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Modal analysis

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Message 1 of 4
skilak
308 Views, 3 Replies

Modal analysis

I am trying to obtain dynamic properties (natural frequencies) of a portal frame 5x5m (pinned bases) using 305x305x137 UC. The modal anaylsis gives me the lowest fn=6.28Hz. Now, I would like to use Elasto-Plastic properties of the sections thus 305x305x137EP UC (elastic-perfectly plastic). The modal analysis gives me the lowes fn=1.87Hz. How is that?

Please could you explain and advise if the above is right?

 

Regrds,

3 REPLIES 3
Message 2 of 4
Artur.Kosakowski
in reply to: skilak

The modal analysis takes the stiffness matrix from the static case defined prior to it.

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.



Artur Kosakowski
Message 3 of 4
skilak
in reply to: Artur.Kosakowski

and where I can compare those matrixes for the two cases? 305UC and 305UC EP? for either prior case I have, both look the same in terms of results e.g. buckling, bending, etc. So for the magniutde of loads in prior cases I cannot fugure out the difference.

 

Can I use elast-plastic properties for modal or not?

 

cheers

Message 4 of 4
Artur.Kosakowski
in reply to: skilak

I have created two examples based on your description. The results are similar but you have bear in mind that for EP analysis the shape of I section is simplified.

 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.



Artur Kosakowski

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