A New Cracked Cylinder Element to Predict Elastic-plastic Behavior of Offshore Structural Systems

Cylindrical shells are a sort of main structural members in naval architecture and offshore structures． Due to heavy cyclic wave loads，fatigue cracks as a kind of common and dangerous damage to safety may occur in the construction．Therefore the research on the cracked cylindrical shell is always a hot SUbject．In general，some material with suficient ductility is used for these structures， then it is possible that there is a large plastic area around the crack front before the crack growths． Thus it is necessary that elastic-plastic analysis of fracture is applied in this case． On the other hand，the evolution of the cracked cylindrical members under loading is closely related to the structural system ，which contains the members．Thus elastic-plastic analysis of the structural system containing the cracked members as a whole is required．However such a calculation by means of the ordinary finite element method is a task of enormous efforts due to the crack existence and nonlinearity．Therefore it is necessary to develop a new structural element considering influences of the elasticplastic crack with the least unknowns．In this paper，incremental derivation is performed to Sanders elastic-plastic analytical solutions for circumferential through-cracked cylindrical shells． The explicit relationships between nodal force and displacement are obtained． The relevant element stiffness equation in tangential incremental form is established．The new element provides the ability to predict the elastic-plastic behavior of structural system with cracks on a necessary theoretical base．