Experimental research has shown the extraordinary potential of the addition of short fibers to cement-based materials by improving significantly the behavior of concrete structures for serviceability and ultimate limit states. Software based on the finite element method has been used for the simulation of the material nonlinear behavior of fiber-reinforced concrete (FRC) structures. The applicability of the existing approaches has often been assessed by simulating experimental tests with structural elements, in general of a small scale, where the parameter values of the material constitutive laws are adjusted for the aimed predicting level, which constitutes an inverse technique of arguable Discussion on this paper must be submitted within two months of the print publication. The discussion will then be published in print, along with the authors' closure, if any, approximately nine months after the print publication.

Im Beitrag wird die Prognosefähigkeit eines numerischen Mehrebenen‐Modells für stahlfaserverstärkte Betonstrukturen aus hochfestem Beton anhand einer die Faser‐ und die Strukturebene umfassenden Testserie systematisch untersucht. Die experimentelle Studie umfasst Auszugsversuche an Dramix 3D 55/60 und 65/60 Fasern in hochfestem Beton mit unterschiedlichen Einbettungslängen und Neigungen zur Rissfläche auf der Mesoskala sowie Dreipunkt‐Biegezugversuche an gekerbten Balken mit drei stark unterschiedlichen Fasergehalten zur Abbildung des Strukturverhaltens. Das numerische Modell ist derart konzipiert, dass es die direkte Verfolgung des Einflusses der Entwurfsparameter wie Faserart, Faserorientierung, Fasergehalt und Betonfestigkeit auf die Strukturantwort ermöglicht. Hierzu werden Submodelle auf der Ebene der Einzelfaser zu Rissüberbrückungsmodellen in Abhängigkeit von Faserorientierung und Fasergehalt zusammengeführt und zum Zwecke numerischer Strukturanalysen in ein Finite‐Elemente‐Modell integriert. Die Validierung der Modelle für endverankerte Stahlfasern zeigt, dass die wesentlichen Interaktionsmechanismen zwischen Faser und hochfestem Beton für alle untersuchten Fälle (Faserorientierung, Einbettungslängen) wirklichkeitsnah abgebildet werden. Auf der Strukturebene zeigen die Ergebnisse der numerischen Simulationen auf Basis des Faserbetonmodells eine sehr gute Übereinstimmung für alle Fasergehalte, sowohl was die maximale Last als auch das Nachbruchverhalten betrifft.

Concrete is a quasi-brittle material, characterized by a non-negligible, finite-sized fracture process zone (FPZ) in which various toughening mechanisms play a significant role on crack development and propagation. Concrete is often reinforced with fibers to improve the serviceability and longevity of concrete structures by controlling the maximal crack widths and providing residual carrying capacity to initiated cracks. In quasi-brittle materials such as concrete, toughening mechanisms such as crack deflection due to the presence of large heterogeneities, contact shielding, i.e., wedging and crack closure induced by debris and rough crack faces, crack bridging by tough aggregates, unbroken ligaments and fibers (in fiber-reinforced concretes), are mostly governing damage evolution under monotonic and especially under cyclic loadings [1]. All these items contribute to a complex non-linear response in terms of load-displacement curves observed in experimental investigations. Many investigations have been performed on plain concrete, but not so many for high-performance fiber-reinforced concrete [2] which is the main subject of investigation within the DFG Priority Program 2020. In order to better understand the influence of these toughening mechanisms on the formation of hysteresis during cyclic loading-unloading of plain and steel fiber-reinforced high-performance concrete, we model these mechanisms and their evolving influence on damage development using a discrete crack approach, and take into account the imperfect closure of cracks and friction between crack faces that come in contact during loading/unloading of the specimen. Within the scope of this contribution, we present the formulation of the model and illustrate its performance through selected numerical experiments under monotonic and cyclic loading of plain and fiber-reinforced high-performance concrete specimens. Model predictions are compared with laboratory measurements.

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Loading assumptions used for the structural design of segmental linings often improperly reflect the complex load combinations that develop during the construction of a bored tunnel. Therefore segment designs used in practice tend to be on the safe side and often rely on conventional reinforcement methods instead of including other reinforcement concepts, such as steel fibres. In this contribution, a multi‐scale computational modelling framework is proposed to investigate the response of steel‐fibre reinforced, traditionally reinforced, and hybrid‐reinforced lining segments to radial loadings with an emphasis on the longitudinal joints. This modelling approach offers an opportunity to directly investigate the influence of type and content of steel fibres on the performance of segmented linings at the structural scale. Using this framework, a method for robust optimization is applied in order to generate damage‐tolerant hybrid segment designs.