Harmonic response analysis

A harmonic response analysis calculates the effect of vibrating load sources on a structure. Typical harmonic load sources include vibrating machines such as crushers, pumps or vibrating tables, footfall excitation caused by people walking, running or jumping, vehicular excitation caused by moving traffic, imbalance in rotating parts of a machine, etc.



Important points

  1. A harmonic response analysis is linear only and therefore cannot be performed if your model contains cable elements.

  2. Because it is linear, a harmonic response analysis treats tension-only and compression-only members as normal members that can take tension or compression.

  3. P-D and P-d effects are not taken into account during a harmonic response analysis.

  4. A buckling analysis cannot be performed with harmonic load cases and therefore compression effective lengths from a buckling analysis are not available when doing a steel member design/check on harmonic load cases. If you are performing a steel member design/check on combination load cases that contain a mixture of static and harmonic load cases then the harmonic load cases will not contribute to the calculation of the compression effective lengths. This may not be correct and so you should consider specifying your compression effective lengths manually in those cases.

  5. A harmonic response analysis requires a dynamic frequency analysis to be conducted first.

  6. The harmonic response analysis must be repeated after a dynamic frequency analysis because its results will have been deleted.

  7. The accuracy of the harmonic response analysis depends on the accuracy of the dynamic frequency analysis on which it is based. It is therefore important that you set up your model correctly to achieve accurate dynamic frequency analysis results. For example, if master-slave constraints are used then positioning of the master nodes is particularly important for correct mass distribution. For more information, refer to "Dynamic frequency analysis".


For a full step-by-step guide on how to prepare for and perform a harmonic analysis, refer to "Step by step guide to harmonic response analysis".