Steel fiber reinforced concrete is usually cast randomly, assuming an isotropic or two-dimensional fiber orientation in the final structural element and applying safety factors to account for the possible unfavorable orientation. On the contrast, fiber orientation could be an opportunity to optimize material performance by exploiting its anisotropy. In this framework, the structural application of a high strength fiber reinforced concrete with a strong one-dimensional fiber orientation is investigated in the field of mechanized tunneling by designing optimized tunnel segments subjected to the jack force of TBM thrust shoes. The optimization will be performed by orienting the fibers in the most favorable way to resist the induced tensile stresses, and by casting the high performance fiber reinforced concrete only in the most critical regions, where maximum stresses arise (i.e. the circumferential joint of the segment or, in a further optimization step, following the curved elastic tension lines which determine splitting and spalling stresses). The rest of the segment will be composed of a normal performance fiber reinforced concrete, with random fiber orientation. The feasibility of the curved casting methodology, as well as the monolithic behavior of the specimens cast with two different concretes is experimentally verified through small-scale experiments. Moreover, segments reinforced with traditional rebars, steel fibers and a hybrid solution of rebars and fibers are designed to achieve the same load bearing capacity. The sustainability of the optimized design is addressed through a global warming potential calculation, normalized to the performance of each reinforcement configuration.
The role of fiber orientation: the way towards structural optimization
Medeghini F.
;Tiberti G.;Plizzari G.;Mark P.
2023-01-01
Abstract
Steel fiber reinforced concrete is usually cast randomly, assuming an isotropic or two-dimensional fiber orientation in the final structural element and applying safety factors to account for the possible unfavorable orientation. On the contrast, fiber orientation could be an opportunity to optimize material performance by exploiting its anisotropy. In this framework, the structural application of a high strength fiber reinforced concrete with a strong one-dimensional fiber orientation is investigated in the field of mechanized tunneling by designing optimized tunnel segments subjected to the jack force of TBM thrust shoes. The optimization will be performed by orienting the fibers in the most favorable way to resist the induced tensile stresses, and by casting the high performance fiber reinforced concrete only in the most critical regions, where maximum stresses arise (i.e. the circumferential joint of the segment or, in a further optimization step, following the curved elastic tension lines which determine splitting and spalling stresses). The rest of the segment will be composed of a normal performance fiber reinforced concrete, with random fiber orientation. The feasibility of the curved casting methodology, as well as the monolithic behavior of the specimens cast with two different concretes is experimentally verified through small-scale experiments. Moreover, segments reinforced with traditional rebars, steel fibers and a hybrid solution of rebars and fibers are designed to achieve the same load bearing capacity. The sustainability of the optimized design is addressed through a global warming potential calculation, normalized to the performance of each reinforcement configuration.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
