NODE COMPATIBILITY, COMPATIBLE NODE

[marcoscerezo0]

Hi,
I´m having troubles with the node compatibility option.
In the attached auxiliary structure, the beam 14 is connected to the tilted beam with compatible nodes (Nodes 1 & 6).

I would like to model the connection allowing the movement of the node 1 along the tilted bar and the rotations. So, just the Y and Z directions would be restrained. 

Checking the displacements, it is not working on. The displacement of both nodes is not the same in the UZ direction.

Dows anyone know how I can model this conditions?

The model can be found in the link:

https://wetransfer.com/downloads/863f16d8df9c73d1ed0a926c5e1aca2120220314080808/94ba878501695337fe98...

[Krzysztof_Wasik]

Hi @marcoscerezo0 

Change compatibility angle sign. It should be  26.6 degree. After sign changing there is no "jump" of axial force between bars 21 and 22. If you are not sure about angle sign you can check it by nodal force definition with requested angle. Nodal force symbol is presented as rotated by required angle.

[marcoscerezo0]

Hi @Krzysztof_Wasik , Thank you for your answer.

Its a good way of checking the correct behaviour of the model. 

Anyway, I think the wrong behaviour is still happenning.

The deformed shape of the vertical element will be out of the line of the deformed shape of the tilted bar, which would be physically impossible.

I verified it is not a matter of a scaled deformation with the values from the nodal displacement table.

May you have any additional comment on this?

[Krzysztof_Wasik · Accepted solution]

Hi @marcoscerezo0 

In my opinion it is problem with compatibility assumption

Node 1 moves in UY direction by the same distance as node 6 (due to compatibility definition)

Simultanously it moves horizontally along bottom beam which is deformed due to applied load

If we expect node 1 position along deformed bottom beam (let us say in point point X) its UY deformation cannot be the same as node 6. Additional delta (lime distance) should be added due to bottom beam deformation. Compatibility assumption (made for not deformed structure) causes nodes separations (bigger for bigger deformation) when deformed structure curvature is presented. See attacehd screenshot. I have tried to explain that in XY projection.

In fact we do not expect distance compatibility between nodes 1 and 6 but we expect node 1 position along deformed bottom beam line (but at the begining we do not know in which horizontal beam point, node 1 should be after deformation). This type of definition is not possible in Robot. Compatibility definition is the most precise solution in Robot which simulates that effect (but is not perfect).

In my opinion regardless that problem, results are precise enough for design purposes..

[marcoscerezo0]

Thanks @Krzysztof_Wasik for your answer.

Please, let me know if any other idea come to your mind.

[Krzysztof_Wasik]

HI @marcoscerezo0 

Let me repeat

Compatibility definition is the most precise solution in Robot which simulates that effect (but is not perfect).

In my opinion regardless that problem, results are precise enough for design purposes.

[mdesjardinsXJ286]

Hi @Krzysztof_Wasik ,

Do you know a software that can make that kind of definition possible. By that I meen making a node able to slide on the axis of a connecting member. 

I am trying to model a pedestrian bridge bearing on a cable with the cable having the ability to slide trought the connector.

Regards,