3x3 square tubing vs 4x2 square tubing

  • #1

Main Question or Discussion Point

Which is stronger 3x3 .25 inch thick square tubing or 4x2 .125 inch thick square tubing?

When positioned vertically about 40inches high (considering that when positioned vertically it is completely secured), and a 20 inch square tubing attached at different levels between the 40 inches (either 3x3 or 4x2 tubing), at any levels of the 40 inch tube can it handle at least 1000lbs? (specially at the top)

In other word: Forming like an upside down "L" shape being 40 inches vertically (with either 3x3 0.25thick or 4x2 0.125thick square tubing) and 20 inches horizontally (considering that this part is strong enough). Will this be strong enough to hand at least 1000lbs?

OR should I angle the L shape instead of being 90 degrees possibly 95 degrees. At maximum I wouldn't want the angle to be more than 100.12 degrees. But overall I would prefer to not add any angle at all.

I was looking at this link for some help but I think I need more help.
https://www.physicsforums.com/showthread.php?t=351727

If none of them will handle it please add suggestions.

Please let me know if any of this is unclear.
 
Last edited:

Answers and Replies

  • #2
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0
Kind of confusing. Assuming that the upside L is anchored into the ground, I think the breaking point would be caused by bending stress in the vertical column caused by the 1000 lb force at the end of the 20 inch span (you said to assume the 20 inch span can support the weight?).

If my above assumption is correct then I would say the 3x3 .25" thick square is stronger than the 4x2 .125" rectangle. I calculated the bending stress in the 40" beam to be as follows:


4x2 .125"
S = My/I
S = (1000 lb * (20"+2")*2"*12 / (2"(4")^3 - 1.75"(3.75")^3)
S = 14,784 psi

3x3 .25"
S = My/I
S = (1000 lb * (20" + 1.5")*1.5"*12 / (3"(3")^3 - 2.5"(2.5")^3)
S = 9,228 psi

Above assumes 4x2 and 3x3 to be outer dimensions. Whether or not it can support the weight depends on the material of course. If the 20 inch beam is heavy you have to add that into the calculation as well. Limiting factor could also be how the 20" beam and the 40" beam are connected to each other. If they are bolted together I could see the bolts failing from sheer.

The above was a rough calculation. More info is needed about the situation to accurately say whether or not the structure would collapse.
 
  • #3
Thanks for the reply. The vertical tubing will be welded on a 3x2 11gauge square tubing. I'm trying to attach a word or paint document to show a quick visual but its too big of a file. The horizontal 20" tubing will be made of a 1" 1/4thick round tubing slipped inside a 1.75x1.75" 12 gauge tubing then another piece of square tubing will form a triangular shape kinda like this:

20"
__ ________________________________
I I I_____________________________I
I I I /
I I I /
About 9" apart I I I /
I I I /
I I I /
I I I /
I I I /
_ I I/
I I
I I
I I
I I
I I
_________________ I I______________________________
I_________________________________________________I

It has similar design as a half powerlifting rack like this one with low bracing of the vertical tubing (Btw for my design purposes I don't want it to be higher than 10" off the ground or 8" from the 2x3 base tubing):
http://www.powertecfitness.com/uploads/wb-hr10/buy.jpg [Broken]
combines with this one:
http://cardiff-sportsgear.co.uk/shop/images/press squat stand.jpg
But I want mine to hold more weight, that is why I am using much thicker steel, and if I am not mistaken. 1/4 thick steel is almost twice as thick as what they use.
OMG I just realized that I didn't say that there are two of them btw like a powerlifting rack lol. Please let me know you opinions or if my explanations are unclear.

Thanks
 
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