Help with cable modeling · Graitec Advantage

Posted Tue, 28 Sep 2010 12:19:57 GMT by Bogdan Mateescu IMSAT SA

i modelised the structure in the image attached. the beam that you see there is attached to that pole by a cable.
when i analyse the structure i receive the next message "vous avez maille des elements modelise en cable" (i have the french version of advance design). at the cables properties panel for the "maillage" section i have unchecked the "automatic maillage" and at the parameters i have put "1" at number so that it will be a single piece.
what have i did wrong and what should i do so that it works?

Attachment: 1_0.bmp

Posted Tue, 28 Sep 2010 13:55:31 GMT by

Hello,

I don't understand your question exactly, as you figured out how to resolve the error message, but I can explain why that error appeared. Because the elements where only tension is allowed and there are only 3 dof at each end: Tx, Ty, Tz - internal nodes are not permitted as the relative displacements between them is impossible, hence the error.

Usually the cable element is used only for nonlinear analysis, as the cable can have large displacements second order effects must be taken into account. Keep in mind that Advance Design takes into consideration only geometric non-linearity.

If a nonlinear analysis is needed... depends only on the loading state of the structural system.

For your particular case (if nonlinearity is not needed) the tensioned element will always be in tension and as compression is unlikely to occur, a "tie" can be used instead of a "cable" element.

I hope this answers your question. For any other query don't hesitate to contact us.

Posted Tue, 28 Sep 2010 14:28:49 GMT by Bogdan Mateescu IMSAT SA

thank you for your answer. I figured out what i did wrong.
it was an another element in my structure which was defined as a cable (the pole - my mistake) :) and i didn't saw it. Now it works fine. i was able to obtain the result that i was looking for.
your answer was instructive though, thank you

Posted Thu, 30 Sep 2010 16:33:37 GMT by

Hello,

There is one more thing that you must take into consideration (as a general knowledge): when using a nonlinear analysis and cables are defined (large displacements hypothesis) you always must mesh the cables because these elements can have large deformations under their own weight and the nonlinear analysis will calculate the next step with loads applied on the last step deformations.
That's why the meshed cable will be calculated only under a nonlinear analysis otherwise, with a meshed cable under static linear loads my statements from the last post will apply and you can end up with a unstable model (the error you experienced).

Regards