Ultimate strength of T-joint in tubular frame of jack-up type oil rig. Report 1: Experimental study of ultimate strength of unstiffened and stiffened T-Joints under normal load

Abstract

A jack-up type oil rig consists of legs and a platform. The legs are tubular frame structures. The degree of redundancy of the legs is generally less than the degree of the platform. As the degrees of redundancy of the legs and the platform decrease, the reserved strength of the rig after the initial local failure (yielding, buckling) decreases. Therefore it is very important to know precisely the ultimate strength of the tubular joints of which failure may become the leading cause of overall failure of the legs. An experimental investigation has been carried out in this study, into the local stiffness and strength of the T-joint of circular tubes under normal lord. The following effects on the local stiffness and ultimate strength of the T-joint were studied, and the mechanisms of strengthening by the guide and the center rib were clarified: (1) the thickness and the yield stress of the chord-wall; (2) the leg guide; and (3) the center stiffening.

ジャックアップ型オイルリグは脚とプラットフォームで構成する。脚はチューブフレーム構造である。脚のリダンダンシーは一般にプラットフォームよりも少ない。脚とプラットフォームのレダンダンシーの減少とともに、最初の局所損傷(降伏、座屈)後、リグの予備強度が減少する。したがって、脚の全体破損の主要原因になる差込継手の極限強度を正確に知ることが非常に重要になる。垂直荷重下で円形チューブのT型継手のローカル剛性と強度について実験した。T型継手におけるローカル剛性と極限強度について、(1)弦壁の厚さと降伏応力、(2)脚ガイド、および(3)センタ剛性にわたる効果を研究し、ガイドとセンタリブによる強化機構を明らかにした。