Axial compression–bending interaction behavior of severely damaged RC columns rapid repaired and strengthened using hybrid FRP composites

This paper investigates the axial compression and bending interaction behavior of reinforced concrete (RC) columns repaired and strengthened with different FRP (Fiber Reinforced Polymer) techniques after severe damage. The columns were initially damaged under different axial compression to bending load ratios. The loads were applied at different eccentricity (e) to depth (h) ratios to have (i) pure compression (e/h = 0), (ii) eccentric compression (e/h = 0.63) and (iii) pure flexure (e/h = ∞). After initial damage, the specimens underwent severe concrete core degradation with the main steel reinforcement reaching its yield strain. Later, the specimens were repaired using high strength cement grout (HSCG) and further strengthened using (i) near surface mounting (NSM) of carbon FRP (CFRP) laminates and (ii) hybrid FRP technique with a combination of NSM laminates and external bonded (EB) fabrics. After that, the columns were loaded again until failure. An axial compression (P) – bending moment (M) interaction diagram was developed experimentally for the severely damaged columns. Also, the interaction curves were developed analytically using strain compatibility procedure with the modified constitutive models. Experimental results reveal that the specimens repaired and strengthened using hybrid FRP technique can effectively restore the original capacity under different eccentric load levels. The analytical predictions showed a close match when compared to the experimental observations