Identification of damage in RC beams using indexes based on local modal stiffness

In recent years, significant efforts have been devoted to developing non-destructive techniques for damage identification in structures. Damage detection techniques based on modal testing and signal processing rely on the fact that the occurrence of damage or loss of integrity in a structural system leads to changes in the dynamic properties of the structure. In this paper, different criteria based on frequencies or mode shapes are applied to detect damage in reinforced concrete beams for which a few natural frequencies and/or mode shapes, obtained by experimental modal analysis, are available. In the same way, a new damage detection methodology is proposed based on what is here referred to as local modal stiffness. This stiffness can be determined from the frequency response functions and, unlike the usual detection methods, it is dependent on both frequencies and mode shapes. The effectiveness of the proposed methods is examined through experimental tests performed on an RC beam subjected to progressive cracking.