Concrete ramp slab intersection

[DETstru]

I'm wondering how engineers typically handle crossing ramp/column interactions in solid slab/PT parking garages.
Attached is a 3D pdf showing the condition I'm talking about and some generic sketches below.

[ul]
[li]Architects seem to want to do it as shown in the attached PDF where one slab goes to the opposite side of the column and the other is only touching one face but I don't like this at all.[/li]
[li]I've seen details let the slabs overlap such that each slab touches 3 faces of the column. This leads to an issue in the location where the slabs are crossing and they are near the same elevation.[/li]
[li]I've also seen details showing the slabs terminate at the midpoint of the columns, which works pretty well as long as the punching shear pencils out. Seems like a nightmare to build though.[/li]
[li]One must also consider what is going to create the barrier between the slabs. Cable rail, concrete wall, CMU wall, or other.[/li]
[li]I've always been able to have a concrete wall running up the intersection, which solves all of this, but in this case the architect doesn't want that.[/li]
[/ul]

 

[DETstru]

Wrong attachment. New one below:

 

[dik]

Do you just have a flat plate? or do you have a flat slab with drop panels? or do you have beams framing transversely between the columns? I couldn't open the second attachment.

Dik

 

[DETstru]

It's just a flat plate. No corbels or drop panels.
The building is a multi story flat plate concrete building with a few underground parking levels.

The second attachment is a 3D pdf version of the second photo in the original post.

 

[KootK]

I'd favor a beam on one side, offset to the side of the column and provided with a corbel, even if that's just detailed integral with the beam. That beam could also be upturned if need be.

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.

 

[dik]

You will have great difficulty with the slab to the column attachment where the slab does not frame around the column without using a corbel of some kind. The developed moment is so high due to the column stiffness becoming very large when the slabs are nearly at the same elevation. A corbel provides a 'real' pin. If there are no beams or slab thickeners, you will have difficulty with reinforcing the slab at the columns.

Dik

 

[DETstru]

Seems like my second option would be feasible if the shear worked out.
Run each slab edge to the midpoint of the column such that the slab is touching 50% of the column perimeter.

Koot, a beam would be my preference as well (or Dik's comment about corbels) but the architect doesn't want that so I'm doing my due diligence first. If it comes down to it, I'll do a beam but I want to be sure I'm doing my best to accommodate.

 

[dik]

Just a caution... you may have difficulty forming the slab support as the slabs converge to the same elevation.

Dik

 

[DETstru]

Dik,
Yes you're right. I think all methods will create issues forming the slab (other than corbels on both sides with the slabs entirely separated by the width of the column).

 

[dik]

With the fixed side, the slab can wrap around the column on 3 sides and you can develop a moment and shear capacity. With the free side, you can have a corbel so the moment is 'zero' and the slab at your corbel support has to resist shear only...

Dik

 

[Deker]

Another option that works for flat plates with split level ramps is to use double columns at the interior with a small gap between the slab edges to facilitate the formwork. Push the end columns out into the landings and pour the double columns together to form one large column.

 

[KootK]

Well, if the name of the game is architect pleasing, then I say put numbers to the option where there's no slab overlap on the column whatsoever. Shear key + couplers for the top steel + essentially one way shear treatment. Frankly, with your columns turned as they are, I don't see this as being all that much worse than the other concepts anyhow. If it works at all, it may take a longer column or a pair of corbels sticking out from the long sides of the columns like ears. From there, the architect can pick their poison accordingly.

I think all methods will create issues forming the slab (other than corbels on both sides with the slabs entirely separated by the width of the column)

Something akin to a beam or drop panel is almost unavoidable at that location I'd think. Unless your up against headroom issues, I think the natural thing to do would be to carry the lower slab sofit through to the other side for a bit.

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.

 

[DETstru]

I'll run the numbers and see what happens.

Koot, a shear key or couplers aren't required since the slab will be placed top of the (short length of) column, then the next (half) level of column will be placed on top of that. Repeat up the parking levels.

 

[KootK]

Koot, a shear key or couplers aren't required since the slab will be placed top of the (short length of) column, then the next (half) level of column will be placed on top of that. Repeat up the parking levels.

Yeah, I'd not do that with the no overlap option. Mechanically, it's pretty much identical. And I'd rather have the shear key in both scenarios as I'd be concerned that shrinkage would tend to cause the slab to pull away from the column and compromise the shear capacity. Although I suppose that there'll be so much moment at that joint that a pull away on the compression side is unlikely. Either way, since the monolithic pour helps little in my opinion, I'd let the contractor pour the columns full height.

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.