In this study, an improved mode shape curvature change-based technique is introduced for detecting the appearance and location of damage in I-section steel beams. The vibration of a steel beam is numerical analyzed in both undamaged and damaged cases using the finite element (FE) method, where damage is introduced by reducing the flexural rigidity of the corresponding beam elements. Next, the damage location is determined based on a defined damage threshold. This research is conducted in two steps of structural health monitoring (SHM): (i) evaluating the occurrence of damage using a vibration characteristics-based method; and (ii) proposing an appropriate damage threshold for detection and assessing its effectiveness through a set of damage detection indices. The findings indicate that the mode shape curvature change-based method has high precision in the damage detection in both the damage’s appearance and location.