lateral torsional buckling of column?

[Lion06]

I recently had a discussion with an engineer in our office who attended a Joe Yura stability seminar some time ago. The idea of column bracing came up and it was stated that if you brace only one flange of a column (for weak axis buckling) and not the web or the other flange, that it can buckle in a lateral-torsional buckling mode. This makes sense to me because the whole section wants to buckle, but part of it is restrained so it has this torsional component to it. That being said, I've never seen anything in AISC regarding this - or in any textbook (including S&J) for that matter.

Does anyone have any literature on this?

Would this same kind of phenomenom happen to wood studs braced on one side by sheathing and not on the other side?

 

[GreenMan1978]

i am a newbie engineer.. graduated in a 3rd world country.. my school sucks..

am still confuse when someone say lateral torsional buckling, out of plane buckling or whatever..

can someone please explain to me these terms..
i just couldnt picture it..

 

[Lion06]

Why don't you tell me how you REALLY feel?! I'm still laughing after reading that.

If you get your hands on a Salmon and Johnson text, it will clear up many of these things.

Out-of-plane buckling is when something buckles out of its own plane. Picture a wall (or a tall, thin plate). Because of its geometry, it has its own plane. If you load it axially, the most obvious buckling mode is for the "plane" to buckle, not for it to distort in its own plane.

 

[GreenMan1978]

so it's the same as bending except it bend due to axial load.. right?

am looking for a good basic book for both concrete and steel...

can you recommend one..

thanks,

 

[BAretired]

It happens in industrial buildings all the time. Girts run continuously past the columns, bracing them only on the exterior flange.

Unless the inside flange is braced at one or more girts by a diagonal strut, its effective length (conservatively) is the overall height whereas the effective length of the outer flange is the girt spacing. If the columns are torsionally restrained by the girts, that is somewhat conservative, but the calculations required to justify a more liberal assumption are too messy for most of us.

GreenMan1978,

Google "lateral torsional buckling" and you will find all kinds of information on the subject.

BA

 

[Lion06]

I would recommend MacGregor and White "Reinforced Concrete Mechanics and Design" for concrete, and Salmon and Johnson "Steel Structures Design and Behavior" for steel.

I don't know of a single book that is good for both.

 

[271828]

This is called "constrained axis buckling." It's like flexural-torsional buckling from Section E4 except that the section twists about a defined axis. Look in the Yura/Helwig Bracing Seminar notes. There's a page or two in there on this buckling mode. It's also in the AISC/MBMA tapered member design guide--whenever it's released. This situation happens so darn often that it really surprises me that it's not in the Spec. I taught this in our advanced steel class this past semester and two of the practicing engineers in teh class came up and said they saw this very frequently and were glad they now knew how to deal with it.

 

[msquared48]

ZSEIT: With regard to wood stud walls abolutely, but unless this is a foundation pony wall in a crawlspace or a non-bearing partition wall, I don't see the condition happening that often. Usually there is at least sheetrock on each side, if not plywood too to stabilize the wall.

I agree with the comments on the wood or steel girts, and purlins, too for metal buildings - a VERY common occurrence.

Mike McCann
MMC Engineering