singhs Reinforced Beam: If main reinforcement is only provided at bottom when concrete at compressionis capable to carry all the compressive stresses. i.e The strain at top fibres are well within limit.
Doubly Reinforced Beam: If main reinforcements are provided at top & bottom due to excessive compressive stresses at top fibre of a beam. i.e The strain at top is more as compared to the capacity of concrete at top fibres.