2002 NEC 250.104(C) Structural Steel.
Exposed structural steel that is interconnected to form a steel building frame and is not intentionally grounded and may become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or the one or more grounding electrodes used.
The bonding jumper(s) shall be sized in accordance with Table 250.66 and installed in accordance with 250.64(A), (B), and (E).
The points of attachment of the bonding jumper(s) shall be accessible.
Also, NFPA 780 Lightning Protection gives some meaning to the term "Structural Steel".
I could not find any specific definition in the NFC.
Anyway here is something I would use for now:
"From NFPA 780 - Structural steel frame construction utilizes a skeletal framing system consisting of large-load-carrying girders, beams, and columns for structural support.
These components represent a substantial weight factor for individual and assembly components.
Floor systems consist of cast-in-place concrete slabs of varying thicknesses poured onto metal pans or structural metal floor decks and also might include precast and posttensioned concrete plank systems.
These concrete/metal pan floor assemblies are supported by the structural steel framing system."
Note: Metal studs are not considered "structural steel", however they are subject to becoming energized, that's why we have to use a listed grommet in the "razor edge holes" of them when using romex.
Here in Massachusetts some time ago, long before I found my why to "NFPA in Quincy", there was an electrocution because of a metal stud that was energized.
I believe electricians had to bond all metal studs with an EGC per 250.122 for some time, and then the Mass Elec Code rule? was changed to call for a "metal box" to be used as the first point of supply where the "home run of romex" would be connected.
I personally would encourage use of metal 4 inch square boxes, because the EGC will provide the necessary bonding.
That would make me feel a little better.
Why don't someone send in a proposal on that issue to NFPA for the 2005 NEC?
[This message has been edited by Joe Tedesco (edited 09-11-2002).]