Structures cannot be created without engineering theory, and design rules have existed from the earliest times for building Greek temples, Roman aqueducts and Gothic cathedrals - and later, for steel skyscrapers and the frames for aircraft. This book is, however, not concerned with the description of historical feats, but with the way the structural engineer sets about his business. Galileo, in the seventeenth century, was the first to introduce recognizably modern science into the calculation of structures; he determined the breaking strength of beams. In the eighteenth century engineers move