Neutral Axis Depth versus Flexural Ductility in High-Strength Concrete Beams

This paper presents an experimental study on the evolution of the neutral axis's depth failure with the ductility at bending on high-strength concrete beams. Nineteen simply supported beams were tested and analyzed. Each beam was loaded by two symmetrical concentrated loads applied approximately at the span's thirds. The concrete strength and the longitudinal tensile reinforcement ratio vary from beam to beam. As far as the ductility is concerned, ductility indexes were defined in order to characterize such property. The ductility's influence on the value of the neutral axis' depth at failure is analyzed and discussed. From the experimental program, the neutral axis' depth at failure in high-strength concrete beams seams to be a valuable parameter to preview the beam ductility. Therefore, the practical rule of limiting the neutral axis' depth of the critical sections presented by some codes of practice for normal strength concrete can be extended to high-strength concrete.