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Old pan joist system

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I am checking out an existing roof for installation of an HVAC unit.  Making
some conservative assumptions, I'd like to be able to show in my
calculations that the system is capable of carrying the additional load.
So, unless the numbers scare me, no testing will be done to ascertain
concrete strength, etcetera.

The HVAC unit will impart a line load of 160 plf on a single joist for a
distance of 7', nominally at center of span.

Concrete pan joist system:
        Design year:  1923
        10" x 2 1/2" joists  x 5" wide @ 25" oc
        Reinforcing:  1- 7/8" Dia BT  +  1- 1" Dia ST
        Span:  23' nominally

Immediate questions:
(1) What strength can I assume for the reinforcing steel?
(2) Would the bars have been deformed in 1923?

Any input is appreciated.
__________________
John P. Riley, PE, SE
Riley Engineering
20 Oakwood Drive, Blue Grass, Iowa 52726
Tel & Fax:  319-381-3949
jpriley485(--nospam--at)peoplepc.com