This paper presents a method to identify the location and severity of the damages in plates. The location of damage is detected using a new damage index (MDC), based on the mode shapes and their derivatives. The mode shapes are calculated via modal analysis and their derivatives are obtained through central finite difference approximation. The results are fed into the proposed damage index to find the location of damaged areas. Thereafter, the quantity of damage in the damaged area is assessed using firefly algorithm (FA). The capability of the proposed damage evaluation procedure is shown through some examples. According to the results, the newly proposed index is capable of finding the damage locations with acceptable accuracy. In addition, FA can assess the damage severities in the damaged zones with an error less than 2%. The proposed approach has the ability to identify the damages even for noisy polluted data
