Study On Seismic Performance Of Concrete Columns Reinforced By Hybird Steel And CFRP Rebars

Compared with traditional steel rabers, Fiber-Reinforced Polymer Bar has the characteristics of lightweight, high-strength, corrosion resistance, electromagnetic interference and so on. Because of the low elastic modulus and brittle failure characteristics of FRP bars, concrete members reinforced by FRP bars may lead to the decrease of the crack width and low ductility. Using FRP bars and steel rebars with good ductility, FRP-steel reinforced concrete(FSRC) column was expected to increase the post yield stiffness, reduce the residual deformation and improve the seismic performance.At present, the experiment and finite element analysis for the FSRC columns are still lacking. In this paper, a preliminary study on the seismic performance of 7 FSRC columns is carried out. Based on the experimental research and Open Sees software, finite element analysis is finished to research the influence of the parameters such as the ratio of the mixed reinforcement ratio and the post yield stiffness on the seismic performance of FSRC columns. And the reasonable mixing ratio is also presented. The main research contents are as follows:(1) seven square columns including 2 RC columns, 4 FSRC columns and one CFRP-confined FSRC columns are carried out. The experimental results show that: a) with the same reinforcement rate, increasing the area of FRP bars has little impact on the initial stiffness, but it improves the ductility and reduces the residual displacement. When the concrete protective layer is peeled off, FRP bars are easy to be sheared. b) When FSRC column is confined with CFRP sheets at plastic hinge zone, FRP bar makes full play to the role of keeping the horizontal bearing Capacit y stable until is was broken. Under the confined of CFRP sheets, the residual displacement of L22-R is reduced by about 20%.(2) Using experimental data to modify the finite element model and making parameter expansion analysis by Open Sees software.The analysis results are as follows: the post yield stiffness can be improved by the way of FRP-steel hybrid reinforcement. The configuration of a few CFRP bars in the FSRC column can lead to premature failure of CFRP bars. In order to achieve available displacement ductility, CFRP bars increasing rate shall reach to 15%, high shear span ratio and low axial compression ratio is good for the work of FRP bars; in low axial compression ratio, addition of CFRP bars can effectively reduce the the residual deformation. Keeping steel reinforcement ratio while increasing the area of CFRP bars is an effective method of increasing ductility and reducing residual displacement; compared to CFRP bars, BFRP bars have lower tensile strength, lower elastic modulus and higher ultimate elongation. Thus BFRP steel reinforcedconcrete column has a lower bearing force and post yield stiffness, larger BFRP bars fracture displacement.