Figure 1.1 Peroblasco bridge over the river Cidacos, La Rioja, Spain

Figure 1.1 Peroblasco bridge over the river Cidacos, La Rioja, Spain
Chapter 1
INTRODUCTION
As if in thanks to someone’s benign effort the most profound of desires, Man’s age old dream, to walk on water and command the earth
had unexpectedly come true.
Ivo Andric – The Bridge Over the Drina
1.1. THE BRIDGE, THE ROAD AND THE RIVER
A bridge is land over water; its purpose is to extend a medium
suited to Man, the road, over another which is not, the river.
A bridgeless river will always interrupt a journey; often it
becomes difficult, hazardous or even impossible for the traveller to cross.
A bridge is a route over a river; it must allow traffic and
water flows to pass one another on different levels at the same
geographical point, thus resolving the most difficult problem
a road will encounter on its route; a bridge forms part of the
road and owes its origin to the river.
Many rivers can be forded when water is flowing at a normal rate, but a ford is always awkward to cross and becomes
impracticable when the level rises; other rivers can be crossed
in a boat, a cable ferry or a ship, but this always complicates
and disrupts the journey. On the other hand, a bridge allows
the road to continue without altering or impacting on the
traveller’s progress, by whatever means he is using; in some
cases, this is so much the case that he will often not even realize that he is crossing a bridge. The modern bridge “has no
intention of being anything other than a road” (Pablo
Neruda1); it must be humble and go unnoticed, since there
can be no break in the route to upset the traveller on modern,
high-speed roads, motorways and railways; he will only realize
Figure 1.2 Normandie bridge over the Seine, France; main span of 856
metres (1995), M. Virlogeux. Photograph taken during construction.
1
BRIDGE ENGINEERING
Figure 1.3 Pont du Gard over the river Gardon. A Roman aqueduct on the Nîmes water supply line, France (first century BC).
values, largely due to the strength of their resistant structure
which, in bridges, achieves some of the maximum dimensions
built by Man.
A bridge is the continuation of a roadway, when the latter
takes off from the ground. This definition is broader and more
up to date than previous ones because, while initially used to
cross a river, a bridge is also used to overcome other obstacles
as the road’s requirements become more complicated. Bridges
must not only include crossing over a river but also over other
types of flows, such as other traffic routes or a crossing over
any other natural or artificial obstacle; the term also includes viaducts which, according to the Royal Academy for the Spanish
there is a bridge when he sees the road rising above the land
and passing over water; and he will only see it from some other
point on the road if the alignment makes it possible or if its
size makes the structure stand out over and above the deck.
Visibility is one reason why suspension, cable-stayed and bowstring bridges are so attractive to bridge builders (the latter
including everyone ranging from designers to construction
workers all of whom contribute to the bridge becoming a reality), this is because theirs is a struggle against imposed humility; they want their bridges to be seen and act as landmarks
breaking the monotony of the traffic route;2 they are satisfied
with their constructions as human creations with expressive
2
INTRODUCTION
Language, are “constructions in the manner of a bridge for a
road to pass over a depression”, i.e. where the distance between
roadway and ground is so great that it cannot or should not be
solved with an embankment.3 According to the Academy’s dictionary, the bridge now accepts this amplitude in its first
meaning: “a stone, brick, cement, wood or iron construction
built and formed to pass over rivers, ditches and other places”.
Continuing the roadway as it separates from the land, i.e.
supporting the road into the air, calls for a structure which
is self-supporting and withstands traffic loads. In most cases,
this structure requires the use of intermediate supports because
it cannot cross the above-ground stretch with a single span.
The environment imposes greatly varying conditions on the
structure, giving rise to a whole variety of bridge types and
shapes.
The definition above still does not include all the potentialities of a bridge, because it may also carry types of flows other
than land traffic, such as water or any other liquid or gas product,
carried in canals or pipes; it may also be built, for example, to
carry utilities or communication conduits.
A bridge is, therefore, a crossing of two very different types
of flow on different levels and, in extending this definition to
the maximum, the bridge is a support for one of these flows
when it rises from the ground.
F1.3/3.10/3.30
F1.4./3.32
F3.33
These new definitions include aqueducts, which are bridges
or viaducts built for the passage of water pipes or canals. In
Roman times, they had as much or more historical significance
than roadway bridges; the Romans’ best-known Public Works
are probably the Pont du Gard for the Nîmes water supply and
the Segovia aqueduct carrying this town’s water supply line.
Although, initially, the word aqueduct refers to any water
carrier, and thus, it is defined in the Dictionary of the Royal
Academy for the Spanish Language, engineering has generally
kept the word for the raised construction, parallel to the viaduct,
and thus, we speak of the aqueduct of Segovia, of Milagros, and
so on, referring only to the bridge and not to the whole duct,
although the correct name should be aqueduct-bridge.
Aqueducts are often water over water and may even be
water over land, reversing the first definition of a bridge we
gave because they may provide passage for a canal over a road.
They also sometimes facilitate traffic flow because some are
Figure 1.4 A barge crossing the Pontcysyllte aqueduct over the river
Dee on the Ellesmere canal, Great Britain; arches of 13.7 metres
(1805), T. Telford.
built as ship canals. Contemplating how a boat passes over a
road or high up over a valley on some English or French canals
is an amazing experience.
A bridge “joins two places isolated from each other and has
no other pretension than to be a road” (Pablo Neruda1). The
attribute of a bridge as a nexus between the two banks of a river,
as a man-made connection where none existed before, has
3
F1.4
BRIDGE ENGINEERING
horseback and so roads and their bridges became narrower and
the route was less cared for. The sixteenth century saw horsedrawn carriages for the first time and their use spread in subsequent centuries, while becoming increasingly more rapid.
Hence, the need for a road with better, wider foundations and
an increasingly careful alignment. Horse-drawn carriages gave
way to self-propelled vehicles, first the railway and then the
automobile, once again forcing routes to be improved until
reaching present-day motorways and high-speed railways.
always been present in people’s minds. This is why the word
bridge has been and is still used on many occasions as a synonym
for a link between two separate elements; hence, the currently
large number of meanings for the word “bridge”. A further characteristic of a bridge is also present in people’s minds: overcoming a difficult obstacle and, therefore, the use of the word
“bridge” in this context has also been adopted; hence, the meaning normally given to the verb “to bridge” and the sense taken by
the word “pontifex”. The origin of this word is Roman and signifies bridge maker (latin pons, pontis, bridge and facere to make).
Afterwards it was a title. The Roman Emperor was “Pontificex
Maximus” and even now the “Pontiff” is the Pope, held to be
the bridge between earth and heaven.
The unchanging nature and demands of river courses plus
the development of the road combined to give the advance
made in Man’s knowledge, which has led to the evolution of
bridges.
In the beginning of history, the greatest difficulty roads
faced was the crossing of rivers, since bridges raised many
problems through lack of technical knowledge. When arriving
at a river, the most convenient place to build a bridge was
sought and the road was adapted to it a posteriori. It may be
said that a bridge defined a road. This initial approach was
reversed over the years as bridge-building techniques developed and the functional requirements for a road grew, arriving
at the current situation, which tends to be from the opposite
angle to the original. A bridge is defined from the geometrical
conditions that the road’s alignment imposes a priori, i.e. the
road now has priority over the river when building a bridge.
However, scale is fundamental in the previously discussed
problem, as in all problems arising in engineering that operates
in geographical space. This is why large rivers will still impose
their law on the design of bridges built over them.
Although the word “bridge” must be given the broad sense
we have just seen, the meaning of a bridge should not be forgotten, and this will always be par excellence that which spans a
river or an estuary.
The influence of the two items that basically give rise to a
bridge, a river and a road, has radically changed throughout
history.
Rivers are much the same as when bridges first came into
being and remain so through to the present times. This is
because nature has not suffered qualitative transformations
over the 2000 years of the bridge’s history. The geomorphological features of river courses are similar, and flows and
floods are in the same order of magnitude. Many bridges have
collapsed throughout history, most through river flooding.
That is why, up to the nineteenth century, their dimensions
were basically determined by the drainage capacity necessary
for the maximum floodwaters flowing under them.
On the other hand, road requirements have changed radically throughout history. Initially, a road needed very little,
just cleared ground over which to travel and a path to follow
from origin to destination without getting lost, i.e. to mark
out the route, one of a road’s basic functions. But roads have
improved as modes of travel evolved. The first great development in roads came about because the Romans needed a
permanent communication system to control their Empire.
Romans travelled mainly on horseback, though they also used
two- or four-wheeled carts for carrying travellers and merchandise. Travel in the Middle Ages was practically all on
Aqueducts evolved in the opposite way to road bridges.
Even though the Romans already knew about the syphon4
and, therefore, understood pressure pipes, they made water
flow unpressurized whenever possible, i.e. open gravity canals,
and this called for a canal profile with gentle gradients often
leading them to overcome significant changes in level. This is
why, save for rare exceptions, the largest bridges the Romans
built were aqueducts. In many cases, using syphons to cross
valleys subsequently reduced aqueduct dimensions, although
large canals still flow unpressurized, and so still need aqueducts
when having to cross a valley.
4
Figure 1.5 Ganter bridge in the Alpine landscape of the Simplon route crossing the Alps from Switzerland to Italy; main span of 174 metres (1982),
C. Menn.
with infrastructure engineering, generally known as Public
Works.
Engineering is always creative, otherwise it is not engineering. But this creativity has very different features. Taking
chemical engineering as an example, it may create a substance
with very diverse uses, but this substance does not make itself
physically obvious and as such has no expressive value for
Man. It is possible for objects with expressive values to be
made from these substances, but that is another technique. On
the other hand, infrastructure engineering operates on land,
transforming and adapting it to Man’s requirements; its constructions blend into the geographical environment and
1.2. THE BRIDGE, AN OBJECT IN THE LANDSCAPE
A bridge is a piece of engineering work and, like any other
engineering construction, involves transforming nature in
order to adapt it to Man’s requirements. It is basically a useful
structure and, as we have seen, is often unnoticed by travellers
crossing over it.
