Condition assessment and damage identification of a steel-stringer bridge using system-identification methods

It is shown that modal analysis and flexibility are valid for condition assessment of civil-engineered structures. Flexibility is used as a condition assessment/damage identification index. The modal test method of multireference impact testing is used to acquire the objective data through which flexibility is derived. Consequently the fundamental question is: Can the linear parameter of modal flexibility serve as a reliable index for infrastructure condition and damage identification? Consideration of this involves not only determining the structural accuracy of modal flexibility, but also how severely it is affected by damage, condition variations and experimental errors. A reinforced concrete deck-on-steel girder bridge (steel-stringer bridge) was subjected to impact and truck-load tests and to damage simulating deterioration. The system-identification based research contributed toward the development of a unique impact test procedure referred to as “rapid” multireference impact testing. The modal data acquired through this method provided an accurate measure of in-situ structural flexibility. Furthermore, the induced damage scenarios revealed that modal flexibility was an excellent objective kernel index for both global and local condition assessment. Observable anomalous changes in deflected shapes derived through modal flexibility permitted detection of global and/or local variations in bridge (superstructure) condition