Ship structural integrity using new stiffened plates

The objective of the present paper is to use novel longitudinal Y (Hat+Conventional) stiffener profiles instead of the conventional stiffener profiles. That helps obtaining more safety margin (the ultimate strength minus the applied compression stress) to weight ratio. Using the hat section (closed section) gives more torsional rigidity and more effective plate allowing an increase of the stiffener spacing, hence a reduction in the number of stiffeners. During the replacement process the following constraints are taken into account: the weight of the stiffened bottom and deck panels, and the unstiffened plate width using the Y-stiffener profiles are less than those of panels with the original conventional stiffeners, whereas the section modulus of the Y-stiffener with the attached effective plate is larger than that of the original conventional stiffener. The safety margin of bottom and deck panels with Y-stiffeners is to be more than that of panels with the original conventional stiffeners. The ultimate strength of stiffened panels with either longitudinal conventional or Y-stiffener profiles were calculated according to the International Association of Classification Societies-Common Structural Rules for double hull oil tanker based on the following failure modes: unstiffened plate buckling, stiffener beam-column buckling, and stiffener torsional/flexural buckling (tripping). The attached effective plate for the Y-stiffener was calculated according to Eurocode. The Y-stiffener is a built-up section and the simplest production method is to weld the lower end of the web of a conventional stiffener to the top of the hat part. The conventional stiffener as a part of the Y-stiffener is fabricated according to the ratios stated in the International Association of Classification Societies-Common Structural Rules, while the hat part of the Y-stiffener is made by a hot-rolling process with inclination angle of the two webs of the hat taken as 30°, 45°, 60°, and 90°.