General remarks on shell structures

This book is about thin shell structures. The word shell is an old one and is commonly used to describe the hard coverings of eggs, Crustacea, tortoises, etc. The dictionary says that the word shell is derived from scale, as in fish-scale; but to us now there is a clear difference between the tough but flexible scaly covering of a fish and the tough but rigid shell of, say, a turtle.

In this book we shall be concerned with man-made shell structures as used in various branches of engineering. There are many interesting aspects of the use of shells in engineering, but one alone stands out as being of paramount importance: it is the structural aspect, and it will form the subject of this book.

Now the theory of structures tends to deal with a class of idealised or rarified structures, stripped of many of the features which make them recognisable as useful objects in engineering. Thus a beam is often represented as a line endowed with certain mechanical properties, irrespective of whether it is a large bridge, an aircraft wing or a flat spring inside a weighing machine. In a similar way, the theory of shell structures deals, for example, with ‘the cylindrical shell’ as a single entity: it is a cylindrical surface endowed with certain mechanical properties. This treatment is the same whether the actual structure under consideration is a gas-transmission pipeline, a grain-storage silo or a steam-raising boiler.