The characterization of the seismic behaviour of multi-storey structural systems subjected to severe ground motions requires the study of the response at global and local levels. This is because it can be characterized by high demands for inelastic displacement and energy dissipation, often causing concentration of damage in limited zones of the structure, as weak or soft stories. In order to evaluate the seismic demands on multi-degree-of-freedom (MDOF) systems subjected to severe ground motions, a simplified procedure based on an equivalent discrete shear-type model is presented. This choice provides a relatively simple numerical procedure which is adopted permitting (i) to extend the analyses to a wide range of strong motion records and structures, (ii) to establish response spectra of the inter-storey drifts, (iii) to investigate the dependence of the results on variations in stiffness distribution pattern and ductility at global and local levels. Finally, the influence of hysteretic and inelastic behavior at the same levels is also analyzed.