This paper presents an innovative 4-leg launched jacket concept, originally developed as a more economical solution for PETROBRAS PRA-1 platform in Brazilian Campos Basin. The concept goal is structural and functional optimization, focusing mainly in minimization / elimination of the usual drawbacks associated with the addition, in conventional 4 leg jackets, of launch trusses and associated structures that are specifically designed for the skidding and launching operations, and that are useless and cumbersome after the completion of the installation, as they do not contribute to the in-situ overall strength and increase the dead weight and environmental loads acting on the structure. Pile cluster design optimization is also addressed, leading to improved load sharing between piles. The concept consists of a structure with four main legs, two of them, located in the rear face, slanted and straight from the top to the base, like in a conventional jacket, and the two other main legs, forming the front face, parallel in the upper region and slanting outwardly in a lower and a transition regions, constituting a widened base, endowed with dihedral external lateral faces. The parallel legs in the upper region are extended into transition and lower regions by reduced diameter ramifications referred as secondary legs, making up the launch rails on which the structure can be loaded out in a barge from the construction site and later launched at sea from the barge. The paper describes the concept main features and performance and its application to the PRA-1 project, a hub platform with a topside operating weight of 16,200 metric tons (mton), recently installed in 106m WD. Advantages, like 20% reduction of steel weight over a conventional light weight jacket, developed in parallel to a same stage of preliminary design for comparison purposes, are quantified. Descriptions of installation and in-situ static, dynamic, foundation and fatigue analyses are also presented.

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