Strength of materials question: square tube vs angle iron
Edward A. Falk
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?
--
-Ed Falk, fa...@despams.r.us.com
http://thespamdiaries.blogspot.com/
Ned Simmons
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?
The strength of a shape (assuming the same material) is proportional
to the section modulus. Stiffness varies with moment of inertia. In
both cases pay attention to the axis the properties are referencing;
i.e., for an non-symmetrical shape, the value will vary depending on
the direction the load is applied.
Machinery's Handbook has the info you need. I'm sure the numbers for
common steel shapes are also online somewhere. Googling - "section
modulus" "moment of inertia" steel - would be a start.
This may be useful:
http://www.engineersedge.com/section_properties_menu.shtml
--
Ned Simmons
Don Foreman
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.
Tim Wescott
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
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
RoyJ
modulous for the various angles and tubes you would consider. Typically,
a tube shape has more strength in both directions than a rectangular
tube of the same weight per foot.
But a word of warning: tube and angle fail in different modes, you
really can't just sub one for the other without a bit of care. That
said, 2x3x1/4 angle is fairly wimpy stuff if used as frame rails.
42
that short of hot dip galvanizing, you can't rust proof the inside of the
tube. Water will get inside and eventually the frame will rust from the
inside out leading to failure. Do yourself a favor and follow the original
plans.
Just my .02 YMMV.
Paul
"Edward A. Falk" <fa...@green.rahul.net> wrote in message
news:ftvrde$h6c$1...@blue.rahul.net...
Tim Wescott
(top posting compulsively fixed)
>
> "Edward A. Falk" <fa...@green.rahul.net> wrote in message
> news:ftvrde$h6c$1...@blue.rahul.net...
>> 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?
>>
>> --
>> -Ed Falk, fa...@despams.r.us.com
>> http://thespamdiaries.blogspot.com/
>
> I wouldn't substitute tube for the angle in a trailer application.
> Reason is that short of hot dip galvanizing, you can't rust proof the
> inside of the tube. Water will get inside and eventually the frame will
> rust from the inside out leading to failure. Do yourself a favor and
> follow the original plans.
> Just my .02 YMMV.
> Paul
Fill it full of linseed oil & roll it around to cover thoroughly.
In general, "follow the original plans" is good advise, unless you know
the ramifications of deviating from them.
On the one hand I'm tempted to say that if you have to use plans to make
a trailer, you should follow them. On the other hand, if you never
deviate from other's plans you'll never make the mistakes you need to
make to learn how to be innovative _and_ correct.
Just check the safety-related stuff often, if you do deviate from those
plans....
--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com
Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Edward A. Falk
Tim Wescott <t...@seemywebsite.com> wrote:
>
>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'.
That was my guess. I'm just hoping to hear something like "2x2x1/8 will
do fine"
Edward A. Falk
42 <pl...@budweiser.com> wrote:
>I wouldn't substitute tube for the angle in a trailer application. Reason is
>that short of hot dip galvanizing, you can't rust proof the inside of the
>tube.
I had not thought of that particular issue. Thanks.
RoyJ
>
> That was my guess. I'm just hoping to hear something like "2x2x1/8 will
> do fine"
>
Anybody who really knows the answer is not too likely to give you the
all clear over the internet. Too many idiots out there. Not to mention
there may be some reasons why the original designer chose angle iron.
(other than hot rolled angle is the absolute cheapest per pound material)
Ned Simmons
wrote:
And anyone who thinks they know the answer without seeing the design,
probably doesn't.
--
Ned Simmons
Ignoramus30238
> In article <%fQMj.32492$pm2....@en-nntp-04.dc1.easynews.com>,
> 42 <pl...@budweiser.com> wrote:
>>I wouldn't substitute tube for the angle in a trailer application. Reason is
>>that short of hot dip galvanizing, you can't rust proof the inside of the
>>tube.
>
> I had not thought of that particular issue. Thanks.
>
What about putting a foam such as "great stuff" inside the tubing?
My own trailer, made from tubing, is sealed on ends with great stuff,
and now I wish I filled the entire tubes with it.
i
Don Foreman
A. Falk) wrote:
>In article <s4ednVimarF6PJ7V...@web-ster.com>,
>Tim Wescott <t...@seemywebsite.com> wrote:
>>
>>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'.
