Cantilevering steel plate design for bending and buckling 1

[tristan_a6]

Hi everyone,

I was going through section F11 of the AISC code, let's say that the plate to be designed is actually cantilevering. The plate is attached to a column on one end, nothing on the other. Imagine some sort of flag pole where the flag would be a steel plate. Plate would be exposed to wind on weak axis and SW on strong axis. Plate will have a 40 ft2 area but be only 3/8" or so thick.

I want to check the plate for bending in weak axis for wind load and bending as well as LTB in strong axis. It seems like F11 section is only applicable for a member that would be supported on both ends. Is it the case?

Thanks for your help

 

[Once20036]

What part of F11 makes you think it doesn't apply to cantilevers?
I just gave it a quick read through and nothing caught my eye.

I`ve definitely used the section for cantilever plans in the past.

 

[tristan_a6]

The fact that they were calling Lb being the length between points that are either braced against lateral displacement of the compression region, or between points braced to prevent twist of the cross section. That threw me off. What would you use for Lb in my case?

 

[WARose]

What are the dimensions of the plate?

 

[tristan_a6]

10' long x 4' deep x 3/8"

 

[WARose]

To me, that is getting outside of the scope of AISC's provisions. (Possibly closer to something in ASME.) Initial imperfections (to name one thing) are going to be critical. I'd find another code/approach.

 

[tristan_a6]

Any recommendations as far as where to go look or what method to follow ?
Thanks for your help

 

[racookpe1978]

I would prefer not to "imagine" anything, but do want to look at your sketches or dwg's of the possible plate configurations.

 

[tristan_a6]

 

[WARose]

Any recommendations as far as where to go look or what method to follow ?

Depends on the application. What is this being used for?

 

[tristan_a6]

Some piece of art, it will just be sitting outside. Exposed to the wind and SW.

 

[WARose]

You could probably just do a conventional plate buckling analysis. (Using Roark's or some other reference.) But I'd be mighty careful about accounting for initial imperfections and the P-Delta effects.

 

[JoelTXCive]

I think you might be in Finite Element Model territory......

But, maybe this could help? At least for the self weight.

"Design of Unstiffened Extended Single Shear Plate connections?"

Your scale is obviously larger, but I would think many same principles apply?

There is a calculation for buckling based on "Muir & Thornton 2004" but they don't go into much further detail. It might be a starting point though......

 

[tristan_a6]

Is there any easy to use finite element software that I could try to use? Any recommendation?

 

[BridgeSmith]

What wind speed / pressure are you designing for? At our typical 100mph / 42psf, a 3/8" plate with a 10' cantilever in pure bending is hitting almost 90ksi bending stress in the plate.

Edit: I see you did say 3/8" "or so". At 1/2" or 5/8" it's not so bad.