Structural Evaluation of Reinforced Concrete Beams Retrofitted using Cold-Formed Steel Plates

Abstract

Shear strengthening of reinforced concrete (RC) beams has become increasingly important for improving the safety and durability of existing structures. Existing studies focus on the use of materials such as Fiber Reinforced Polymer (FRP) and bonded steel plates. The use of cold-formed steel plates as retrofitting material in reinforced concrete beam remains limited; thus, this study focuses on the behavior of RC beams strengthened using cold-formed steel plates installed diagonally at a 45-degree angle and bonded with epoxy adhesive. Two beam specimens with dimensions of 250 × 400 × 1500 mm were evaluated through three point bending test: a control beam (B0) without strengthening and a strengthened beam (B1) with a single cold-formed steel plate bonded to the beam web. The load was applied under quasi-static monotonic loading using a load-controlled protocol, where the deflection was monitored by Linear Variable Differential Transformer (LVDT) placed at midspan, ¼ span, and ¾ span. Test results showed that the initial yielding load for the control specimen B0 was 283.07 kN, while the strengthened specimen B1 yielded at 288.91 kN, indicating a 2.44% increase in initial yield load due to the presence of the cold-formed steel plate. Loading was continued up to 350 kN, at which point the midspan deflection of B0 was measured at 21.40 mm, whereas B1 exhibited a lower deflection of 17.81 mm, demonstrating improved stiffness and reduced deformation. The study confirms that retrofitting RC beams with diagonally installed cold-formed steel plates can effectively enhance their shear capacity and stiffness, especially in the early stages of the loading phase. Cold-formed steel plates can also prevent early shear cracks propagation in the beam. This strengthening technique offers a practical and efficient method for extending the service life of existing concrete structures.