In the framework of developing a non-destructive damage identification technique, vibration monitoring is a useful evaluation tool that relies on the fact that the occurrence of damage in a structural system leads to changes in its dynamic properties. The damage identification techniques are based on the observed shifts in eigenfrequencies and modeshapes and relate the dynamic characteristics to a damage pattern of the structure. The presented technique makes use of the calculation of modal bending moments and curvatures to derive the bending stiffness at each location. Damage identification results are compared with results from a classical sensitivity based updating technique. The basic assumption in both techniques is that damage can be directly related to a decrease of stiffness in the structure. Damage assessment techniques are validated on the progressively damaged prestressed concrete bridge Z24 in Switzerland, tested in the framework of the BRITE-EURAM project SIMCES. A series of full modal surveys are carried out on the bridge before and after applying a number of damage scenarios.