Issue 78

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

5. K IC of fiber-reinforced beams decreased with increasing a/d ratio from 0.25 to 0.5, indicating the effectiveness of fiber bridging decreases with the crack depth. 6. Increasing the a/d ratio from 0.25 to 0.5 reduced the ultimate load capacity of the MC-FRC beams by about 10% and lowered their stiffness, toughness, and ductility, with crack initiation occurring earlier at the higher a/d ratio. Consistent with this trend, the failure-mode observations confirmed that steel fibers actively restrained crack widening and controlled the propagation path across the tested a/d ratios, producing narrower and shorter main cracks than in the fiber-free specimens, where cracks were wider and extended through the full depth of the section. 7. The study is exploratory and not confirmatory because each of the fourteen beam configurations was tested as a single specimen without replication due to the large material and casting and testing resources (up to 1600 mm long, individually reinforced, cured for 56 days, and tested on a 1000 kN frame) required for full-scale reinforced concrete beams. Only the material-characterization tests (compressive and splitting-tensile strength) were repeated three times per mix, as per standard practice (BS EN 12390-3:2019; ESS 1658-6/2018); however, this is still not enough for rigorous statistical treatment. Future work should include at least duplicate large-scale beam testing to permit a coefficient-of-variation-based assessment of the reported load capacity, stiffness, and fracture-toughness values. [1] Roesler, J., Paulino, G., Gaedicke, C., Bordelon, A. and Park, K. (2007). Fracture behavior of functionally graded concrete materials for rigid pavements, Transportation Research Record: Journal of the Transportation Research Board, 2037(1), pp. 40–49. DOI: http://dx.doi.org/10.3141/2037-04. [2] Dias, C.M.R., Savastano, H. and John, V.M. (2010). Exploring the potential of functionally graded materials concept for the development of fiber cement, Construction and Building Materials, 24(2), pp. 140–146. DOI: http://dx.doi.org/10.1016/j.conbuildmat.2008.01.017. [3] ACI Committee 544 (2018) ACI 544.4R-18: Guide for design with fiber-reinforced concrete. Farmington Hills, MI: American Concrete Institute. [4] Iskhakov, I., Ribakov, Y., Holschemacher, K. and Mueller, T. (2013). High performance repairing of reinforced concrete structures, Materials & Design, 44, pp. 216–222. DOI: http://dx.doi.org/10.1016/j.matdes.2012.07.041. [5] Abbass, A., Abid, S. and Özakça, M. (2019). Experimental investigation on the effect of steel fibers on the flexural behavior and ductility of high-strength concrete hollow beams, Advances in Civil Engineering, 2019(1). DOI: http://dx.doi.org/10.1155/2019/8390345. [6] Kytinou, V.K., Chalioris, C.E. and Karayannis, C.G. (2020). Analysis of residual flexural stiffness of steel fiber reinforced concrete beams with steel reinforcement, Materials, 13(12), p. 2698. DOI: http://dx.doi.org/10.3390/ma13122698. [7] Ammendolea, D., Greco, F., Leonetti, L., Lonetti, P. and Pascuzzo, A. (2023). A numerical failure analysis of nano-filled ultra-high-performance fiber-reinforced concrete structures via a moving mesh approach, Theoretical and Applied Fracture Mechanics, 125, p. 103877. DOI: http://dx.doi.org/10.1016/j.tafmec.2023.103877. [8] Wan-Wendner, L., Wan-Wendner, R. and Cusatis, G. (2018). Age-dependent size effect and fracture characteristics of ultra-high performance concrete, Cement and Concrete Composites, 85, pp. 67–82. DOI: http://dx.doi.org/10.1016/j.cemconcomp.2017.09.010. [9] Yixin, C., Jianye, Z., Jicheng, M., Shunli, Z., Yongsheng, L. and Zhixuan, Z. (2022). Tensile strength and fracture toughness of steel fiber reinforced concrete measured from small notched beams, Case Studies in Construction Materials, 17, p. e01401. DOI: http://dx.doi.org/10.1016/j.cscm.2022.e01401. [10] Yoo, D.Y., Yoon, Y.S. and Banthia, N. (2015). Flexural response of steel-fiber-reinforced concrete beams: Effects of strength, fiber content, and strain-rate, Cement and Concrete Composites, 64, pp. 84–92. DOI: http://dx.doi.org/10.1016/j.cemconcomp.2015.10.001. [11] Ghasemi, M., Ghasemi, M.R. and Mousavi, S.R. (2019). Studying the fracture parameters and size effect of steel fiber reinforced self-compacting concrete, Construction and Building Materials, 201, pp. 447–460. DOI: http://dx.doi.org/10.1016/j.conbuildmat.2018.12.172. [12] Zhang, P., Wang, C., Gao, Z. and Wang, F. (2023). A review on fracture properties of steel fiber reinforced concrete, Journal of Building Engineering, 67, p. 105975. DOI: http://dx.doi.org/10.1016/j.jobe.2023.105975. [13] Elakhras, A.A., Seleem, M.H. and Sallam, H.E.M. (2021). Intrinsic fracture toughness of fiber reinforced and functionally graded concretes: An innovative approach, Engineering Fracture Mechanics, 258, p. 108098. DOI: http://dx.doi.org/10.1016/j.engfracmech.2021.108098. R EFERENCES

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