24 May 06 16:03
artnkman - Here is the abstract of reference 7.15 that is referred to in the commentary:
Title: Influence of Ties on the Behavior of Reinforced Concrete Columns
Author(s): James F. Pfister
Publication: Journal Proceedings
Date: May 1, 1964
To aid development of the 1963 ACI Building Code, 11 rectangular tied columns were tested under concentric load to explore the influence of arrangement and spacing of lateral ties on the strength and behavior of tied columns. In three of the columns, full ties were provided as required by the 1956 Code, and in another three columns only exterior ties were used. Two columns had ties only at the ends and at midheight of the columns, and three columns were provided with ties only at their ends. It was found that the primary function of the ties was to restrain the concrete laterally so that it could develop its full strength in a gradual type of compression failure.
Exterior ties surrounding the longitudinal reinforcement were found to be as effective as combined interior and exterior ties conforming to the 1956 Code. It is concluded that the new tie requirements of the 1963 Code should be entirely adequate.
So this seems to be referring to the need for interior ties vs. no interior ties, not ties in general. Also, the first sentence of the commentary states, "All longitudinal bars in compression should be enclosed within lateral ties".
I don't see that you can justify going to 8" instead of 7" based on the commentary. But I do think that if the columns are over-designed a bit, that the longitudinal bars are not stressed too high under your design loads, then the few ties "missing" shouldn't be that critical.