On the strength assessment of pitted stiffened plates under biaxial compression loading

Structural components of ships are subjected to corrosion, especially when exposed to sea environment. It is, therefore, essential to seek rational standards for the structural integrity of aging structures without economic penalties with respect to the repair and maintenance costs incurred over the life cycle of the structure. To make proper decisions about costs and safety, knowledge about the effect of corrosion and other degradation phenomena on the strength is of crucial importance. The main objective of the present study is to investigate the strength of pitted stiffened plates under biaxial compression loading. For this purpose, systematic numerical FE investigations of ultimate collapse and post-ultimate responses for the stiffened plates with pit corrosion wastage are undertaken, varying the degree of pit corrosion intensity (DOP), pit depth and the location of the densest pitted zone. The focus here is on local plate failure mode which is desired to be governing failure mode in designing of stiffened plates. Geometric imperfections and residual stresses were included in the models. It is found that the ultimate strength of a stiffened plate can be significantly decreased due to pitting corrosion. The ultimate strength of pitted stiffened plates is governed not only by the level of DOP, but also by the smallest sectional area and the location of densest pitted zone. This improved knowledge of the damage tolerance assessment of stiffened plates can be used to schedule repairs more efficiently, while risk or reliability assessment schemes are normally applied for that purpose.