Active-Bending - No Equilibrium


I’m currently studying another active-bending structure (membrane + frp profiles) and I was wondering why I got no equilibrium during the first formfinding step. I wonder if it is a problem with the structure definition.

I already tried reducing the FMAX to a minium, increasing the iterations to 900, decreasing the tolerance but always I get no equilibrium in the structure.

Then I checked the example ASE - active_bending - active_bending_membrane and I got the impression that also there is no equilibrium during the first formfinding step. Is this normal? Why does it happen?

In the example that i was talking, the last iteration information is:

In my structure I can’t get stability in formfinding no mater what.
Can you please help me by telling me what I am missing ou?

I’ve tried to upload the model but I couldn’t do it directly, so I leave a link here for download:

Link to download the model.

Thank you!


Normally the first ASE run should find an equilibrium. As you can see in the picture, the iteration stopped with a residual force of 0.055. The warning appears because of the small tolerance (TOL -0.01) of the iteration. If you increase the tolerance (TOL -0.06), the warning should disappear.

This means for you: Please check the residual force of the iteration and increase the toleration. If the residual force is to high the system might be to weak. Try to optimise the stiffness or the geometry of the system.

Best regards
Frederik Höller
Your SOFiSTiK Support Team

1 Like


Thank you for your answer.

Is there any recommendation to define the limit to that tolerance for a given structure?
Those residual forces are the limit tolerance of the nonlinear analysis, right? So let’s say that if I have a membrane structure with 0.50 kN/m2 of pre-tension should I limit the tolerance to a reasonable value, like 0.01 kN/m2? Or can it be higher?

Also, is there any easy way to find out if my structure is unstable in any way?

Thank you.

Hello @JFH,

I can’t seam to get stability in my structure.
It is basically an active bending skeleton with two arches and two vertical beams that flex when the membrane between them is tensioned.

The problem that I’m getting is that I can’t get no stability in the formfinding.
I’ve tried a lot of configurations and the only stability possibile was for very low level of prestress, around 0.04kN for the both directions of the membrane.
Can you spot what I maybe doing wrong?

Thank you.

The structure should be doing something like this:

But along the iterations it does stuff like this:

PS: Sorry for third reply but I can only post one picture for reply.