The different branches of engineering have a common
base, which is their performance in the environment, but their
field of action and manner of implementation is highly
disparate. Each branch operates on a different dimension of
nature; chemical engineering, for example, has nothing to do
5
BRIDGE ENGINEERING
A reservoir is a store of water, a scarce asset, which provides
many benefits but also causes great harm to those who have to
give up their homes and land, which are to be submerged by it.
This always leads to the disappearance of a geographical area
with values that should not be lost.
Appraising the changes which an engineering construction
causes to the environment and the corrective measures which
may be taken to minimize the negative effect on the landscape
has recently become a new engineering activity to be taken
into account on the different operating levels when planning,
designing and in construction. At the planning stage, it may be
decisive in deciding on one or another solution. In designing
and construction, the measures required for the negative effect
to be as minor as possible will be examined; this is what is currently known as environmental impact, an unsuitable term in
our opinion.
The controversy arising from environmental disturbance
caused by engineering constructions in society gives rise to
very different attitudes ranging from the approach gathered
from the idea of A. Malraux: “it is good to conserve places, but
even better to create them”6 to the position of radical ecologists, who consider that any disturbance involving the existing
environment is negative and should not be undertaken; there
is, therefore, no chance for engineering. This radicalization of
positions, which also suffers from many vicissitudes in shorttime scales, is largely due to the general public’s lack of knowledge with respect to engineering problems; engineering is used
but is not understood and, therefore, is held to be of no value.
A bridge may bring about a positive or negative impact
on the landscape, depending on different causes, such as the
physical environment where it is located, the construction
matching the surroundings, the quality of the construction built,
changes occurring in the environment and so on. There is no
doubt that the environment often does not admit disturbance,
and even though the bridge to be built is a fine one, it is an
aggression and thus a negative disturbance; the best bridge in
this case will be a lesser evil. But in other cases, an engineering
construction enriches the landscape; in our opinion, the Firth
of Forth in Scotland has had greater landscape value since the
building of the railway bridge, one of the great achievements
of bridge engineering, the biggest in the world for many years.
It was harshly criticized at the time, and for many years after,
become part of it, geography is made.5 The new landscape
with the addition of the construction is different to the previous one and provides a different expression for the spectator
because it cannot avoid being seen. Expressive values of infrastructure constructions are diverse in kind and give rise to different approaches ranging from problems raised by altering the
environment to the aesthetic values they may have.
Some of the most fundamental infrastructures are roads, in
all their alternatives, because different modes of travel have
existed throughout history – on foot, horseback and in
wheeled vehicles. These modes have evolved over time and
each one has given rise to different routes, from pathways for
travelling on foot to high-speed railways and motorways. They
have each brought about different changes in the land, altering
the landscape to a greater or lesser extent by bringing new elements into it.
A road is a linear construction, which can never be fully
taken in because it is necessary to travel it to see it; perceiving
it is sequential in time. A bridge is part of the road and should
thus be included in the general alteration the latter brings
about, but it is a singular object on the road, and can be seen
and appreciated in a single moment, which is why its presence
in the geographical environment is different.
The first problem raised by engineering constructions in the
landscape, which is a problem shared with architectural constructions normally found in an urban landscape, is that they
are unavoidable and this does not happen with other human
creations. We can stop reading a book, looking at a painting or
a sculpture, watching a film or listening to a piece of music if
we do not like it, but we cannot stop seeing a building, a bridge
or a dam if we are in its vicinity. This creates a particular
responsibility for their makers because they are constructions
imposed on the viewer, whether the latter wants it or not.
The second problem involves alteration to the natural environment or to the environment, which has now come to be
thoroughly accepted, such as the urban environment; this
problem will always be the most controversial issue engineering raises for society. The Public Work is always social in
nature and will be an asset to many, but at the same time may
be a bad thing to a few or even cause irreversible ecological
damage. A motorway favours communication and so benefits
its many users, but no one wants it running past their house.
6
INTRODUCTION
Figure 1.6 Forth railway bridge, Scotland; two main spans of 521 metres (1890), J. Fowler and B. Baker.
F1.2/4.6
F1.6/1.8/6.12/
6.25/6.82
A bridge should match the environment where it is located,
i.e. the landscape surrounding it – the river, its banks and its
vicinity. This first attribute that a bridge should have has been
achieved by stone and timber bridges more easily than other
types, mainly because of their quasi-natural material. This does
not mean to say that bridges built with such materials are the
best solution in any event for any bridge and even less so at
the present time, but that the alteration they have caused to
the environment is less marked.
because it was deemed to be ugly, an example of the ugliness
that engineering can produce.7 The reaction was similar to that
occurring with the Eiffel Tower, which was concluded a few
years later. San Francisco bay has also had greater landscape
value since the completion of the famous Golden Gate bridge
which, like the Forth bridge, was the biggest in the world for
many years and is often used as the city of San Francisco’s
emblem.8 We could continue indefinitely citing old and modern, large and small bridges considered by public opinion to be
landscape-embellishing elements and, thus, diffused in all
kinds of images, postcards, tourist guides, etc. It is traditional
to use the bridge as a reference item or for setting the landscape; in short, the humanization of nature is being sought. In
these cases, the Malraux approach quoted earlier, while being
a criterion we think excessive in general, is true.
A bridge is not always located in the natural or, to be more
exact, rural landscape, because the countryside cannot be
considered natural in the strict sense of the term in most of
developed or developing countries’ territories; we may deem
naturalness as a function of the greater or lesser alteration Man
7
BRIDGE ENGINEERING
The urban bridge has enjoyed and still enjoys favourable
treatment because, like any urban construction, it is more
in people’s minds than constructions located in the rural
environment:
“The bridge is an exceedingly main part of any town or city; in
building bridges, it is advisable to be extremely wary in choosing
the site where the bridge is to be made…”
The Twenty One Books of Devices and Machines10
This is why urban bridges have been generally built with more
technical and formal care than others; many of the great
bridges, which have made history were built in towns or their
surroundings; they were also built with greater care and wealth
of materials. When laying down his rules on arch and pier
dimensions in the sixteenth century, Alberti11 distinguishes
between urban bridges and the rest, accepting greater slenderness ratios in the former.
Urban bridges are naturally best known and most appreciated, generally in complete groups in one and the same city, for
example the bridges of Paris, London, New York, etc., and are
a major part of these cities’ heritage of monuments. But save
for these differences, it cannot be said that urban bridges form
a group apart from the rest because rivers are the same within
and outside the city. Nevertheless, the urban environment may
lead to solutions which are different to those in other places
but then so do the different morphologies of the river course
lead to different solutions; a bridge on a plain is not the same
as over a gorge. The condition of being urban is thus a further
detail to be taken into account when building a bridge, but it
is not a differentiating fact.
The conclusion may be drawn from the above that the
bridge fulfils a social end, which is to facilitate communications by making a road over a river and this is why they are
built. However, when making a bridge, we must be aware of
the responsibility involved in disturbing a pre-existing, natural
or urban environment with a new construction. A condition
inherent to any engineering activity, the search for minimums,
should be applied in this case. The change brought about in
the environment where built must be positive or minimum.
But the approaches described do not mean to imply that
there must be a feeling of guilt accompanying making a bridge.
The bridge builder is as satisfied with his work as any other
Figure 1.7 Via Mala (Italy). Drawing by Gustavo Doré on his last
journey to Italy. Illustration in the article entitled Paisaje (Landscape)
(1886) by F. Giner de los Rios, and frontispiece on the subject Paisaje
in the “Boletin de la Institución Libre de Enseñanza” (May 1999).
has brought about there.9 A bridge may also be found in the
urban landscape, the environment most opposite to the natural, because human intervention is in everything in a town.
When a bridge is built in this environment, a change will be
brought about in the urban landscape which, in turn, once
altered the natural or rural landscape; but the former has now
been thoroughly accepted and so the same reasoning we
used when analysing change in the natural landscape can be
made in this case, even though the terms of appraisal will be
different.
Like any other change in a town, new urban bridges often
produce a negative reaction in the inhabitants; but once built,
they come to be completely accepted and those same inhabitants or their descendants may even defend them against any
change with a passion that it would not seem initially possible
for a bridge to generate.
8
human creator. As we have seen, the change brought about when
building a bridge is often positive and we must always aspire to
such by making bridges with good designs, blending in suitably
with the environment where located and good construction. A
bridge should not impose on the environment, but should form
part of it existing in harmony with its surroundings.
1.3. THE BRIDGE, A WORK OF ENGINEERS
F1.33
F1.34
If the difference between engineering and architecture is
nowadays relatively clear, it was not so during most of history
because up until the end of the eighteenth century, the two
professions were as one or were closely linked. For Andrea
Palladio, in the sixteenth century, the bridge was that part of
architecture pertaining to the ornamentation of the town or
province.12 That same century, Michelangelo stated that “A
bridge should be thought out and built the same as a cathedral,
with the same attention and the same materials.”13 Also in the
same century, Juan de Herrera built El Escorial monastery and
the Segovia bridge in Madrid. In the eighteenth century, the
Prado museum’s architect, Juan de Villanueva also designed
bridges and routed roads; the new Villalba to Segovia road over
Navacerrada mountain pass is his design. In the eighteenth
century, Pedro Ribera built the Virgen del Puerto hermitage
and the Toledo bridge, both in Madrid.
Up until the nineteenth century, many bridges were the
work of architects. The separation between the two professions
coincided with the Industrial Revolution which, in bridges,
determined what may be considered as a change in period: the
period of stone and timber bridges gave way to the period of
metal and concrete bridges (see Chapter 2).
In the eighteenth century, the engineer began to understand the resistant behaviour of structures, which enabled
dimensioning constructions on a scientific basis to begin;
the strength of materials, a science studying the resistant behaviour of materials and structures, commenced (see Chapter 4).
The new materials allowed larger constructions to be built
and it, therefore, became necessary to better understand
how they performed. Thus, engineering began to have a
scientific basis and moved increasingly further away from
architecture.
