This study investigates the structural performance of reinforced concrete double corbels strengthened using hollow steel sections as an innovative composite strengthening technique. Six corbel specimens with a constant shear span-to-depth ratio (a/d = 0.2) were experimentally tested under monotonic loading until failure. One specimen served as a control, while the remaining specimens were strengthened using different hollow steel section configurations in the tie region, strut region, or both. The effects of concrete compressive strength and strengthening configuration were evaluated in terms of cracking load, ultimate load capacity, stiffness, toughness, ductility, and failure mode. The suggested strengthening method considerably enhanced the corbels’ structural performance, according to the results, with ultimate load capacity increases ranging from 58.6% to 152.6%. Strengthening the strut region provided the highest improvement in load-carrying capacity and stiffness, while strengthening the tie region enhanced tensile resistance and delayed crack propagation. Combined strengthening produced balanced structural behavior with improved stiffness, toughness, and crack control. Augmenting concrete compressive strength improved stiffness and ultimate load capacity, although it diminished ductility, resulting in a more brittle response. Overall, hollow steel sections proved to be an effective strengthening technique for improving the behavior and load resistance of reinforced concrete double corbels.
