CALCULAR LOS BALANCES DE MASA Y ENERGIA EN LOS EQUIPOS ENERGETICOS 4) DETERMINACION DEL RENDIMIENTO EN CADA OPERACIÓN Y EQUIPO ENERGETICO

The visual vocabulary which is associated with steel structures contains some of the most powerful images of modern architecture. The glass-clad framework (Fig. 3.6), the use of slender, precisely crafted structural com- ponents as visual elements (Figs 3.1 and 3.9) and the celebration of structural virtuosity in the form of either breathtakingly long spans (Fig. 3.10) or very tall buildings (Fig. 3.11) are all different aspects of the expressive, and impressive, possibilities of steel. These aesthetic devices have been used from the beginning of the modern period and are still part of the twentieth-century architectural palette. They are often the primary reason for the selection of steel as the structural material for a building.

Steel became available as a building material in the second half of the nineteenth

century, following the development of econom- ical processes for its manufacture, and,

although its expressive possibilities were not used initially, it was quickly absorbed into the well-established tradition of metal-frame building which had arisen in connection with the use of cast and wrought iron (Fig. 3.2). Iron

Fig. 3.1 Channel 4 Headquarters, London, England, 1994. Richard Rogers & Partners, architects. Concepts such as neatness, precision and high quality control are readily conveyed by the use of an exposed steel structure. [Photo:

Fig. 3.2 Cross-section and details of Bage's Mill, Shrewsbury, England, 1796. This is a very early example of an iron-

frame industrial building. The floors consisted of brick jack-arches, topped by a non-structural filling, supported on a skeleton framework of cast iron beams and columns. No walls were required in the interior. Columns were not provided in the perimeter walls which were therefore of loadbearing masonry. [Illustration. Mitchell's History of Building] 50

Iron roof frames Fireproof floors Normal column Window Special column machinery shaft for Iron columns Special column for machinery shaft Smallest section near top and bottom of column Maximum at ground floor 150mm/6 inches Iron column Iron tie-rod Iron beam Swelling at middle of column Brick jack-arches Iron -column 2.6m ( 8 . 5 f t ) high Column swells out at middle Floor, Detail of typical column beam and jack-arches Typical column 100mm (4 inches) across at top and bottom

Floor. Column top Tie-rod Socket for column Skewback

Skewback Tie-rod _{for column}Socket •Wall SIDE VIEW won TOP VIEW •Tapering flange .Skewback 100 mm 5 inches Brick jack-arch Floor surface 10 metres Iron column Socket for column Tie-rod CUT-AWAY VIEW showing iron frame and fireproof floor

Tapering flange Skewback Fireproof ceiling Brick wall SECTION BEAM SECTION Iron beam 5 5 15 20 25 30 feet 10 0 5 1 0 0 0 Underside of iron beam COLUMN SECTIONS OF SOLID CAST IRON

frameworks had been developed in the early nineteenth century principally for industrial buildings such as factories, warehouses and railway stations but were little used in the types of building which, at that time, were considered worthy of the descriptive term Architecture. As the century progressed,

however, metal frameworks were gradually absorbed into the world of architecture. They were used mainly for 'new' types of building, such as department stores and multi-storey offices, where they allowed uncluttered inter- iors to be created within buildings which were of conventional external appearance. In Europe, this was the age of revivals and the streets of the commercial districts of late nineteenth-century European cities became filled with imitation Greek and Roman temples and Italian Renaissance palaces which were in fact steel frameworks clad in masonry and which, in their scale and internal arrange- ments, bore little resemblance to their historic predecessors. In North America, the techno- logy of the steel frame and the existence of a rapidly expanding economy generated a new type of building, that of the skyscraper, which found architectural expression in the work of Louis Sullivan.

The structural technology on which these buildings were based was that of the skeleton framework, a characteristic of which was that loads were channelled into slender elements of low volume in which stress levels were high. Large-scale interior spaces were created with minimal interference from vertical structure, and plan arrangements were varied between levels in multi-storey buildings, within the constraints of a regular column grid, because walls were simply non-loadbearing partitions. The frameworks themselves were normally hidden. Internal columns were cased in fire- proofing materials and finished frequently as one of the classical orders of architecture within a conventional scheme of interior decoration (Fig. 3.3). External walls were of loadbearing masonry and were fashioned into historic stylisations. Eventually, the frame was to take over the structural function of the external walls, although, in the maioritv of

cases, the walls would continue to be of masonry until well into the twentieth century.

