Is this a column? The word stirrups is throwing me - I usually think of column "stirrups" as ties, but it's pretty uncommon to have a circular stirrup in a beam. I don't think you can have spiral reinforcing at 9" o.c. Every time I've worked on a column or caisson that used spiral reinforcing, the minimum required a max "spacing" (so to speak) or around 4 or 5 inches.
Probably is a column, and tie is the correct term. But I don't know why a spacing of 9" is a problem. The spacing or pitch of helices is normally controlled by the same rules as for individual ties. Haven't looked at the ACI Code, but the Australian code AS3600 requires the spacing of either to be limited to not greater than the column diameter or 15 x column vertical bar size.
Detailed on of these the other day with ties with a 300 pitch (12"). Unless you are relying on the column or pile to resist a large shear force there is really no need to go any closer than a 9" pitch that you suggest.
Like hokie recommended, if it is a pile make sure they have and extra flat turn at the bottom for full development.
ACI has a minimum volumetric requirement that, if you use #5 or larger, may be ok with a larger pitch. For number 4, it is difficult to get that allowable pitch higher than about 7" (using a reasonably sized column). Additionally, ACI has a max clear spacing requirement between spirals of 3". That seems awfully tight, but it is in there (7.70.4.3).
I have seen spiral tie reinforcement at 8" pitch in practice here in the top six meters of in situ drilled piles of concrete, then injected from the axis of the helical drill. More nominal than anything, no particular bending assumed. The detail may be supported by the Normas Tecnológicas de la Edificación (NTE), some set of nonenforceable yet official codes making recommendations to improve the quality of buildings in Spain in the seventies.
Attention to shear in building columns has not been precisely a favorite theme; even the more used program for building structures here (CYPECAD, which is by now quite an achievement from the viewpoint of entry of data and detailing, so the production of plans) has started to contemplate the check some years ago (not many). This is not to say the EHE code was negligent, that was not; more a thing of practice.
Maybe that's the difference. ACI allows a higher phi factor for spirally reinforced columns. This is based on the idea that the spirally reinforced column core with the cover spalled off will be AT LEAST as strong as a comparably designed tied column without the cover spalled off. The spirals are counted on for confinement - it's more than just a qualitative recognition that there is a difference between ties and spirals.
I have never looked into that possibility, but I don't think so. The reason is that ACI has, in addition to the volumetric rho requirements, a max clear spacing between spirals which is pretty restrictive.
This issue intrigued me, so I looked it up in ACI318-08. The way I read it, you are certainly correct for a "spirally reinforced column" to get the higher capacity. But I think you can use the provisions for a "tied column", with a spiral used as a "continuous circular tie" with the same pitch as the required tie spacing. See the Commentary to Paragraph 7.10.5.
You got it right, this what I was looking for, I have drilled piers with 4 #5 bars to be tied up at 9" OC -- the spiral with 9" (or less) pitch will do the job.
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