In previous editions of API 650, the failure of anchorage system was implicitly limited with the yielding of anchor bolts (which is ductile failure). That is, other failure modes ( pull out of anchor, concrete shear failure, chair failure, tearing of tank shell ...) are implicitly forbidden with limiting the allowable Shell Stress and Anchor Attachment with 170MPa. for seismic , wind and test cases.
The design approach for the previous versions was, to limit the allowable stress to 170 MPa to warrant the bolt will yield before the tank shell or chair yields. That is, after selection of anchor bolt (with the applicable load cases ) one can design the attachments, anchor chair with using the anchor bolt tension capacity.
The new version of 5.12.13
IMHO, the new version explicitly states the requirement for ductile failure with limiting the anchor attachment design load to yield strength of anchor bolt or 3 X seismic design uplift load per anchor.
The multiplication with 3 , ( which is the average of Response Modification Factors for ASD Methods ) to obtain elastic seismic force , that is to keep the anchor attachment , shell , anchor chair still elastic when anchor bolt yielded.