Instead of CONCATENATE, you can just build the string:

=$B$4 & "." & $I$2

There is no way to increment automatically, but you can either refer to
another part of the sheet in your formula that has incremental numbers
ORyou can try using the ROW command which will increment as you copy
down:

= $B$4 & "." & ROW($A1)

If you copy this formula down, the $A1 reference will increment along
with the row value.

Hope that helps...