Report on Floating and Float-In Concrete Structures

Description

Prestressed or reinforced concrete structures are used as either permanently floating structures or temporary float-instructures to facilitate marine construction. In this report, the definition of a floating structure is a structure that is temporarily, intermittently, or continuously afloat. For those floating structures that have a bow or stern, the bow or stern may be raked or shaped as required. Certain floating structures included within this definition are designed for towing and subsequent grounding, and afterward function as fixed struc-tures. Later, these structures may be refloated and transported to a new location. Other structures are designed to remain continuously afloat, with or without permanent mooring.

Permanently floating structures serve a variety of uses such as industrial plant ships, floating bridges, floating drydocks, offshore terminals, navigation structures, and parking and hotel structures. Applications of temporary float-instructures include the bridge pier foundations, offshore gravity-based structures, locks and dams, immersed concrete tunnels, and storm or tidal surge barriers. In 1943, the first prestressed concrete barge was built by the U.S. Navy (U.S. Department of Transportation[USDOT] 1981). Today, the preferred construction approach for large structures is to use prestressed concrete instead ofordinary reinforced concrete.

The ability of prestressed structures to control net tensile stresses and to close cracks that develop from temporary overload situations enhanceswater tightness and durability. Composite concrete-stee lconstruction is also becoming popular. Concrete is used inthe exterior bulkheads and base to provide durability, and steel is used for the internal framing and deck to provideweight savings (Gerwick 1975a, 1978).The design of concrete floating structures requires knowledge of many disciplines. The designer should have a thoroughunderstanding of concrete design principles, concrete as a mate-rial, and construction practice. Also, the designer should have an understanding of environmental loadings, marine operations, requirements for vessel certification, and the importance of structure inspection, maintenance, and repair. All of these aspects have been addressed in this report to provide the readerwith a background in the subject of concrete floating structures.