Steel fiber reinforced concrete (SFRC) is currently the material of choice for a broad range of structural components. Through the use of SFRC, the entire, or a large portion of, conventional rebar reinforcement can be replaced, in order to improve the load-bearing behavior but also the serviceability and durability characteristics of engineering structures. The use of fiber reinforcement therefore plays a vital role in acute current and future construction industry objectives, these being a simultaneous increase in the service life of structures and the reduction of their environmental impact, in addition to resilience to extreme loads and environmental actions. Next to the extended use of SFRC, modern construction relies heavily on structural connections and assembly technologies, typically by use of bolt-type cast-in and post-installed concrete anchors. This paper addresses the influence of fiber reinforcement on the structural performance of such anchors in SFRC and, particularly, the load bearing behavior of single headed anchors under axial static loads in uncracked and cracked concrete. Along with a presentation of background information on previous studies of SFRC with a focus on anchor concrete breakout failure, the experimental investigations are described, and their results are presented and elaborated on by consideration of various research parameters. A comparison with current design approaches is also provided. The conclusions are deemed useful for structural engineering research and practice.
The benefits of including fibers in ultra-high performance concrete (UHPC) are attributed to their good bond with the matrix and, hence, an optimal utilization of their properties. At the same time, though, fiber reinforcement may contribute to anisotropy in the composite material and induce weak areas. The influence of the fibers’ orientation on the material properties is a matter of current scientific discourse and it is known to play a vital role in structural design. In the case studies presented herein, mechanical laboratory tests using pulsating load regimes on UHPC with a strength of more than 200 MPa were simulated by use of finite element models. The orientations of the fibers were measured for each test sample prior to failure using an X-ray computed tomography (CT) scanner, and these orientations are explicitly implemented into the model. The paper discusses the methodology of merging data retrieved by CT image processing and state-of-the-art FE simulation techniques Moreover, the CT scanning was carried out throughout the testing procedure, which further enables the comparison of the mechanical tests and the FE models in terms of damage propagation and failure patterns. The results indicate that the overall fiber configuration and behavior of the samples can be realistically modelled and validated by the proposed CT-FE coupling, which can enhance the structural analysis and design process of elements produced with steel fiber reinforced and UHPC materials.
Stahlfaserbeton (SFB oder SFRC) ist aufgrund seiner vielen Vorteile ein Standardbaustoff für verschiedene Anwendungsbereiche und seine Verwendung scheint weiter zuzunehmen. Dies spiegelt sich neben zahlreichen wissenschaftlichen Veröffentlichungen und Fachkonferenzen auch in den aktuellsten Regelwerken wider, wie z. B. der DAfStb-Richtlinie Stahlfaserbeton und ihrer jüngsten Ergänzung [1], und vor allem in seiner Aufnahme in die nächste Ausgabe des Eurocode 2 [2]. Die Einbringung von Faserbewehrung zielt darauf ab, Zugkräfte über den Riss hinweg zu übertragen. Dies bedeutet, dass Zugspannungen und Rissfortschritt durch die Fasern lokal aufgehalten werden, bis (i) die Faser selbst reißt, (ii) die Faser aus der Betonmatrix herausgezogen wird oder (iii) der Riss sich lediglich in der Matrix zwischen den verteilten Fasern entwickelt. Es ist daher wichtig darauf hinzuweisen, dass dieses Gesamtverhalten von SFB stark von Art, Form, Material, Zugabemenge, Verteilung, Orientierung und Verbundeigenschaften der Faser in Verbindung mit der Zusammensetzung der Matrix beeinflusst wird (vgl. auch [3-5]). Aufgrund der Vielzahl an Einflussfaktoren wird die Faserwirkung in der jeweiligen Matrix üblicherweise als Zugfestigkeit sowie als Nachrissfestigkeit (z. B. beschrieben durch sogenannte Leistungsklassen) bezeichnet und versuchstechnisch bestimmt [3,5].
Anchorage to concrete is a recurring application in construction. For such applications, bonded anchors, formed by means of a polymer adhesive injection into a borehole, are a widely used product due to their flexibility in regards to the construction logistics and positioning of the attached element as well as high load capacities. At the same time, fibre-reinforced concrete is the material of choice for many engineering applications where anchors have to be installed. Moreover, the use of steel fibre-reinforced concrete is likely to increase, since it now falls in the scope of the second-generation Eurocode 2 (exp. 2023). Therefore, the condition of the anchor installation borehole—mainly the roughness and grip of its internal surface—is known to play a critical role in the stress transfer from the attached component, through the fastening and into the concrete, and, hence, to the load-bearing performance. At the same time, drilling through the steel fibre reinforcement, along with the accelerated wear of the drilling tools, can in turn influence the borehole’s roughness and the overall installation quality. Furthermore, steel fibre may lead to an additional local stiffening of the concrete where the anchor is installed. These complex elements are discussed herein on the basis of multiple tests on anchors in plain and steel fibre concrete, as well as numerical analyses. The results indicate particular aspects of bonded anchor design and product certification for different polymer-based construction adhesives.
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