Boiler wrote:

I'm not sure if you still are deciding here, but here goes.

How are these tubes being loaded? I'm mildly unsure, but I think they will be loaded at one end with the other end welded to a "fixed" point, like a cantilevered beam?

I assume by the size that these are A500 tubes. That may not be true, but that is the most readily available to me at my work. A500 has an average yeild strength of 46,000 psi. I would assume that they are a minimum of 30,000 psi no matter what they are made of.

Now to find how much force you can safely apply perpendicular to the beam at the end:

3 x 2 x 3/16 tubes, neglecting effects of corner radii, have a Section Modulus:

S = 1.37 in^3 in the hard bending direction, and

S = 1.06 in^3 in the easy bending direction.

Assuming a 14" long cantilevered beam and a safety factor of 3:

Bending Stress = Moment / Section Modulus

Bending Stress allowable = 30,000 psi / 3 (safety factor) = 10,000 psi

Moment = Design Load "F" x 14" = 14F in-lb

S=1.06 in^3 in easy bend direction

S=1.37 in^3 in hard bend direction

10,000 lb/in^2 = 14F in*lb / S in^3

F lb = 10,000 lb/in^2 * 1.06 in^3 / 14 in = 757 lbs. in easy bend direction

F lb = 10,000 lb/in^2 * 1.37 in^3 / 14 in = 978 lbs. in hard bend direction

There are likely other forces present, but if your load is like I think it is, the bend stress is the primary load. Keep in mind that if you do have A500 tubing you can multiply these loads by about 1.5. Also if you want a lower safety factor you can adjust them proportionally too. There is some generalization here, but I think this might help a little if I understand the loading right.

Yes

That's a real answer

If you did that off the top of your head - I'd be really really impressed -

I'd have to dig out a design handbook I haven't seen in a long time

_________________

2005 CRD

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