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up set beam stability

up set beam stability

up set beam stability

(OP)
I have a situation where I need to provide an upset steel beam - unbraced top flange full length. Beams only frame into one side, and the beam is 40' long. What are opinions on putting a continuous plate on the back side of the beam along its length to create a 'tube' section for LTB? is a single fillet along the flange, in a stitch pattern, sufficient to distribute the 'stability torsion' through the section such that LTB can be mitigated?

RE: up set beam stability

Sorry for not addressing your question directly, but would stiffeners on the outboard side (acting as torsional braces between the bottom flange/tributary beam and free top flange) be a simpler solution?

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The name is a long story -- just call me Lo.

RE: up set beam stability

It would work but is substantial overkill in my opinion. I'd use the beams tying in as roll beams for LTB bracing. At most, maybe some one sided vertical stiffeners generously spaced.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: up set beam stability

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: up set beam stability

(OP)
I guess the info not here is that this is a free standing port cochere, where the beams that tie in are 30' long. I was leery to rely on their torsional stiffness to brace the beam without having to make them a lot stiffer. It was certainly my first thought, but the size and flexibility had me question it.

RE: up set beam stability

Ah. Well, thanks to AISC appendix 6, you can just calc it, no?

The fact that your bottom-ish loaded ought to help as well. I think you'd be fine here, even with your original connection unless you were planning slotted holes in the clip angles.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: up set beam stability

Doh, KootK's idea is even better. (as usual)

If you do end up reinforcing the beam, a cap channel would be the more conventional route. I don't know if it's better than your plate except for non-structural reasons (not having a void, material handling, etc.)

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The name is a long story -- just call me Lo.

RE: up set beam stability

Things that are upset tend to be very unstable, including humans...

Koot's sketch will work very well, and even better if there is another stiffener on the opposite side of the attached purlin.

Mike McCann, PE, SE (WA)


RE: up set beam stability

It's at times like this that I regret that I can't find a publication I used to have. I believe it was a US Steel paperback handbook that gave formulas for calculating allowable bending for a totally unbraced top flange, when the beam is loaded below the shear center. Does that ring a bell with any of you older guys? This scenario comes up from time to time, and I'd love to find a copy. I don't think there are any copyright issues.

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