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Active Contributor
dziub7
Posts: 29
Registered: ‎02-26-2013

structure par phase (cables - assembling load case)

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03-12-2013 10:03 AM

Bonjour,

je dois modéliser une passerelle tenue par des câbles via un mât, je voudrais savoir si dans Robot on peut créer des phases de montage, qui tiennent compte des résultats des phases précédentes?

par exemple: j'applique une prétension dans les câbles dans la phase 1, le mât bouge, la passerelle se déforme,

dans une deuxième phase je tends les câbles encore plus, en tenant compte de l'état déformé de ma structure...

et ainsi de suite.

merci d'avance

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Rafal.Gaweda
Posts: 4,971
Registered: ‎04-26-2010

Re: structure par phase

03-13-2013 02:02 AM in reply to: dziub7

It is like that for cable structure.

 

"Assembling Load Case

Robot includes the structure assembly stage. It is recommended that this is the first load case"

http://docs.autodesk.com/RSA/2013/ENU/filesROBOT/GUID-C718E208-2359-49A0-9C8E-FAB4EA496948.htm

 

 

For any other structure (nonlinear) you can force program to do it this way

 

startingcase.jpg



Rafal Gaweda
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Active Contributor
dziub7
Posts: 29
Registered: ‎02-26-2013

Re: structure par phase (cables - assembling load case)

03-13-2013 04:25 AM in reply to: dziub7

Ok i understand, but cables have to be pretens in only one time in the first case??

could we apply the shortening of the cables step by step?

could we apply shortening of 2 cables, and the other are unloaded (cable lying on the floor)?

and then we add 2 other cables etc

 

thank you in advance

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Product Support
pp2008
Posts: 475
Registered: ‎06-23-2008

Re: structure par phase (cables - assembling load case)

03-13-2013 09:02 AM in reply to: dziub7

Yes, it can be done, but it requires more work and some iterations.

Below some extract of explanations prepared for analogous situation some time ago.

 

It is possible to define cables in Robot by tension. But if all cables are defined this way Robot will try to obtain required tensions in all cables  (by changing length of each cable) SIMULTANEOUSLY for assembling load case and then to fix cable lengths for all consecutive load cases and load combinations. In practice obtaining convergence for such model is impossible - see some remarks in Help:

http://docs.autodesk.com/RSA/2013/ENU/filesROBOT/GUID-DCDD6D6E-D1BA-4535-9A21-AA28C9277CF7.htm

 

In reality the assembling of cables is usually made in SEQUENTIAL way:

1/ one group of cables is assembled with some pre-tensions and if required tension forces are obtained these cables (cable lengths) are fixed

2/ then another group of cables is assembled with some pre-tensions and if required tension forces are obtained these cables (cable lengths) are fixed too. Usually the assembling of the second group results in changing tension forces in cables of the first group comparing to their original tension forces (from point 1).  So it is different than simultaneous assembling of all cables

3/ then another group of cables is assembled....

....

 

The practical approach may be sequential creation of the model like below:

a/ adding cables corresponding to step 1/ above defined by tensions and running analysis

b/  checking regulations of cables added in step a/  (see the description of cable regulation in help:  

http://docs.autodesk.com/RSA/2013/ENU/filesROBOT/GUID-0F586BFB-4CFD-4D6F-8DFB-322CEC428E76.htm) and replacing tensions in definitions of these cables by their regulations (input as positive or negative absolute elongations)

c/ adding cables corresponding to step 2/ above  defined by tensions and running analysis

d/ checking regulations of cables added in step c/  and replacing tensions in definitions of these cables by their regulations (input as positive or negative absolute elongations)

e/  adding cables corresponding to step 3/ above ...

... 

 

In the final model only the last assembled group of cables would be defined by tensions - all the previously assembled would be defined by elongations but these elongations would correspond to tensions from previous stages of assembling.

 

---------------------------------------------
If this post answers your question please click "Accept as Solution". It will help everyone to find answer more quickly!

 

Regards,

 

 

 



Pawel Pulak
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Active Contributor
dziub7
Posts: 29
Registered: ‎02-26-2013

Re: structure par phase (cables - assembling load case)

03-13-2013 09:55 AM in reply to: pp2008

OK, thank you very much for this explanation!

more work=no problem if it does the job!

 

for now, we enter tension in the 12 cables by specifying the cable lengths, in one time. (we already red the remarks in Help).

 

we have to try the sequential way now, as you describe the process, we have to create different models corresponding to the number of step?

 

but the problem i see is: the post, where the cables are fasten, has a ball joint in the ground, so in step a) defining cables with tension--> Robot will not converge.

 

How should we do? 

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Product Support
pp2008
Posts: 475
Registered: ‎06-23-2008

Re: structure par phase (cables - assembling load case)

03-14-2013 12:55 AM in reply to: dziub7

                  for now, we enter tension in the 12 cables by specifying the cable lengths, in one time. (we already red the remarks in Help).

 

12 is a total number of cables or is it only the number of cables assembled in the 1st step?

 

                we have to try the sequential way now, as you describe the process, we have to create different models corresponding to the number of step?

 

Yes, it is recommended to save different models corresponding to consecutive steps of adding/assembling cables.

 

 

                  but the problem i see is: the post, where the cables are fasten, has a ball joint in the ground, so in step a) defining cables with tension--> Robot will not converge.

 

In case like this analysis will be convergent only if cable tensions will be precisely tuned to keep equilibrium of the post. But above you mentioned "specifying the cable lengths"- if you know cable lengths there is no need to define them by tensions.

 

Regards,

 



Pawel Pulak
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Active Contributor
dziub7
Posts: 29
Registered: ‎02-26-2013

Re: structure par phase (cables - assembling load case)

03-14-2013 01:00 AM in reply to: pp2008

by specifying the cables lenghts I mean DILatation RELative...

 

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Active Contributor
dziub7
Posts: 29
Registered: ‎02-26-2013

Re: structure par phase (cables - assembling load case)

03-14-2013 01:08 AM in reply to: dziub7

sorry i didn't see your answer,

12 is the total number of cables

 

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Product Support
pp2008
Posts: 475
Registered: ‎06-23-2008

Re: structure par phase (cables - assembling load case)

03-14-2013 01:42 AM in reply to: dziub7

          by specifying the cables lenghts I mean DILatation RELative...

 

It is only the other way of definition of cable by length. In such case:

the unloaded length of cable = (the unloaded distance of end nodes of cables) * (1 + DILatation RELative)

 

            sorry i didn't see your answer,

            12 is the total number of cables

 

If it is a total number of cables and all of them are defined by length and you need to analyse the effects of the seqence of assembling them then the actions required are much more simple than I have written.

It is enough to create several models with some of above 12 cables deleted - corresponding the the sequence of assembling. No need of "replacing tensions in definitions of these cables by their regulations"

 

Regards,

 

 



Pawel Pulak
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