Pre-engineered building foundation (thrust) 1

[RRBegin]

I am detailing columns and footings for a pre-engineered metal building. This building will sit on a concrete foundation wall with a continuous footing. The plans show a detail at the column locations for a wall bump-out that is two inches bigger, all around, than the base plates for the building columns. Because the size and location of the columns were dependant on the building manufacturer, this is all the information that the plans contain.

I now have the building details provided by the building supplier. The frame reactions shown include a 12 kip horizontal thrust (DL + LL)at the baseplates. If I carry this load in the columns only, assuming that the soil offers no resistance, then I end up needing relatively large footings to accomodate this load.

How does one normally carry this load? Do you assume that the adjacent foundation wall carries it to the soil and the soil resists it via active pressure? Or, do you anchor the floor slab to the wall and take out the thrust this way? (This is what I am considering).

The building is a tapered rigid frame with a 48 foot out to out span, with bays at 12 and 15 foot spacings. The top of the foundation wall (and top of finish floor) is about 4.5' above grade, and extends another 4' below grade. The floor slab will consist of a slab on grade.

 

[jheidt2543]

RRBegin,

Check out Thread No. 256-46157 in the Foundation Engineering Forum, it discusses various design alternatives. You also must consider the effect of having your building columns 4.5' above finished floor. This will induce moments into your column design.

Just an observation, if your bay spacings are only 12'-15', the 12 kip horizontal load seams a little high to me even for a 48' wide building. What is your eave height? I assume the loadings were provided to you by the building manufacturer?

 

[RRBegin]

jheidt2543-

How do I locate the thread? I tried using the search engine, but it came up with "hundreds" of matches.

In response to your comments/questions:

I designed the column for the full height (8.5'), assuming that the walls, soil, and floor provided no support and the column base was fixed. Needless to say, I end up needing a fairly well reinforced column.

I was a little surprised at the magnitude of the thrust, also. The loads, that were provided by the manufacturer, were for a building with an eave height of 11'. The live load that induced the majority of this load is actually the snow load, which in my part of the world is 30 psf on the horizontal projection of the roof. (Hmm, thats only about 11,000 lbs vertical per column) Can the thrust load be greater than the vertical load?

Thanks for the input and (I hope) follow up.

Ron

 

[baueng]

Have you never heard of "Hairpins"? Wrap the rebar around the anchor bolts and out into the concrete floor at a 30 degree angle each leg. 12kips No problem.

 

[jheidt2543]

RRBegin,

If you go to Search, type in "Hair Pins" and click on "Key Word Search" it will take you to a search screen. On that screen you will have a number of obtions to select from. Use the ones that check all forum and all dates. That search should return two threads, #256-46157 and #507-39027, both of which discuss metal building foundations. The three alternatives are hair pins, tie-rods and concrete foundations reinforced for overturning.


Hair pins work just fine, but in your case the hair pins would be at the floor level and your column at 4.5' above the floor. So, there is some added moment in the column to account for. You also have to make sure that the floor slab is poured either before the building goes up or certainly before the snow load is applied to the roof. Because, without the floor poured, you have no hair pin capacity.

The Metal Building Dealers Association has a small handbook that discusses this and other topics related to metal buildings that may still be in print.

 

[RRBegin]

Thanks everyone, this information was exactly what I needed.

Ron

 

[RRBegin]

Sorry, me again.

Can anyone give me the url for a detail?

Thanks,

Ron

 

[scherry]

Another source of information on the design construction and etc for metal buildings is the MBMA handbook. it was not terribly expensive and has some good data, or at least i thought it did.

 

[Stumpy]

I always use rebar ties within a concrete beam (say, 8"H x 12"W) directly beneath the floor slab. Of course, the bars are hook anchored to opposing piers. Size the bars to keep stress low, reduces elongation. Use ties at bar splices.

Hairpins don't work on paper, so I don't use them.

 

[jheidt2543]

Stumpy,

Please explain your statement that "hair pins don't work on paper". There are an hundreds, if not thousands, of buildings built using hair pins.

 

[chicopee]

place rebar between concrete floor and foundation wall; also place rebar between concrete flooring and any pedestal to the column footing if design calls for them. These tie rods will reduce the moment that causes the bearing pressure exerted by footing on the ground and also you get to reduce the size of the footing.