Contribuição ao dimensionamento de pórticos de concreto reforçado com fibras de aço a partir de análise numérica

Abstract

Fibers are known to improve the performance of concrete in post-cracking behavior, particularly in terms of mechanical properties such as tensile strength, flexural capacity, and toughness. The stress transfer bridging effect of the steel fibers and the confinement caused by them alter the moment redistribution in the frames. In this context, this study aims to contribute to the design of steel fiber-reinforced concrete (SFRC) frames based on numerical analysis by applying the ABNT NBR 16935 (2021). The constitutive relationship of SFRC is made by means of the plastic damage model Concrete Damaged Plasticity (CDP), when a nonlinear behavior of the composite is adopted. To validate the applicability of the model, a numerical validation was performed, reproducing in ABAQUS the beams and frames tested experimentally. Initially, the numerical validation was carried out by simulating the SFRC beams tested experimentally by Conforti et al. (2018) and Buttignol et al. (2017). Next, the reinforced concrete frames tested experimentally by Cranston (1965) and Li et al. (2022) were simulated. Subsequently, the same frames were analyzed with the addition of steel fibers. Finally, reinforced concrete and SFRC columns subjected to centric and eccentric compression were analyzed numerically. In general, the numerical results indicate a good correlation with the experimental results, thus validating the methodology proposed in this work. In the SFRC frames, the steel fibers increased the stiffness of the beam-column joint, leading to a change in the moment redistribution. The SFRC frame nodes began to resist a higher bending moment, and with a smaller rotation, compared to the reinforced concrete frame. The addition of steel fibers also allowed for the reduction of longitudinal reinforcement in the beam and improved the performance of the column, especially regarding tensile forces. However, the addition of fibers did not increase the load capacity and ductility of the columns. Regarding the shear behavior of the beams, for the two volumes of fibers studied, the possibility of partially or totally replacing the transverse reinforcement was confirmed. The importance of using a minimum amount of flexural reinforcement in SFRC beams was also highlighted, even though the ABNT NBR 16935 (2021) allows the total replacement of conventional reinforcement.