200ftx200ft PEMB Foundation Design 2

[NA110]

Recently, I have been awarded a project to design the foundation for a 200 ft x 200 ft x 28 ft tall pre-engineered metal building (PEMB). Can anyone guide me on the suitable type of foundation for this large PEMB? The frame spacing is 25 ft center-to-center. Initially, I was considering a spread footing with piers and grade beams, tying the columns in both directions with pedestal columns and grade beams. However, the client wants to minimize costs and prefers a slab on grade with haunches. Is a slab on grade with haunches suitable for this type of large PEMB? Please, can anyone guide me on this?

 

[Aesur]

Another thing to consider and this is going off memory and lack of sleep, but I believe tension members such as these that have permanent tension are required to be mechanically spliced therefore you may not even be allowed to use the slab beyond the influence area of say a hairpin, which basically means plan concrete design for the influence area of the max length of a hairpin unless you have mechanical or welded splices.

 

[phamENG]

Aesur - yes, you are correct.

 

[JLNJ]

Those relatively short columns make for higher thrusts.

You have enough different details here that the contractor shouldn't be so worried about multiple concrete pours. It's not like it's a little 40x40 barn where he can pour all the footings in a single afternoon. The slab on grade is probably a 4 day effort all on its own.

 

[NA110]

Thank you so much everyone for your responses and guidance.

 

[Brad805]

The path of this thread seemed largely predicable from the start. If you do this in the future start with a well thought out sketch with forces and details of your proposal after you have done some preliminary checks.

Those are some very large shear forces. I wonder how you would set those anchor bolts if this were a typical thickened edge design? We had a discussion about that a few years back when a member noted this type of slab and could not understand how they were dealing with that problem.

I agree with Pham about the general detail included.

 

[DoubleStud]

NA110, can you post the anchor bolt pattern detail they provide? I am just curious what it looks like and what size.

 

[TRAK.Structural]

Structure Magazine occasionally has some good reading that condenses topics. See below for a link to one such article. Obviously this doesn't cover many complexities to each foundation type listed, but I think it's a decent overview.

https://www.structuremag.org/?p=342

 

[bones206]

Those are some very large shear forces. I wonder how you would set those anchor bolts if this were a typical thickened edge design? We had a discussion about that a few years back when a member noted this type of slab and could not understand how they were dealing with that problem.

Yes, and if a tie beam design is adopted, it’s a good opportunity to develop horizontal anchor reinforcement in the pedestal out into the grade beam. Couplers help with constructability.

 

[jerseyshore]

Those are some big forces, no chance this works with a haunch or hairpins IMO. Simple cheap foundation solutions should only be used for the smaller backyard type PEMB's. Something of this size with that large of spacing between columns is going to require big footings.

 

[Smoulder]

@NA110 I think you're getting good advice already. Just remember to play the game. Client has a preference for slab so if you go down that track and it looks more expensive than pad footings then you tell the client that in writing. They're allowed to play dumb because they hired you to do the thinking. Maybe also slip in there might be possibility for the building designer to look at options to reduce overall cost by reducing foundation loads. Your don't need to solve that because you're not the building designer but you are the only engineer hired by the client. The building engineer works for a sales company and doesn't have the same obligations.

 

[structSU10]

I think continuous tie beam between frame columns will be required for these thrusts. You should also consider the amount of elongation over that length.

The PEMB guys assume a rigid support at the bottom so I usually try to limit the elongations as otherwise you induce extra moments the frame was not designed for.

 

[lexpatrie]

Worth referring to......

PEMB: 240k Kickout Tie-Beam

I may as well float this concept/query. Delegated design for PEMB operates backwards, if you ask me. The PEMB guy is delegating the foundation design to the "engineer of record" running the delegation backwards compared to a standard building. Is this even correct/sanctioned?

Traditional delegation of design involves an engineer of record and a set of drawings and design criteria.

In this case, it isn't like an engineer of record produces the criteria, wind loads, seismic loads, presumed dead load "budget" and foundation and presumed reactions from the metal building and then it goes out to bid for a supplier to address the "delegated" metal frame and panel system. PEMB construction so frequently has problems, ...... they get limped through construction eventually to varying degrees of success.

I don't see how there's an EOR in these projects that is equivalent to a conventionally designed building with a clear EOR involved beginning to end, shop drawings, RFIs, etc. Usually there's a building that's designed, one presumes the correct wind/seismic and gravity criteria are employed, but it isn't as if the PEMB drawings divulge the interior guts of that design.

Then "we" come to the foundation and there's a new guy drops into the area and does the foundation design and stamps it. The process doesn't feel equivalent to me.

I'm also going to side with pham and AESUR that the original description OP sounded very new to the process. I am, however, super happy that the post title had PEMB in it.