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Tim Wescott Tim Wescott is offline
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Default Strength of materials question: square tube vs angle iron

Don Foreman wrote:
On Mon, 14 Apr 2008 14:57:50 +0000 (UTC), (Edward
A. Falk) wrote:

Hi all; about to start building a trailer. The trailer plans I
bought from trailerplans.com call for 2"x3"x1/4" angle iron. I
want to use steel tube instead. Can anybody give me an idea of what
size steel tube would have the same strength? Is there somewhere
this can be looked up?


2" x 3" x 1/8" rectangular tube should be as strong as 2" x 3" x 1/4"
angle and have about the same weight per foot.


Actually it'll likely be stiffer in bending and way stiffer in twist.
It'll have less strength at any one weld 'cause you're going into 1/8
inch of material instead of 1/4 inch, although that could be overcome
with gussets if necessary.

If the trailer is designed to have a stiff chassis and well-sprung
wheels it'll probably be better with the tube; if the trailer needs to
have some flex in the chassis (unlikely if it's remotely normal) then
the stiffer tubing plus weaker welds may tear it apart over time.

Chances are the thing was designed for angle iron because the folks
doing the plans felt that'd be easiest to build, and because for a lot
of things 'easy' is better than 'absolute optimal weight/strength ratio'.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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