High Performance ■ This paper discusses the unique design and construction challenges encountered in the development of large-scale precast concrete cryogenic storage tanks, along with special considerations necessary when fabricating, handling, erecting, temporarily supporting, integrating, and posttensioning long and slender precast concrete wall elements. ■ This concept takes advantage of the unique features of precast, prestressed concrete technology applied to a market currently held by cast-in-place concrete and welded steel.

Oil companies are considering large Gravity-Based Structures (GBS) as a potential solution to support operations in new offshore oil and gas field developments in the Arctic seas that are designed for year-round production in potentially 100meter-deep waters. These structures support multibillion-dollar drilling, production, and storage facilities that are typically commissioned with topsides and consumables before entering the Arctic, and are towed with these elements already installed on the GBS to the installation site. However, the tow not only presents a high risk during the installation phase of the platform, but also has a significant influence on the design and cost of the GBS. Movement of these large offshore structures through the Bering Straits and into position at the installation location includes unique risks that result from the minimal precedence of these tows and the scarcity of local support and contingency ports. This situation suggest that typical approaches to risk identification, design criteria development, and application of risk mitigation approaches may merit reevaluation. This paper will discuss the logistics related to the movement of these large structures and discuss the various cost-and schedule-related risks that have to be identified to support the early design phases of the GBS.

The oil and gas industry is considering deploying large gravity-based structures (GBS) into the high Arctic seas for yearround production where they will be exposed to multiyear ice loads. Conceptual studies of such structures suggest that the design for the ice load and the low draft requirement during deployment to the Arctic become key design aspects, focusing the attention on efficient force-resisting strategies and ice wall design. An appropriately designed ice wall in combination with a well-thought-out ice resistance strategy can significantly reduce the cost and construction/installation schedule of a GBS. Ice walls made of steel/concrete/steel composite have the potential to provide significant robustness at a lower weight than typical all-concrete ice walls. Composite ice walls also provide the potential of more robust behavior than all-steel ice wall concepts. Composite walls, thus, promise great value as ice walls for Arctic structures. To validate the behavior of composite ice walls, a testing program was conducted that applied high-intensity loads to beam specimens 1.8 meters long and 0.3 meter thick with varying degrees of plate stiffening and concrete confinement. Strength, stiffness, ductility, load paths, and failure mechanisms were evaluated. Test variables included temperature, concrete density and strength, load paths, and type of composite load-carrying system. This paper demonstrates the viability of composite ice walls. It presents the results of the testing program, discusses the proposed ice wall configuration and appropriate design procedures, and proposes the steps that have to be taken to allow low risk application of composite ice walls for design and construction of an actual GBS.