Discussion Groups

Robot Structural Analysis

Reply
Valued Mentor
376 Posts
97 Kudos
Registered: ‎05-16-2011

Re: Is it possible to limit a bar force to a certain value?

07-06-2012 07:28 AM in reply to: Artur.Kosakowski

Ok Artur,

 

Thanks!

Product Support
5,219 Posts
757 Kudos
Registered: ‎12-17-2010

Re: Is it possible to limit a bar force to a certain value?

03-31-2014 06:18 AM in reply to: Artur.Kosakowski

As far as I can see Robot starts to have difficulty to converge the last of many non-linear cases for the BFGS method and the multi-threaded solver (when you restart calculations or delete some of the previous cases then divergent cases will converge). Thank you for pointing this situation out - we will check what exactly happens.

 

Corrected in Robot 2015.

 

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
Valued Mentor
376 Posts
97 Kudos
Registered: ‎05-16-2011

Re: Is it possible to limit a bar force to a certain value?

03-31-2014 07:27 AM in reply to: Artur.Kosakowski
Great!!
Valued Mentor
376 Posts
97 Kudos
Registered: ‎05-16-2011

Re: Is it possible to limit a bar force to a certain value?

10-31-2014 05:42 AM in reply to: Rafacascudo
Is it possible to limit a bending moment (directly) in a shell structure?? thx
Product Support
5,219 Posts
757 Kudos
Registered: ‎12-17-2010

Re: Is it possible to limit a bar force to a certain value?

10-31-2014 08:12 AM in reply to: Rafacascudo

No, it is not possible.



Artur Kosakowski
Valued Mentor
376 Posts
97 Kudos
Registered: ‎05-16-2011

Re: Is it possible to limit a bar force to a certain value?

10-31-2014 09:34 AM in reply to: Artur.Kosakowski

   I think ( still testing) I found a way to do it using non-linear bar releases .

Structure to the left - panels are normally connected

Structure to the right - Exact same structure ,(with same load ,10tf/m2 on the top slab area) except that the vertical panel is 2cm shorter   . Mesh is 1 mt . Created very stiff bars (2cm) connecting the panels at each node. Then I created a non-linear release limiting the moment at 25tf.m(12.5tf.m on the sides) using " rigid with linear hardening" type. Seems to be working nicely. For a load that does not reach 25tf.m on that edge , both structures show the same bending moment. Is there anything else that I should be aware?

 

Non linear releases for shells.jpg

*Expert Elite*
332 Posts
110 Kudos
Registered: ‎07-06-2011

Re: Is it possible to limit a bar force to a certain value?

10-31-2014 03:34 PM in reply to: Rafacascudo
Very very nice work Rafacascudo, take a look to the stress distribution in the panels. I think that the over value of the bending moment is due to the shear force applied in the point linked by the 20mm non linear released bar. This could be a solution for your problem, my suggestion (I've never tested before) is to try to use compatible nodes in common line of the panels. Just for test, this can be an elegant solution.

Greetings

PasProStudio

Structural + Detailing engineers
Valued Mentor
376 Posts
97 Kudos
Registered: ‎05-16-2011

Re: Is it possible to limit a bar force to a certain value?

11-01-2014 11:32 AM in reply to: Rafacascudo
Hi Stefano,
I used the 20mm bars as rigid links. I didn't show the panel moment maps but they are perfectly normal with no spike moments values. I thought about compatible nodes but I think they can only be used with bars.
Product Support
5,219 Posts
757 Kudos
Registered: ‎12-17-2010

Re: Is it possible to limit a bar force to a certain value?

11-03-2014 02:43 AM in reply to: Rafacascudo
 I thought about compatible nodes but I think they can only be used with bars.
It is the only way you can define (or shall i wrote control to which object they are assigned) them but you may achieve this goal in the following way:
1. Define compatible nodes (with the intended nonlinear function) at the intersections of bars created at the intended location of a common edges of panels.
2. Delete bars
3. Move one of the set of nodes either vertically or horizontally
4. Define panels with (temporarily separated) edges at the lines of these nodes and mesh them (make sure the generated meshes match number of nodes along the edges)
5. Freeze meshes
6. Move the 'shifted' nodes (as well as the panel's edge if you want) to their 'original' locations

 



Artur Kosakowski