Figure 1.8 The Forth bridge. Triangulation on supports. The
compression members are tubular and the tension members are
triangulated.
The strength of materials and the theory of structures are
recent knowledge. It is amazing to see the gigantic constructions built throughout history with no scientific knowledge of
their resistant performance. The large vaults and domes of the
Romanesque, Gothic and Renaissance were built thanks to
intuitive knowledge and accumulated experience.
The resistant status of structures did not start to be quantified up until the eighteenth century. The first theoretical study
9
Figure 1.9 Golden Gate bridge in San Francisco bay, California; main span of 1280 metres (1937), J.B. Strauss.
1847 by Squire Whipple and general understanding of these
structures came to be in 1866 with Karl Culmann’s studies on
graphic statics.14 From the current perspective, it is surprising
to see that large constructions of this type had already been
built before any command of the theoretical knowledge of a
structure’s resistant performance was held.
of an arch’s resistant behaviour was published at the end of the
seventeeth century (1695) by the Frenchman La Hire; this study
served later engineers in making the first stone arch dimensioning calculations. The first study on the phenomenon of bending in prismatic pieces, which may be considered as scientific,
was undertaken by Galileo Galilei but was far from correct; it
was not until the nineteenth century that the true distribution
of stresses in cross-sections of a piece subjected to bending were
known. The 1826 publication of Louis Marie Henri Navier’s
courses at L’École des Ponts et Chaussées in Paris finally clarified
this problem, which is a fundamental piece of data for
dimensioning members which are to withstand bending. The
first trussed girder calculation procedures were published in
Understanding the resistant behaviour of structures in general and bridges in particular allowed their spectacular development in the nineteenth century, the finest century in the
history of bridges; the audacity and capability of enterprise of
some bridge builders in that century amaze us and inspire
admiration. They had theoretical knowledge and resources to
10
INTRODUCTION
construction that, while being inseparable from the problem of
resistance or strength, goes beyond it. It has frequently been
considered that someone who can best design bridges is the person who knows most about the theory of structures, but this
does not have to be so; there have been many examples in the
history of bridges and at the present time which prove this; it is
not the best artist who knows most about art. To design a
bridge, it is also necessary to understand its resistant performance well but, as we have seen, the creative process goes beyond
this knowledge. The engineer frequently earmarks little time to
a bridge’s conception and definition; time and effort are basically earmarked to structure problems.
Even today, some engineers engaged in bridge designing,
conditioned by the problem of resistance and its quantification
to which they give excessive importance and protagonism, still
ignore engineering’s creative dimension, waiting for some
architect to embellish their construction. They consider that
aesthetics is something that can be added afterwards and “aesthetic treatment” is heard of as something that can be superimposed on the engineering construction. The engineer
frequently misunderstands or does not know the meaning of
the word aesthetics and uses it improperly. Much has been
written on the aesthetics of bridges and many “aesthetic rules”
have been given for them, because, in fact, many engineers
seek regulations that allow them to affect ignorance of this
problem to a certain extent and apply recipes they have been
given to make their bridges “aesthetic”. In short, endeavour is
made to objectivize a problem which cannot be made objective, to reduce it to formulas without understanding that
designing a bridge is a cultural deed comprising all the dimensions of a creative process, and that is how the great bridgebuilding engineers, and there have been many, have seen it. We
would hereafter cite four of these great engineers as examples
of the most representative.
Jean Rodolphe Perronet, the great stone bridge innovator,
is a good example of the aesthetic concern of eighteenth century engineers; he cares for bridges down to their last details
and many of his innovations are motivated rather by reasons of
form than achieving a technological advance.
Thomas Telford, whose contribution to the development of
metal bridges was one of the most decisive in the history
Figure 1.10 L’Isle de la Cité and L’Isle de St. Louis on the Seine,
Paris. The Pont Neuf in the foreground (the city’s oldest) and the Pont
Marie and Pont Sully in the background.
build their constructions, which were far inferior to the size of
the bridges they made. But the intense development of the construction and theoretical understanding of structures also gave
rise to problems and disorder. The technical difficulties
involved in bridges were increasingly greater, so engineers in the
nineteenth and first half of the twentieth centuries paid their
greatest attention to these problems, frequently forgetting and
occasionally rejecting the creative process leading to a good
11
BRIDGE ENGINEERING
F1.11
Figure 1.11
Craigelachie bridge over the river Speys, Scotland, arch of 45 metres span (1815), T. Telford.
Figure 1.12
Plougastel bridge over the river Elorn, Normandy; three arches of 186 metres span (1930), E. Freyssinet.
a new technique. Telford is a good example of the nineteenth
century British engineers, whose constructions played a decisive
role in the spectacular development of bridges in that century.
Robert Maillart, one of the instigators of reinforced concrete, created one of the most expressive and attractive sets of
of bridges, reflects a constant concern for aesthetic values in
all his work and in his memoirs, which gave rise to such
well-designed bridges as the series commencing with Bonar
bridge and continuing with Criagelachie bridge over the river
Spey, both in Scotland, despite being the first steps taken in
12
INTRODUCTION
Figure 1.13
Salgina-Tobel bridge on the Schiers to Schuders road, Switzerland; arch of 90 metres span (1930), R. Maillart.
the three-arch, 186-metre span Plougastel bridge, Orly airport
hangars and many other constructions of his, are engineering
master works of all times.
Many other engineers who have also made the history of
bridges may also be cited. But, while there have been and are
engineers with a determined concern to make beautiful constructions, their cultural training in issues of aesthetics, composition and shape has been somewhat deficient in general.
This has led some of them to ignore the formal problems of
their constructions and others to excessive “artistic” concern.
The metal neo-Gothic towers of some of H.D. Robinson’s and
D.B. Steinman’s suspension bridges are good examples of the
latter, particularly those of the 240-metre span Waldo-Hancock
bridges in the whole of history. His works and his writings
reflect his clear vision of the formal and technological problems raised with the new material, reinforced concrete. His
criticism of Hennebique’s structures for their mimetism of
timber structures and his proposals, as to how concrete structures should be, are good examples of his culture and ability to
analyse engineering in all its dimensions.15
Eugène Freyssinet, another of the great engineers in the history of bridges, a reinforced concrete innovator and the creator
of prestressed concrete, was also a great bridge builder. All his
writings reflect concern for the aesthetic values of his constructions with which, in general, he was satisfied. Although his
greatest historical significance lies in his technical innovations,
13
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BRIDGE ENGINEERING
Figure 1.14 Britannia bridge over the Menai Strait, Wales; two main spans of 140 metres (1850). The timber inside the box girder burned out in
1970, R. Stephenson.
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F1.14/2.31/6.59
F1.17/8.138
bridge over the river Maine, those of the 366-metre span
Mount-Hope bridge on Rhode Island and those of the 368metre span St. John over the river Willamette in Portland,
Oregon, which may be included in late eclecticism because
they were built in the first half of the twentieth century. In our
opinion, there is an excessively “artistic” approach in them.
(The Waldo-Hancock and Mount-Hope bridges received respective awards from the American Metal Construction Institute as
“Artistic Bridges.”)
Engineers have become disorientated on many occasions
when new large-dimensioned elements appeared in bridges, to
which they were unable to give shape. This often led them to
reproduce shapes from previous architectural styles, unsuccessfully in general. One of the styles frequently used was that of
ancient Egypt, probably because of its colosallism. One example is the towers of the Britannia tubular railway bridge over the
Menai Strait built by Robert Stephenson, concluded in 1850,
with four box girder spans of 70 140 140 70 metres,
one of the fundamental constructions in the history of bridges:
these towers were never used as such because the chains from
which it was planned to suspend the bridge girders were eliminated.17 Another example is the towers of the 214-metre span
Clifton suspension bridge built by Isambard K. Brunel, finished
in 1864; also an important bridge in history. The most negative
thing about both examples is the Egyptian look. The towers of
many of the first French suspension bridges reproduced the
shapes of the Roman triumphal arches; these shapes evolved
Figure 1.15 St. John bridge over the river Willamette; main span of
368 metres (1931), H. Robinson and D. Steinman.
14
Figure 1.16
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8.111/8.118
Brooklyn bridge over the East River in New York; main span of 468 metres (1883), J. Roebling.
even though he used pointed arches, we cannot speak of a neoGothic style, in our opinion, as we can for some buildings of
American architecture of that time. The size of this bridge and
the power and simplicity of its towers make it the origin of
modern suspension bridges.
It must be borne in mind that the constructions we have
cited, from Stephenson’s Britannia bridge on the Menai Straits
to Roebling’s Brooklyn bridge, were built in the second half of
the nineteenth century, where eclecticism dominated in architecture and, like all trends in nineteenth and twentieth century
architecture, wielded significant influence over engineering.
towards those of Othmar H. Ammann’s bridges. He used the
semicircular arch as a finishing piece for most of his towers and
piers. But here this situation is quite different to the earlier one
with Ammann’s towers; they are dominated shapes, perfectly
suited to their function; his three great suspension bridges,
namely the 1067-metre span George Washington over the river
Hudson, the 700-metre span Bronx-Whitestone and the 1298metre span Verrazano Narrows, all in New York are and always
will be master works of suspension bridges.
John Augustus Roebling considered that stone constructions are “art” and the rest “engineering”. He drew many solutions for his bridge towers using lots of different architectural
styles including Egyptian, Roman, Romanesque, Gothic,
Byzantine and Baroque.18 Not all the towers in his bridges are
very fortunate but with regard to those of the Brooklyn bridge,
Many general books on bridges written by illustrious engineers on bridges address the subject of aesthetics, but not
always successfully.19 Congresses and meetings on the subject
15
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BRIDGE ENGINEERING
contributed with his works and studies. Maillart’s arches will
always be one of the best examples of good engineering.
