ABSTRACT
In 2014, Manitoba Infrastructure and Transportation implemented a load test and structural monitoring program on a historic bridge to provide essential bridge management information. The Selkirk Bridge is vital to the town of Selkirk, Manitoba as it is a primary access across the Red River. The structure is composed of several riveted steel deck truss spans and a lift span. Due to its fracture critical nature and deteriorated condition along the bottom chord of the stationary spans, the bridge had unsatisfactory load ratings. Additional concerns related to the bridge’s long-term performance were thermal stresses that may develop throughout the year or, even worse, the effects of river ice loading along the bottom chord, which had occurred some years during spring floods.
Stantec Consulting Ltd. together with subconsultant Bridge Diagnostics, Inc. performed diagnostic load tests and installed a structural monitoring system on the span with controlling load ratings. Field verified analyses and load ratings were generated from the load test results and through the process, several structural conditions were identified to significantly reduce stress levels on various truss members compared to previous calculations. Nine months of monitoring results also provided information towards the long-term performance of the structure. While load tests indicated significant resistance at the truss bearings, measurements obtained during the daily and extreme seasonal temperature ranges showed that the truss bearings did occasionally slip and release built up thermal stresses. This result alleviated concerns of excessive force being applied to the piers and truss chord members during extreme temperature conditions.
This paper illustrates a case study for practical use of structural monitoring systems to solve real problems facing bridge owners and how those results influence bridge management decisions.
