z factor and aci 350-01
 

"z" factor and aci 350-01
a couple issues i am hoping you guys can help me with regarding the z-factor as defined in the aci 350-01 code.
first regarding the upper limits of 115 and 95. if you have a concrete tank with a precast roof do these factors apply to the roof as well or only to the components in direct contact with liquids?
second, if these limits can not be met with passive reinforcing can post-tensioning be used to reduce "z"? if so is it simply a matter of revising the flexural stress in the rebar to reflect the effect of the tensioning and recalculating "z"? or is it more complex than that?
i would appreciate your input.
thanks,