Distributed Fibre Optic Sensing to Assess Support Reactions and Behaviour of Composite Steel Bridges

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Gillham, Jack
Distributed Fibre Optic Sensing , Composite Steel Bridges , Strain , Support Reactions , Structural Health Monitoring , Flexural Stiffness , Composite Behaviour , Damage Detection , Field Monitoring
The method proposed in this investigation involves using distributed fibre optic sensing (DFOS) strain measurements to estimate support reactions in beams through an experimental investigation that involved beam, model bridge, and field load tests. Five steel beams were instrumented with fibre optic sensors and loaded in simply supported and continuous beam configurations. Disturbed regions in DFOS strain measurements were found to extend a distance equal to the depth of the section from supports and loading points. An estimate of flexural stiffness was used to calculate support reactions, which were found to be inconsistent with results obtained from load cells. The error between DFOS calculated support reactions and load cell support reactions was then minimized to determine calibrated stiffness values for each beam. The five slender steel beams were then assembled into a two-span bridge configuration and connected by a series of steel deck plates. Stiffness values determined from the individual beam tests were used to calculate support reactions for each beam at each support. The sum of the support reactions was compared with load cell measurements at the loading points and showed good overall agreement in tests involving consistent loading between beams. Non-linear strain profiles were observed in tests involving concentrated loading in the centre of the bridge, which decreased the accuracy of the DFOS calculated support reactions. DFOS strain derived neutral axis measurements were used to estimate the level of composite action in the bridge and adjust the flexural stiffness of each beam. Part of a girder in a steel beam with concrete deck bridge in Kingston, Ontario, was instrumented with fibre optic sensors and loaded by a truck driving across the bridge deck at a range of speeds. DFOS calculated shears were compared with the results of a numerical analysis to determine that the girder carried approximately 25% of the truck load when the truck was near the instrumented region, compared to 79% of the truck load calculated using live load distribution factors from a design code. Load sharing between girders was found to have a greater effect when the truck was positioned further from the pier.
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