Short Columns yielding in compression

[E720]

Does anyone have any information on when (what KL/r) you could realistically expect a short column to yield in compression instead of buckle. In the AISC 360-16 code as KL/r goes to zero, Fe will go to infinity, and the Fcr term will go to Fy. Obviously you could solve for the Euler buckling length that would result in a critical buckling stress of Fy, but if you plugged that length into the AISC code then you would get <Fy (you will only get Fcr = Fy when KL/r goes to zero). I am assuming also the column's elements are compact so no local buckling will occur. Any information is appreciated. Thanks

 

[bugbus]

In the Australian codes, the modified slenderness factor (below) has to be less than about 15-25 for there to be no reduction in capacity due to slenderness/buckling. This also includes the material strength.

The exact ratio depends on another factor alpha_b, which accounts for things like residual stresses from welding or hot rolling, and possibly geometric tolerances.

 

[Agent666]

Just work back and solve the equation to give you the length where the behaviour changes, or plot the curves and pick it off.

 

[Settingsun]

Agent, the US code doesn't have the horizontal part of the capacity function, hence the question.

 

[Agent666]

Ah, I see, my bad.

So in a design sense, they have the answer then. L=0? There is no transition from full section short column squash load behaviour to member buckling behaviour, so the question has no definite answer.

 

[GastonLagaffe]

My understanding is that the buckling formulas incorporate an additional factor of safety to account for imperfections / accidental eccentricities. That'd be why you're not getting your full 50 ksi with the formulas. Imperfections wouldn't have much of an effect at short lengths. Eccentricities however definitely would - the column sitting on the baseplate at short length would behave much more like a fixed connection than a pinned connection.

That said, there's some judgement involved here. I don't think anyone would blame you for taking the squash load if you have a stubby column (eg wider than its height). Short like that and you might start seeing pretty significant stress triaxiality in your column which would increase your effective yield strength.

 

[E720]

Thanks for everyone's comments. This is not for any particular application, just the stuff that keeps me up at night.

 

[thereitcomestoday]

Thsi might be helpful: Sakino, K., Nakahara, H., Morino, S. and Nishiyama, I. (2004), “Behavior of Centrally Loaded Concrete-Filled Steel-Tube Short Columns,” Journal of Structural Engineering, ASCE, Vol. 130, No. 2, pp. 180–188.