Column Slenderness Ratio > 200

[LSPSCAT]

Does anyone have a reference which specifies the limits for columns with a slenderness ratio greater than 200?

I have read several of the column posts and have referenced most of my textbooks and the best information I have found states "columns bounded by l/r < 200".

I have a safety factor of 2X the design load as compared to the critical column buckling load, however, l/r is 218.

Pcr = 200,000 lbs
Pdl = 100,000 lbs

This may be more of an academic interest at this point, however, I would like to understand the behavior above 200.

 

[ToadJones]

The theory doesn't change based on KL/r<200 so even a good mechanics book will provide some insight, no?
KL/r<200 is a code privision, no?

 

[slickdeals]

Kl/r < 200 is not a code provision anymore. It is merely a recommendation. But I don't think many engineers would want to even get close to 200. 120 to 160 might be optimum, but I am sure there will be exceptions.

 

[ToadJones]

In fact, the 2005 AISC Spec has completely eliminated that provision if I am not mistaken.
Assuming you are using AISC, with a slender column you'd be using equations E3-3 and E3-4....you'll just have a very low Elastic Critical Buckling Stress.

 

[dik]

The Canadian code limits the slenderness ration to less than or equal to 200... and from the wording there is little 'wiggle room'... you might consider adjusting the effect of fixity required to bring the value down to 200.

Dik

 

[ToadJones]

At KL/r = 218, Fcr = 5.3 ksi....pretty darn low.

 

[ToadJones]

Also, you may want to reference the Commentary on section E2 as to the reasoning for limiting KL/r to 200.

 

[JAE]

I believe that AISC took out the KL/r < 200 "preference" in the body of the specification and now has it only in the commentary (gray shaded areas - see chapter E, section E2).

Dr. Joseph Yura, speaking at a seminar once, commented that the compression formulae for columns applies past KL/r = 200 but that at higher slenderness levels, all those secondary influences on buckling become much more influential on the column stability.

Secondary influences might include unexpected lateral loads, construction out-of-plumb installation, eccentricity from insufficient bearing plate grout, load eccentricity at the top of the column, unbalanced loading, etc.So the 200 limit is still preferred.

Even if a design (architect) called for a skinny column, I might still use a very thick section and perhaps fill it with concrete to overcome any [blue]heebee jeebees[/blue] I might have with a high KL/r.

 

[LSPSCAT]

The application is not specific to AISC, however,it is not my intention to ignore the guideline. This is more of a mechanical engineering type application and a question as to the effects as you approach this limit. Numerous parameters outside my control have selected the maximum column size. I agree that the Euler load is applicable in this range, in my application the critical stress is around 3 ksi. I realize this is inefficient, however, that is not an issue at this point. I guess I am looking for comparision for the stability as you approach this limit. My specification actually states "fixed-pinned" which I consider extremely generous for the end conditions, at fixed pinned kl/r is around 154. Pinned-pinned kl/r is 216. So per specificaiton I meet the criteria, per engineering judgement I exceed a rational l/r ratio.