A parametric finite element (FE) model of layered shells is developed to investigate large-sized steel fibre reinforced concrete (SFRC) slabs or shell structures. It accounts for variability in the most sensitive parameters like geometry, discretisation, loading and material properties. Additional reinforcement by means of rebar and prestressing tendons is considered by embedded 3D truss elements as well as deviation and anchorage forces. The material model for plain concrete, formulated in the framework of an elasto-plastic damage theory considering smeared cracks, is elaborated in its material equations and parameters to widen its field of application to SFRC. Plastic strains and stiffness degradation model the damage induced by cracking. Mesh sensitivities due to localisation phenomena are minimised employing a two-step regularisation strategy. First, energy criteria in tensile and compressive domains and corresponding analytically derived characteristic length parameters are defined based on the balance of energies in the crack band. Second, the mesh pattern is initially aligned with respect to supposed crack lines to simplify the analytical procedure. The FE model is applied to loading tests of SFRC slabs on pile supports with and without rebar and prestressing tendons. Comparisons of numerical results in terms of load–deflection curves, reaction forces as well as crack patterns proof a good accordance to experimental data. Effects of unavoidable uncertainties when determining parameters from test reports are illustrated in parametric studies.

Redistribution Effects of Steel Fibre Reinforced Concrete Slabs Numerical Computation and Design The bearing behaviour of steel fibre reinforced concrete (SFRC) slabs is mainly affected by nonlinearity due to cracking and redistribution effects leading to an increased bearing capacity. A nonlinear approach for structural analysis and design of such structures is presented. It is based on an elasto-plastic damage theory to model material behaviour of SFRC and allows for additional embedded rebars. By adopting a finite element discretisation of the slab structure a regulated smeared modelling of cracking is achieved. Further the nonlinear model is applied to a full scale test of a SFRC flat slab structure and results are compared to alternative already well established methods, namely a linear elastic analysis and the yield line theory. The proposed method is proven to be very suitable for design but alike the alternatives depends on assumed crack patterns, residual tensile strength of the SFRC and geometrical parameters.

AbstractStahlfaserbeton findet häufig Verwendung bei Bauteilen mit kombinierter Biege‐Normalkraftbeanspruchung, wie beispielsweise bei wasserundurchlässigen Wannenkonstruktionen oder bei Tübbingen im maschinellen Tunnelbau. Dabei können bei Zugbeanspruchungen – beispielsweise aus Zwang – durch die Stahlfasern aufgrund feinerer Rissverteilung und somit reduzierter Rissbreite Vorteile im Hinblick auf die Dauerhaftigkeit entstehen. Für die Tragfähigkeit erweist sich eine andauernde, moderate Druckbeanspruchung – oft auch in Kombination mit zusätzlicher Betonstahlbewehrung – als günstig, da somit die Forderung eines duktilen Bauteilverhaltens nach Rissbildung bereits auf Querschnittsebene erfüllt werden kann. Zur einfachen rechnerischen Erfassung der Beanspruchbarkeit von Bauteilen aus Stahlfaserbeton mit oder ohne zusätzliche Betonstahlbewehrung unter Biegung mit Normalkraft werden im Folgenden die klassischen M‐NInteraktionsdiagramme für Stahlbeton um die Wirkung der Stahlfasern erweitert. Untersuchungen zur Effizienz der Faserwirkung und ein Anwendungsbeispiel schließen den Beitrag ab.

Structural Elements of Steel Fibre Reinforced Concrete with or without Bar Reinforcement Tools for Design and Deflection Estimations according to the Guideline "Stahlfaserbeton" by DAfStb The expected release of the guideline "Stahlfaserbeton" [1] by 'German Committee for Reinforced Concrete'(DAfStb) offers a wide application range for the composite material steel fibre reinforced concrete (SFRC). Due to additional steel fibres in concrete considerable tension forces can be transferred between crack edges after reaching plain concrete's tensile strength. These forces can be accounted for in calculation of load bearing capacity. Adapted from common design methods and tools for plain reinforced concrete new procedures, tools and a computer application - based on spreadsheet analysis and optimisation methods - for SFRC are presented in this article. These allow for both bending design as well as deflection estimation of cross-sections and structural systems made of SFRC with and without additional rebars. Their application - also in case of deflection estimation using non-linear methods - is demonstrated in two elaborated examples.