Research On Anti-Racking Design Concept And Racking Strength Assessment Method Of Large Car Carrier

Car carriers are specially made for transportation of cars or other vehicles, can also alarge ro-ro goods, it is a kind of high tech and high value added ship type. The history of itsconstruction and operation is about30years or so. Car carrier belonging to the ro-ro category,but because of the particularities of the carriage of goods, the ship-type layout, especially thestructure is of speciality, such as high molded depth, more decks, spacious cargo hold areawithout transverse bulkhead, and the ability of the entire hull to sustain transverse strengthdepends mainly on the transverse frame. If incorrect design, due to the Racking deformationin the state of heel, transverse frame at the side joint areas are easily torn risk of damage, sodue attentions should be paid to transverse strength of car carrier.According to the resistance of transverse force, there exist two different structural designconcepts for car carriers: rigid design and flexible design. The former means that the verticalside webs are in line with the deck transverses, a considerable fraction of the Racking momentcreated above the freeboard deck is then mainly to be carried by the frame section itself; thelatter means that the vertical side frame is not in line with the deck transverse girder, the bowregion and the stern are then activated and contribute as Racking constraining structuretogether with other main structure such as engine casing. Two design concepts have differentfeatures. Based on the example of the6600car carrier, the structural characteristics, directcalculation method, simplified analysis method and difference between the two designconcepts are further studied in this paper by using global FEM analysis. The contentscompleted in this paper are as follows:First, the car decks which are the main loading members of car carriers are analyzed. Theplans and particulars for design of car decks are thoroughly discussed, then, by theoreticalanalysis and calculation of examples, the difference among different Class Rules for car decksis studied. Also, the difference between the two design concepts for car decks is clarifiedbased on results from3-D beam analysis; and the design procedure of car decks issummarized.Secondly, the Racking strength analysis method is studied about two different designconcepts based on DNV rules, including structural modeling, load applying process, boundarycondition as well as the stress assessment; according to the vessel, the flexible design carcarrier global hull Racking strength is studied, including stress distribution characteristics, size of transverse deformation and the range of hotspot region; then, the flexible design ismodified to conventional rigid design, the global FE model and cargo hold model in Rackingcondition are analyzed, and, the differences among different boundary conditions of cargohold model in rigid design are clarified, and the difference between rigid design and flexibledesign of the finite element analysis of the whole ship.Finally, on the basis of the finite element analysis of the whole ship，how to adopt asimplified Racking assessment method to estimate the Racking strength in flexible design carcarrier at the beginning of design is discussed. And, the load, stress and deformation resultsobtained by simplified assessment method are same as the finite element analysis of the wholeship. Therefore, the simplified method can provide a reference for the corresponding structurearrangement in flexible design car carrier at the preliminary design stage.