Il progetto delle strutture armate in calcestruzzo ad alta resistenza meccanica a compressione

High Strength Concrete (HSC) is characterized by physical, elastic and mechanical properties which are significantly different from those of Normal Strength Concrete (NSC). From the civil engineering point of view, compressive strength alone is not sufficient by itself to design reinforced concrete structures. Other properties, such as drying shrinkage, creep, modulus of elasticity, Poisson's ratio, tensile and flexural strength are also needed for a safe design of concrete structures. Relationships between the above mentioned properties and the compressive strength are available in codes or norms for NSC in form of equations or tables based on consolidated experimental data. On the other hand, these relationships can change from NSC to HSC as a function of the compressive strength itself. The analysis of codes and norms of HSC has shown how for the application of this material it has been necessary to change the existing relationships between these concrete properties and compressive strength. Moreover for HSC the relationship between elastic modulus or tensile strength on one hand, and compressive strength on the other, significantly changes from one code to another. Therefore there is the need to concentrate the research efforts to identify the factors that determine the considerable variation of the elastic-mechanical properties of HSC. High strength concrete is characterized by a higher brittleness compared to NSC. However, a fragile behaviour of the material by itself does not necessarily correspond to an equally brittle behaviour of the reinforced concrete structures. Therefore, it is just as important to concentrate the research efforts to have more realistic data for the design of the reinforced high strength concrete members. There is the need to direct the research on HSC not simply on the peculiar features of the material per se but, above all, on the aspects of the design of reinforced members. In fact, the concrete behaviour can be substantially changed by the interaction with the reinforcement. The lack of knowledge about these interactions forces the various codes to adopt too much restrictive requirements that presently reduce the advantages of using HSC in structural applications.