Metal Building - Lateral Load Question

[H57]

I am designing the foundation system for a metal building. Due to poor soils and large building loads (100' spans and bridge cranes), the building will be supported on auger cast piles. The outward thrust of the exterior columns is ~30 kips. Additionally the high interior slab loads may cause slab settlement greater than 6".

I have designed foundation for alot of metal buildings using hairpins, direct ties and drag struts, but all of these systems may be compromised with the potential settlement of the interior slab. Is there another type of lateral restraint that I can consider for these footings?

Thanks for any help.

 

[JLNJ]

6" of slab settlement? Wow! That has to create a host of its own problems.

Did you look at inclining a few of the auger cast piles?

 

[hokie66]

You need to use either inclined piles or ground anchors; or groups of piles which form rigid frames. Inclined piles or ground anchors would be at the top of my list.

 

[JAE]

The inclined piles would certainly provide a lateral restraint component for the horizontal shear at the column base.

But you'd also be helped by spreading out the piling and creating a tension-compression couple between piles in a group to resist the lateral moment at the column footing due to vertical eccentricity between the column base reaction and the pile cap elevation.

 

[smb4050]

I assume a geotechnical engineer issued a report saying its ok? Regardless if a report has or hasn't been issued, I would make sure the owner is aware of the problem and recommend, in writing -no email- with copy in file, they address the large soil consolidation issue due to the potential for structural problems, and increase construction costs. If problems arise, it could be claimed you didn't fulfill your fiduciary responsibilty.

 

[MikeE55]

If you are looking at potential settlements of 6", the geotechnical report should have suggested supporting the slab on piles also. I suggest using a reinforced structural slab.

 

[ztengguy]

How fast can you run away from this project? Seems like a different review by another geotech is in order.

 

[structSU10]

why is the slab not a structural slab supported on piles? That level of settlement is insane and would cause major problems.

 

[msquared48]

I totally agree with the above comment, and that was my first reaction too. The client will not be happy with the result from a utility as well as aesthetic and employee safety aspect. It will be an insurance and maintenance nightmare.

Even with over-excavating and pre-consolidation I have seen slabs become unusable after 10 or 15 years with potential settlements of that magnitude. Spend the money now and do it right.

Mike McCann
MMC Engineering