ABSTRACT
High Performance Concretes (HPC) open new opportunities in the utilization of the material concrete. Their use implies significant changes in the conceptual approach and in the construction methods for concrete structures. Various simplified diagrams have been proposed for the HPC such as triangular or trapezoid diagrams. After comprehensive studies the French Codes kept the classical parabola-rectangular diagram for HPC up to C 60. Tests confirm the validity of the French approach concerning the allowable shear stress, at least for HPC with a strength smaller than 60 MPa. The behavior diagrams of HPC differ according to the maximum concrete strength. The behavior of concretes under sustained loads depends upon their mode of microcracking. As a matter of fact the question of the brittleness of HPC is a false problem since structural engineers deal with reinforced and/or prestressed concretes the ductility of which can be adjusted according to any particular needs.
