THE EFFECT OF CARGO ON THE CRUSH LOADING OF RAM TRANSPORTATION PACKAGES IN SHIP COLLISIONS

Recent intercontinental radioactive material shipping campaigns have focused public and regulatory attention on the safety of transport of this material by ocean-going vessels. One major concern is the response of the vessel and on board radioactive material (RAM) packages during a severe ship-to-ship collision. These collisions occur at velocities less than the velocity obtained in the Type B package regulatory impact event and the bow of the striking ship is less rigid than the unyielding target used in those tests (Ammerman and Daidola, 1996). This implies that ship impact is not a credible scenario for damaging the radioactive material packages during ship collisions. It is possible, however, for these collisions to generate significant amounts of crush force by the bow of the impacting ship overrunning the package. It is the aim of this paper to determine an upper bound on the magnitude of this crush force taking into account the strength of the radioactive material carrying vessel and any other cargo that may be stowed in the same hold as the radioactive material. During ship collisions, the kinetic energy of the striking ship is initially absorbed by plastic deformation of the struck side of the hull. If the striking ship has sufficient kinetic energy, the hull wiU be penetrated and further energy will be absorbed by plastic deformation of the decks, bulkheads, and cargo. Eventually, again if the striking ship has enough kinetic energy, the RAM package will be impacted. Initially, this will be merely an impact load due to the inertia of the RAM package. The RAM package will then be tom from its tiedowns, and subsequently experience crushing between the contacting ship and cargo on the side of the hull away from the point of impact. The magnitude of this crush force is limited by the strength of the bulkheads, decks, hull structure of the ship, and the material properties of the cargo. Previous studies have shown that, for a vessel with no other cargo, the maximum crush force that can be applied to a package is equal to the force required to push the package through the far hull of the ship into the ocean (Ammerman and Ludwigsen, 1998). An upper-bound for this force is about the same as the inertial crush force seen during the regulatory impact accident. This paper extends the research, using finite element analysis, to the crush forces that may develop when there is other cargo in the hold with the RAM package.