Flexibility of tubular joints in offshore structures

Within the Linear Elasticity theory and the Small Perturbations assumption, a general methodology is presented, to introduce the shell behaviour of tubular joints and its influence on the overall structural analysis of 'Jacket' offshore structures. Thus the flexibility, or the semi-rigidity, of the joints will be taken into account, which is not the case in a conventional analysis (with hinged connections). The general methodology was illustrated on a T-joint, in the following way: - Boundaries of the joint An original critical study was conducted, presenting the various degrees of approximation of circular shell existing models (FLUGGE, TIMOSHENKO, SANDERS-KOITER, KOITER-MORLEY-NIORDSON), and showing the interest of the KOITER-MORLEY-NIORDSON model; then a semi-analytical study resulted in the definition of adequate boundaries for the connection. - Determination of joint stiffness matrix using the Finite Element Method and the static condensation technique, the stiffness matrix was determined for 23 joints, with a parametric study being made to evaluate the effect of geometric parameters on joint flexibility. - Determination of a simplified equivalent model. Using the available stiffness matrices, a simplified equivalent model (beams-springs model) was proposed, and the dependence of spring values upon the joint geometric parameters was analysed. - Taking joint flexibility into account in the overall structural analysis The effect of joint flexibility upon the overall structural behaviour was illustrated on a planar four storeys frame. (author)