Upturned Concrete Beam Design Checks
Upturned Concrete Beam Design Checks
(OP)
For simplicity assume I have a single span one way slab supported by upturned beams on each end. In my case this is a 14" very heavily loaded slab and the upturned beams are full story walls. In practice I know that this will be two pours, the 14" slab and then the rest of the wall/upturn beam. I'm ok with this part.
What special consideration/check should I be doing at the slab to beam interface? The slab needs to deliver shear to the beam, the shear strut needs to develop sufficiently into the vertical bars to effectively 'hang' from the rest of the beam. This implies that I should have development of my vertical bars past some point in the joint correct? Measured from where? It can't be from the bottom of beam or upturned beams wouldn't work.
I've done upturned beams in that past but this one has > 1200psf on the slab so I want to make sure I'm covering my bases.
What special consideration/check should I be doing at the slab to beam interface? The slab needs to deliver shear to the beam, the shear strut needs to develop sufficiently into the vertical bars to effectively 'hang' from the rest of the beam. This implies that I should have development of my vertical bars past some point in the joint correct? Measured from where? It can't be from the bottom of beam or upturned beams wouldn't work.
I've done upturned beams in that past but this one has > 1200psf on the slab so I want to make sure I'm covering my bases.






RE: Upturned Concrete Beam Design Checks
2) Practically, you'll want to use small diameter vertical wall reinforcing with lapped u-bars at the bottom. There will be longitudinal bars in the corners of the U-bars and you'll want to run your slab bottom steel up over top of those longitudinal bars.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Upturned Concrete Beam Design Checks
What is the hanger beam concept, is there any quick summary/example that you can point to? I don't believe we have anything like this in aci (or I've missed it).
My concern is the development into the vertical bars from the slab shear. Do you agree that this is a design check and if so how do I show that I am ok. With 14" I should have Ldh if I'm measuring past the compression block of slab - so I'm likely fine if that's sufficient. Just want to make sure - I can imagine a failure mode where I'm left looking at some nice u-bars projecting from a freestanding wall.
Part 2: Back to the old favorite of punching. This upturned beam/wall is actually two columns below. There is no way to get punching to work on these columns if the punching perimeter is the column. I'm using the wall above as a continuous support, the same as if it was below, and ignoring punching around the column perimeter. kosher?
RE: Upturned Concrete Beam Design Checks
RE: Upturned Concrete Beam Design Checks
RE: Upturned Concrete Beam Design Checks
The detailing that I've been describing basically gets you a hanging support incapable of serious moment transfer. If you want moment transfer, you'll need to do something like what hokie has suggested. And that's basically what the stem/footing wall connection looks like for retaining walls in the CRSI manual. Serious stuff.
In my heart of hearts, I would love to run your wall a foot or so below the underside of the slab. I've never been able to sell that for one of my projects, however, so I won't engage in the hypocrisy of pretending that it's a truly viable option for you.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Upturned Concrete Beam Design Checks
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Upturned Concrete Beam Design Checks
I agree with the bit of a downturn, I was thinking the same thing. I may try and sell this. Feels a lot better.
RE: Upturned Concrete Beam Design Checks
RE: Upturned Concrete Beam Design Checks
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.