Ch 1B_4_1 Historical Development

STEEL CONSTRUCTION: INTRODUCTION TO DESIGN

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STEEL CONSTRUCTION:

INTRODUCTION TO DESIGN

Lecture 1B.4.1: Historical Development of

Iron and Steel in Structures

OBJECTIVE/SCOPE

To appreciate how steel became the dominant structural material that it is today, it is

essential to understand how it relates to cast iron and to wrought iron, both in its properties

and in the way that all three materials evolved.

PREREQUISITES

None.

RELATED LECTURES

Lecture 1A.2: Steelmaking and Steel Products

SUMMARY

The properties of the three ferrous metals, cast iron, wrought iron, and steel, are described

and the evolution of their production is summarized. The evolution of their structural use

is also given and the prospects for further development introduced.

1. PROPERTIES OF THE THREE FERROUS

METALS: CAST IRON, WROUGHT IRON AND

STEEL

Cast iron, as the name implies, is "cast" or shaped by pouring molten metal into a mould

and letting it solidify; a wide variety of often very intricate forms is thus possible. It is

very strong in compression, relatively weak in tension, much stiffer than timber, but

brittle.

Wrought iron is strong both in tension and compression and ductile, thus making it a much

safer material for beams than cast iron. Its main disadvantage is that, never reaching a

fully molten state, it can only be shaped by rolling or forging, thus limiting its possible

structural and decorative forms.


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The properties of mild steel are similar to those of wrought iron but it is generally stronger

and can be cast as well as rolled. However, it has a lower resistance to corrosion than

wrought iron and is less malleable and thus not so suitable for working into elegant,

flowing shapes.

These properties, in terms of strength and carbon content, are shown in Figure 1; the

values shown should be considered as indicative rather than absolute limits. They do not

include malleable or ductile cast irons which have strengths in tension considerably above

those shown.

2. EVOLUTION OF FERROUS METALS

2.1 Blacksmith's Wrought Iron

Iron has been known and used for more than three thousand years, but it was not until the

development of the blast furnace around 1500 AD that it could be produced in molten

form. In China, molten iron goes back much earlier but this is not generally thought to

have been known in the Western World until well after the independent invention of the

blast furnace. There is slender evidence that the Romans knew how to produce cast iron

but, if they did, the knowledge was certainly lost.

Before the blast furnace, iron was extracted from ore by chemical reduction in simple

furnaces or hearths. Inevitably, the scale of the operation was small and the process quite

laborious, the iron coming in a hard pasty form, far from liquid, which was then refined

and shaped by hammering. Essentially, this was 'blacksmith's iron'.

2.2 Molten or Cast Iron

Although possible in the 16th Century, molten or cast iron was hard to produce on a large

scale before the change from charcoal as a fuel to coke. With charcoal, the practical size of

furnace was limited by the crushing of the fuel by the weight of the charge of the ore and


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thus the stifling of the blast. Abraham Darby I is generally credited with the mastery of

coke smelting and, even though this was in 1709, coke smelting did not dominate the

industry until about 1750 in Britain and considerably later in other parts of Europe.

2.3 Industrialised Wrought Iron

Large scale wrought iron, as opposed to blacksmith's iron, became possible mainly as a

result of the developments culminating in Henry Cort's puddling furnace patented in 1793.

In this furnace, the carbon in cast pig iron was burnt off in a reverbatory furnace while the

impurities were drawn off by 'puddling'. As the process continued and the iron became

purer, its melting point rose and the furnace charge became more viscous, eventually

being removed in a stiff plastic form for rolling or forging. It was the enlarged scale of the

operation which was significant rather than any change in the actual material which was

effectively the same as the blacksmith's variety.

The modernising of wrought iron depended not only on the puddling process, but the idea

of grooved rollers which made possible the economic production of angle and tee sections,

and later channels and joists. Here again, Henry Cort, who patented the grooved rollers in

1784, gets the credit although the due financial rewards eluded him.

2.4 Steel

Although steel-type iron had existed for many centuries, steel as used today dates from the

18th Century. It was produced either by cementation, a process by which bars of pure

wrought iron absorbed carbon during prolonged heat treatment, or after about 1750 in

molten form by Hunsman's crucible process. Cementation was largely confined to the

cutlery and tool trades and has no real relevance to construction. Crucible steel continued

to be made, although at a decreasing level of production, until after the Second World

War; however it is uncertain how much of this was used structurally in construction

works.

