Failure of Over-Reinforced Hybrid Fiber Reinforced Polymer Concrete Beam Columns

Concrete-filled fiber reinforced polymer (FRP) tubes provide an alternative to conventional reinforced and prestressed concrete columns. The tube helps turn normal strength concrete core into a high performance concrete, i.e., one with high strength, ductility, and durability. The over-reinforcement in concrete-filled tubes helps avoid split rupture of the FRP reinforcement in tension, which is catastrophic in nature. A total of 8 concrete-filled FRP tubes were tested as beam-columns under a combination of axial and flexural loads. The tubes were 9 feet long, and had an outside diameter of 13-11/16 in. with a wall thickness of about 0.55 in.. The study showed that over-reinforcement concrete-filled FRP tubes generally behave well as beam columns. They deflect to a lesser extent than the corresponding under-reinforced sections. They are also more efficient than under-reinforced sections, because a small portion of their sectional capacity is consumed by secondary moments and P-delta effects. Their failure, while in compression, is considered to be gradual and progressive.