Abstract Summary
Among the compendium of highway civil infrastructures built in the last decades, many repetitive or quasi-periodic configurations can be found, such as multi-span simply supported bridges. Structural Health Monitoring (SHM) strategies for this kind of structures should properly consider such structural periodicity. Of specific interest to this paper are SHM methods based on Operational Modal Analysis (OMA). These techniques allow inferring the presence of damage by means of persistent variations in the modal features extracted from response time histories under ambient excitation. Literature studies already demonstrated that multi-span bridges are particularly challenging target structures for OMA. Such difficulties arise from the fact that the modal properties of the spans typically appear as dense clusters of poles with closely spaced frequencies and mode shapes with similar wavelengths. Hence, this circumstance considerably hinders the identification of physical poles using standard stabilization diagrams. Only slight differences arise as a result of the imperfect independence between spans, which is typically due to weak deck/asphalt connections and/or imperfect expansion joints. In this context, the coupling degree of spans manifests through global mode shapes and frequencies spanning between the limit cases of simply supported and continuous multi-span conditions. In this light, this paper proposes a novel method to interpret the results of OMA of partially continuous multi-span bridges. The proposed method is based on the analytical modal solution to the free vibration problem of multi-span beams with weak rotational coupling between adjacent spans. Through comparison analyses against experimental results from OMA, the developed model can be used to infer the elastic coupling between adjacent spans and the location/severity of damage. The developed formulation is validated against finite element simulations, and numerical results and discussion are presented to evidence its potential for the modal identification of a real-world in-operation multi-span reinforced-concrete girder bridge.
