Dan,
"If the electrodes & electrode/flux combinations meet the requirements for H8, do they then also meet the requirements for H16?"...........Yes, 8 ml will of course be less than 16 ml and would therefore exceed the H16 requirement.
And I haven't read D1.8 yet but if thats the language I'm surprised. It seems the language should have stated something along the lines of equal or exceed, or minimum or something of greater clarity. But then if they made it too clear we wouldn't need consultants. OK, thats my sarcasm for the day.
"Am I correct in assuming (I hate that word) that the electrodes and electrode/flux combinations that we use for FC projects will meet the requirements for a seismic project."........Yes......As long as the diffusable hydrogen desginator of the fillers you have equals or exceeds the requirement.
All of course in my opinion.
A word of warning from one who's erected an oil refinery in a Class 4 seismic area (the one in which the worst earthquakes on earth can happen).
The whole steel structure, including its concrete foundations, must be anti-seismic, not just the welds. AISC must have some written material on that.
Giovanni S. Crisi
Sao Paulo - Brazil