Metal Building Foundation. 2

[shin25]

I am trying to design a slab on grade for a metal warehouse building. This slab also needs to act as foundation for column vertical tension and compression loads. This is my first time designing a foundation like this. I would like to know, how the moments due to these vertical loads can be closely calculated?

Also, I shall appreciate any other design consideration.

 

[MattJM]

Awhile ago Butler produced a document called Foundation Design and Construction Manual. It is out of print , but if you can get your hands on it, there is some good advice on hirpins, slab reinf., etc. etc. (Some previous threads in this forum also metion it).

Large footings for uplift are very common for PEMB. Often, downward soil presuures become very very small. Engaging the slab for uplift may result in slab cracking (and then what), and I would avoid it if possible. With use of hairpins or foundation tie-beams and centrally loaded foundations (if this is possible), you can drastically reduce the moments created by the horizontal and vertical forces.

Also, refer to ACI for embeddment of anchorage for the uplift forces. A thickened slab region may not be sufficient for very large loads.

 

[msquared48]

MattJM:

Regarding the last paragrph of your last comment, this can be true, but with top steel and the anchor bolts welded to an embedded plate placed deep in the footing, it should not be an insurmountable problem. Or you can deepen the footing, at least locally in the area of the anchor bolts, to make sure it works in uplift without thickening the whole footing if the dead load is not needed.

Also, 271828, yes, that's right. I'm too fixed on WSD for the overall view of things I guess.

Mike McCann
McCann Engineering