A contemporary of Maillart, Ammann emigrated to the
United States of America, seeking a country where he would
have a chance to build great bridges, following the tradition of
John A. Roebling, Gustav Lindenthal, Ralph Modjeski and
Leon S. Moisseiff; in addition there were engineers from
Central Europe, who emigrated to the United States. They
were some of the main architects of the Golden Age of
American bridges, which coincided with the end of the nineteenth century and first half of the twentieth century. One of the
most outstanding of them all is Ammann, as we have said, the
designer of George Washington bridge over the river Hudson,
the first bridge to exceed 1000 metres in span, Bayonne bridge
over the Kill Van Kull, a 511-metre span arch, the longest in
the world for many years and the 1298-metre span Verrazano
Narrows bridge which, like the George Washington, was the
longest in the world for many years.
A. Sarrasin was also a contemporary of the foregoing and
another of the reinforced concrete pioneers. His beam bridges
and his arches are master works in this material.22
Like the others, Maurice Koechlin studied at the Zurich
Polytechnic, but before them. He was a pupil of Culmann.
Koechlin worked with Gustave Eiffel for many years and is the
co-designer of many of his great works, the Tower being
among them.23
But criticism of the low level of knowledge of the creative
dimension of engineering that engineers frequently hold should
not lead us to the opposite position, which also currently exists.
The power of existing calculation tools, based on computer programmes, which may be used without any deep knowledge of
structures has led some engineers and architects to think that the
phenomenon of strength is a secondary one in bridges, and thus,
a new figure has appeared: the bridge designer. The bridge
designer can be detached from the other problems an engineering project bears with it; for some, the bridge becomes an object
of pure design and there are many examples of this in the world.
For others, a 20-metre span bridge is the same as a 200-metre
span one, and the scale factor, which is fundamental in any
strength phenomenon, is forgotten.
The two aforementioned attitudes are equally negative
because the problem is only partially addressed in both cases;
Figure 1.17 Clifton bridge over the river Avon, England; single
span of 214 metres (1865), I. Brunel.
are also held, but they teach and contribute little to anyone
wishing to learn how to make a bridge.20 While specific
aesthetics of the different arts can be made because they
have different languages, it is difficult to cover such a large
specialization such as that of bridges, with their own specific
problems. However, an understanding of good bridge building
can be developed, as in any other profession.
There have been situations where that lack of training in
what could be called the engineer’s creative dimension did not
exist. These situations generally gave good results. An example
was the Zurich Polytechnic in the second half of the nineteenth
and beginning of the twentieth centuries, with teachers of the
stature of Karl Culmann or Wilhelm Ritter; among other engineers, Maurice Koechlin, Robert Maillart, Othmar H.
Ammann21 and Alexandre Sarrasin22 were all educated there.
As we have seen, Maillart was one of the greatest, most original creators of bridges and one of the instigators of reinforced
concrete to whose development and maturity he decisively
16
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INTRODUCTION
the engineer must be aware that a bridge project does not consist of just designing the bridge or understanding its resistant
behaviour, but that the bridge project must be addressed in
overall fashion from the first drawing to the construction procedure to be used. This approach does not exclude the creative
process being undertaken through cooperation between professional people nor dialogue with people who may have a
different view of the object, nor other possibilities that, as
shown below, may be procedures which enrich the process.
F5.9/5.41/5.60
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5.28/5.41
Many people from different professions participate in any
bridge of a certain size. Ranging from the designers to those
who manually build it, they all contribute to making it a reality, the final result being the one determined beforehand and
no other. A bridge cannot be deemed as an individual or personal construction; it is the result of a process, which commences in planning the route, continues in the design and
ends with construction.
In some cases, the bridge construction problem could have
been decisive in planning the road. On learning about the
María Pía bridge over the Douro in Oporto, which the Eiffel
company had made, Leon Boyer decided to change the alignment of the Marvejols to Neussargues line in the Central
French Massif and sent it over the Truyère ravine via the
Garabit viaduct, similar to María Pía, which he had not considered feasible in the initial studies. This change significantly
shortened the railway line.
While the above is true, so is the individual value of many
engineers who have undertaken great constructions and contributed to the development of bridge engineering; we have
already been introduced to some of them:
“As Maillart’s work demonstrates, this connection between innovation and art applies to small bridges as well as to large ones.
Each overpass has the potential to be a work of art, but it requires
the vision of a single artist. The best bridges of the past 200 years
have regularly been the design of one engineer. Poems are not
written by committees.”
David P. Billington24
When examining Gustave Eiffel’s work, we come across a historical engineering problem, which teamwork frequently faces.
In the case of Eiffel, the gigantic construction undertaken by the
Figure 1.18 Verrazano Narrows bridge at the entrance to the port of
New York; main span of 1298 metres (1964), O. Ammann.
17
Figure 1.19
Garabit viaduct over the Truyère, France; arch of 166 metres span (1884), G. Eiffel, L. Boyer and M. Koechlin.
tury and beginning of the twentieth century. In the middle of
this century, the complexity of the problems finally disassociated these activities.
Eiffel built his first bridges in association with Théophile
Seyrig, who was the company’s project manager and they were
awarded the international tender for the María Pía bridge over
the Douro at Oporto with Seyrig’s design. When this bridge
teams he formed cannot be solely attributed to him because he
always relied on collaborators whose participation in the
design and construction of the work his company carried out
was decisive, but he knew how to focus all the team’s achievements back to himself. This is the best example of engineer
entrepreneurs, who were decisive in developing technology in
general and bridges in particular during the nineteenth cen18
F5.9
INTRODUCTION
F1.19
bridge is built after being designed, the construction system
must be part of the design; how a bridge is going to turn out
cannot be known without knowing how it is going to be made.
The construction process is a determining factor in large
span bridges; here the different types of structure dominate or
disappear depending on the greater or lesser difficulty in their
construction. The maximum span of bridges is basically limited by the possibility of building them; we can design a 5000metre span bridge, but one of the fundamental problems in its
design will be how to build it.
was completed, their association broke up and Eiffel took on
Maurice Koechlin, to whom we referred earlier, who then
became Eiffel y Cie’s project manager and, later, general manager. His participation in the designs drawn up in the company was decisive, including the Eiffel Tower. As we have seen,
the administration’s engineer Leon Boyer played a decisive role
in the design of the Garabit viaduct and then went on to form
part of the Eiffel company.37
So, the great work normally attributed to Eiffel personally
should be attributed to a whole team, where there were people
similar in stature to him. One of his great merits was probably
knowing how to surround himself with people of great value.
The scale factor, so important in structural engineering,
reappears. The need to make bridges with increasingly longer
spans does not become just a difficulty and technological challenge but also has an aesthetic value. One of the basic aesthetic
values of the Forth cantilever bridge with two 521-metre spans,
of the Golden Gate bridge in San Francisco bay with a 1280metre span, of the Verrazano Narrows bridge with a 1298-metre
span in New York and the Humber bridge with a 1410-metre
span is precisely their dimension; they would not be the same
if their spans were half of what they are.
It is rare for a large-span bridge to be ugly, although it has
sometimes been achieved but, in general, the power of their
structure and their size dominate the remaining aesthetic values; they impress beholders, making them lose their critical
sense as regards other values, which in smaller-scale bridges
would become more obvious.
The aesthetic value of scale is evident in many of the opinions given on large bridges:
The conclusion to be drawn from above is that the creative
process cannot be the sum of partial, separate performances of
different professionals in one and the same construction without
a person or team that understands it overall. This process management is lacking in many bridges, particularly in the United
States, Germany and Japan and, regrettably, it is spreading to
many other countries. It is difficult to know who are the makers
of the bridge; different professional people intervene in the
design with different missions, with no governing idea and the
result normally shows it. It is increasingly frequent, and we have
seen many examples in France, for an architect to design the
piers independently from the rest of the bridge. These methods
of operating forget that the creative process should be a unity,
even though the process is complex and has different aspects and
stages which may be grouped into three basic actions:
• Formalization of the construction to be built.
• Qualitative and quantitative analysis of its behaviour.
• The process to be used for materializing the ideas into a
“The Forth bridge is impressive but not beautiful in the ordinary
sense of the term. Although its lines and proportions may seem
heavy, clumsy and ungainly, the observer cannot but be
impressed by the solidness of this stupendous, gigantic structure.
The awesome effect of power and strength has its own aesthetic
quality. The same design, on a smaller scale, could be unpleasant,
as the outstanding character of powerful dimension which
gives the Forth bridge its primordial aesthetic impact would be
missing.”
David B. Steinman and Sara Ruth Watson16
reality.
That is to say, design, calculation and construction process,25
although these words do not fully reflect the previously
described approaches as they are more limited. Design should
include the whole organization and formalization of the structure, not just its image; and calculation, everything referring to
its resistant performance, not only to the mathematical procedure used to resolve it.
If design and calculation define how the structure is, the
construction system defines how it is made. But, while the
“In relation to a bridge of this soul-stirring immensity, artistic
judgement must follow humbly: it cannot dictate. It is like
beholding a great natural phenomenon such as the Grand
19
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BRIDGE ENGINEERING
Canyon of Colorado or sunrise on the peaks of Kanchenjunga as
seen from Darjeeling. Feelings cannot be expressed in words,
terms of comparison cannot be found and artistic criticism is
rendered speechless by awestruck wonder and admiration.”
C.E. Inglis – On the Golden Gate Bridge 26
Concentrating on the bridge, the issue is to organize matter such that forces acting on the deck carriageway continuing
the road are transmitted to the ground at isolated points, the
piers, so that the river water can flow between them. The
forces acting on the bridge are:
“The enormous scale of suspension bridges bears within it the
germ of the heroic … Everything is clear and simple. One feels
small and insignificant before something so great and so simple.
(a) its own weight
(b) traffic loads crossing
(c) forces produced by the environment: wind, temperature
variations, rises in water level, earthquakes, etc.
It all causes criticism to dissipate”
M. Aguiló Alonso27
In the structural engineering sphere, the resistant structure
manifests most powerfully in the bridge for several reasons.
Firstly, because it is almost exclusively a resistant structure with
minimal additions. And secondly, because of its scale which, as
we have seen, is fundamental in any resistant phenomenon
(see Section 1.3); bridges are the largest resistant structures
and, therefore, most technical advances in structural engineering started with them: new materials, new techniques, new
types of structure, etc.
