Performance-based design of berthing/mooring dolphin structure considering geotechnical and structural constraints under offshore load conditions
Résumé
A number of terminals have been extended through the use of berthing and/or mooring dolphins aligned with the existing berth structures. These dolphins allow larger ships to safely moor at the berth. They serve to counteract mooring loads from mooring lines and fenders, restrict the motion of the moored ship, increase the available fender contact length, and absorb part or all of the berthing energy, thus protecting the existing harbor structures. Regarding the design techniques for berthing dolphins, the yield limit has been approached more optimally over the years to make better use of the load-bearing capacity of the dolphins. The present study aims to provide a better understanding of the application of available design methods in engineering practice. This study is conducted within the context of the project assessing the reinforcement of existing harbor facilities and the extension of the “Mole Croisière” cruise berth in Ajaccio, France. The project involves the addition of a berthing dolphin structure located at the end of the existing berth. The optimal design of the dolphin structure was achieved using advanced numerical modeling techniques. These techniques were applied to the structural analysis of the dolphin-fender system, the interaction between the dolphin and the soil it is embedded in, and the fully dynamic mooring analysis. The mooring analysis was used to assess the mooring loads for several design ships under various wind, wave, and current conditions at the site. Several technical aspects were evaluated. The primary structural design challenge was related to the limited load-bearing capacity of the pile foundation at the seabed level, in a water depth ranging from 20 to 30 meters. The optimization of the dolphin structure design was carried out by employing rock-socketed foundation piles embedded in the seabed. Additionally, X-tie-braces were installed at the mid-height of the dolphin's piles to transform bending moments into axial forces (compression and tension exerted on the steel bracing system). A predetermined displacement for the dolphin was set, along with a desired fender performance, to achieve the desired energy absorption capacity of the quasi-flexible system.
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