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Английский язык для студентов строительных специальностей
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SUPPLEMENTARY READING | 285
^ТЕХТ 2
ENGINEERING DESIGN IN THE TIME OF THOMAS TELFORD
By Bill Addis
Thomas Telford, the Institution of Civil Engineers' first president, was born 250 years ago this year. His career spanned a half-century that saw some of the most remarkable changes in the way European engineers approached the design of buildings, bridges and machines. This paper reviews the development of engineering design, science and education during Telford's era, revealing that Britain was then far behind France, Germany and other European countries. Through the work of Telford and others, Britain's engineers embraced the practical experimental approach that scientists throughout Europe had developed in the eighteenth century to generate new engineering knowledge and understanding. By the early nineteenth century Britain was emerging as a leading engineering nation.
The era spanned by Thomas Telford's life (1757-1854) is usually characterised as being the period when wrought and cast iron began replacing the traditional materials of stone, bricks and timber for the construction of buildings, bridges and machines. However, these were not the only changes to the world of engineering.
The same half century saw many other developments that affected how engineers undertook design and construction. These developments were taking place all over continental Europe — from Scandinavia to Russia, Italy and Spain — and news of them usually travelled fast, either through open visits by leading engineers, via non-technical travellers, or by means of military and industrial espionage.
Telford was a gregarious man — indeed, promoting contact between engineers was one of his reasons for becoming president of the newly formed Institution of Civil Engineers in 1820 — and it is more than likely that he was aware of everything mentioned in the following review of the world of engineering design during his lifetime.
Building with new materials.
Concrete.
Telford's life covers the half-century when the use of concrete became firmly established in the construction industry. It had been widely used in France in marine engineering and for bridge foundations by the mid-eighteenth century.
John Smeaton (1724—1792) discovered hydraulic cement on a trip to the Netherlands and experimented to achieve the best mix design before using it for concrete (or beton as it was then called) in his Eddystone lighthouse (1756—1759) and in the foundations of Hexham Bridge (1777). By the early nineteenth century, it was being widely used in Britain in the construction of the docks and harbours, for example in London's docks, as foundations for the docks and buildings and for mass concrete walls.
Telford used a bed of concrete for the foundations of his St Katherine's docks (1826). Although the chemistry of concrete was established in the late eighteenth century, mainly by French scientists such as Vicat, the modern understanding of mix-design was not gained until the early twentieth century through the work of US engineering scientist Duff Abrams.
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Wrought iron.
Wrought iron had been in widespread use in Europe since the late middle ages, both for military use — armour, cannon, other engines of war and shipbuilding, and for civil use — in tools and for load-bearing applications where timber was insufficiently strong, stiff, or durable. Notable uses were for tied masonry arches in many large churches, a practice dating from the sixth century in the Middle East, and the iron chains used in the dome of St Peter's in Rome (1550-1570) and by Christopher Wren at St Paul's cathedral in London (1670—1710). Most large timber roofs had iron straps to carry tension forces across joints and support long timber tie-beams. Wren used iron ties to support a mezzanine floor at Hampton Court near London, and to help support large, first-floor bookcases at Trinity College library in Cambridge. Making best use of Jean Tijou, his French iron master at St Paul's, Wren also used wrought iron in 1692—1693 to make columns to support the balcony in his refurbishment of the chapel of St Stephen at the House of Commons in Westminster.
286 Английский язык для студентов строительных специальностей
SUPPLEMENTARY READING 287
Cast iron.
The use of cast iron in Europe also had its origins in military applications — notably the barrels of cannon in Germany from the mid-fifteenth century. The columns used to support the kitchen chimney in a monastery near Lisbon in 1752 were almost certainly an example of market diversification by the local cannon foundry. Smeaton was one of the first engineers in the 1750s to use cast iron consistently for the components of mills that were most subject to wear, and the first all-cast-iron machinery for a flour mill was built in 1784. The first cast-iron I-section rails were made by Jessop in the 1780s.
The iron bridge, completed in 1779 in Shropshire near the modern town of Telford, was built as a massive advertisement for new uses of cast iron, and a number of nearby churches featured the earliest use of cast iron in an architectural context, where columns were used to support balconies. Cast-iron columns in industrial buildings were used by William Strutt (1756-1830) in a number of buildings in the Derwent Valley, beginning with the cotton mill in Derby in 1792 — 1793. The first cast-iron floor beams were used by Thomas Bage in the flax mill at Shrewsbury in 1796-1797.
Steel.
The manufacture of both wrought and cast iron improved during this period, both as a result of the direct practical experimentation in foundries and also using the results obtained by a number of scientists, notably by the French physicist Reaumur, whose book "The art of converting iron into steel and making cast iron softer" (more malleable), was published in 1722, and the Swedish metallurgist Т. О. Bergmann, who established the important effect of carbon content on the properties of alloys of iron in the 1760s. Riveted, wrought-iron boilers for steam engines were being made from the 1750s and flat sections and rods of wrought iron were being rolled (rather than hand-forged) in Sweden in the 1740s and in England from the early 1780s.
Making buildings more fireproof.
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The increase in use of wrought and cast iron in buildings was largely a consequence of many fires in theatres and in multi-storey factories and warehouses that had often resulted in terrible loss of
life as well as the loss of buildings and the expensive manufacturing or theatrical stage machinery inside.
