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SynopsisThis paper presents a new theory for the shear capacity of reinforced concrete members without shear reinforcement. While recognizing that there are multiple failure mechanisms, the theory attributes the opening of a critical flexural shear crack as the lower bound of the shear capacity. It proposes that the shear displacement of an existing flexural crack can be used as the criterion for the unstable opening of the critical flexural shear crack. Based on the theory, a simplified shear evaluation model is presented in the paper. Compare to the current shear provisions in the design codes, the model is characterized by good accuracy and a solid physical background. It shows great flexibility to deal with complex design conditions. As an example, the paper discusses the possibility of extending the theory to the shear resistance of higher strength concrete. The suggested method provides a more logic and fluent transition from normal strength to high strength concrete and shows good agreement with experimental observations.

Acoustic emission source localization is a promising monitoring technique for concrete structures. However, the accuracy of acoustic emission source localization is influenced by many factors, such as the presence of cracks, which are commonly observed in existing reinforced concrete structures. In this article, the acoustic emission source localization is evaluated using a numerical model with a total number of 11,827,200 independent simulated tests. In this work, the investigated influential factors include the presence of cracks, arrival time picking error, and senor layout. The accuracy of source localization is quantified by the characteristic error defined in this article. Using the proposed wave propagation properties, a relatively stable characteristic error of 150 mm is estimated in the detection zone with the maximum sensor spacing less than 1 m. The evaluation approach and simulated characteristic error are validated experimentally by comparing the 200 manually generated signals using hammer hits on a cracked concrete beam.

A large number of existing reinforced concrete solid slab bridges in the Netherlands are found to be insufficient for shear upon assessment. However, research has shown additional sources of capacity in slab bridges, increasing their total capacity. Previous testing was limited to half-scale slab specimens cast in the laboratory. To study the full structural behavior of slab bridges, testing to failure of a bridge is necessary. In August 2014, a bridge was tested to failure in two spans. Afterwards, beams were sawn out of the bridge for experimental work in the laboratory and further study. Though calculations with current design provisions showed that the bridge could fail in shear, the field test showed failure in flexure before shear. The experiments on the beams study the transition from flexural to shear failure and the influence of the type of reinforcement on the capacity. The experimental results were compared to predictions of the capacity for the bridge slab and the sawn beams. These comparisons show that the current methods for rating of existing reinforced concrete slab bridges, leading to a sharper assessment, are conservative. It was also found that the application of plain bars instead of deformed bars does not increase the shear capacity of beams.

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