ch 1b_4_2 historical development of steelwork design
DESCRIPTION
A detailed view design, production, and erection of steel structures according to the new European code EC3.TRANSCRIPT
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STEEL CONSTRUCTION:
INTRODUCTION TO DESIGN
Lecture 1B.4.2: Historical Development of
Steelwork Design
OBJECTIVE/SCOPE
To outline the developments in the design of iron and steel for structures.
PRE-REQUISITES
Lecture 1B.4.1: Historical Development of Iron and Steel in Structures
RELATED LECTURES
Lectures on the metallurgy of steel; a useful background to many other lectures, notably
those dealing with the design of particular structural types.
SUMMARY
Structural theory as known today owes most of the intellectuals of France while in the late
18th Century and the early part of the 19th, Britain took the lead in practical design and
application. 18th Century empiricism was replaced first by large-scale proof-loading and
tentative calculation, followed after 1850 by component testing allied to elastic analysis
with testing soon relegated to quality control. In the late 19th Century, the powerhouse of
engineering thought shifted gradually to France, Germany and America. Elasticity and
graphical analysis held sway for about 100 years until they were challenged by plastic
theory and the computer, with automation replacing hand work in production and erection.
The developments in materials, theory and technique were all related but varied from
country to country due to different needs, shortages and opportunities. This lecture
outlines the developments in design methods for structural steelwork, illustrating this with
a number of examples of iron and steel structures.
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1. HISTORICAL DEVELOPMENT OF STEELWORK
DESIGN: STATE OF STRUCTURAL
KNOWLEDGE IN THE 18TH CENTURY AND
BEFORE
Up to the late 18th Century, structures were designed essentially on the basis of
proportion. To some extent, this meant no more than deciding whether sizes looked right -
that is, familiar - but in many, perhaps almost all periods, there were some rules or
statements by authorities which were almost as firm as our codes of practice today. The
difference is that they were not based on strength or stress but on shape and scale. Stress,
in the sense that the word is used in engineering today, did not exist. The materials were
essentially masonry and timber with a little iron.
With masonry the real problem has almost always been one of stability rather than
crushing of the material and, until quite recently, stability was usually established visually.
Early tie-bars of iron in masonry construction were, it seems, also sized by eye.
With timber in the 18th and early 19th Centuries, deflection was the main problem. If it
was stiff enough, it must be strong enough. This may seem illogical to us today but with
timber, which tends to indicate its distress by creaking, sagging and even splitting long
before failure, stiffness was not a bad criterion for adequacy. Nevertheless, timber floors
did sometimes collapse, perhaps most often due to ill-conceived joints.
Until the early 19th Century it is far from clear who fixed the sizes of timbers or the
connections in trusses. Probably, it was the carpenters working on experience, observation
and possibly copy books of details. In spite of growing knowledge of the strength and
stiffness of different materials, this unscientific approach sufficed for the majority of
construction until well into the 19th Century - at least in Britain, but perhaps less so in
other parts of Europe.
2. STATE OF STRUCTURAL KNOWLEDGE IN
BRITAIN IN THE EARLY 19TH CENTURY
In the early 19th Century, intuition gave way to calculation for all materials and theory
took over to an ever increasing extent. However, the aim of this lecture is not to outline
the development of structural theories for which most credit must go to the intellectuals of
France, but to show how, in Britain particularly but also elsewhere, these theories were
gradually incorporated in the work of ordinary engineering designers.
The fact that some of the theories were incorrect was of no importance provided that these
were related to tests and that like was being compared with like. For instance, having
established that for a rectangular beam the bending strength was proportional to:
(bd2) x (a constant depending on the material)
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where b and d are breadth and depth of section, respectively, it did not matter whether you
used Galileo's or Mariotte's incorrect theories of the 17th Century or Parent's elastically
correct one of the 18th, provided that the constant was derived from bending tests and
used in comparable circumstances for the assessment of the bending strength of other
cross-sections. In 1803, Charles Bage developed a perfectly valid method of designing
cast iron beams on the basis of tests and Galileo's bending theory.
Among the earliest mathematical design handbooks in Britain, if not actually the first,
were Peter Barlow's book on timber, originally issued in 1817, and Thomas Tredgold's
books on timber and cast iron, first issued in 1820 and 1822, respectively. Both Barlow
and Tredgold made acknowledgements to earlier work by Girard and others on the
Continent. It is worth looking quickly at the methods advocated in these books to get some
idea of how at least a British engineer could have tackled the problems of fixing the sizes
of structural members in the 1820s. The extent to which these handbooks were actually
used is uncertain.
