Issue 78

M. Adel et.al, Frattura ed Integrità Strutturale, 78 (2026) 168-185; DOI: 10.3221/IGF-ESIS.78.10

at large deflections, indicating better post-cracking ductility and toughness. At larger deflections, the MC-RC-FRC curve again sustains more load than the TTC-RC-FRC curve, showing greater energy absorption capacity. The MC beams specimens perform better in terms of load-carrying capacity and ductility at larger deflections. TTC beam specimens lose load capacity more quickly after the peak. However, the MC was a proper approach to measure the realistic fracture toughness of RC, taking the significant effect of fiber bridging into account. Fig. 15 illustrates the failure modes of steel reinforced concrete beams containing a fiber matrix (MC) and beams containing TTC.

(A) (B) Figure 14: Effect of crack surface pattern on load-deflection: (A) a/d = 0.25, (B) a/d = 0.5; deflection measurements were limited to a maximum of 13 mm.

Main crack

Main crack Tension crack

Shear crack

Tension crack

Shear crack

a/d = 0.25, TTC-RC

a/d = 0.5, TTC-RC

Main crack

Main crack

a/d = 0.5, MC-FRC-RC

a/d = 0.25, MC-FRC-RC

Main crack

Main crack

a/d = 0.5, TTC-RC-FRC

a/d = 0.25, TTC-RC-FRC

Figure 15: Mode of failure for different a/d and crack patterns.

Impact of a/d Ratio on the load-deflection response of RC beam The effect of a/d ratios (0.25 and 0.5) on MC and TTC FRC beams was studied. Fig. 16 a and b illustrate how varying the a/d ratios affects the load-deflection curves of MC beams that have been enhanced with SF. Increasing the a/d ratio from 0.25 to 0.5 resulted in a reduction of the ultimate load capacity by approximately 10%, along with decreases in stiffness and toughness. Conversely, beams with a lower a/d ratio (0.25) exhibited a lower tendency to fracture and were able to absorb more energy. This indicates that beams with reduced a/d ratios are stiffer and more capable of resisting bending under load. Moreover, toughness, indicated by the area under the load-deflection curve, was enhanced at reduced a/d ratios. This suggests that the material can absorb larger quantities of energy and is more effective at halting crack growth. Additionally, increasing the a/d ratio led to earlier crack formation, decreased load-carrying ability, and reduced ductility once the cracks emerged. These results support the notion that a lower a/d ratio improves the flexural performance of fiber-reinforced concrete beams by enhancing their stiffness and toughness against cracking.

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