Issue 35

T. Holušová et alii, Frattura ed Integrità Strutturale, 35 (2016) 242-249; DOI: 10.3221/IGF-ESIS.35.28 246 Steel / Plane Stress Elastic Isotropic E [MPa] 210 000 μ [-] 0.3  [kg/m 3 ] 7 850 Table 2 : Input parameters of the Plane Stress Elastic Isotropic numerical model for steel bars. Concrete / 3D Non Linear Cementitious 2 f cu [MPa] 10 25 37 45 55 67 75 85 E [MPa] 18 470 28 060 33 010 35 570 38 170 40 610 41 890 43 170 f t [MPa] 1.114 2.052 2.665 3.036 3.471 3.959 4.268 4.640 f c [MPa] 8.5 21.25 31.45 38.25 46.75 56.95 63.75 72.25 G f [J/m 2 ] 27.85 51.30 66.62 75.91 86.77 98.98 106.7 116 μ [-] 0.2  [kg/m 3 ] 2300 Fixed crack model coefficient 0.5 Aggregate size [m] 0.02 Table 3 : Input parameters of the 3D Non Linear Cementitious 2 numerical model for concrete. R ESULTS AND DISCUSSION he numerical results are presented via L-COD diagrams for studied cases; selected examples are shown in Figs. 5- 6. The horizontal axis represents the displacement, in this case the crack opening displacement (COD) measured on the loading axis (labeled COD_F in the diagrams) and also on the axis of the steel bars. The vertical axis is represented by the applied load, giving us the Load-COD diagrams. The fracture energy value was also calculated and compared for all curves. Fracture energy ( G f ) is a relevant fracture parameter which characterizes concrete. Its value is obtained from work of fracture ( W f ) divided by the area of the ligament ( A lig ). The work of fracture value corresponds to the area under the corresponding curve. The applicability of the MCT test for the determination of the fracture energy of concrete was investigated with promising conclusions (see [17]). Fracture energy G f [J/m 2 ] f cu [MPa] 10 25 37 45 55 67 75 85 Current grips 48.61 95.52 120.95 134.93 134.08 211.48 218.68 225.25 Eye Nuts 31.01 67.58 90.15 103.16 122.73 135.66 148.20 163.35 Ratio Eye/Curr 0.638 0.708 0.745 0.765 0.915 0.642 0.678 0.725 Table 4 : Fracture energy values calculated according to RILEM recommendations and obtained from loading curves from numerical calculations. The fracture energy values calculated from loading curves are shown in Tab. 4. According to the results obtained from numerical simulations, the loading curve for the value f cu = 55 MPa with the current grips shows a significant anomaly. In the other cases, the use of eye nuts at the ends of the steel bars plays a significant role. The curve of the fracture energy values from the numerical models in which eye nuts were used display approximately the same trend as the input fracture energy values. Tab. 4 contains the calculated ratios between the values obtained from the loading curves for the numerical T