The road’s geometry, the valley’s morphology, the features
of the river and the forces acting on the bridge are going to
conform but not determine it. There are different types of
structures, different materials, different span layouts and different shapes for each of the possible solutions. The design of
a bridge is determined by many factors and has a highly specific aim. In short, it is a useful form but also has sufficient
degrees of freedom for its designer to make a construction with
an expressive value. As in all human creations where a certain
degree of expression is possible, there are good bridges and bad
bridges, handsome bridges and ugly bridges.
Bridges are included in many useful forms and have a number of degrees of coincidence with architecture, using this term
in a broad sense. The architecture of the engineer, an expression that has been used on several occasions to analyse engineering, is an important term to mention.29 This is why
aesthetics of bridges is not a subject that can be studied separately; bridges can and should be studied, how and why they
are made should be understood and a culture on them
acquired, which is necessary in order to know how to make a
new one.
The aesthetics of engineering works in general and bridges
in particular is a much discussed subject and often badly
1.4. THE BRIDGE, A FORM BUILT
As we have seen, the bridge has a very simple, specific function: to continue the road when it becomes separated from the
ground, i.e. to sustain the road in the air. This “sustaining in
the air” is the bridge’s fundamental challenge, which is why it
is basically a resistant structure and thus an engineering construction.
A resistant structure is the way to organize material in order
to withstand forces acting on it; and apart from resisting, it
must also persist, i.e. remain unmoved and undisturbed by
these forces throughout time. This immobility and unalterability refers only to human perception because structures
become deformed and move by the effect of forces but this
must be as unnoticeable as possible to the user who is seeking
something permanent and, therefore, unalterable in it:
“The bridge seemed to be amongst those things which lasted for
ever; it was unthinkable it might fail.”
Thornton Wilder28
“However, no-one could guess what they wanted to do with the
bridge, which represented something eternal and changeless to all
citizens, like the earth over which they walked and the sky which
covered their heads.”
Ivo Andric – A Bridge Over the Drina
There are many ways to organize matter to make a resistant
structure and there is always the possibility of using different
materials; this is why the possible forms are unlimited.
20
Figure 1.20
Humber estuary bridge, England; main span of 1410 metres (1981), Freeman Fox and Partners.
in the same way that the development of construction technologies has influenced architecture.31
In general, when a technique has not reached maturity
through lack of theoretical knowledge, it is applied through
rules, which have accumulated through experience.
Sometimes the impression is given that writings and theories
on bridge aesthetics suffer from similar immaturity.
focused (see Section 1.3). We have seen that it is normal
among engineers to seek regulations and rules allowing them
to make their bridges “aesthetic” as if it were an external, added
value; this has given rise to a succession of clichés on the subject throughout the history of bridge engineering that have
largely ruled its activity.30 Some are a reflection of the trends in
architecture, which have always heavily influenced engineering
21
BRIDGE ENGINEERING
being well designed and functioning properly, its aesthetic
value will follow as a natural consequence:
“What above all ensures the right of these creations to be
acknowledged on the aesthetic plane is that they are perfectly
functional and useful, that they are the expression of an
extreme economy of means, of a strict intellectual discipline.
Even if the useful and functional concepts do not explain the
secret of beauty, there can be no beauty that avoids these basic
definitions. Moreover, what is perfectly functional and useful
can never be ugly because it represents a perfect simplicity. It is
precisely this perfect matching that our new aesthetics consider good taste to be.”
J.A. Lux32
This paragraph perfectly expresses that way of thinking,
which, in our opinion, is not valid and this can be seen by
just recalling innumerable works and utensils that, while
useful, are ugly. There are many ugly bridges, but vehicles
nevertheless cross them without problems.30
(b) The approach contrary to the ones discussed has had
greater influence on engineering: any useful piece of work
cannot be or does not have to be beautiful. The engineer
must concern himself with his works being well designed
and functioning; the rest is superfluous, useless and alien
to him:
“What is called the ‘Industrial Revolution’, which straddled
the 18th and 19th centuries and was the decisive step for engineering towards the current stage, left us a regrettable disdain
for aesthetics in our constructions, which was specified in the
thesis of incompatibility between usefulness and beauty. This
thesis has remained as an axiom with such strength that even
today, over a century and a half later, it has not been possible
to delete it from the ordinary Man’s mind and what is even
more serious, from that of engineers themselves.”
Carlos Fernández Casado33
Figure 1.21 Moving railway bridge over the river Willamette in
Portland, Oregon (1912).
We shall now expound the different proposals on the aesthetics of bridges as made throughout their history, without
trying to lay down new doctrines on the subject or defining
what to do to design “aesthetic” bridges.
There are many engineers whose concern is to build beautiful constructions. Good examples are Telford and Rennie in
Great Britain, or those called by the French, Ingenieurs
Artistes,34 or those named earlier in this chapter, Maillart,
Freyssinet and so many others; however, as we have seen
(Section 1.3) and shall continue seeing as we progress through
this book, engineers have frequently ignored the aesthetic
1. The first is based on the relationship between usefulness
and beauty, and two opposing proposals leading to one and the
same result were made here.
(a) If well designed, i.e. if it functions properly for the end
proposed, any useful object is beautiful; therefore, the
engineer only has to concern himself with his construction
22
INTRODUCTION
Figure 1.22
Motorway overpass at Ölde, Germany. Prestressed beam of 33 metres span (1938), Ways and Freytag.
had a decisive influence on it. This approach has been very frequent in engineers throughout time:
value of their constructions, even more than the approach discussed above, which identifies usefulness with beauty,
although such approach has also had great influence on the
attitude of engineers to aesthetics.
While it is true that such approaches may be considered as
opposing each other, it is also true that they lead to the same
result, i.e. to ignore the aesthetic values of engineering works;
in the former, these would come by addition, and in the latter,
no value is given to them.
It may be deduced from the previous discussion that beauty
cannot follow as a consequence of usefulness, because useful
things may be beautiful or not; a piece of engineering work is
always useful because if not, it is not engineering; but engineering works are often not beautiful.
“The current artistic sense considers the structural function and
expressivity of its resistant phenomenon as a coadjuvant of aesthetic value; it even believes it to be essential in those cases where
the work is eminently a structure.”
Eduardo Torroja35
When Gustav Eiffel replied to the letter of the “Artists”
against the Tower, his approach was as follows:
“The first principle of the aesthetics of architecture is that the
essential lines of a monument be determined by a perfect matching to its destination. What condition did I bear in mind in my
tower before anything else? Wind resistance. Now, I seek to have
the curves of the monument’s four edges give an impression of
beauty, as calculation has given me them, since they will translate
the audacity of my conception to the eyes.”36
2. The second is based on the resistant structure’s power and
determinism: there can be no other aesthetic expression in a
bridge than that due to its structure, and this is a direct result of
its function. It is the functionalist approach taken to its limit,
which does not have to be necessarily as radical as we have
expressed it; there are different degrees of determinism.
Functionalism in architecture was largely generated by the
influence of new techniques in engineering and, in turn, has
Though it is true that a bridge is basically a resistant structure and, therefore, its formal expression will be that of the
structure’s, it is not true that the resistant structure’s formal
expression is an exclusive consequence of its function. As we
have seen, different types of structures may be used and different formalizations may appear in each of them; details may be
23
BRIDGE ENGINEERING
Figure 1.23
Elevations of the Eiffel Tower: initial drawing by M. Koechlin, drawing by the architect S. Sauvestre and final tower.
dealt with differently; Flaubert’s phrase: “God is in the details”
quoted by Mies Van Der Rohe is too often forgotten by engineers who tend to dedicate all their efforts to large magnitudes.
All these will distinguish a good result from a bad one. An
infinity of examples of bridges with the same resistant structure
proving radically different in form could be given. Not all arch
bridges, for the mere fact of being such, are good to look at.
As Eiffel says, calculation may give us the definition of a
curve, but we first have to define conditions for it. The Eiffel
Tower could have been more or less slender and could have
had many different shapes. A comparison of M. Koechlin’s initial drawings, the subsequent ones of the architect S. Sauvestre
and, finally the final Tower design suffices to this effect.37 The
isoresistance wind curves of the edges are the same in them all.
The tower’s beauty is due to many factors, not only to these
curves.
3. The third cliché refers to “good bridges” and “bad bridges”.
Taking each type of bridge to be good or bad per se is a widely
held idea: “Arches and suspension bridges are good, lattice or
trussed girders bad, concrete bridges difficult, etc.”7
The difficulty involved on occasions in accepting new
shapes on the one hand, and the lack of appreciation generally
held for constructions from the immediate past on the other,
have largely influenced this standpoint; the appraisal nowadays made of the lattice and trussed girder bridges of the second half of the nineteenth century and first half of the
twentieth is not the same as that made 40 or 50 years ago;
24
F1.6/6.25
some of them should be included among the best constructions in bridge history.
One of the greatest constructions in bridge history,
the Forth bridge, was classed at the time as a maximum in
ugliness:
“There never would be an architecture in iron, every improvement in machinery being uglier and uglier, until they reach the
supremest specimen of all ugliness, the Forth Bridge.”
W. Morris 26
Its appraisal nowadays is everything to the contrary and
proof is given by the interest its centenary celebrations have
awoken; many books and articles have been published on it.38
Good and bad bridges are not the same in all ages. Trussed
girders, which dominated bridges in the second half of the
nineteenth century have been badly considered by many twentieth century engineers, who preferred web girders which have
dominated this century. On the other hand, Pablo Alzola
wrote at the end of the nineteenth century: “Full walled (web)
girders became generalized and many are still made in Spain;
and even though we would repeat that the invention of this
system provided very useful services, particularly in that age of
hectic activity, when the railway system was built so rapidly, it
was soon acknowledged that these solid walled (web girder)
bridges looked heavy and were completely lacking in art and
taste.”39 Opinion is the opposite nowadays; the web girder
bridge is considered to be “better” than the trussed one.
There is no doubt that some types of bridge are more difficult to fit in than others; but in reviewing history, it can be
easily seen that there are constructions of exceptional standard
in all types.
