Structural Iron and Steel, 1850–1900

Robert Thorne, Robert Thorne

• Editore: Routledge
• Anno: 2017
• ISBN:
  9781351897372
• Edizione: 1
• Argomento: Histoire
• Categoria: Histoire du monde

This volume covers the second great period of developments in iron construction from 1850, following its establishment as a structural material described in volume 9 of this series. Using the Crystal Palace of 1851 as a starting-point, the papers trace the history of iron-frame construction in Britain, France and America, and show its importance in fireproof construction, and in lattice truss and arch bridge design. A final group of papers illustrates the emergence of steel in framed buildings in both Britain and America. The selection brings out the important and daring contribution of individual engineers in their use of this material.

1
Some structural problems encountered in
the building of the Crystal Palace of 1851

Tom F. Peters

For the modern architect, and to a certain extent by association, even for the civil engineer, the Crystal Palace of 1851 has come to represent a structure, futuristic in intent, which the builders of the 19th century had but to follow in order to attain the fully developed modern steel structural system. The truly pioneer structure has been so idealized and its problems reduced to fit historical preconceptions and euphemism, essentially in order to provide an historical rationale for the “modern movement”, that the true value of the effort made by the builders and the real structural problems have been long obscured¹.

It is certainly correct to state that this innovative structure was indeed materially responsible for the proliferation of iron as a new structural material and for the widespread use of glass in representational building, officially termed architecture. It was however, not the first to use cast iron structurally.

The first major structure to use cast iron successfully had, of course, been the famous Ironbridge of 1779. Many greenhouses particularly in Britain but also some notable examples in France, had also preceeded the Crystal Palace, and indeed, the structural detailing, if not the actual system itself, had been largely developed and tested in advance several times and in several stages in greenhouses built by Joseph Paxton ranging from his first experiments in 1828, through the Great Conservatory he built at Chatsworth from 1837–1840, to the hastily built Lily House of 1850, also at Chatsworth. These were however, not representational structures, not counting officially as architecture. But here too the Crystal Palace had been presaged by Bunnings’ Coal Exchange of 1849 in London which also had a visible cast-iron structure. This in turn leads us back to the elegant use of cast iron in early neo-gothic church building in Liverpool, to Thomas Rickman’s St. George’s of 1813, St. Michael’s of 1814 and St. Philip’s of 1816. John Nash had also used undisguised cast-iron columns in the Brighton Pavilion of 1818–1821, not only in the famed palm-frond columns of the kitchens, but also for instance in the Red Drawing Room. And in France, Henri Labrouste had built the interior of the small reading room, called “La Reserve” of the Bibliothèque Sainte-Geneviève in Paris with the same material in 1843. Tredgold had advocated the use of the material especially as a fireproof construction in his book “Practical Essay on the Strength of Cast Iron and other Metals” of 1824. The early mills of Manchester had used post and beam construction in cast iron in conjunction with massive outer walls of masonry for precisely this reason ever since the end of the 18th century, and it has been shown that this idea had been imported from France where wrought-iron roof trusses had not been uncommon, especially for theaters, after 1780. James Bogardus had built a fireproof warehouse of cast iron in New York in 1848. However, these were all individual experiments, and a single great symbolic effort was needed to coalesce these disunited events into a new direction.

It was of course not to be the brittle cast iron, but the more flexible wrought iron in standardized sections from the rolling mills and the various forms of steel which were to make frame construction successful in the field of building. Many historians have been blinded to this fact by a misunderstanding of the structural role played by the many fascinating precast iron structures built in the latter half of the 19th century, and by the many attempts to make these structures work as frames in spite of the very obvious disadvantages inherent in the material they used. It is indeed rare in the history of architecture to hear any reference to the material and structural problems of expansion, stiffness, bending, shear, torsion and buckling which were the main concerns of builders intent on the introduction of the new material into the field of building.

