Curved Concrete Balcony Slab with Edge Beam

[engstructural]

Hi,

I am looking at a design of a rectangular balcony slab with 1 outer curved edge, the slab is well supported on the ends (built in) and also has a small amount of support at the ends of the curve, I would estimate the curve has a max. offset of 550mm and has an edge beam (down stand). As the edge beam will be cast monolithically with the slab am I right in assuming if the reinforcement is detailed correctly the beam will not develop torsion as the slab will provide restraint. therefore the beam can be designed as simply supported with the span = curved length but detailed to tie adequately into the slab.

 

[ishvaaag]

Yes, since you´ll be restraing torsion with monolithism, tension (cantilever) rebar atop and (cantilever) compression at the bottom of the slab, the situation for your beam is one of secondary torsion and may be (usually) disregarded. Anyway any 3D model showing all the intervening elements will show what to take unto account.

 

[ishvaaag]

For a curved steel beam at the edge more deep than the slab, better also add the precaution of adding inner vertical stiffeners passing the torsional restraint to the bottom flange.

 

[engstructural]

Thanks,

I am designing by hand but have the design done. Also I would be interested in anyones thoughts on this situation if the beam is an up stand. (up stand maybe 215 wide X 300mm Ht.)

 

[csd72]

The upstand beam would be no different than the downstand.

Ishvaags comment was based on the assumption that it is a steel beam but it is apparent that the beam is concrete.

You should always provide closed ties to these things mainly for serviceability.

 

[BAretired]

Are you relying on the curved beam to carry part of the slab?

BA

 

[engstructural]

I am not relying on the beam totally but am assuming it will stiffen the edge of the slab and support 1/2 - 2/3 of the slab on the curvature ( approx. width supported 400mm) I designed the section of slab supported at the ends as simply suported and carrying the load applied to its own area and the load from the unsupported curved area. I also designed the distribution reinforcement to act as a cantilever carrying the curved area and assumed support at the edge of the imply supported section.

 

[BAretired]

If you are relying on the curved beam to carry a portion of the slab, I do not agree that torsion in the beam can be assumed to be zero, although the torsional moment in the beam will be reduced. Can you provide adequate torsional reinforcement in the curved beam assuming it carries all of the torsion?

I do agree that the curved beam will provide edge stiffening.

BA