Engineering 4 (2018) 267–276

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Engineering
journal homepage: www.elsevier.com/locate/eng

Research
Bridge Engineering—Feature Article

Forms and Aesthetics of Bridges

Man-Chung Tang a,b,c
a
Chinese Academy of Engineering, Beijing 100088, China
b
US National Academy of Engineering, Washington, DC 20001, USA
c
T.Y. Lin International Group, San Francisco, CA 94104, USA

a r t i c l e i n f o a b s t r a c t

Article history: The objective of a bridge design is to produce a safe bridge that is elegant and satisfies all functionality
Received 2 June 2017 requirements, at a cost that is acceptable to the owner. A successful bridge design must be natural, sim-
Revised 6 September 2017 ple, original, and harmonious with its surroundings. Aesthetics is not an additional consideration in the
Accepted 13 December 2017
design of a bridge, but is rather an integral part of bridge design. Both the structural configuration and the
Available online 15 March 2018
aesthetics of a bridge must be considered together during the conceptual design stage. To achieve such a
task, the bridge design engineer must have a good understanding of structural theory and bridge
Keywords:
aesthetics.
Form
Aesthetics
Ó 2018 THE AUTHOR. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and
Bridge Higher Education Press Limited Company. This is an open access article under the CC BY-NC-ND license
Concept (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Design
Environment

1. Introduction successful bridge, or any successful structure. Beauty has never

ceased to be one of the basic requirements of a successful bridge.
Humans are separated from wild animals by the existence of A successful bridge that is ‘‘safe, functional, economical, and
civilization. Elephants today still roam the earth with lives that beautiful” will provide both comfort and convenience.
are similar to those of elephants of thousands of years ago, but
we humans have significantly improved our lifestyles—thanks to 2. Form follows function
civilization!
What is civilization? The Merriam-Webster Dictionary defines A bridge makes up one element of a highway or a city street,
‘‘civilization” as ‘‘modern comforts and conveniences, as made pos- which in turn is an element in the master plan of a city or a com-
sible by science and technology.” Convenience can thus be munity. Hence, the function of a bridge is not defined by a bridge
achieved through technological advancement. Comfort, however, engineer. When the need arises to cross a river or a valley, or to
can only be achieved by improving the quality of our environment, connect two points, the planning calls for the design and construc-
which includes the form and aesthetics of the things surrounding tion of a bridge. This need drives the purpose of the bridge design.
us. Without quality in our environment, we cannot have quality The purpose further defines the function of the bridge. The func-
and comfort in our life. tion of a bridge is established based on traffic planning, in conjunc-
Approximately 2000 years ago, the great architect Marcus tion with socioeconomic and urban studies. These studies identify
Vitruvius Pollio advised the Roman Emperor that ‘‘Structures shall how much traffic is predicted for a certain design life of the bridge.
be safe, functional, and beautiful!” [1]. Although these require- The traffic engineer determines the number of lanes required
ments are still valid today, we must add economy to the list. There- based on the volume of the predicted traffic and the design speed.
fore, today’s standard should be that ‘‘Structures shall be safe, The local topography and other local conditions then determine
functional, economical, and beautiful!” the desired geometry of the deck including the length, minimum
Cost was less important for Vitruvius because he worked for the span length, maximum grades, and minimum clearances.
Emperor. We engineers of today do not have that kind of luxury. Once the function of a bridge is determined, the bridge engineer
Aside from that, not much has changed in how we define a selects the form of the bridge to satisfy the given function—hence
the motto ‘‘form follows function.” However, before establishing
E-mail address: mtang@tylin.com the form of the bridge, the engineer must understand what

https://doi.org/10.1016/j.eng.2017.12.013
2095-8099/Ó 2018 THE AUTHOR. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
268 M.-C. Tang / Engineering 4 (2018) 267–276

