A parametric study of non-classically damped base-isolated systems

The aim of this paper is to compare the rate of convergence of two different methods for the dynamical analysis of non-classically damped base-isolated linear systems, both based on mode superposition. The first, strictly derived from the standard modal analysis, requires the numerical solution of a truncated set of equations of motion in terms of undamped modal coordinates, which are coupled by the off-diagonal terms of the generalized damping matrix. The second is the complex modal analysis. It is shown that, in general, the rate of convergence depends on the amount of damping and that the complex modal analysis converges more quickly than the other method. However, if compared to the standard modal analysis for classically damped systems, the complex modal analysis requires, in some cases, a larger number of modal contributions in order to ensure a sufficient accuracy of the results.