Foundations for a spread footing
Foundations for a spread footing
(OP)
I have been asked to design some foundations for a metal building. I asked for a soils report, was told it was not going to be provided, and assume its clay.
So, I was going to use 2000psf as a bearing capacity, and notes all over the drawings to confirm in field, and 6" of stone under all footings.
What do you guys think?
So, I was going to use 2000psf as a bearing capacity, and notes all over the drawings to confirm in field, and 6" of stone under all footings.
What do you guys think?






RE: Foundations for a spread footing
Check with your local jurisdiction to see what they require. Not trying to be rude, but rt doesn't really matter what we think as we are not there. You are.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Foundations for a spread footing
RE: Foundations for a spread footing
I know its up to me to decide what to do, but just wanted some 'second opinion' type stuff.
RE: Foundations for a spread footing
I do disagree with jeffhed regarding spread footings not working on expansive soils. Performance expectations definitely need to be examined, but in my area, we build over expansive clays all the time. The building pad needs to be improved with the proper fill material with an adequate thickness, but the footings might still bear on expansive clays. A typical metal building design might incorporate a spread footing at the base of the rigid frames (typically at the exterior edge of the foundation) that has a continuous perimeter grade beam and probably a tie-beam from one leg of the rigid frame to the other. I generally use a 36" minimum grade beam depth (generally 30" minimum below surrounding grade) to help reduce soil desiccation. Owners in my area are typically aware that some movement (and maintenace) can be expected, but are willing to accept this level of performance as opposed to the added cost of a suspended foundation.
RE: Foundations for a spread footing
RE: Foundations for a spread footing
BA
RE: Foundations for a spread footing
It's truly amazing how cheap a Geotechnical Report is. I've seen quotes of about $4000 with borings for a decent one. I'm sure a shoddy one is cheaper. If the project isn't worth enough to justify that, it isn't worth your engineering it.
You can be sure there will be plenty of money available to study the building if it sinks into the swamp.
RE: Foundations for a spread footing
RE: Foundations for a spread footing
Its a 6000 sf metal building. I know that its still a building, but small at that. I think the biggest reaction is about 15K
RE: Foundations for a spread footing
In our areas, we have loess soils which are silty clays - if you put gravel anywhere near footings you could get underground erosion - transfer of materials from one area to the other and result in sinkholes or settlements.
RE: Foundations for a spread footing
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Foundations for a spread footing
RE: Foundations for a spread footing
Rather substantial I'd say 2.5 tp 3 yards per footing? $1000 in place per footing?
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Foundations for a spread footing
Jeffhed has a valid point. I looked at a 5 story building with shallow mat foundation on expansive soils. The building was designed by national firm and the soils report was done by another national firm. The mat cracked and the room seperators has had buckled. The building owner decided not to hire the soils firm to do observations- an outside less experienced firm was brought in and they did not catch it.
About 15% of our revenues are from structures like these mentioned above. If your client insists on no geotechnical investigation report, use drilled piers & grade beams with structural slab and assume mud (100 psf skin friction).
RE: Foundations for a spread footing
EIT
www.HowToEngineer.com
RE: Foundations for a spread footing
And I agree with the nickle and dime stuff on the geotech report is ridiculous. They end up paying for it anyway at some point. Either we assume ridiculous design parameters and give them an overly conservative design that costs more than what they need or we require the contractor to confirm any of our other assumptions during construction (which means they pay for the borings and charge a markup on it). I just don't get it.
PE, SE
Eastern United States
"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi