Unsupported compression length of beam 3

[tdawgye]

Hi there,

For beams under gravity loading, what would you consider the unsupported compression flange to be? If its supports a metal roof deck with no joists framing into it, would the unsupported compression length be the total span from column to column? Or do you consider the unsupported length to be 0, as the deck is welded to the beam?

Thank you.

 

[r13]

There are perhaps millions of linear feet of simple span beams "out there" with no bottom chord bracing in buildings.

Joists, trusses and many others.

My statement was in response to the suggestion that we shouldn’t omit bottom bracing without “more research” etc. That isn’t valid for GRAVITY beams.

How often we have/see pure "gravity" load building system in our designs, "zero" maybe quite close to the fact, otherwise the importance of our profession will shrink very fast.

Also, I don't think Dr. Yura agrees your interpretation that limits his teaching to "gravity load case" only. Admittedly, there are many things in Dr. Yura's works we don't fully understand, therefore when we state/cite his idea, a little reservation deliveries a more accurate message. Note that the research includes, and shall start with, the review/reading of Dr. Yura's works, and understand, digest it fully.

 

[JAE]

You are all correct that uplift, spandrel beams, beams that have applied torsion, offset loads all produce issues that may require full bracing against twist.

I thought I was clear on confining my statements to a typical simple span gravity case where none of these “other” situations were present.

The OP did say “roof” and I missed that.

For gravity case only I’ve personally discussed bracing requirements with Dr Yura numerous times. I know what he teaches and what I said is consistent with his views.

 

[r13]

Please read that paper cited in my response, then you'll understand where my objection came from. Unless I was too lazy in continue in reading, the author simply discredited the effectiveness of the bottom bracing. The gravity only case is essential in addressing the whole stability phenomenon, but it can be considered a special case out of the vast general applications that we deal with daily.
Note that the concerns I stated, exists on all floors, doe not limit to the roofs.