LOCAL ICE PRESSURE AND PLATE STRESS

摘要

In ISO 19906 there are recommendations on deterministic Local ice pressure values that are expressed in terms of a pressure-area relationship Pressure = 7.4 Area~(-0.7). These pressure values are used as input for determining the size and thickness of the exterior plating of Gravity Based Structures (GBS). ISO 19906 indicates The size and placement of the local contact areas shall be selected to ensure that the most critical cases are addressed but does not provide detailed guidance on how this Local pressure should be applied to the structure. One method that is commonly used is to calculate a constant Local pressure over the plate area defined by the spacing of the bulkheads and stiffeners (ISO A.8.2.5.5). Elastic analysis is then used, along with other design constraints, to determine an appropriate thickness for the exterior plating. In this paper we use the fluctuating high pressure zones that generate the majority of the ice load and which produce plate pressures that are far from uniform. The elastic bending stress in the plating for both a uniform pressure distribution and various non-uniform distributions representing high pressure zones are calculated. Simply supported and clamped boundary conditions to the plate are addressed. It is shown that even with a uniform pressure distribution in combination with a range of pressure-area relationships, unexpected results can be produced, namely that as the spacing between bulkheads increases the plate bending stress can decrease. For non-uniform loading while the total applied load is less than for the uniform loading case, particular loading geometries produce elastic plate bending stresses that are much higher. Guidance is provided on selecting appropriately dimensioned load patches that may be used in conjunction with numerically intensive design tools such as non-linear finite element modelling.