BS8110, a British Standard for structural concrete design, mandates secondary reinforcement, also known as skin reinforcement, for beams deeper than 750mm. This reinforcement is positioned at approximately two-thirds of the beam’s depth from the tension face. Experimental studies have revealed that flexural cracks in deep beams can reach widths two to three times larger near the mid-depth compared to their surface width.
The presence of such cracks is not only unsightly but also poses a risk of reinforcement corrosion. To mitigate these issues, skin reinforcement is strategically placed on the sides of deep beams. Its primary function is to control and limit the width of these flexural cracks, thereby safeguarding the aesthetics and structural integrity of the beam.
While crack width control is the primary objective, skin reinforcement can also contribute to the overall bending resistance of the section. This added benefit further justifies its inclusion in deep beam design, making it an essential element in ensuring both durability and structural performance.