concrete balcony supported by the threaded rod design

[dannyypk]

I am designing a concrete balcony supporting by (3) 1" dia threaded rod embedded into the concrete balcony 12"
(see attachment.) The balcony is designed to supported by the rod not by the block veneer below.

I believed the threaded rods had to extended and tied to the blocking in between the TJI in order to resist the uplift forces created by the balcony.

I think shear is not a problem. Just want to see the (3) threaded rod is enough or not.

Please input any suggestion.

 

[kslee1000]

Correct me if I am wrong:

Assume normal weight concrete (125 pcf), for 8" slab, the dead load is about 82 psf, would there be a uplift problem (by natural forces)? If so, what is the cause?

Yes, I would extend the rod at least another foot or so. How far apart are the rods? Is there any bar in the transverse direction. Any concern for cracks?

It looks like the lower trangle fillet is to be attached to the 4" block by anchors/studs. Are they capable of holding the fillet in position when experiencing forces exerted by the cantilever slab due to deflection?

Sorry for posting questions as answers to your question. Just want to share the thinking.

 

[Lion06]

Is this a precast balcony or cast in place? Either way, I would use a nut on the end that's embedded in the concrete.
Also, what are the 3 - 2x's attached to? You could have a pretty significant lateral load on those from the threaded rods because you have a relatively short moment arm between the compression face and the rods.

 

[concretemasonry]

After looking at the detail, I see a bolt with a 4 - 1/2" (3-2xs) non-structural space between the nut/washer and the face of the precast (drilled holes in wood do not provide and support). This eccentricity and rotation can cause bending of the bolt, which may have to be partially resisted by the bearing of the cornice(?) below depending on the actual construction. This could lead to cracking since the veneer wall ties are not designed to resist concentrated horizontal loads.

Not a pure structural opinion but based on movement and water penetration and mold problems.

Dick

 

[JAE]

What keeps the concrete balcony from rotating? The threaded rod won't.

And with all that tension on the bolt, what keeps the wood blocking from rotating? How is it connected to the floor structure and do those connections have the strength and stability to resist those forces.

 

[concretemasonry]

The more rotation, the more load put on the non-structural masonry, which is only intended to transfer wind load to the back-up.

If the actual detail/construction is "loose" the cantilever will rotate more and allow the water to drain off before the wood (unflashed detail) rots or a group of people end up below.

Dick

 

[hokie66]

This doesn't look like a "balcony" to me. It is part of the architectural adornment, and thus should be supported on the veneer vertically, with lateral support back to the floor joists.

 

[bigmig]

JAE is right. Your bm will be rolling. EIT is right in that you need a nut on the end of your rods to develop the embedment. Concretemasonry is right in that any gap will bend your shear bolts.Your rods are way oversized. 1" A307 supports something like 15,000lbs, and you have 3? (45k capacity). You will not be connecting 45 kips to a wood floor system and having a good day with.

Reduce the rod size appropriately and run it back so that it connects into a hold down (i.e. Simpson) doh!! I'm not supposed to say that. Admin please don't delete my post ! Anyways, some type of connector that attaches itself to a wood member in your floor.

This wil drag all your lateral forces through your floor diaphragm into some shearwalls that you will in turn need to design. Do not make the mistake of thinking that this load goes into your floor and than magically disappears. Trace it all the way to the foundation.

 

[asixth]

Salvadori and Levy has a good example on what not to do for landings supported by threaded rod.

 

[msquared48]

The eccentricity here concerns me.

I would add an angle to bear on the top of the three wood rim joists, through the vertical leg of which the threaded rod could pass. If necessary, the angle could be set into the top of the joists so that it was flush with the top of the joists.

If the space was available, I would feel even better if the angle was a "Z" section, where the lower leg of the "Z" also supported the small concrete ledge directly, further eliminating the eccentricity.

Mike McCann
MMC Engineering