Mobile Drilling Platform
Bethlehem Steel Corporation designed and built over 80 mobile, mat-supported drilling platforms for the offshore oil industry. These rigs, capable of drilling in water depths up to 114 m (375 ft) consist of a bouyant platform, a cellular mat, three cylindrical legs, and a hydraulic jacking system. The platform contains the derrick, drilling machinery, and living quarters. The mat rests on the ocean floor and serves as a foundation for the rig. The three cylindrical legs or columns -- approximately 3.6 m (12 ft) 91 m (300 ft) tall, and fabricated from steel plate 38.1 to 63.5 mm (1.5 to 2.5 in) thick -- are integral to the mat and pass through hydraulic jacking systems located in jack-houses on the upper deck of the platform.
Reference: "Observations, Predictions, and Prevention of Fatigue Cracking in Offshore Structures," by H. S. Reemsnyder in Case Histories Involving Fatigue and Fracture Mechanics, ASTM STP 918, C. M. Hudson and T. P. Rich, Eds., American Society for Testing and Materials, 1986, pp 136-152.