What is the advantage of hidden beams in a flat slab
A hidden beam is simply a beam so built into the slab that there is no protrusion below the slab. This is achieved by placing the reinforcement for the beam on it’s side.
To answer the question there is one major advantage. Aesthetics. There are just those situations where one doesn’t want the structural members to be seen.
Another advantage is that it is easier to apply a finish to the underside if the slab, often saving time in the construction process.
Concept of hidden beams in a flat slab is meaningless design approach which I have seen used by some contractors (who doesn’t have design experience). Structural behavior wise, the so called hidden beam is going to deflect along with slab.
The slab cannot get enough stiffness to get a support from this hidden beam since the stiffness of both slab and beam are equal (since the depth remains the same). In actual, though the design of considering hidden beam done on paper, will not work in real life. There would be lots of cracks associated and there will be undesirable load distribution.
Someone can argue that, the hidden beam provided are still standing. But it should be noted that the design of concrete has inherent safety factors and the membrane bahavior of slab would re-distribute the loads with alternate load path.
Hidden beam concept may be used just to increase the punching shear capacity or shear capacity for the slab. That means the local shear reinforcements may be increased to get good shear capacity.These are the advantages of the hidden beam in flat slab.