Chapter 18 - Fatigue Loading and Stresses

Abstract

This chapter discusses fatigue loading and stresses. Marine structures may be exposed to a variety of loads during their life cycle. The loads are commonly classified as functional loads, dead loads, live loads, environmental loads, sea loads, wind Loads, seismic loads, and accidental loads. Fatigue loading is one of the key parameters in the fatigue analysis. The objective of this chapter is to present a general procedure for long-term fatigue stress, described using Weibull distribution function. In this chapter, fatigue loads for ship and offshore structures have been discussed for simplified fatigue assessment and spectral fatigue assessment. For ship structures, key fatigue loads are the global wave loads local pressure and internal loads. These fatigue loads are applied to a structural response model. The fatigue loads may be applied using simplified fatigue assessment and spectral fatigue assessment. Areas that required future research include calculation of the loads accounting for nonlinearities, development of a theoretical method to combine high-frequency and low-frequency responses, development of hull-stress monitoring system that may link ship's service experience with anticipated fatigue failure, and quantification of uncertainty in load predictions including load combinations. This chapter presents three approaches for the estimation of long-term fatigue stresses that will be used, respectively, by the subsequent chapters. They are long-term fatigue stress based on the Weibull distribution, long-term fatigue stress based on the deterministic approach, and long-term fatigue stress based on the stochastic approach.