ABSTRACT
The present works illustrates a simple deformation-based damage index that exploits the potentialities of advanced 3D optical systems for markers displacements measurements in shaking table testing of historic masonry prototypes. The application of passive 3D motion capture systems to shaking table testing proved very efficient in recording a large number of measurement points, which provide accurate and complete description of the field of displacements of the studied structure. The proposed index was built as a function of the global residual deformation obtained from the measured distances between each couple of adjacent markers located on the tested structure. The results were validated by correlation with a consolidated stiffness-based index calculated through modal analysis of the structure. The proposed index considers only the residual deformations, while neglecting the effects of energy absorption and of different collapse mechanisms on the assessment of damage. Nonetheless, its simplicity of computation directly from the markers measurements represents a big advantage with respect to other more used damage indices that were mainly developed for numerical analysis and need to estimate structural capacity parameters. Besides, the stiffness-based indices might sometimes provide controversial results in shake table tests, as prototypes dynamic behavior is dependent on the boundary conditions, i.e. the observed stiffness reduction might be caused by fixing loosening and/or changes in the prototype constraints to the table. In order to avoid misleading conclusions, the crack pattern and the deformations arisen in the tested specimen should always be considered of utmost importance for assessing the actual state of structural damage. After application with several historic masonry prototypes, encouraging results were obtained in terms of good correlation (R 2 > 0.9) with the consolidated index.
