A METHOD FOR "PUNCH-THROUGH" PROOF DESIGN FOR INDEPENDENT LEG JACK-UPS

"Punch-through" is one of the most common types of failure affecting independent leg self-elevating-type mobile offshore drilling units , and existing rules do not provide any guidelines to design for "punch-through" induced forces. This paper presents a systematic method for analysis and design of independent leg jack-ups for such forces, identifying the important design and operating parameters and evaluating their effects. The method can be used to design the jack-up legs for a given set of operating parameters, or for an existing unit it can be used to define the limiting values of these parameters. Based on these limitations, operating procedures can be developed to eliminate or minimize the chances of leg damage due to punch-through. A realistic example is worked out to demonstrate the application of the method.