Experimental Investigation of Flexural BehavioUr of Conventionally Reinforced Concrete Beams Strengthened with Near-surface-mounted Mild Steel Strips
Keywords:
conventional reinforcement, flexural strengthening, Mild steel strips, retrofitting, moment capacity, near-surface mounted techniqueAbstract
Due to material degradation with age, design and construction inaccuracies, reinforced concrete (RC) beams may develop flexural strength deficiencies during service life and require strengthening. This study experimentally investigates the flexural performance of RC beams strengthened with near-surface-mounted (NSM) hot-rolled mild steel strips, considering the influence of pre-loading conditions on the effectiveness of the strengthening. Flexure-dominant beams were tested under four-point loading, and performance was evaluated in terms of peak load capacity, elastic stiffness, and energy absorption derived from load–deflection responses. Results showed that NSM strengthening increased flexural capacity by 30% and 53% for preloaded and directly strengthened specimens, respectively, compared to the control beam, although failure in strengthened beams was governed by shear rather than flexure, indicating a shift in the critical failure mode following strengthening. Elastic stiffness improved by 3% and 49% for preloaded and directly strengthened specimens, respectively, while energy absorption decreased by 65% and 63%, reflecting reduced ductility and a shift toward more brittle behaviour. Notably, NSM strengthening altered the governing failure mode from ductile flexural failure in the control beam to brittle shear failure in the strengthened beams, a significant behavioural shift with important design implications. A design equation to estimate the required area of steel strips for retrofitting was derived from EC2-based sectional analysis and modified to account for near-surface strips.
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