ULTIMATE STRENGTH OF A SHIP'S HULL GIRDER IN PLASTIC AND BUCKLING MODES

Knowledge of the limiting conditions beyond which a ship's hull girder will fail to perform its function is important in assessing accurately the true margin of safety in the design of ships. Such information is essential also for developing design procedures, requirements, and rules which achieve uniform standards among vessels of different sizes and types. In this report, these limiting conditions were analyzed with the objective of determining the ultimate strength of a hull girder. The ship was considered to be subjected to a realistic loading consisting of vertical and lateral bending moments and torsional moment. Buckling and instability of the hull stiffened plates, the fully plastic yield moments, and the shakedown moments were further developed in a procedure for estimating the ultimate capacity of the hull. New interaction relations for the ultimate strength of ships subjected to combined moments were developed in this study. The fracture (fatigue and brittle) modes of failure were not included. An application to a 200,000 ton displacement tanker was carried out to show the details of the procedure and to examine the effects of various factors on the ultimate capacity of the hull. Lack of adequate formulations in certain areas were pointed out particularly when the collapse mode involved coupling between several mechanisms of failure. Analytical studies as well as a two-part test program were recommended with their objectives outlined. (Author)