Ultimate strength of stiffened aluminium panels exhibiting primarily torsional buckling is investigated by experimental and numerical analysis. Such failure modes are of particular interest in flat bar/bulb stiffeners, which are attractive from a fabrication point of view. Current approaches to assess torsional strength are uncertain. For instance, formulations for torsional buckling of stiffeners in steel panels are still debated. In the present paper, an experimental and numerical investigation of torsional buckling strength of longitudinal flat - bar stiffeners in aluminium panels subjected to axial compression is carried out. All 25 stiffened plates with various aluminium material (AA5083 Hl16 and AA6082 temper T6), web height, thickness were tested. Some test results are presented and compared with numerical calculation using ABAQUS (1998), considering initial deflection, welding residual stresses, as well as heat affected zones (HAZ). The experimental and numerical results are also compared with buckling strength formulations used in DNV Rules for Classification of High Speed and Light Craft (1996), NORSOK (1998) for steel, using the relevant values of the modulus elasticity and yield strength of aluminium, as well as the most recent Eurocode 9 (1998) for aluminium.


In recent years, large-scale lightweight high-speed vehicles, were constructed using high strength aluminium alloy. Stiffened panels constitute the main building block of such structures. The load carrying capacity of plates can be significantly increased by using stiffeners. These stiffened panels are required to resist extreme loading conditions, e.g. in terms of axial compressive loads. As aluminum is a quite new structural material compared to steel in ship building industry, most existing design codes for plates and stiffened panels are mainly based on the experiences with steel structures. However, the strength (buckling, yielding, collapse) of welded aluminum structures is influenced in a different manner than steel structures by the initial deflections.

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