1 Fakultet for ingeni248;rvitenskap IV NTNU（1 Fakultet ingeni248;第四rvitenskap巴克）.doc

Design considerations for stiffened plates subjected to ice action introduction The intention of the present technical note is to perform a brief review of deign requirements to plating and stiffeners subjected to ice pressures. Plate analysis General The structural resistance to ice action may be assessed by means of elastic – or plastic methods of analysis. Both principles are used; e.g. the ice strengthening rules adopted by the ship classification society Det norske Veritas are based on elastic methods of analysis. On the other hand, the International Association of ship Classification Societies, (IACS), is in the process of issuing new unified rules for Polar ships. These rules are based upon plastic methods of analysis for plating, stiffeners and girders. Although the principles are different, the two approaches may yield very similar results. The actual dimensions have to be considered in relation to the action effects and partial safety factors (implicitly) assumed in the requirements. Plastic methods of analysis are generally accepted if the action effects are dominated by a few extremes and not cyclic of nature. Furthermore, the structure should possess redistribution capability of action effects and ductility. This applies notably to resistance of shell plating; the ice action is one side excursion and the plate resistance increases for finite deformations (membrane effect). As regards stiffeners/girders plastic methods may be applied; notably for combined bending and shear action. In the present case, the scantlings tend to be governed by shear action.. Thickness of shell plating –plate strip analogy When the plate the plate is subjected to uniform pressure over a continuous plate field, the plate boundaries may be assumed clamped (due to symmetry). Fpr large aspect ratios ( 2.5) plate stripe analogy may be adopted to predict the plate stresses. This model is shown in Figure 2.1. According to the rules by Det norske Veritas, the bending stress is