ABSTRACT

One class of X-joint, commonly known as trunnion, with the brace subjected to combined shear and moment loads, is designed to transfer the sling forces to the adjoining structural members and system during the lift installation of a jacket or deck structure. Present offshore codes provide design guidelines for X -joints subjected moment and other loads, except shear loading: In this paper, the in-plane moment strengths of X-joints computed using the ABAQUS software are shown to correlate closely with results published by Vegte (1995). Based on the parametric studies carried out to investigate the influence of applied shear/moment ratio on the strength of X -joints, it is found that the reduction in in-plane moment capacity for increasing shear load ratio, Q/Qp, is less significant for X-joints with smaller ß For joints with ß =0.25, there is a strength reduction up to 25% while joints with ß =0.73 indicate a reduction up to 55%.

INTRODUCTION

X-joints are commonly used in onshore and offshore tubular structures. The books by Wardenier (1982) and Marshall (1992) provide excellent background and basis for design. Extensive studies on the strength of Xjoints, made from circular hollow sections, under different loading conditions (axial load, in-plane bending and out-of-pIane bending) have been carried out by Vegte (1995). There is one class of X-joint, with the brace subjected to combined moment and shear loads, which has received little research interest. This class of joint, commonly known as trunnion, is designed to transfer the sling forces to the adjoining members and structural system during the lift instaI1ation of a jacket or deck structure. The usual design approach for pipe-to-pipe trunnion design is to provide a slotted shear plate through the main pipe, and only include the contribution of the shear plate to carry the sling load. The simpler configuration, with the chord member provided as a main plate and denoted as plate trunnion, has been investigated by Choo et. al. (1995).

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