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Old Concrete Design

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Richard,

Back in the "old days" (not necessarily the same as the "good old days") the 
specification for deformed reinforcing required that two specifications be 
called out.  The first specification, A15 or A16, covered material specs for 
*deformed and plain* reinforcing and A305 covered the specs for 
deformations.  If only A305 was specified, then there was no material 
specified, but I will assume that it is A15.  (Put a "6" before the 15 
or 16 and you would have the comparable current spec.)

ASTM A15 had three different grades of reinforcing, Structural, Intermediate 
and Hard, with yield strengths of 33,000, 40,000 and 50,000 respectively.  
A16 (Rail steel reinforcing) had only one grade and the yield strength was 
50,000 psi.

With regard to the bent bar question, it is a question of economics.  The 
cost of placing bars is more than the cost of the steel.  Placing straight 
bars is easier and faster than placing bent bars.  The premise in using bent 
bars was that as positive moment reinforcing bars approached the support, 
they could be reduced.  Similarly, negative moment reinforcing needed to be 
increased, so why not bend the bar up to provide negative reinforcing.  And 
while the bar is being bent up at a 45 deg angle, that part of the bar can 
also be used to resist shear.

Referring to the 5th Edition (1956) of the AISC manual, store live loading 
would be 125 psf.

Hope this answers some of your questions.  Remember, *all* concrete in 1955 
era was designed by WSD.  As such, some of your lap/splice lengths will be 
nowhere near the lengths currently required as all the laps/splices were 
required to do was to transfer, with an appropriate factor of safety, the 
working stress in the reinforcing.

Roger Turk, P.E.(Structural)
Tucson, Arizona

Richard Lewis wrote:

. > While we are on the subject of Old Timers for steel, I would like to ask a
. > concrete question for the same group. 
. > 
. > I am working a renovation project of an old department store structure 
. > built in 1956 or 1957. It is a flat slab, 2 way construction.  The 
. > general notes state the reinforcing steel is ASTM A305 and state the 
. > following:
. > 
. >      Only Rail or Hard Grade shall be used for column verticals.
. > 
. >      All other reinforcing may be intermediate grade steel.
. > 
. > What does this mean?  What is the yield strength of rail, hard and
. > intermediate steel?
. > 
. > Also, older concrete design typically used bent truss bars, bending the
. > bottom bars up to top bars as they neared the support.  I am pretty sure 
. > we don't do that anymore.  Unfortunately my experience in pure concrete 
. > frame design is limited so I'm not totally positive about that, but, why 
. > don't we use bent bars like in the olden days?
. > 
. > There is not any indication on the drawings for Live Loading.  I would 
. > assume it was designed for at least 100 PSF, but I need to do some
. > calculations to verify it. Do any of you remember what the code 
. > requirements would have been for a department store designed in 1955?
. > 
. > Any other suggestions that would be helpful in working with older concrete
. > buildings would be appreciated.
. >