In the context of damage quantification during long-term monitoring (SHM), one of the main open problems is to correlate the level of structural and non-structural damage with an observed variation of natural period of a building. The aim of this paper is to correlate local damage detection on structural components (i.e., columns) to the global damage at building level. For this purpose, an existing reinforced concrete (RC) building has been selected as a case study and non-linear dynamics analyses have been carried out on its FEM model to estimate local and global structural damage. In detail, the local damage level for each RC column is assessed correlating the maximum interstorey drift ratio (IDR) with a damage scale previously defined by the authors on such structural components. Then, the global damage level is quantified and the variation of local and global periods is correlated to define a relationship between local and global damage.