The design engineer rather than the code would establish the joint type. CJP or PJP..... It’s a pretty safe bet that CJP would be selected.
On an inside corner joint a backing fillet might serve the same purpose as a backing bar. Place backing weld, gouge to sound metal from the other side, clean gouge, weld CJP.
If D1.1 is the constitution code, there are prequalified details that might be used.