Strength and Ductility of Hybrid FRP-Concrete Beam-Columns

High strength-to-weight ratio and resistance to electro-chemical corrosion have made fiber-reinforced plastic (FRP) materials attractive to civil engineers. This paper presents a study on the beam-column behavior of a high-performance structural member made of concrete-filled FRP tubes (CFFT). The angle-ply FRP tube is a stay-in-place formwork, providing confinement as well as flexural and shear reinforcement. It also acts as a protective jacket for concrete core in harsh environments. A total of five 178 × 178 × 1,320 mm specimens were tested at various combinations of axial and transverse loads to develop a full moment-thrust interaction diagram for the hybrid column. In the compression control region, CFFT columns proved as strong as equivalent conventional reinforced concrete (RC) columns with as high as 6% reinforcement. Failure of CFFTs was ductile, and with considerable warning. Furthermore, toughness and energy-based ductility of CFFTs were quite comparable to those of conventional RC columns. It was also shown that the Euler-Bernouli beam theory is applicable to CFFTs, provided that composite action between the tube and the concrete core is fully developed.