3. UNDERSTANDING OF TIMBER IN THE EARLY
19TH CENTURY
Much of the present practice with steel derived originally from timber which makes a
good starting point.
In the simple case of direct tension, Barlow used the word 'cohesion' which is
'proportional to the number of fibres or to the area of section'. He tabulated 'cohesion on a
square inch', as did Tredgold, both basing their values on their own experiments or those
by Musschenbroek, Emerson, Rondolet and others. Thus, for direct force, the concept of
stress was there in all but the name.
For timber, Barlow stated in relation to 'absolute strength' that 'practical men assert that
not more than one fourth of this ought to be employed' but implied that so large a
reduction was not necessary. Neither the effect of knots and other defects nor the concept
of an overall factor of safety to cover all variables seemed to come into his thinking.
Tredgold merely accepted a factor of safety of 4 on the ultimate strength of timber as
disclosed by tests.
With timber, there was little need to consider beams of anything other than rectangular
section. Barlow and Tredgold gave practical rules both for strength and deflection. For
instance, for a rectangular beam of length L with a load of W, Tredgold's rule for strength
amounted to:
W =
where the constant C allowed for the strength of the material, the loading conditions and
different units for length and cross-section. There was no reference to bending moments or
section moduli. All was direct, the tabulated values of C being derived from tests on small
sections of comparable timber loaded in the same way.
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It is notable that both Barlow and Tredgold devoted as much space to deflection as to
strength, a clear follow-on from the time when sagging was the first and, perhaps the only,
indication of inadequacy.
Tredgold suggested 1 in 480 as a reasonable limit for deflection in relation to span.
When considering floor joists, Tredgold's emphasis on deflection was particularly strong.
He gave a rule, again controlled by a mysterious constant, which rightly relates the span,
spacing and breadth of the joists to the cube (not the square) of their depth but, curiously,
is independent of the load. He explained that the constant was based on scantlings 'found
to be sufficiently strong' whereas 'it is difficult to calculate the weight that a floor has to
support'. Thus, in this field anyway, the dominance of strength rather than proportion was
not yet complete.
4. UNDERSTANDING OF CAST IRON IN THE
EARLY 19TH CENTURY
For cast iron, Tredgold, who certainly produced the first real calculator's guide to the
material, moved closer to modern thinking than in his book on timber, but in some
respects went very wrong, although pardonably so.
Again, he advocated a deflection limit of 1 in 480 for beams but also what we would call a
safe working stress (f) of the frighteningly high value of 106 N/mm2 (6,8 tonf/in2). This
value he considered to be the elastic limit in bending (based on tests on 25 x 25mm bars of
cast iron). He also found the 'absolute strength of cast iron bars to resist a cross-strain'
(modulus of rupture) of these small bars to be 280-400 N/mm2 and thus thought he had
what amounted to a factor of safety of 2,6 to 3,8.
He then assumed, or so it seems because he said very little directly about it, that using the
same working stress (f) in direct tension he would have a similar margin of safety as in
bending. He assumed further and with more justification that using this stress (f) again in
compression, the safety margin would be at least as high. Thus all one needed to do was to
design to the elastic limit as a working stress and all would be well.
In the case of direct tension, Tredgold discounted the testing techniques which had given
ultimate tensile strengths of around 110-120 N/mm2 and had no reason to know that later
bending tests on larger beam castings were to show a modulus of rupture of as low as 110
N/mm2 for comparable iron. The last of these errors was specially understandable because
the variation in the modulus of rupture with size of casting has still not been fully
explained. Nevertheless, his thinking led to a potentially dangerous set of assumptions. He
even suggested cast iron links at his universal working stress of 106 N/mm2 as more
robust than wrought iron ones for suspension bridges.
It must not be implied that Tredgold got it all wrong. His method of calculating deflection
appears to be generally correct. Further, with cast iron, there was a demand for cross-
sections other than rectangular and Tredgold went into the properties of these sections at
some length, getting the right answer with the symmetrical ones, but possibly not for quite
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the right reason, and going only slightly astray on the position of the neutral axis with T-
sections and similar shapes.
