Mobile home frame for short span bridge?

[Dargo]

</font><font color="blue" class="small">( 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.)</font>

Okay, we'll simply have to agree to disagree. No problem. You may want to let some of the structural engineers in on your 2X4 secrets. I'm sure that every home builder in the country would be interested not only in how to save costs using 2X4 floor joists as compared to the 2X12 (what I have), but also how to make their homes as strong as a manufactured house or mobile home. My house was designed on a CAD program that indicated where structural steel was to be used, the size footers to be used, the thickness of my basement walls etc., as well as minimum acceptable lumber size for code and preferred lumber size. On those computer runs, as well as the run where I said that I wanted maximum strength, the program never did call for any 2X4 use. I could have saved a ton of money.

 

[mboulais]

<font color="blue"> </font> "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. " <font color="black"> </font>



I was going to calculate the beam loading on 2 x 4's spaced 6" apart and supported every 4 feet over a 12 span vs 2 x 8's spaced 16" apart spanning 12' only supported at the ends, but I don't need to. I know your wrong. What's more, I'm pretty sure 2 x 4 floor joists on a house porch would violate building codes in every municipality in the U.S. Yes, adding piers or a supportting beam under the joists at some interval on the span does increase the carrying capacity of a floor system, but not enough to make a 2 x 4 floor joist outperform a 2 x 8 or 2 x 10 joist.

 

[radair]

My recommendation would be to get dimensions of the beams and the proposed span and bridge width, then have a structural engineer do an evaluation. I would be glad to do this via PM, however I can only do engineering work in states where I am licensed (New England and mid-Atlantic), so I could only give you an "unofficial" opinion.

I agree with Dargo that a tractor is too valuable to take unnecessary risks. I would urge anyone to do some homework and/or get an expert opinion before using bridges with unknown capacities or in unknown condition.

And I'm not going to touch the 2x4 floor joist discussion. /forums/images/graemlins/grin.gif

 

[Clyde]

MMM First off, if this frame has been in a fire, I don't care what it looks like now, but we ARE talking about an unknown temperature it withstood. You make no mention as to the buttresses or shoring you plan to build on either side of this creek or how deep the gap you are trying to cross. If it is a 50' chasm, I'd give it a lot of thought. To do it correctly and that is even if you plan to use the trailer frame, it is not a cheap venture. I think you want to give this some thought and consider it as a long term structure. I wouldn't consider just placing these beams on the bare ground without thought of collapsing the creek bank. Good luck! Clyde

 

[EddieWalker]

</font><font color="blue" class="small">(
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.
)</font>

Sir, may I suggest avoiding the intake of adult beverages in large quantities before posting advice on a subject that might lead to somebody who doesn't know any better, to actually listen to such advice.

Eddie

 

[thcri]

</font><font color="blue" class="small">(
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.
)</font>


By chance do you have two brothers named Larry? I really don't think I want to sit on any of your porches.

 

[mudcat]

</font><font color="blue" class="small">(
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.
)</font>
/forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif

 

[Tom_H]

</font><font color="blue" class="small">( <font color="blue"> The wood floor joists and sheathing give the frame a lot of rigid strength.
Tom.
=========== </font>

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.
)</font>

The original poster was asking whether the frame could carry the weight of a vehicle crossing it. The frame on the mobile home is nothing more than a flimsy way to tie the subfloor to the axles. The metal frame, axles, and wheels are for transporting the home. Much of the strength is in the wood framing and sheathing. Now you are correct that one might take the mobile home frame and make a strong bridge by building a well engineered wood frame atop it. But then the strength would be in the wood structure, so what's the use in having the steel frame? It would not be a needed part of the structure because one would not be building this as a "mobile bridge". You just build the wood structure with proper anchorages and leave it in place.

Yes, a 2" x 4" frame could give more support than those other dimensions if you have vertical support posts much closer together and the joists closer on center. Let's say you are building a house atop solid rock. You could continue reducing the dimensions even smaller than a 2" x 4" as long as you also reduce the span distances and distances on center. Eventually you reach infinite reduction and the house is sitting on one monolithic vertical post. But this proves nothing. These observations of yours do nothing to support the proposition that a mobile home frame would make a good bridge substructure. I have a credential to teach physics and my I.Q. is 140. There is no coherent logic to your arguments. People have tried to tell you repeatedly that you not only come across as belligerent, but that you also are very uninformed regarding that which you write. You sometimes make posts complaining about the way people react to you. I and others have tried to tell you how you could relate better with others, but you continue to make caustic, acerbic posts full of nonsensical drivel. You just never learn, do you?

 

[TOMLESCOEQUIP]

Why not just get a complete older MH, cut off both ends & dump it long ways into the creek, and use it as a giant culvert. Given the claimed structural integrity of such a unit being stronger than a stick built house, just cover the approaches with earth & presto= a doublewide bridge, PROBLEM SOLVED !

 

[Tom_H]

I can only speak here regarding the techniques of the one company I worked for; others may well be different.

Ours was the first station and we built the subfloors which we constructed out of 2" x 10"s with 3/4" plywood sheathing, all bolted to the steel frame, so there was some substance. At the second station, padding, carpet, and sometimes linoleum vinyl were stapled on top of the subfloor. Walls were constructed on a gantry while we were doing the subfloor. The walls were 2" x 3"s with flimsy metal sheeting on the outside and thin veneer paneling inside. After the carpet was stapled down at station 2, the gantry rolled the suspended walls down and the sill plate was laid on top of the carpet at the perimeter edge and secured with a nail gun. No tie rods, not even screws. The roof support was the sorriest piece of junk I've ever seen: a 2" x 2" collar tie with a shaped member sort of like an archery bow attached above it to give the roof a bit of pitch. (This was south GA-no snow load. I lived in trailers at Tahoe and Stowe where I had to get on the roof and shovel snow off, so those obviously had something stronger up top.) Walls and roof each had a couple of inches of fiberglass batting. I think the roof was secured to the perimeter walls with a nail gun and a few long screws (I wouldn't even call them lags.) There certainly were no threaded rods running through from frame to roof as there should have been, not even any Simpson strong tie type connectors.

The plumbing, wiring, and ductwork were pathetic as well. Compound angles in ductwork were not afforded any quality sheet metal work; rickety connections made from paneling scraps and 1" x 2"s were thrown together instead. Duct sections were often secured with pieces of duct tape, no screws and sealers. Wiring was aluminum, I don't even recall any copper ground wire. Any shortcut to save a penny was taken.

It's easy to see how tornadoes and hurricanes destroy these things. I can hardly see how they survive rainstorms or even the air resistance of being towed down the highway. This was almost 33 years ago and code requirements may well be better in many places. Still, if you ever think you will buy a MH, do some careful inspecting and give it some serious thought. What's inside those walls and joints ain't what most of us would call quality.

Oh yea, I didn't see how the steel in the frame was smelted and formed. I do know however, that there's such a thing as inferior grade steel. Having seen what I have, there's no way in @&*$ I'd drive a car, tractor, or even a bike across a bridge built from a frame designed for a trailer that had been distempered in a fire.