Use of structural health monitoring to extend the service life of the Diefenbaker Bridge

A structural health monitoring system was installed on the 60-year-old Diefenbaker Bridge, located in Prince Albert, Saskatchewan, Canada, to investigate in-situ bridge behaviours, such as the degree of composite action, lateral load distribution, and dynamic load influence. The 304 m long, seven span bridge consists of two separate fracture critical superstructures, each comprising a cast-in-place concrete deck supported by two non-composite welded wide flange girders. Previous studies, based solely on a structural analysis, concluded that the connection of the lateral bracing to the girder web had less than 5 years of remaining fatigue life. Due to the uncertainty involved in this calculation, the data acquired from 6 months of field monitoring were used to define the structure's response to live loading, and to calibrate a finite element model that was used to characterize the three-dimensional stress state at that connection. It was found that unexpected composite action, increased load sharing between the girders, and minimal dynamic load influence exist in the bridge. Results were compared with those obtained using the Canadian Highway Bridge Design Code (CAN/CSA S6-14). Based on the monitoring results, it was concluded that costly improvements to the connection detail were not required, since the remaining fatigue life was estimated to be at least 52 years. In addition, it was found that the exterior girders are more heavily loaded than the interior girders, and the northbound structure is more heavily loaded than the southbound, permitting the location of the most critical connection for fatigue life to be identified.