material is available for the construction of the bridge. This process bridges, and large and slender arch bridges. By combining steel
is represented in Fig. 1. with concrete, we have also been able to build many long-span
Aesthetics is another ingredient used in finalizing the bridge reinforced concrete bridges.
design. We shall not build ugly bridges. An ugly bridge pollutes High-strength steel wires are produced by a cold drawn process.
the environment. The high strength of these wires makes long-span suspension
bridges possible. Before high-strength steel wires were commer-
cially available, suspension bridges were built using steel chains
3. Historic evolution of bridge forms
and eye bars; however, the span length of such bridges was
limited.
Bridges all over the world can be placed into four basic cate-
The introduction of high-strength steel wires also stimulated
gories: girder bridges, arch bridges, cable-stayed bridges, and sus-
the development of cable-stayed bridges. A cable is not effective
pension bridges. All of these major bridge types are almost as old
if the sag due to its own weight is too large. The sag is a function
as human civilization. In some primitive form, all were first built
of the tension in the cable. Therefore, a cable can only be effective
many, many centuries ago. However, the evolution of today’s more
if it can be stressed to a very high force under permanent load con-
sophisticated and versatile bridge forms can be traced to the intro-
ditions, which is possible only if the cable is made of very high-
duction of various construction materials of different times.
strength materials so that it can still have reserved capacity to
Some 4000 years ago, and until the beginning of the 19th cen-
carry live loads. High-strength steel wires also improved the econ-
tury, the only construction materials available were wood and
omy and versatility of prestressed concrete. As a result, many pre-
stone. Wood from tree trunks could be used as girders; therefore,
stressed concrete bridges have been built.
felled trees were used to create bridges. For larger crossings, stone
It is evident that the availability of specific materials affects the
piers were created so that tree trunks could span between them;
selection of bridge forms. Thus, bridge development can be divided
however, these bridges were not sturdy. They did not last long
into two eras: the arch era, and the contemporary era with all four
and could not encompass large spans.
types of bridges. The arch era spans over 4000 years, while the con-
Stone is much stronger than wood, albeit only in compression.
temporary era is less than 200 years old.
It is also more weather resistant. All early Egyptian and Greek
Looking to the future, many new materials such as carbon fibers,
buildings were built of stone. Because stone cannot sustain high
ultra-high-performance concrete, and nano materials may be use-
tensile stresses due to bending, these buildings have very closely
able in the development of new bridge forms. However, these mate-
spaced columns. Brick, which is also a compression material, was
rials are not yet ready for large-scale applications. Therefore, we can
later produced to replace stone in some applications.
conclude that in the last four to five millennia, humans have only
The arch bridge was the most ingenious invention by the
invented four bridge forms, as identified in Fig. 2.
Romans and the Chinese that fully utilized the compressive
strength of stone. The Romans built the barrel vault by connecting
successive arches together to create a large inner space. The dome 4. The basic structural elements: The ABCs of structures
was created by rotating the arch around its vertical axis. Using the
dome, the arch, and the vault, the Romans built many spectacular Even though the four basic forms of a bridge—girder, arch, cable-
structures. The Pantheon, with its 43.3 m diameter dome, was the stayed, and suspension (Fig. 3)—may look very different from one
largest dome in the world for about 1800 years. The arch allowed another, each of these bridge types is comprised of only three basic
the Romans to build many bridges and viaducts, some of which structural elements: axial, bending, and curved elements (the ABCs
are still in existence today. of structures). By combining and mixing these three types of basic
Iron, with its greater strength and formability than stone, pro- structural elements, different bridge configurations can be created.
vided chains to build iron chain bridges, which are a type of For example, a truss bridge mainly consists of axial elements.
‘‘stress-ribbon bridge”—that is, an early form of suspension bridge. Bending moment may exist, but it is secondary. The same is true
The very first major iron chain bridge is reported to have been built for a cable-stayed bridge. However, an arch bridge carries its load
in China around 60 AD: the Lan Chin Bridge [2] in Yunnan Province, by the change of curvature, and this is also the case with the main
which has a main span of about 60 m. Many iron chain bridges cables of a suspension bridge. In comparison, a girder bridge is
were constructed in China, some of which are still accessible today. mainly a bending element (Fig. 4).
One of the longest span iron chain bridges, the Luding Bridge [2] in
China, was built about 400 years ago. Iron chain was also used as
5. Engineering is an art, not a science
the main cables of suspension bridges; however, these bridges tend
to be smaller structures because, like stone, iron lacks high tension
Engineering is not a science. The aim of science is to discover
capacity.
truth, which is unique. Therefore, science is rigid because it is
It was steel that revolutionized bridge construction, because
not possible to change truth. Science is either right or wrong, and
steel can take both high tension and compression. Once the mass
there are no ‘‘good” or ‘‘bad” sciences. Unlike scientists, engineers
production of steel became possible in the mid-19th century,
do not make discoveries; rather, engineers create things based on
engineers were able to build long-span girder bridges, truss
their subjective experiences and preferences. Therefore, engineer-
ing is flexible, and this flexibility affords engineers the possibility
to select, or even to create, new structural forms that satisfy the
given function of a bridge, within certain limitations. This process
of selection and creation is an art!
Engineering is not an applied science either. When building
the pyramids and the Great Wall, what science was applied?
Science was a mere tool used by engineers to judge and explain
the behavior of a structure. In addition to understanding science,
engineers require knowledge and skills in many other fields such
as economics, aesthetics, and politics in order to be successful
Fig. 1. Bridge design flow chart. bridge designers.
 M.-C. Tang / Engineering 4 (2018) 267–276 269

