Ever since switching to the 19 version of ACI-318 in RAM Concept, I have noticed that a handful of top bar callouts above columns in our standard two-way flat slab with drop panel designs have increased dramatically. In the example pictured below, based on the surrounding columns and comparative negative moments in the slab, one would expect somewhere in the range of 4 to 6 #8 bars in each direction above the column. Concept appears to be specifying roughly that much top steel, but then is also adding in an additional (roughly) 18 #8 in each direction. This seems to happen in conditions where the laod is a little higher, and the drop panels are a little thicker. Lastly, when I switch the code year back to ACI318-14, the additional bars go away.
With all of this evidence, I Suspected it has to do with the updated minimum flexural steel requirements of 8.6.1.2. It appears to be one of the few hcanges in this version of the code that ffect flexural steel, and is related to shear stress, size of drop panel, and other factors that would correlate with the cases where the software is specifying the additional bars. The confusing part is the quantity. when I check this acse by hand, I do get that the minimum required top steel is above the As required by design, but only slightly (7 bars instead of 5, not 18). Does anyone have nay idea why this is happening?
In the example below, my column size is 16x24, my slab thickness is 14" (6ksi) and the drop panel depth is typically 24", though at the location in question it is 26". I've also attached a snip of the punching audit at this location.
