Characteristics of stiffness and strength of V-joint in tubular offshore structures

Abstract

In this report, simple (unstiffened) V-joint of tubular offshore structures for oil exploitation is investigated as one of three-dimensional joints, of which two braces exist in a plane perpendicular to the axis of the chord. The mechanical behaviors under various loads (normal force and bending moments) are analyzed by PNM (Plastic Node Method) which is one of very efficient and accurate methods for elastic-plastic analysis. Based on the results, the characteristics of the stiffness and strength of the V-joint are made clear, comparing with those of the T-joint which has the same dimensions. The elastic-plastic behavior is dependent on the loading condition, and the mechanism of influence upon the stiffness and strength is clarified. One of the most important results from this study is that the stiffness and strength of V-joint is reduced to 70 percent of those of T-joint in a severe loading condition. So the reinforcing method by using a stiffener is discussed.

本研究では、部材の軸に垂直な平面上に2本のブレースのある、3次元継手の1つとして、石油採掘用の管状海洋構造物の単純な(補強していない)V継手を検討した。種々の負荷(法線力と曲げモーメント)における機械的挙動を、弾塑性解析に極めて有効で正確な、PNM(塑性交点法)を用いて解析した。その結果に基づいて、V継手の剛性と強度特性を明らかにし、同一寸法のT継手のそれと比較した。弾塑性挙動は負荷条件によって決まる。剛性と強度に及ぼす影響の機構を明らかにした。本研究のもっとも重要な結果の1つは、苛酷な負荷条件下では、V継手の剛性と強度はT継手のそれらの70％に低下するということである。そこで、補強材による補強法を考察した。