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Bétons renforcés de fibres métalliques : du matériau à la structure. Etude expérimentale et analyse du comportement de poutres soumises à la flexion et à l'effort tranchant

Abstract : Steel fibre reinforced concrete (SFRC) are rarely used in truly structural applications. This fact is mainly due to the lack of design tools, and consequently to the difficulty in quantifying the structural part due to these materials. The objective of this work is to give an answer to this matter in the case of beams. The structural performed tests have two goals : firstly, to study the failure mechanisms and, secondly, to validate the models developed in this work. Tests are thus carried out in bending and shear. A global investigation tool, stereophotogrammetry, is used to study the cracking pattern: it shows clearly an early crack localization and the onset of a block mechanism which leads to a block type failure. These tests point out that the main mechanical characteristic of SFRC is their post cracking behaviour in tension. A uniaxial tension test on notched specimens is used, and developed, to measure a load - crack opening relationship. Specimens are cored, in the direction of the main load, to take into account the anisotropy due to concreting. A first type of model consists in postulating a failure mechanism, then in calculating the equilibrium of the structure, as a function of the crack opening, starting from the experimental relationship obtained in tension. Modelling of bending leads to good results. Concerning shear behaviour, the fibre part is correctly calculated and an equivalence relationship with classical stirrups is achieved. To take into account the observed scale effects, it is necessary to consider the evolution, with the crack opening, of the residual strength in tension. An empirical relationship is necessary to quantify the structural part of shear resistance. This illustrates the limits of simple models. Therefore, it seems necessary to use finite elements to model structures submitted to complex loading. A continuous approach (plasticity) and a discrete one (the LCPC's probabilistic model) are used. To conclude, a complete study was carried out from the material to the structure. This study, experimental and theoretical, presents methods of analysis that, coupled with a global procedure from mix design to mechanical characterization, allow to optimize the design of SFRC structural elements.
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Pascal Casanova. Bétons renforcés de fibres métalliques : du matériau à la structure. Etude expérimentale et analyse du comportement de poutres soumises à la flexion et à l'effort tranchant. Matériaux. Ecole Nationale des Ponts et Chaussées, 1995. Français. ⟨tel-00523261⟩

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