On cast iron columns, as on timber ones, Tredgold's recommendations were basically
sound. He was certainly aware of the problem of buckling and Timoshenko gives him
credit for being the first to introduce a formula for calculating safe stresses for columns
(see comparison in Figure 1). However, for ties he got into a tangle once more on the
effect of length. He thought long ties to be stronger than short ones, visualising them as
being subject to something like buckling in reverse which increased their strength with
length.
The sad point about Tredgold's safe working stress, apart from his curious error on direct
tension which had only a limited effect, is that if it had been applied to wrought iron it
would have been almost universally sound. Also it would have been well ahead of any
other practical guidance of the time, at least in Britain. The detailed thinking behind some
of Tredgold's methods is not always easy to understand today, and it is doubtful whether
many of his contemporary readers succeeded or even tried to follow this in detail. It is
even more doubtful how many engineers in Britain read or understood the writings of men
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like Thomas Young or John Robinson or the works of the vast galaxy of theorists in other
parts of Europe. Some certainly tried and the level of success would be hard to measure
today.
Tredgold's book on cast iron was translated into French and German and ran into five
editions, with the same errors perpetuated, the last being issued in 1860. However, from
the 1830s onwards his practical advice was challenged by Eaton Hodgkinson's advocacy
of his 'ideal section' for cast iron beams and his simple formula related to this.
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Eaton Hodgkinson showed by direct loading tests that cast iron was about six times as
strong in compression as in tension and proportioned his beam accordingly. His simple
formula (Figure 2) has been repeated in engineering handbooks until well into this
century.
All was derived from bending tests and would be equivalent to saying:
Ultimate resistance moment = N.D.A.t
where t is the ultimate tensile strength of cast iron. If N = say 0,9, the value of t derived
from his formula would be 6,7 to 7,2 tonf/in2 which is a very plausible range. The
significant point is that even Eaton Hodgkinson was not thinking in terms of stress but of a
constant relating tests under one set of conditions to practical use in the same form. Eaton
Hodgkinson also made extensive tests on cast iron columns and published the results with
practical advice in 1840. This advice formed the basis for further recommendations for
many decades.
5. UNDERSTANDING OF WROUGHT IRON IN THE
EARLY 19TH CENTURY
Until towards the middle of the 19th Century, wrought iron was used almost exclusively in
tension for such applications as chains, straps, tie rods and boiler plates.
The tensile strength of wrought iron was fairly well understood throughout Europe from
early in the 19th Century, the mean value being about 400 N/mm2. Thus, even allowing
for quite wide variations, its tensile strength could be relied upon to be about three or four
times that of cast iron and with an incomparably greater ductility.
It was the behaviour of wrought iron in bending which eluded engineers until towards the
middle of the 19th Century. There were, of course, the French wrought iron flooring units
associated with Ango and St. Fart but these units were really tied arches.
Discounting the seemingly empirical wrought iron beams of 1839 (Figure 3) used in the
Winter Palace at St Petersburgh which had no wider influence, the wrought iron beam
dates from the mid 1840s when small rolled I beams were produced both in Britain and
France. However, the really important breakthrough came from the research and testing
for the Britannia and Conway tubular bridges. This work was a major achievement which,
more than any other event, established the technique of building up structural sections of
all sizes from rolled angles and plates by riveting. It made riveted wrought iron the
premier structural material for almost 50 years. It also marked the climax of an era of
component testing and proof-loading and heralded its end.
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6. THE YEARS OF TESTING 1820-1850
Whatever may have been written about the strength of materials, engineers in this period
tended to feel happier with tests than theory when facing new or uncertain conditions.
Proof-loading was widely applied to cast iron beams, in many cases all beams being
individually tested. Records of important buildings indicate that the modulus of rupture
under test often approached Tredgold's high figure of 106N/mm2. However unwise this
figure may have been if the beams passed with a central point load, with the usual
distributed loadings they must have had a factor of safety of 2 against the proof load.
Not only were full-size components such as beams and columns tested, but also small
sections of different materials to establish their properties. Further, the development of
new forms depended almost entirely on tests. Effectively the tubes for the Menai and
Conway bridges were designed by experiment (Figure 4). Starting from the concept that
wrought iron was just a less brittle form of cast iron, initial calculations were based on
Eaton Hodgkinson's formula for cast iron beams. Tests then showed that unlike cast iron,
wrought iron was apparently weaker in compression than in tension. Further tests proved
that this was not a property of the material but due to plate buckling, a phenomenon not
found in cast iron beams because of their heavy section. Other tests proved that for tubular
beams, a rectangular shape was more efficient structurally than a circular or elliptical one,
provided that its top and sides were stiff enough.
