Elastic design of skid beams in offshore load-out systems

Abstract

Skid beams are essential components in skidded load-out systems, widely used in offshore operations, and are usually made in plate or box girder forms. They are continued from the jetty to the barge for a relatively long length and are the foundation of portable superstructures to transfer the distributed vertical load to the jetty/barge. Finite element analysis is usually used to verify the strength and stability of the skid beams' components, including flange, web, and stiffener. As FEM usually includes many analyses with a trial-and-error process, this study presents a general and explicit design procedure for skid beams in load-out operations. The main design criteria are the flange's bending capacity as well as the web and stiffener's buckling capacity. The generalized integral transform technique (GITT) is applied to solve the bending equation of the flange and the buckling equations of the web and stiffener with hinged and rigid connections. An algorithm is suggested by which some design curves (concise formulas) are obtained to find the maximum slenderness ratios of the skid beam's components. Accordingly, a step-by-step design procedure is presented, which can be easily used for practical purposes and can be a better replacement for finite element analysis. Comparing the analytical method with FE modeling, there is acceptable agreement and excellent convergence. A realistic design shows that the reduction of skid beam weight is not more than 10% due to rigid connections. In addition, the weight is reduced by increasing the web and decreasing the stiffener aspect ratios.