Service loads. Typically, in API-650 and AWWA D100, you use the seismic design loads with allowable stress, with allowable stress increased 1/3 for seismic.
I agree that the loads of Appendix E are service loads.
Be carefull in applying the 1/3 increase in allowable stresses. Codes are eliminating the 1/3 increase. AISC has removed this from their specification.
IBC2003/ASCE 7-02 allow the use of API design codes with use of allowable stresses noted in these codes but specifically state that no increase in stresses is allowed for load combinations for allowable stress design.(See 2.4 of ASCE 7-02)
After spending a few minutes reading through ASCE-7 (and what a garbled mess it is), it's still not clear what stresses would be used there. Section 2.4 does say not to use 1/3 increased stresses "unless it can be demonstrated that such an increas is justified by structural behavior caused by rate or duration of load". But then it also uses a 0.7 factor on seismic loads, so the loads themselves aren't really comparable either. 9.14.1.2 says "Where applicable strength and other design criteria are not contained in, or referenced by Section 9, such criteria shall be obtained from approved national standards", and those standards contain the 1/3 increase.
API and AWWA both give clear-cut methods to use for calculating seismic loads, whereas ASCE 7 drops the ball on the issue. Which is truly ironic, given that the entire purpose of the standard is to specify required loads.
Life used to be so simple. Without offending anyone here I'd like to opine that the one-third increase was simple to understand and simple to use. And it worked.
Even though the API loads are service level, the tank bottom plate resistance is based on plastic action.
