How to analyse a hyperbolic paraboloid panel in Robot?

[Anonymous]

Hello,

I want to analyse a hyperbolic paraboloid panel in Robot, I've created it in Rhino and imported in Robot to a panel element, but I can't successfully caculate it, two main problems:

1 I can't give a surface load on the panel.

2 I can't well mesh it cause there's always some parts that couldn't be meshed

When I assign a surface load to the panel or do the caculation, there's always an error saying "twisty element!"

Could anyone please help with that, thanks!

[Artur.Kosakowski]

Too many bar releases.

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[Anonymous]

Yes, I released many bars cause they are supposed to work in compression/traction and I think I add enough diagonal bars to keep it to be statically determinate. In fact in the four lateral faces of a block, it only lacks one diagonal which is replaced by the panel itself, and the three bars on the edge of the panel are not totally released, they are fixed between each two of them.
I also tried to add this lacking diagonal bar but it's the same nodes of instability, then I delete the panels and calculate in 3D truss and it works well. So it's quite strange.
The instability happens only to the nodes on the axe X7 Z2 and the axe Y7 Z1.

[Artur.Kosakowski]

Try to block RX in the definitions of releases. Check MX values and see if you need to apply them in particular locations of the model. You may want to define them as elastic with small value of stiffness (http://forums.autodesk.com/t5/Robot-Structural-Analysis/Steel-design/m-p/3573540)

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.