skirt supported vessel - seismic calcs

huangyhg

skirt supported vessel - seismic calcs
when using table 9.14.5.1.1 of asce 7-02 what would you use as a value for r when calculating the seismic loads.  there are two areas of the table the could apply.  the 4th line of the table is for elevated tanks, vessels, bins, or hoppers.  here a value of 2 is suggested for irregular braced legs single pedestal or skirt-suported.  the 12th line suggests a value of 3 for all other steel and reinforced concrete distributed mass cantilever structures not covered herein including stacks, chimneys, silos, and skirt-supported vessels that are not similar to buildings.  
so, what would be the correct value to use for a tank supported at grade by a short skirt?  i would lean towards using 3 because i feel that the value of 2 is for vessels supported inside buildings or other structures, not at grade.  any thoughts would be appreciated.
we typically use r = 2 for this application.  just our interpretation.  this is because we consider the tank (silo for our applications) elevated and thus falling under the elevated tanks, vessels, bins, and hoppers section.
as best i can tell, in both the 02 and 05 versions, this is just a flat-out contradiction that should be addressed by the code people.
tanks supported in a building are covered under mechanical equipment, rather than here.
for cement silos and bins i generally use r=3 for braced and unbraced supports if relatively uniform in the general arrangement.  frequently they are not in which case i would think r=2 applies.  however, the last two lines in the "elevated tanks, vessels, bins, or hoppers" section are for welded steel or concrete in which case i wonder what the first three lines are about.  maybe bolted steel?  i must have missed something elsewhere in the code.
i'm just a one man office so i haven't really discussed this yet with anyone.
just thought i'd mention it.
regards,
-mike