Flexural tube buckling
Flexural tube buckling
(OP)
Hi, I'm working with hollow tubes for poles (cantilever bending). I'm trying to estimate where the tube will buckle - I'm currently using diameter from the base as an estimate, but I'm having difficulty confirming this anywhere.






RE: Flexural tube buckling
Mike Halloran
Pembroke Pines, FL, USA
RE: Flexural tube buckling
What are the tube dimensions?
Interesting problem.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Flexural tube buckling
RE: Flexural tube buckling
good luck
RE: Flexural tube buckling
it'll buckle at the section with the highest compression stress ... i'd look at the section with the highest moment, probably at the base (since you say "tall", i'm picturing a flag pole (or mast) with a side load creating bending).
no apologies for stating the obvious.
RE: Flexural tube buckling
RE: Flexural tube buckling
For a cantilever pole/column, assuming a lateral load, the compressive stress in the compression side/flange will be highest at the base. This is not where it will buckle, as the tube is connected to the base at that point. It will buckle at some distance from the base, maybe between one diameter from the base and 5 diameters from the base, as the original poster said. Buckling occurs at some combination between compressive force and out of plane stiffness of the element in question. The buckling in this case will be lateral torsional buckling.
RE: Flexural tube buckling
but if i was doing a hand calc i'd use the maximum moment to keep something in my back pocket (other than my wallet). this conservativism is only a few percentage points (< 10%, L = 3660 mm, dia = 210mm), and modelling the real world stiffness would be more trouble than it's worth (IMHO).
and with less than 1 minute's thought on the problem, i don't see where the torsion's coming from ...
RE: Flexural tube buckling
RE: Flexural tube buckling
Does fibre reinforced plastic buckle the same way metal does? Are the calculations meaningful?
JHG
RE: Flexural tube buckling
Thinner materials tend to buckle a bit more similarly to metals,
RE: Flexural tube buckling
I have no expertise or experience with plastic. Typically plastic is ductile, so I'd guess it would buckle out of plane before crushing, but I really don't know. Sorry I'm of no help to the original poster.
RE: Flexural tube buckling
RE: Flexural tube buckling
RE: Flexural tube buckling
RE: Flexural tube buckling
http://assist.daps.dla.mil/quicksearch/
There is also NASA document NASA-97-TP3659 which is free at the NASA technical report server.
Regards
MNLiaison
RE: Flexural tube buckling
Dik
RE: Flexural tube buckling
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