Bridge Columns - Openings

[Anonymous]

Hi i want to modelate the columns seen in the atachment. They belong to a bridge and they make the connection betwen the arch and the deck. The problem is that i´m using a bar model and i dont know how to do it. The only away i came up with is to create a secction with a width equal to the sum of the massive parts not counting with the opening. 

[Rafal.Gaweda]

Attachment missing

[Anonymous]

Sorry i forgot. Its there now 🙂

Edit: I forgot to mention that the main objective of the model its to do a modal analysis. 

[Anonymous]

hm can anyone help me?

[Rafal.Gaweda]

Maybe like that.

(It depends how the rest of structure is modeled)

[Rafal.Gaweda · Accepted solution]

or this way:

[Anonymous · Accepted solution]

Thanks a lot for the answer. You can see how the rest of the bridge is being modeled on the attachment. Witch of the approaches do you think is the best? I´m thinking in the second one.

Thanks a lot 😄

[Anonymous]

here´s one more foto of the brige so you can have a better idea of what i´m talking about. 

[Rafal.Gaweda]

Now, it is more clear.
Second approach much convenient.

[Anonymous]

Hi I´ve created the model. Unfortunately the results I am receiving are absurd. Plus for some reason I´m getting instability of type 3 on one of the nodes. I believe the problem i on the rigid links created, Can you give me some tips of how to fix it?

I´ve attached the model. Sorry for all the bother.

Thanks for all the help .

[Rafal.Gaweda]

This instability can be neglected

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Instability/m-p/3855698/highlight/true#M1246...

in your case 

Stiffness matrix diagonal elements
Min/Max after decomposition:3.034729e+004 2.523399e+020 

if you replace all sections by C 18x18 it will disappear(Min/Max after decomposition:8.557681e+005 9.945693e+015 ).

[Anonymous]

OK thanks. But still, the results for the modal analysis are absurd. Look at those modes of vibration. Can you find a reason for that?

Thanks a lot. 

[Rafal.Gaweda]

I do not know how you did it but rigid links between nodes  208to214 216to218 224to226 232to234 240to242 248to250 260 274 281 302 309  are either corrupted or not well defined or ....

Corrected file attached.

[Anonymous]

Again Thanks for all the help 😄