Issue 30

O. Sucharda et alii, Frattura ed Integrità Strutturale, 30 (2014) 375-382; DOI: 10.3221/IGF-ESIS.30.45 378 It follows from the test that the collapse in the beams without shear reinforcement occurs as a diagonal-tension failure. This is similar as in tests performed by Bresler-Scordelis. Examples of the failures are shown in [19]. This also shows the process of testing and the collapse. N UMERICAL MODELLING he numerical modelling was performed in ATENA [10] which uses FEM as a basis. That software includes a number of constitutive models of the concrete. It was decided to use a fracture-plastic material model for concrete and 2D computational models for the numerical analyses. Considering the numerical calculations performed in [19], very similar calculation models of the beams were created. The calculation model is a regular mesh of four-node finite elements. The finite elements in the concrete form a grid: 16x46, 16x56 and 15x66. Because the non-linear analysis depends much on the modelled boundary conditions, supports and loading plate from a linear elastic materials were also modelled. The calculation models were formed by a symmetric half of the real beams. In order to solve a system of non-linear equations, the Newton-Raphon method and deformation loads were chosen in ATENA [10]. Fig. 3 shows the final calculation models. The reinforcement was included into the calculation model as a smeared reinforcement. Beam OA1 Beam OA2 Beam OA3 Figure 3 : Computer models of beam (OA1, OA2, OA3). The analysis focused on development of cracks during the loading, maximum bearing capacity P u and deformation w u . The calculations have been performed in two alternatives in Tab. 4 a 5. The first alternative includes all properties of the concrete which are mentioned in Tab. 3, while the second alternative takes the compressive strength of the concrete as a basis. The basis is the recommended values for standard concrete. The remaining values are calculated in ATENA [10]. The software calculates also the tensile strength and modulus of elasticity of concrete. Those data are not so frequently available and their values are rather distributed in practical engineering. Beam number Ultimate load Midspan deflection P u, Test [kN] P u, Calc [kN] P u, Test /P u, Calc w u, Test [mm] w u, Calc [mm] w u, Test /w u, Calc OA1 331 332 1.00 9.1 6.8 1.35 OA2 320 358 0.89 13.2 13.2 1.00 OA3 385 374 1.03 32.4 30.6 1.06 Mean 0.97 Mean 1.14 Table 4 : Comparison of the numerical calculations and experiments – alternative 1. T