Axial Behavior of Slender-Concrete-Filled FRP-Tube Columns Reinforced With Steel and Carbon-FRP Bars

Abstract

Synopsis: Concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) system is one of the most promising technique to protect the reinforced concrete structures from aggressive environmental conditions. Most of the experimental investigations which have been conducted on CFFT columns under compression load were on unreinforced and short concrete stubs. This paper presents the results of an experimental investigation on the strength and behavior of thirteen RC and CFFT columns. The effect of two parameters and their interactions on the buckling behavior were investigated; namely, the type of internal reinforcement (steel or CFRP bars) and the slenderness ratio. The eleven CFFT columns of different slenderness ratio 4, 8, 12, 16 and 20 were tested under pure compression load. Also, two spiral-steel reinforced concrete columns were introduced in the test matrix as control specimens. Filament-winded FRP tubes were used as a stay-inplace structural formwork for CFFT columns. The internal diameter and the thickness of the FRP tubes are 152 mm and 2.65 mm, respectively. Also, the fiber orientations are mainly in the hoop direction. The uniaxial compressive strength of steel and CFRPreinforced CFFT columns was reduced by 13% to 32% with increasing the slenderness ratio from 4 to 20. The CFRP bars can be used as a longitudinal reinforcement for CFFT columns, and their behavior as a compression reinforcement was generally similar to that reinforced with steel bars. The test results indicated that the axial capacity of CFRPreinforced CFFT columns is 13% lower compared to steel-reinforced CFFT columns.