Maximum ratio of longitudinal tensile reinforcement in high strength doubly reinforced concrete beams designed according to Eurocode 8

This work deals with the maximum ratio of longitudinal tensile reinforcement compatible with a given level of local ductility in reinforced concrete beams, when considering the effect of high strength concrete. First, the evaluation method of the ductility factor is revealed, where an assessment procedure is presented. Then, the influence of the tension reinforcement ratio on the local ductility is discussed for high strength concrete. Furthermore, the Eurocode 8 provision concerning the criterion of the local ductility in dissipative beams is illustrated. In this respect, this criterion is examined in sections having the maximum tension reinforcement ratio adopted by Eurocode 8, by varying the strength of concrete by up to 90 MPa. The obtained tensile reinforcement ratios for a given value of curvature ductility factor by means of the setting procedure of the equations of equilibrium and compatibility show that the amount of reinforcement should be less than that proposed by the Eurocode 8 equation. Finally, a modified formula for the maximum tension reinforcement ratio ρmax is suggested instead of that recommended by Eurocode 8, which takes into consideration the effect of high strength concrete, where the validity of this formula is checked by a comparative study with other formulas for ρmax.