Cantilever balcony?

[MIStructE_IRE]

My gut instinct is that I just don’t want to...But an architect is pushing to use tapered tee section cantilevers for a series of residential balconies? It could work in theory I suppose but I just don’t like how flimsy it all seems.

A concern I have at the moment is that no one seems to have done it anywhere before?! I can’t even find photos of one online and it has me questioning if perhaps there’s good reason for that?

Has anyone done it? I’ve done it for light bus shelters and canopies but supporting a metal deck slab working as a balcony just seems too flimsy.

 

[Agent666]

What proportions are we talking here, balcony and tee member cross sections/spans, etc?

Anythings possible if the numbers work out. Just because it's not common doesn't mean you couldn't get the numbers to work out for example. Depths of tee vs other structural section might be deeper, heavier, etc. They probably just think it looks nice, without considering its twice the depth or something which takes away from the aesthetic they were potentially trying to create....

https://engineervsheep.com

 

[TLHS]

The common issues with cantilever balconies tend to be pretty wood specific. The back span is a pain for wood. I'm not sure why it'd be much of an issue in steel of concrete. With steel specifically you'll have some stability things to look out for.

You still have to deal with back spans, but they should be easier to detail than the sketchy details that lead to collapse in wood.

 

[MIStructE_IRE]

Ive done plenty of steel balconies, just never a tapered tee.

We’re looking at about a 1.5m cantilever, 150mm dp @ 1.5m crs. It works in terms of bending/deflection etc, but it still seems to light to my mind. The fact that i can’t find a single photo of one concerned me...

 

[phamENG]

You can. I've done something similar, but the architect wanted tapered wide flange beams, so designed it as a tapered WT and then added a plate to give the impression of a tapered WF. It supported a CIP concrete slab 8" thick with a varied projection from 8ft down to nothing over a 100ft run.

The question is really with what it attaches to. If you're going to clip the flange and try to bolt the stem to a stud, then to. If you're going to have a steel backup in the wall, then I think it'll work. Depending on the projection and the thickness of the deck you may have to get a pretty heavy WT to avoid stem buckling.

 

[To Madeira]

Can you apply the methodology outlined in this design reference and check along the length of the cantilever?

http://www.newsteelconstruction.com/wp/wp-content/uploads/TechPaper/TechNSCapril2016.pdf

 

[KootK]

I'm also in the camp that this is something that I'd be fine with as long as the numbers check out. That said, I might be a little more rigorous with the numbers:

1) These shapes suck for LTB so I'd want the balcony deck and its connections to the WT's to provide positive rotational restraint.

2) I might study a portly fellow loading one tee in combination with outward guard loads to see if I could get the stem to buckle.

The dearth of examples of this might have something to do with thermal performance. It would be a nightmare in cold climate regions without some serious attention to the thermal bridging and the solutions to that can get a bit expensive.

 

[MIStructE_IRE]

Thanks guys. I’m thinking a couple of fin stiffeners down from the retrained flange which will be shear studded to the slab above. Its a small aesthetic price to pay for the added LTB resistance.