Post-repair behaviour of seismically damaged precast GFRP-RC columns retrofitted with CFRP wraps

Glass fibre-reinforced polymers (GFRP) have shown promising applications in precast concrete columns. Under extreme loading events, these columns may experience structural damage, often accompanied by significant concrete damage. However, the method of repair and evaluation of the post-repair performance of precast GFRP-reinforced concrete (RC) systems remain largely unexplored. This study presents experimental results on five repaired columns, including four precast and one cast-in-place (CIP) specimen. The precast columns were connected to RC footings using various grouted corrugated duct connections (GCDCs). After testing to failure, the columns were repaired using patch mortar and externally confined with carbon fibre reinforced polymer sheets (CFRP) and retested under a combination of axial load and cyclic lateral load. Their failure mode, hysteresis response, residual drift, initial stiffness and energy dissipation were compared with those of the original columns. The results revealed that the proposed repair methodology effectively restored the structural performance of the damaged columns. At a drift ratio of 4 %, the repaired specimens exhibited comparable capacity to the original ones. While the original specimens showed no further strength gain beyond 3.2 % drift, the repaired specimens demonstrated enhanced deformability and continued gaining strength up to 8–10 % drift. An ultimate improvement in lateral capacity ranging from 10 % to 44 % was achieved compared to the original columns, with failure shifting away from the CFRP-confined zone. Specimen with ducts embedded in the footing showed the greatest capacity improvement, with performance identical to that of the CIP column. On average, the repaired specimens retained approximately 83 % of the initial stiffness and dissipated around 219 % more energy than the original specimens. Finally, an analytical approach was developed to support the experimental results. Overall, the study demonstrated the feasibility of repairing damaged precast GFRP-RC columns, with GCDCs remaining effective in load transfer. As failure in GFRP-RC members is mostly due to concrete failure, CFRP wraps enhance confinement, improve deformability and capacity, and hence overall improved performance. • Repair and testing of damaged precast GFRP-RC columns. • Evaluation of the seismic resistance of the repaired columns. • Effectiveness of a repair method combining patch mortar and CFRP wrapping. • Improved strength, deformability, and energy dissipation of repaired columns. • Analytical study and design recommendations.