PSI - Issue 28

Zuzana Marcalikova et al. / Procedia Structural Integrity 28 (2020) 957–963 Author name / Structural Integrity Procedia 00 (2019) 000–000

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offer of fibers with regard to material, shape, finish and cross section is illustrated in the Fig. 1. It was proved many times that the addition of fibers to concrete improves the mechanical properties compared to plain concrete, especially tensile strength (Marcalikova et al., 2020a, Marcalikova et al., 2020b). In case of fiber reinforced concrete, it is necessary to monitor the quality (Katzer and Domski, 2012) and control mechanical properties (Kobaka et al., 2019) very carefully. Fiber reinforced concrete is widely used in the case of industrial floors (Cajka et al., 2020, Pazdera et al., 2019, Tomasovicova and Jendzelovsky, 2017), parking areas, foundation slabs, thin-walled structures or in reinforced concrete beams (Zhao et al., 2018). Among the important researched areas of concrete structures where fibers can be used is research of the failure or capacity of concrete in shear (Halvonik et al., 2020, Sucharda, 2020) and punching (Augustin et al., 2020, Kozielova et. al., 2020), where it can contribute to a more significant effect compared to classic approaches reinforcement. Still, existing knowledge and recommendations allow the use of fiber reinforced concrete for load bearing structures to a very limited extent. The aim of authors is to contribute to enlarge the knowledge in specific investigated area of reinforced concrete (RC) beams without shear reinforcement.

Fig. 1. Shapes and types of fibers according to Marcalikova et al., 2020a.

Positive feature of fiber reinforced concrete is that when first cracks appear, the fibers in the concrete are activated, which are stressed until they are torn or broken, Fig. 2. With adding the dispersed reinforcement to the concrete, the tensile strength increases, but also the shape of the load displacement diagram changes (Cajka et al., 2020, Marcalikova et al., 2020a, Kurihara et al., 2000, Koniki and Ravi, 2018). A change in the shape of the curve of the load displacement diagram of fiber reinforced concrete in comparison with plain concrete is illustrated in the Fig. 2. Magnitude of residual tensile strength is influenced not only by the type of fibers used, but also by the dosage of the fibers. Fiber reinforced concrete structures are still able to carry external loads even after exceeding the tensile strength. Fracture mechanics or specialized constitutive relations are often used to describe mechanical properties of fiber reinforced concrete (Karihaloo and Wang, 2000, Kormanikova and Kotrasova, 2011, Zaborski, 2016). Inverse analysis also is used to determine the mechanical parameters (Sucharda et al., 2018, Sucharda, 2020). It is possible to use approach the use of small beams experiments to obtain design parameters (Giaccio et al., 2008). In structural design, modeling of fiber reinforced concrete structures is usually performed using specialized software, which are based on non-linear analysis (Sucharda et el., 2014) and finite element method (Cervenka et al., 2007, Brozovsky et el., 2009). The biggest differences in the creation of the numerical model are in the choice of the material model, when the fracture-plastic material model (Cervenka and Papanikolaou, 2008) was used for the performed numerical modeling (Sucharda and Konecny, 2018). In numerical model of reinforced concrete, it is necessary to take into account the real behavior of concrete, i.e. crush of concrete in compression and formation of cracks in tension (Kralik, 2013, Kralik, 2006).