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Behaviour and design of unstiffened plates

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Behaviour and design of stiffened plates

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Introduction to plate behaviour and design


To introduce the series of lectures on plates showing the uses of plates to resist in-plane and out-of-plane loading and their principal modes of behaviour both as single panels and as assemblies of stiffened plates.


This lecture introduces the uses of plates and plated assemblies in steel structures. It describes the basic behaviour of plate panels subject to in-plane or out-of-plane loading, highlighting the importance of geometry and boundary conditions. Basic buckling modes and mode interaction are presented. It introduces the concept of effective width and describes the influence of imperfections on the behaviour of practical plates. It also gives an introduction to the behaviour of stiffened plates.


Plates are very important elements in steel structures. They can be assembled into complete members by the basic rolling process (as hot rolled sections), by folding (as cold formed sections), and by welding. The efficiency of such sections is due to their use of the high in-plane stiffness of one plate element to support the edge of its neighbour, thus controlling the out-of-plane behaviour of the latter.

The size of plates in steel structures varies from about 0.5mm thickness and 1200mm width in a corrugated steel sheet or a flat cassette for facade to about 150mm thick and 5m width in long span bridge girder, composite or not. Whatever the scale of construction, the plate panel will have a thickness t that is much smaller than the width b or length a. As will be seen later, the most important geometric parameter for plates is b/t and this will vary, in an efficient plate structure, within the range 30 to 250.

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