It is a common fallacy that the use of steel dates from Bessemer's converter of the mid

1850s; not only did Kelly in America get there first with an almost identical process, but

the amount of steel already being produced was quite substantial. Some 60,000 tons of

steel were produced each year around 1850 in Britain alone which is far from negligible,

except perhaps when compared with an annual world production of 2,5 million tons of

iron in the same period. Bessemer's steel was certainly cheaper and could be made in

larger quantities, but its quality was uncertain. It was not until the perfection of the

Siemens-Martin open-hearth process in the 1880s that steel moved in a big way into the

construction and shipbuilding industries.

Today, very little truly structural cast iron is being used and no wrought iron is being

made. Steel is wholly dominant. There are, however, some signs of a limited revival of

cast iron, particularly in the new ductile form only available since the 1940s.


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3. ACHIEVEMENTS WITH STRUCTURAL IRON &

STEEL

In looking at the structural achievements with iron and steel in the last 250 years, it is

convenient to class these in relation to the period, or age, when each of the three ferrous

metals was dominant. Inevitably, these periods overlap and it is significant that in each

case it took quite a long time - up to 50 years - before what was found to be possible

became commercially widespread. The periods are broadly as follows:

Cast Iron Period 1780-1850 (Columns up to 1900)

Wrought Iron Period 1850-1900

Steel Period 1880 - Present Day


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These dates are essentially based on Britain where the iron industry was more developed

in the first half of the 19th Century than elsewhere. In France, there was no real cast iron

period, while in America both cast iron and wrought iron were comparatively little used

before the middle of the 19th Century, after which there was a positive explosion in their

application. Steel on the other hand, became popular at roughly the same time throughout

Europe and America. Figure 2 emphasises how short the overall period of structural use of

iron and steel has been in relation to man's knowledge of iron.

4. THE PERIOD OF CAST IRON (1780-1850)

Given availability, new materials are introduced either for greater economy or to solve

specific problems.

4.1 Cast Iron Arched Bridges

All the early cast iron bridges were arched forms in which cast iron merely replaced

masonry, the advantages being greatly reduced weight and horizontal thrust, economy and

speed of erection. The first iron bridge of any magnitude was the famous Coalbrookdale

one completed in 1779 and spanning some 33 metres (Slide 1), a structure full of apparent

illogicalities mixing carpenter's and mason's detailing but still standing proudly today. The

construction of this bridge was followed by a whole succession of cast iron arch bridges in

Britain, including Thomas Wilson's Wear Bridge of 1792-6 with wrought iron strapping to

the cast voussoirs and a span of 72 metres (Slide 2) and Rennie's Southwark Bridge of 73

metre span completed in 1819. The climax, but by no means the last, cast iron bridge, was

perhaps Telford's Mythe Bridge at Tewkesbury (1823-26) with a span of only 52 metres

but great lightness and total structural logic (Slide 3).

Slide 1


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Slide 2

Slide 3

In other parts of Europe, cast iron arch bridges were a rarity until well into the 19th

Century, the number of schemes greatly exceeding the number built. Le Pont des Arts in

Paris of 1801-3 by Cessart was, perhaps, the most famous, now, alas, replaced by a not

wholly convincing welded lookalike. There were several early cast iron arch bridges in

Russia.

4.2 Cast Iron in Buildings

With all buildings, fire was a recurring problem with timber structures. It was almost

certainly the reason for one very early application of cast iron, the columns supporting the

vast cooker hood and chimney of 1752 at the Monastery of Alcobaca in Portugal. In

Britain, cast iron was used in the early 1770s in churches, partly for the cheap

reproduction of Gothic ornament, but also for structural columns. In Russia architectural


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cast iron was used extensively throughout the 18th Century but it is not clear to what

extent it was also used to support floors and roofs.

It is hard to see any trend arising from these early applications of iron to buildings. It was

in the multi-storey textile mills in Britain in the 1790s that cast iron was first shown to

have a major future in building structures. The disastrous fire at Albion Mill in 1791 was

perhaps the biggest incentive for change. Bage and Strutt were the great pioneers.

