The use of high strength concrete is already a reality and many countries are adapting their design codes to take into account the properties of this material. For the design of slender columns and sections subjected to combined axial force and bending, the most important property is the stress-strain relationship. While for normal concrete the strain at ultimate, ecu, can be considered constant and equal to 0,0035, for high strength concrete ecu depends on the concrete strength, decreasing as the strength increases. For a concrete with fck of 80 MPa, for instance, ecu is around 0,0022 according to the CEB Model Code (1990). Stress-strain relationship with ecu dependent of fck will affect the nondimensional interaction diagrams for the design of slender columns and sections of high strength concretes. Nondimensional interaction diagrams moment-axial load-curvature (m,n,f) and diagrams moment-axial load- slenderness ratio (m,n,l), for the design of slender columns, and nondimensional interaction diagrams (md,nd) and (nd,mdx,mdy) , for compression plus axial and biaxial bending of sections, are constructed in this work. The diagrams were constructed for concretes with strength between 50 MPa and 80 MPa, adopting suitable stress-strain relationships recommended by the CEB Model Code 1990. The diagrams for slender columns were constructed with the aid of an existing computational program developed in an earlier thesis, while the diagrams for the design of sections were constructed with a new program, specially developed in this work. The results have shown that all these diagrams are affected, even when presented in a nondimensional form, when stress-strain diagrams with ecu dependent of fck are adopted. The use of traditional nondimensional interaction diagrams, constructed with ecu constant and equal to 0,0035, may lead to errors against structural safety.