A strain-flexibility-based approach to damage location

The effectiveness of mode-shape-based damage location methods is investigated, with specific regards to their application to the assessment of civil structures. Different location approaches proposed in the literature are compared and theoretically analysed. It is observed that, when damage is modelled as a loss in stiffness, the most direct way of exploiting mode-shapes information consists of estimating the flexibility matrix in a strain coordinate system. This matrix, referred to as strain-flexibility matrix, can be easily computed from the natural frequencies and the mode shapes expressed in terms of strain. Each diagonal element of the strain-flexibility matrix represents a local flexibility, thus changes in these quantities can be directly utilised as damage indexes. These findings have been validated through numerical and experimental examples. More specifically, the newly proposed damage indexes have been employed in the structural assessment of a 42.0 m long single-span steel bridge. The strain-flexibility indexes have been calculated comparing the experimental dynamic response, measured at 30 different locations, with that predicted through a simple FE model, representing the structure in the undamaged situation. Outcomes are consistent with the visual evidence of damage and with the outcomes of a static load test.