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T. Dolesch:
"Shear tests on the influence of the surface condition of bent-up bars in reinforced concrete beams";
Supervisor: T. Huber, J. Kollegger; Institut für Tragkonstruktionen, 2021; final examination: 2021-06-18.

Reinforced concrete slab bridges with short spans are strongly represented in Austria. However, some of these structures have already reached a considerable age and were built at a time when plain bars were used instead of ribbed bars, which are common today. In addition, the shear reinforcement of these structures was often achieved by bending up the longitudinal reinforcement near the support. These bent-up bars often represent the only shear reinforcement in the historical concrete slab structures, since stirrups were generally not really common. This reinforcement layout does not comply with current design codes. Therefore, bent-up bars often cannot be taken into account using current design codes for the verification of the shear bearing capacity, as it may be required in course of structural assessment. In former research work Huber [2] developed the so called potential shear crack model (PSC-model), which allows a more realistic assessment of the bent-up bars with a superposition of steel and concrete components in the verfication of the shear bearing capacity. Due to a lack of experimental data, this superposition is currently not allowed for plain bars [2]. Therefore, a reasearch project was started at the Vienna University of Technology in cooperation with ÖBB, DB Netze AG and Asfinag to evaluate the PSC-model on plain bent-up bars and as a part of this project, the present diploma thesis was prepared. The purpose of this work is to develop a better understanding of the shear bearing behavior of concrete slab bridges with plain bent-up bars.
For this purpose, the very extensive experimental investigations carried out under the supervi-sion of Dr. techn. Tobias Huber are presented and supplemented by the author`s own theoretical investigations. The experimental program included pull-out tests to describe the bond behavior of plain reinforcement and shear tests to experimentally investigate the shear bearing capacity. In the shear tests, mainly the shear reinforcement ratio and the surface conditions of the reinforce-ment were varied in order to analyze the e˙ects of these variables on the load bearing behavior. A comprehensive description of the experimental investigations is followed by an evaluation of the obtained data. In addition, a comparison of selected test specimens with respect to the influence of the surface conditions of the reinforcement on the shear bearing behavior is made. In this context, a partly considerable increase in the ultimate limit load was observed for the beams with ribbed reinforcement as well as for those with plain reinforcement due to the bent-up bars and stirrups. Finally, the photogrammetric measurement data is evaluated in order to conclude on the activation of the shear reinforcement on the basis of crack kinematic input variables and by applying constitutive models from literature.
Probably the most significant insight of the shear tests is that a superposition of steel and concrete components is quite possible for the here considered construction method with plain bent-up bars. Otherwise, the ultimate loads observed in the tests cannot be justified. In future, this purely qualitative statement on the superposition of steel and concrete components must be investigated in more detail in order to develop a reliable verification concept for a more realistic assessment of the shear bearing capacity of concrete slab bridges with plain bent-up bars.