This paper contributes a novel numerical study to assess the potential of the two most widely used modalstrain based damage indices for damage detection in structural components under flexure for post-earthquake damage characterization of reinforced concrete multi-storey planar frame buildings. To this aim, buildings are treated as transversely vibrating beam-like structures and modal strains (i.e., second derivatives of mode shapes) are computed from lateral translational mode shape ordinates known at each floor/slab level along the height of buildings before (healthy state) and after (damaged state) a damaging seismic event. In this setting, the change of modal curvature (MC) along the height of the building as well as the change of modal strain energy (MSE) are adopted as damage sensitive indices and their effectiveness to localize damage to column or to beam elements at different floors and to characterize damage severity is gauged vis-Γ -vis. This is accomplished by considering computer-generated mode shape data obtained from linear modal analyses applied to finite element models of two different 10-storey r/c planar frames, a single-bay one and a two-bay one, under healthy and several different relatively light damaged states of varying severity. The furnished numerical results demonstrate that both the MC index evaluated based on first mode shape data and the MSE index determined from the first three mode shape data are equally able for both damage localization and severity characterization for most of the damaged case scenarios considered. Further research is warranted to account for the influence of noisy field-recorded mode shape data as well as for sparse instrumentation in which acceleration sensors are not deployed on every building floor
