Confinement of reinforced concrete columns with fibre-reinforced composite sheets - an experimental study

The wrapping of fibre-reinforced composite sheets around concrete columns is a promising method for structural strengthening and repair. This rehabilitation technique is of practical interest, as the lay-up of the sheets is rather easy; it does not require specialized tools, and the epoxy resins employed cure at ambient temperatures. Here, results of an experimental investigation are reported for 16 round reinforced concrete columns 300 mm in diameter and 1200 mm high. These columns were confined by means of carbon-epoxy sheets and loaded concentrically in axial compression. The effects of various parameters on the structural behaviour of the confined concrete columns are investigated. These parameters included the concrete strength, longitudinal steel reinforcement, steel stirrups, steel corrosion, and concrete damage. The test results show that composite confinement can considerably enhance the structural performance of concrete columns, especially with regard to ductility. The potential to restore the full strength of severely damaged columns is also demonstrated, as retrofitted columns exhibit axial load carrying capacities equal or superior to those of undamaged columns, along with significant increases in ductility. The contribution of the transverse steel reinforcement is seen to be minimal, as long as the stirrup spacing is medium to lame. For such cases tests on plain concrete cylinders are sufficient for further investigations of this retrofit method, as the key parameters which really affect strength and ductility are the concrete strength, composite fibre type, and sheet thickness.