Are you bonding the Building Steel to the Electrical system via a connection at the Sub Panel, or are you planning to ground the Sub Panel by bonding it to the grounded Building Steel?
If Bonding the Steel to the Grounded Electrical System, then do so via approved lugs and bolt sizes according to the lug. Torque all to the specifications only ONCE!!! Do not re-torque the lug.
If the bolt used to land the lug snaps off when torqued, find a better bolt!
Maybe someone can suggest what to do here. I have broke bolts during torquing, but they were few and far between [and sometimes the "Cheap'os" from the Home Depot's open bins].
Lugs have been known to strip out during torquing. Can't really elaborate much on this one except that "Doo-Doo Occurs"
Now, if you are planning to ground bond a panel by connecting it to a grounded Steel frame, this would be something that falls under 250-32.
Could you expand a little more on your topic?