Introduction to plate behaviour and design

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Behaviour and design of unstiffened plates


To discuss the load distribution, stability, and ultimate resistance of unstiffened plates under in-plane and out-of-plane loading.


The load distribution for unstiffened plate structures loaded in-plane is discussed. The critical buckling loads are derived using Linear Elastic Theory. The effective width method for determining the ultimate resistance of the plate is explained as are the requirements for adequate finite element modelling of a plate element. Out-of-plane loading is also considered and its influence on the plate stability discussed.


Thin-walled members, composed of thin plate panels welded together, are increasingly important in modern steel construction. In this way, by appropriate selection of steel quality, geometry, etc., cross-sections can be produced that best fit the requirements for strength and serviceability, thus saving steel material.

Recent developments in fabrication and welding procedures allow for the automatic production of such elements as plate girders with thin-walled webs, box girders, thin-walled columns, etc. (see Figure 1a). These can subsequently be transported to the construction site as prefabricated elements.

Due to their relatively small thickness, such plate panels are basically not intended to carry actions normal to their plane. However, their behaviour under in-plane actions is of specific interest (see Figure 1b). Two kinds of in-plane actions are distinguished:

a) those transferred from adjacent panels, such as compression or shear

b) those resulting from locally applied forces (patch loading) which generate zones of highly concentrated local stress in the plate

The behaviour under patch action is a specific problem dealt with in the lectures on plate girders (Design of box girders and Advanced design of box girders). This lecture deals with the more general behaviour of unstiffened panels subjected to in-plane actions (compression or shear) which is governed by plate buckling. It also discusses the effects of out-of-plane actions on the stability of these panels.

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