Effect of Cyclic Damage on the Performance of RC Square Columns Strengthened Using Hybrid FRP Composites under Axial Compression

The effectiveness of hybrid fibre-reinforced polymer (FRP) strengthening is evaluated for rapid repair of the pre-damaged plain concrete (PC) and reinforced concrete (RC) columns. The objective of this study is to understand the efficiency of hybrid technique for completely restoring the initial stiffness, load carrying capacity and ductility of pre-damaged columns under cyclic compression loads. Two series of PC and RC square columns were cast. The columns were pre-damaged by loading up to 80% of peak load capacity for three cycles under pure compression. After cyclic damage, the columns were strengthened with two techniques, namely (a) near-surface mounted (NSM) carbon FRP (CFRP) laminates and (b) hybrid FRP technique, which uses a combination of NSM and externally bonded (EB) CFRP fabric. Analytical modelling was carried out for predicting the behaviour of columns with initial cyclic pre-damage. Additionally, a phased three-dimensional nonlinear finite element (FE) analysis was performed to validate the behaviour of pre-damaged columns with different strengthening techniques. Test results show that cyclic pre-loading and resulting damage causes a reduction in axial stiffness of all damaged specimens. Hybrid strengthening completely restored the stiffness and strength under compression. Prediction of analytical and FE analysis correlated well with the tests.