The Reference Stress Method in Creep Design

In the 1970 Iutam Symposium on Creep in Structures, Marriott [1] reviewed an astonishing new and simple technique for predicting creep deformations — the reference stress method. Originally devised by Anderson, Gardner and Hodgkins in 1963, in the form suggested by Mackenzie in 1968 the method maintains that steady state creep deformations in a component could be related to the result of a single creep test conducted at the so-called reference stress. In 1968 Sim had demonstrated that the reference stress itself could be derived from the limit load for the component. At the same time several researchers also noted that the reference stress was related to the stress at the skeletal point — a location in a creeping structure where the stress scarcely varied during creep — this was further discussed by Anderson [2] in the 1980 Iutam Symposium. During the 1970’s and early 1980’s there was considerable activity in the United Kingdom to verify and extend the capabilities of the reference stress method beyond steady creep; this was summarized at the time [3,4]. Eventually a robust procedure for high temperature life assessment was derived — this is elegantly summarized in the monograph by Webster & Ainsworth [5]. Apart from this, interest in the reference stress method has declined somewhat during the past decade — it was barely mentioned in the 1990 Symposium.