Study On Axial Compressive Performance Of Concrete Columns Reinforced By Hybrid Steel And CFRP Rebars

Because of the propertie of high ratio strength to weight and corrosion resistance, Fiber Reinforced Polymer Bar( FRP Bar) has been wildly used around the scholars. There has been a small amount of research showed that FRP Bars and steel bars can effectively increase the secondary stiffness and reduce the residual displacement of concrete columns, which, has a good application prospect. However, the compression performance of this kind of reinforced concrete column has seldomly been researched. This situation has restricted it s application in practical engineering. In addition, throughout the domestic and foreign related research, the conclusions of the compression behavior of concrete columns reinforced by CFRP bars has not been unified completely. In view of this, this paper carried out the compression test of CFRP bars, axial compression test of steel and CFRP reinforced concrete column and used the finite element analysis to simulate the operating mode of the meterials. The paper also systematically studied the failure mode and the performance of hybrid reinforced column under the axis pressure. The main research contents are as follows:1. Four methods of testing CFRP plain bars were used to test the strength, two of them in this paper are the first time ever proposed:(1) 4 CFRP bars were embedded in concrete standard cylinder wrapped by FRP cloth, the whole system was then tested. Taking out the strength of concrete standard cylinder bounded by CFRP plate, we can get the compressive strength of CFRP bars.(2) A particular anchorage was designed to test 4 CFRP bars at one time. In the mean time, considering the effect of different length to diameter ratio on the failure modes and failure strength. The paper made a comparison of the two methods above together with the national standard and other scholars’ testing methods. The compressive strength of CFRP bars in the first test method was used more effectively, with the compressive strength up to 800 MPa, 50% of the maximum tensile strength, The failure mode is mostly the CFRP bar’s compression or shear failure under the combination of the pressure and concrete lateral deformation.The other three testing methods get the compressive strength from 380 MPa to 570 MPa.2. Considering the effects of the CFRP increasing rate, degree of restraint, a total of 10 concrete column with section of 300 mm×300mm and 900 mm in hight were tested. Through the experiment it came out that the increase of CFRP bars improved the bearing capacity of the axial pressure compared with common reinforced concrete column, about 14% to 20%. While the small space between stirrups had little influnce on the peak force, large spacing made a great influnce on the CFRP failure mode. At the same time, the experiment found that the plain CFRP bars can’t perfectly work together with concrete.3. Based on the Open Sees finite element software, the numerical simulation of multi-parameter expansion analysis was carried out. Comparing with the experimental data, the exploration of different configuration mode of CFRP bars used in reinforcement column was carried out. This paper put forward three configuration modes:(1) Remain the quantity of steel bars and increase CFRP bars;(2) Replace the steel with CFRP bars of the same area;(3) Replace the steel with CFR bars with the same totle strength. Combined with the experimental research, this paper suggests that using the way of increasing CFRP bars can effectively improve the bearing capacity of the reinforced column.