Browsing by Author "Maçi, Nilde"

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Open Access
Influence on the load‐displacement behaviour of steel‐to‐concrete connections with post‐installed adhesive anchors
(2023) Maçi, Nilde; Hofmann, Jan
Designing frame structures requires knowing the behaviour of each member of the frame (beam, column, joint, etc.) regarding the axial forces, shear forces, and bending moments. Furthermore, the ductility of the structure under seismic loading is essential in earthquake regions. Nowadays, structural frames are built from different materials such as concrete and steel, to achieve better performance. Therefore, the behaviour of the connections between steel and concrete is essential. The steel‐to‐concrete joints were the focus of the INFASO project, where joint solutions with easy fabrication, quick assembly, applicability in old structures, sufficient ductility, and high loading capacity were developed. They proposed the use of anchor plates with welded studs or post‐installed fasteners such as adhesive anchors to connect the steel and concrete members. This paper focuses on the performance of post‐installed adhesive anchors. During their service life, post‐installed anchors are subjected to monotonic, constant, and seismic loading. Each of these loading approaches is described in the current standards. Seismic and constant loading tests are of importance to the long‐term behaviour of the anchors. Seismic loading tests are carried out using a predefined cycle pattern. According to TR049, seismic tests of category C1 (tension and shear) are performed with 140 load cycles, where the load amplitude decreases after 10, 30, and 100 cycles. On the contrary, C2 category tests increase the amplitude within 75 or 59 cycles, depending on the test. Constant loading tests apply when the anchors are installed in cracked concrete. In contrast to the mentioned patterns, this study observes the behaviour of the adhesive anchors when the amplitude of each cycle is increased by 5 % until the anchor fails. Standard short‐term pull‐out tests are carried out to determine the load increments. Various parameters such as the embedment depth, bond line thickness, hole cleaning, wet concrete, and elevated temperatures are studied. Confined and unconfined tests are performed. Overall, the reference short‐term failure loads are higher than those in the tests with incremental and cyclic loading. The anchors installed with reduced hole cleaning, in wet concrete or subjected to elevated temperatures have a lower failure load compared to the reference series. Two additional bond line thicknesses are used for comparison. The increase in the thickness influenced the failure load differently for confined and unconfined test setups.
Open Access
Influences on the bond behaviour of anchorages under short-term and long-term loading
(2023) Maçi, Nilde; Hofmann, Jan (Prof. Dr.-Ing.)
This thesis focuses on the load-bearing behaviour of adhesive anchors. The influences on the bond strength of the anchors under short-term and long-term loading are investigated. The first part describes the current state of the art of bonded anchors under tensile loading and the influences on the load bearing capacity under short-term loading. In the second part, the factors influencing the long-term loading of adhesive anchors are presented. This section is a summary of various external and internal research. The influence of different parameters on the bond behaviour under long-term loading is then discussed. The third part focuses on the influence of incremental loading on the bond behaviour of adhesive anchors. The tests were part of a research project at the Institute of Construction Materials of the University of Stuttgart. As reference tests served short-term tests where the maximum load was reached within 3 minutes. To achieve incremental loading, the anchors were loaded at five percent steps. After loading, the anchors were unloaded and then reloaded within five minutes. Different parameters are varied throughout the test program: the embedment depth, the support width, concrete condition, drilling diameter, hole cleaning and the temperature while testing. Lastly, the short-term influence on the bond behaviour is investigated. High-strength concrete is used as anchorage base material to test epoxy adhesive anchors. This section describes this behaviour concerning the embedment depth, the bond length of the anchor, the type of steel component and the support width. A comparison between the failure load and the predicted load using the design models from the literature is carried out. Based on the results of the previous parts, the most critical influences on the bond behaviour of adhesive anchors are presented in the last section.