Looks like this is an argument over engineering terminology rather than anything more serious...
Well Beachnut I am floored. I certainly expected a neutral answer from a Structural Engineering forum like this, and the fact that he quoted from a 9/11 Truth website takes away his neutrality. I obviously had no idea this guy had this kind of connection to 9/11 Truth (note to MM, Ergo, Chris7: "non-neutral" doesn't mean wrong or woo, it just means he is a participant in the 9/11 debate and therefore not neutral). Thanks Beachnut for catching this. I have the same questions out on another forum; we'll see what comes back from that. In the meantime, your research kind of knocked the wind out of me, in a good way.
Well, I'm obviously not "neutral" at all but I'd support the responses you got from this other fellow, no matter what his leanings are:
1) My limited understanding was that column buckling and column breakage were two different things...They are.
This is correct. In some situations a column that buckles, i.e. is loaded to the point of instability -- after which it only provides a minimal amount of support to the load -- only displaces a small amount. This would be the case if there were many other columns with sufficient reserve capacity, and stiff enough beams, to carry a concentrated load. Provided the buckled column only strains a little bit and remains elastic, once the load is removed it will regain most or all of its former strength.
A column that buckles under a load that is not carried by other members, on the other hand, will almost surely fracture in short order.
If a building is collapsing and the support columns are "buckling," can that term apply to columns that are breaking at the welded connections and/or bolts breaking...No!
Well, maybe. There's a lot going on here. Since we're talking about a building that
is collapsing, columns that buckle are almost certainly going to break as well. But the term buckling does not describe the actual rupture of welds or bolt failures.
There is also plastic buckling, different from elastic buckling, that applies in certain situations. In plastic buckling there will be some damage, probably appearing first at the connections. Yet it is still not correct vocabulary-wise to equate plastic buckling with rupture.
or does buckling specifically refer only to a column that is bending at something like a right angle until it loses most of its strength?...buckling refers to a column which has reached a critical load (Euler's formula) and becomes unstable.
I don't follow the question. A column usually buckles long before reaching a 90-degree bend. The answer above is correct -- when a column reaches its critical load and becomes unstable, i.e. any further displacement leads to a rapid decrease in its strength, it is said to have buckled.
2) From the point of view of loss of strength, does a badly bent column have much more resistance than a column that has snapped apart at its welded connections? Does a completely bent column have less than 5% of its initial strength? Less than 2%?...A column which has buckled is not badly bent. If load is removed, it will regain its initial shape and strength. If load is not removed, it will collapse. During collapse, it will probably become badly bent.
Again, there are situations where a buckled column has gone plastic and will not regain its previous shape and strength, but the answer above is close.
You cannot meaningfully compare a buckled but intact column to a column that has snapped under load -- the first has reached a point of instability, but still behaves according to the same governing stress-strain equations; whereas the other has undergone a sudden structural change, and its behavior is accordingly discontinuous.
3) I'm somewhat familiar with Euler's theorem and am aware that this is a purely mathematical construct...no, it is not. It is accurate for slender columns within the elastic range.
The Euler buckling equation is often an overestimate in real situations, but it is a pretty good model in many cases. I would not deprecate it as purely mathematical.
In the real world, if a column is suffering from major stresses during a building collapse, is it likely that it would "buckle" by bending in half, or would it be much more likely to snap apart at the welded connections or other weaker spots? Depends what is causing the building collapse. If a column is buckling, that would trigger a partial or complete building collapse.
Lots of possible "real world" effects here. A buckled column that cannot transfer its load (as in a building collapse) will rupture. This rupture is likely to happen at the ends and midpoint of the column, but there may also be other forces involved, not to mention impacts. Failure at the connections is likely in modern steel-frame construction. This is particularly true for bolted connections.
4) Is this a good working definition of "buckling"? The term buckle refers to the instant in time that the column assembly goes unstable...that is a pretty good definition.
Minor nitpick, "buckle" does not describe a moment in time, it describes the behavior of the column. That behavior is the column instability. But keep in mind the instability is not "it's gonna fall over," rather it describes the slope of the stress-strain curve reversing. In practical terms this means that even if weight is removed once the column starts to buckle, it still may fracture and collapse if weight isn't removed fast enough.
It doesn't pretend to define the other 99% of the process, of how each piece comes apart...99% of what process, the collapse process? No, it does not deal with anything beyond the buckling process
Agreed, this is semantics though
Most of the time, buckles are studied as "3 point hinges",one weak point at the top of the failure, one at the bottom and one someplace between those two...Not true. A column can buckle with no hinges present.
Also agreed. Whether you have "hinges" depends on whether the column continues to displace, and if it does, the areas of highest strain can go plastic. You get three such "hinges" if your column is fully fixed at both ends -- one "hinge" near each end, and one in the middle. If the column is free to rotate at each end (think of stacking weight on a pedestal that isn't bolted to the floor or welded to the weight above), you will only get one such hinge, in the middle.
(The middle hinge point is frequently shown half-way between the other two, but this is far from a rule.)...very far from a rule.
Agreed. If you have a complex built-up column, or one that thins as you go up, the middle hinge may not be at the midpoint in height. This should be inuitive.
When a multisegment column assembly buckles, the hinge points form at weak points in the assemblies, which are again at the connections...Not necessarily true.
Agreed -- in a built-up column one tries to design and place connections where they can handle their anticipated loads. Column buckling may lead to failure at the connections or in the component members. Note, however, if the column isn't being loaded in the way we thought it would when we designed it (e.g., building collapse versus simply standing under load), then all bets are off. Connections that are totally adequate for an intact structure may become susceptible to secondary damage in a collapse, simply because that's just not part of their design requirements.
Hope this helps. I welcome other SE's to chime in. Newtons_Bit would be a good one to try, he's much more up on this than I am if he's still around.
