Browsing by Author "Vita, Norbert"

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Enhanced performance of anchorages in uncracked concrete with steel fibres or post-installed reinforcement
(2024) Vita, Norbert; Sharma, Akanshu (Prof. Dr.-Ing.)
Due to the development of anchor technology over the last few decades, it is no longer the anchor but often the concrete that is the decisive factor in the design. In most cases of anchor design, concrete failure is the dominant failure mode, which limits the load-bearing capacity of the anchor. This work examines two different approaches to increase the capacity anchorages, namely by improving the material properties of the base material (concrete), and by supplementing the tensile resistance of the concrete member by providing post-installed reinforcement. The first approach can be used for the new designs, while the second approach is useful for both new and existing anchorages. Part I of the thesis focuses on the performance of bonded anchors in steel fibre reinforced concrete (SFRC). In the performed tests, the influence of the steel fibres (with hooked-end) on the load-bearing behaviour of the post-installed anchorages was investigated. Concrete parameters such as concrete strength, fibre content, as well as the installation parameters such as anchor diameter, effective depth of the anchor, edge distance, anchor spacing, and eccentricity were investigated. The tests were carried out on single anchors and anchor groups under tension and under shear loads. In addition, the hardened concrete properties (such as compressive-, splitting and flexural tensile strength and fracture energy) of the steel fibre reinforced concrete used were determined. The test results confirm the positive influence of the steel fibres (e.g. crack-bridging effect) on the load-displacement behaviour of the anchor, provided certain requirements of the size and quantity of the fibres are fulfilled. A significant load increase and a more ductile failure mode were observed. Based on the detailed evaluation of the test results, a new model is proposed on the basis of the CCD method for anchors in plain concrete, that takes into account the positive influence of the steel fibres on the concrete breakout resistance of anchors in SFRC. Part II of the thesis presents the method of adding post-installed supplementary reinforcement (PISR) to enhance the concrete cone or concrete edge resistance of the anchorages. The tests were carried out on single anchors and anchor groups formed with bonded anchors. This approach combines the benefits of post-installed reinforcement with the function of supplementary reinforcement to enhance the resistance of anchorages against concrete breakout failure modes. The experimental investigations (tensile and shear tests) examined various variables such as the amount of reinforcement, the position and number of reinforcements, the spacing of the reinforcements and the anchorages. The results showed that the addition of post-installed reinforcement can lead to a significant increase in the load carrying capacity and displacements at peak load. A new approach for calculating the failure loads of PISR-reinforced anchors is proposed that considers different failure modes such as reinforcement yielding, bond failure and a new approach to consider the possible strut failure.