Hi, I had a look through the rulebook but the answer wasn't jumping out at me...

When do you add the +10 Strength bonus of a bionic arm? Before or after Unnatural Strength?

Cheers Craig

after you took unnaturak Str. in account

I had a feeling it would be, but just couldn't find it. Thank ye kindly.

After, I'd say. The robotics doesn't have unnatural strength, just like your power armor doesn't.

I believe it is neither. The Bionic arm adds +10 to strength checks, not the strength stat. So it would count for when you want to try and pick up a tank barrel and throw it at something, but not to your general damage of melee weapons and the like.