Design of hybrid steel girders

• Published in: Journal of constructional steel research 2004-03, Vol.60 (3-5), p.535-547
• Main Authors: Veljkovic, M., Johansson, B.
• Format: Article
• Language: English
• Subjects: Design; Economy; High strength steel; Hybrid girder; Steel Structures; Stålbyggnad
• ISSN: 0143-974X; 1873-5983; 1873-5983
• DOI: 10.1016/S0143-974X(03)00128-7

A hybrid steel girder is a welded girder with different steel grades in flanges and web. Usually, the flanges are made of high strength steel (HSS) like S690 and the web of a lower grade say S355 but combinations like S460 and S355 are also used. Such girders are more economical than homogenous girders. Hybrid girders have been used in the US since long but they are not commonly used in Europe. Some examples of the use of hybrid girders in Sweden are presented together with economic comparisons. Design rules for hybrid girders are presented together with justifications. Typically, hybrid girders are of cross-section class 4 according to Eurocode 3. The resistance in bending in ultimate limit state is influenced by the local yielding of the web, which limits the stresses in the web and affects the effective width of the web as well. Simplified formulae for the bending resistance are presented. For serviceability limit states, the local yielding of the web has to be accepted but the requirement of reversible behaviour will still be fulfilled. For the limit state of fatigue, Eurocode 3 states a restriction that the stress range should not exceed 1.5 times the yield strength. For hybrid girders, it is shown that this restriction applies to the yield strength of the flanges and that yielding of the web does not influence the fatigue strength.