>
>That was my guess. I'm just hoping to hear something like "2x2x1/8 will
>do fine"
You meant 2x3, right? It will do fine -- the only question is "do
what?". Some of the light utility trailers sold by Northern et al are
considerably less robust than this, as are many small boat trailers.
It depends on what load rating you need or want. It would "do fine"
for camping gear, a couple of bikes, a lawn mower, a few sheets of
plywood, etc.
I figure my 5 x 9 trailer made of 2 x 4 x 3/16 rect tube is good for
3000 lb with the limit being the tires rather than the frame. I've
never loaded it that heavily but I'm sure my neighbor has. We put a
3500 lb springset on it so it wouldn't bottom out with a good load.
Gussets and braces can add a lot of strength without adding much
weight. They also provide redundant welds.
Don Foreman
>I wouldn't substitute tube for the angle in a trailer application. Reason is
>that short of hot dip galvanizing, you can't rust proof the inside of the
>tube. Water will get inside and eventually the frame will rust from the
>inside out leading to failure. Do yourself a favor and follow the original
>plans.
>Just my .02 YMMV.
>Paul
Rect tube has some nice attributes for trailers:
1. As Tim noted, it has considerably higher torsion strength than
angle
2. It is very easy to weld in crossmembers -- recommended.
3. The bottom provides a good place for spring mounts.
The cross members don't add much weight while providing bed support
and further stiffening the rails against twist.
A well-constructed evenly-loaded trailer made of 2 x 3 x 1/8" rect
tube should be good for 1500 lb. Peak stress is under 10 KSI. I would
rate it at 1000 lb.
Ignoramus15568
My trailer is made of a unibody steel bed, and 2x4x1/8" tubing frame
underneath. (not 2x3 as in in your example).
Because the bed is rigid, it distributes the weight across the frame
nicely without big stress areas. The points where the leaf springs
are attached to the frame are reinforced with 1/4" thick 2x2" steel
angle, to which the spring mounting hardware is welded. On both sides,
there are two 12" long pieces of the angle welded on.
I loaded this trailer to slightly over 6k gross, to carry 4,500 lbs
power supplies. (happened twice).
Both times there were unloaded rudely, one was dropped into the bed
from about 4" height, another was dragged through the bed to the very
back end of it and only then lifted with a forklift. Both times the
trailer held up without any visible damage.
That tubing is good stuff. I would personally recommend 2x4 instead of
2x3. Also, filling them with Great Stuff foam inside, is a good idea.
This trailer is one of the few homemade things that work well for me.
i
haroonbro...@gmail.com
www.sites.google.com/site/haroonfurnitures
My firm is looking stockiest and importers from all parts of the world
Lloyd E. Sponenburgh
aace-63f...@googlegroups.com:
> My firm is looking stockiest
Lloyd
Larry Jaques
--
Courage and perseverance have a magical talisman, before
which difficulties disappear and obstacles vanish into air.
-- John Quincy Adams
Tim Wescott
> On Sat, 28 Nov 2015 06:36:01 -0600, "Lloyd E. Sponenburgh"
> <lloydspinsidemindspring.com> wrote:
>
>>haroonbro...@gmail.com fired this volley in
>>news:2a3d1097-c162-4cc6-
>>aace-63f...@googlegroups.com:
>>
>>> My firm is looking stockiest
>>
>>Well, "Stockiest" companies is goodest!
>
>
>>>and importers from all parts of the world
>
> Importersing is also quite goodier.
--
www.wescottdesign.com
Larry Jaques
>On Sat, 28 Nov 2015 07:39:00 -0800, Larry Jaques wrote:
>
>> On Sat, 28 Nov 2015 06:36:01 -0600, "Lloyd E. Sponenburgh"
>> <lloydspinsidemindspring.com> wrote:
>>
>>>haroonbro...@gmail.com fired this volley in
>>>news:2a3d1097-c162-4cc6-
>>>aace-63f...@googlegroups.com:
>>>
>>>> My firm is looking stockiest
>>>
>>>Well, "Stockiest" companies is goodest!
>>
>>
>>>>and importers from all parts of the world
>>
>> Importersing is also quite goodier.
>
>Not spamming is bestest.