For steel with a nominal fy less than or equal to 460 N/mm² and greater than or equal to 275 N/mm² the design yield strength is adjusted to account for material thickness according to Table 3.1, BS EN 1993-1-1:2005, EN10025-3 rules. Both nominal and design Fy appear on all design output. Steel with a nominal fy larger than 460N/mm² or less than 275 N/mm² is assigned no design yield. For steel with a nominal Fy outside of the ranges specified no steel material will be found and the section will be assigned a small yield strength and fail in design. A large interaction value on a design is indicative of assigned yield strength outside the ranges indicated above. Yield strength depends on the thickness of the elements (flange, web etc) of the cross section being designed. Refer to table 3.1 of BS EN 1993-1-1:2005 for details on the material and yield strengths for different thickness elements.