FRP stay-in-place formwork for seismic resistant high-strength concrete columns

Abstract

Fiber reinforced polymer (FRP) casings, in the form of stay-in-place formwork, provide an attractive alternative to conventional confinement reinforcement for concrete columns. These casings can fulfill multiple functions of; i) formwork, ii) confinement reinforcement, and iii) protective shell against corrosion, weathering and chemical attacks. This paper investigates the use of stay-in-place FRP formwork as concrete confinement reinforcement for HSC columns with circular and square crosssections. Large-scale specimens with 270 mm cross-sectional dimension and up to 90 MPa concrete strength, were tested under combined axial compression and incrementally increasing lateral deformation reversals. FRP casings were manufactured from carbon fiber sheets and epoxy resin. One of the square columns was provided with internal FRP crossties, a new technique introduced by the authors, to provide welldistributed lateral restraints along the column face, thereby improving the mechanism of confinement. The results indicate that the deformation capacity of HSC columns can be improved significantly by using FRP casings. The results further indicate that the confinement effectiveness of casings of square columns is significantly affected by the corner radius of casings. Confinement efficiency of these casings improves with the use of FRP crossties.