3.0m RCC Cantilever Slab

[osa2549]

Hi
A collogue of mine has designed 3.0m Cantilever slab of 460mm thickness with sufficient back span (Back span slab depth is 250MM. I would like to know the best way of detailing the reinforcement.

 

[BAretired]

Terrible drawing! Where the hell is the 3m cantilever?

 

[osa2549]

@Baretired here.

 

[BAretired]

I don't like the concept. Additional support is needed under the cantilever so that the 460mm slab can be reduced to 250mm, possibly tapered to reduce dead load. Deflections are going to be difficult to predict, particularly if live load occurs on the cantilever, but not on the span. Could be some serious torsion on the beam on grid 06.

What is the live load? What are the beam sizes shown as dashed lines? One beam, running vertically on plan seems to have no support. Is the crossed area open?

I would like to know the best way of detailing the reinforcement.

Hard to say. I think your colleague will have to be convinced that this concept will not work.

 

[Tomfh]

Seems wrong having a 460 slab cantilevering off a much thinner slab.

 

[BAretired]

I agree Tomfh...that seems wrong to me too. Without additional support for the cantilever slab, it will be problematic.

 

[osa2549]

Live load taken is 3 Kn/m2.
Beam size is 350mmX920mm.

 

[hokie66]

460-250 = 210mm of dead load, which increases deflection. Just more concrete without reason. Your colleague doesn't know how structures work.