Ductility Classes in prEN 1998-1. Comparative Analysis on Eccentrically Braced Frames

During severe earthquakes, it is desirable for a structure to be able to undergo significant plastic deformations and to develop a plastic mechanism. Codes usually manage this plastic behaviour ability of structures using ductility classes. The future version of the European code EN 1998-1, defines three such classes, DC1, DC2 and DC3, which are different from DCL, DCM and DCH that are used nowadays in the present version. The behaviour factor q is better managed in this future version and the difference in requirements among the three ductility classes is more accurately expressed. Under these circumstances, numerical testing of the new requirements is necessary. The present paper focuses on differences that can be noticed when designing eccentrically braced frames according to the three new approaches. An eccentrically braced frame with short links was considered. Three solutions were obtained for the cross-sections of members, using the requirements defined for DC1, DC2 and DC3. As the “mathematical” procedure is put to test, the influence of the designer’s skills was minimised as much as possible. All three structures were designed based on resistance requirements. The material consumption and the post-elastic behaviour were observed for each one of the three structural solution and comparisons are presented.