Cost-Effective Marine Fender Design Using an Elastoplastic Support Element: An Investigation

Abstract

This manuscript investigates the potential cost savings of installing a steel elastoplastic element in series, structurally, with a commercial rubber marine fender. Along with cost savings, the results also provide insight into the design requirements for the elastoplastic element. The approach to the study began with calculating abnormal impact energy for common classes of ships. Using that information, reaction force and required deflection for different levels of plastic deformation were determined. As the level of plastic deformation increases, the requirement for the rubber marine fender decreases. This allows the designer to use a smaller, less expensive, marine fender for a given kinetic energy associated with ship impact. The elastoplastic contribution to energy absorption was estimated using a steel reference element that was tested beyond yield. A Ramberg–Osgood model was fitted to the force-deflection data from the test and then scaled to the anticipated reaction for a full-size ship impact. From this, cost and required deformation of the elastoplastic element were compared. There is a clear trend of cost savings with increasing elastoplastic deformation. The results of the analysis indicate that an elastoplastic element installed in series with a fender might reduce fender costs by several thousand USD to over USD 40,000 per fender. To realize such savings, the full-size elastoplastic element will have to tolerate deflections of 100 to 400 mm while supporting the reaction from a ship coming to rest at berth. Commentary on performance for pre- and post-yield conditions is also provided.