wisted rebar

huangyhg

"twisted" rebar
i think there's a thread out there somewhere about this one, but i couldnt find it in the search.
i've got a one way concrete slab.  the reinforcing is approximately 1 1/4" x 1/4" flat bar that is twisted like a cork screw.
does anyone know if there's a name for this type of rebar, and approximately when it was used for slab construction?  all i can find is square bars that are twisted and used for rebar, and no date on about when that was used.
i think crsi has a data sheet on old rebar usage.  i'm not at my office right now but i'll see if i can dig it up tomorrow and post whatever i find.
twisted bar was used at the beginning of the last century for reinforcing.  the twisting imparted a bit of a bond as well as strain hardened the steel... it's not likely that you will be able to obtain any reliable information on it.  if critical, cut coupons and test them, else ignore the existing reinforcing and fix accordingly.
i've encountered one project where the beam reinforcing was twisted and bundled... the bundle still had on the metal tag identifying the beam mark... the contractor placed it in a 'lump' not realizing that the bars should be separate.
the concrete reinforcing steel institute published :evaluation of reinforcing steel systems in old reinforced concrete structures in 1981.  try crsi to see if it is still available.  it provides most of what you will need.  
also, the portland cement association used to publish "engineered concrete structures" triannually, and an article entitled "reinforcing bar specifications - 1911 through 1968", by gustav g. erlemann, provides some additional technical data on the subject.  i would think pca would have this article in their archives.
my reference is:  handbook of building construction edited by george a. hool, mcgraw-hill, 1929.
concrete reinforcement pages 1002-1021:
fig. 36: page 1003  cold-twisted square bar. i know you said yours is rectangular, i haven't seen a ref. to that yet.  there is a table that shows round and square bar up to 1-1/4" size.
article 125, page 1003 working stress:
"the generally accepted working stress for mild steel is 16,000 psi and 18,000 to 20,000 psi for high steel and cold-twisted steel.  a stress not greater than 16,000 psi is recommended by the joint committee (1924) for all grades of steel."
article 130 deformed bars.  shows ten (10) different types of deformed bars with a table of bar areas and weights.  i haven't seen anything regarding a rectangular bar twisted to make a rebar.
hope this is of some help!