This good bridge and bad bridge view is another reflection
of the tendency of some engineers to approach their formal
expression through a set of defined rules, which leads to unsustainable radical criteria.
Figure 1.24 La Muletière railway bridge over the Saône at Lyon,
France; continuous trussed girder (1914), M. Koechlin.
Figure 1.25 Bonn South Bridge over the Rhine, Germany;
continuous metal web girder of 230 metres span (1967), G. Lohmer
and Hein Lehmann.
4. The fourth is the relationship between technology and creation in engineering works.
We know that engineering has to be necessarily creative
because its activity involves changing nature. The dialectic raised
between technology and creation refers to what we could call
technological determinism and the expressive potentialities of
the engineering construction, which will substantially vary
between one branch of engineering and another. This relationship is often approached by considering that engineering works
are a combination of technology and art.
25
BRIDGE ENGINEERING
“We have seen that three elements enter into all human work in
a greater or lesser proportion: the scientific, the aesthetic and the
mechanical.”
Fernando García Arenal 40
The idea that engineering works are the result of calculations, that the engineer’s work is more deductive than inductive, is a common one. We have already seen that Eiffel thought
that the Tower’s expressive value is largely a result of the curves
he obtained from calculating wind isoresistance. But this does
not mean to say that the Tower’s design is the result of calculations, but of the wind isoresistance curves that were adopted as
the shape of the edges; other shapes could have been adopted,
among other reasons because the Tower’s cross-sections at different heights are not the same and, therefore, the Tower’s
response to the wind is not homogeneous over its whole height;
this gives it a relative value to the idea of wind isoresistance,
which does not invalidate the expressive value of the Tower’s
curves but does invalidate the technological determinism of its
shape.
A bridge is never the result of a calculation, because a calculation is really a mathematical model of a prior idea. But it
is also true that calculation acts as a check that the bridge conceived is valid, that it may be valid once corrections have been
made or, in some cases, that it must be re-designed. The calculation process normally obliges more or less significant corrections to be made in the prior design and, therefore, influences
the result and the bridge’s final dimensions, but it never gives
it shape. The resistant structure must be configured in the initial idea for the bridge. We have already seen that this is an
essential part of the latter and there is always a technological
dimension in the definition of that structure because we do
not design the bridge from zero but from a current state of
technology. That technology’s determinism will be all the
greater, the greater the bridge’s scale is. Those with the greatest
spans are all suspension bridges, there are no other possibilities
at the present time, and little variation in structure is possible;
but, there is a great difference between them all. The two
biggest bridges in the world, both finished in 1998, are the
1624-metre span Storebaelt over the Grand Belt in Denmark
and the 1990-metre span Akashi-Kaikyo in Japan; despite having the same kind of structure, they are different, as can be
seen in general views of them. Unlike in large bridges, pure
Figure 1.26 Storebaelt bridge over the Grand Belt, Denmark; main
span of 1624 metres (1998), Cowiconsult.
Figure 1.27 Akashi-Kaikyo bridge near the city of Kobe, Japan;
main span of 1990 metres. Under construction.
26
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Figure 1.28 Bayonne bridge over the Kill Van Kull in New York; between Staten Island and New Jersey State, arch of 504 metres span (1932),
O. Ammann.
design projects that are quite regrettable in general are being
undertaken in small bridges.
The approach to an engineering work as a combination of
technology and art frequently tends to dissociate these two
components; this is why it is sometimes said that a bridge is
technically good but, nevertheless, ugly. A bridge may be well
calculated, well built and work well, but if it is ugly, the overall result is bad:
6
and protagonism, relegating all its other values; that is why
it sufficed for the bridge to be “technically good”; whether
it were well or badly designed, were ugly or beautiful, was
secondary.
The dissociation of technology and art also poses the problem of collaboration between engineers and architects in
bridge designing. Architects have always participated in the
latter, particularly in Germany and the Nordic countries. This
collaboration has also been frequent in the United States.
Architects appear in most of the great bridges in that country;
the architect Cass Gilbert worked with Othmar H. Ammann
on the George Washington bridge over the river Hudson and on
the Bayonne over the Kill Van Kull; the architect Aymar Embury
worked on the Bronx-Whitestone, also Amman’s; the architects
John Eberson first and then Irving F. Morrow worked on Joseph
B. Strauss’ Golden Gate; and, like them, many other American
“If this were not so, how could a distinguished engineer claim
that the design of a bridge may be a scientific marvel and at the
same time UGLY? No, a thousand times no; let him cite a single
case where this contradiction occurs. We, on the other hand, can
cite a hundred, a thousand, as many as you wish, where at one
and the same time, science and aesthetics have been offended.”
Fernando García Arenal 40
But, as we have seen (Section 1.3), the engineer has
tended to give the problem of strength excessive importance
27
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BRIDGE ENGINEERING
F1.29/8.99/8.157
them the Severin bridge in Cologne and the Bendorf bridge
in collaboration with Ulrich Finsterwalder, both over the
Rhine.44
There is a common idea in the cable-stayed bridges of the
city of Düsseldorf over the Rhine: all three have few stays and
they are parallel. The city’s architect, Friedrich Tamms, intervened decisively in this approach, which gave them that unitary
character, although all three, the Nordbrücke, the Kniebrücke
and the Oberkassel, are different.45
Danish architects from Dissing and Weitling collaborated with
the designers, Cowiconsult, on the 1600-metre span Storebaelt
suspension bridges of the first half of the twentieth century can
be mentioned.41
There have been and are architects who have participated in many bridges because they have devoted a large
part of their professional lives to them; we can name two
Germans among them: Paul Bonatz, who worked with Emil
Mörsch in the first half of the twentieth century42 and also
with Franz Dischinger and Fritz Leonhardt, with whom he
built the Rodenkirchen suspension bridge over the Rhine43
and Gerd Lohmer who participated in many of the bridges
built in Germany after the Second World War, among
Figure 1.29
Rodenkirchen bridge over the Rhine, Germany; main span of 370 metres (1941), F. Leonhardt and P. Bonatz.
28
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8.165
INTRODUCTION
64/
F1.32
bridge finished in 1998 and their intervention was significant
in the final physiognomy of the towers, which is good in our
opinion.
Apart from the above discussions, innumerable bridges
where this collaboration existed and the result was positive in
many of them may be quoted, which does not exclude the fact
that there is an infinity of good results in bridges designed
solely by engineers.
Collaboration between architects and engineers may be
positive in many bridge designs, but it must lead to a design
drawn up jointly, not by the addition of different interventions. The participation of architects in bridges is increasingly
widespread nowadays. In some cases, it is authentic collaboration between professionals, which can give positive results;
in others, the architect’s intervention is to give shape to piers
or decorate bridges afterwards and the results obtained
with the latter way of working are not fortunate in general.
This is a very French tradition because decoration of the
107-metre span Alexandre III bridge (Section 5.5.3) over the
Seine in Paris, designed by Jean Resal and finished in the first
year of the twentieth century, went out to tender separately
from the bridge design and the architects Cassien-Bernard and
Caussin won the award.46 Despite the floral motifs, the result
Figure 1.31
is not at all bad, because the power of the arch is fully
preserved.
What we do think is a very negative trend, is to try to
relegate engineers onto a plane of subordination compared to
Figure 1.30 Severin bridge over the Rhine in Cologne, Germany;
main span of 301 metres (1962), Gutehoffnungshütte Sterkrade A.G.
and G. Lohmer.
Bendorf bridge over the Rhine, Germany; main span of 208 metres (1962), U. Finsterwalder and G. Lohmer.
29
Figure 1.32
Alexandre III bridge over the Seine in Paris; arch of 107 metres span (1900), L. Resal and M. Alby.
bridges are, in the first place, the engineer’s creation. The
audacity of the construction depends on his talent, his knowledge, his valour and courage. He is fully responsible for the
work’s safety and stability.”47
architects in bridge designing, as has recently occurred in some
tenders. An example is the tender as issued by the Paris Mairie
in 1988 to design a new bridge over the Seine upstream from
Austerlitz bridge, where architects were prequalified on the one
hand and bureaux d’études techniques on the other. Architects
then had to choose a bureau to form a team in which the architect was the mandataire.45 The result was a bridge of no particular interest.
A bridge is and always will be basically a resistant structure
and, therefore, the engineer must play a fundamental role in its
design. However, scale is fundamental in this approach as in all
infrastructure engineering and the resistant structure in small
bridges has, therefore, stopped being a problem and this may
well change the terms of collaboration. As the size of a bridge
increases, the engineer’s role will be more decisive in its general
conception even though, as we have seen, collaboration with
architects may be positive. The architect Gerd Lohmer who, as
we have seen, participated in many German postwar bridges,
when addressing the collaboration of engineers and architects
in bridge designing, said “It is obvious that large modern
5. The fifth is based on simplicity and sobriety, which
should govern in any engineering work; the rationalists’ “ornamentation is a crime” and “less is more” very soon penetrated
engineers’ minds. This is partly due to the rationalist architect’s
influence, but fundamentally to a basic approach of engineering – the search for minimums which should be present in any
engineering solution, i.e. minimum alteration to the physical
environment and minimum cost, or, in other words, maximum economy, taking such economy in a broad sense, not just
the minimum direct cost of the work:
“Let the least possible material be hewn from the mine, let the
least amount of stone and sand be diverted from their evolution
process, let the minimum of fuel be used in transport and let the
fewest new ideas be introduced into the landscape.”
Carlos Fernández Casado30
30
INTRODUCTION
In our opinion, the previous approach does not oblige an
engineering construction to be always simple and sober, but it
may have baroque dimensions compatible with the approach
of minimums given before, although in principle, this may
seem to be a contradiction; the simplest things are not always
the most economical in the sense that should be given to economy referring to Public Works where many variables intervene. The Segovia and Toledo bridges over the river Manzanares
in Madrid are so valid as pieces of engineering work and the
latter is the baroque bridge par excellence among Spanish
bridges. Making simple, restrained constructions is a perfectly
valid approach and the most suitable in many cases, but
there may be others which are equally so. This leads us to the
problem of style in bridges, which different architectural styles
in different ages have reflected as in any other type of
construction.
