Mobile home frame for short span bridge?

sandman2234 · Dec 4, 2005

Years ago, I built a 40' trailer out of a 65' mobile home frame, using all the steel beams as cross reinforcements or 2 main beams. After moving the container, I built it for, I cut it down to a 20' but couldn't see wasting the beams, so I put 4 beams lengthwise, and the rest for cross reinforcements. I mainly carried junk on it, and later sold it to a guy that hauls a JD 450 on it.
Twin mobile home axles, about 5' from the rear to the first one, open span to the front tongue.
David from jax

crazymike · Dec 6, 2005

We use old tractor trailer flat decks.

Mobile homes are generally not as sturdy.

I would recomend finding an old tractor trailer flat deck, or just some scrap I beams, etc...

Tom_H · Dec 16, 2005

Between my 1st & 2nd years of college, I spent the summer working in a mobile home factory in S. GA. I did carpentry, building the subfloors on top of the frames. The wood floor joists and sheathing give the frame a lot of rigid strength. When those frames come into the factory with nothing bolted to them, they are quite flexible; I'd even describe them as downright flimsy. I know that the frames in some structures (such as airplane wings) have to flex in order not to break, but these frames are simply not designed for this purpose. There is no way I would use one of those frames as the substructure for a bridge.

flusher · Dec 16, 2005

Depends on the weight that the frame is designed to carry.

I have a 66'-long double wide made by Golden Pacific (about 1800 sf total). The front module was shipped with 7 axles and weighs about 40,000 pounds. The rear module had 6 axles and weighs about 33,000 pounds.

A lot of this weight is in the 2x6 exterior wall frame, the 7/16" OSB sheathing for the exterior walls, and the Hardipanel/HardiPlank siding. And the drywall adds quite a bit of weight to the total.

Each module has a pair of I-beams running the length of the module. These I-beams are about 10" tall and use 1/4" steel for web and flanges.

Don't know if this info helps you, but the guys in the transport crew said these were two of the heaviest modules they've transported so far. I would guess that the frames weigh about 5000 lb each.

Louisiana_John · Dec 22, 2005

I found 2 old flat deck trailers yesterday. 8.5' x45' they need a new deck but the price seems OK. $400.00 each. They still have the running gear. I am going to think hard on it.
John

RobA · Dec 22, 2005

Would you buy them both and lay them side by side?

$400 sounds like a good price. A local salvage guy near me wants $1,250 for a 1965 Fruehauf flat bed that is only 32' long. I'm not even sure of its condition. Here is the dealer's web page with a picture and description.

He said he would come down to $1,000 if I took it without the wheel assembly. I think his prices are way too high. I haven't looked too hard for a trailer since I'm not sure that is the route I want to go with a creek crossing.

LBrown59 · Dec 22, 2005

( The front module was shipped with 7 axles and weighs about 40,000 pounds.
The rear module had 6 axles and weighs about 33,000 pounds.
)
If the frames will support a 33000 to 40000 pound house looks like they'd support an 80000 to 10000 tractor don't ya think???

Dargo · Dec 22, 2005

NO. As opposed to a semi trailer or a rail car trailer, a mobile home frame is designed for 2 trips (as mentioned earlier) and the box on top of them provides much of the rigidity. Even if one weighed 40k pounds, it is NOT designed to carry that much weight crossing it. This is besides the point that your average mobile home weighs about half that much. Anyway, that works out to be about 600 pounds or so per foot. Your 8000 pound tractor will put about 6000 pounds on a 1 foot section. Everything is designed for a specific purpose, a mobile home frame is NOT designed to support any great weight. As of yesterday there were still some wrapped around 6" trees from the tornado we had. I'm sure they would be happy for someone to take the frame. For their specific purpose, they are adequate. For a bridge, I spent too much money on my tractor for that.

LBrown59 · Dec 22, 2005

The wood floor joists and sheathing give the frame a lot of rigid strength.
Tom.
=========== 

So then wouldn't that also mean the rigidity of the frame could be as good or better than it was on the trailer depending on the specs of the bridge deck being installed on the frame?
Another thing to consider is the length of the span and the placement of Supports/ piers under the frame as well as the beefiness of those Supports/ piers

There is also the method of how the frame is installed / constructed to consider.

Ps:
I've used two by four floor joists in floors in house porches and out buildings and I guarantee those floors are stronger than floors with 2x6 2x8 or 2x10 floor joist.
The secret is in spacing span and support of the joists.
This is the same reason that a 2x6 floor is stronger in a Manufactured House than a 2x8 or 2x10 floor in a stick built house.

LBrown59 · Dec 22, 2005

NO. As opposed to a semi trailer or a rail car trailer, a mobile home frame is designed for 2 trips 

Well at least that's 2 more trips than a stick built house is designed for.

Although I don't agree that 2 trips are the Max they're designed for.
Lots of them make more than 2 or 3 trips.