In order to basically investigate collapse mechanism of damaged ships as well as to validate numerical/analytical analysis such as FEA and smith method, a large scale model test was carried out for a damaged box girder with a hole at side which is assumed to be damage due to collision. The box girder has a simplified cross section with stiffeners. The model is quasi-statically loaded by 4 points bending moment, and is collapsed from a midship of a box girder. Load, strain and displacement are measured and compared with those estimated by explicit non-linear finite element analysis. Accuracies of numerical results are discussed in details as compared with experimental results. Especially effect of friction coefficients and loading speed are investigated in detail. Bending stress measured in the experiment is compared with those estimated by NLFEA, and good correlation can be confirmed between the experiment and NLFEA. It can be said that NLFEA can estimate the experimental results with reasonable accuracy.
In the experiment the highest bending stress at midship is observed not in upper deck which is the farthermost from the neutral axis, but in close the damge hole due to stress concentration.
From the viewpoint of ship structural design, a breaking of ships into two parts is one of the most disastrous accidents which should be avoided.
Ultimate longitudinal strength (ULS) of global hull girder of ships under vertical bending moment can be decreased in damaged condition. "Damaged condition" can be defined as the ship's condition suffering from accidents such as collisions and groundings as well as buckling of structures. Significant decrease of ULS may lead to breaking of ships into two parts, consequently total loss of ships may take place which should be avoided. Therefore it is important to keep residual ULS of ships so that ships do not break into two parts until damaged ships could arrive at ship yards for repair.
Goal Based Ship Construction Standards (GBSCS) for oil tankers and bulk carriers was adopted as a new SOLAS convention in IMO. Consequently "residual strength" of ships after damages becomes mandatory to these ship types.