Structural Safety Assessment of Damaged Ships

In the design of ships, structural strength is generally assessed for the intact condition. In intact condition, the critical load case for mono-hull ship is the vertical bending moment, which reaches its maximum in head seas. Both horizontal bending moment and torsional load may play insignificant role. The torsion is considered only when there are large opening on ships. This methodology has been successfully applied to ship design for many years. But when a ship is damaged the whole scenario for the safety assessment changes. In damaged condition its floating condition could be changed dramatically. Its draught is increased and it may heel. It could also have large holes in the structure. So the load combination becomes very essential part of structural safety assessment in damaged scenario. Different damage scenarios in two tankers have been studied. A rational way to combine the vertical, horizontal wave-induced bending moments and still water bending moment is presented. For the deterministic analysis a rational interaction equation, combining vertical and horizontal bending moments is discussed. The reliability index and the probability of failure at different damage scenario are studied. The combined effect of torsional, vertical and horizontal bending moments is discussed. Finally the survivability of the damaged ships is discussed.