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Due to the demand for sustainable constructions, composite structures have become more important and lead to slim and economic solutions with a low structural self-weight. EN 1994-1-1 distinguishes between four different cross-section classes for the determination of moment resistance. For the plastic moment resistance, it is assumed, that each cross-sectional fibre can plastify without any limit on the strain. For standard composite beams with sagging moments and a high plastic neutral axis, plastic resistance and strain-limited resistance give similar results. For sections with a large compression zone height x pl and limited rotation capacity, concrete failure in the compression zone can occur before the plastic moment resistance M pl,Rd , is reached. The strain limit design becomes critical. This paper points out the impact of the concrete part on the design of composite beams. A parametric study comparing plastic and strain limited moment resistance of a considerable variety of cross-sections has been carried out to develop the beam design methods considering compression zone height for the next generation of Eurocodes. [Display omitted] • Point out limitations for plastic bending resistance • Comparing plastic and strain-limited bending resistance • Parametric studies of more than 200,000 cross-sections • Considering both conventional and slim-floor composite beams\ [ABSTRACT FROM AUTHOR]