Rectangular Vs Square Vs Channel....Amazing picture included

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Rectangular Vs Square Vs Channel....Amazing picture included

Postby Davagio » Sun Jan 31, 2016 10:42 pm

This is something i have been researching on lately since my last frame build, and i would like you all's input.

Premise: Since my last drop floor standy frame (which in my opinion was built extra strong, and almost too strong for what it was intended for) i have been trying to think about the lightest possible frame design that will have just enough strength to be a good trailer.

For my drop floor standy frame build I used 2x2 1/8" inch wall tubing for almost the entire frame (minus the drop floor). Currently i have a 1972 Fiberglass Boler which is built out of 3x1.5 Rectangular Tubing (minus the drop floor in that which is maybe 1x1 angle) and im not sure if the Rectangular tubing is 1/8" wall or 14 gauge) Since having the Boler i have put about 30,000+ miles on it as i almost never unhook it from my vehicle. I have put that thing through some nasty terrain, and hit so many potholes that i swear i have broke my own suspension on my vehicle as well as the lonely trailer hanging out back. But to this day i havent really seen anything structurally crack on the Rectangular tubing of the boler. So this leads me into the Questions. How light can a person really go, and my real world knowledge (not book knowledge) is telling me a lot lighter than a person might think.

Square, Vs Rectangular, Vs Channel:

Round one: 2x2 1/8" Square vs 3x1.5 14 gauge Rectangular.............

Round two: 2x1 1/8" Channel vs 2x2 14 gauge Square....................

Round three: 3x1.5 14 gauge Rectangular vs 3x1.5 Channel...............


Round one winner? round two winner? round three winner? then best to worst in your opinion!!

This is minimal trailer i was thinking about building, and heres the awesome engineered CAD drawing i did for you guys!

Image
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Re: Rectangular Vs Square Vs Channel....Amazing picture incl

Postby yrock87 » Mon Feb 01, 2016 12:02 pm

Mine isn't finished but I did a simple "figure 8" frame, just two squares each 5ftx5ft with a composit tounge attached. The two 5x5 squares are made of 2x2 at .092 thickness (13 Guage?) and it was plenty strong when the trailer was driven across the state. There is zero flex on the frame when two adults stand or hop on the corners.
The SJ Cruiser, my 5x10 Benroy build http://www.tnttt.com/viewtopic.php?f=50&t=64944
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Re: Rectangular Vs Square Vs Channel....Amazing picture incl

Postby drhill » Mon Feb 01, 2016 12:34 pm

Square, Vs Rectangular, Vs Channel:

Round one: 2x2 1/8" Square vs 3x1.5 14 gauge Rectangular.............

Round two: 2x1 1/8" Channel vs 2x2 14 gauge Square....................

Round three: 3x1.5 14 gauge Rectangular vs 3x1.5 Channel...............


Round one winner? 3x1.5 14 gauge Rectangular
round two winner? 2x2 14 gauge Square
round three winner? 3x1.5 Channel

then best to worst in your opinion!!

Winners based on the resistance to bending. I assume that the 3x1.5 channel you are referring to is C3x5 structural channel. I used C3x4.1 on the two side rails of my utility/teardrop trailer and it can easily haul a 2000 lb load with the current springs and the frame is certainly strong enough for 3500 lbs with a change in springs. If you can get 3 x 1.5 x 14 guage hollow rectangular section it would be a great choice. That isn't available near me that I know of and I was building a multi-use trailer so a bit heavier frame was the penalty to be paid.

