Single degree of freedom system/equivalent mass

[CWatters]

It's possible to use Comsol to model a simple truss and the resulting frequency response looks like a single degree of freedom system. Using that data you can calculate a value for the spring constant, damping, and equivalent mass of the system etc and plot the frequency response of an ideal system with those parameters. Let's say you get a curve that's a good fit to the curve Comsol produced.

Is it possible for the equivalent mass to be greater than the mass of the truss and an applied load mass? Or would that indicate you have made a mistake?

 

[Dr.D]

I don't know anything about Comsol, but most attempts to model a structure as a single degree of freedom are based on approximating the energy using an assumed deflection form to approximate the lowest mode vector. Is this how Comsol works, or do they have something else going on?