Mode Participation Factor and Effective Mass — Lesson 4

This video lesson answers the questions: How do I determine the sufficient number of modes to extract, and how do I find the most critical natural frequencies or modes? The answer is by using the mode participation factor and the effective mass of the structure. This lesson is part of the Ansys Innovation Course: Modal Analysis.

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[amiraboodi]

thank you very much. these videos are very helpful and informative. please continue.

[omoniyitope]

I have created a finite element model of a bridge and noticed that the modal mass participating in the x-direction is very low while other in the y and z directions have reached 80%. Please what can i do to improve the mode participation in the x-direction.

[pmillan]

Does anyone know how to get the phi matrix (matrix containing the eigenvectors) from a modal analysis in ANSYS mechanical?

[emreatay]

I think there is an error in the value of the participation factor shown in @4:54, where the second participation factor should be positive (0.2379), but instead it is written as negative (-0.2379)

[chinannabella]

Thank you for the lesson Sir.
I am actually working on the dynamic analysis of a reinforced concrete bridge structure. But when I carried out numerical modal analysis considering 30 modes I realized the sum of my mass participation ratio for each mode is not even up to 80% of total mass, highest was at 77%. My main problem is: about the first 20 mode shapes had really small mass participation and instead of the first modes contributing a lot to the mass, I had the last modes contributing instead (to have up to 77% mass participation). From my knowledge of modal analysis, the first modes are usually the most important and the ones contributing a lot, but that's not the case with my analysis results.
What could possibly be the problem Sir?
(I assigned boundary conditions to both ends of the bridge)

[AssiadMokdad]

Hello I am using the equations you mentioned to calculate the effective mass of a simple cantilevar beam
are this equations useful in my case after applying boundary conditions ? it should the the sommation of all effective mass equal to the total mass?

[aymanzoor]

So the sum of mass ratios should approach 1, for each direction of motion separately, or when the ratio-sums of each direction are all combined?

[Ajaykumarkakumani]

In modal analysis solution, .full file is missing hence Participation factors are missing. How do we insert command to write .full file?

[massoxibeuventura]

I would like to know how to extract the matrix shape model, matrix stiffness and mass matrix in modal analysis using Ansys

[marufyanuareffendi]

Hello Sir. How to find stiffness matrix in modal analysis ?

[melissaferrara]

Very nicely explained videos, thank you! Although I don't understand why mode 11 is seen as a dominant one, since participation factor and effective mass are not higher than in the other modes. Am I missing something?