Mass Participation factor vs Modal Mass?

I struggle to understand the relationship/difference between the mass participation coefficient and modal mass. Would it be possible to provide some definitions?

In my simple mind modal mass = total mass of system x mass participation factor.

I believe that Karamba outputs the participation factor in kg in which case as such I don’t understand the difference between the two. More specifically I am a little confused why the participation factor outputs a higher mass than the modal mass.


If anyone could offer any clarification it would be greatly appreciated.

Hello @alexander.griffiths,
I think the post under this link could help: Karamba Modal Analysis - Grasshopper.
– Clemens

Hi Clemens,

Thanks for this. I read this post previously but found it quite hard to follow. I have spent some time reading through all the links in the post over the weekend and I now understand that the modal mass is the generalised modal mass or
transposed(eigenvector) . mass matrix. eigenvector
where the max resultant displacement on the eigenvector is scaled to 1m

Am I correct in thinking the participation factors are scaled to 1 so the resultant displacement would be larger than 1?

I am still a little confused as to why the participation factor is greater than 1 though as I thought the scaling factor for the eigenvector should cancel out in eq 4 below if the same factor is used for phi and r

Hi Alexander,
in Karamba3D the participation factors are calculated like described here so that the largest modal displacement is “1”.
I think the confusion with respect to the modal participation coefficients comes from different definitions in here as compared to the source you cite above.
– Clemens