ssc-367 - Ship Structure Committee

The different methods and their applicationsequences are discussed
in the following sections.
4.1.2
Simplified Analysis and DesictnMethods
The simplified analysis and design methods applicable to ship
structures and offshore structures are based largely on both
theoretical knowledge and past experience and account for the
environmentlikely to be encountered. Typically, ship hull girders
are designed to resist maximum bending moments due to still water
plus awave-induced conditionderivedfrom harsh North Atlanticwave
data (Reference 4.1). The basic hull girder, designed for the
extreme environment loading, is intended to have ample crosssectional
area and moment of inertiato keep the magnitude of stress
reversalslow and exhibit low susceptibilityto fatiguedamage. The
minimum plate and scantling sizes specified and the detailing
developed are intended to keep the nominal and peak stress ranges
low to prevent fatigue failures in the secondary members. In
addition,steel is specifiedto ensurethat its chemical composition
and mechanical propertieswill make it less susceptible to fatigue
failure.
Similarly, offshore platform joints are designed to resist maximum
punching shear and crushing stresses. The joint details are
developed to minimize the SCFS and cyclic stress ranges to make them
less susceptible to fatigue failure. Such an indirect approach to
fatiguedesign shouldbe supplementedby an empirical approach based
on constant stress range cycle fatigue life test data.
ShitIStructures
An allowable stress method for ship structuredesign should be used
to assess applied stresses against allowable stresses. The
objective of applying the method is to identify those conditions
that requireno furtherfatigue assessmentand those conditionsthat
require more comprehensive fatigue analyses.
4-2