Ultimate Strength of Hull Plates under Monotonic and Cyclic Uniaxial Compression

Abstract

As the most fundamental structural components of the ship hull, the hull plates' ultimate strength not only affects their own load bearing capacity, but also contributes to the ultimate strength of the whole ship hull. Through the literature survey of the ultimate strength of hull plates, it can be found that most of the ultimate strength research studies focused on the ultimate strength behavior of hull plates under monotonic increasing loading. Considering the motion and deformation of hull girders among sea waves, the ultimate bearing capacity research of the hull structures under cyclic loading maybe more in line with reality. In this article, the local instability tests of plates under cyclic uniaxial loading carried out by Fukumoto and Kusama is reanalyzed. Based on the tests carried out by Fukumoto and Kusama, some fundamental behaviors about the ultimate strength and unloading and reloading paths of the plates under cyclic uniaxial compression are summarized. Then, a simple approach to construct the average stress-average strain relationship of the hull plates exposed to cyclic compression is proposed. Finally, tests on six square-column models are carried out to simulate the collapse behavior of the hull plates under cyclic uniaxial compression. The present study shows that the average stress-average strain relationship of hull plates under cyclic compression can be constructed by a simple approach conveniently and accurately. Meanwhile, the ultimate strength behavior of the hull plates under cyclic uniaxial compression can also be reflected well by the simple approach. 1. Introduction Ultimate strength is a critical and fundamental consideration in the design of ship and offshore structures. An appropriate level of the ultimate strength of a ship hull is perhaps its most important guarantee of structural safety. Accurate assessment of the ultimate strength and/or residual ultimate strength of a ship is pertinent not only for the initial design, but also for the operation, maintenance, repair, and even disaster management, rescue, and salvage assessment of the ship hulls in accident situations. The first attempt to calculate the ultimate hull girder strength was developed by Caldwell (1965), who applied "Rigid Plastic Mechanism Analysis" to evaluate the ultimate strength of the hull girder. From then on, the ultimate strength of ship structures (including plates, stiffened plates, and hull girders) was widely studied by numerous scholars. Certainly, a great deal of developments have made naval architects obtain a clearer understanding of the ultimate strength behaviors of ship structures. However, because of the complexity and importance of the problems related to the ultimate strength, they still need to be explored more deeply. As described in the report of 19th International Ship and Offshore Structures Congress (ISSC 2015), "with these developments ultimate strength assessment is now becoming a more important issue to ensure the safety of ship structures."