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## Robot Structural Analysis

Member
Posts: 5
Registered: ‎04-10-2012

# Results: Buckling

501 Views, 2 Replies
04-10-2012 01:11 AM

Hello,

I'm trying to do a buckling analysis of a compressed beam.

The section type is CAEP (L-shaped cross section) L60x6 Length=800mm (OTUA catalog).

But the results that I get are different from the analytic calculation of the critic force and length.

My theoretical calculus results are:

Frc = π^2 * E * I / (Lcr^2)

Fcr_u = 3,14^2 * 210000 [N] * 361400 [mm^4] / (800 [mm]^2) = 1170380,87 [N]

Fcr_ v = 3,14^2 * 210000 [N] * 94400 [mm^4] / (800 [mm]^2) = 305711 [N]

Where u and v are respectively the major and minor principal axes.

In the calculus above I used a critical length equal to

Lcr = L * K

where K = 1 for a simply-supported beam.

So what I can't understand is why am I obtaining such different results compared to those of Robot?

Maybe there is a problem in my beam model?

Thanks for the help!

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Product Support
Posts: 477
Registered: ‎06-23-2008

# Re: Results: Buckling

04-10-2012 02:38 AM in reply to: federico.albertengo

Hello,

the precision of buckling analysis results depends on the number of divisions of bars - the higher the number of finite elements modeling the bar the closer are the critical loads to Euler's formula.

I have made the simple test model analogous to yours - but with applied load of 100000 N.

Below are screen captures made before and after division. As you can see after division in 10 parts the results are coherent with theoretical ones.

Before division:

After division in 10 parts:

So after division:

Fcr_v = 1,17040e+001 * 1000000 N = 1170400 N

Fcr_u = 3,05715e+000 * 1000000 N = 305715 N

Additional note: when analysing results of buckling analysis it is recommended to use critical coefficient values and not critical force ones - because for more complex models critical force may be not related to specific bar and for instance it is not displayed for bars divided internally in smaller calculation elements.

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Regards,

Pawel Pulak
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Member
Posts: 5
Registered: ‎04-10-2012

# Re: Results: Buckling

04-10-2012 02:43 AM in reply to: pp2008

Ok thank's a lot for your help!

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