The first steel-framed building in Britain with a non-loadbearing external wall was the Ritz Hotel, of 1903-06, in London's Piccadilly. It is often said that the reason for the adoption of the elaborate stone facade, which did not bear any load, was that the London Building Bye- Laws did not permit otherwise but, given the conservativeness of the architectural establish- ment in England at the time, it is difficult to imagine that a building of less conventional appearance would have been erected on this very prominent London site.

The constructional system which was devel- oped in the nineteenth century in connection with metal-framed buildings, that of the complete separation of functions between structural framework and non-loadbearing walls, was to become the standard pattern for the steel-frame architecture of the twentieth century. Structural skeletons would be made to support external cladding of many different materials and the building-type would offer architects new opportunities for architectural expression. Masonry, which has ideal proper- ties as an external walling material, would still be used but other, more fragile materials, such as sheet metal, glass and plastics, would also become part of the architectural vocabulary.

The promotion of the steel framework from the status of a purely supportive role to that of a major contributor to the aesthetics of a building was accomplished by the Modernist architects of the early twentieth century. It was inevitable that they would find the material exciting. In the 1920s and 1930s they were engaged in the project of inventing a new architectural vocabulary for the modern world of industry and technology, and, from their point of view, this new structural material had many virtues. Perhaps the greatest was that it was new, but it was also appealing because it was a product of a complex and sophisticated industrial process which made it an appropri- ate medium with which to develop an architec- tural vocabulary celebrating industry and technology. Steel also had excellent structural

Fig. 3.3 Part cross-section of Selfridge's Department Store, London, England, 1907.

The structure of this building is a skeleton framework of steel beams and columns which support reinforced concrete floor slabs. Unlike in the mill building of Fig 3.2, the exterior walls do not support the floors and consist principally of glazing. The elaborate giant- order columns with their bases and stylised entablature are a non-structural screen designed to give the appearance of a Beaux Arts style 'palace'. [ Illustration, Milchell's

History of Building]

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1 0 5 10 15 metres

10 0 10 20 30 4 0 50 feet

ESCALATOR MACHINE ROOM Concrete

wall Steel beams inside

false stonework

Stone columns on Oxford Street front

Steel beams inside false stonework Canopy OXFORD STREET Pavement Revolving door Void Window Steel beams GALLERY GROUND FLOOR BASEMENT

tension and compression. Its deficiencies - poor durability, poor performance in fire, the difficulty of shaping it into useful components, the high weight of the components - were not significant, and would be overcome by employ- ing other technologies. The large ecological cost, in terms of transportation of raw materi- als and of the high energy consumption and pollution associated with its manufacture, were not an issue at the time. So far as the modernists were concerned, here was a new and exciting material whose expressive possi- bilities, if explored, might lead to a truly appropriate architectural vocabulary for the twentieth century.

The technology of the steel framework contributed to the aesthetics of architecture in the 1920s and 1930s in two quite separate ways. Firstly, it was crucial to the development of the glass-clad building; secondly, it made tenable the overt use of structural elements as constituents of a modern visual vocabulary. These two aspects of the aesthetics of

Modernism were, and still are, often combined by architects and confused by critics. They are, however, different and distinct aspects of the relationship between architecture and the structural technology of steel frameworks.

The aesthetic programme of the glass-clad framework is concerned with 'transparency'. This, and the use of 'crystalline' form, were given symbolic meaning in the 1920s by the Expressionists, notably Bruno Taut. One of the most striking images to be published by this group, however, was the well-known glass skyscraper project of Mies van der Rohe (Fig. 3.4). Despite its Expressionist genesis this building form survived the gradual triumph of Rationalism - the Rationalists could regard the glass-clad frame as a logical and honest reduc- tion of the elements of a tall building to its bare essentials - and was used at every scale in the architecture of Modernism, from small domestic buildings to the corporate sky- scrapers which dominate the skylines of most capital cities.

