# Length of the column where buckling is likely to occur

by mattyh3
Tags: buckling, column, length, occur
 P: 25 1. The problem statement, all variables and given/known data i am struggling with a question i have.. i cant find the right equation to use to find what the minimum length of the column at which buckling is likely to occur?? can anyone offer any help with this as my lesson books show me nothing on how you find length? i have D=80mm d=60mm youngs modulus 200GNm-2 yield stress 140MNm-2 2. Relevant equations 3. The attempt at a solution Attached Thumbnails
 Sci Advisor HW Helper PF Gold P: 6,041 The minimum length at which the column will buckle depends on the applied axial compressive load which is not given...
 P: 699 The question seems to be a tube. IN that case there are at least two modes of buckling. First, there is the overall buckling of the member as if it were a long thin rod and Euler's formula might be said to apply. But this could be preceded by a local buckling of the tube, especially if it is thin in relation to the diameter. I think you are probably looking to apply the Euler equation of buckling, in which you will be interested in the EFFECTIVE length.
P: 25
Length of the column where buckling is likely to occur

 Quote by pongo38 The question seems to be a tube. IN that case there are at least two modes of buckling. First, there is the overall buckling of the member as if it were a long thin rod and Euler's formula might be said to apply. But this could be preceded by a local buckling of the tube, especially if it is thin in relation to the diameter. I think you are probably looking to apply the Euler equation of buckling, in which you will be interested in the EFFECTIVE length.
well at present i am trying to find the length so been looking at using these...

to find I... I = (D^4-d^4)*pi / 64
and for area,,,, A = (D^2-d^2)*pi / 4

E.S.R = (sq) (pi^2*E)/oc(critical stress)
and then
L = E.S.R * (sq) I/A

am i going down the right route with these as someone has told me the answer for length 5.94 but i need to find it my self as i cant just put that lol
HW Helper
PF Gold
P: 6,041
 Quote by PhanthomJay The minimum length at which the column will buckle depends on the applied axial compressive load which is not given...
Since P_cr = pi^2(EI)/(kL)^2, you cannot solve for the effective length unless you know the value of the compressive load. Are you sure you have stated the problem correctly as worded?

Edit: Maybe the problem is looking for the max length before buckling occurs prior to the material reaching its yield stress?? If so, P_cr = (yield stress)*A, then solve for L using the buckling formula for a fixed-fixed column. I can't do the math...too many zeros.
 P: 25 my question i have says... what is the minimum length of the column at which buckling is likely to occur ... and the values i have put down are all i have on the sheet.. then i have what will mode of failure be and at what load.. i have included an image of my workings out so far for length,, which i have seen on the internet that 5.94 is the length just needed to find it myself... could anyone confirm this??? Attached Thumbnails
 Sci Advisor HW Helper PF Gold P: 6,041 I painstakingly did the math and i get about 6 meters length when the column buckles at yield stress $\sigma_{cr} = \sigma_y$ , hope the math is Ok but in any event the problem statement is poorly worded.
 P: 7 That all pans out. I get the same.
 P: 3 Isn't the diagram in post 1 a annulus? which would mean that second moment of area formula is pi (R^4 - r^4) / 4?