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Design of SFRC beams aided by a multiscale model

Grant number: 19/24487-2
Support type:Regular Research Grants
Duration: June 01, 2020 - May 31, 2022
Field of knowledge:Engineering - Civil Engineering - Structural Engineering
Principal Investigator:Luís Antônio Guimarães Bitencourt Júnior
Grantee:Luís Antônio Guimarães Bitencourt Júnior
Home Institution: Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Assoc. researchers:Renata Monte

Abstract

Nowadays, it is well known that the addition of a small volume of steel fibers may increase the ductility and thoughness of concrete matrices, resulting in so-called Steel Fiber Reinforced Concrete (SFRC). However, although the use of SFRC for structural applications has increased in last years, its use among practitioners is still limited with respect to its potentials due to the lack of international building codes.The lack of confidence to use SFRC as structural material is also directly related to the variability presented by experimental laboratory tests, since the composite behavior can be influenced by several parameters such as concrete matrix; material, shape and geometry of the fiber; fiber content; distribution of the fibers and the fiber/matrix interface structure. Covering all the cases, by using only experimental investigations would be very expensive and time-consuming.Recently, a number of numerical models have been proposed using an approach that considers the contribution of steel fibers, concrete and concrete/fiber interaction in a fully independent way. These numerical models may be very useful for simulating a range of cases by varying the type, arrangement and distribution of the fibers and their interaction with the concrete, which is very important on the post-cracking behavior. Hence, a numerical model with this approach seems to be a natural way to simulate the post-cracking behavior of the composite.In this sense, this research aims to contribute to the design of SFRC elements aided by a mesoscale model recently proposed by Bitencourt Jr. et al. (2019) with discrete and explicit representation of steel fibers. Firstly, experimental tests will be performed to improve and to validate the numerical model. Pullout tests will be carried out to obtain the fiber/matrix behavior, including the influence of the end hook of fibers; characterization tests to obtain the performance post-cracking parameters; beams with combined reinforcement of steel fibers and rebars (RC-SFRC beams) to uderstanding the influence of the fibers in terms of serviceability (SLS) and ultimate limit states (ULS); and inductive tests to asses the content and the distribution of steel fibers and to include them as a variable that influences on the responses of the experimental tests performed. Secondly, the numerical model will be improved in order to capture the fiber/matrix interaction, using as reference the results obtained in the experimental testes performed; development of models to consider non-uniform fiber distributions, to taking into account the effect of segregation of fibers, direction of the material casting and molding procedure; and optimize the computational program to perform more robust analyzes with shorter time-consuming, using nonlinear system solution libraries such as "pardiso", and concurrent multiscale models, in which the fibers are only used where cracks are expected. Thirdly, the RC-SFRC beams designed and experimentally tested are numerically simulated and the results are compared in terms of crack width, mean crack spacing, deflection and ultimate and service loads. Herein, it will also be studied the influence of use experimental and numerical parameters on the design of RC-SFRC beams according to fib Model Code 2010 (2013). It is expected in this research to obtain a numerical tool able to simulate the behavior of structural elements composed of steel fiber reinforced cementitious composites, including its failure process in order to contribute for future code for fiber reinforced cementitious composites as a structural material. (AU)