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Old Metal Building - Tapered Moment Frame

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Hello everyone, 
I'm looking at an old metal building (~20 years old, this is a guess) to which new rooftop units need to be placed upon.  The building system consists of tapared beams ranging from 24" deep to 31" deep w/ 6" wide flanges (tf = .3" and tw=.25").  4 bolt stiffened moment connections at midspan (max span = 46'-0") and over the columns and full welds connecting the tapered sections at about 8'-10' from the columns.  Z-sections at 4' o.c.
Can I analyze the beam lines as a continous beam w/ supports at the column?  Which would mean the largest moments should be at midspan and at the columns.  This makes sense to me and confirms the 4 bolt stiffened connections at those locations. 
My main question is did they use 33/46/50 ksi steel for these things?  I tried looking for a shop stamp on the beams, no luck.
These metal buildings sure are designed to the gnat's ass, aren't they?  I'm guessing that these beams will have to be reinforced w/ plates.
Alden Manipula
Structural E.I.T.