composite steel box girder
"No element can be designed. Make sure that Element, Section and Material types are Beam, Composite steel-I, and SRC respectively. In addition, check whether Rebar Data is defined."
Same problem in performing Composite Design in the Design tab everytime I use the Steel Box Type II section. I prefer this type because of unsymmetrical deck slab. Using SPC gives me the same error. However there is no problem when I use the Steel box type 1.
Apparently, you are trying to design it as per AASHTO. At the moment, Steel Box Type II sections and SPC sections are not supported for design. Hopefully, it can be supported in the future release.