DAMAGE IDENTIFICATION ON STRINGERS BY MODAL ANALYSIS

The paper is dedicated to damage identification on stringers of a steel truss bridge. Different damage types on the railway bridge, like cracks, rust, permanent deformation and so more are well known but rarely identified. One of the most common type of the damage is loss of material in stringer flanges caused by rust. In practice different methods for damage identification can be used. This paper focuses on higher mode shape and eigenfrequencies of stringer web vibration, which are more sensitive to damage locations. Parametric study has been performed where the effects of different damage locations along the stringer has been investigated. Later, changes in local eigenfrequencies and modal shapes of the stringer web have been analysed with respect to different location of damage. In global analysis identifying of corresponding higher frequencies is very difficult, because the values of the eigen modes are quite close to each other. Therefore, an original subroutine has been prepared that helps to find the corresponding modal shapes of the substructure used for damage identification. Using this method it is possible to identify a location of the damage by comparing changes in eigen modes.