modal analysis and modal participation factor

[uriel78]

After doing a pushover analysis and getting the V-d curve I need to convert the curve with a bilinear curve that represents the behaviour of an elasto-plastic equivalent SDOF.
Before construcing the bilinearcurve, I need to "scale" the original pushover curve qith a coefficent got from a modal analysis... this coefficent is sthg as the modal participation factor...
Now...is it possible that the modal participation factor is <1....??
I can't understand the physical meaning of a MPF<1...

 

[franck]

Hi Uriel78,

I am not sure if I am going to answer properly your post but yes a participation factor can be lower than 1. Really, if you take the example of the cantilever beam, the effective mass of the first mode represents 61% of the overall mass of the beam. Now, if in your modal analysis, you set the generalized mass matrix to be normalized to the identity matrix, your participation factor will be equal to the square root of the effective mass. Thus, if the mass of your system is low, it is likely that you will get a participation factor below 1.

Franck