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Hello,
I was looking for a solution to make an articulated union between the pink beams and yellow beams in the intersection nodes. Note that I want the pink beams to be continuous and the same with the yellow beams, so finally I have 4 pink beams and 2 yellow beams. I´ve read about releases but I think it doesn´t work for this case as i want the beams to be continuous. Should I do it with compatible nodes?
@Anonymous Artur Kosakowski edited the topic for better findability
You should define compatible nodes. Please check these topics:
https://forums.autodesk.com/t5/robot-structural-analysis-forum/compatible-nodes/m-p/3689964
https://forums.autodesk.com/t5/robot-structural-analysis-forum/compatible-nodes/m-p/3797147
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Artur Kosakowski
Ok, so I´ve done with compatible nodes as you said me. In the images below you can see how I´ve done it. Could you please check it?
As I want to block that degrees of freedom in the local Coordinate System of Pink Beam I think I should enter the Alpha Beta and Gamma angles
Are these angles defined as you can see in the last image . That´s how I understand that angles.
Last question, would this compatible nodes work if I introduce an Offset to one or both of these beams?
Thank you.
Mind that the degrees of freedom are referring to the global coordinate system so your understanding of rotations is correct but you should block RZ instead of RX (I assume you want to block in-beam plane rotations and the pink one are parallel to the global X). I'd rather not use offsets but define beams on different levels with connections done via rigid links instead.
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Artur Kosakowski
In general for this type of connection you just block displacements so that there is no need to rotate the compatibility as there is no such need (applied load will not cause any significant rotations in planes other than the parallel to the local Z of beams). I'd check what other boundary conditions are (perhaps you allowed beams to rotate about their own axes at both end supports or defined such releases).
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Artur Kosakowski
1.-Please find attached the example, If you try to calculate the model without blocking RX you have inestability, that´s why I´ve blocked it. I´ve used compatible nodes and i´ve blocked degrees of freedom respect local system as you can see.
Indeed as you have free ends for purlins you have to block RX. For connections among the columns and rafters you may use releases at the top column ends instead.
2.-I would need to place the horizontal beams above the others. As you said you wouldn´t use offset, so how can I do it with rigid links?
As for rigid links d.o.fs are in the global coordinate system with no option to rotate them I defined dummy bars with their local coordinate system as per lines of beams and defined releases at their top ends (the same principle would apply to rigid links where you release d.o.fs in the same way as I defined releases).
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Artur Kosakowski
As in offsets you 'move' a bar without moving nodes you may get inaccurate values of forces which was already discussed both on the forum and during Robot webinars e.g. check Offset in Beam
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@AnonymousIf I use rigid links it gives me Inestabilyti (Blocking UX UY and UZ and RX ) and i Can not see information.
Please create a new topic for this issue and attach your model.
@Anonymous Could you please help me defining the code parameters of the columns and beams in the same exercise in order to verify the structure please? I´m not sure if I´m doing it well.
Please create a new topic for this question and confirm that outer parts of magenta beams (e.g. bar 1) are indeed cantilevers.
Artur Kosakowski
Hello again Artur, I´m doing a similar case to this one and I´m doing it without offsets, using rigid links as you told me. I prefer doing it with rigid links instead of using dummy bars with releases in order not to have a lot of beams. The problema is that even if I blocked de 6 dof in the rigid link I still have inestabilities. How can it be posible? How can I get no inestabilities? I just want to make and articulated union as in the old example.
I attach some images so it´s easier to understand the prblem.
Thank you.
Hi @Anonymous,
I will not be able to tell without ruining your model. Could you attach it?
Artur Kosakowski
Hi @Anonymous
If you change the solver to Skyline there is no instability which suggests just a difference in stiffness of elements of the stiffness matrix caused by using RLink elements for Rigid links (required for Sparse and MKL solvers).
I hope this helps.
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
Hi Artur,
I changed to Skyline and there is still inestability when I block only the translations. I´m using my own sections, could this be a problem?
Thank you.
Hi @Anonymous
Try to keep Skyline but unmark RLinks.
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
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