Toshio Iwasaki

An Analysis on Applicability of Fatigue Data to Design of Offshore Tubular Joints

Fatigue strength of welded tubular joints is one of the most important items in the design of offshore structures. Various design formulas have been proposed both on the stress concentration factors and on the fatigue failure life. However, most of these design curves do not involve any informations on the relationship between the crack initiation life Nc and the failure life Nf, nor on the relationship between the fatigue design curves and the detailed procedure of hot spot stress estimation.This paper presents a reanalysis of fatigue data of various welded tubular joints obtained in Japan. The relationship between the fatigue crack initiation life Nc and the failure life Nf was examined in wide range of fatigue life. Scatters in fatigue life estimation were also examined in relation with various procedures of hot spot stress estimation : 1) measurement, 2) finite element method, 3) Beales formulas and 4) Kuangs formulas. Applicability to design is discussed with reference to the confidence limits of fatigue lives Nc and Nf.