Analytical Investigation of CFRP- and Steel Plate-Strengthened RC Beams with Partially Unbonded Reinforcement

This study investigates the flexural behavior of reinforced concrete (RC) beams strengthened with externally bonded Carbon Fiber Reinforced Polymer (CFRP) or steel plate (SP), with partial debonding between internal steel reinforcement and surrounding concrete. A finite element model was developed using ABAQUS (v2021) and validated against existing experimental data by others. A total of 296 beam models were analyzed to assess the effects of shear span-to-depth ratio (av/d), reinforcement ratio (ρ), debonding degree (λ), strengthening material type (CFRP/SP), and material thickness (t) on residual flexural strength. Based on the finite element analysis (FEA) results, analytical models were proposed using a dimensionless parameter Ψ, defined as the ratio of equivalent plastic region length to neutral axis depth. Analytical models were developed in IBM SPSS Statistics (Version 30) and showed strong agreement with FEA results. The findings provide insight into the influence of reinforcement debonding on structural behavior and support improved prediction of residual flexural capacity in strengthened RC beams with partially unbonded reinforcement.