Between them, they developed totally incombustible interiors in cast iron and brick but

with floor spans still of only about 2,5 to 3,0 metres in each direction, as had been the case

with timber interiors. Later, this iron mill construction spread to warehouses with a

gradual increase of spans.

While fire was the main reason for change in the mills, there was a growing desire in

public buildings and large houses for long-span floors which did not sag or bounce.

Timber had generally proved inadequate for spans above 6-7 metres. Between about 1810

and the early 1840s there was an increasing interest in cast iron floor beams, some with

spans of 12 metres or more such as those in the British Museum of the early 1820s (Figure

3). Sometimes these castings were used as simple substitutes for the main timbers in

essentially timber flooring, but in other cases brick jack arches, as in the mills of around

1800, or stone slabs were combined with long span cast iron beams to give rigidity, sound

insulation and fire protection. Another form of 'fire proofing' consisted of wrought iron

plates within the ceiling space arching between the cast iron beams. The climax of the

development of cast iron flooring was reached in Barry's Palace of Westminster of the

1840s. Up to the mid 1840s, cast iron was seen as the wonder material everyone was

looking for.

It is tantalising how little is known about who actually fixed the size and shape of the

beams used by Nash, Barry and other architects of this period. Thomas Tredgold's book on

cast iron of 1824 was undoubtedly influential but dangerously in error in some respects. In

most cases, it is probable that proof-loading of beams, which was widely used, provided

the main safeguard against misconceptions and poor workmanship.

Apart from the mills and the long span floors, there was a whole range of new uses of cast

iron between 1810 and 1840, sometimes on its own for complete structures as in

Hungerford Market of 1836, or Bunning's highly decorated Coal Exchange of 1847-49. In

Russia, there was also a considerable quantity of cast iron building construction in the first

half of the 19th Century, as in the Alexandrinsky theatre of 1829-32 and the Dome of St

Isaacs Cathedral (1837-41).


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Towards the close of the 1840s, cast iron had lost much of its golden image and was being

seen as an unreliable material, especially for beams. The progressive collapse of five

storeys of Radcliffe's Mill in Oldham in 1844 and the failure of the Dee Bridge in 1847

were both highly damaging to its image.

4.3 Composite Cast and Wrought Iron in Building

Not all iron in the 'cast iron period' was cast. Some of it was composite cast and wrought

iron and some simply wrought iron. There is little evidence of steel being used structurally

in this period.

In Britain, cast iron was sometimes used in combination with timber as at New Tobacco

Dock of 1811-14 or with wrought iron, as in the 1837 roof at Euston Station (Slide 4).

Slide 4

After 1840, the scale of iron construction and the proportion of wrought to cast iron in

composite structures, increased substantially. The Palm House at Kew 1844-47, by

Richard Turner and Decimus Burton, was a marked advance on earlier glasshouses and

arguably incorporates the world's first rolled I sections. Wrought iron roofs of increasing

span on cast iron columns proliferated both in the naval dockyards and for railway stations

culminating in Turner's roof of 47 metres span at Lime Street, Liverpool (1849).

In France, some highly innovative wrought iron floors and roofs had been built before the

Revolution, such as Victor Louis's 21 metre span roof of 1786 at the Palais Royal Theatre

in Paris (Figure 4). In this roof, as in the case of the bridge at Coalbrookdale, the structural

logic is not altogether clear. However, the flooring system of arched wrought iron flats

devised by M. Ango in the 1780s (Figure 5) is clearly understandable and derivatives of

this system continued in use until they were largely replaced by a number of 'fire-proof'

systems, still based on wrought iron, in the late 1840s. Cast iron impinged in France to

quite an extent in the 1830s and after, notably in the great iron roof of 1837-38 at Chartres

Cathedral and the Bibliotheque St Genevieve 1843-50, but it seems that wrought iron

always retained its dominance.


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Composite construction featured quite widely in Russia. In St Petersburg, a form of

riveted plate girder was devised in 1838 for the repair of the Winter Palace after the fire of

1837. This development was just ten years before the independent development of riveted

wrought iron beams in Britain.

