Numerous experimental and analytical investigations have been conducted on the shear strength of steel fibre reinforced concrete (SFRC) members. However, most existing strength evaluation models are empirical equations based on limited experimental results lacking in theoretical basis, and these models may lead to overly conservative, uneconomical designs owing to the assumption of 45° crack inclination. They also cannot be expanded to estimate load–deformation responses of SFRC members. In order to overcome these limitations in existing models, this study proposes a theoretical model in which the contribution of steel fibres to shear resistance mechanisms of SFRC members, considering the random distribution characteristics and directionality of fibres at the crack interfaces, is reflected in a smeared-truss model. In particular, the pull-out failure of fibres caused by bond failure between fibres and the surrounding concrete is considered. Shear tests on SFRC beams were also conducted in this study with the primary parameters of fibre volume fraction and compressive strength, and experimental results from the literature were used for validation purpose. The proposed model shows a high level of accuracy in strength evaluation for a total of 103 experimental results. The crack inclination angles estimated by the proposed model range from 22° to 30° and agree well with the experimental results of this work. This demonstrates that the 45° crack angle assumed in the existing shear strength evaluation models is unnecessarily conservative.

The consumption of structural concrete in the construction industry is rapidly growing, and concrete will remain the main construction material for increasing urbanization all over the world in the near future. Meanwhile, construction and demolition waste from concrete structures is also leading to a significant environmental problem. Therefore, a proper sustainable solution is needed to address this environmental concern. One of the solutions can be using recycled coarse aggregates (RCA) in reinforced concrete (RC) structures. Extensive research has been conducted in this area in recent years. However, the usage of RCA concrete in the industry is still limited due to the absence of structural regulations appropriate to the RCA concrete. This study addresses a safety margin of RCA concrete beams in terms of shear capacity which is comparable to natural coarse aggregates (NCA) concrete beams. To this end, a database for reinforced concrete beams made of recycled coarse aggregates with and without shear reinforcement was established, collecting the shear specimens available from various works in the existing literature. The database was used to statistically identify the strength margin between RCA and NCA concrete beams and to calculate its safety margin based on reliability analysis. Moreover, a comparability study of RCA beams was conducted with its control specimens and with a database for conventional RC beams.

Recognizing that steel fibers can supplement the brittle tensile characteristics of concrete, many studies have been conducted on the shear performance of steel fiber reinforced concrete (SFRC) members. However, previous studies were mostly focused on the shear strength and proposed empirical shear strength equations based on their experimental results. Thus, this study attempts to estimate the strains and stresses in steel fibers by considering the detailed characteristics of steel fibers in SFRC members, from which more accurate estimation on the shear behavior and strength of SFRC members is possible, and the failure mode of steel fibers can be also identified. Four shear behavior models for SFRC members have been proposed, which have been modified from the softened truss models for reinforced concrete members, and they can estimate the contribution of steel fibers to the total shear strength of the SFRC member. The performances of all the models proposed in this study were also evaluated by a large number of test results. The contribution of steel fibers to the shear strength varied from 5% to 50% according to their amount, and the most optimized volume fraction of steel fibers was estimated as 1%–1.5%, in terms of shear performance.