Flexural testing of concrete filled fibre reinforced polymer tubes (CFFT) with and without internal fibre reinforced polymer (FRP) reinforcement

FRP reinforcement has emerged as an attractive alternate of steel reinforcement due to its higher ultimate tensile strength and weight ratio, and corrosion resistant properties. This study presents the behaviour of Concrete Filled Fibre Reinforced Polymer Tubes (CFFT) with and without longitudinal FRP reinforcing bars under flexural loading. Four circular normal strength CFFT (two carbon FRP tubes and two glass FRP tubes) specimens and a steel reinforced concrete specimen (Reference) of 204 mm and 200 mm diameters respectively were cast and tested. One of the CFFT of each type of CFRP and GFRP CFFT was unreinforced while the other was reinforced. The reinforced CFRP and GFRP CFFT were reinforced with longitudinal 6Ø15 CFRP reinforcing bars and 6Ø15.875 GFRP reinforcing bars, respectively. All the CFFT were tested under increasing flexural load until the fibres at the bottom of the CFFT were ruptured. Significant increases in the ultimate flexural load and ultimate midspan deflections were observed for reinforced CFFT than unreinforced CFFT. GFRP and CFRP reinforced CFFT demonstrated identical flexural behaviour while GFRP CFFT attained even higher ultimate flexural load than the Reference specimen, although both CFFT have similar ultimate midspan deflections.