ACI-318 110.15 ù column loads through floor sys

[boffintech]

Say you have an elevated slab, your columns are 12Ksi, your slab is 5ksi, and you have 24dx24w beams. The 12ksi mix is 8-10" slump mix (high range water reducer) and really runs laterally in the form. So the contractor it going to puddle the 12ksi mix through the depth of the beams and follow the instructions below:

ACI318 10.15.1 — Concrete of strength specified for the column shall be placed in the floor at the column location.
Top surface of the column concrete shall extend 2 ft
into the slab from face of column. Column concrete
shall be well integrated with floor concrete, and shall
be placed in accordance with 6.4.6 and 6.4.7.

The contractor wants to use Stay-form to block-out the 2' zone around the column through the depth of the beams. This will prevent the 12ksi mix from running away. Stacking concrete at the columns doesn't work and placing the 12ksi at a low enough slump to prevent running risks too fast a set and a potential cold joint.

http://amico-stayform.com/

Will the use of this product satisfy the requirements of 10.15.1? Of course the two concrete mixes will not be "well integrated" but both mixes will be well consolidated on either side of the Stay-form.

Any thoughts?

 

[JAE]

My thoughts are that you are potentially creating a cold joint which is contrary to what ACI 10.15.1 is intending with the words "well integrated".

This could be a potential problem in that with a cold joint you would have a whole set of development lengths to consider....your shear capacity at your beams would be possibly affected, etc.

My initial thought would be to use the forms, but use them not as "stay" forms but rather as temporary forms, allowing separate placements of the two types of concrete, then once the concrete is in place, pulling the forms vertically up and then vibrating around the perimeter to mix and integrate the two mixes.

 

[hokie66]

I think it is a terrible idea. The 12 ksi concrete for development of the column strength through the floor should not be the same mix as the columns. It should have similar slump characteristics as the floor concrete, but strength to suit the code condition. I sympathise with your having to use the ACI Code, as I did for many years. In the Australian Standard, we need not "puddle" until the column strength is 1.4 x the floor strength, or 2.0 x the floor strength if adequate confinement exists in the floor.

 

[slickdeals]

HOKIE66, I think ACI uses the 1.4 factor as well. See section 10.15. If column strength > 1.4 floor strength, then restrictions apply.

 

[hokie66]

Yes, but in boffintech's example, he has 12 ksi columns and 5 ksi floor concrete. Our solution in Australia would often be to increase the strength of any floor affected to 6 ksi, thus eliminating puddling, which is tough to control. To do this, we have to comply with confinement conditions.