the base to support a deck and equipment above the water surface. Structures of this kind were installed in the North Sea during the mid-1970s. figure 3 illustrates the main features of these structures.This particular structure is referred to as a CONDEEP(concrete deep-water)structure and was designed and constructed in Norway One advance was of the gravity structure over the template type is the reduced time needed for on-site installation. This is especially important in hostile areas such as the North Sea, where unpredictable weather conditions make it highly desirable to limit the construction time needed to 时国场 斜 一E. Fig 3 Illustration of a concrete gravity platform used in the North Sea fix the structure in place. Another advantage is the very decks weights that can be carried by the massive concrete columns Deep-water design forms For water depths greater than about 1000 ft, the weight and foundation requirements of traditional offshore structures make them less attractive than other design forms Two such forms re the guyed tower and tension-leg platform The guyed tower concept is illustrated in Fig 4. It consists of a uniform cross-sectional support structure held upright by several guy lines that run to clump weights on the ocean floor. From the clump weights, the lines then run to conventional anchors to form a dual stiffness mooring system Under normal operating loads, the clump weights remain on the seafloor and lateral motion of thethe base to support a deck and equipment above the water surface. Structures of this kind were installed in the North Sea during the mid-1970s. Figure 3 illustrates the main features of these structures. This particular structure is referred to as a CONDEEP (concrete deep-water) structure and was designed and constructed in Norway. One advance was of the gravity structure over the template type is the reduced time needed for on-site installation. This is especially important in hostile areas such as the North Sea, where unpredictable weather conditions make it highly desirable to limit the construction time needed to Fig. 3 Illustration of a concrete gravity platform used in the North Sea fix the structure in place. Another advantage is the very decks weights that can be carried by the massive concrete columns. Deep-water design forms For water depths greater than about 1000 ft, the weight and foundation requirements of traditional offshore structures make them less attractive than other design forms. Two such forms are the guyed tower and tension-leg platform. The guyed tower concept is illustrated in Fig.4. It consists of a uniform cross-sectional support structure held upright by several guy lines that run to clump weights on the ocean floor. From the clump weights, the lines then run to conventional anchors to form a dual stiffness mooring system. Under normal operating loads, the clump weights remain on the seafloor and lateral motion of the