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Distributed Sensing to Assess Bond Degradation



It is well known that reinforced concrete beams with low shear span to depth ratios have higher shear capacity due to the change in load carrying mechanism from beam action to arching action. However, up until now it has not been possible to understand the development of these mechanisms, which in turn makes it difficult to assess these beams. Distributed fiber optic strain sensing offers the ability to capture strain distributions along the full length of the reinforcement. When coupled with dynamic sensing capability, it then becomes possible to capture the formation of bond degradation that leads to arching action, as well as the impact that load cycling has on further bond degradation. In this study two beams were tested with identical shear span lengths but different effective depths, resulting in different a / d ratios. One beam carried load through beam action while the other beam carried load, once degradation had taken place, through arching action. The beams were loaded, then cycled for 3600 cycles, before being tested to failure. The behavior of the two beams is investigated by comparing the deflection and longitudinal strain behavior during the load cycles and just before failure. Significant differences in the longitudinal strain distribution developed during the tests, clearly highlighting the formation of arching action in the specimen with the smaller a / d ratio. The results of these experiments could be used to refine assessment techniques such as code models and finite element analysis.


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