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Fiber‐reinforced concrete (FRC) has been proved to be a competitive solution for structural purposes. Extensive research has highlighted the benefits of adding fibers on the post‐cracking strength, reduced crack spacing and crack width, and improved durability, among others. However, these aspects are related to serviceability limit states, and significant work remains to be done in terms of ultimate limit state behavior of FRC members. As recent publications have emphasized, reinforced concrete beams with low reinforcement ratios may result in a reduction of deformation capacity and, hence, to a loss of ductility. To further investigate this topic, this paper presents the results of a numerical parametric study of simply and continuous supported hybrid‐reinforced concrete (HRC) beams made with different amounts of fibers and reinforcement ratios. The deformation, rotational, and moment redistribution capacity of those were assessed by means of a finite‐element model previously calibrated using experimental results available in the literature. The results showed that there is a significant reduction of rotation capacity and moment redistribution for lightly reinforced (hybrid) members. Finally, the paper contains practical recommendations in terms of minimum reinforcement ratios that guarantee adequate rotation and redistribution capacity of HRC members. As such, the results of this study can provide a contribution toward more reliable structural designs of HRC members.

Fiber-reinforced concrete (FRC) is an attractive alternative to traditional steel bar-reinforced concrete structures, as evidenced by the constantly increasing market consumption of structural fibers for this purpose. In spite of significant research dedicated to FRC, less attention has been given to the effects of low temperatures on the mechanical properties of FRC, which can be critical for a variety of structural typologies and regions. With this in mind, an experimental program was carried out to assess the flexural behavior of macro-synthetic fiber-reinforced concrete (MSFRC) at different temperatures (from 20 °C to −30 °C) by means of three-point bending notched beam tests. The tested MSFRCs were produced by varying the content of polypropylene fibers (4 and 8 kg/m3). The results proved that the flexural strength capacity of all MSFRCs improved with decreasing temperature. Finite element analyses were then used to calibrate constitutive models following fib Model Code 2010 guidelines and to formulate empirical adjustments for taking into account the effects of low temperatures. The outcomes of this research are the basis for future experimental and numerical efforts meant to improve the design of MSFRCs subjected to low temperatures during service conditions.

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