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KinAlberta
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# Posted: 31 Jul 2015 03:18pm - Edited by: KinAlberta
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I was thinking of buying I beams to shore up one of our old buildings. Then I thought that maybe I could buy an old travel trailer for its beams. Might be able to get one for a few hundred bucks. This way my beams would come with their own wheels for transport to the lake.
Has any one done anything like this?
I imagine that a couple old 25-30' trailer frames side-by-side could serve as a base for a small cabin. 
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creeky
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# Posted: 1 Aug 2015 10:49am
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Got a hack saw? You could cut the beams off of one trailer and use them. Course you could also make a couple of beams with some adhesive, a nail gun and 2x10s for less money. Hmm.
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toyota_mdt_tech
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# Posted: 1 Aug 2015 10:55am
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The problem is any money you saved on an old trailer would be consumed in the heavy labor to dismantle it and to dispose of all the waste material after its stripped.
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bldginsp
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# Posted: 1 Aug 2015 10:39pm
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Trailer frames have two I beams, or C beams, that are set in from the outside edges by 18" or so. Then they have 18" supports welded to the C beams at 90 degrees every 24 or 36 inches or so, which support the outside side walls. You may need to cut these off before you slide in the frame. It's do-able, but after the effort and cost of disposing of the trailers as Toyota said, and the problems of adapting the frame, have to say I agree with creeky you are better off with a wood girder alternative. The size of girder you use is a function of the span you give it, so with a lesser span (more piers) you could use a 4x6 or even 4x4. If you use piers as support, the more the merrier, I always say.
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Don_P
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# Posted: 2 Aug 2015 03:11pm
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With steel and bolts or preferrably a welder you can actually make a moment resisting connection between a pier and a beam. I'd let the meth heads scrap a mobile home and then offer them slightly more than scrap value for the frame. Recover the C channel and get a copy of the AISC manual from the library for strength tables and design equations. Keep what is oriented up, up. Cut and weld a complete rectangular frame and posts, box the frame for more strength if needed. You then have a one piece rigid foundation ready to be welded to steel cast into the footing piers.
I just held up a farmhouse on recovered steel prior to pouring a real foundation. Experience usually does create some level expertise.
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creeky
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# Posted: 2 Aug 2015 03:28pm - Edited by: creeky
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Don, would steel be lighter? I have a chance to pick up another old trailer. Everything is pretty much gone but the undercarraige... wheel bearings gone. Pretty nice camper once, gone.
I'll say the guys who built this had some good ideas. The camper was hard sided and well thought out.
I want to put up a tree house. Really just the lightest deck I can get away with and a tent or canvas building on top.
Uh. Just day dreaming, what would a sketch of a welded box frame look like.
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creeky
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# Posted: 2 Aug 2015 03:31pm
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Sorry. Don or anybody else.
And what is "A moment resisting connection"?
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MtnDon
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# Posted: 2 Aug 2015 04:40pm - Edited by: MtnDon
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A "moment" is a combination of a physical force (like a push or pull on the top of a pier) and a distance with reference to a fixed point.
Beam on top of a pier example.... The force may come from the wind pushing on the side of the building wall and roof. The taller the wall the longer the 'arm' of the moment; the longer the arm (taller the wall), the greater the force. If the pier is well fixed in the ground and not moving, the beam then tries to roll over sideways. A moment resisting connection will, well, resist that rolling motion.
Those forces can also act lengthwise down the structure. Or in a combination, diagonal direction. The forces can also come from below as in a earthquake shaking the building piers. Or a force from Elmer backing into a corner of the cabin with the backhoe.
There are various ways to accomplish a moment resisting connection, many of them are missing in the typical DIY cabin pier and beam structure.
That is pretty much the idea... I hope that helps.
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Don_P
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# Posted: 2 Aug 2015 10:17pm
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Or, a moment is a tendency to rotate... so a moment resisting frame is a rigid frame. In this case welding a steel post to a steel beam to resist the tendency of that connection to rotate. Wood is hard to make rigid connections in, they are very often considered to be pinned connections, free to rotate. Steel is much easier to make rigid connections with.
When you torque a bolt there is that rotation. The unit of measure of the applied moment is usually in foot pounds. Hang a 1' long wrench on a bolt and hang a 100 lb weight on the free end of the wrench... 100 ft-lbs. A 2' breaker bar with a 50 lb force provides the same 100 ft-lb moment on the bolt.
In the case of the post and beam with a strong wind on the side of a building that connection is seeing many hundreds or several thousand ft-lbs depending on the geometry. Look in the Simpson catalog for some other examples of moment frames.
2 bolts with 1' torque wrenches on each, ends of handles welded together to form a beam, hang a 100 lb weight from that center weld, the moment is (100lbs x 2')/4... the equation for a beam with a center point load
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KinAlberta
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# Posted: 5 Aug 2015 09:59pm
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Quoting: bldginsp It's do-able, but after the effort and cost of disposing of the trailers as Toyota said, and the problems of adapting the frame, have to say I agree with creeky you are better off with a wood girder alternative. The size of girder you use is a function of the span you give it, so with a lesser span (more piers) you could use a 4x6 or even 4x4. If you use piers as support, the more the merrier, I always say.
Or wood with a flitch plate I suppose.
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Don_P
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# Posted: 6 Aug 2015 06:06am - Edited by: Don_P
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It requires more steel to create the same strength beam using a flitch plate than an I beam. You are buying steel by weight. Assembling a flitch plate beam is an exercise in misery. Floppy, heavy, hard, and it wants to bite you. Since LVL's have come along we typically go from built up wood beams, to lvl's, to I beams. I've had one flitch plate specced in the last 25 years or so for a kind of unique situation. Used I beams turn up at some of the junk yards, look them over carefully but that would be money better spent than a flitch plate in most cases.
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KinAlberta
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# Posted: 7 Aug 2015 11:36am - Edited by: KinAlberta
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In my case I really just want to strengthen the existing beams (2x8"s) to spread the load more and prevent sagging. I've noted in another post somewhere that I have two old cabins on blocks and they have stayed very stable and level for about 60 years. However they are getting out of level and need a bit of levelling so I'm thinking that if I built up the beams I could pretty much eliminate much of the need for levelling for many, many years.
Still, my added thinking was that for those building a new small cabin, the idea of pulling in a trailer over top of blocks, dropping the wheels and then building beams beside or on top of the trailer beams might provide an extra layer of foundation reinforcement to keep a pier and beam structure level for years or at least more easily re-levelled.
In the case of the cabin above, I'm wishing that it its foundation beams had been overbuilt decades ago making levelling and re-levelling a simple task.
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