ABSTRACT

Considerations for correction of the design fatigue curves for application to the fatigue design of marine and ship hull structural details are discussed. The aim of correctionsis to allow for differences between the base-line specimen, upon which the design curve was based, and the particular structural detail geometry and loading belong considered. A numerical example illustrates the approach.

INTRODUCTION

Fatigue design of marine and ship hull structural details is based, at present, on the use of design fatigue curves, derived from comprehensive experimental data obtained from welded specimens, and the linear damage accumulation rule (Fatigue Reliability, 1982, Munse et al, 1983, etc). At first glance, this constitutes a fairly simple technique, but in reality it may require highly specialist application. Moreover, in certain instances It cannot provide an effective solution to the problems of structural reliability. The problems of Implementation of the approach are being addressed at present (Huther et al, 1992, Petinov et al, 1995) and may be summarized as following:

  • a problem is met in the procedure for identifying the welded joint in a structural detail and hence the appropriate design S-N curve

  • the present experimental database does not permit estimation of fatigue resistance parameters of a detail under complicated loading modes, e g in combined axial-bending-shear loading modes, in arbitrary plane stress fields in plating and webs at openings and welded joints, etc

  • the loading components in marine and ship hull structures are, in general, statistically dependent and the approach falls to predict the fatigue behavior of details for which the mentioned factor is essential, etc introducing of an average correlation factor, demonstrated in (Cramer et al, 1995), may serve as an approximation, but is not valid physically, in general.

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