Column Bracing by Girts 1

[palk7 EIT]

Hi,

For Industrial buildings when I have long column (32' height). For determining column compression capacity, when I have the girts connected to the column outer flanges at 5' spacing and the Inside flange of the column is braced by Fly brace from the girts at Mid-height of column (16'). Can I consider the unbraced height of the column as 16' at the mid-height where both the inside flange and outside flange will be braced by the girts? for finding the compression capacity

Thank you

 

[HTURKAK]

Probably yes ..It depends on the vertical bracings and horizontal struts ..


The following doc. is useful to get the concept of stability of columns and beams for single storey industrial bldgs..













Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[palk7 EIT]

Thank you!,

The girts run to a Vertical braced bay line. Regarding Horizontal struts?, you mean the struts at the roof level right?. (the perimeter beams)

 

[HTURKAK]

Pls look to the item ( 8.1.4 Bracing to restrain columns ) at my previous post. In order to assume the column is braced at mid-height, side rails or struts shall extent to the braced bay to stabilize the mid height.

the following doc . is also useful ..

Tim was so learned that he could name a
horse in nine languages: so ignorant that he bought a cow to ride on.
(BENJAMIN FRANKLIN )

 

[XR250]

So the girts and mid-height brace take care of the side-to-side stability, what is bracing it perpendicular to the girts?

 

[SteelPE]

So the girts and mid-height brace take care of the side-to-side stability, what is bracing it perpendicular to the girts?

Nothing. Presumably you would have the strong axis of the column orientated perpendicular to the wall girts, and you would use KL/rx to calculate the capacity in this direction.

This is a similar question to one I had a few months ago and we ended up with the same answer as found in HTURKAK's post (which goes against what I was originally taught.... back when we used to use through fastened corrugated metal siding with blanket insulation).

https://www.eng-tips.com/viewthread.cfm?qid=489609

 

[XR250]

Nothing. Presumably you would have the strong axis of the column orientated perpendicular to the wall girts, and you would use KL/rx to calculate the capacity in this direction.

Presumably but it is not clear from the post.

 

[SteelPE]

Presumably but it is not clear from the post.

I am not sure about that.

Inside flange of the column is braced by Fly brace from the girts at Mid-height of column (16'))

Why have a fly brace at mid height of the column if the strong axis of the column is in the plane of the wall girts? And why would you delineate the inside and outside flanges if the strong axis is not orientated perpendicular to the wall girts?

 

[XR250]

@SteelPE.

I am not questioning the column orientation. I was merely questioning whether the OP is considering strong axis buckling as well.

 

[JoshPlumSE]

For columns that are frequently braced, but only on one side, I think you'll find that the controlling buckling mode is "constrained axis torsional buckling".

To my knowledge, this failure method isn't discussed much in the code documents themselves. The best reference I have for it is in the AISC / MBMA design guide on "Frame Design Using Web-Tapered Members" by Richard Kaehler, Donald White, and Yoon Duk Kim. The discussion there should apply to non-tapered members as well.