Possible Instability Types in the Structural Analysis

'Instability' messages that may display during the structural analysis

1. Type 1: There is a zero value element on the diagonal of stiffness matrix.
2. Type 2: There is a zero value element on the diagonal of inverted stiffness matrix.
3. Type 3: Some values of the stiffness matrix element are very disproportional.

The first, second and sometimes the third type of the instability are caused by mechanical instability of a structure, for example a part of the structure is a mechanism or the structure support parameters (number, type and positions of supports) are not sufficient. The third type can also occur because of large differences in dimensions of section profiles of some elements.