In trusses most of the weight is in chord members, so using high strength steels in chords is crucial for weight and cost savings. On the other hand, the brace members bring in lot less of the total mass, while fabricating them creates most of the fabrication costs. So it pays off to use milder steel grades in braces so the welding can be done according to milder steel grade. This has been proven as the most cost efficient truss design in various analyses, especially with long span trusses. Using hybrid design is especially easy with SSAB Domex Double Grade hollow sections (link to product page), as it comes with two test certificates, one for S355J2H and second for S420MH, so the designer can choose the best alternative for each particular case.
Selecting the right material for the chords (and braces) is case sensitive, but in many cases using Strenx Tube 700 has proven to be the best choice. SSAB has a CE marking to all its hollow sections up to Strenx Tube 700, also welding to cold formed corners is allowed. For more information see the design guide (link to article at hollow section landing page) and our design guides (link to hollow section landing page).
High resistance columns from SSAB’s hollow sections
SSAB manufactures cold formed and welded hollow sections, which according to EN 1993 (Eurocode 3) fall into buckling curve c (curve a or b in concrete filled columns). The buckling behavior of steel columns leads to situations, where utilizing high strength steels is difficult especially with longer and slender columns, in these cases the geometry dictates the performance.
However, the SSAB Domex Double Grade hollow sections have been tested for their compressive strength and have been granted buckling curve b (link to document at hollow section landing page). The higher strength of the tube gives benefits with shorter columns and improved buckling curve with longer ones. The combination creates a very high resistance and cost efficient column.
For even more stressed columns SSAB can offer hollow sections up to steel grade S700MH (Strenx Tube 700) with wide dimensional range.