I am trying to create a model where some of the steel is S275 and some is S355 as per the Eurocodes, how do I add this command?
What software are you using?
Staad pro V8i
If you want to create such material, go to General -> Material vertical page and click on the Create button on the right hand side.If you want to consider such steel strength during the design, use the SGR design parameter.