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This paper addresses the issue of localizing and quantifying damage using changes in the vibrational characteristics of structures. The method considers the mode shapes of the structure pre-and post-damage measured via modal analysis. Values of the modal shapes are used to compute the strain energy distribution in the structural elements. Using the assumption that the element modal strain energy is the same pre-and post-damage, and characterizing the damage as a scalar quantity of the undamaged stiffness matrix, an expression is obtained for element damage factors that quantify the magnitude of the damage for each mode shape. Due to numerical instabilities in the computation of this expression, filters are applied that overcome some of the instabilities but reduce the true amplitude of damage. The modified-filtered expression was very effective in localizing the actual damage. After localization, the magnitudes of damage are computed using the original unfiltered expression.The method is tested using experimental data from a three-dimensional scale model of a space structure, subjected to 18 different damage scenarios. The damage forms consist of a 1 800 cut (Type I), a 50%reduction of the area over one-third the element length (Type II), and a complete cut through the element section (Type III). These types of damages correspond to magnitudes of a equal to -0.17, -0.5 and -1.0, respectively. The method is able to detect Type I damage for only one of four cases, Type II for all the three cases and Type III damage for all single and double-location cases, excluding the cases that involves a damage insensitive element.

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