Experimental and Design-Oriented Investigation of Rectangular Concrete Columns: Leveraging Low-Cost Steel Clamps and Waste Aggregates

Steel clamps provide a low-cost method for strengthening concrete, but their role in confining rectangular specimens remains underexplored. This study performed monotonic compression tests on rectangular specimens confined with steel clamps, examining unconfined compressive strength, number of clamps, and coarse aggregate type, including recycled brick aggregates. All specimens showed two-phase stress–strain behavior, with significant strength and ductility gains from passive confinement. Strength improved up to 91.19%, while peak strain increased by 150%, especially in specimens using recycled brick aggregates from higher-strength bricks (CB1). CB1-based concrete exhibited the greatest enhancement. Confinement ratio strongly affected efficiency. Analytical models predicting peak strength, peak strain, and post-peak modulus achieved high accuracy (R² 0.85).