At the request of FCC Construccion, S.A. in connection with the Danube Bridge project between Vidin (Bulgaria) and Calafat (Romania), a Nautical Risk Analysis was developed to assess the probability of impact of vessels on the unprotected piles of the bridge located in the secondary channel of the river. The project consists of a combination viaduct - cable-stayed
bridge taking advantage of the small island in the middle of the channel. In each of the piles of the main channel a circular fender is arranged. Piles in the secondary channel are not protected.
The objective of the study was to evaluate eventual risk of impact on unprotected piles, assessing the probability of occurrence and making a proposal for preventive or corrective measures. Complete traffic statistics were available, as well as information on the river flow, current velocities and wind, from which the actual navigation conditions in this section of the river were modeled.
The study analyzed the consequences of exceptional situations (breakdowns in propulsion or steering of vessels, lack of visibility, errors in position estimation, sudden bad weather, etc.), beyond the normal difficulties in sailing the river.
The analysis identifies, analyzes and evaluates different expected risk situations in the development of manoeuvres in order to establish effective preventive or corrective measures in accordance with the most stringent recommendations. Applying a ship manoeuvrability numerical model, the response of the vessels to each of the measures was analyzed according to
the different possible situations.
Consequently, it was possible to evaluate the effectiveness of these countermeasures by determining, where appropriate, the "point of no return", which serves as a basis for the definition of restricted areas and development of contingency plans. During the development of the work a program of emergency simulations was established using model SHIPMA (Delft Hydraulics and MARIN (The Netherlands)). This model reproduces the behavior of a specific vessel during the execution of port access or exit maneuvers, subjected to the action of environmental agents (wind, current, waves, limited depth, shore suction, etc.) and aided by tugs, if any. For this purpose, it has an autopilot and tug control, which develop the necessary actions to maintain a desired track.
The working procedure was developed in the following phases:
• Identification of risk events
• Assessment of response manoeuvres
• Accidental risk assessment
• Definition of preventive and corrective measures