Seismic Behavior of Square and Circular Concrete Columns with GFRP Reinforcement

This paper presents results from tests on seven reinforced concrete square columns under simulated seismic loading and demonstrates their satisfactory behavior even when axial load is high. All seven specimens were confined by glass fiber–reinforced polymer reinforcement (GFRP) rectilinear ties, while five specimens were reinforced with steel longitudinal bars and two with GFRP longitudinal bars. The results showed that irrespective of the longitudinal bar type, GFRP confinement effectively improved the seismic resistance of columns. The difference in the type of the longitudinal bars resulted in significant changes in column behavior. A comparison was made between these test specimens and earlier circular columns from literature, and the confinement effectiveness of the GFRP rectilinear ties and circular spirals was evaluated. Lateral GFRP was found to have a greater influence on the flexural strength enhancement of columns with GFRP longitudinal bars versus steel longitudinal bars. Results indicate that available methods for predicting flexural strength enhancement due to confinement invariably miscalculated the true strength enhancement by a substantial margin, particularly when GFRP longitudinal bars are used. A new model for predicting the flexural strength enhancement of square and circular columns confined by lateral GFRP is proposed.