Effects of dented members in offshore tubular structures

摘要

Several types of steel structures employed in offshore petroleum activities are composed of tubular members. Accidental loads may affect the legs or bracings of these structures, due to supply boat collisions and falling objects frm platform decks. Such accidents cause damages like local denting of the member, permanent lateral deflection or combination of both. At the moment of the accident these damages may not have great influence in the member performance since they usually occur under moderate environmental loads. However, the strength reduction of the damaged member may have serious implications later when the structure is subjected to more severe environmental loads before the member is repaired. It is very expensive and difficult to make repairs in submerged members. So, it becomes essential an accurate addessment of the damage influenece on the member strength and on the structure as a whole, in order to take a decision regarding an optimum balance between safety and economy. The object of this paper is to present a systematic method for the assessment of the damage influence on the structure behavior in a quick and precise way. A reduced stiffness matrix is presented to represent the behavior of the dented member including permanent lateral deflection. Procedures for determination of the member ultimate strength are also presented. Stress analyses by finite elements are performed for the prediction of maximum stresses for fatigue analysis.