Among the visual sources of this architec- tural vocabulary of glass and steel were the iron-framed warehouses, factories and railway

Fig. 3.4 Glass skyscraper project, 1922, model. Mies van

der Rohe, architect. In the early twentieth century many visionary architects considered mass-produced high quality glass to be the ultimate modern building material, principally because it allowed the exterior of a building to be 'dematerialised'. The almost featureless high-rise struc- ture faced in glass was an important architectural innov- ation of the early modern period.

Fig. 3.5 Crystal Palace, London, England, 1851. Joseph Paxton, architect/engineer. This glass-clad framework made a significant contribution to the visual vocabulary of the architecture of the twentieth century. Unlike the later buildings which it inspired, the arrangement was fully justified here on technical grounds.

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stations of the nineteenth century. These had largely been ignored in their own time by the architectural mainstream but were destined to exert great influence on the visual vocabulary of twentieth-century Modernism - rather as the motifs of the architecture of Roman antiquity, as interpreted by the scholars of the Italian Renaissance, had laid the foundations for Neoclassicism and the Beaux-Arts school. A well-known example was the famous Boat Store at Sheerness Dockyard in England (1858-66) in which aspects of twentieth- century Modernism were anticipated, but other types of industrial building, especially the large train-sheds of the railway termini, were also important. Extreme versions of this type of building were the glasshouses - glass-clad frameworks of timber and iron - which had been developed for horticultural purposes in the late eighteenth and early nineteenth centuries. This particular tradition of frame building reached its climax with the Crystal Palace in London (Fig. 3.5), which was built to house the Great Exhibition of 1851.1 It was

virtually a cathedral in glass and iron and was

1 The designer of the building was the landscape

gardener loseph Paxton.

destined to exert a profound influence on the architecture of the twentieth century.

It is appropriate, in a book which is concerned principally with technical matters, to dwell briefly here on the relationship between technology and aesthetics in the context of the glass-clad framework. It was, of course, principally the look of the frame build- ings of the nineteenth century, and the Crystal Palace in particular, rather than the novelty of their technology of construction, which appealed to the architects of the Modern Movement. The buildings did, in fact, have a number of technical deficiencies. The poor thermal and acoustic properties of the external walls and the poor durability of the junctions between the individual panes of glass in the transparent skins were problematic. The latter caused leaks to develop, which in turn brought about a deterioration in the condition of the structural frameworks of timber and cast iron. None of these was a particularly serious consideration in the context of most of the glass-clad frameworks of the nineteenth century. The Crystal Palace, for example, was a temporary building designed to house a very large exhibition of short duration, and, from a technical point of view, the glass-clad frame- work was actually an ideal, and probably inevitable, solution to the problem posed,

especially as there was a requirement that the building be erected very quickly. The glass-clad metal framework, as a genus of building type, also performed well in the context of train- sheds, where generous provision for daylight- ing and natural ventilation were essential and where high levels of thermal and acoustic insulation were not required. The indifferent weathertightness of the external envelope was tolerable in the context of a large railway station where a programme of maintenance was accepted as normal.

The technical deficiencies of the glass-clad framework were serious drawbacks in the context of other types of buildings, however, and especially of those within which a 'well tempered environment' was a reasonable expectation. The buildings in which people lived, worked, became educated or were ill - the glass-clad houses, offices, schools and hospitals of the modernist twentieth century, in other words - were seriously deficient in their technical performance. Glass, if used as the sole covering for a building which is intended to be occupied by humans, actually performs rather badly in a technical sense. A masonry wall, which is pierced with glass windows for light and ventilation, is a much better technical solution to the problem of cladding a frame building.

The early Modernists, however, despite their declared allegiance to the idea of celebrating technology, were more interested in aesthetics than in technical performance. Both the Rationalists2 and the Expressionists, were

dealing in metaphor and the symbolic attrac- tiveness of the glass-clad framework ensured that mundane, practical considerations were overridden. The glass-walled building became one of the cliches of twentieth-century

Modernism - a triumph of ideas and aesthetics

2 In the context of architecture the terms Rational or

Rationalism should never be taken literally. They did not mean 'that which is logical, sensible and practical'. The Rationalists produced an architectural vocabulary which symbolised the idea of being logical, sensible and practical.

