Shear behaviour of RC deep beams without web reinforcement strengthened with 4D steel fibers exposed to elevated temperatures

Reinforced concrete (RC) deep beams are widely used in heavily loaded structures where efficient shear transfer is essential. However, exposure to elevated temperatures can significantly degrade their shear capacity. Despite the widespread use of steel fibers to enhance the shear behaviour of RC members, the post-fire performance of deep beams reinforced with 4D steel fibers has received limited experimental investigation. This study experimentally evaluated the shear behaviour of 12 RC deep beams with (200 × 450 × 1900 mm) incorporating six steel fiber volume fractions (0, 0.25%, 0.5%, 0.75%, 1%, 1.25%) under ambient conditions (23°C) and after exposure to 600°C for 3 h. Shear capacity, load–deflection behaviour, stiffness, energy absorption, and failure mode were evaluated. At 23°C, the ultimate load increased by (20.1%-103.8%) at compared to the control beam, while at 600°C the improvement reached (40.5%-145.7%) compared to the heated control beam. Furthermore, the reinforced beams retained 92–96% of their capacity after exposure to 600°C, compared with only 79.1% for the control beam, along with a significant improvement in energy absorption and crack control. These findings demonstrate that Hooked-End 4D steel fibers provide an effective strategy for enhancing the fire resilience and residual shear performance of reinforced concrete deep beams.