Another misconception is the widespread belief that the Crystal Palace was built only of cast iron and glass. This statement was culled uncritically from the many lay reports of the time which appeared in journals and newspapers all over Britain, Europe and the United States. What fascinated these many reporters was the large-scale use of glass to an extent unknown before, and the thinness of the cast-iron columns. Understandable exaggeration of these novel and surprising features was the result. For instance, the skin of the building was not a curtain wall construction as has since been often presumed, but rather hung between the outermost posts of the structure. It was made of wood, and the cast-iron frame with its characteristic circle in the upper portion of the panel and the arch below was a superimposed decorative element. On the ground floor, no glass was used at all except for that in the panels immediately adjoining the entrances. Indeed the skin of the lowest floor consisted almost entirely of ventilation louvers in the uppermost and lowermost portions of the panels and of boarding between them. On the other hand, however, the two upper storeys were glazed over about 80% of their surface. The ground floor was ⅓ higher than the upper storeys which were also smaller in area. On an estimation, the glass surface accounted therefore for about 45% of the total outer skin, far less than is usually supposed. The roof, on the other hand, was about 90% glass, built according to Paxton’s ridge-and-furrow patent, only a small part of the building adjacent to the barrel vault of the transept being flat and covered with lead sheeting.

In the interior, the partition walls, the flooring of both the gallery and the ground floor levels, the floorbeams, all trusses of the one-storey areas which made up about 30% of the total surface, and the great trussed-arches of the barrel vaulted transept, were made of timber.

The 48 and 72 foot trusses of the double and triple spans were manufactured in a combination of wrought iron, cast iron and timber. However, all trusses of whatever material were painted the same colour throughout the building so that evidently only professionals noted that they were made of varied materials. The famous window mullions and the gutter-cum-joist structure of the ridge-and-furrow patent roofing for which Paxton had developed his famed money saving machinery, were also all of wood.

So the Crystal Palace was in fact not quite as simple and evident a structure as has been claimed. There were also essential structural differences between it and the many Victorian greenhouses from which it had originally evolved and with which it is always compared. Perhaps the most essential of these differences were the complex organisation of the erection process² and the use of a modular structural unit of 24 × 24 ft. (7.3 × 7.3 m). This element was made up of several components, the chief of which were four cast iron posts and four trusses of the same material which interconnected them. This unit was incremental and could be extended by simple addition both in plan and in height. In fact, and this too was new, the building was entirely conceived as a structural system rather than a building in the conventional sense from the very outset³.

The concept of the additive, three-dimensional module is in itself one of the most important aspects of this structure for the history of technology. Therefore we say that the Crystal Palace was basically different in structural concept from all greenhouses from which it derived, even if it was similar in detailing.

The degree of innovation in the design of the system and details was astonishing for such a rapidly conceived structure. It can only be explained by the long experience which the designer, Joseph Paxton had gained in his work on the design of greenhouses while in the service of the Duke of Devonshire. For example, the hollow posts of the system permitted rain water to be evacuated from the roof every 7.3 m in both directions. Paxton had originally developed this drainage system for the Great Conservatory at Chatsworth in 1837, and he adapted it cleverly for the exhibition building. New was that the hollow posts permitted the thickness of the sections to be varied according to their required height of one, two or three storeys or to account for the additional eccentric loading due to an unusually large span. By adjusting the thickness of the post on the inside instead of increasing the diameter, the outer dimensions could be kept constant and the joint geometry consequently be retained throughout. It appears to be the first time that this type of consideration, essential for any adaptable system of modular prefabrication, had entered the field of building.

This adaptability in section as opposed to our more modern and far less subtle overdimensioning of all components to account for unique cases involving maximum conditions, was of course rational only in a period when the cost of material was appreciable in relation to manufacturing costs. Considerations of this kind were obviously a direct consequence of the use of the new material iron in structural work, as neither masonry nor timber construction could ever have given rise to such detailing.

As in so many instances, the original idea for the development of modular elements built up of complex combinations of individual components stems from an entirely different area, in this case from the planning concepts of the architects of the French revolutionary period. In particular, the work of J. N. L. Durand (c. 1750–1833) whose repetitive spatial units of identical size and form corresponded well to the stone construction he envisaged using while inadvertently pointing the way toward later steel construction. Structurally Durand’s buildings were as traditional as the classic Greek ashlar architecture from which he derived his formal expression, but such modular problems gave rise to new structural possib...