Compliance-based structural damage measure and its sensitivity to uncertainties

A basic concept of structural damage assessment including carrying capacity, recently proposed by the authors, is complemented in the present work by a new global damage measure and a systematic study of its sensitivity to relevant uncertainties. The damage measure is based on the maximum compliance recovered from the structural eigenfrequencies and mode shapes. The uncertainties associated with a limited number of measured modes, their alteration due to damage, a limited number of measurement points, errors of the structural mass estimates as well as the accuracy of the measured frequencies and mode shapes are numerically simulated and consequently analyzed. In addition, the uncertainties of the damage type, location, orientation and, finally, its relationship to a given loading are studied. The damage assessment concept including uncertainties is applied to a simply supported elastic beam and a reinforced concrete girder analyzed by the finite element method. The new damage measure shows a good correlation with the actual damage degree and is quite insensitive to many uncertainties. The scatter of measurements thereby is successfully mitigated by averaging of the damage estimates. The present paper certifies the new damage measure as a simple and reliable tool for condition assessment and health monitoring of structures with dominant bending modes, able to reflect correctly the overall reduction of structural bearing capacity.