Channel or Rectangular tubing?

Which would be stronger (least deflection) or a better choice- "6 x 2" rectangular tubing or channel? Or would it make a difference?

What wall thickness for both/either?

I asked my neighbor (a mechanical/structural engineer) this exact question after I made a 28 ft trailer out of the 2"x6"x.188 material (after the fact) and he had an answer, so he is familiar. Give me the numbers and I can get you answers.

In my case, I think the channel was better, but I already bought the rectangular tube.....

Probably 1/4 wall for both.

Thanks leisureexpress

I don't see how a channel could possibly be stronger than tubing in this case. More strength per pound yes, but not stronger over all.

Ok, I'll ask him to run the numbers with 2"x 6"x.250 vs the channel which is sold lb/ft. It comes in 8.2 lb/ft, 10.5 lb/ft and 13 lb/ft. It shouldn't take much more than a day or 2, but when dealing with favors, ya know...... Standby.....

Yair . . . RobVG. leasureexpress has made a very helpful offer, it can cost a lot of money to get definitive answers to such a question.

Generally speaking, for a given wall thickness a closed tube will be stiffer. However for some structures the possibility of unseen internal corrosion may pose an unacceptable risk.

It is or this reason I believe many structures are fabricated from channels, flats and angles even though there may be a weight penalty involved.

Cheers.

The black book will show the wide flange, then the C, then the tube in that order for strength from a efficiency standpoint (pound for pound). Note this: The builder is responsible for the alignment of the piece under load (eg an unblocked wide flange will quickly fold if allowed to roll).

We use tube steel often since it performs under torsion; many times on equipment and trailers the load path as we use and abuse these things may vary widely.

Then there is the cost of joining and coping around those flanges, but that wasn't part of the question.

And a wide flange can be purchased in grade 50 while the other items are not typically. The grade 50 helps in the strength. Deflection another topic.

Example: Hi rise frame (red iron buildings), steel buildings, etc:
wide flange, cee or zee shapes.....rarely if ever tube.
Sure: an Unbraced column in a warehouse?: pipe or tube many times. But P delta business here, not a simple beam.

Span is an issue. What are you trying to support? For how long (lol)? Will it be loaded evenly or all on one spot? I'm not an engineer but I have a steel data book that will give safe loads. If you want I can look up the second moment of inertia.

Just trying to get a general idea.

Would think the square tubing would have the least deflection . I & H beams work well for the load you show in post #1 Rob.

The section properties are:

Rectangular tube (2X6X.188 wall) = 6.33 in^4
6x8.2 = 13.1 in^4
6x10.5 = 15.2 in^4
6x13 = 17.4 in^4

So you will be twice as stiff in deflection with the 8.2 variety.

I asked him about the 2x6x.250 wall and he said he will get the numbers, but it still falls short (in the deflection category) of the lightest wall channel.

Thanks!

But could you tell me what the numbers for the rectangular tubing mean?

Well I say it depends on application more then anything, square tube on something like a trailer may hold dirt salt etc... that could cause rust easier then channel(harder to clean out). As far as strength again it would be based on how it is used. Over all the square/rectangular would be stronger, 4 angles compared to 2. I'm no expert but I would have to write, application is the deciding factor.

Beams and angles are great for static loads like in a building where loads are truly vertical. For a trailer which has to endure side loads as well as vertical loads tubing is good for resisting side loads as well as vertical loads comparing an equivalent weight per foot of steel. As has been said by others here, torsion and twisting is handled better by the box tubing better than channels or I beams but up here in Canada where they put a lot of salt on the roads in winter, those cheap trailers with lightweight rectangular steel tube frames rot from the inside out from corrosion.

Tubing will weigh more and cost twice as much per pound

As a structural engineer....the tube is the better choice for a few reasons:

As others have mentioned, the tube has a higher section modulus (bending stiffness) than the channel.

Tubes are more resistant to lateral torsional buckling (LTB) which is the most common mode of failure after yielding. All that means is that the parts in compression (the top) buckle to the side before the bottom yields in tension.

As for corrosion, if you weld the ends completely, the tube will be sealed. You will actually have less section loss with the tube over time than with the channel.

This is more academic, but the "center of stiffness" of a channel is actually outside the "C" (to the left of a proper C). This means that a load applied directly on the channel will want to twist it instead of purely bend it.

Channels have their uses, but if you really have a bending load GO WITH THE TUBE. If you send me the forces/dimensions I can run some numbers for you in an unofficial capacity. If you aren't dealing with a large amount of material, go with the tube over the channel unless money is absolutely critical. It will perform far better.

I had wondered about this before this thread just to be clear what your saying I have approx. 50 roll off dumpsters that haul concrete only every day and tubing would stronger for cross members than C channel the C channel is collapsing just like you say @ the back of the C and the only reason none of the body builders use tubing is because of cost. but it would be stronger to the impact loads from loading large pieces into bodies. I had a job back in summer that we hauled about 60 pieces of a large footing that had to be wire sawed out the pieces ended up about 4'X5'X16' and weighed 15-19 TONs each they loaded them with a 100 ton over head crane so there was no impact loading but on the 20 mile haul on the interstate it was bending floors in dumpsters P.S. I had the dumpsters custom built 3" channels 12" on center THANKS

Based on the tremendous loads you describe, you'd probably get more bang for your buck with W shapes or (better yet) S shapes. S shapes are heavier than W's and will tolerate much more abuse. They may be cheaper than tubes, but I haven't priced them out recently. Otherwise, I'd recommend one of the beefier 4" W's.

Thanks