Several methods are available for the eigenvalue analysis:
- Direct Methods
- The direct methods (Lanczos, roots of characteristic polynomial, subspace iteration method) are suitable for small to medium-sized models. These fast methods for equation solvers benefit from a lot of the computer memory (RAM). 64-bit systems use more memory so that even bigger structural systems can be calculated quickly.
- ICG iteration method (Incomplete Conjugate Gradient)
- This method requires only a small amount of memory. Eigenvalues are determined one after the other. It can be used to calculate large structural systems with few eigenvalues.
The RF-STABILITY add-on module can also perform the non-linear stability analysis. Also for nonlinear structures, results close to reality are provided. The critical load factor is determined by gradually increasing the loads of the underlying load case until the instability is reached. The load increment takes into account nonlinearities such as failing members, supports and foundations, and material nonlinearities.
