Research On Ultimate Strength Of Bulk Carriers And Residual Strength Of Damaged Ships

The ultimate load bearing capacity of ship hull structure is an important index expressing the safety and reliability of the structure, and it has widely been paid much attention and concern. The perfect construction design is closely related to the true strength reserve of the ship girders. However, in order to understand the actual strength reserve of ship hull girders, we must have a right assessment of the ultimate strength of ship hull girders.On the other hand, a ship in navigation may happen to accidents of grounding or collision. The ultimate strength and the local strength of ship hull girder weakened very much after grounding or collision, a further destroy may be happened because the residual strength of hull girders is insufficient during rescuing or dragging. In order to rescue the damaged ship and prevent from polluting marine, the ship hull should be sufficient level of the residual strength. Since the damaged hull is in extraordinary state, it is necessary to know and assess the residual strength. There are only some commence works on the calculation and assessment method for damaged ships at the moment.According to IACS Common Structural Rules for bulk carriers(JBP), a program is developed by using the Progressive Callopse Analysis Method to calculate the ultimate strength and the residual strength of ship hull girders. The influence of different damaged position and extension due to collision or grounding on residual strength is reflected by the residual strength index and sensitivity analysis. Firstly, progressive Callopse Analysis Method needs to separate the girder hull into many elements under tension or compression. Secondly, when the ship is in hogging or sagging, you should assume one curvature value so you can get the moment value of every element at this curvature. And then you may add up all the moment of every element. Thirdly, you must judge whether the moment is the ultimate moment. If not, increase the curvature, and redo the above steps until get the ultimate strength. These procedures can be realized by one circulation. In every step, the curve of stress-strain is modified, so the result is more precise.Comparing the results from many examples of actual ship structures with those from some famous experts of International Ship & Offshore Structures Congress, it verifies that the adopted methods are correct, and the developed program is effective. To damaged ship in different accidental situations, the calculation method, results and conclusion are useful in drawing up the rules and regulations relating ship safety, assessing the residual strength, taking technical measure to salvage, rescue and tow the damaged ship.