The effect of fire on pre-cast steel fiber reinforced concrete for tunnel linings: from microstructure to structural simulation.

• Ano de defesa: 2021
• Autor(a) principal: Serafini, Ramoel
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Comportamento pós-fissuração; Concreto reforçado com fibras; Elevadas temperaturas; Elevated temperature; Estrutura de túneis; Exposição ao fogo; Fire exposure; Modelagem numérica; Numerical modeling; Post-crack behavior; Simulação estrutural; Steel fiber reinforced concrete; Structural simulation; Tunnel structures
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/3/3146/tde-25102021-114027/

The occurrence of fire in fiber reinforced concrete structures is one of the main concerns regarding the use of this material. Although fire is a deleterious event, limitations are found in studies focused on evaluating the effect of elevated temperatures on the mechanical properties of the composite, as well as in terms of extrapolating the results to design. In this context, this thesis aims to understand the tendencies in the mesoscale behavior of steel fiber reinforced concretes (SFRC) after temperature exposure and simulate the fire-related stability condition of tunnel sections built with this material. The changes in the microstructure of steel fibers, cementitious matrix, and fiber-matrix interfacial transition zone were evaluated as a function of temperature. Later, the effect of elevated temperatures on the tensile strength of fibers; bond-slip behavior of fibers embedded in the cementitious matrix; and the compressive, tensile, and post-crack parameters were evaluated. Furthermore, the composite was exposed to a large-scale fire test to experimentally determine the distribution of temperatures and the post-fire tensile properties of the material. At last, a numerical model was developed to compute the effect of a fire and thermal spalling on the bending capacity of reinforced concrete, fiber reinforced concrete, and hybrid solutions. The thermal spalling model was based on a simplified approach that shutdown the layers spalled. The results show that the the post-crack parameters ffts and fftu were more considerably influenced by the properties of the fiber-matrix ITZ than the bulk matrix properties. In terms of fftu, no statistically significant change was observed for T <= 300 °C, which as explained based on the mineralogical changes in the fiber-matrix ITZ and the changes in the pull-out kinetics due to the expansion of iron oxides and shrinkage of the cement paste. Moreover, the bond-slip mechanism have shown to prevail, without fiber rupture, up to ~600 °C. Considering the 11 numerical simulation without thermal spalling, FRC and RC-FRC solutions have shown to be less sensitive than the RC30 solution, while the increase in concrete cover in RC50 solution considerably mitigated the reductions in terms of bending capacity. Nevertheless, the increase in concrete cover has negligible influence on mitigating the reductions caused by thermal spalling, being the FRC and RC-FRC the least sensitive solutions due to the diffuse reinforcing capacity of fibers in the cross-section. In this sense, the advances acquired in this thesis supported a tool for assessing the bearing capacity of tunnel sections exposed to fire with and without thermal spalling and contributed to improving the safety conditions for this type of structure.