Plastic response of ship shell plating subjected to loads of finite height

The paper addresses the plastic response of plating subjected to loads of finite height. The need for understanding this response arises from the severe loads on midbody plating when ships are caught in compressive ice. However, the results are also applicable to level icebreaking loads in the bow and stern regions. The purpose of the paper is to develop deflection-based response equations for both transversely- and longitudinally-framed plating. Finite element analyses are used to study 344 load cases in which both structural configuration and load extent is varied. The characteristics of the plating response are examined, as well as the influences of the relevant structural and load parameters on permanent set. The plating response equations are developed by comparing finite element results for loads of finite height to results obtained with yield line theory for uniform loads. By comparing the ratios of loads required to obtain equal levels of permanent set for each structural and load configuration, equations for pressure correction factors are obtained. The factors are primarily functions of the load height to frame spacing ratio, but also include secondary influences of structural configuration. The correction factors and yield line theory are then used to examine reported damages to Baltic class vessels and to estimate the damage pressures for assumed load heights.