# Mode filtering for response spectrum analysis

19.0

We have been thinking, how to further enhance our powerful solution for response spectrum analysis in SCIA Engineer. We have succeeded and It is my pleasure to describe what we did for you. We have introduced a new feature for mode filtering. It is a simple way how to reduce the number of needed eigen modes to fulfil the condition of 90% of moving masses. Sometimes it is very difficult to know how many modes you need to fulfil the condition. It could lead to large number of modes which slows done the calculation. Mode filtering helps you in this area - to have reasonable number of modes whereas condition is still met.

Highlights |
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Faster analysis with mode filtering |

Decreasing number of needed eigen modes |

Mode filtering decreases number of needed modes and time needed for calculation of the response spectrum analysis. You can choose from two filtering methods - total mass (where you are prescribing percent of the total moving masses) and mass threshold (where you are prescribing the smallest amount of mass to be taken into account).

The selected mode filtering method decreases number of need modes from 70 to 8.

The internal forces of the filtered and unfiltered analysis don't show any big variation. You can observe it from following pictures.

Finally, you can compare results for both mode filtering options and full analysis

Method | Number of used modes | Wi/Wtot | |
---|---|---|---|

No mode filtering X direction | 70 | 0.93 | |

No mode filtering Y direction | 70 | 0.93 | |

Total mass X direction | required total modal mass 90% | 7 | 0.9 |

Total mass Y direction | required total modal mass 90% | 8 | 0.9 |

Mass threshold X direction | required minimal modal mass 5% | 4 | 0.81 |

Mass threshold Y direction | required minimal modal mass 5% | 3 | 0.79 |