reinforcing splice lap class explanation

huangyhg

reinforcing splice "lap class" explanation
i've always used the standard aci 318 equations for determining tension and compression lap splices.  i see a lot of the newer material (specifically the 2002 crsi design handbook) uses something called "lap classes" types a and b.  type "b" being either worst case or more conservative depending on the definition.  crsi does not define what these classes are.  i could not find the definition anyway.
could somebody please explain what exactly what these classes mean and how to determine what class to use.  thanks.
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aci 318 12.15.2:  all are class b unless there is twice the required rebar or 1/2 or less of the rebar is spliced within lap length.  
the requirement is to "encourage the location of splices away from regions of high tensile stress."
yup, i see it now.  you would think that crsi would address this as well, would't you.  thank you ozzwald.