FEA of cables

[Anonymous]

Hi,

I am creating a simple model of cable bridge to do finite element analysis of each part about their forces and deformations. I get stuck when dividing the cables. Nodes were created along all cables but during FEA they are shown as isolated nodes. As they are 1D components, how can I divide the cables properly to carry out the FEA? I cannot see any numbers of calculation elements at this stage. Do they show up only when I divide the cables correctly? I am using version 2019 of Robot.

Thank you 

[Rafal.Gaweda]

---

Hi @Anonymous 

I get stuck when dividing the cables. Nodes were created along all cables but during FEA they are shown as isolated nodes. As they are 1D components, how can I divide the cables properly to carry out the FEA?

I think there is no need to divide cables for for model  but maybe @Rafacascudo can hive You more hints

See : https://forums.autodesk.com/t5/robot-structural-analysis-forum/robot-art-gallery-real-structures-and-their-models/td-p/7221752

I cannot see any numbers of calculation elements at this stage.

Cables are not divided automatically by nodes on them.

If You want to do it, You have to do it manually (Edit \ Divide or Edit \ Intersect)

[Rafacascudo]

  That project was done on 2001. By then ,it was done considering the cables as normal bars . That was a valid aproximation as the bars were short and not very inclined (minimum sag).

   You can do that with RSA for a preliminary stage to find the cables initial forces .

But for a true and complete Cable stayed bridge analysis you will have to dig further . See what is necessary now for a complete analysis here .

[Anonymous]

I am starting from finding the forces and elongations of all the cables under the self-weight of the panels. But I am new to RSA so not familiar with all functions. If dividing the cables is not needed, could you explain in more detail the process of achieving the above goal please? Thank you.

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous 

Generally there are 2 ways of defining cables in Robot:

1/ defining them by force i.e. specifying tension (Force Fo) or

prestress (Stress SIGMA) - in such case program will search for

such lengths of each cable that the demanded tensions will be obtained

under assembling loads. After assembling load case for other load cases

these cable lengths are fixed (cables are "clamped").

2/ defining them by length i.e. specifying length (Length L), absolute

or relative elongation (elongation dl) or zero elongation (which

corresponds to nothing in text file). In such case cable lengths are

specified and fixed on the very start of analysis.

In the case 1/ program calculates regulation value as such cable

dilatation that will produce demanded tension under assembling loads for

displaced cable nodes.

In the case 2/ program calculates assembling force as such cable tension

that will be observed when cable ends will be not displaced under

assembling loads.

You may find the attached document helpful.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[alfredmx]

Hello ty16439,

You may also want to check:

https://forums.autodesk.com/t5/robot-structural-analysis-forum/suspension-bridge-problem/m-p/7953023...

You can do “form finding” in RSA, but it will take you some extra work. Also mind that phases in Robot is limited and not suited for cable stayed bridges. You will have to do it outside RSA.

Regards,