There are presented in this paper the results of tests on the ultimate strength of beams subjected to combined bending and axial compression. They are compared with the collapse solutions based on simple plastic theory, to determine the correlation curves of the beams relating applied bending moment and axial compression. For ease of computations, is developed the FORTRAN PROGRAM LIST for the interaction curves of the beams with arbitrary I-section including hybrid beams. On the basis of the interaction curves, the hybrid beams, in the flanges of which high strength steel is used, are discussed from the viewpoint of cost performance.