4.4 Suspension Bridges

Some of the most creative work on the suspension bridge dates from the 'cast iron period'

but is wholly related to wrought iron, although Tredgold did have the temerity to suggest

cast iron support cables. In most fields of construction, America clung to timber rather


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than iron in the first half of the 19th Century, but must be given credit for introducing the

level deck suspension bridge, as patented by James Finley in 1808 with wrought iron

chassis (Slide 5). Thereafter, there was a minor battle of principles on the form of cable.

Britain favoured wrought iron chains with eye-bar links, as had Finley, while the French

preferred wire cables, the difference being largely due to the states of the iron industries in

the two countries.

Slide 5

By 1850, France had built several hundred suspension bridges, mainly due to the

enterprise of the Seguin brothers, while Britain could claim scarcely more than a dozen. If

the French had confined the wires to the sections of the cables above ground, all might

have been well, but they did not. Corrosion became a major problem brought to a head by

the collapse in 1850 of the Basse-Chaine suspension bridge with a death toll of 226.

Thereafter, substantial remedial works followed and the building of suspension bridges all

but stopped in France for many years. Nevertheless, based on French influence, wire

cables did take over from eye bar chains in America and became virtually standard

throughout the world.

5 THE WROUGHT IRON PERIOD (1850-1900)

5.1 Wrought Iron in Bridges

The wrought iron period was primarily the period of the riveted wrought iron beam which

dates from the late 1840s, although by then wrought iron had established a fairly firm

position in composite construction. Seen in the long term, wrought iron beams owe their

birth, in part, to growing doubts both on the safety of cast iron in bending and in part to

successful experience with iron ships. However, by far the biggest single contribution, not

only to the development of riveted beams, but to the whole establishment of wrought iron

as the dominant material of the period, was the design and construction of the Britannia

and Conway tubular bridges, particularly the former.

The key figures here were Robert Stephenson, engineer to the Chester and Holyhead

Railway; William Fairbairn, the practical man with experience of iron ships; and Eaton

Hodgkinson, the theorist and experimenter.


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Faced in 1845 with the then seemingly impossible task of taking trains over the Menai

Straits, when shipping interests ruled out arches and suspension bridges as they had been

shown to be inadequate for railway loads, they developed a new structural form, the box

girder, and demonstrated it on a large enough scale for trains to run inside (Slide 6).

However, it was not the bridges which mattered so much as the understanding which

resulted from the crash programme of research and testing which made them possible.

Slide 6

Between them, these three men dispelled the initial belief that wrought iron was weaker in

compression than in tension, proved that a rectangular tube was stronger in bending than a

circular or oval one, isolated the problem of plate buckling, and showed how to counteract

this behaviour with cellular flanges and web stiffeners. Thus, these three men and their

assistants established riveted wrought iron as a calculable material for beams of almost

limitless size. Further, they demonstrated the benefits of continuity in beams, even for

deadload (based on theoretical work from France) and proved that the strength of rivets

depended on clamping as much as on dowel action. The extent of material and model

testing for these bridges was prodigious.

The speed of the work was almost as remarkable as the result. The problem of crossing the

Menai straits was posed early in 1845, the Conway Bridge was opened in December 1848

and the Britannia Bridge in March 1850. In both cases, work on the supporting masonry

started in the spring of 1846 well before all the problems of the spanning structures had

been solved. Other smaller wrought iron bridges of the same period, with cellular

compression flanges were, it seems, all spin-offs from this basic development.

It is, perhaps, worth noting that concurrently with this major innovative work, Stephenson

was responsible for a mass of other railway construction, including the six-span Newcastle

High Level Bridge with cast iron tied arches of 1846-49 (Slide 7) and the ill-conceived

Dee Bridge at Chester based on trussed


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Slide 7

cast-iron beams, which collapsed disastrously in 1847 soon after it was opened. The

pressure on the leaders of the engineering profession at this time are hard to imagine and it

is no surprise that, sometimes, relationships became strained, as they did between

Stephenson and Fairbairn.

The evolution of the plate girders of today from these beams with cellular compression

flanges took place largely in the 1850s. Figure 6 shows some steps in this transformation.

