Effectiveness of hybrid fibre-reinforced polymer retrofitting on behaviour of fire damaged RC columns under axial compression

Reinforced concrete (RC) members when subjected to elevated temperatures due to fire undergo a significant reduction in material strength, concrete cover damage, and loss of bond of reinforcing steel with concrete. In such cases, to ensure the safety of the structure and to allow its future use, it is essential to assess the performance of the fire-affected RC elements and strengthen them appropriately. The objective of this study is to understand the effectiveness of hybrid fibre reinforced polymer (FRP) retrofitting technique on the emergency repair of the severely damaged RC columns under combined fire and axial compression loads. The hybrid FRP retrofitting technique uses the combination of near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) reinforcement and externally bonded (EB) CFRP wrapping for lateral confinement. In total, eleven short RC columns were damaged under a combination of thermal and axial compression loading conditions. The damaged columns were then retrofitted using an innovative hybrid FRP retrofitting technique. Experimental results reveal that the hybrid FRP retrofitting technique restored 71%-116% of the original capacity of columns before the fire damage.