View non-flash version
it is suspected that those used in the Titanic structure had insucient fracture tough- ness to withstand low temperatures. In other words, the vessels hull structure was prone to brittle failure in the face of local impacts. Second, the impact velocity at the moment of Titanics collision with the ice- berg is reported to have been 23 knots (or 11.8m/s), which is likely to have caused a large amount of initial kinetic energy and, subsequently, to have created large holes that allowed a signicant amount of water to enter the ship. ird, accidental ooding most likely altered the hull girder load dis- tribution and amplied the maximum hull girder bending moments. Fourth, because the water ingress following the collision with the iceberg subjected the ship to sag- ging moment in the boiler room, the large axial compressive loads bearing on the deck structures led to their buckling and collapse. It is clear that ultimate limit state design methods that consider buckling and plastic collapse should be applied in the design of ship structures if hull breakage is to be pre- vented. e total loss scenarios for ships are shown in the graphic on this page. Another well-known incident is the sinking of Derbyshire , a Capesize bulk car- rier, in the northwest Pacic on September 9, 1980. e vessel was approximately 400 miles south of Japans Shikoku Island when it went down during Typhoon Orchid, and was carrying ne iron ore concentrates from Canada to Japan. Derbyshire had been in operation for only ve years at the time of the accident, and thus was thought to have su ered very little age-related degradation such as corrosion wastage. Another distinct characteristic of this ship was its double-sided hull arrangement, the aim of which was to prevent unin- tended water ingress into the cargo holds in the event of side shell structural failure. e signicant wave height just prior to the carriers sinking was reportedly 14 m. e vessel issued no distress signal, and there were only two sightings of oil upwelling to indicate the position of the sunken craft several days later. ere was a sighting of a damaged lifeboat from the ship, but it was not recovered, and it subsequently sank. is evidence suggests that Derbyshire sank very quickly. The incident has several lessons for structural design engineers. First, abnor- mal waves that are not anticipated at the structural design stage may occur, thereby amplifying the maximum hull girder loads, which may reach or even exceed the cor- responding design values. Second, the unintended water ingress into cargo holds that may result from hatch cover failure can further amplify these loads. Finally, the allowable working stress design approach that was applied in the structural design of Derbyshire is clearly insucient to deal with these issues. e ultimate limit state design method should thus be employed to prevent hull girder collapse accidents. e total loss scenarios shown in the total loss graphic can also be used to explain this accident. Hull collapse performance A more recent maritime accident occurred on January 18, 2007. Napoli , a British con- tainer ship capable of carrying up to 4,419 20-foot equivalent unit containers, suf- fered a leak and the failure of its steering April 2012 www.sname.org/sname/mt LOSS OF RESERVE BUOYANCY HULL GIRDER COLLAPSE LOSS OF STABILITY WATER INGRESS/CARGO OUTFLOW TRANSVERSE BULKHEAD FAILURE HOLD FLOODING PROGRESSIVE FLOODING TO ADJACENT HOLDS ROLL IMPACT (Aged side shell failure) GREEN WATERINDUCED DAMAGE (Hatch cover failure) ACCIDENTRELATED DAMAGE (Collision, grounding, explosion, ?re) AGERELATED DAMAGE (Corrosion, fatigue cracking, local denting) DECREASE OF HULL GIRDER STRENGTH INCREASE OF HULL GIRDER LOADS PARTIAL LOSS OF STRUCTURE VESSEL LOSS TOTAL LOSS SCENARIOS FOR SHIPS