There has been a simple technique throughout most of history for building durable bridges, which has remained practically unchanged for many centuries, for example the stone
voussoir arch. However, there are variations in architectural style
in them and, therefore, we can speak of Roman, Romanesque,
Gothic, Renaissance or Baroque bridges. These variations in
style have a minimum effect on their main elements: the
Roman bridge’s arch and pier are basically the same as the
Romanesque or Renaissance arch and pier; variations occur in
the arch, as we have seen, which in some cases may be deemed
as structural, but in others are really formal variations which
do not involve any improvement to this effect; the pointed
arch works worse for a bridge’s loads than the semicircular
arch, because its directrix is further from the loads’ antifunicular polygon, which is the ideal from the strength point of view;
but the stone voussoir arch enables directrices far from the
antifunicular polygons to be used and so very different shapes
may be used, from pointed to basket handle arches.
It may be concluded that architectural styles in stone
bridges affect the shapes of some of their elements, without
changing their structure; on the other hand, different styles in
another type of construction, both religious and civil, affect
the building structure’s organization: the Romanesque barrel
or tunnel vault has a resistant structure basically different to
the Gothic vault. Thus, the architectural style did not have the
same influence on a bridge as on a church; in the former, it
Figure 1.33 Segovia bridge over the river Manzanares, Madrid;
arches of 12 metres span (1584), J. de Herrera.
Figure 1.34 Toledo bridge over the river Manzanares, Madrid;
arches of 11.5 metres span (1735), P. Ribera.
affected its composition and the shape of its elements, such as
arches, piers, cutwaters, rear cutwaters, flood arches, etc. but
its structure in the latter.
Like any other construction, bridges can be made with
greater or lesser formal and technical wealth, which will give
them greater or lesser stylistic definition. The more care shown
31
Figure 1.35
Coalbrookdale bridge over the river Severn, England; span of 30 metres (1779), T. Pritchard, A. Darby III and J. Wilkinson.
architectural bridge and the craft bridge. We do not think the
dichotomy proposed is correct, because treatment of form and
care in construction occur to a greater or lesser extent in all
bridges and grading from the most complex to the most elemental is established.
There is also an influence of architectural styles in bridges
subsequent to stone ones, but, in turn, bridges in particular
and engineering in general have had a decisive influence on
architecture: architecture in iron commenced with Coalbrookdale bridge over the river Severn in England, a 30-metre
span arch; engineering’s influence on the functionalist and
rationalist movements in architecture is also significant.
At the present time, postmodern movements in architecture
are also influencing bridges. In quite a few cases, there is an aprioristic search for shapes or, better still, appearances, detached
in the treatment of their form and construction quality, the
more easily different styles may be spoken of and this will
enable them to be dated because of their morphology. But
most stone bridges have simple shapes, which have changed
little or not at all with time; they are sober engineering works.
A definite style cannot be referred to in these bridges, but,
reduced to strict shapes, they may have been built in any age
and so it would be difficult to date them by their morphology;
other data will have to be turned to because if their dating is
based solely on morphological data, the risk is run of being out
by several centuries; it would not be the first time that a
medieval or sixteenth or even eighteenth century bridge has
been taken for Roman.
It is not the intention with the foregoing to lay down two
categories of stone bridges as P. Gazzola proposes, namely48 the
32
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INTRODUCTION
Figure 1.36
Alamillo bridge over the San Jerónimo meander on the old Guadalquivir river course, Seville; single span of 200 metres, S. Calatrava.
be cases, where the greater or lesser strengthening of this value
may be justified, because society will always make and demand
monumental works. As we have seen, Michelangelo (Section
1.3) thought that bridges should be designed and built with
the same care as cathedrals and the intention is always to build
a monument with the latter. In bridges, as in all human construction, an expressive value should first be sought, everything else will follow. This expressive value will be more or less
strengthened in each project according to the circumstances
concurring in it. If we take this strengthening to a maximum,
we shall be making a monument over which vehicles or pedestrians cross. This problem was raised in the bridges of Seville
from all creative processes for bridges, which should be based on
their resistant structure. In this way, the bridge becomes an
object of design, which then has to be given a structure, as in
many architectural works, where this way of operating is frequently justified, but we think it is never justified in bridges.
In certain cases, the expressive values of engineering have
been forgotten but have later been given an almost absolute
value, as though the purpose of a bridge were purely as a monument, while forgetting that a bridge is, firstly, a useful construction with a very specific purpose, i.e. to make a way over
a river. However, this does not mean negating the value bridges
may have as monuments, particularly the largest. There may
33
Figure 1.37
F1.36/8.206
Alcántara bridge over the river Tagus; main arches of 28.8 metres (second century AD), C.J. Lacer.
this book; the bridge “joins two places isolated from each other
and has no other pretension than to be a road”. But we think
greater, more generalized concern among engineers for the
expressive ideas of engineering is positive, and this is also creating
greater interest in bridges among the population. An example is
the importance given to the new Seville bridges built for Expo
92; they have become one of the symbols of the new city and
have been publicized as an important part of its urban heritage.
built for the 1992 Universal Exposition, especially in Santiago
Calatrava’s Alamillo bridge; like the other Expo constructions,
the bridges shared in that intention to monumentality which
all Universal Expositions have. The problem, therefore, does
not arise in terms of yes/no but how far to go with this intention in each case; it is a problem of seeking equilibrium, as are
all those in bridge engineering.
Even though an excess of monumentality has occurred in
quite a few cases and seems negative to us, it is not a general phenomenon nor it is the approach of most engineers. It is not out
of line to recall here the last verses of Neruda’s poem prefacing
It may be deduced from the above discussion that a bridge,
like any other human creation, is subject to opinion trends and
34
INTRODUCTION
styles that may change in different ages. Although it is true
that technological progress has a decisive influence on bridges
and, therefore, brings about an irreversible advance in them
like any technology, it is no less true that certain types of structure are recovered and revitalized and this may well be motivated for technical reasons or for basically reasons of form.
Bridges are largely a consequence of the environmental
conditions where they are built; that is why there are 15- and
1500-metre span bridges, which have nothing to do with each
other. Different systems of structures and different materials
can be used in bridges, which also give rise to differences
between them.
We, therefore, think that pontificating on an idea of a general nature on how bridges should be, cannot and should not
be practised; what should be done is to understand their
expressive potentialities or, in other words, their language.
One of their greatest values is that many factors influence
them, giving rise to a broad range of more or less valid possibilities of the bridge to make. It is, therefore, necessary to
know all these possibilities, know how they have developed
throughout history and what their current situation is.
Theoretical understanding of the behaviour of different types
of bridge structure, added to construction technology, should
be completed with this knowledge all of which we may call
historical–cultural, even though parts of bridge technology are
rooted in it (see Chapter 2.6). Architects are aware of the need
and importance of understanding their own activity; on the
other hand, engineers are generally not. A synthesis of this
knowledge will enable us to have a broad view of how and why
bridges prior to that we are going to build were made and this
will give us sound criteria to build the new one.
It may be concluded from these considerations that there
may be different approaches in bridges as in any other engineering works, and they will depend on the place where they
are located, on their surroundings, on the social demand for
their construction, etc. When commencing a specific project,
all these problems will have to be approached from the factors
intervening in it and this will lead us to decide how the bridge
should be in order to give society what is deemed best in that
specific case. Like in all human actions, bridges will sometimes
be built well and will last because they are good and others will
be forgotten because they are not.
Figure 1.38 Triana bridge over the river Guadalquivir, Seville;
three arches of 46.5 metres (1845), G. Steinacher and F. Bernadet.
The original bridge and the bridge in its present condition.
1.5. THE BRIDGE, HERITAGE OF MANKIND
Bridges are part of a country’s transport infrastructure and,
therefore, form part of the heritage of Public Works.
35
BRIDGE ENGINEERING
Figure 1.39
First Carrousel bridge over the Seine in Paris; three arches of 48 metres (1839), A. Polonceau.
cases ranging from radical rejection of a new construction
changing the environment to its acceptance as an urban heritage enrichening object; from the most absolute oblivion to
passionate defence as something fundamental to the town.
The immense majority of society feels that a bridge falls
outside any aesthetic appraisal;48 aesthetic values are reserved
solely for art where architecture is included but engineering
not, and, save for rare exceptions, is deemed to have nothing to
do with it. This is largely due to the dichotomy between usefulness and beauty, which we have already analysed and which
Plato dealt with in his Dialogues, but which has continued
throughout history and has led a large part of the population
to ignore the artistic value of useful things.33 Stone bridges are
somehow saved from this situation by their value as being “an
antiquity”49 and because they are often included in architecture, as we saw earlier.
But while all the above discussion is true, it is no less true that
bridges have been more in the citizen’s mind than the above
situation would seem to indicate, and this becomes manifest
when it is proposed that a bridge which has come to be totally
accepted in a town be demolished, replaced or changed, which
does not call for it to be very old; at that time, the value of
the bridge it is intended to suppress or transform, which has
lain subconsciously in the citizen’s mind, suddenly becomes
Society appraises this heritage in general and bridges in particular in a varying, indecisive manner; its appraisal goes from
positive to negative in short-time periods and between different social groups. At any given moment, bridges may be
appraised in a positive fashion, they are deemed to be a necessary, enrichening asset, but shortly afterwards, they may be
deemed as items degrading the natural, rural or urban landscape and so must be prevented whenever possible.
Two fundamental factors intervene in this variability and,
on occasions, radicalization of criteria:
• Firstly, the expressive, monumental value of bridges is generally ignored, except in exceptional cases.
• Secondly, as we have seen (Section 1.2), Public Works change
the pre-existing geographical environment, giving rise to the
most controversial problem engineering poses to society.
This is why, like all engineering works, bridges are not generally considered as part of mankind’s cultural heritage. They
are used, but ignored and, therefore, not valued. Only the
small world close to them knows them and is interested in
their different values.
