Error during calculation: “Structure is instable. instabillity found.”
If you get the following error message during a calculation ...
... it means that there is a problem with the degrees of freedom in the structure.
The node or member where the (first) instability is found, is indicated.
Let’s take a look at the example below. The problem is found in node N1, direction fiX (rotation around the X axis).
The supports in the end nodes of the beam are both fully hinged (Rx, Ry, Rz = Free). This means that a rotation of the member around its own axis is not prevented: the slightest torsion in the member will result in an instability. Putting Rx = Rigid in one of the supports in the end nodes will solve the unstability in this case.
TIP: In a large project, it won’t always be easy to find the indicated member or node. The ‘selection’ command can prove to be extremely useful there: