Deformation ability of precast concrete columns reinforced with steel-FRP composite bars (SFCBs) based on the DIC method

Abstract

A steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a novel reinforcement composed of an inner steel bar and outer continuous FRP. Moreover, SFCBs have excellent corrosion resistance and stable positive post-yield stiffness and can be used to control structural damage. However, the relatively small fracture strain of the outer FRP may limit the deformation ability of the concrete members reinforced with SFCBs. Bundled reinforcement can weaken the interfacial adhesion to improve the structural deformation capacity and reduce the connections of the reinforced precast structures to enhance the construction efficiency and quality. In this paper, a quasistatic test of six concrete columns was conducted, and the deformation of the column foot was observed by the digital image correlation (DIC) method to investigate the effects of the reinforcement type (steel bar and SFCB), the number of bars in each bundle (1, 2, and 3), and the construction method (cast-in-place, general precast, and precast with full-length grouting) on the deformation capacity. The crack spacing of the precast concrete column reinforced with single-bar SFCBs increased by approximately 10% compared to the precast reinforced concrete (RC) column, and the crack spacing decreased with an increasing number of bars within each bundle. The proportion of the lateral displacement caused by rigid body rotation due to strain penetration of the longitudinal reinforcement at the precast column foot in total lateral drift was approximately 35%; the smaller growth rate of residual rotation in concrete columns reinforced with SFCBs produced a superior post-disaster resetting ability. The curvature distribution range of columns reinforced with SFCBs was wider and more uniform than that of RC columns. Overall, the utilization of SFCBs as longitudinal reinforcement improved the equivalent plastic hinge length by approximately 120% compared with RC columns, thus greatly reducing the curvature requirement of the column bottom. Moreover, the bundled reinforcement reduced the growth rate of plasticity. The precast specimen with full-length grouting altered the failure mode and achieved a considerable deformation capacity with the longest equivalent plastic hinge length of approximately 435 mm, which is 2.77 times that of the conventional RC column.