Large beam-column tests on concrete-filled composite tubes

The concept of concrete-filled composite tubes was developed to address the corrosion problems associated with reinforced and prestressed concrete pil es. Beam-column tests on a total of sixteen 2.75 m long specimens demonstra ted the feasibility of off-the-shelf fiber-reinforced polymer (FRP) product s. Two types of tubes were used: spin-cast (I) and filament-wound (II). Bas ed on their respective brittle-brittle reinforcement ratios, Type I and II specimens were considered as over-reinforced and under-reinforced concrete sections, respectively. The tests showed that over-reinforced specimens per formed superior as beam-columns. They deflected to a lesser extent, and fai led at much higher axial and lateral loads, while their failure was still g radual and ductile. They were also more efficient, as a smaller portion of their sectional capacity was consumed by secondary moment effects. Bond fai lure was not an issue in beam-columns. Therefore, off-the-shelf tubes can b e used as long as end conditions and connections are properly designed. It is necessary, however, to provide a shear transfer mechanism for beams. In comparison with prestressed concrete columns, the 348 mm diameter Type I sp ecimens were found comparable to 584 mm diameter circular sections prestres sed with 20 strands of Grade 1862 MPa, whereas the 369 mm Type II specimens were found comparable to 460 mm square sections prestressed with eight str ands.