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Temporary structure footings
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Posted by: hjens56

12/12/2006, 15:12:27

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Hi everyone,

I am a mechanical engineer with a structural engineering question. I will have an actual structural engineer look at this at some point, but I'm looking for some general ideas for now. We are designing a temporary steel structure that is supported by a number of steel poles. My question is how you would suggest placing and securing the poles to the ground? As the structure needs to be erected and removed from the site easily, we don't want to dig and pour concrete footings. I was thinking of possibly using a flat steel plate as a base for the poles and securing it with stakes driven into the ground. Any thoughts would be appreciated.








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Re: Temporary structure footings
Re: Temporary structure footings -- hjens56 Post Reply Top of thread Forum
Posted by: swearingen

12/13/2006, 10:17:20

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What kind of loads are we talking about?

For the compression case, I would conservatively use between 250 and 500psf and design the plate area for that for a first pass. Make sure the plate is thick enough to take the moment.

The tension case is another problem entirely. It really depends on what kind of loads you're talking about. If you just want to stop it from moving laterally, sure a few stakes may be in order. However, if you have significant uplift, it may require some deadmen or some screw in anchors.








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Re: Re: Temporary structure footings
Re: Re: Temporary structure footings -- swearingen Post Reply Top of thread Forum
Posted by: hjens56

12/13/2006, 12:10:44

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swearingen,

How conservative is your 250 to 500psf estimate? I ask because that would make a fairly large plate (if I remember the initial estimates correctly somewhere around 25 ft^2). That gives you an idea of the load too. Some random soil load numbers that I have come across have been between 1000 and 3000 psf.

Also, there shouldn't be any significant uplift, however, there will be some medium sized lateral loads. I guess my question is how to relatively easily anchor the structure without pouring a concrete footing. Note again, that this is not a permanent structure, it should only be in place for a maximum of one month.








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Posted by: Kelly Bramble

12/13/2006, 10:24:10

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Have you considered a concrete anchoring stud system? Search the internet for "Hilti Anchoring Systems". These stud-concrete systems allow you to drill or cure the studs into the concrete. Then you bolt the structure to thye studs. When you are done, you can cur off the studs flush.







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Re: Re: Re: Temporary structure footings
Re: Re: Re: Temporary structure footings -- Kelly Bramble Post Reply Top of thread Forum
Posted by: swearingen

12/13/2006, 13:21:58

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Kelly, the supports are on ground; there's no slab/footing to drill into.

The 250-500 is somewhat conservative, but you must remember that the numbers you get from a geotech normally refer to the bearing capacity at least a foot or so down. It is normally assumed that the surface soils aren't worth much. If you're willing to dig down 12" to 18" to undisturbed soil and put your plates there, I could see going up to 1000psf. That would reduce your plates (according to the info you gave me) to a max of 42" square.

If you do dig down, you could put some "cleats", or plate shear lugs under the plate to dig in and provide lateral resistance. Don't neglect the friction effect between the soil and the bottom of the plate, either.








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Posted by: hjens56

12/13/2006, 13:33:20

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swearingen,
Thanks for the responses, they were very helpful. Good ideas, I'll look into some of those.







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