Vibration-based damage monitoring in model plate-girder bridges under uncertain temperature conditions

Dynamic modal parameters are appealing features for a prompt diagnosis of structural conditions, since they are relatively simple to measure and utilize. The feasibility of using them for damage detection, however, is limited when their changes go undisclosed due to uncertain temperature conditions, particularly for large structures. In this paper, a vibration-based damage monitoring scheme to give warning of the occurrence, the location, and the severity of damage under temperature-induced uncertainty conditions is proposed. Firstly, experiments on a model plate-girder bridge, for which a set of modal parameters were measured under uncertain temperature conditions, are described. Secondly, a damage warning model is selected to statistically identify the occurrence of damage, by recognizing the patterns of damage-driven changes in natural frequencies of the test structure, and by distinguishing temperature-induced off-limits. Thirdly, a frequency-based damage index method based on the concept of modal strain energy is implemented into the test structure to predict the location and the severity of damage. In order to adjust the temperature-induced changes in natural frequencies that are used for damage detection, a set of empirical frequency correction formulae are derived from the relationship between temperature and frequency ratio.