Texas Towers. During 1 955 and 1 956, three offshore radar platforms, 

 Texas Towers, were installed along the East Coast of the United States as part 

 of an Air Force early warning defense system (Anderson et al., 1954; Rutledge, 

 1956 and 1969). 



The first tower was constructed in the summer of 1 955. It was located 

 on St. George's Bank approximately 95 miles east of Cape Cod, Massachusetts. 

 The mean depth to the seaf loor was 55 feet. Bottom sediments at the location 

 consisted of 10 feet of loose sand underlain by over 150 feet of dense sand. 

 Scattered through the area were pockets of organic clays and silty clays. The 

 bearing capacity of the sand at a depth of 30 feet or more below the sea bot- 

 tom was estimated at 24,000 psf. The three legs, each 1 5 feet in diameter at 

 the base, were sunk as caissons 48 feet into the seaf loor. Maximum design 

 loads for each caisson were: 5,300,000 pounds vertical compression, 720,000 

 pounds horizontal force, and a bending moment of 1 ,800,000 ft-lb. 



The second Texas Tower was located off Nantucket Shoal approximately 

 45 miles southeast of Cape Cod. Foundation conditions were essentially the 

 same as were found at St. George's Bank. The tower was supported by three 

 1 4-foot-diameter legs sunk as caissons to a depth of 60 feet. Each caisson was 

 designed for maximum vertical loads of 7,100,000 pounds, maximum horizon- 

 tal force of 1 ,1 00,000 pounds, and maximum moment at the seaf loor of 

 33,000,000 ft-lb. 



The location of the third Texas Tower was approximately 75 miles 

 southeast of New York Harbor in water 180 feet deep. The structure was 

 designed with 1 2-1 12 -foot -diameter legs and an underwater bracing system. 

 The three legs were sunk simultaneously as caissons. Each caisson was designed 

 for maximum vertical force of 6,800,000 pounds, maximum horizontal force 

 of 820,000 pounds, and negligible bending moment. 



On January 1 5, 1 961 , the radar tower off New York was destroyed 

 by sea action. Cause of failure was attributed simply to "structural failure 

 of the supporting system." Subsequently, the two remaining towers were 

 dismantled. 



General Petroleum Experience. The vast majority of offshore platforms 

 belong to the petroleum corporations and related companies. As a result, spe- 

 cific information on design or performance is often considered proprietary and 

 therefore not available. Much information of a more general nature and of 

 great value to a study such as this is, however, available (Noorany, 1969; Reese, 

 1969; Smoots, 1969; Kochler, 1969). 



Of several hundred offshore permanent platforms, only a few failures 

 are known (Howe, 1968 and 1969; McClelland, 1969; Lubinsky, 1969). These 

 failures have usually occurred during severe storms. Several failures not related 

 to storms have also occurred however. 



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