The paper describes a simplified technique, based upon an extension of the upper bound shakedown theorem, for the evaluation of ratchet boundaries for a plate subject to a through-thickness temperature transient and in-plane loading. The study of a range of cases indicates that transient effects can have a significant effect upon the deformation properties and that strain growth can occur for zero applied loads at quite moderate levels of thermal loading. As a result the identification of transient thermal stresses as F stresses in ASME design codes does not seem acceptable.