Necessity of Doubly Reinforced Section

Doubly reinforced sections are used in the following conditions:

1. When the dimensions (b x d) of the beam are restricted due to any constraints like availability of head room, architectural or space considerations and the moment of resistance of singly reinforced section is less than the external moment.
2. When the external loads may occur on either face of the member i.e. the loads are alternating or reversing and may cause tension on both faces of the member.
3. When the loads are eccentric.
4. When the beam is subjected to accidental or sudden lateral loads.
5. In the case of continuous beams or slab, the sections at supports are generally designed as doubly reinforced sections.