The French architect Jacques-Germain Soufflot was probably the first to take what would now be called a fire-engineering approach to the design of buildings for his theatre in Lyons, completed in 1754. He not only sought to avoid the use of flammable materials, he also installed water tanks and hosepipes above the stage, he created strict compartmentalisation between the stage, dressing rooms and auditorium, and the stairways were made entirely of stone and enclosed by sturdy fire doors.
Towards the end of his life (1781) he was responsible for the first all-iron, fireproof roof truss, in the Louvre palace. This idea was used a few years later by the architect Victor Louis in his Theatre Francais in Paris, which had an iron roof trass spanning 22 m as well as a ceiling to the auditorium made using fireproof poteries — hollow clay pots and iron. News of this fireproof construction soon reached William Strult in Derbyshire, who used hollow clay pots in some of the jack arches in his fireproof mills and warehouses from 1792. Drury Lane theatre in London was the first to be fitted with an iron safety curtain in 1794.
Material strength and stiffness.
One characteristic of engineers is that they use calculations to raise their confidence that a proposed design will work. For load-bearing applications, the two key quantities are the strength and stiffness of materials. In Telford's time, these properties of materials were effectively embodied for common applications in well-known standard dimensions of, for example, timber floor beams or roof trusses of various spans. The dimensions of the elements of masonry buildings and retaining walls were also well known among the specialist dealing with these crafts; this tradition went back many centuries.
The use of iron, however, presented new challenges. Not only were its properties little known in the mid-eighteenth century, but there were no long-established standard designs and, most importantly, being a manufactured material, its properties varied significantly according to the source of the iron.
It was both the need for engineers to know materials properties and the general inquisitiveness of scientists that led to the growth of
29Q | Английский язык для студентов строитель ны х специальностей
includmg one 15 m long at a scale of 1:20 - to establish the tension at the ends and to verify the shape of the chain under bridge-deck loads.
Drawing in three dimensions. ort ™e Pla"s' sections and perspective drawings were well established before the eighteenth century, these were of limited use m dealing with complex three-dimensional geometry. This problem attracted the growing interest of engineers in the early eighteenth century, especially for drawing large stones of irregular shape -me science of stereotomy. By drawing stones before construction began it was possible to prefabricate all the stones necessary to construct a vault, for example, and then assemble them quickly -very much more quickly than the traditional technique of cutting a stone only when the adjacent stones beneath and to the side had SfiS if*! Pl3Ced- Mthoueh this technique was well established in the whole of continental Europe by around 1740, it was little used m Britain and there is no evidence that Telford used it. о*ь T№°d,of graphical representation familiar today as orthographic, or third-angle projection, was devised by the French engineer Gaspard Monge (1746-1818). Called "descriptive geometry by him, it was developed as a new means of setting out
япн I «!f г/" 7gg,ed terrain in order t0 balance the cut and fill ™ de,?Jh? Мсайоп - which means ensuring defending cannon could attack key surrounding areas and that the fort was not vuinerab e to attack by cannon mounted on nearby vantage points, l he whole process was extremely complex to calculate using three-dimensional co-ordinate geometry, highly prone to error, and could take several weeks.
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iu™ginC t]f 8и.ф,"8е ofhis commanding officer when the young Monge completed this task in only a few days. The commandant's
Ц16?10?38 d,lsbelief but' on checking the work, this turned to wonder. Monge s technique was quickly declared a state secret and by around 1800, was taught in all the French military academies. Its use gradually escaped into civil projects and the public domain including England, by the mid-nineteenth century facilitating calculations. Jhe calculations that could be performed using drawings and geometrical constructions had been enhanced by the development ot orthographic projection by Monge.
SUPPLEMENTARY READING | 291
Generally speaking, though, it was the surveyors rather than draftsmen who were the most numerate among those involved in construction. Their work involved mapping the terrain and landscape, setting out new works such as bridges, roads and canals, as well as estimating the quantities of materials involved, including excavations, cut and fill, and construction materials ranging from brick, dressed stone, mortar, timber and iron to glass, lead and tiles for buildings. Land surveying required great accuracy that could be achieved only by hand calculations and the use of six-, eight- or sometimes ten-figure tables of logarithms, trigonometric ratios, squares, cubes and roots.
By the late eighteenth century there was a small but growing number of engineers, especially in continental Europe, who were highly trained in mathematics and were familiar with both complex analytical geometry and calculus. Belidor's book "Architecture Hydraulique" (1737—1753) was the first engineering book to use calculus, for calculations of water flow. Nevertheless, such sophisticated mathematics was beyond most engineers' abilities and
needs.
Most significant of all, this period saw engineers starting to use the slide rule for calculations that required no more than three-figure accuracy — that is most of their day-to-day calculations. The slide rule had been devised in the 1620s, very soon after the invention of logarithms, and was used mainly by astronomers and navigators. By about 1770 it was known to some engineers, but we can only guess at how widespread its use was.
The firm of Boulton & Watt recognised the usefulness of the slide rule and, from the mid-1770s, began making what came to be known as "Soho Scales" — named alter the company's Birmingham works — as a sideline to its steam-engine business. The first guidance in an engineering book on how to use a slide rule was in "A Treatise on the Steam Engine" by John Farey (1827), at a time when slide rules generally still did not have moving cursors to ease
their use.
Although Telford would have been aware of the use of contour lines to show depths of the sea, which were devised by the French geographer Ph. Buache in 1737, he did not live to see the rapid
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