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Sanitary Structures

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I do a lot of concrete tank design and I was wondering how other engineers tackle the problem of cracking.  The process I go through is vigorous and time consuming, but I feel it is necessary.
Step 1:  Find Steel that satisfies phiMn >= Mu
Step 2:  Find the actual steel stress (unfactored)
Step 3:  Find the maximum spacing for that steel stress and bar size that satisfies Z <= 115 k/in.
Step 4:  If that spacing is less than I found in Step 1, I shorten my spacing and perhaps change
            bar size and go to Step 3.  I repeat steps 3 and 4 until I have the most economical section
            that satisfies both strength and cracking.
I've found out that most of the time if the steel stress is under about 24 ksi, cracking is ok.  I was wondering if others just use working stress design and make the whole process simpler.  I was taught using ultimate strength and I feel the need to check it even though it never governs.
Chris Towne, E.I.T.