The rationalisation of truss forms and their full structural evolution is another feature of

the 1850s. Many of these forms derived from timber construction in America but given

riveting and wrought iron the scope opened up enormously. The Britannia Bridge has been


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criticised for wasting material in comparison to an equivalent structure with open trussed

sides, but this is unfair when one considers how little was known about true truss action in

the mid 1840s. Figures 7a and 7b show typical intuitive and mathematically rational truss

forms of this period. There were many variations on these forms.

Numerous wrought iron bridges of all forms and sizes followed in all countries. In Britain,

I.K. Brunel's Saltash Bridge completed in 1859 and Thomas Bouch's fatal Tay Bridge

opened in 1878, stand out for very different reasons. In France, Gustave Eiffel's great

arches at Oporto and Garabit, of 1875-7 and 1880-84 respectively, are now world famous.

In America, Charles Ellet's Wheeling Suspension Bridge of 1847-9, Roebling's Niagara

Bridge completed 1855, and James Ead's St Louis Arch Bridge of 1867-1874 are all

rightly famous, although one must add that the last of these is partly of steel.

5.2 Wrought Iron in Buildings

In buildings the scope for drama in the use of iron was generally more modest, the largest

outlet being in flooring systems both in Britain and in other parts of Europe. It was almost

certainly the development of these flooring systems in France in the late 1840s and early


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1850s which provided the impetus for the commercial development of rolled joists,

regardless of whether the first ones of all were rolled there or in Britain. The size of the

joist sections gradually increased but until liquid steel took over, size was limited by the

problems of handling large quantities of puddled iron.

Cast iron continued to be used extensively for columns well after 1850. In America there

was a great vogue for cast iron facades which lasted for several decades. Bogardus and

Badger were the two main suppliers. Internally, the structures vary, with iron, masonry

and timber all represented.

Apart from these useful, but often unseen, applications of iron to traditional buildings,

some spectacular iron build structures, mainly long span roofs, were built in all countries.

Most commonly, but far from exclusively, they were over railway stations. They included

the ribbed iron dome of the British Museum Reading Room (1854-57), the 73 metre

wrought iron arches at St Pancras Station (1868) and the dome of the Albert Hall (1867-

71). These buildings were matched in France, for instance, by the Bibliotheque National

(1868), Les Halles (1854-68) and the Bon Marche Department Store (1867-78); and in

America by the dome of the Capitol in Washington (1856-64).

Throughout this period most buildings, particularly those of more than one storey,

depended on masonry walls for stability, whether or not the floors and roof were of iron.

The route to full structural framing in iron or steel is uncertain. It is often stated that the

Home Insurance Building in Chicago of 1884-85 was the first fully framed tall building

which formed part of a continuing development. Perhaps the earliest example of a stiff-

jointed frame was Godfrey Greene's four-storey Boat Store at Sheerness of 1858-60. The

Great Exhibition Building in London of 1851 and the Chocolat Menier Factory outside

Paris of 1870-71 have also been claimed for this 'first', but they both had diagonal bracing

and, anyway, had no apparently direct influence on the multi-storey steel construction of

today.

6. THE STEEL PERIOD (1880-PRESENT DAY)

Steel is not only stronger than wrought iron, but being produced in a molten state made

larger rolled or forged units practicable. However, it is not easy to identify which is which;

for several decades, steelwork was fabricated by riveting in the same way as wrought iron

and, when riveted, the two look almost exactly the same. The Forth Bridge in steel and the

Eiffel Tower in wrought iron, were completed at almost exactly the same time (1889-90).

Looking at them, who could tell the difference?

Figure 8 shows how steel took over in quantity from wrought iron in Britain. Figure 9

shows how the proportion of open-hearth steel increased until it had all but cornered the

market by 1920. The biggest incentive for change to steel lay in the ship-building industry.

Lloyds Register allowed steel plating of 4/5 the thickness of wrought iron and, by 1908,

Lloyds was insisting that all steel for shipbuilding should be produced by the open-hearth

process.


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In bridges, the steel period was mainly one of increasing size and span. Here the initiative

shifted away from Britain mainly to America where the need for major bridges, was

greatest at this time. All the great suspension bridges up to 1945 (Golden Gate, George

Washington, Transbay, etc.) were built of riveted steel with spun cables of high tensile

steel wire.

