Slenderness criteria for plate or bar element

[blackmaddog]

If you have a solid rectangular plate or bar in compression, what slenderness criteria applies in section B4 of AISC 13th?

Section B4.1 indicates that unstiffened elements are supported along only one edge parallel to the direction of the compression force. A bar in compression is not supported at all.

I am wondering if you can't have local buckling in a unsupported bar or plate, it would be controlled by Euler buckling.

 

[JStephen]

If a bar or plate has no stiffeners on the sides parallel to the load, it is just acting as a column, and you'd use the column equations. r = thickness divide by square root of 12, if I remember right.

 

[blackmaddog]

I sent the same question to AISC Solutions Center and received the following reply:

Section B4.1 doesn’t apply to a solid bar or plate that is only supported at the ends, but not along the edges parallel to the load. The strength of the plate you’re describing would be determined by either Section J4.4 or Section E3 depending on the KL/r ratio.

Section B4.1 applies to members such as W-shape columns that have an overall member buckling mode such as flexural buckling per E3 along with possible local buckling modes that must be ruled out or dealt with using E7. For a single plate, there’s no way for a part of it to buckle locally. If it buckles, the mode will be flexural buckling of the entire plate, so there is no need to separate out a local buckling mode and head over to B4.1.

Brad Davis, Ph.D., S.E.
Consultant
American Institute of Steel Construction
866.ASK.AISC

 

[racookpe1978]

If the bar (or plate) has uniform properties - and that's almost certainly the case - then, when it is under compression it will buckle "grossly" rather than "locally".

Or, looking the other way, the first place it buckles IS the "local buckling" that will be at the weakest point of the bar, and that "local" failure is the whole column's point of failure. (Probably near the middle of the column).

Obviously, it will buckle about the thinnest side of the bar.

Your use of "plate" seems odd. A plate probably would not ever be used as a compression member, since we commonly only use "plate" for wide, flat, thin rolled steel pieces purchased and specified by their thickness.