Effect of Carbon Fibre Reinforced Polymer Strengthening on the Axial Capacity and Ductility of Non-slender Square Concrete Columns

Abstract

This research investigated the effect of Carbon Fibre Reinforced Polymer (CFRP) strengthening on the axial capacity and ductility of non-slender square concrete columns. There is a problem of buildings collapsing in Kenya. Retrofitting of the buildings vulnerable to collapse is of great importance to ensure the safety of the occupants and to address the housing deficit in the country. An experimental research programme was conducted on 95 non-slender square concrete columns to find out the gain in axial capacity and ductility of the columns strengthened by CFRP. The specimens (150mm x 150mm x 350mm) were made of plain and reinforced concrete. Three different concrete grades: C8/10, C12/15 and C16/20 were used. The specimen had varying configurations of CFRP wrap: partial and full confinement in one and two layers. Four parameters are investigated in this study: concrete grade, steel reinforcement, degree of confinement and the number of layers of CFRP wrap. The specimens were subjected to uniaxial compression up to failure, and the stress-strain curves were plotted. This study found that the weakest concrete grade experiences the highest effect due to CFRP strengthening. Concrete C8/10 was 5.42 times more affected than Concrete C16/20 in terms of axial capacity (542%) but the effect was comparable in terms of ductility. Plain concrete specimens experienced higher effect in both axial capacity (114%) and ductility (145%) than reinforced concrete specimens. Full confinement was more effective in both the axial capacity (383%) and ductility (275%). Similarly, two layers was more effective in both axial capacity (435%) and ductility (292%). Experimental design optimisation showed that, partial CFRP confinement offers better material efficiency as compared to full CFRP confinement. These findings are instrumental in developing a rationale and a design method for retrofitting existing columns with CFRP wrap.