Jack-up type oil rigs are composed of legs and platforms. The degree of redundancies of legs are generally fewer than those of platforms. As a structure becomes less redundant, reserved strength after the initial yielding tends to decrease. So, it is important to clarify the ultimate strengths of tubular joints which are leading causes of overall failures of the legs.
In the 1st report, the authors carried out theoretical and experimental investigations into the rigidity and local strength of T-joint of circular tube under a concentrated normal load transmitted from the brace. The T-joint model used in the study is composed of a chord reinforced with a built-in center-rib and a brace, and is supported by a leg guide.
In the present paper, they studied the rigidity and local strength of the same T-joint model under both a concentrated normal load and bending moment transmitted from the brace. They performed series of theoretical analyses and experiments on the models.
Main conclusions obtained in this study are shown as follows.
1) The rigidity of the T-joint can be evaluated by formulae developed in consideration of the effects of various sizes of the chord and brace.
2) The ultimate strength interaction curves of the T-joint are presented.
3) The failure modes of the T-joint are clarified.