BIAS IN THE ESTIMATION OF WAVE-INDUCED FATIGUE DAMAGE OF OFFSHORE STRUCTURES

The most widely adopted approach for estimating the wave-induced fatig ue damage of the tubular joints of offshore structures relies on a wav e scatter diagram to characterise the wave environment. This paper sho ws that the commonly adopted approach to compiling the wave scatter di agram and the subsequent selection of characteristic individual wave h eight and period pairs for analysis purposes will almost invariably le ad to bias in the estimation of fatigue lives. A statistical argument is developed to show the sources and nature of this bias. This is supp orted by fatigue calculations based on individual wave data collected in the northern North Sea. It is found that the current practice in mo st cases introduces a substantial conservative bias into estimated fat igue lives. An alternative procedure for producing wave scatter diagra ms and selecting wave heights and periods for subsequent finite-elemen t analysis is presented which should lead to unbiased (or at least muc h less biased) estimates of fatigue lives. Copyright (C) 1996 Elsevier Science Limited.