Experimental Investigation Of Axial Compressive Behavior On Square Concrete Columns With Corner Radius Confined By BFRP

In actual engineering,many existing concrete structures has different degrees of reduction in structural bearing capacity and durability due to concrete strength degradation,environmental effects,durability decline,seismic fortification standards,and use load changes.How to effectively improve the safety and durability of existing old concrete structures have become a hot issue in the field of engineering reinforcement and renovation.In recent years,FRP materials have been widely used in the field of structural reinforcement and transformation due to their advantages of light weight,high strength,corrosion resistance,and convenient construction.Compared with carbon fiber reinforced plastics,basalt fiber reinforced plastics(BFRP)as a strengthening method for structures or components will have a better cost performance.Meanwhile,it can further enhance the application of BFRP sheets in civil engineering.Use FRP sheets to reinforce the rectangular concrete columns in the circumferential direction.When FRP is bent along its fiber direction,it will cause stress concentration and fiber breakage,which will affect the reinforcement effect.Before the reinforcement of rectangular concrete columns,chamfering the cross section is a common practice adopted by relevant domestic and foreign reinforcement codes and regulations.The corner radius will affect the effective hoop strain value of the fiber and the hoop constraint effect of the FRP sheet.Considering that BFRP still has a big difference in tensile strength and ductility compared with the carbon fiber reinforced plastics,this article focuses on the corner radius.An experimental study was carried out on the influence of BFRP sheets on the bearing performance of concrete columns.The mainly completed work as follows:(1)Axial compression loading tests on 18 square concrete columns(14BFRP-confined concrete columns and 4 concrete contrast columns)were completed to study the influence of the corner radius and the number of BFRP layers on the bearing capacity and deformation properties of the specimens.The test results show that with the increase of the corner radius and the number of BFRP wrapping layers,the bearing capacity and ductility of the specimens are improved to a certain extent,and the number of BFRP layers improves the bearing capacity of the specimens better than the chamfer radius.(2)Measure the hoop strain distribution of BFRP at the height of 0.25 H,0.5H and 0.75 H,and draw the hoop strain distribution diagram.The analysis results show that the fracture strain of BFRP basically occurs at 0.5H.The hoop strain increase mainly occurs in the range of 75%-100% bearing capacity.As the corner radius increases,the hoop strain of BFRP increases.The calculation method of BFRP hoop effective tensile strain is presented.(3)The applicability of the related classic strength model of FRP confined concrete is verified.Based on the Al-Salloum model and test data,an improved strength model of confined concrete is proposed and the BFRP confined concrete column calculation formula of bearing capacity is established.The test results are in good agreement with the calculation results,which can provide a certain reference for the further engineering application of BFRP.