Eccentric behaviour of GFRP-reinforced square columns with composite spiral ties

In this study, a new type of glass fiber reinforced polymer (GFRP) composite spiral ties was proposed to provide effective lateral restraint in square concrete columns. The GFRP-reinforced square columns with composite spiral ties were experimentally tested with both eccentric and concentric loadings. The effect of eccentricity-to-width ratio, tie spacing, and tie configuration was investigated. The test results indicated that the failure mode of the eccentric column showed more ductile failure characteristics than the concentric column. The compression-ductile failure observed at small and moderate eccentricity transformed to tension-controlled failure observed at high eccentricity with the increase of eccentricity. The ultimate load decreased significantly with increasing eccentricity, and a similar variation law also occurred for cracking loads. By applying GFRP composite spiral ties, a higher ultimate bearing capacity and cracking load could be attained, showing excellent lateral restraint performance. The eccentric behaviour of GFRP-reinforced square columns with composite spiral ties was evaluated by drawing experimental and theoretical normalized (Kn -Rn) diagrams.