Elsevier

Thin-Walled Structures

Volume 45, Issue 2, February 2007, Pages 171-184
Thin-Walled Structures

Empirical formulations for predicting the ultimate compressive strength of welded aluminum stiffened panels

https://doi.org/10.1016/j.tws.2007.02.003Get rights and content

Abstract

The present study was undertaken by the support from Ship Structure Committee (http://www.shipstructure.org), a North American-based interagency research and development committee, in association with SR-1446 project, and also from Alcan Marine, France. Empirical expressions are developed for predicting the ultimate compressive strength of welded aluminum stiffened panels used for marine applications. Existing data of the ultimate compressive strength for aluminum stiffened panels experimentally and numerically obtained by the SR-1446 project is used for deriving the formulations which are expressed as functions of two parameters, namely the plate slenderness ratio and the column (stiffener) slenderness ratio. The formulae implicitly include the effects of weld induced initial imperfections, and softening in the heat affected zone.

Introduction

In recent years, high-strength aluminum alloys have increasingly been used for building high-speed vessels, and other types of weight-critical structures. In such structures, stiffened panels are the basic strength members. In this case, the calculation of collapse strength of stiffened panels in deck and bottom structures is required for structural design and safety assessment.

The stiffened panels of ship structures are generally subjected to combined loads arising from hull girder actions, but a primary load component is axial compression. Theoretically, possible collapse modes of a stiffened panel subject to predominantly axial compressive loads can be categorized into the following six types [1], [2], namely

  • Mode I: Overall collapse after overall buckling.

  • Mode II: Collapse of plating between stiffeners without failure of stiffeners which may typically occur under biaxial compression.

  • Mode III: Collapse as a beam-column, i.e.,plate-induced or stiffener induced failure of stiffeners together with attached plating.

  • Mode IV: Buckling of stiffener web.

  • Mode V: Torsional-flexural buckling or tripping of stiffeners.

  • Mode VI: Gross yielding.

The collapse of stiffened panels will occur at the lowest value of ultimate loads calculated from each of the above six collapse patterns, although some interactions between the various collapse patterns may exist in some cases. A number of theoretical and numerical methods have been suggested in the literature for predicting the ultimate strength of stiffened panels made of steel [3]. The numerical methods take an “implicit form” where numerical computer programs or procedures have been provided. However, it is often desirable to use closed-form expressions for the calculation of ultimate strength of stiffened panels, because they can be more useful in terms of design formulae, or failure functions for reliability analysis [4], [5], although some precautions must be paid to adjust factors of safety in association with uncertainties and deviations due to the strength modeling.

In contrast to steel stiffened panels, the related study in aluminum stiffened panels is limited at least for marine loading intensities and geometries [6], although some useful formulations of the ultimate compressive strength of aluminum stiffened panels have been found in the literature [7], [8], [9], [10], [11]. Some benchmark studies between the existing formulations are undertaken by Collette [6] and Paik et al. [12].

The present study was undertaken by the support from Ship Structure Committee, a North American-based interagency research and development committee (http://www.shipstructure.org), in association with SR-1446 project titled “Mechanical collapse testing on aluminum stiffened panels for marine applications” [13], and also from Alcan Marine, France.

The aim of the present study is to derive closed-form expressions for predicting the ultimate compressive strength of stiffened panels used for marine applications. The formulae are developed by the regression analysis of existing data on ultimate compressive strength of welded aluminum stiffened panels, experimentally and numerically obtained by the SR-1446 project [13]. The present paper is a sequel of the author's two papers previously published in the literature [11], [14].

Section snippets

Nomenclature: aluminum stiffened panels

Fig. 1 shows a stiffened plate structure for marine applications, composed of plating and support members (longitudinal stiffeners, longitudinal girders and transverse frames), typical for aluminum high-speed vessel structures. Due to the relatively low stiffness of aluminum as compared to steel, and in consideration of response to global hull bending loads, most aluminum vessels are longitudinally stiffened, that is, the plating between longitudinal girders and transverse frames is rigidified

Experimental and numerical data used for the formulae developments

A series of collapse testing on welded aluminum stiffened panels under axial compressive loads were carried out by the author [13]. A total of 78 prototype aluminum structures which are full scale equivalent to sub-structures of an 80 m long all aluminum high-speed vessel were considered. They were designed in terms of single and multi-bay stiffened plate structures as those shown in Fig. 4. Although various methods for fabricating aluminum ship structures are today relevant, the test program

Derivation of the ultimate strength formulations

In ship design, the hull girder strength of ships is often governed by the buckling collapse behavior of deck or bottom panels. Hence the calculation of the buckling collapse strength of stiffened panels in deck and bottom structures under axial compressive loads which are a primary load component due to ship's hull girder actions is an essential task.

Closed-form empirical ultimate strength formulae for aluminum stiffened plate structures under axial compressive loads are now derived by the

Concluding remarks

The aim of the present paper has been to develop closed-form formulations for predicting ultimate compressive strength of welded aluminum stiffened panels. Extensive experimental and numerical results on welded aluminum stiffened plate structures obtained through the SR-1446 project of Ship Structure Committee were used for the present purpose.

It was seen that the ultimate compressive strength characteristics of aluminum panels with flat bar stiffeners differ from those with angle or Tee type

Acknowledgments

The present study was undertaken at Ship and Offshore Structural Mechanics Laboratory, Pusan National University, Korea, which is a National Research Laboratory funded by the Korea Ministry of Science and Technology (Grant no. M10600000239-06J0000-23910). The author is pleased to acknowledge the support of Ship Structure Committee in association with SR-1446 project, and also Alcan Marine, France.

References (16)

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