Brief overview of Doubly Reinforced Beam
The term doubly reinforced section is associated with the design of beams and moment of resistance. Reinforced Beam is used when there is little scope in maintaining adequate depth of the beam to transform it as a singly reinforced one.
In a Beam, it is essential to arrange Reinforcement(Steel Bars) in Compression and Tension zone. In a beam, when the reinforcement only exists in tension zone, it is defined as Singly Reinforcement Beam and when the reinforcement exists in both at Tension and Compression zone, it is defined as Doubly reinforced Beam. In both the situation, rod is used in tension and compression zone.
The moment of resistance is considered as the most vital factor of beam. The beam is designed in such a manner so that it does not collapse because of bending moment functioning on it. The depth and area of beam is arranged consistent with the bending moment functioning on it. The performing bending moment is avoided with the formation of the tension and compression forces in beam. These forces produce moment with liver arm as distance among them.
To create the moment of resistance the same as bending moment acting on it, often liver arm should be raised which in turn can enhance the depth of the beam. Once the depth is raised, the free height among floor and beam is reduced and brings about uncomfortable to roam in room. Under this situation, the width of the beam is raised to balance the moment as compressive force = 0.36*f ck*b*x.
Because of architectural point of view, to maintain appealing look, both depth and width are controlled.
Under this situation, the reinforcement is set on the top as compressive reinforcement and in bottom as tension reinforcement. Thus, the moment of resistance is raised by escalating the compressive force devoid of increasing in width and depth.