Damage detection by means of structural damping identification

Vibration measurements in structures under ambient or controlled excitation open a way to damage assessment by correlating changes in the dynamic system parameters–natural frequencies, modal shapes or damping–with damage. Most methods proposed in the literature are based on the measurement of natural frequencies or modal shapes, associating damage to local reduction of the structural stiffness while completely ignoring damping, both in the identification procedure as well as in the correlation of changes in the spectral properties of the structure with damage. In numerous applications these methods, however, present some practical limitations on account of the low sensitivity of natural frequencies or modal shapes to damage. The main objective of this paper is to present a novel scheme to detect structural damage by means of the instantaneous damping coefficient identification using a wavelet transform. Laboratory tests as well as numerical simulations showed that in many commonly used structural systems damage causes important changes in damping. Thus, parameters that characterize structural damping can be used as damage-sensitive system properties. It is further shown that the wavelet transform can be conveniently employed in a procedure for instantaneous frequencies and damping identification from free vibration structural response.