Study On Axial Capacity Of FRP Reinforced Concrete Filled Steel Tubes

Concrete Filled Steel Tube (CFST) structures have been applied in practical engineering more than50years in our country. Part of structures inadequat bearing capacity and need to Reinforce and Strengthen as the corrosion, earthquake, vehicle impact and improper construction. In recent years, some researchers exploit (FRP) sheet transversely wrapping outer face of steel tube in order to repair the defective CFST columns and proposed the new FRP-CFST structure.FRP-CFST composite structure is composed of FRP, steel and concrete. In order to a further more research, theoretical and experimental studies on mechanical properties of FRP-CFST composite structures were carried out, considering the factor of different layers of FRP and different kinds of FRP such as Basalt fiber reinforced polymer (BFRP) and carbon fiber reinforced polymer (CFRP). The specific research contents and conclusions include:(1) Theoretical formula of axial bearing capacity of FRP-CFST structure was proposed under two limit states. Utilize Tresca yield critetion and limit equilibrium theory to deduce the axial capacity when steel tube yields and FRP ruptures.(2) Parameter analysis was conducted on theoretical formula, including strength grade of concrete, pipe wall thickness, the type and number of layers of FRP and self-stressing. The results showed that:axial capacity increases with strength grade of concrete, pipe wall thickness, the type and number of layers of FRP and self-stressing. Axial bearing capacity improved most significantly due to the increasing of FRP layers, improved more significantly as the increasing of pipe wall thickness, improved less significantly as the increasing of strength grade of concrete and self-stressing. Therefore, increasing FRP layer to improve the structure bearing capacity is the most effective method.(3) Test research on axial bearing capacity was carried out including different kinds of FRP and different layers of FRP. Load-displacement curve, load-strain curve, ultimate bearing capacity and failure mode of the specimens were obtained by means of the axial compression test. Accuracy of theoretical formula was demonstrated by the deviation of test result and theoretical calculate result less than10%, and the ratio between0.9-1.(4) Comparison on axial bearing capacity of unreinforced specimens and reinforced specimens, the results showed that the axial bearing capacity of two layer BFRP reinforeced specimens, two layer CFRP reinforeced specimens, three layer CFRP reinforeced specimens were improved by17.73%,61.47%,86.16%. Although the price of CFRP is much higher than that of BFRP, the comprehensive cost performance is better than BFRP, CFRP clould take precedence during reinforcement design.