A METHOD TO EVALUATE THE CONSEQUENCES OF MEMBER FAILURE IN JACKET-TYPE OFFSHORE PLATFORM STRUCTURES

An evaluation of the consequences in a structural system caused by the failure of a component within the system is a necessary part of reliability based design. Presented in this dissertation is a method to determine the consequences of member failure in offshore jacket-type platform structures. The method presented herein utilizes the same computer model of the structure that is used for the initial analysis of the structure. In this dissertation, failure is defined as the complete loss of a member's resistance to load. Such failures can occur as the result of fatigue, poor construction, excessive load, or mechanical damage caused by dropping heavy equipment or ship collisions.; To evaluate the consequences of a member failing, the behavior of the remaining members in the structure was determined. This was accomplished by mathematically removing a single member from the structure and computing the change in the behavior, i.e. the change in stressses, of the other members. This member then was replaced and another member was removed; the process was repeated for all members in the jacket structure. Each member can be classified quantitatively according to the change in the stresses in the other members in the platform and also the serviceability of the platform.; Four member categories have been proposed: Non-Redundant Members, Primary Structural Members I, Primary Structural Members II, and Redundant Members. Failure of a Non-Redundant Member causes a collapse of the platform or necessitates shutdown of the platform due to a loss of serviceability. Failure of a Primary Structural Member I causes the stresses in other members of the platform to become inelastic but the structure does not collapse. Members in the second category of primary structural members cause a significant change in the behavior of the platform when they fail but the stresses in the other members remain in the elastic range of the material. A Redundant Member is one which does not cause significant change in the behavior of the platform when it fails.