Keywords: corroded steel plate, in plane axial compression, corrosion, post-buckling strength, ultimate strength.

Marine environments are recognized to be very corrosive for mild and high tensile strength steels. For reasons of economy, such steels are still the preferred materials for offshore structures, ship hulls, sheet piling and harbour-side facilities. Statistics for ship hulls show that around 90% of ship failures are attributed to corrosion, including corrosion fatigue [1,2,3]. For oil tankers and bulk carriers there have been a number of sinkings and environmental disasters attributed to poorly maintained and highly corroded hulls.

Unstiffened and stiffened plates are the main structural elements within the marine structures such as ships and offshore floating production units. The plates between stiffeners experience significant compressive loading as a result of the longitudinal bending of the hull girder in a seaway and, therefore, the compressive strength of the steel plates is of primary concern to the designer. As a consequence the evaluation of plate compressive strength has mainly been achieved through laboratory experiments in recent decades. For a realistic assessment of the buckling and post-buckling behaviour of steel plates large deflection theory must be used. The solution of this mathematical model for the post-buckling behaviour of plates is extremely complicated and tedious, and only a few particular approximate solutions have been derived. Many of the compressive strength models in use today reflect analyses made on the results of the laboratory experiments. Small deflection theory for plates is well established [4]. But unfortunately small deflection plate theory is of limited practical value for the analysis of ship plates since the deflections experienced by these plates in severe loading conditions are usually several times the plate thickness, which is well beyond the range of validity of this model. The large deflection mechanics of steel plates is a highly non-linear problem whose solution relies on the use of numerical techniques such as non-linear finite element analysis. However, the use of non-linear finite element methods to analyse the buckling and post-buckling behaviour of plates was not practical until relatively recently because of the computational resources required by this method.

An investigation into the buckling and post-buckling behaviour of corroded plates used in ships and other marine structures is presented in this paper. The non-linear finite element analysis was performed using ANSYS. The plates are selected among the real steel plate dimensions used in marine structures. They have initial deflection induced by welding and fabrication processes. The plates are considered to have corrosion on one side.

1

H. Emi, A. Kumano, N. Yamamoto, Y. Nakamura, N. Baba N and H. Shihara H., "A recent study on life assessment of ships and offshore structures", Tech Bull Nippon Kaiji Kyokai, 9:27-49, 1991.

2

C.P. Gardiner and R.E. Melchers, "Corrosion analysis of bulk carrier ships", Proceedings of the Conference on Corrosion & Prevention, 9-12 November, Brisbane, 1997.

3

American Bureau of Shipping, "Final report of Investigation into the damage sustained by the M.V. Castor on 30 December 2000", 1991.

4

S.P. Timoshenko, S.P. and S. Woinowsky-Krieger, S., "Theory of Plates and Shells", Second Edition, McGraw-HillBook Company, London, 1959.

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