T-beams in RC solid slab

[ramihabchi]

hi,
In case monolothically casted drop beam in a solid slab are we always able to consider it as a T-beam?
Are the transverse reinforcement in this case at top of slab used to make the T-beam section as rigid?
Why don t we always, in the mentioned case at the top,consider beam as T beam.I mean it would resist more bending moment with reduced deflection with lesser reinforcement.and slab moments will be the same,therefore reinforcement would be the same(except transverse reinforcement mentioned of course)

 

[KootK]

In case monolothically casted drop beam in a solid slab are we always able to consider it as a T-beam?

Usually yes, at least for positive bending moments and within the limits on effective width etc provided in most codes.

Are the transverse reinforcement in this case at top of slab used to make the T-beam section as rigid?

The stirrups are usually extended to the top of the slab and often assumed to be part of the connection mechanism that makes a composite member of the slab and beam web. Slab bars perpendicular too the beam are also often envisioned as being necessary for the flange force to effectively spread out laterally from the beam stem and into the slab. Quite often, however, designers will not consider this aspect explicitly.

Why don t we always, in the mentioned case at the top,consider beam as T beam.

1) Sometimes it's just a matter of laziness / computational expediency.

2) Sometimes, when the decision has been taken to ignore negative bending T-beam action, it's thought to be of little benefit to go to the trouble of accounting for positive T-beam action.

 

[rapt]

Agree with everything Kootk has said.

WE do always consider it as a T beam. Not sure why you do not.

Additional checking is required by most codes to ensure Longitudinal Shear capacity is sufficient to transfer the stresses etc to the flange.

 

[babun1]

for continuous beam with negative bm this will not help.

 

[rapt]

Not for ultimate strength, but it will for serviceability calculations to decide whether or not the section is cracked for deflection calculations and for PT design for crack control.