Confinement Properties of GFRP-Reinforced Concrete Circular Columns under Simulated Seismic Loading

Abstract

Columns in earthquake-resistant reinforced concrete (RC) structures need to be adequately confined to provide satisfactory levels of stability and deformability. In circular RC columns, confinement can be provided by spirals or hoops. This paper presents an investigation of the glass fiber-reinforced polymer (GFRP) confinement reinforcement requirements in columns of moment-resisting frames. Six full-scale circular RC columns were tested under simultaneous axial loading and unidirectional cyclic lateral drift reversals. The studied parameters were longitudinal reinforcement type, transverse reinforcement shape and pitch, and axial load level. Test results indicated that the maximum spiral pitch of one-fourth the gross diameter of the column as per the Canadian code for FRP-RC structures was reasonable and sufficiently conservative. In addition, GFRP circular hoops require larger lap splice length than that specified by the Canadian Highway Bridge Design Code to provide comparable confinement to GFRP spirals. The experimental results were estimated by a simplified method based on available confinement models, codes and guidelines for FRP-RC structures. It is recommended to consider the compressive strength of GFRP longitudinal bars with a compressive strain limit of 0.002 in circular GFRP-RC columns.