Lets you determine the lowest natural frequencies and mode shapes corresponding to the free vibration of an undamped linear structure when no externally applied loads are computed. AxisVM verifies whether the required number of the lowest eigenvalues has been determined.
The system mass matrix has a diagonal structure and includes only translational mass components. Select load cases or combinations in the tree view. AxisVM will perform vibration analysis for the selected load cases and shows a progress dialog.
The solution technique applied to the associated generalized eigenvalue problem is designed to find the lowest real and positive eigenvalues. It is not suitable to find eigenvalues that are zero or nearly zero.
The program uses a diagonal mass matrix by default. Due to the lumped mass modeling technique to achieve the required accuracy the elements must be divided into more elements (by refining the mesh). Usually at least four finite elements must correspond to each half wave. A good rule-of-thumb is that beams must be divided into at least eight elements.
Among the classical setting parameters i would highlight the Diaphragm converter.
When running a vibration analysis with the option Convert slabs to diaphragms checked, all slabs (horizontal plates) will be temporarily replaced by diaphragms. The running time is reduced if the model contains only columns and slabs. If structural walls are included, the number of equations will be reduced but the bandwidth will be increased. The resultant running time may be greater than without diaphragms.