Bearing Wall Question / Opinions Please

[00Z]

I am designing a 4,000 sf office area wholly contained inside a 10,000 square foot building. Thee office is a big box 40'x 100'. The perimeter walls will support ceiling joists only. There is a clear space between the office ceiling and the warehouse roof of around 14 feet. My questions are:

Would you design the ceiling joists for 10 PSF or 20 PSF live load?

Would you consider the walls supporting the ceiling joists to need a footing (ie saw cutting slab to provide 12" deep footing or can the wall just attach to the slab. I could check the slab for shear and I think it will probably work). The max load along a wall will be around 500plf. The slab is 5" thick, but I don't know what kind of reinforcing it has?

PS. The building within a building will be designed for seismic loads and footings will be provided at shear walls.

Thanks in advance for your opinions.

 

[msquared48]

If those ceiling joists shield a space for mechanical ducting, electrical, etc. where a workman can access in the future for remodels, use 20 psf live load. If not, use 10 psf.

Mike McCann
MMC Engineering

 

[00Z]

Thanks msquared48 I appreciate the advice. They are supporting some mechanical equipment and I will use the 20psf.

 

[Triangled]

I've seen spaces like that become very tempting for storage.

 

[00Z]

I was worried about that too. I emailed the client and put the email in my file... They said it wouldn't be used for storage.

 

[AELLC]

Doesn't the geotechnical report specify what uniform load is OK for a slab w/o footing? Ask for an addendum.

 

[00Z]

They don't have a geotech report. The existing warehouse was built back in the 60's.

 

[AELLC]

If the soil is reasonably competent (enough sand content) I don't see a problem with 500 plf.

 

[00Z]

Thanks for the input AELLC!

 

[steellion]

I would use 20 PSF ceiling load and 5 PSF minimum lateral load on each wall for stability. I would put the bearing walls on footings even if the numbers worked out to bear it on the slab.

 

[XR250]

500 plf should not be a problem on most slabs. I usually jump on the slab or hit it with a hammer. If it sounds hollow underneath, it means some settlement of the subgrade has occurred and the capacity may be questionable. I believe slabs-on-grade on decent subgrade have significantly more capacity than we give them credit for.

 

[a2mfk]

Even though the loads are pretty light, I would want to inspect the slab exactly where the walls are going and have a chance to address cracks and joints (fill with epoxy). I would probably drill a few holes in the slab and probe with a CPT to see what the soil looks like. It may be overkill, but fast and cheap insurance just to know what is under the slab.

However, compared to a rack or forklift, those are light loads. And 500plf is presumably with a full live load, which that roof will never see, and most of its life there will be next to zero live load.

Agree with Triangled, this roof looks like a mezzanine and someone will want to stack crap up there. At a minimum I would put your live load very clearly on the drawings and indicate this is not designed for storage.

 

[00Z]

Thanks for the input steellion, excelengineering, and a2mfk.