Fatigue of Maritime Structures – A Wider View

Maritime structures were traditionally designed for static maximum loads (design loads). However, ship and offshore structures are very much subject to dynamic loads, coming from, Fig.1: propellers and diesel engines excite elastic vibrations in local structures. The number of load cycles is usually much higher than for those due to seaways. Seaways excite local changing pressures. Typical frequencies are 0.1 Hz leading to load cycle number of 10 to 10 over the life span of ships. In addition, sudden impacts in seaways (slamming) can trigger ship vibrations called “whipping”. Changing loading conditions (cargo and ballast cycles) yield few load cycles with high stress amplitudes In extreme cases, fatigue failure can lead to total loss of offshore structures or ships, Fig.2.