| It's very important to analyse the ultimate strength of hull girder in ship design. And the aim of the analysis is to get the numerical value of the loads or assembled loads which conduce structure invalidation. Structure invalidation is almost non-linear-geometry non-linear and material non-linear which brings the difficulty to the problem. The panels of hull girder may collapse or buckle before it reaches the yield stress. The curve of the stress-strain is usually constituted by stable zone-, non load-shedding zone and load-shedding zone. The author analyses the tripping of stiffener and three patterns of panel's invalidation, so to get the curve of stress-strain of panel. This step is the core of the thesis.Progressive callopse analysis method is also named Smith method. Firstly, it needs to separate the girder hull into many elements-pulled one and pushed one. 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.According to the above, in this thesis, the author checks results from his program which has been compiled by FORTRAN 90 on two steel boxlike models and four ships. The author's program can resolve the following problems: ultimate strength of hull girder, the panel's curve of stress-strain. The author analyses the influence of welding stress and inner stain to the ultimate strength of the model and hull girder, and then checks with some famous experts' results from International Ship & Offshore Structures Congress. The result is approving .
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