I have a masonry structure façade with different percentage of openings (0%, 10%, 20%, 30%, 40%, 50%) The structure length is 40m by 8m high.

Is there any useful source that shows how the equivalent stiffness is calculated?

I found a formula in: Paper ( Evaluation of Building Stiffness for Building Response Analysis to Excavation-Induced Ground Movements ) if this can work, how can I calculate the moment of inertia?

Many thanks in advance