December 4, 2002

Steel concrete sandwich for bulker construction
With IMO's Maritime Safety Committee coming to grips with the issue of bulk carrier safety, Det Norske Veritas is promoting the advantages of using a steel-concrete "sandwich" concept. It has been developed through a joint industry project sponsored by Aker Kvaerner Yards and DNV. Intended for bulk carriers, chemical tankers and other ship types, the concept is claimed to reduce stress concentrations, fatigue and corrosion problems, and eliminate local buckling problems.

The sandwich concept is applied to the cargo hold area of a bulk carrier, while the fore and aft ship is of traditional design. The sandwich can also be applied fully or partially in other ship types.

The sandwich consists of steel plates as the surface skin, and lightweight aggregate concrete as the 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 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.

Ballast water is carried primarily in the cargo holds, and none is carried in the side or double bottom structures.

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.

The research project is sponsored by Aker Kvaerner Yards and DNV AS and executed by DNV Research.

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