Foundation

[hello12345hello]

I have to design footing for metal building. Building is very small. I have uplift 6 kip and 4 kip shear. I am trying to use 12" continuous wall with 2ft wide footing. column will sits on wall. i check 4-3/4" anchor bolt as per appendix - D. it's fine. Now question is to check for uplift i will consider 45 degree cone from column to take into account for dead load. To check against over turning at bottom of footing do i have to consider hori load 4kip times height 3'-0" = (12 kip ft) or i should say that this hori load will resist by passive pressure ?? 4 kip shear is out of plane of continuous footing. does it matter weather this acts outward or inward?? slab is isolated floating slab. there is no bent rebar from slab in to footing. Does it helps to add bent bar from slab to footing to resist this horizontal load.?
thank you

 

[msquared48]

Depending on your detail, hairpins into the slab from the footing would take the lateral of that magnitude without relying on any passive pressure. With these hairpins, you need not worry about the overturning either.

Mike McCann
MMC Engineering

 

[hello12345hello]

if the load acts outward we can resist lateral load by hairpin reinforcement as shown in figure aci 318-08 appendix D but how about when load acts inward ? this hairpin rebar helps to transfer shear to slab. So with hairpin rebar i don't have to check footing overturning from horizontal load and concrete breakout strength for shear ? Correct? If the load acts inward haairpin rebaar won't be enough developed due less edge distance.

 

[SteelPE]

When I design similar footings I only use hairpins to resist forces away from the building (putting the hairpins in tension). If I have forces acting into the building I will design the footing for the overturning and sliding forces....... this is because I don't want to design a 6" slab as a RC column.

I have details where the engineer will provide a 10'x 10' thickened slab at each column location (9"-12" thick). I'm not sure if this to increase the strength of the slab to resist the compression forces or not. I did find this intriguing.

If I were to design a footing for a 12'k overturning moment I would only count on the dead load of the footing/structure and any soil above the footing to resist this moment (run through the load combination of 0.6D + 1.0W). I would not rely on passive pressure to resist overturning moment...... only the 4k of shear will be resisted by the passive pressure.

Hope this helps.