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Length of the column where buckling is likely to occur 
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#1
Jul1212, 03:04 PM

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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 200GNm2 yield stress 140MNm2 2. Relevant equations 3. The attempt at a solution 


#2
Jul1212, 04:18 PM

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The minimum length at which the column will buckle depends on the applied axial compressive load which is not given...



#3
Jul1312, 12:56 PM

P: 696

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.



#4
Jul1412, 06:48 AM

P: 25

Length of the column where buckling is likely to occur
to find I... I = (D^4d^4)*pi / 64 and for area,,,, A = (D^2d^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 


#5
Jul1412, 05:18 PM

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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 fixedfixed column. I can't do the math...too many zeros. 


#6
Jul1512, 06:37 AM

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??? 


#7
Jul1612, 05:48 AM

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I painstakingly did the math and i get about 6 meters length when the column buckles at yield stress [itex]\sigma_{cr} = \sigma_y[/itex] , hope the math is Ok but in any event the problem statement is poorly worded.



#8
Jul213, 05:30 PM

P: 7

That all pans out. I get the same.



#9
Aug1413, 10:45 AM

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?



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