Flexural Behavior of Double-Layer Concrete Beams Composed of Normal and Steel Fiber-Reinforced Concrete

This investigation studies the flexural performance of double-layer reinforced concrete beams composed of ordinary concrete and steel fiber reinforced concrete (SFRC). The study evaluates the effects of bottom layer thickness, shear span ratio (a/d) and straight steel fiber volume fraction on structural behavior. The study project comprises twenty reinforced concrete beams, all specimens had across-section size of (125 mm × 250 mm) and different length of (1300, 1740, 2180) mm. The specimens were simple support and strengthened with flexural reinforcement of (4Ø12mm) and transverse reinforcement employing (Ø10@110mm) bars as stirrups. The results demonstrate that the double-layer concrete configuration significantly improves crack control, resulting in reduced crack widths compared with conventional beams. Increasing the shear span ratio from (2, 3 and 4) increased the crack widths and reduced the ultimate load capacity by (33.1% and 47.23%) respectively. Augmenting the thickness of the bottom layer of SFRC resulted in a rise in the ultimate failure load when =0.5% by (0.8%, 4.9%, 12% and 19.1%) and when =1% by (7.4%, 12%, 17.7% and 21.8%) in comparison to the control beam with the complete thickness of conventional concrete. These findings confirm that incorporating SFRC in the tension zone of double-layer beams effectively enhances flexural capacity, crack resistance, and overall structural performance