Etude de l'influence des parametres structuraux sur les lois de comportement des betons fibres pour la conception de structures

Fibre reinforced concrete allows ductile structural behaviours, as well as reduction of the number of rebars or reduction of the concrete section. Today's numerical tools can reproduce the behaviour of concrete structures and help engineers optimize their designs. However, to use such tools, the engineer must have a good understanding of the material constitutive laws adopted and know how static conditions affect these laws.;To achieve the objectives of this research project, we developed a direct tensile test, allowing characterizing the tensile behaviour of concrete. We then tested tension specimens made with BHP50, BRF50 and BFUP120 concrete with and without rebars in order to obtain tensile laws that accounted or not the tension stiffening effect.;We elaborated two different flexural tests: one in isostatic conditions and one in hyperstatic conditions. Isostatic and hyperstatic flexural beams with reinforcement ratios of 0%, 0.5% and 1% have been made for each type of concrete tested. These tests gave us a comparative base for the finite elements models. These tests indicated increased cracking in the negative flexure zone for the fibre reinforced concretes (BRF50 and BFUP120). This observation supports the assumption that redundancy increases the performance of fibre reinforced concretes by favouring multi-cracking.;Finally, we have reproduced each flexural tests using the finite elements analysis software ATENA and the tensile relations obtained with direct tensile tests. We have determined with these models that a calibration of the tensile relations was necessary in order to correctly localize cracking. Furthermore, the study of the "characteristic size" parameter led us to the conclusion that a value of comparable size to the size of the meshing used gave the best results. The finite element models of the beams allowed us to see that fibre orientation played a major role in the accuracy of the results. We have also noticed that hyperstatic beams using fibre reinforced concrete (BRF50 and BFUP120), compared to similar isostatic beams, required respectively an 18% and 10% increase of the load carried by the fibres in their tensile law. This increase is caused by an incapacity of the finite element software to reproduce the multi-cracking effect observed in the negative flexural zone.;The first objective of this research project is to characterize the tensile response of different types of concrete, namely high strength concrete 50 MPa (BHP50), fibre reinforced concrete 50 MPa (BRF50) and ultra high performance fibre reinforced concrete 120 MPa (BFUP120). The second objective is to study the influence of static conditions on the behaviour of flexural beams. Finally, the last objective is to successfully reproduce the nonlinear behaviour of structural elements using the three types of concrete studied using a finite element software.