Rigid Frame Column w/ Boxed-In Flange

[thaidavid40]

I encountered something this week I had not run into in nearly 40 years of practice. Please refer to the attached file for the column section specifics. This is from an old (1968) industrial metal building frame. The columns have the “boxed-in” angles added to the inside column flange only. The reinforcing angles extend to the column haunches, but do not follow the bottom flanges of the rafter beams; i.e.: they are column flange supplements only.
Has anyone ever encountered these before? What is their specific purpose (I have some theories, but that is all they are at the moment.)? I have not yet had an opportunity to contact the manufacturer for their information (it’s Sunday!).
Any and all experiential insights are appreciated. Thanks.


Thaidavid

 

[JAE]

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[thaidavid40]

Dang it!
Here's the attachment.

Thaidavid

 

[BAretired]

My guess is that the combined axial load and bending moment overstressed the column flange in that location and that the angles were added to alleviate the overstress.

BA

 

[KootK]

Relative to other kinds of reinforcement, like flange plating etc, one of the nice features of this method is that it increases section resistance to torsional/lateral torsional buckling effects. That might be helpful to keep in mind in the determination of the "why".

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.

 

[hokie66]

Are the bottom flanges of the rafters braced in any way? Maybe they could brace the rafters, but didn't want to use fly braces or the like on the columns?

Another idea is that the angles were added just to reinforce the columns against impact. Industrial buildings take a lot of abuse, particularly columns near doors.

 

[thaidavid40]

@hokie66 -
The remainder of the structure is oddly typical of what you would see everyday - except for this. From a structural standpoint, I don't understand why they would reinforce just one flange as they did, since it makes the column very eccentric, and it no longer matches the rafter profile. My thinking was along the same lines as yours - this was simple "armoring" to reinforce the flange against forklift impacts. However, for what ever good it did them, the bottoms of the columns still look like hell anyway. These columns have no girts to brace the compression flanges when in reverse bending, so that could have been a reason also, as you suggested. However, that seems an expensive way to get additional allowable compressive stress and column height, when simply going to heavier flange plates would have worked just as well - and without the expense of all those welds!
Thanks for your inputs thus far, guys.

Thaidavid

 

[KootK]

From a structural standpoint, I don't understand why they would reinforce just one flange as they did, since it makes the column very eccentric

It makes the column asymmetric but probably more concentric with the applied load.

that seems an expensive way to get additional allowable compressive stress and column height, when simply going to heavier flange plates would have worked just as well - and without the expense of all those welds!

From the outside, it's often hard to say what makes sense with a manufactured product. Maybe their fabrication process didn't suit flanges as wide/thick as they needed to be. Maybe they just had some of these columns laying around the yard from a job that went south.

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.

 

[thaidavid40]

I was finally able to call the company rep today. He has 40 years experience in the industry, and this is the first he has heard of this also. His best guess was that it was simple armor for strengthening the flange against impact damage. He was going to call on some retirees he knew, but he didn't hold out much hope that they would have any better ideas.

Thaidavid

 

[BadgerPE]

I have done similar retrofit work when adding load to PEMB buildings and have used the attached paper as a bit of a reference. I agree with KootK that this was probably done as a retrofit to an existing fabricated column or possibly something was added to the building during the fabrication process that forced the designer to retrofit. Either way, it is something that shouldn't cause too many headaches.

 

[thaidavid40]

Thanks, @BadgerPE
Now I have seen this type of detail printed in TWO places! More "food for thought".
Dave

Thaidavid