damage detection of multi-girder bridge superstructure based on the modal strain approaches

The research described in this paper focuses on the application of modal strain techniques on a multi-girder bridge superstructure with the objectives of identifying the presence of damage and detecting false damage diagnosis for such structures. the case study is a one-third scale model of a slab-on-girder composite bridge superstructure, comprised of a steel-free concrete deck with frp rebars supported by four steel girders, similar to north perimeter red river bridge in winnipeg, manitoba. the modal test data of the slab-on-girder specimen are analyzed by two mathematical methods and mindlin approach. the mindlin approach uses a small number of sensors and only the fundamental mode of vibration to obtain the modal strains. the unit-area normalization method produces a more precise damage patternbased on the mindlin approach than the widely used unit-norm method and is thus a superior method for locating damage in multi-girder bridge structures. a new method is proposed to distinguish the false damage diagnosis that is common in multi-girder systems. based on the invariant stress resultant theory and direct stiffness assumptions, a level iii damage detection process is applied successfully to indicate damage localization and severity estimation of the damaged girder.