S. Tarasovs et alii, Frattura ed Integrità Strutturale, 35 (2016) 271-277; DOI: 10.3221/IGF-ESIS.35.31 271 Focussed on Crack Paths Modelling of the fracture toughness anisotropy in fiber reinforced concrete S. Tarasovs, J. Krūmiņš, V. Tamužs Institute of Polymer Mechanics, University of Latvia, Aizkraukles St. 23, Riga, LV-1006, Latvia tarasov@pmi.lv A BSTRACT . Steel fiber reinforced concrete is potentially very promising material with unique properties, which currently is widely used in some applications, such as floors and concrete pavements. However, lack of robust and reliable models of fiber reinforced concrete fracture limits its application as structural material. In this work a numerical model is proposed for predicting the crack growth in fiber reinforced concrete. The mixing of the steel fibers with the concrete usually creates nonuniform fibers distribution with more fibers oriented in horizontal direction, than in vertical. Simple numerical models of fiber reinforced concrete require a priori knowledge of the crack growth direction in order to take into account bridging action of the fibers, which depends on the fibers orientation. In proposed model user defined elements are used to calculate the bridging force during the course of the analysis when the crack starts to grow. Cohesive elements were used to model the crack propagation in the concrete matrix. In cohesive zone model the cohesive elements are embedded between all solid elements to simulate the arbitrary crack path. The bridging effect of the fibers are modeled as non- linear springs, where the stiffness of the springs is defined from experimentally measured pull-out force and the angle between the fiber and crack opening direction. K EYWORDS . Fiber reinforced concrete; Fracture; Cohesive elements. I NTRODUCTION n recent years concrete reinforced by short steel fibers became very popular material in such applications as floors and concrete pavements. However, lack of robust and reliable models of fiber reinforced concrete fracture, limits its application as structural material. The fracture of fiber reinforced concrete is complex phenomenon occurring at different length scales. Different models were proposed in the last years for the prediction of the fracture process in the fiber reinforced concrete. One of the most common approaches is cohesive zone model where the traction-separation law for the fiber-reinforced concrete is derived by averaging the pull-out forces of all fibers crossing the fracture plane [1]. Such models work well for sufficiently homogeneous distribution of fibers and in situations, where direction of crack growth can be predicted a priori . More complex models, which take into account the effect of individual fibers, may be necessary in other cases. Only few works with such models were published recently. The 2D and 3D lattice model with cement matrix, aggregates and discrete steel fibers was used in [2] to simulate the fracture behavior of fiber-reinforced concrete. Cunha et al. [3] used 3D smeared crack model to simulate concrete cracking and the truss elements were used to model the bridging action of steel fibers. Radtke et al. [4] used the damage model for matrix material and the steel fibers were indirectly modeled as traction forces I

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