3x1.5 14 gauge Rectangular, Ixx=.7998 in4
2x2 14 gauge Square, Ixx=0.3703 in4
The 3x1.5 rectangular will give you more than double the bending strength.
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Re: Rectangular Vs Square Vs Channel....Amazing picture incl

Postby OP827 » Mon Feb 01, 2016 6:16 pm

I saw that BPW makes the probably the lightest trailer frames, which I think were engineered to be lighter. To make the lightest possible frame, an I-beam or C-channel beam structure would be most weight effective. There are some videos on youtube, bailey trailers using the bpw frames for example. I do not think you'll see such frames in N.America much.
My foldable foam trailer build: http://www.tnttt.com/viewtopic.php?f=50&t=61344
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Re: Rectangular Vs Square Vs Channel....Amazing picture incl

Postby Davagio » Mon Feb 01, 2016 9:30 pm

yrock87 wrote:The two 5x5 squares are made of 2x2 at .092 thickness (13 Guage?) and it was plenty strong when the trailer was driven across the state. There is zero flex on the frame when two adults stand or hop on the corners.


That is a strange thickness, but then again maybe most metal is plus or minus a gauge depending where it was made?? Glad that yours is working out so good brother!
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Re: Rectangular Vs Square Vs Channel....Amazing picture incl

Postby Davagio » Mon Feb 01, 2016 9:49 pm

drhill wrote:
I assume that the 3x1.5 channel you are referring to is C3x5 structural channel..


Actually im not sure what it is but here is the link http://www.wheelermetals.com/catalog/products/details/17639/3-x-3-5-number-channel

The channel looks to be somewhere in the 9-10 guage area i think? So you think pound for pound (sounds like a boxing ring lol!) the 3" inch channel would be more stout than the 14 guage 3x 1.5 rectangular? I know the channel is one lb. heavier than the rectangular tubing. I am guessing the 3x 1.5 1/8 would be a better match and stronger contender than the 14 guage. But just for giggles im curious what the math is on the 14 guage rectangular vs the 9-10 guage 3" inch channel. Thanks for answering my questions by the way i do appreciate it.
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Re: Rectangular Vs Square Vs Channel....Amazing picture incl

Postby drhill » Tue Feb 02, 2016 1:49 pm

That C3x3.5 that Wheeler Metals sells is an unusual size. But give them a call and make sure they have it. It wouldn’t surprise me at all as Tulsa and area has a long long history in steel products, especially oil and gas production equipment.

Structural channel is designated by the height and weight. So C3x3.5 is a 3” High C channel with a weight of 3.5 lbs/ft. Most tables list C3x4.1, C3x5 and C3x6. Most tables don’t list C3x3.5. But now that I know it exists, I Googled and found a section properties calculator that includes it. http://www.webcivil.com/readusShapec.aspx

It calculates Ix=1.57 in^4 (moment of inertia about the x axis)

You had referred to C3x1.5 channel. So I assumed you meant 3” high and a flange width of 1.5”. Each “weight” of C3 has a different flange width and C3x5 has a flange width of 1.5”. The Ix=1.85 in^4

You can use Google to read all about beam bending formulas, but the just of it is that the stiffness or resistance to bending is proportional to the moment of inertia (Ix). So the bigger the Ix, the stiffer the beam. For a teardrop trailer, it is pretty easy to overbuild. Especially considering that a lot of stiffness is provided by the teardrop cabin bolted to the trailer frame. In my case, I was building a trailer that can and is used as a utility trailer and has been subjected to such loading as a fork lift operator setting a pallet of 26 bundles of shingles at the back end of the trailer, before adjusting his fork positions and sliding the pallet forward to be over the axle. That kind of things puts the frame and coupler to a good test, but a dedicated teardrop trailer would never this sort of loading.

A lot of small light weight trailers are built with a C shape that is cold formed. ie- a piece of 14 gauge or some other thickness steel bent into a C shape. I have never seen this for retail sale but if must be somewhere. Probably some old barn on the edge of Broken Arrow. Haha

2x2x1/8 wall Ix=0.486 in^4 (from table, standard section)
I calculated the Ix for the two sections below. These are non-standard, may not be available
2x2x0.078125 wall Ix=0.37 in^4 (Calculated, radius corners ignored)
3x1.5x0.078125wall Ix=0.79 in^4 (Calculated, radius corners ignored)

Cheers,
Don
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