Contribuições para a modelagem termomecânica do concreto de ultra-alto desempenho reforçado com fibras de aço submetido a elevadas temperaturas

Abstract

Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) has emerged as a promising structural material due to its high mechanical strength, durability, and ability to maintain post-cracking performance. However, its numerical modeling still faces challenges related to the high computational cost of explicitly representing steel fibers and accurately reproducing the residual behavior after exposure to elevated temperatures. In this context, this study aims to develop and validate a numerical methodology for the thermal and mechanical analysis of UHPFRC using the Finite Element Method, investigating thermal homogenization techniques and strategies to represent temperature-induced mechanical degradation. Three-dimensional models were implemented in Abaqus, with the spatial distribution of steel fibers automatically generated through Python scripts, considering different fiber volume fractions and average orientation coefficients. The thermal analysis compared a biphasic model with explicit fiber representation to several homogeneous models based on different homogenization techniques. The mechanical response was simulated using the Concrete Damaged Plasticity model for concrete and an equivalent elastoplastic pullout model for steel fibers, while also incorporating temperature-dependent degradation of the mechanical properties. The results showed that combining Maxwell’s model for thermal conductivity with the density-weighted rule of mixtures for specific heat accurately reproduced the behavior of the biphasic model while significantly reducing computational cost. The mechanical model also showed good agreement with experimental results, successfully reproducing the stress–strain response and the residual strength degradation after thermal exposure. It is concluded that the proposed methodology provides an efficient tool for the thermomechanical analysis of UHPFRC and can contribute to the development of more accurate and computationally efficient numerical models for structural applications subjected to elevated temperatures.