Residential Slab Footing - Two Pour

[Choppme]

Hello, I have an architect that disagrees with my detail for the exterior footing of the slab. It is detailed as a two pour slab and I have shown the 12" wide, 12" deep footing with the inside top of footing angled at 45 degrees toward the exterior edge instead of the typical 45 degrees toward the interior of the slab.

I was told that as long as the cold joint at the top meets the minimum stemwall width (6"), that inside corner area in question could be angled either way.

Any help would be appreciated, thank you.

 

[14159]

You're going to have to describe this situation better for dense people like me anyway. I've done lots of this kind of stuff and can't visualize what you're typing about.

DBD

 

[Choppme]

I will try to be a bit more descriptive.

The concern is with the direction of the chamfer between the slab and the footing. Picture a cross-sectional view with the slab sitting on top of the 12" deep, 12" thick exterior wall footing. Some will draw the inside line of the 12" thick footing straight up (to the bottom of the slab), some will draw it 45 degrees away from the footing (to the bottom of the slab) and I have drawn it 45 degrees towards the stemwall, leaving only the minimum 6" width for the cold joint between the slab and the footing.

This is gonna be rough! And it's so clear in my head....

 

[blake989]

I think I see what your saying, but ask yourself, how will the contractor form that into the slab? That area is usually cast against terra firma.

 

[Choppme]

Exactly, it usually is cast against the ground. However, I understand the top of the footing would be formed with boards leaving an opening at the top of the footing for the slab to rest on (cold joint).

Maybe this will help......

111111111 111111111
111111 1 111 1
1 1 instead of 1 1
1 1 1 1
1 1 1 1
111111 11111

 

[Choppme]

well, that didn't work. Thanks for your help anyways, I'm in to see the local building officials!

 

[AggieYank]

2 things + a disclaimer:

1) I don't see why you'd have a cold joint on top of a footing. We wouldn't specify a footing having a cold joint in the top portion of it, we'd place it in the beam somewhere, preferably not at the end of a beam.

2) As far as slope of the footing, we leave it straight (vertical), with a slight slope towards the interior which simply is easier for the contractor to form (since the soil at the edge tends to fall into the footing). This is what a typical exterior footing looks like for us:
____________________
| ________
| /
| |
|_________|

Disclaimer: I'm still not perfectly sure this is what you're talking about. If it is, and I were you, I'd thank the architect for the advice, and change my detail.

 

[AggieYank]

well the sketch didn't turn out so hot. imagine that the part at the bottom is even with the rest.

_________________
| _________
| /
| |
| |

if this doesn't work, i'm giving up.

 

[Lutfi]

Choppme,

Why not place the slab monolithically. What you are trying to do is not the normal way of doing it. I always use 45-degree slop when the slab transitions into the footing.


Regards,
Lutfi

 

[Ingy]

Choppme, I have to agree with AggieYank. The contractor is going want to cut the grade beam/footing with a backhoe and only form the outside edge. The inside edge will slope with the natural earth. (as an aside, my crews always wonder why we engineers draw a perfect 45 degree chamfered interior corner when no one is ever going to do it exactly that way...)

In any case, I would say the extra concrete is worth avoiding the hassle of forming the inside edge at an angle.

I also agree with Lutfi that a monolithic pour would be best. One mobilization is always cheaper than two.

 

[lsmfse]

Choppme, we have done this with the angle towards the edge tapered to 6+ inches. The client was using some type of insulation below the slab and intended to seal as much temp. infiltration as possible. You should provide slab dowels from the footing for the second pour. As with the above posts, the slab angle to the outside is more expensive to form(some guys just try to "stack" the concrete which is no good)You still want good concrete consolidation by use of a vibrator.

 

[Choppme]

Thank you Ismfse....at least it's been done before! Well, I think I will redo the detail. It is apparent that placing the chamfer towards the outside is much more confusing (even to structural engineers!!) than it is placing it towards the interior of the slab. I'll stick w/ the typical and save myself the headache!

Thank you everyone for your ideas/opinions......