Multiscale modeling of plain and steel fiber reinforced concrete and its application to predicting the behavior of structural members

Abstract

This research project aims to improve multiscale models developed by the proponent and collaborators for plain and steel fiber reinforced concrete and apply them to predict the behavior of structural elements.The 2D mesoscale model developed by Rodrigues et al. 2016 has been improved in recent years through the proposition of a mesh adaptive methodology (Rodrigues et al., 2018) to reduce the high computational costs typical of heterogeneous models and, additionally, its formulation has been extended to 3D analysis (Rodrigues et al., 2020) considering the composite as a material with three phases: cement matrix, interfacial transition zone (ITZ) and coarse aggregates. In this project, the generation of coarse aggregates will be performed from X-ray microtomography images. A methodology will be developed to create the geometry of the material structure from the images obtained. In addition, a mesh generator will be adapted to consider the presence of steel fibers in the numerical model in order to better understand the influence of reinforcement on the propagation of cracks in the cementitious matrix. These models will also be applied to predict the behavior of simple and reinforced concrete structural elements.The numerical model with discrete and explicit representation of steel fibers proposed by Bitencourt Jr. (2015) has been improved within the scope of a current research project financed by FAPESP (Regular Grant Nº 2019/24487-2) under the responsibility of the proponent, aiming at its application to the design of concrete beams reinforced with steel fibers. In this period, the model was applied to obtain the parameters of the post-cracking behavior of the material (Trindade et al., 2020) and, later, to predict the behavior of beams in the service and ultimate limit states (Trindade et al., 2020). In this project, the model will be adapted aiming at two applications of great practical interest. In the first, the model will be applied to predict the behavior of segments for tunnels reinforced with conventional reinforcement and steel fibers. In this project, the model will be used to predict the behavior of the structural members separately, and as a component of the segmental ring, considering the effects on the interaction between the segments (joints) and loading of the surrounding mass (soil or rock). In this context, the second application of the model with a discrete fiber representation will be in the prediction of the behavior of ultra high performance fiber reinforced concrete. In this project, the model will be adapted to consider typical fiber distributions for a high volume of fibers and to properly describe the fiber-matrix interaction. Initially the model will be calibrated from experimental results of characterization tests. Then, the model will be used to represent the behavior of reinforced concrete beams under bending reinforced with the characterized material. A numerical strategy will be developed to represent the interface behavior of reinforced concrete beams strengthened with UHPFRC layers.It is expected at the end of this research, to obtain a numerical tool capable of predicting the mechanical behavior of concrete considering the influence of its ingredients and translate this information to predict the behavior of structural elements. (AU)