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RE: Old pan joist system

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I have a copy of an article entitled "Reinforcing Bar Specifications - 1911
through 1968" by Gustav G. Erlemann. It was published by the Portland Cement
Association. I believe it came from a publication called Engineered Concrete
Structures. However, I am not sure and I don't know the date of publication.
I only have the 2 pages from that article.

The first Standard Specifications for Billet Steel Concrete Reinforcement
Bars was adopted by ASTM in 1911 and revised in 1914. Apparentlly, no
modifications were maded until 1928 when the US Department of Commerce made
some recommendations. Three clases of bar were specified:
1. plain
2. deformed
3. cold-twisted
For plain and deformed bars three grades were available:
1. structural 33 ksi yield
2. intermediate 40 ksi yield
3. hard 50 ksi yield
The paper states that a conservative estimate of stell grade between 1910
and the mid 1920's is structural.

-----Original Message-----
From: John Riley [mailto:jpriley485(--nospam--at)]
Sent: Wednesday, January 10, 2001 9:03 AM
To: seaint(--nospam--at)
Subject: Old pan joist system

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