Abstract: As damage accumulates in structure, the stiffness of the structure changes. Changes in stiffness are reflected in changes in the frequencies and mode shapes vibration of the structure. A theory of structural damage evaluation in which changes in the dynamic characteristics of a structure are used to predict the location and severity of damage has been developed by Stubbs et al. The objective of this study is to investigate the feasibility of using such technique for detecting loss of prestress in a prestressed concrete bridge. In order to achieve this goal the following tasks were performed: (1) a review of the state of the art modeling of prestressed concrete using finite elements, (2) a finite element model of a 3-D prestress beam using a commercial finite element code (ABAQUS/PATRAN) was developed, (3) dynamic modal analyses of the undamaged and damaged (less prestress) models are performed, (4) evaluation of an existing damage location algorithm for predicting location and severity of damage. The inability of the algorithm to predict loss of prestress is observed and explained. An improved version of the algorithm is qualitatively presented. !7
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