Use of elastic follow-up in integrity assessment of structures

This paper reviews the concepts and definitions related to elastic follow-up, Z, together with its potential use in stress classification. Based on the principles governing benchmark multiple bar structures elastic follow-up (EFU) is quantified. Local nonlinearities arising within a structure influence elastic follow-up. These include variations in the geometry of structure, its material properties, effects of plasticity and creep, structural discontinuities and boundary conditions. Elastic follow-up is shown to be simple to evaluate, is physically meaningful (as it relates strain accumulation in the structure to its cause) and is useful in design practice. In this generalised definition Z = 1 indicates no follow-up and represents a fully displacement controlled situation. In contrast Z = ∞ represents the extreme case of fully load controlled situation. Presence of mixed boundary conditions is interpreted as 1 < Z < ∞. A methodology that overcomes the singularity problem of cracked structure to determine Z is then proposed. The distinctive characteristic of the proposed approach is that it takes account of situations where the structure contains defects.