The tubes were designed for continuity over the intermediate supports even for self-weight
(Figure 5) but it is not clear whether the continuity analysis in Edwin Clark's book of 1850
was used in the design or in retrospect. Here again, modelling and testing probably paid a
large part in the decision making. Irrespective of how the thinking may have developed, it
led to the seemingly perfect form of a continuous tube with cellular top and bottom
flanges, web stiffeners on its sides and trains running through the middle. At this stage, the
form of web and flange stiffening seems to have been arrived at empirically. The tubular
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form of compression member gradually evolved into the simple I beam of today. Figure 6
shows some steps in this transition. It would, perhaps, be unfair to speculate on the amount
of iron which might have been saved if the sides of the tubes had been open and
triangulated. Such trusses could not then have been analysed, but nor, when work started,
could riveted wrought iron box or I beams.
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There is no space here to go into all the advances in understanding which accrued from the
two year development programme for this seemingly impossible structure nor to try to
disentangle the disputed contributions of Stephenson, Fairbairn and Eaton Hodgkinson.
The more one looks at this stupendous achievement, the clearer it becomes that it was the
testing which came first and showed 'how' and the theory which followed up and
explained 'why'. Engineers in Britain throughout the 19th Century were frightened of
mathematics.
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It is notable that in this same book with the analysis of continuity, Edwin Clark still felt
constrained to say of 'transverse strain':
"The complete theory of a beam, in the present state of mechanical science, is involved in
difficulties. The comparative amount of strain at the centre of the beam where the strain is
greatest, or at any other section, is easily achieved but the exact nature of the resistance of
any given material almost defies mathematical investigation".
Because of the magnitude of the achievement, we may be overestimating the
understanding of those responsible. Certainly the dispute over the Torksey Bridge in 1850
showed that continuity was not widely understood.
7. TERMINOLOGY: STRAIN, STRESS, COHESION,
ETC.
This may be the point where a short diversion on terminology is appropriate. In the first
half of the 19th Century the word 'stress' virtually did not exist in engineering. What is
referred to as stress today was called strain or sometimes, if tensile, cohesion, but 'strain'
also seems to have been used to denote a force (e.g. a strain of 10 tons). There was some
uncertainty in the use of these terms.
The relationship which really meant something was the proportional one between member
size and load. If, in Tredgold's words, "the strain in lbs. a square inch which any material
would bear was x then four square inches would bear 4x". That was alright for direct
tension and compression but with bending, the explanations are less clear.
According to Timoshenko the concept of 'stress on an infinitesimal plane' was due to
Augustin Cauchy and published in 1822. Cauchy also developed the valuable concept of
principal stress but again, according to Timoshenko, it was St. Venant who first defined
stress in its final form in 1845. Both Todhunter and Pearson, Timoshenko and others give
W.J.M. Rankine the credit for being the first to provide rigorous definitions of stress,
strain, working stress, proof strength, factor of safety and other phrases which are now
commonplace in engineering.
8. STRUCTURAL DESIGN BETWEEN 1850 AND 1900
While there is a danger of over-elevating the Menai Bridge designers today, there is an
even greater risk of assuming that their new-found understanding was immediately
absorbed by all other engineers. It was not, but there was a very great change in attitude
mainly in the years between 1850 and 1870. This was the period when ordinary engineers
learnt to calculate the sufficiency of most simple structural forms, beams in particular, and
to believe in their calculations - even for major structures - without testing.
1850-1870 was also the period when it became possible to analyse the forces in trusses
with certainty. Several researchers contributed to the understanding of the forces in
complex but determinate trusses. Practical textbooks were published in different countries
and translated into other languages, all telling roughly the same story. Rankine's "Manual
of Civil Engineering" (1859) was very widely read and frequently reprinted. W.C.