Fig. 3.6 The Seagram Building, New York, USA, 1957.

Ludwig Mies van der Rohe, architect. This was the arche- typal glass-clad framework of the late modern period.

over that which was practical in building terms (Fig. 3.6). That triumph was to make a signifi- cant contribution to the alienation which subsequently developed between the world of architecture (architects and their apologist critics) and the mainstream of society.

It is worth noting that, although the tech-

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Fig. 3.7 German Pavilion, World Exhibition, Barcelona,

1929. Ludwig Mies van der Rohe, architect. The slender steel structural columns, faced in thin coverings of stain- less steel, made a significant contribution to the aesthetics of this seminal building.

questioned, the structural performance of the glass-clad steel frameworks of the twentieth century was normally satisfactory. Most of the buildings fall into the category of 'structure accepted'3 in which the technical performance

of the structure was not compromised for visual reasons.

In many of the buildings discussed above, and especially the multi-storey buildings, the steel which formed the loadbearing structure

3 See Section 2.2, and Macdonald, Structure and

Architecture, Chapter 7.

was not actually visible. It was hidden, encased in fire-proofing materials for good technical reasons, and its presence was acknowledged only in the architectural treatment. It is for this reason that a distinction is made here between the role of steel in the glass-clad framework, where it served a purely structural function which happened to make a new aesthetic possible, and the other aesthetic part which it has played in modern architecture, that of a distinctive element in a visual vocabulary.

Metal components can be shaped with great precision and this, together with the low volume of the elements in skeleton frameworks of steel, can be used to create structures of great elegance. The exposure of steelwork and its incorporation into the visual vocabulary is an aesthetic device which has been used extensively in the twentieth century. The archi- tectural intention in this case was more-or-less

the same as with the glass-clad framework - the creation of an aesthetic which celebrated the idea of progress, of industrial technology and of the modern lifestyle which these made possible - but the method of expression was more overt. The visual and tactile qualities of steel became important factors in the aesthetic make-up of the building.

Again, Mies van der Rohe is one of the principal exemplars. In the Barcelona Pavilion of 1929 (Fig. 3.7) the steel columns act in conjunction with new treatments of traditional materials, such as marble, to create a new aesthetic. In the Farnsworth House of 1946-50 (Fig. 3.8) the l-shaped structural elements of a glass-clad framework are exposed and bring the visual vocabulary of the engineering workshop into the world of the country retreat.

The exposure of steel frameworks for aesthetic reasons was one of the favoured stylistic devices of the so-called 'high-tech' architecture of the 1970s and 1980s (Fig. 3.9). These buildings, which also were frequently glass-clad frameworks, were visually spectacu- lar and among the most memorable architec- tural images of the late twentieth century.

The relationship between the structure and the architecture in all of these cases was one of 'structure symbolised'4 and this way of treat-

ing structure usually had the paradoxical effect of compromising its technical performance, because it resulted in structural forms being manipulated predominantly in accordance with visual rather than with technical criteria.

Other problems associated with the exposure of steelwork were those of mainten- ance of the structure and of fire protection. The second of these arose only in the case of multi-storey structures and was the principal reason why steel structures were rarely exposed other than in single-storey buildings. A notable exception was the Centre Pompidou in Paris, where fairly elaborate fire-protection systems were provided to ensure that the steelwork which was exposed on the exterior of the building would meet the required fire

4 See Section 2.2.

Fig. 3.8 The Farnsworth House, Illinois, USA, 1951.

Ludwig Mies van der Rohe, architect. The mass-produced structural steel beam and column I-sections form impor- tant elements in the aesthetic vocabulary of this building.

Fig. 3.9 Sainsbury supermarket, London, England,

1986-89. Nicholas Grimshaw & Partners, architects. Exposed steel structures with exaggerated connections were one of the prominent features of the 'high-tech' style.