Floating production vessels are planned to mainly be on the same location without scheduling any shutdowns for maintenance and repair. This implies stricter requirements to a reliable fatigue design than the standard procedure that is used by the ship industry, with inspection and repair every fifth year. One of the areas that has been subject to improved fatigue design requirements is scallops in a three perpendicular plate intersection. A general model applicable for several structural details in ships is used in the present study. Four different methods of calculating hot spot stress have been considered. Five different geometries of scallops have been modelled by three-dimensional 20 node isoparametric elements and analysed. The results from these analyses are presented and discussed in this paper.
Different damage reports show that fatigue cracks initiate at ends of brackets, scallops and other irregular geometries in ship structures, see e. g. Tanker Structure Co-operative Forum (1997). Scallops in comers of plates are primarily used for efficient construction and drainage. They are primarily situated in two or three dimensional intersections where a weld is passing. They are made to make the fit-in process easier. Besides the term "scallop" also designations such as "cut-out" and "mouse-hole" are used for these details. Scallops are used in several types of welded structures with plate intersections such as ships, offshore structures, steel bridges, etc. Therefore it is important that such details are assessed with respect to fatigue at a design stage to avoid problems during service life. After fatigue cracks at such regions have been detected it has also been questioned how to most efficiently repair those who have cracked and improve the other details such that the structure achieve sufficient reliability with respect to fatigue for a further life.