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Unwin's "Wrought Iron Bridges and Roofs" of 1869 showed how graphical statics now
dominated truss analysis (Figure 7). Unwin and others also showed how to build up
flanges and cover plates to match the bending moments (Figure 8). Another interesting
practical textbook is that written by Professor August Ritter of Aix-La-Chapelle
Polytechnic and published in 1862. This book gives complete analyses of several notable
British structures of wrought iron and was considered worth translating into English in
1878. Many of the methods of the 1850s and 1860s, although perfectly practicable, proved
tedious until R.H. Bow introduced his famous notation in 1873. This was exactly the sort
of systematic and almost foolproof graphical method to appeal to engineers. It has retained
its popularity through many generations and has been superseded only recently for speed
by the computer.
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In spite of growing confidence, load testing took some time to die. Large scale tests were
still being used around 1850-60 although possibly as much to satisfy clients as to reassure
designers. In the late 1840s three of the crescent trusses of 47m span for the first Lime
Street Station in Liverpool were erected as a unit in Turner's works in Dublin and tested
first for a uniform load of almost 2kN/m2 and then for eccentric loading. These trusses
have a record span and the need for assurance was understandable.
The proving of the 65m trusses for New Street Station in Birmingham (another record
span completed in 1854) was even more elaborate, as show in Figure 9. Apart from testing
the performance of a complete section of the roof, each tie member was proved to 139
N/mm2 before incorporation.
After about 1860, confidence in wrought iron had grown enough for testing even of major
building structures to be played down, although bridge testing continued.
Provision was made for testing in the contract for St Pancras Station (completed 1868) but
it was never used. The Albert Hall roof (1867-71) was erected in Fairbairn's works in
Manchester to make sure it fitted together but was not load-tested. These are just
examples. One could cite others to illustrate the change from intuition and physical
verification to the calculation of sizes with confidence.
One reason for this change was, of course, the displacement of cast by wrought iron.
Wrought iron was now recognised as a reliable material and, with rivets of definable
strength it could be built up into structures virtually limitless in scale in spite of
restrictions on the sizes of plate and angle which could be rolled. Further, and most
important of all, by 1850 or soon after, it had become a calculable material, not just for
ties and struts but also for beams.
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While it was mainly the triumvirate of Stephenson, Fairbairn and Hodgkinson who
established the riveted wrought iron beam, it was the 'elasticians' of the mid-century like
Rankine who translated this knowledge into practical advice and showed engineers how to
design with it.
With increased understanding of structural behaviour, there was a swing at this time from
intuitive feelings that strength and stiffness could be increased by redundancy to
simplification of forms so that they would be more amenable to precise calculation and
thus to more economical sizing.
The reality of the known behaviour of wrought iron was limited to the range of stress
within which the theorists were thinking. With a working stress generally not exceeding
77 N/mm2 (the Board of Trade figure in Britain) there is no doubt that wrought iron
behaved elastically and that the theory of elasticity, which became the gospel for engineers
in the third-quarter of the 19th Century, was wholly relevant.
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Hooke's law held. Young's modulus was a constant. There was no need to think about
factors of safety. You had a working stress to control your design, even though you might
still have been calling it a strain, and you had every reason to feel confident.
Stress, as we understand it, had not only been born but, by now, was the controlling factor
in almost all structural design, at least with iron, and iron was becoming increasingly
dominant where a high level of performance was needed. Elastic theory, graphical analysis
and definite rivet strengths were all that the designer required for full confidence. Around
1850, Britain had such confidence and was still leading the field in iron construction,
although much was being done in parallel elsewhere, in particular in France, Germany and
America. As the century progressed, the initiative moved from Britain with engineers like
Moisant (Chocolat Menier Factory) and Eiffel and his colleagues catching much of the
limelight.
The commercial transition from wrought iron to steel roughly between 1880 and 1900,
permitted higher working stresses (generally 93 N/mm2 instead of 77N/mm2) and the use
of larger rolled sections. Initially, it had virtually no effect on design and detailing.
Cast iron columns continued to be used widely until about 1890-1900 but were then
superseded first by wrought iron but mainly by steel. Further theoretical work on buckling
went in parallel with more advanced formulae for safe loads. It seems that amongst
practising engineers the question of buckling of struts and of thin plates remained the least
well understood aspect of structural design throughout the 19th Century.
It is not the intention of this lecture to chart the development of theoretical knowledge but
rather to show how this related to the ordinary engineer in the design office. To follow the
understanding of bending, shear and instability in more detail, the works referred to in the
list of Additional Reading should be consulted.
9. POSTSCRIPT ON THE 20TH CENTURY
In the early part of the present century, the greatest advances both in theoretical
understanding of structures and in practice were associated with the airship and aircraft
industries. For bridges, buildings and other 'heavy' structures the changes were mostly
associated directly or indirectly with welding.
