Deep Column Weak Axis Buckling
Deep Column Weak Axis Buckling
(OP)
I have some very deep columns (W40x249) that are very tall. I'm trying to reduce the unbraced length of them along the weak axis by adding vertical bracing between columns.
Normally, I'd say framing a braced frame strut into the center of the column web would be enough, but on a W40 column a W10 strut seems kind of... puny.
Do I need to brace both flanges? Add full depth stiffeners? Use two struts (one at each flange of the W40)? I'm curious how others would tackle this problem.
Normally, I'd say framing a braced frame strut into the center of the column web would be enough, but on a W40 column a W10 strut seems kind of... puny.
Do I need to brace both flanges? Add full depth stiffeners? Use two struts (one at each flange of the W40)? I'm curious how others would tackle this problem.






RE: Deep Column Weak Axis Buckling
RE: Deep Column Weak Axis Buckling
I am curios if there is any literature on double clip connections and there use to brace the top and bottom flange of the columns. My columns are W24-W30. So I am thinking aI cannto count on a Double clip grapping close enough to the flange to truly prevent twist, but I know it would prevent some twist.
RE: Deep Column Weak Axis Buckling
RE: Deep Column Weak Axis Buckling
Our office has actually done a lot of conveyor bents with W24 bent legs. We've typically put a full depth stiffener on the opposite side of the connection and they've performed find (some of them have even been hurricane tested). A couple of guys in our office have been doing conveyor bents for 30+ years this way.
For some reason doing this in the W40 range makes me a little uneasy though. My application is a perimeter "wind column" spanning 140' (hence the deep column to control deflection).
RE: Deep Column Weak Axis Buckling
However I will add this for now and hopefully someone can correct me if I'm wrong:
I think it depends on what unbraced length you are considering: Flexural Buckling or Torsional Buckling.
For flexural buckling, the concern is lateral movement, which to me seems like a member framing into the web would be able to meet this criteria. For the axial strength/stiffness requirements of the brace, I would look at AISC Appendix 6.
For torsional buckling, the concern (I believe) is rotation. In this case you would need to check if the brace member can restrain rotation. For the moment strength/stiffness requirements of the brace, I would look at AISC Appendix 6.
EIT
www.HowToEngineer.com
RE: Deep Column Weak Axis Buckling
RE: Deep Column Weak Axis Buckling
RE: Deep Column Weak Axis Buckling
A centreline brace would stop the lateral translation of the section, regardless of the connection to the flanges. The lack of connection to the flanges just leaves the chance that the brace causes some sort of torsional failure at the brace location. I assume it would end up happening at some load level just due to initial imperfections. However, this seems like a failure mechanism that requires a lot more energy.
I'm curious about this and if I have time I'll dig a bit.
RE: Deep Column Weak Axis Buckling
In this scenario I think the brace has adequate strength, it is the connection to the brace that I am worried about
RE: Deep Column Weak Axis Buckling
RE: Deep Column Weak Axis Buckling
The compression flange should be braced to prevent translation or the entire cross section should be braced so to prevent twist relative to the restrained end of the beam. But I think we are ahead of all that at this point.
Stiffener seems logical.
As for torsional strength/stiffness I was referring to A-6-9 and A-6-11.
EIT
www.HowToEngineer.com
RE: Deep Column Weak Axis Buckling
By the way how do I change my discipline to structural on this website. I set it up as civil/environmental but I am structural.
RE: Deep Column Weak Axis Buckling
At the bottom of the page, there is a "contact us" link. Suggest you try that and request the change.
RE: Deep Column Weak Axis Buckling
The paper "Fundementals of Beam Bracing" does given an example on how to find the rotational stiffness and does talk about stiffeners. The detail shown does not seem to provide much torsional restraint but at the same time that is a HUGE section.
http://www.aisc.org/store/p-994-fundamentals-of-be...
EIT
www.HowToEngineer.com
RE: Deep Column Weak Axis Buckling
RE: Deep Column Weak Axis Buckling
Thanks!
EIT
www.HowToEngineer.com
RE: Deep Column Weak Axis Buckling
RE: Deep Column Weak Axis Buckling
RE: Deep Column Weak Axis Buckling
EIT
www.HowToEngineer.com