Seismic Performance of RC Short Columns Retrofitted with a Novel System in Shear and Flexure Using CFRP Composites

Abstract

Shear is the predominant failure mode in most reinforced concrete (RC) short columns under seismic loads. The overall structural performance of short columns can be improved by shear strengthening the columns accompanied by confinement. Nevertheless, as the aspect ratio of short columns is lower than that of other columns within the same story, the formation of plastic hinges at low drift ratios can be of high risk during an earthquake. Therefore, in addition to providing adequate shear capacity and confinement for short columns, it may be necessary to strengthen them in flexure to transfer the plastic hinges to the beams. In this study, five RC short columns, one unstrengthened and four strengthened in shear/flexure by fiber-reinforced polymer (FRP), were tested under constant axial load and reversed lateral cyclic loadings. The test parameters included the number of longitudinal carbon FRP (CFRP) layers (0–2), the installation method as externally bonded reinforcement on grooves (EBROG) and externally bonded reinforcement (EBR), and the partial use of longitudinal FRP sheets. The results indicated that shear–flexural retrofitting of short columns using longitudinal CFRP sheets applied through the EBROG method plus an adequate number of confining CFRP wraps improved the load-carrying capacity, ductility, and dissipated energy by up to 83%, 168%, and 1,200%, respectively, compared to those obtained for the unstrengthened specimen. These enhancements were respectively 29%, 26%, and 137% compared to the specimen strengthened in shear using confining CFRP wraps. When the EBR method was used to install the longitudinal FRP sheets, however, no positive effect on the overall behavior of the retrofitted short column was observed.