WHAT CLIFTON IS TO BRIDGES, THE CRYSTAL PALACE IS TO BUILDINGS
One of the engines driving the penetration of iron, and later, steel, structures into a marketplace dominated by masonry and timber was that of the architectural or engineering competition.
Particularly in the early development of the material, the freedom to innovate afforded by competitions did much to increase the understanding of the behaviour of iron and steel in buildings and structures. Moreover, key structures helped to show the possibilities and advantages of these 'new' materials.
The idea that the gorge over the River Avon at Clifton should be bridged was not particularly new, but the means to do so practically with a bridge that would allow the navigation of tall ships ruled out masonry, and the elegant but precarious timber structures of, say, the American railroads were some years (and several cultural leaps) away. Thomas Telford had already bridged the Severn in several places - the Mythe bridge demonstrating a precursor to the now ubiquitous diagrid, his bridge over the Menai Strait at Anglesey being the first iron suspension bridge.
It was natural to develop technology in the 1829 competition for Clifton, but Telford was on the panel of judges and was unable to enter the competition in the normal way. It did not, however, stop him from promulgating his own ideas during the deliberations and proposing his own design.
Telford must have had more than a few proprietorial feelings towards what was essentially his milieu and one can sympathise with his frustration in being unable to inform the debate, other than by choosing a winner.
The other judges and the profession in general baulked at the idea of an assessor indulging in such self-aggrandisement and a second competition was run in the following year. This was eventually won by Brunel, who produced the design which has become the logo for all suspension bridges.
What Clifton is to bridges, the Crystal Palace is to buildings. Another aspect of these early competitions is that the prime mover, at least initially, was not an architect. The early adopters of iron and steel technology were those best placed to understand the materials' advantages in construction applications - engineers and specialist contractors. The Crystal Palace is attributed to Joseph Paxton, the head gardener on the Duke of Devonshire's estate at Chatsworth. In his position he had been responsible for the construction of several greenhouses, ostensibly designed by Paxton but realised by the specialist firm of Henderson and Fox.
For the competition to house the Great Exhibition of 1851, the winner would enjoy royal patronage. As such there was huge interest, with 245 entries, and a huge committee to oversee the selection process. In an echo of Clifton, Brunel was on that committee and must have felt equally frustrated at the monster which was being cobbled together from various bits of schemes around the table. The committee rejected all of the submitted designs and elected to do the work itself. Paxton's 'design', initially outlined on a piece of blotting paper, was adopted because it had the shortest programme of any of the schemes under consideration.
The building itself is often used as a paradigm for the subsequent waves of interest in modular building. In some respects this is justified. Paxton's idea allowed for disassembly and subsequent relocation. However these techniques had been in use for some time in other botanical and industrial applications; Paxton had the advantage of a somewhat larger audience.
Structurally, cast iron, wrought iron and timber were used; cast-iron main beams spanned across from columnar aisles on either side of the main promenades. Post-tensioned timber elements, perpendicular to the main structural elements, known as 'Paxton gutters', supported cloche-like ranks of glass rooflights.
Part of the cleverness inherent in the design was the recognition that standardisation requires a commonality of detail; most structural elements of the Crystal Palace had identical outside dimensions. Columns, for example, were the same size but had different internal thicknesses, which were dependent on their position and loading.
Architectural competitions also have a reputation for breaking new talent. The proposal by relative unknowns Renzo Piano and Richard Rogers for the Pompidou centre in Paris was a new kind of structure. Though its antecedents were in the tradition of the glasshouses and exhibition halls of the 19th century, its use of materials was firmly in the 20th.
Cast iron has certain properties - casting imparts a brittleness, so cast iron is, generally speaking, good in compression but poor in tension. Its performance can be improved by forming, heating and shaping a raw bloom of iron into the preferred shape.
Paxton used this wrought iron for the longer spans in the Crystal Palace because of its superior structural properties. Working the iron aligns the metal's molecular arrangement - cast iron is almost fibrous at a microscopic level while wrought iron has a much finer 'grain' and more closely resembles steel.
Steel, which is iron reduced to remove most carbon, can also be cast, but this technology was not yet widely used for construction at the time of the Pompidou competition. Piano and Rogers, with engineer Arup, proposed a cantilevered cast steel 'gerberette' for the Pompidou, which took load from a lattice floor beam on its short end and, using a hollow steel column as a support for the gerberette and a fulcrum point, resolved the load by use of a steel tension column placed at the extremity of the long end of the gerberette's cast-steel arm.
The floor is, essentially, levered up. This method allowed for clear-span internal spaces and created a service zone between the floor edge and the tension columns, a clear example of the material informing the architecture.
This has informed some of the recent Student Architectural Design Award entries and Constructional Steelwork Award winners. It has also informed the call for expressions of interest for a new sustainable housing competition, 'Living Steel' - for this and for entering the two above awards for 2006, see page 66. The development of iron and steel structures is closely bound to the competition format and, as a producer, so is Corus.