Historical development of steelwork design
To outline the developments in the design of iron and steel for structures.
Structural theory as known today owes most of the intellectuals of France while in the late 18th Century and the early part of the 19th, Britain took the lead in practical design and application. 18th Century empiricism was replaced first by large-scale proof-loading and tentative calculation, followed after 1850 by component testing allied to elastic analysis with testing soon relegated to quality control. In the late 19th Century, the powerhouse of engineering thought shifted gradually to France, Germany, and the United States of America. Elasticity and graphical analysis held sway for about 100 years until they were challenged by plastic theory and the computer, with automation replacing hand work in calculation, production, and erection.
The developments in materials, theory, and technique were all related but varied from country to country due to different needs, shortages, and opportunities. This lecture outlines the developments in design methods for structural steelwork, illustrating this with a number of examples of iron and steel structures.
1. HISTORICAL DEVELOPMENT OF STEELWORK DESIGN: STATE OF STRUCTURAL KNOWLEDGE IN THE 18TH CENTURY AND BEFORE
Up to the late 18th Century, structures were designed essentially on the basis of proportion. To some extent, this meant no more than deciding whether sizes looked right - that is, familiar - but in many, perhaps almost all periods, there were some rules or statements by authorities which were almost as firm as our codes of practice today. The difference is that they were not based on strength or stress but on shape and scale. Stress, in the sense that the word is used in engineering today, did not exist. The materials were essentially masonry and timber with a little iron.
With masonry the real problem has almost always been one of stability rather than crushing of the material and, until quite recently, stability was usually established visually. Early tie-bars of iron in masonry construction were, it seems, also sized by eye.
With timber in the 18th and early 19th centuries, deflection was the main problem. If it was stiff enough, it must be strong enough. This may seem illogical to us today but with timber, which tends to indicate its distress by creaking, sagging, and even splitting long before failure, stiffness was not a bad criterion for adequacy. Nevertheless, timber floors did sometimes collapse, perhaps most often due to ill-conceived joints.
Until the early 19th century, it is far from clear who fixed the sizes of timbers or the connections in trusses. Probably, it was the carpenters working on experience, observation, and possibly copy books of details. In spite of growing knowledge of the strength and stiffness of different materials, this unscientific approach sufficed for the majority of construction until well into the 19th Century - at least in Britain, but perhaps less so in other parts of Europe.Read more