Performance of corner strips in CFRP confinement of rectilinear RC columns

Confining of concrete columns by means of fiber reinforced polymer (FRP) composites is the most common method used for enhancing strength and ductility of concrete compression members. The shape of the column section is from the significant parameters affecting the efficiency of composite in confinement. In rectilinear columns, due to stress concentration at corners, the concrete is non-uniformly confined and the effectiveness of confinement is much reduced compared to circular columns. In this study, the compressive behavior of 9 rectilinear RC columns confined with CFRP strips is experimentally examined. To improve the confinement effectiveness in the columns, some of the specimens are locally strengthened with CFRP strips at corners, before the application of horizontal CFRP wrapping. The number of confining layers and the shape of rectilinear section (square or rectangular) are the main parameters under investigation. Based on results of the current study,local reinforcement at the corners of rectilinear columns before horizontal wrapping eliminates stress concentration at the corners and avoids premature rupture of CFRP confining layers at these parts; thus increases the efficiency of composite in confinement. Furthermore, local reinforcement of corners of column section is more effective in RC columns with square sections compared to rectangular sections.