Detection of damage in civil engineering structures by direct stiffness derivation

In the framework of developing a non-destructive damage identification technique, vibration monitoring is a useful evaluation tool that relies on the fact that occurrence of damage in a structural system leads to changes in its dynamic properties. In this paper, a technique will be presented to derive from experimentally determined modal characteristics of a reinforced concrete structure its dynamic bending stiffness. The degradation of stiffness, due to the cracking of the reinforced concrete, gives information on the position and intensity of the occurred damage. From the dynamic stiffnesses in each section, one obtains directly an idea of the extension of the cracked zones in the structure. The technique is validated on a progressively damaged prestressed concrete bridge in Switzerland, on which a series of full modal surveys are carried out before and after applying a number of damage scenarios.