Operational modal analysis is a non-destructive structural investigation that considers only the loads resulting from service conditions. This approach allows the measurement of vibrations on a given structure with no need to interrupt its use. The present work aims to develop a numerical model to represent the global structural behavior of a vessel breasting dolphin using a technique that is simple and cheap in order to obtain a fast answer about the stiffness of a pier after the collision of ships with capacity up to 400,000t. To determine the modes of vibration, one accelerometer was installed on the breasting dolphin located on the pier and a frequency domain technic was conducted over recorded data to obtain modal parameters of the structure. In situ measurements were compared to data from a finite element model based on the original structural design in order to adapt the model to accurately represent the actual behavior of the system. This allowed a reliable structural analysis that accounted for existing structural damage and imperfections. The results of the experiment presented herein are the numerical characterization of the structure, along with the structural analysis to assess the degree of damage currently observed on the system. It is noted that the dolphin subjected to ship impacts presents a reduction in stiffness of approximately 10％ and its global damage level can be monitored from now after new accidents.