LD1
Epic Contributor
For example....
2x2x1/4 tube has a moment of inertia (i4) of 0.745
2.5x2.5x1/4 is 1.63.....which means it over twice as strong.
3x3x1/4 is 3.02....which is more than 4x as strong as 2x2 and almost twice as strong as 2.5" square tube.
Stress formula is the distance to the center axis (half the tube size) times the force times the length in inches.......all of that divided by 4 x moment of inertia.
So if you span 36" with 2x2 tube....and apply 5000# of force.......
(1x5000x36) / (4 x .745)= the stress on the member. About 60,000psi....which likely exceeds the rating of the tube. Most tube is 50ksi
If you used the 2.5" X1/4 wall tube....with 1.25" center distance and i4 of 1.63.....
(1.25 x 5000 x 36) / (4 x 1.63) you are down to 34.5ksi stress.
The 3" tube would drop to 22ksi stress.
Can also factor deflection.....the force times the weight cubed.....dived that by 48 times the i4 times the modulus of elasticity constant. (29,000,000)
So for 2" tube
(5000 *36^3) /(48x29,000,000x.745)
Your tube will flex about 1/4"
2.5" tube would be about 1/10th of an inch
3" tube would be about 1/16th of an inch.
Hope I didn't loose you. But that's the crash course on stress and deflection and how to apply it. Of course you may be spanning more than 36" or less. And you may be applying more than 5000# or less.
But span.....force....and the moment of inertia are what you can look at, at a glance and get a feel for how strong something will be with just a few calculations.
The strength of that round bar you propose adding.....1.5" only has a moment of inertia of 0.24
So even 2" tube with round bar added is not even close to the strength of 2.5" tube.
2x2x1/4 tube has a moment of inertia (i4) of 0.745
2.5x2.5x1/4 is 1.63.....which means it over twice as strong.
3x3x1/4 is 3.02....which is more than 4x as strong as 2x2 and almost twice as strong as 2.5" square tube.
Stress formula is the distance to the center axis (half the tube size) times the force times the length in inches.......all of that divided by 4 x moment of inertia.
So if you span 36" with 2x2 tube....and apply 5000# of force.......
(1x5000x36) / (4 x .745)= the stress on the member. About 60,000psi....which likely exceeds the rating of the tube. Most tube is 50ksi
If you used the 2.5" X1/4 wall tube....with 1.25" center distance and i4 of 1.63.....
(1.25 x 5000 x 36) / (4 x 1.63) you are down to 34.5ksi stress.
The 3" tube would drop to 22ksi stress.
Can also factor deflection.....the force times the weight cubed.....dived that by 48 times the i4 times the modulus of elasticity constant. (29,000,000)
So for 2" tube
(5000 *36^3) /(48x29,000,000x.745)
Your tube will flex about 1/4"
2.5" tube would be about 1/10th of an inch
3" tube would be about 1/16th of an inch.
Hope I didn't loose you. But that's the crash course on stress and deflection and how to apply it. Of course you may be spanning more than 36" or less. And you may be applying more than 5000# or less.
But span.....force....and the moment of inertia are what you can look at, at a glance and get a feel for how strong something will be with just a few calculations.
The strength of that round bar you propose adding.....1.5" only has a moment of inertia of 0.24
So even 2" tube with round bar added is not even close to the strength of 2.5" tube.