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# Thread: Determining Max Load For C Channel Trailer Beam?

1. Senior Member
Join Date
Nov 2009
Posts
124

## Determining Max Load For C Channel Trailer Beam?

I am renovating an older RV that is made of 4" 3/8 c channel members and has a length of 33'. The original trailer is about 5500# dry weight and I intend to add two 5000# axles and swap out the springs to boost the capacity to 8000# to 9000#. What I am wondering is if the c channel frame can take the extra weight.

I know how to compute simple beam deflection but what I dont know is how to determine the load strength of the C channel beams on the two sides of the frame. I could calculate for a static load at the center of the beam but that would result in massive overkill in design since the load wont be all at one point. So right now I dont know how to calculate it.

So the question is, given a target GVWR on a trailer, how do you calculate the size of the steel members of the frame and how do you calculate the number of cross members other than the two ends are necessary?

Finally does anyone know a good mechanical design book that doesnt require a mechanical engineering degree?

2. Senior Member
Join Date
Jan 2008
Posts
328

## rv frames are designed for even loading

If you try to drive a car on the back of a trailer made from a travel trailer frame, expect problems. The load of a travel trailer is nearly equally spaced along the trailer frame. The travel trailer frame might even get some rigidity and strength from the wood frame trailer box. Cutting it down to 12' or 14' may be ok. Look at some old posts here in the project section.

3. Senior Member
Join Date
Jul 2006
Posts
1,508
Originally Posted by deafman
The travel trailer frame might even get some rigidity and strength from the wood frame trailer box.
I would think it all works together, wood frame, sheetmetal skin, all to form a box.

C-4 x 7.25, I don’t have any load information on that small of a C-Channel. This chart is too short and too small to be of any help.

4. Member
Join Date
Mar 2009
Location
DFW, Texas
Posts
71
RV's generally do get a lot of deflection strength from the box. The steel in a 5,000 Lb travel trailer is generally nothing like the steel in a shorter 5,000 flatbed trailer.

5. Senior Member
Join Date
Dec 2009
Location
Williams Lake, British Columbia
Posts
722
Travel trailer frame are very weak on their own. They are not utility trailers by all means.
Please dont try this at home

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