If you look to the regs for §168, to which §179 refers, you will see that the definition is to be found under §1.48-12(b)(3)(iii), which very clearly stipulates (especially when read in conjuction with subparagraph (ii)) what forms part of the internal structural framework and what does not.

Definition of internal structural framework. For purposes of this section, the term “internal structural framework” includes all load-bearing internal walls and any other internal structural supports, including the columns, girders, beams, trusses, spandrels, and all other members that are essential to the stability of the building.