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RC balcony on different level than the rest of the slab 5

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mats12

mats12

Geotechnical
Dec 17, 2016
181
What is the best reinf.detail so you get a good moment transfer from balcony to the inner RC slab?

Is what I draw any good?

I'd like to see some opinions and suggestion.

Thx.


balcony_g3vkjv.png
 
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It looks to me like you don’t understand even the most basic concepts of reinforced concrete design.
 
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I'm not an expert in RC design by any means, but I can tell your rebar is all out of whack. You have positive reinforcement in negative moment regions, and no meaningful negative reinforcement anywhere. Don't crowd source this one. Go sit down with one of your senior engineers and talk through it.

Balcony failures are serious problems that cost lives. Granted, most of the issues are with poorly detailed wood balconies, but if you continue down this path you could be setting the stage for a poorly detailed concrete balcony failure.
 
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Aside from the obvious structural issues identified above, I've never seen a balcony slab set higher than the internal slab. I hope the architect has a tried and tested weatherproofing/waterproofing detail to handle this situation.
 
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What you have wont work. utilize an engineer in your office or hire one to do your concrete design please. and then you learn something for the next job so a win overall!
 
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Mats,

I believe you've asked similar questions about reinforced concrete slabs. Although I believe one in particular was going from a thicker slab for a cantilever to a thinner slab inside the house. Refer back to those for a better start on how to detail cantilevered slab reinforcement. Then go and look on the site for slab dropping details (there are quite a few) and try to incorporate the recommendations there.

Of note, it wouldn't be a bad idea to flip your green piece of reinforcing upside down, and you still need top reinforcing in the lower slab.

The key to reinforced concrete is to provide steel wherever the tension is from the moment. Your moment diagram is correct, reinforce accordingly.

Edit: I also agree with nineninenine, I've never seen a balcony slab higher than the interior. Especially 280mm higher, that's like two steps up to get out.
 
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Tough room. Like all things structural, the first step is to tell an elegant story about your load path.

c01_zbiu7d.jpg


c02_w4zxlm.jpg
 
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Including the structural issues, you will likely get sued over the waterproofing issue you created with the balcony slab higher than the interior slab. Terrible ideas, both. Don't do this.

@kootk....if the OP is in a high wind area, your detail won't work.

 
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Maybe they'll have a quarry tile floor...with a really thick mortar bed?
 
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Look at the moment diagram you drew. Imagine the horizontal axis is the midheight of the slab. Your main reinforcing steel will be placed on the face of the slab corresponding to where your moment diagram is drawn. But don't leave the other side unreinforced.

I really don't understand why a balcony slab would be at a higher elevation than the interior slab. Terrible detail.
 
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Ron said:
@kootk....if the OP is in a high wind area, your detail won't work.
Click to expand...

OP showed gravity load so that's what I spoke to. I would expect any competent engineer to know their load cases and design accordingly. I feed animals; I don't hold their furry little paws. Showing bottom bars would only have obfuscated the principles that I was trying to convey.
 
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Weird to have the balcony higher than the inside. Is there a fish pond inside?

As for reinforcement, for a cantilever the critical
thing is continuity of top steel. Yours isn’t continuous. Kootks bottom diagram is how I would detail it. A cage with slab top bars hooked into the far side
 
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It looks like someone sketched out what you should do and you accidentally flipped the paper over when you brought it back to your desk. Flip the paper over and everything looks good.
 
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Maybe the sketched detailing actually is a regurgitation of it done the other way 'round. It would be just right even down to the diagonal bar that way.
 
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We really shouldn’t be encouraging this kind of pretend engineering, it has the serious potential of being downright dangerous. He/she should be going to their boss for guidance and assistance with this engineering design, so the boss can look over their shoulder and keep them, the company, and the general public safe and out of trouble. They certainly shouldn’t be doing this engineering design without guidance and supervision, and that guidance shouldn’t be coming from the internet. If they don’t have a vague idea what they are doing, they shouldn’t be doing it. And, we shouldn’t be encouraging this pretend engineering, by answering their questions. And, except for member numbers and ad dollars, they certainly shouldn’t be a member here on E-T, since they are so obviously not an engineer by any stretched definition of that word or work.
 
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I think the OP received the design from a structural engineer for a project involves both, however the OP accidentally flipped the page, otherwise everything looks normal (except the use of old, reversed sign convention for moment diagram).
 
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It is not upside down.

And none of what has been proposed will work, because the sketch is out of scale. Draw it with the dimensions the OP gave, and the picture gets worse.
 
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Like this? The cantilever can be a canopy over door/window, although called as balcony.

b_yektgh.png
 
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This is to scale. I think it's doable. Sure, I'd widen the beam thing a bit if I had the option but I feel that it's build-able either way. If lap & development lengths are a problem, on can over specify the rebar and prorate the development as required. Or use stirrup hooks around longitudinal bars. Given that this is a linear thing rather than a beam step, demand ought not be too serious.

c01_th2t5d.jpg
 
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One could even do something like this if they had to, pairing tall and short stirrups.

c02_lylse3.jpg
 
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