Compression behavior of RC wall-like columns strengthened using NSM/CFRP system without shape modification

Abstract

The wall-like columns are commonly employed in high-rise buildings for carrying heavy loads without affecting the usable space. However, the retrofitting of these columns often becomes essential under some circumstances. Thus, the designers are looking for strengthening schemes that do not cause changes in the column section for which a combination of near-surface mounted (NSM) bars and carbon fiber reinforced polymer (CFRP) confinement can be adopted. This study was undertaken with the objective of developing such a scheme and studying the confinement provided by CFRP wrapping on wall-like columns. In this study, besides testing two control columns, four columns strengthened using different schemes were tested in axial compression. The performance of the schemes was assessed in terms of the failure modes, load-carrying capacity, and different characteristics of the load-displacement plots. The best scheme was found to be the one wherein the column was strengthened using NSM steel bars connected to the column heads, along with the wrapping of three CFRP sheets covering the NSM rebars. Two analytical models were proposed to estimate the peak load. The first model used the approach of both the ACI 318-19 code and ACI 440.2R-17 guidelines, whereas, the second model utilized the formulas of both Eurocode 2 and the ACI 440.2R-17. The second model predicted the peak load of retrofitted columns more accurately than the first one with prediction errors for the second model varying from 2% to 9%.