Evaluation of ductility limits for structural steel design

Abstract

Structural steels used in buildings and infrastructures have to meet ductility requirements of the design codes to ensure the constructional steelwork ability to resist localized stress concentration in details and cyclic loads. Such requirements are usually minimum ultimate-to-yield strength ratio, uniform elongation and elongation at failure. While not usually a problem for ordinary steel grades, fulfilling these general criteria tend to be difficult for new high-strength grades. This paper presents a refined method for evaluating the ductility requirements, which can be applied for structural details in particular design situations. Such limits might be easier to satisfy than general criteria. The method was applied in a large parametric study of details with circular hole or notch in tension and several selected cases of bended beams with circular holes in their lower flange. The results of the study are formulated as alternative ductility criteria including the new concept of minimum difference between the elongation at failure and uniform strain, the “necking capacity”, of the tension coupon.