Condition assessment of steel stringer highway bridges using experimental modal analysis

Abstract

An experimental modal testing procedure has been developed for assessing the condition of steel stringer highway bridges using an optimized rapid impacting testing procedure. A 30 m to 90 m long two lane bridge can be instrumented and tested in a 5- to 6-h period using a multiple reference impact testing procedure. A special spatial domain multiple reference parameter estimation algorithm is used to obtain a modal model from the measured multiple reference impact data. The modal model is used to predict the static response of the bridge to various loading conditions. This predicted flexibility of the bridge is a good indication of the state of the bridge and can be use to assess the bridge. In the development phase of this procedure, the reliability of the resulting flexibility was verified by comparing measured truckload displacements against simulated truckload displacements, which were computed by virtually loading the modal flexibility matrix with a truckload. Furthermore, induced damage scenarios revealed that modal flexibility was an excellent objective, kernel index for both global and local condition assessment. The modal model is also used in the calibration of a nominal 3-D–FE model which is used in evaluating the rated load capacity of the bridge.