The general introduction of welding in the 1930s (with Britain lagging behind other parts
of Europe and America) radically altered techniques of fabrication and introduced the
possibility of joints as stiff as the members they connected. This development in turn had
its effect on design with more emphasis on 'portal framing' for buildings and stability
through stiff joints rather than diagonal bracing.
The big change in design thinking came with plasticity in the late 1930s although ultimate-
load thinking with the concept of the plastic hinge has taken some time to replace elastic
theory. In fact, it has not wholly done so yet. Safe stresses are still quite dominant after a
reign of nearly 150 years, but their use is declining.
In the future, engineers are likely to be able to achieve far greater efficiency by
considering 'whole structure' behaviour including the effects of cladding and partitions
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especially for stiffness. This approach only becomes practicable with computers but offers
attractive possibilities for the years to come. The disadvantage could be a reduction in
adaptability. Also the understanding of designers needs to keep pace with the growing
sophistication of the design aids at their disposal.
10. CONCLUDING SUMMARY
Up to the late 18th Century, structures were designed essentially on the basis of
proportion.
Intuition gave way to calculation for all materials and theory took over to an
increasing extent in the 19th century.
Much of the present practice in steel design derived originally from timber in the
19th century. At that time the understanding of cast iron and wrought iron grew
largely on the basis of component testing and proof loading. Rigorous definitions
of stress, strain, working stress, proof loading and factor of safety appeared in the
mid 19th century and gradually ordinary engineers learnt to calculate simple
structural forms on the basis of assumed elastic behaviour and believe in the
calculations without testing.
In the 20th century, the greatest advances in the theoretical understanding of
structures were associated with the airship and aircraft industries.
The introduction of welding in he 1930s and the development of the theory of
plasticity led to major changes in design thinking.
For the future, the wider use of computers offers the possibility of achieving
greater efficiencies in structures by considering 'whole structure' behaviour
including the effects of cladding and partitions.
11. ADDITIONAL READING
I. Those who wish to delve deeply into the way in which structural theory as we know it
today first emerged in the late 18th and early 19th Centuries, would do well to go straight
to the classic authors: Coulomb, Bernouli, Euler, Navier and others.
For a more general view of structural theory and how it developed, the following books
are recommended:
1. Timoshenko S P. "History of the Strength of Materials", McGraw-Hill, New York,
1953.
2. Todhunter I & Pearson K. "A History of the Theory of Elasticity and of the Strength of
Materials from Galileo to the Present Time", Cambridge University Press; 3 volumes
1886-93.
3. Charlton T M. "A History of the Theory of Structures in the Nineteenth Century",
Cambridge University Press 1982.
4. Mazzolani F. "Theory and Design of Steel Structures" Chapman & Hall, London.
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5. Heyman J. "Coulomb's Memoir on Statics: an essay in the history of civil engineering",
Cambridge University Press 1972.
II. For a guide to practice with iron and later steel, there were many guides and text books
published, especially after 1850.
Taken as a sequence, the following books give some idea of how this advice developed:
1. Tredgold T. "Elementary Principles of Carpentry", London: Taylor 1820.
The major British work on the structural use of timber, first published in 1820 and being
reprinted as late as the 1940s. There are some details on the use of iron with timber,
particularly for the lengthening and strengthening of timber beams.
2. Tredgold T. "Practical essay on the strength of cast iron and other metals", London:
Taylor 1822.
Also several later editions.
3. Barlow P. "A Treatise of the Strength of Timber, Cast Iron, Malleable Iron & Other
Materials", London: J Weale, 1837.
The 1837 and later editions were extensively revised and added to to take account of
developments in the science of the strength of materials in the railway age.
4. Unwin W C. "Wrought Iron Bridges & Roofs", 1869.
Originally lectures to the Royal Engineer Establishment, Chatham.
5. Rankine W J M. "A Manual of Civil Engineering", London 1859, and later editions.
Rankine's manuals mark the turning point in Britain, of engineering as a science founded
on theory as against an art founded on practical experience and observation. They
summarise and extend earlier theoretical texts, notably on theory of structures and
strength of materials, and remained standard works throughout the 19th Century.
6. Warren W H. "Engineering Construction in Iron, Steel & Timber", Longmans, London
1894.