Discrete meso-modeling of steel fiber reinforced concrete: simulation of flexural behavior

Concrete provides with a variety of innovative designs, but two characteristics have limited its use: it is brittle and weak under tension. One way to overcome this problem is to add steel fibers into the concrete matrix, a technique introduced in the 70's called Steel Fiber Reinforced Concrete (SFRC). Fibers shape, length and slenderness characterize its behavior. It is also necessary to take into account the orientation and the distribution of the fibers in the concrete matrix. Different flexural tests are reproduced considering SFRC in order to characterize and analyze the influence of the fibers. Inthe present work, a numerical tool for including fibers into plain concrete is presented. The numerical approach considered is based on the idea of the Immersed Boundary (IB) methods which were designed for solving problems of a solid structure immersed on a fluid. Herein, the IB method is applied for SFRC considering the concrete accounting for fluid and the steel fibers playing the role of the solid structure. Thus, the philosophy of the IB methodology is used to couple the behavior of the two systems, the concrete bulk and the fiber cloud, precluding the need of matching finite element meshes. Note that, considering the different size scales and the intricate geometry of the fiber cloud, the conformal matching of the meshes would be a restriction resulting in a practically unaffordable mesh. Concrete is modeled considering a nonlinear model and to take into account the whole process between fibers and concrete, the constitutive equations of the fibers are based on analytical expressions available in the literature describing the pullout test behavior. The constitutive expressions depend on (1) the angle between each fiber and the crack of the concrete specimen and (2) the shape of the fiber