Assessing the net section resistance and ductility requirements of EN 1993-1-1 and EN 1993-1-12

In Eurocode 3 the strength functions are derived from simple engineering models, which always require a certain degree of material ductility. With regard to high-strength steels and the accuracy of the design models themselves, several problems are involved due to a lack of sound consideration of the plastification and damage process. Additionally, the current ductility requirements of EC3 obstruct the use of high-strength steels with fy > 500 MPa. Within the current revision of EC3, comprehensive investigations have been conducted to overcome these obstacles. To complement extensive experimental tests, improved numerical methods considering damage mechanics have been used to predict the real plastification and damage process for relevant details. The numerical models were validated by comparing them with experimental results. Subsequently, a parametric study was conducted to investigate the influence of strength and toughness properties separately. It could be shown that the reduction factor of 0.9 to account for the net section resistance can be omitted if cracks can be excluded. Furthermore, it became clear that a strain requirement based on the uniform elongation &egr;u is not appropriate. Moreover, it was revealed that the yield ratio fu/fy has a significant impact on the toughness requirements necessary to reach the full net section resistance. Owing to a lack of minimum upper-shelf toughness requirements in delivery standards, which would secure an appropriate inner damage resistance of the material, a substitution criterion is proposed.