Rehabilitation assessment of a steel railway bridge by dynamic field testing

The seven-span steel railway bridge crossing the River Nile near Qanater, Egypt, has been reported to have excessive sway under the current railway traffic loads. A rehabilitation plan has been made previously to preserve and enforce the structural condition of this main bridge. Dynamic testing techniques were used here to evaluate the modal properties of the bridge system at different stages of the repair plan. Ambient vibration measurements together with measurements after the passage of trains were conducted. The dynamic parameters of the bridge were extracted using both the Frequency Domain Decomposition (FDD) and the Eigen Realization Algorithm (ERA) techniques. Comparisons were made to understand the basic behaviour of the bridge and to evaluate the effectiveness of the current repair method. The modification in the stiffness of the bridge due to rehabilitation was evaluated. The current rehabilitation strategy proved effective; as a result of this study, further recommendations are made.