Issue 77

Ays-S.S.Elsayedet alii, Frattura ed Integrità Strutturale, 77 (2026) 27-44; DOI: 10.3221/IGF-ESIS.77.03

CMOD behavior of cracked SCB specimen In this section, the CMOD behavior of the cracked SCB specimens was examined for different specimen radii at the same a/R, and vice versa, as shown in Figs. 6 and 7, respectively.

Figure 6: Load-CMOD behavior for various SCB specimen sizes at a/R = 0.2.

Figure 7: Load-CMOD behavior for various crack-depth ratios of the SCB specimen at R = 75 mm.

Effect of SCB specimen radius on CMOD for the same a/R Fig. 6 shows the applied load plotted against the CMOD for four different SCB samples: SR50-0.2-F, SR75-0.2-F, SR100 0.2-F, and SR125-0.2-F. All specimens had a constant a/R ratio of 0.2 and contained 1% steel fibers. The curves exhibit an initial linear-elastic rise to the peak load, followed by a strain-softening branch governed by fibers bridging across the crack. This is a typical response for fiber-reinforced concrete under bending conditions. The maximum load increases significantly with the specimen size. The SR50-0.2-F sustains a maximum load of just less than 7 kN, whereas the SR125 0.2-F reaches about 13 kN. Beyond the peak load, all specimens exhibit a steady decrease in load with increasing CMOD, indicating that steel fibers control multiple cracking. The area under each curve represents the energy absorption capacity, fracture energy. The SR50-0.2-F shows the most brittle drop after the maximum load, although residual load-carrying capacity is still present. In contrast, specimens SR75-0.2-F, SR100-0.2-F, and SR125-0.2-F show a more pronounced and stable post-cracking plateau. These results demonstrate that specimen size influences not only peak load but also the shape and stability of the post-peak softening response. The smaller specimen (SR50-0.2-F) loses load-carrying capacity more rapidly after cracking. The SR100-0.2-F specimen seems to have the best performance after cracking in this set. This suggests that the specimen size, fiber distribution, and crack-bridging efficiency interact in a complex manner. The results show that steel fibers change the material's behavior from brittle to quasi-ductile. The observed post-peak behavior of SR125-0.2-F, which shows a more significant drop in load despite its larger size, can be explained by statistical variations in fiber distribution and orientation within the larger volume, rather than a violation of the general size-effect trend. Previous studies have shown that the post-cracking behavior of fiber-reinforced concrete is more sensitive to the random distribution of fibers as the concrete specimen size increases [20]. This can lead to localized fiber clustering or alignment, which diminishes bridging efficiency in certain areas. Furthermore, Zhang et al.

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