Issue 35

T. Holušová et alii, Frattura ed Integrità Strutturale, 35 (2016) 242-249; DOI: 10.3221/IGF-ESIS.35.28 247 model with eye nuts at the ends of the steel bars and the model featuring the current method by which the specimen is gripped by the test apparatus. Except the ratio for f cu = 55 MPa, the ratios range is from 0.63 – 0.76. For better clarity Tab. 4 is reproduced as a graph in Fig. 7. Figure 5 : The final Load-COD_F diagrams for f cu 10 and 37 MPa used for the calculation of fracture energy values. Figure 6 : The final Load-COD_F diagrams for f cu 55 and 85 MPa used for the calculation of fracture energy values. C ONCLUSION he numerical simulations of the modified compact tension test were performed with the use of ATENA 2D finite element software. A cylindrical shape was chosen for the specimen, the dimensions of MCT are listed in Tab. 1. Eight cubic strength values ( f cu  {10, 25, 37, 45, 55, 67, 75, 85} MPa) were considered as input values for the numerical model used for the concrete part of the structure, 3D Non Linear Cementitious 2. The results are presented by the Load-COD_F diagrams and by the fracture energy values calculated according to RILEM recommendations [15] and summarized in a graph depending on input cubic strength values. From the numerical point of view, the results show that the use of eye nuts at the ends of the steel bars plays a significant role on the behavior of the conducted test. Nevertheless the obtained fracture energy curves show the same trend as the curve of input fracture energy values. In further research and experimental procedures it is recommended that eye nuts are used at the ends of the steel bars in order to avoid undesirable moment. The current method by which the steel is gripped by the test machine does not allow torsion at the ends of the steel bars. This can cause undesirable moment to arise, along with the deformation of the steel bars as you can see in Fig. 8 a) – marked by the red line (at the start point of the loading process) and by the green line (at the end point of the loading T