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RE: "z" limit requirement

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Dick,

Regardless of ACI paragraph 10.6.5, z *is not* required to be calculated for 
Grade 40 reinforcing.  Paragraph 10.6.4 states, "When *design yield 
strength* ... exceeds 40,000 psi, ..." [emphasis added] you have to comply 
with the z requirements.  If you base your design on a yield strength of 
40,000 psi, you don't have to comply with the z-limits.

For ordinary interior and exterior exposure conditions, it is absurd to 
provide more reinforcing than would be required if Grade 40 was used.  For 
very aggressive exposure conditions, an appropriate investigation should be 
performed by the structural engineer.

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

Dick Horning wrote:

. > But if the structure is exposed to more severe conditions than just the
. > weather, notice ACI 318-95 Paragraph 10.6.5.  Allowable z could be as low 
. > as 95 kips/in.
. > 
. >         -----Original Message-----
. >         From:   Roger Turk [SMTP:73527.1356(--nospam--at)compuserve.com]
. >         Sent:   Tuesday, December 08, 1998 7:45 AM
. >         To:     seaint(--nospam--at)seaint.org
. >         Subject:        "z" limit requirement
. > 
. >         Ah, yes!
. > 
. >         The notorious z-limit requirement!
. > 
. >         When the z-limit requirement starts requiring what I consider a
. > ridiculous 
. >         amount of reinforcing at a ridiculously close spacing, I calculate
. > the amount 
. >         of Grade 40 reinforcing that would be required and provide only 
. > that amount, 
. >         whether or not the reinforcing supplied is Grade 40 or Grade 60.
. > Z-limit 
. >         does not have to be calculated for grade 40, therefore implying 
. > that the 
. >         crack width for reinforcing stressed under service loads up to 
. > about 24ksi is 
. >         not a concern.
. > 
. >         A. Roger Turk, P.E.(Structural)
. >         Tucson, Arizona
. >