Through a joint industry project sponsored by DNV and shipbuilder Aker Kværner Yards, a new steel-concrete sandwich concept has been developed to offer greater levels of safety for bulk carriers.
The new bulker construction method looks to exploit the claims made for high tensile steel plates sandwiching lightweight concrete. The project is currently focused on the use of the new technique in cargo holds, while the fore and aft is of traditional design. It can also be applied fully or partially in other ship types.
The concept utilises sandwich elements with steel plates as the surface skin, and lightweight aggregate concrete as core material. The function of the concrete is to support the surface steel plate and eliminate the need for secondary stiffeners.
The concrete provides a stiff spacing between the surface steel plates, and has sufficient strength to transfer relevant transverse shear forces. Bonding between the steel surface plates and the concrete core material is ensured partly by bonding and partly by dowels or connectors.
Solid sandwich elements are used in the deck. Partly hollow sandwich elements are used in the ship sides, transverse bulkheads and double bottom structure to reduce weight. The width of these elements is determined from local loads. Global strength is based on a longitudinal stiffening system with steel girders in the double bottom, the sandwich deck structure and a continuous hatch coaming beam structure.
Structural advantages of the sandwich concept are significant compared to a hull of traditional stiffened steel structures. Stress concentrations, fatigue and corrosion problems are reduced. Plate stiffeners, stringers, brackets and internal transverse structures are virtually eliminated, as are local buckling problems.