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Robot Structural Analysis

Posts: 5
Registered: ‎04-10-2012
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Results: Buckling

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04-10-2012 01:11 AM



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: 461
Registered: ‎06-23-2008

Re: Results: Buckling

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


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:

no division.png

After division in 10 parts:division.png


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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Pawel Pulak
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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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