On the EC2 Minimum Flexural Conventional Reinforcement Requirement for SFRC Beams

The revision of EN 1992-1-1 (Eurocode 2) published in November 2023 includes an Annex (L) for SFRC structures. Its provision for minimum flexural reinforcement is derived by solving the condition M_R,min ≥ M_cr. This is similar to the plain RC provision, yet it includes the effects of the fibers, by considering their effective residual tensile strength f_Ftu,ef. However, for the common ultimate limit state plastic design of reinforced SFRC (R/SFRC) beams or slabs without any direct check of their rotation capacity, the code requires to increase A_s,min by a factor ‘α_duct’. The default value of α_duct is 2.0 and it can be different according to the National Annex. The reason for this provision is the effect of cracking localization on reducing the flexural ductility, as observed in R/SFRC beams with relatively low conventional reinforcement ratios. Experimental data shows that there exists a transition point (TP) in terms of the ‘effective reinforcement ratio’, below which a decrease of the reinforcement decreases the flexural ductility (opposite to plain RC beams). This paper presents examples of A_s,min calculated by the code’s provisions with the default factor and inspects their resulted values with experimental data. It is shown that if minimum ductility is wished to be maintained, as indicated by the TP, the default value should indeed be increased.