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Old Sep 10th 2013, 07:22 AM   #1
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Im trying to apply a force at the middle a column, how do i predict the maximum force

Hey guys:
Im trying to apply a force at the middle a column, how should i predict the maximum force it will be able to take before break?
Here is some data i've got, critical buckling load is P(critical) , the elasticity is 3GN/m^2, standard deviation of that is +2.4/-2.1 MN /m^2.
Thanks a lot.
Eason
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Old Sep 10th 2013, 09:11 AM   #2
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Failure of the column will come from either of two effects:

1. Buckling. You say you already have data for the critical buckling load for the column. The critical load for a column where load is aopplied at the midpoint rather than the end is 4 times greater, since P_crit is proportional to the inverse of the column length squarred.

2. Crushing. For short columns failure comes from crushing of the material rather than buckling. To calculate the crushing load you need data on the yield stress of the material, then multiply by the cross-sectional area to get the corresponding load.

The column fails when the load exceeds either the critical buckling load or the crushing load.
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Old Sep 10th 2013, 08:04 PM   #3
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Originally Posted by ChipB View Post
Failure of the column will come from either of two effects:

1. Buckling. You say you already have data for the critical buckling load for the column. The critical load for a column where load is aopplied at the midpoint rather than the end is 4 times greater, since P_crit is proportional to the inverse of the column length squarred.

2. Crushing. For short columns failure comes from crushing of the material rather than buckling. To calculate the crushing load you need data on the yield stress of the material, then multiply by the cross-sectional area to get the corresponding load.

The column fails when the load exceeds either the critical buckling load or the crushing load.

Thank you for replying, sorry for not making it clear, here is some more details, two end of the column is fixed(two rocker on each end), and there is the force applied at the midpoint is perpendicular to that column,
so does that mean the maximum force it can take at midpoint is 4*P(critical) or i need some more datas ?
Best regards

Last edited by yichenli; Sep 10th 2013 at 08:14 PM. Reason: Add a picture
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Old Sep 11th 2013, 04:47 AM   #4
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You would use standard beam equations: find the max moment the beam can withstand using yiield stress=Mc/I. So you need to know (a) the yield stress of the beam and (b) its cross-section to determine c and I. The max moment will occur at the two fixed ends and is magnitude FL/4. I don't understand what you meant by "two rockers" - if you mean the ends aren't fixed but rather are pinned (so the ends can rotate when as the beam bends) then the max moment is at the center and is magnitude FL/2. Hope this helps.

Last edited by ChipB; Sep 11th 2013 at 08:54 AM.
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Old Sep 13th 2013, 03:13 PM   #5
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Originally Posted by ChipB View Post
You would use standard beam equations: find the max moment the beam can withstand using yiield stress=Mc/I. So you need to know (a) the yield stress of the beam and (b) its cross-section to determine c and I. The max moment will occur at the two fixed ends and is magnitude FL/4. I don't understand what you meant by "two rockers" - if you mean the ends aren't fixed but rather are pinned (so the ends can rotate when as the beam bends) then the max moment is at the center and is magnitude FL/2. Hope this helps.

THanks for replying,
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