Existing Steel Stair Assesment: Rivet and Bolt size vs. head dimension?

[KirkGH]

I'm assessing an existing 4 story fireescape stair. I can't get an exact year of construction, but based on the evidence presented we're going to assume 1927.
I measured the heads and diameter where I could and here's what I'm left with.

Bolts (square head):
.394"dia. .... head
... dia. .84" head
... dia. .605" head
1" dia. .... head
1/2" dia. .... head

Rivet:
... dia. .70" head
.50" head
.88" head

I need some help converting these approximate 1927 head sizes to diameters. Any guidance?

I got material strengths from AISC design guide 15 for a conservative 25 ksi yield and 46 ksi ultimate on the steel.

For rivets I can get an ALLOWABLE 1928 value of 13.5 ksi tension and shear. But this tells me nothing about the nominal stress I need for current AISC. Any guidance?

For bolts I can get an ALLOWABLE 1936 value of 10 ksi shear. But this tells me nothing about the nominal stress I need for current AISC. Any guidance? I'm tempted to just use the old allowable values with the new allowable load criteria of current Code.

Thanks.

 

[JedClampett]

Why don't you just check vs. allowable? Don't try to fit a square peg in a round hole.