Idealized RC Wall in a FEM

[myosotis]

I have built up a finite element model of a RC turbine building for use in a seismic analysis using GT STRUDL. I have explicitly modeled the lateral force resisting system using 2D finite elements and frame members. I am now in the process of placing mass within my structure to represent the various non-structural systems and components. I am looking for some input on a method to idealize a non-structural RC shield wall so as to accurately capture it's mass and stiffness without having to use finite elements. Some sort of simplified lumped mass stick model comes to mind, but i'm not sure how to accurately capture the mass, rigidity, and boundary conditions without using FE. Any suggestions would be greatly appreciated!

Regards,