A616 was withdrawn in 1999. I would be concerned since quite a few thing have changed since then. When it was withdrawn, there were two grades, namely 50 ksi and 60 ksi, so you may be looking at a much older version.
As far as A996 is concerned, is there a reason you are looking at A996 rail steel instead of A615 billet steel. A996 bars are not widely available. Also, true rail steel bar are not typically fabricated (only cut to straight lengths), since these bars are not as ductile as other types of reinforcing steel.
Thanks TXStructural, You are correct, this spec I am looking at was written a long time ago. It is used for fabricating pipe anchors. I have attached the pdf file.
DO NOT WELD A996 or A615. Particularly in rail steel, the carbon content is too high for proper welding. While A615 can be welded, it does require special pre- and post-weld procedures (and the associated expense.)
Specify ASTM A706 reinforcing bar, since it is weldable when work is done to AWS D1.4. Or use another weldable bar stock if deformations are not required.
Also, be sure the radius of bend is within the limits for the material. Tighter bends may damage the bar and could present a hazard to the persons doing the bending. The radii/diameters shown in CRSI publications or ACI 318 are sized for the steel ductility AND for the concrete inside the bend. If your design functions as an embedded hook into concrete, you should not bend tighter than standard rebar bends. Where concrete crushing inside the bend is not critical, tighter stirrup bends can be used.
It's not so much the standard as what we know about the materials, and the evolution of the materials involved.
In particular, the nature of rail steel changed as steelmaking changed and as the demands on the rail changed. Heavier wheel loads, attempts at increased durability, and advances in metallurgy demanded a change in related ASTM specifications. The rebar spec most likely changed when the kinds of retired rail steel and the processing methods changed.
ASTM specs change in response to the supply, not typically because of changes in demand. The dynamic of this is that it is the producers who sit on ASTM committees, because those are the people committed to the work. If structural engineers were more involved in the A01.05 subcommittee (I was the only structural engineer with recent design experience at each of the ASTM A01.05 meetings I have attended. CRSI now has a another design engineer liaison to the committee.)
As an off-topic example, I am on the newly formed F44 committee on general aviation aircraft, as a pilot and consumer. This group meets during different ASTM committee weeks from A01, so if I attend, it will be at my own expense. The organization of the committee and subcommittees will be run by the industry (mainly the manufacturers of certified light aircraft) which may or may not represent the interests of the consumer very well. This happens because they have the funding and need to "control" their industry. They know what people buy, but what people buy is what is being currently manufactured. To correlate this to our industry, the industry produces a product and contractors buy the product. When the available scrap supply, or energy prices, or environmental regulations require changes to steel making, the producers will change the ASTM. The main parameter engineers specify is yield strength, followed by weldability, and then ductility (for seismic uses.) Producers try to respond to market pressure (higher strength, for example), but there are complications, like ACI 318, which limits the use of high strength bars for functional and safety reasons. Without good coordination, there can be a disconnect between supply and demand.
