-damage on the axial compressive performance of reinforced concrete circular columns.The test results showed that the longitudinal bars have a great influence on the ultimate stress of the BFRP-confined damaged concrete columns,and the stirrups have significant influence on the ultimate stress and the ultimate strain.The BFRP confinement can effectively improve the ultimate stress and ultimate strain of the damaged reinforced concrete circular columns.The reduced elastic modulus of reinforced concrete circular columns due to damage cannot be restored by BFRP confinement;the elastic modulus and ultimate compressive strength of confined damaged columns will be reduced compared to BFRP-confined intact columns,and with the increase of damage level,the degree of reduction increased.(2)Based on the in-depth analysis of the test results and the use of existing models,the ultimate stress model,ultimate strain model and stress-strain relationship model of BFRP-confined intact reinforced concrete circular columns under the co-occurrence confinement of BFRP and stirrups and subjected to uniaxial compression were proposed for considerations.(3)The damage evaluation indexes based on the area,stiffness and strain were analyzed in detail.And based on this,the ultimate stress model,ultimate strain model and stress-strain model of BFRP-confined damaged reinforced concrete circular columns showed a good agreement with the test results and subjected to uniaxial compression were proposed.