Question
What is reason of skin reinforcement for deep beams?

Answer
In BS8110, it declares that secondary reinforcement have to be provided for beams greater than 750mm deep at distance calculated 2/3 depth from tension face. Investigational works exposed that at, close to mid-depth of cavernous beams, maximum width of cracks arising from flexure might be about two to three times larger than the width of the same crack at level of surface where crack at first forms.

Presence of crack is objectionable from aesthetic point of view. Furthermore, it poses potential corrosion trouble to reinforcement of deep beams. To maintain against these crack formation, skin reinforcement is calculated on sides of deep beams to boundary formation of flexural crack widths. Though principal function of skin reinforcement is to manage crack width, it could be employed for providing flexible resistance of section.