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Performance Monitoring of an Existing Concrete Bridge using Strain Measurement Data



This paper presents the real-time monitoring results of operational RC Kawane Bridge in the suburbs of Mito in Ibaraki Prefecture of Japan. The effects of seasonal changes and earthquake occurrence in addition to the traffic loadings over an interval of six months were evaluated in terms of global and local modal parameters. The response of bridge to ambient and controlled traffic conditions was monitored using accelerometers, conventional strain gauges and long-gauge (FBG) sensors mounted on the underside of the bridge girder. The objectives of the study were to: (1) evaluate the performance of the long-gauge FBG sensors packaged in the laboratory for longterm monitoring of existing bridge structure, and (2) condition assessment of Kawane Bridge using dynamic response measurements due to operational and environmental loading on the bridge. The modal frequencies extracted from the different measurement data agreed. The condition of the bridge was assessed on the basis of the proposed data normalization approach using the normalized modal macrostrain (NMMS) vectors between the target and the reference macro-strain measurements. This procedure, previously deployed to laboratory setups, was an improved modal curvature method with potential to conveniently detect and localize small degrees of damage. Some changes in first modal frequency of the bridge were observed which was mainly due to the variations in environmental parameters. However, no significant changes in the slope of the fit lines were noticed indicating the healthy condition of the monitored bridge. Intensive visual inspection of the Kawane Bridge during the experimentation confirmed the same. The algorithm was verified to be suitable for practical civil SHM applications where variability in response and modal parameters due to measurement noise and environmental influence is often inevitable.


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