Hello, was reaching out to see if anyone had any resources on calculating the torsional stress on a unistrut channel, specifically a P1001 (using a P2542 post in reality, which comprises the P1001). I can’t find any technical literature on their website.
Since they are full of holes, it's not likely to have much torsional strength, and it would be a huge science project to figure out the capacity anyway. You're better off getting rid of the torsion.
Funnily enough I was dealing with exactly this situation recently - P1000T in torsion
It's an open section, they're rubbish
I decided to do as much as I could to avoid the torsion, as canwesteng said
Loads are really small but it’s for such a procedure driven industry that it will be really tough to justify/write off. Will look at changing the member instead. Thanks all!
What's the context?
In my case we were hanging a few panel heaters off 2 rows of unistrut
I got them to stick a vertical member in between the two rows and then hang the panel heater off that which they preferred anyway for maximum flexibility/tolerance on site
There is some potential residual torsion but I hand waved that away as the vertical member will allow the torsion to be somewhat taken out as a fixed frame leading to strong-axis push-pulls on the unistrut
It’s a P2542 post support supporting two tubes (1” and 1.25”). Seismic loads are totally ridiculous and I mean that wholeheartedly (max. 25g). Unrealistic but I am bound to using them, so what would normally be an easy handwave becomes load I need to show on paper won’t cause an issue. The P2542 is also a 2-bolt baseplate so no appreciable stiffness in the longitudinal/axial direction of the tubing. The tubes have a very small eccentricity but like I mentioned, the accelerations are what are causing this to actually be an issue
I’m taking the eccentricity as the distance from the center of the tubing to the center of the P2542. Each P2542 is supporting around 10’ of tubing.
Not sure I understand the suggestion about resolving the torsion as a major axis moment. You mean consider it as major axis moment on the tube and ensure the axial capacity can withstand the induced stress?
I don't really understand the geometry of this thing in all honesty so not sure if what I said applies
But the P2542 will be torsionally flexible AF so this thing is either a) unstable or b) resolves elsewhere
Depending on how your pipes are connected, they may actually have moment capacity in the connection that allows them to resolve the eccentricity into a push-pull on the tube at its supports
Not a lot @Tomfh id say 25 ft-lb. I just don’t know whether a P2542 can even withstand that. The other issue is that the P2542 is a two-bolt baseplate so load axially along the tubing won’t be resisted. Ideally i would love some way to write-off any of that longitudinal/axial load, I just don’t think I can/I don’t know how to.
A simple approach would be to design the opposing walls as warping torsion using the bi-moment method as is common with steel wide flange and chanel beams. Unistrut is setup so that local buckling is probably a non-issue.
I certainly don't go out of my way to use unistrut in torsion for primary loads but, for small stuff, I'm sure it works. .unistrut is usually unbraced or lightly braced such that the stuff would be buckling all over the place if it didn't possess some torsional strength and stiffness.
For very modest torsional loads I agree the bi moment approach is fine. Same as you might check a channel for incidental torsion. The span makes a big different. Open sections are often ok for short lengths of torsion, before the torsional stiffness falls off a cliff.
What is causing the torsion? What is the framing and loading
unistrutohio.com
