Marine Technology - October 2008 - Page#73

<BODY> <span id="lblContents">? Marine Technology, Vol. 45, No. 4, October 2008, pp. 228?240 Mechanical Collapse Testing on Aluminum Stiffened Plate Structures for Marine Applications Jeom Kee Paik,1 Celine Andrieu,2 and H. Paul Cojeen3 The present paper is a summary of the R&D results obtained through SSC SR-1446 project sponsored by Ship Structure Committee together with Alcan Marine, France, and Lloyd's Register Educational Trust, UK. It is recognized that the use of ultimate limit state (ULS) design method in addition to more conventional structural design standards will help make possible to move high-speed vessels to open-ocean transiting of large high-speed vessels, which is what the US Navy is certainly trying to do. The aim of the project is to investigate the collapse characteristics of aluminum stiffened plate structures used for marine applications by mechanical testing, together with nonlinear finite element analysis (FEA). Fabrication-related initial imperfections significantly affect the ULS behavior, and thus it is of vital importance to identify the features of initial imperfections prior to ULS computations. In the present study, a statistical database of fabricationrelated initial imperfections on welded aluminum stiffened plate structures is also developed. The database and insights developed will be useful for design and building of welded aluminum high-speed oceangoing vessel structures. Keywords: buckling; high speed craft; U.S. Navy 1. Introduction THE USE of high-strength aluminum alloys in shipbuilding provides many benefits, but also presents many challenges. The benefits of using aluminum versus steel include lighter weight, which helps increase cargo capacity and/or reduce power requirements, excellent corrosion resistance, and low maintenance. Challenges include reduced stiffness causing greater sensitivity to deformation, buckling, and plastic collapse and different welding practices. The benefits noted previously are now well recognized, particularly for the design and construction of warships, littoral surface crafts, and littoral combat ships as well as fast passenger ships. The size of such ships is increasing, causing various design-related challenges compared with vessels with shorter length. In addition to aluminum alloys being less stiff than mild steel, no refined ultimate limit state (ULS) design methods involving local and overall ULS assessment exist, unlike steel structures where the necessary information is plentiful. The use of ULS design method in addition to more conventional structural design standards will be able to help design and build large ocean-going aluminum high speed vessel structures. The present paper is a summary of the R&D results obtained through SSC SR-1446 project sponsored by Ship Structure Committee together with Alcan Marine, France. Buckling collapse characteristics of welded aluminum stiffened plate structures were investigated by mechanical test- Pusan National University, Busan, Korea. Alcan Marine, Issoire, France. 3 US Coast Guard, Washington, D.C., USA. Originally presented at PRADS 2007, Houston, Texas, USA, 30 September?5 October 2007. Reprinted with the permission of American Bureau of Shipping ("ABS") and the 10th International Symposium on Practical Designs of Ships and Other Floating Structures ("PRADS"). Material originally appearing in 2007 PRADS publications may not be reprinted without written permission from ABS. Manuscript received at SNAME headquarters February 2008. 2 1 ing on a total of 78 single-bay and multibay prototype structures, which are full-scale equivalent to substructures of an 80 m long aluminum high-speed vessel structure. Weldinginduced initial imperfections significantly affect the ULS behavior, and it is thus of vital importance to identify the features of initial imperfections prior to the ULS computations and design. In this regard, the statistics of welding-induced initial imperfections on the prototype structures are measured and analyzed. The buckling collapse testing is undertaken until and after the ULS is reached. Nonlinear FEA solutions are also obtained for the prototype structures. Based on the experimental and numerical results, closedform ULS formulas are developed. In the past, useful studies on mechanical collapse testing of welded aluminum structures have of course been undertaken. In the early 1980s, a series of 76 aluminum unstiffened plate collapse tests were carried out by Mofflin (1983) and Mofflin and Dwight (1984) at the University of Cambridge, UK, and these are regarded as perhaps one of the largest and most relevant test programs for the collapse strength of aluminum plating (unstiffened plates) until now. After tungsten inert gas (TIG) welding in the longitudinal direction and metal inert gas (MIG) welding in the transverse direction, weld-induced initial distortions and residual stresses were measured and their influences on the plate collapse behavior were studied on two of the most common aluminum alloys used for the construction of high-speed vessels, that is, 5083 and 6082 alloys. In the late 1980s, Clarke & Swan (1985) and Clarke (1987) at the Admiralty Research Establishment (ARE), UK, carried out the buckling collapse testing on a total of five aluminum stiffened plate structures. This was one of the earliest collapse test programs to use ship-shaped aluminum stiffened plate structures using full-scale prototype models of allwelded construction with multiple frame bays. All material of the test structures was equivalent to 5083 aluminum alloy. More than a decade after the ARE tests, several collapse test programs on aluminum stiffened plate structures constructed by welding were carried out together with various MARINE TECHNOLOGY 228 OCTOBER 2008 0025-3316/00/4504-022800.00/0</span> <br /> <br /> <a href="http://www.digitalwavepublishing.com/" title="Digital Magazine">Digital Wave Publishing</a> </BODY>