Probabilistic Background of Eurocode Ship Impact Forces and a Remaining-Life-Based Reduction Rule for Existing Bridges

Abstract

Ship impact on bridges represents a highly complex load case due to its dynamic and probabilistic nature. Experimental research gained momentum in the mid-20th century, with seminal studies laying the foundation for understanding of impact mechanics. The key influencing parameters include the vessel’s mass, geometry, stiffness, and velocity. This variability makes it difficult to derive representative impact forces for design and analysis. The load models in the Eurocode have been derived from probabilistic analyses; however, verifications are typically carried out deterministically. This paper reconstructs the probabilistic framework underlying the Eurocode ship impact provisions and clarifies the link between collision models, impact force distributions and return periods. Building on this framework, a rational approach is presented that allows ship impact loads for existing bridges to be adapted depending on the remaining working life of the structure. The proposed approach is also, in principle, applicable to other types of accidental actions. The method enables impact-action levels to be related to a finite remaining assessment period while preserving the nominal cumulative exceedance probability assigned to the reference action, thereby fostering more efficient and sustainable use of resources.