Interior Storage Build Out

[kmart30]

I have a client that bought a unit in a newly built PEMB with traditional portal frame construction, party walls between units, and a slab on grade. He wants to construct a 2nd floor storage area for his shop about 30'x50' in area. He reached out to his architect and to the other tenants that did similar upgrades and he said they didn't need to install footings for the new interior walls/supports. The slab has no traditional reinforcing (fiber reinforced I believe), no post tension, and is 5" thick....how can a design professional, contractor, plan reviewer, ect. say no footings are required for 125 psf live load on a 5" S.O.G? Am I missing something here????

He shared a letter with me written and sealed by the architect for the build out next door confirming the 125 psf design load and I didn't see any saw cuts or areas where they installed new footings under the new framing....

 

[TEDstruc]

In the automotive assembly world, it's pretty (very) common to install mezzanine columns on slab on grade, although it is typically reinforced. That being said, the live load is generally far less than 125 psf. Maybe you can design the structure and provide the reactions for the columns. And tell your client, you aren't comfortable anchoring the columns to the slab on grade, and maybe they can ask the architect to take that portion of the job on.

Otherwise, Maybe you can space the posts close enough together and reduce the reactions enough that you can use the un-reinforced concrete provisions of the ACI code.

i.e. 10'x10' column spacing x (125 psf LL + 15 psf DL) = 13.5 kips / 2 ksf allowable bearing pressure = 6.75 sq ft needed for bearing. Now check a 3.6' x 3.6', 5" thick unreinforced footing for moment and shear. Who knows? It might just work out.

 

[jittles]

This is a decent summary of using a slab on grade for concentrated loads:

[URL unfurl="true"]https://www.structuremag.org/wp-content/uploads/2014/08/C-StructuralDesign-Azzi-Apr081.pdf[/url]

 

[kmart30]

No columns all wall loads....We have about 3 kips/ft along some of the interior walls with the trib. areas and floor framing layout. I just cant wrap my head about using concrete tensile strength with only 5" depth of slab. Regardless if we can make it work or not we are the first ones they call when the cracks start to pop up. We would have to make a good amount of assumptions for how the existing slab and sub-grade was prepped, compacted, and installed....

 

[Ron247]

I would check the un-reinforced concrete in the ACI as TED suggested. If it works, OK, if not, let the Architect do it. I think the 5" gets checked as 4" since I think there used to be a "spoil" provision of 1". I have little faith in the Architect to really know what the slab can hold.

You say it is walls, not columns. Are your newly load walls at the Tenant separation? If so, do you know if there are saw cuts on the other side, or if they have loaded their walls also?

 

[kmart30]

One wall will butt up against the separation wall and the other far side will be at the exterior of the building. There will be 2 interior wall lines as well.