Lack of knowledge of engineering in general and of bridges
in particular has led to different stances with regard to them;
sometimes extreme, sometimes contradictory and in some
36
INTRODUCTION
Figure 1.40
F1.38
Roman aqueduct in Segovia on the town’s water supply.
preserved as a dock basin. Designed by two French engineers,
the bridge, a copy of Polonceau’s old Carrousel bridge in Paris,
had three 46.5-metre span cast iron arches and was obviously
outside the safety limits as nowadays required of bridges; this
was why a proposal was made to replace it with a new one. The
proposal led to fierce opposition in the city with an unheard of
aggressiveness in the press; its appearance was successfully kept
and the decks over the arches were replaced by self-resistant
a conscious asset and he will defend it with more passion than
might be initially expected. There are several cases where popular opposition to a bridge replacement has managed to save
the old one or where more or less valid solutions have been
reached to preserve its physiognomy.
Such is the case with Triana bridge over the river
Guadalquivir in Seville, built in the mid-nineteenth century;
currently, the river follows another course and the old bridge is
37
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BRIDGE ENGINEERING
Figure 1.41 Pont Neuf over the Seine in Paris; arches of 19.5 metres (1607), B. du Cerceau and G. Marchand.
F1.3/F1.40/F1.37
F1.16
F1.6/1.8/F1.13/F1.9
priority was given to this possible monumental nature in
their design, which is difficult to justify in an engineering
construction.
We also saw earlier that there are recent bridges, usually larger
ones, which have been given a monumental value or rather a
tourist value (adding this rather doubtful value to Riegl’s50) as a
man-made construction to be visited in the region or town where
located and that is why they appear in tourist guides. The
Brooklyn and Verrazano Narrows bridges, both in New York, have
been classified with two stars in the Michelin Guide to that city
(the maximum is three stars).
San Francisco’s Golden Gate bridge is one of the biggest
tourist attractions in that city and is shown as such in all its
tourist guidebooks.
Eiffel’s Garabit viaduct has been given two stars in the
Michelin Guide to France and the Pont Neuf and Pont Marie
one star in the Paris Guide.
ones with the arches remaining separate from the decks, with
no structural purpose. The physiognomy was quite faithfully
maintained, but it is another bridge.
Some of the great engineering works have achieved a monumental value for overall society, though they are exceptions;
this is largely due in most of them to their value as “an antiquity”,49 such as the Pont du Gard, Segovia aqueduct or Alcántara
bridge, which UNESCO has declared as monuments forming
part of the heritage of mankind; but others are relatively recent
and have also achieved that monumental value, such as Brooklyn
bridge, the Forth bridge, the Salgina-Tobel or the Golden Gate,
which date from the end of the nineteenth and beginning of
the twentieth centuries.
As we saw earlier (Section 1.4), the discovery of the possible monumental values of bridges has led in some of them to a
distortion of engineering because they were approached
from their beginning as monuments or, to be more exact,
38
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INTRODUCTION
F8.203/8.227/
8.295
Secondly, negative actions taken on bridges to adapt them
to current traffic requirements (see Chapter 2). Such actions
may be very different in nature, from demolition so as to
replace it with a new one, to more or less radical transformations which, in some cases, are almost as grave as demolishing
it, because the damage done is irreversible. Nobody defends
the existing bridge in most of these interventions, nor are the
transformations undertaken monitored from the point of view
here raised: the degradation of an object which has a value as
human heritage. Many are the transformations carried out on
old and not so old bridges, with no care taken; the functional
problem is solved in the simplest, most economical way possible, even though the result is an attack on the original construction.52 Different endeavours are currently being made to
rectify this sad situation of the historical heritage of engineering works; they are starting to be evaluated as cultural heritage
and various organizations engaged in studying and protecting
them are being set up. In fact, the Council of Europe has commenced intense activity, organizing meetings and issuing publications on the subject.53
We have seen the Sancho el Mayor bridge over the river
Ebro in Navarre mentioned as something to visit in that region
in several Spanish tourist guidebooks.51
Some bridges also appear in general, even modern, architecture history texts but, as a general rule, they are excluded
from what is deemed to be the cultural heritage of Man.
The most serious problem, the lack of appreciation of the
immense majority of engineering works has raised, is their
inability to defend themselves against any critical situation
affecting them. This situation may be caused by opposing phenomena, but both equally negative.
Firstly, abandoning the construction when it is no longer
used. When a bridge is replaced by a new one, the former no
longer is part of the road and is left to its own devices; it no
longer belongs to the Ministry of Public Works or any other
similar entity. No one will bother to conserve it, so in many
cases it will gradually disintegrate until it disappears in a more
or less lengthy period of time. This cannot be applied to all historical bridges because many stone bridges have not needed
preservation measures and it is often better to leave them as
they are in order to keep them in use than to change them.
REFERENCES
4
1 Pablo Neruda. Al Puente curvo de la barra Maldonado en Uruguay. Las manos del día. Classical and
Contemporary Library. Losada, Buenos Aires, 1968.
2 Patricia Niet. Así se hace una autovía. Ministry of Public Works, Transport and the Environment
(MOPTMA) Magazine, December, 1995.
3 Diccionario de la Lengua Española, 20th edition. Spanish Royal Academy, Madrid, 1984.
4 Carlos Fernández Casado. Ingeniería Hidráulica Romana. Colegio de Ingenieros de Caminos Canales y Puertos,
Madrid, 1983.
Carlos Fernández Casado. La conducción romana de aguas de Almuñecar. Archivo Español de Arqueología.
No. 77, 1949.
Dossiers de L’archeologie, No. 38. Aqueducts romains.
5 Carlos Fernández Casado. Expresión geográfica de las obras del ingeniero. Estudios Geográficos. Consejo
Superior de Investigaciones Científicas (C.S.I.C), February 1948 to May 1954.
6 Auguste Arsac. L’Architecture des ponts. In Ponts de France. Presses de L’Ecole Nationale des Ponts et
Chaussées, Paris, 1982.
7 Antony Sealey. Bridges and Aqueducts. Hugh Evelyn, London, 1976.
8 Javier Manterola and Leonardo Fernández Troyano. Criterios de diseño en puentes, una experiencia particular.
O.P. Revista del Col-legi de Enginyers de Camins, Canals i Ports. Catalunya. No. 7/8, Design in Civil
Engineering.
39
BRIDGE ENGINEERING
9 Arturo Soria and Puig. El territorio como artificio. O.P. Revista del Col-legi de Enginyers de Camins, Canals i
Ports. Catalunya, Comunidad Valenciana, Extremadura y Baleares. No. 11, Spring, 1989.
10 Los veintiun libros de los ingenios y máquinas de Iuanelo, Fascimile Edition. Published by the Fundación
Juanelo Turriano, Madrid, 1996.
Book written in the sixteenth century, initially attributed to Juanelo Turriano, but not written by him and,
therefore, in a first edition produced by the Civil Engineers Association in 1983, García Diego calls him
“pseudo-Juanelo Turriano”. Nicolás García Tapia (Ingeniería y arquitectura en el renacimiento español.
University of Valladolid, Valladolid, 1990; Técnica y poder en Castilla durante los siglos XVI y XVII. Castile and
León Regional Government) attributes it to the Aragonese Pedro Juan de Lastanosa, an engineer who was in
the service of Philip II, as “machinario”.
Books 14, 15 and 18 are of particular interest for understanding the techniques of bridge making in the
Spanish Renaissance, although this treatise was not released at all during its time nor later until its recent publication in 1983.
Book 14. Libro de las barcas que sirven en lugar de puente para passar los rios y de otras puentes.
Book 15. De puentes de solo madera.
Book 18. De como se an de hazer las pilas de las puentes de piedra en diversas maneras.
11 Alberti. De re aedificatoria. Florence, 1545.
12 Andrea Palladio. I quattro libri dell’architettura Venice, 1570, Facsimile Edition. Ulrico Hoepli editore
librario, Milan, 1945.
13 Enzo Siviero and Stefania Casucci. Il ponte e la cultura architettonica. In Il ponte e l’architettura.
CittàStudiEdizioni, Milan, 1995.
14 Stephen P. Timoshenko. History of Strength of Materials. Dover Publications, New York, 1983.
15 Robert Maillart. Design with Reinforced Concrete. Schweizerische Bauzeitung, January 1, 1938. Part of this
article’s text is included in that of Jörg Schlaich. The Bridges of Robert Maillart. Concrete International, June,
1993.
16 David B. Steinman and Sara Ruth Watson. Bridges and Their Builders. Colegio de Ingenieros de Caminos,
Canales y Puertos, Ediciones Turner, Madrid, 1979 (1st English Edition, New York, 1941).
17 Michael John Ryall. Britannia Bridge. North Wales: Concept Analysis, Design and Construction. Proceedings.
International Historic Bridges Conference, Columbus, Ohio, USA, August, 1992.
18 Alan Trachtenberg. Brooklyn Bridge Fact and Symbol. The University of Chicago Press, Chicago, 1965.
19 Charles S. Whitney. Bridges. Their Art, Science and Evolution. Greenwich House, New York, 1983. Reprinting
of the original book. W.E. Rudge, New York, 1929.
Fritz Leonhardt. Brücken/Bridges. The Architectural Press, London, 1982.
Bridge Aesthetics Around the World. Transportation Research Board, National Research Council, Washington
DC, 1991.
20 Stewart C. Watson and M.K. Kurd, editors. Aesthetics in Concrete Bridge Design. American Concrete Institute,
1990.
Adele Fleet Bacow and Kenneth E. Kruckemeyer, editors. Bridge Design. Aesthetics and Developing Technologies.
Massachusetts Department of Public Works, Massachusetts Council on the Arts and Humanities, Boston,
1986.
The Architecture of Bridge Design. Conference papers. Mayfair Hotel, London, 1994.
21 David P. Billington. Wilhelm Ritter: teacher of Maillart and Ammann. Journal of Structural Division, May,
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40
INTRODUCTION
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41
BRIDGE ENGINEERING
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42