post buckling strength

[Lion06]

Is the idea behind post buckling strength of columns this: A column that buckles elastically has much higher post-buckling strength than a column that buckles inelastically because the elastic column has greater moment capacity for no other reason than the section hasn't yielded and lost capacity? Once the column begins yielding, then buckles, its moment capacity (and, as a result, its post-buckling strength) is greatly reduced.

 

[rb1957]

in my experience post-buckling strength relies on the structure redistributing the load to an alternate loadpath, for example, in stiffened skin panels, the panel can buckle (typically in shear) and the panel can react additional shear (as tension stresses along the skin buckles, refer diagonal tension, wagner beams).

as i think you're implying, once a column starts to buckle in compression, wouldn't it be the equivalent of a plastic hinge and so the allowable load would drop significantly.

just possibly there are some "funky" designs whereby a small part of the section can buckle and the rest of the section can remain stable, and so take additional load ??

 

[ash060]

It has to do with the column wanting to locally buckle before it buckles gobally. If you have a light gauge section the web will be begin to buckle locally and at the stiffened edges it has not buckled, and this usually occurs at a very low stress.

The system as a whole has not buckled becuase of your stiffened areas.

So codes allow you to take an increase in strength to account for the time between local buckling (individual components) and gobally buckling (overall section).

 

[Lion06]

What I read talked about columns that buckle elastically having greater post buckling strength than columns that buckle inelastically. It doesn't make sense to me that this difference in strength would be the result of a local buckling. This was in reference to Steel columns, not light gage metal.

 

[msquared48]

Strain Hardening?

Mike McCann
MMC Engineering

 

[csd72]

This is a common problem in offshore engineering where platforms need to be designed for impact. I suggest you direct your search in that direction.

 

[bootlegend]

Structural EIT,

Where did you find the info you are referring to? I was not aware that columns are counted on for postbuckling strength, especially elastic buckling. Elastic buckling is due to the column being long or slender, so after buckling I couldn't imagine it having any strength after buckling due to instability.

 

[271828]

ash060 is correct. Read in S&J the section at the end of the chapter on columns. It's the part on plate buckling, lambda values, etc.

It definitely doesn't have anything to do with elastic vs inelastic overall member buckling.

Here's the easiest explanation I can think of, contrasting overall member buckling vs local buckling with post-buckling strength.

With overall member buckling such as flexural buckling or LTB, once the member begins to buckle, that's pretty much it. Its load can't be increased much or at all.

Now imagine a web of a vertical W-shape column. If it's under compression and locally buckles, horizontal normal stresses (membrane stresses) develop and restrain the web buckling further. Because of this, more load can be applied to the web. This is where all of the Q business in AISC and beff business in AISI come from.

 

[rb1957]

yeah, imagine a section with a wide, thin web and big heavy stiffeners at the edges. the web can elastically buckle by exceeding it's buckling allowable, and effectively not react more load. but the heavy stiffeners are still stable, prevent the web from permanently buckling, and can react additional load.