8 main piles -48-in diameler wetted at we 300p# 4 skirt Fig. 2 Typical offshore template structure off Louisiana in the Gulf of Mexico (a)------installed(b)-----substructure illustrating skirt pi these, four skirt piles are placed around thethe base of structure. All piles are driven 200 to 300 ft into the seafloor. The structure is designed to withstand a result lateral force of about 3 million pounds from wind, waves, and currents during extreme hurricane conditions. Because the wave forces are greatest near the water surface, this resultant force acts near the top of the structure The structure is therefore also designed to withstand a base-overturning moment of the order of 700 million foot-pounds. These loads and moments are five to seven times those caused by extreme winds on a typical 25-story, 300-ft-tall building on land For structures designed for waters greater than about 350 ft, two variations of the basic eight-leg template design have been considered. The first has been to increase the number of legs of the structure so that, with skirt piles, the structure can carry additional deck loads and resist the increased lateral loading and overturning moment A second modification has been based on the observation that, with taller structure and increased base widths, the interior piles become less effective in resisting overturning moments. As an alterative to the eight-pile structure, consideration has thus been given to the four exterior corners of the structure Template structures, as described earlier, are especially suited to soft-soil regions such as the Gulf of Mexico, where deeply driven piles are needed to fix the structure in place and carry the required deck loadings. In regions where hard soil conditions exist and pile driving is more difficult, an alternative structural form has been developed which, in place of piles, relies on its own weight to hold it in place against the large lateral loads from wind, waves, and current. These structures have large foundational elements which, when ballasted, contribute significantly to the required weight and which spread this weight over a sufficient area of the seafloor to prevent failure. Such structures are generally referred to as gravity structures In their more popular form, gravity structures. Are constracted with reinforced concrete and consist of a large cellular base surrounding several unbraced columns which extend upward fromFig. 2 Typical offshore template structure off Louisiana in the Gulf of Mexico (a)------installed (b)------substructure illustrating skirt piles these, four skirt piles are placed around the the base of structure. All piles are driven 200 to 300 ft into the seafloor. The structure is designed to withstand a result lateral force of about 3 million pounds from wind, waves, and currents during extreme hurricane conditions. Because the wave forces are greatest near the water surface , this resultant force acts near the top of the structure. The structure is therefore also designed to withstand a base-overturning moment of the order of 700 million foot-pounds. These loads and moments are five to seven times those caused by extreme winds on a typical 25-story, 300-ft-tall building on land. For structures designed for waters greater than about 350 ft, two variations of the basic eight-leg template design have been considered. The first has been to increase the number of legs of the structure so that, with skirt piles, the structure can carry additional deck loads and resist the increased lateral loading and overturning moment. A second modification has been based on the observation that, with taller structure and increased base widths, the interior piles become less effective in resisting overturning moments. As an alterative to the eight-pile structure, consideration has thus been given to the four exterior corners of the structure. Gravity Structures Template structures, as described earlier, are especially suited to soft-soil regions such as the Gulf of Mexico, where deeply driven piles are needed to fix the structure in place and carry the required deck loadings. In regions where hard soil conditions exist and pile driving is more difficult, an alternative structural form has been developed which, in place of piles, relies on its own weight to hold it in place against the large lateral loads from wind, waves, and current. These structures have large foundational elements which, when ballasted, contribute significantly to the required weight and which spread this weight over a sufficient area of the seafloor to prevent failure. Such structures are generally referred to as gravity structures. In their more popular form, gravity structures. Are constracted with reinforced concrete and consist of a large cellular base surrounding several unbraced columns which extend upward from