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Personne# Raffaele Cantone

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Béton armé

vignette|Armatures métalliques de renforcement du béton.
vignette|« Cancer du béton » : lorsque le front de carbonatation atteint l'armature métallique, celle-ci est atteinte de rouille qui fait augme

Béton de ciment

thumb|upright=1.0|Un mètre cube de béton (représentant la production mondiale annuelle de béton par habitant).
Le béton de ciment, couramment appelé béton, est un mélange de ciment, de granulats, d'e

Déformation d'un matériau

La déformation des matériaux est une science qui caractérise la manière dont réagit un matériau donné quand il est soumis à des sollicitations mécaniques. Cette notion est primordiale dans la conce

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Reinforced concrete planar members, as slabs and shells, are structural elements commonly used in the construction technique, which are typically designed without the arrangement of shear reinforcement. Despite the fact that this solution allows for fast and economic construction, the absence of shear reinforcement can give rise to the potential localization of strains within a critical shear crack and eventually to the shear failure of the member. In the case of redundant systems, most research on the mechanics of shear failures has been devoted to the strength of the member, neglecting in many cases the development of shear deformations due to inclined cracking as well as the redistributions of internal forces, which are instrumental for the analysis of the response of these members. The contribution to the state-of-the-art includes a series of theoretical works explaining the observed responses for a series of experimental programmes. These experimental campaigns comprise tests in tension, shear tests in one- and two-way slabs as well as punching tests. For their instrumentation, in addition to classical measurement devices, Fibre-Optic Measurements and Digital Image Correlation were intensively used.This thesis starts by revisiting the basis of the interaction between reinforcement and concrete. A series of bond tests show the stress concentrations occurring near the ribs and its complex transfer of forces with the surrounding concrete. In addition, tests on beams failing in shear show a complex interaction between bond stresses and kinking on the reinforcement due to the development of dowel action. These phenomena are normally neglected for concrete design due to the ductile nature of reinforcement, but may be relevant for fatigue and negative tension-stiffening effects.An important step in the knowledge is performed on the understanding of the shear response with respect to the characterization of the deformations in concrete members. Based on a series of test results, a complete description of the deformation field (including shear strains) is presented. On that basis, a rational model is proposed, consistent with the mechanical model of the Critical Shear Crack Theory. This model allows for a precise description of the response and also to describe the through-thickness distribution of the shear deformation.A general frame for modelling of reinforced concrete slabs is thus presented accounting for the redistribution of internal forces during propagation of the shear crack. This approach is used to investigate a testing programme performed on three wide slabs, analysing in a scientific manner the influence of the width of the member on the shear resistance. The detailed experimental data allow to capture the crack propagation and internal forces redistributions. Clear conclusions and answers are obtained, showing the influence of the shape of the failure surface and of its propagation on the load-carrying capacity.The research ends with a final investigation on the dowelling action of compression reinforcement, with an application to slabs failing in punching. Based on a large testing programme including eleven axisymmetric punching tests, an analytical approach is developed to estimate the contribution of the dowel action on the load-carrying capacity. This approach is formulated within the frame of the Critical Shear Crack Theory, and is incorporated in a consistent and efficient manner for design purposes.

Raffaele Cantone, Miguel Fernández Ruiz, Aurelio Muttoni, Andri Setiawan

The load-carrying capacity of many reinforced concrete structures is governed by shear failures, occurring before reaching the flexural capacity of the member. For redundant systems, such as slabs subjected to concentrated loads, local shear failures (typically initiated at locations with highest shear forces) can however occur after redistributions of internal forces due to the propagation of the shear cracks. Such process can depend upon the development of shear strains and the softening response of the member and can be stable or unstable. A suitable understanding and modelling of the complete shear response of reinforced concrete, including its deformations both for its pre-and post-peak branches, is thus instrumental for a consistent and comprehensive analysis of the shear response and strength of redundant elements.Such topic has received little attention in the past and analyses of redistributions of internal forces in concrete structures are often performed on the basis of refined flexural models, but coarse considerations for shear strains (typically elastic laws). This situation is a consequence of the lack of consistent experimental measurements on the shear deformations of reinforced members both before and after reaching the maximum shear capacity. Currently, however, the advent of refined measurements techniques such as Digital Image Correlation allows for an accurate tracking of the shear strains and for a fundamental understanding of its development. In this paper, taking advantage of such techniques, a comprehensive approach for determining the shear strains and their distribution across the depth of a section is presented. This approach allows reproducing accurately the development of shear strains and to predict the load-carrying capacity of redundant systems. The model is validated with selected test data and is considered as an effort to contribute to future numerical implementations of reinforced concrete shell models with realistic out-of-plane responses.

Raffaele Cantone, Miguel Fernández Ruiz, Aurelio Muttoni

Redistribution of shear forces in reinforced concrete members without shear reinforcement is a key aspect for the assessment of the shear capacity of wide beams and slabs. Such redistributions are due to the nonlinear response of reinforced concrete (both in bending and shear) and have the potential to significantly modify the internal forces during loading. This phenomenon allows in many cases, as for slabs linearly supported and subjected to concentrated forces, to increase the level of load even when some regions have already attained their local shear resistance. This work introduces the results of an experimental programme performed on three cantilever slabs subjected either to strip loads or to concentrated loads. Shear redistributions close to failure are investigated on the basis of refined measurements performed on the concrete surface and on the reinforcement bars. The results show the significance of several mechanical parameters, as well as how shear redistributions occur when some regions are in softening (post-peak behavior) while others have still not attained their local shear resistance. On this basis, a comprehensive approach is presented for determining the redistributions of internal forces and to predict the shear capacity of reinforced concrete slabs subjected to concentrated loads near linear supports. The performance of such approach is eventually validated against test data and practical recommendations are proposed for design and assessment.

2021