Constraint effects in R6 for combined primary and secondary stresses

In 1995, a new Appendix 14 was added to the R6 defect assessment procedure to allow an estimate to be made of any increase in reserve factor arising under conditions of low constraint. The Appendix set out two procedures, one involving a modification to the FAD and the other using a modified toughness, but was restricted to loads giving rise to primary stresses acting alone. This paper examines how the methods of R6 Appendix 14 may be extended to combined primary and secondary loadings. It is shown that both procedures may be extended in a straightforward manner. However, a remaining issue is the estimation of structural constraint under combined loading. A methodology for estimating this constraint is proposed and the results of adopting the methodology are presented. However, finite-element analyses are required before detailed proposals can be made.