In buildings the 'Skyscraper' came of age in steel, again with the initiative mainly in

America. Long span roofs also took a leap in scale with steel both in France and America.


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First there were the great three-pin arch structures over the Philadelphia railway stations of

1893 (79 and 91 metre spans) followed by the Galerie des Machines for the 1889 Paris

Exhibition of 111 metres span - over 50% up on St Pancras. These spans, in turn, have

been dwarfed by the post-war domes over sports arenas. The span of the Louisiana

Superdome of 1975 at 207 metres is more than 3 times that of the Albert Hall.

The one big change in technique with steel was the introduction of welding, mainly from

the 1930s, although possibly earlier. Today, the rivet is as dead as the production of

wrought iron. Now welds and bolts dominate all construction in steel.

In all fields, new developments tend to follow new needs and this certainly seems to have

been the case with bridges. Since the Second World War, most new thinking on

suspension bridges, especially aerodynamic design and weight-saving, has been in Britain

while Germany has led the field on the design of cable-stayed bridges.

7. PRESENT TECHNIQUES AND FUTURE

PROSPECTS

One of the most noticeable moves in construction in the last ten years, in Britain certainly,

but it seems elsewhere in Europe as well, has been towards a revival of structural steel for

bridges and buildings. Fashions change in constructions, as in clothing, and so do needs

and costs. It is, thus, interesting to look at some of the recent variants on normal structural

steel and at rival materials to see how they have fared and to speculate on what may

happen in the future.

Weathering steel (unpainted with stabilised corrosion) and exposed steelwork fire-proofed

by water in hollow sections are both innovations of the 1960s but neither shows signs of

wide adoption. On the other hand, stainless steel, although in itself much more expensive

than mild steel or even high tensile steel, is being found to be increasingly worthwhile

when the cost of maintenance is considered.

Plastics have yet to make any significant impact except as a protective coating or for

architectural trim.

Aluminium was once thought to be a dangerous rival to structural steel but, so far, it has

made little impact in bridge or building structures. Reinforced concrete - still dependent on

steel - has been a strong and growing competitor of fabricated steelwork since the 1890s,

largely because of its in-built fire resistance, helped in the 1950s and 1960s by an

architectural desire to 'expose the structure'. This trend is now being reversed and, since

1980, there has been a vigorous rebirth of structural steel. The increasing use of structural

steel has been encouraged by the pursuit of 'fast-track' construction and the realisation that

reinforced concrete is not a maintenance-free material. There has also been a swing in

taste from visually expressed concrete to 'high tech' styling or to the complete wrapping of

buildings in glass or masonry.

Future developments with structural steel in buildings are likely to be associated with fire

protection. Thin intumescent coatings which froth up when heated and form a protective

layer, are becoming still thinner - more like paint - but the need for such protection may be


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substantially reduced by the development of fire engineering. This development could lead

to a new era of exposed steelwork with increasing attention to the shape and form of

members and the appearance of joints. Castings of steel or ductile iron could well be in

demand once more.

8. CONCLUDING SUMMARY

The use of iron and steel in structures evolved through development in the

production and properties of the three ferrous metals, cast iron, wrought iron and

steel.

Cast iron is formed into its final shape from molten metal a liquid which is poured

into a mould and solidifies. Wrought iron never reaches a fully molten state and is

shaped by rolling and forging. Mild steel can be cast as well as rolled but has a

lower resistance to corrosion than wrought iron.

Iron has been known and used for more than three thousand years but it is only in

the last 250 years that new production methods have allowed the large scale use,

first of cast iron, then wrought iron and finally steel. Cast iron was widely used in

bridges and buildings in the period between 1750 - 1850.

Wrought iron became popular during 1850 - 1900 allowing the construction of

many novel bridges and building structures of increasing size and span.

Steel came into increasing use from about 1880, and being stronger than wrought

iron, has been used to build even larger structures. The introduction of welding of

steel was a major innovation in connection techniques which facilitates the wider

use of steel.

For the future, stainless steel is being found to be increasingly attractive despite its

greater cost. The development of fire engineering may lead to a new era of

exposed steelwork together with a wider use of coatings of steel or ductile iron.

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Ch 1B_4_1 Historical Development

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