Fig. 2. The introduction of steel stimulated the development of new bridge forms. (a) Iron did not change the bridge form much (Coalbrookdale Iron Bridge by Pritchard);
(b) high-strength steel wires stimulated new bridge types; (c) after high-strength steel wires became available, bridge construction started a brand new chapter.

In engineering, the question is always, ‘‘Does it work?” Engi- type today. Fig. 5 identifies how the maximum span of each bridge
neering can be either good or bad, but never right or wrong. type has evolved. All of these curves show a trend: The maximum
We already know that all possible forms of bridges are com- span length is increasing.
prised of only three basic structural elements: axial, bending, and Knowing that the state of the art is changing with time, we
curved elements. The art of bridge engineering lies in knowing should be humble in predicting the future. New materials are
how to integrate these elements in order to arrive at the best struc- showing promise for construction, such as composite materials.
ture that satisfies the fundamental requirements of ‘‘safe, func- However, the actual application of these new materials will require
tional, economical, and beautiful” features. This is similar to a more testing and an actual record of performance before the mate-
cook combining various ingredients in a certain way so the food rials can be used in a very long-span bridge design and construc-
will taste best. tion; a bridge is inherently a major investment that usually calls
However, in practice, the task of coming up with a good combi- for more conservatism.
nation requires experience and training, just as in cooking, playing Given what is available today, high-strength steel is still the
piano, or playing golf. Although the basics are simple, playing the only real high-strength material suitable for long-span structures.
piano well requires many years of hard work and practice. Thus, the question becomes: ‘‘What are the limits of steel bridges?”
Besides, there are limitations to what we can do. To extend the Steel with a higher strength is currently available for bridge
analogy of playing piano, it is impossible to have a piano produce a construction. In the late 1960s, a cable-stayed bridge—the
human voice. Thus, it is important to understand these limitations Duisburg-Neuenkamp Bridge in Germany (Fig. 6)—used a very
before practicing combinations of the ABCs. high-strength steel for the towers, which are predominantly com-
pression members. The steel had a yield strength of about 700
6. Span length MPa. The bridge has been performing well, so we may consider
using this steel strength for future bridges, especially for compres-
When a large river or bay needs to be crossed, the question that sion members. Steel wires with a breaking strength of up to 2000
always comes up is ‘‘How long of a span can we build?” History MPa are now available. Based on these steel strengths, the maxi-
may provide some help in answering this question. Table 1 mum span length of a suspension bridge can be 10 000 m, the max-
identifies the top three longest spans in the world for each bridge imum span length of a cable-stayed bridge can be 5500 m, and the
270 M.-C. Tang / Engineering 4 (2018) 267–276

maximum span length of an arch bridge can be 3500 m. There are Having the ability to build a very long span does not technically
no distinct criteria for a girder bridge. However, practical and eco- mean that we can freely choose longer spans even if they are not
nomic considerations most likely limit the span length of a girder necessary. Longer spans usually cost more. Since economy is one
bridge to approximately 550 m. of the basic considerations for the success of a bridge design, it
must be kept in proper perspective. Therefore, we must address
the cost of a bridge as part of the design. If a bridge is not econom-
ically feasible, it will not be built.

7. Value versus cost

A bridge is economically feasible if its value is equal to or higher

than its cost. The value of a bridge is the sum of several compo-
nents—generally, these include its functional value, social value,
and aesthetic value.
The value of function is obvious. Because of the bridge, a user
can reduce the time required to travel from point A to point B. This
convenience saves money and time, which can be represented by a
dollar value. Multiplying the value of the bridge to an individual by
the number of users yields the functional value of the bridge. As
the standard of living in a society increases, the value of this con-
venience also increases. A bridge project that was not economically
feasible in the past may become feasible today.
A bridge connects not only places, but also people. Very often, a
bridge is built to symbolize a unification, friendship, or other bond
between two communities. The value of this symbolism is difficult
to determine numerically; however, under certain circumstances,
it can be very significant, and can even be the sole reason for the
construction of a structure.
Consider this famous saying: ‘‘Beauty is in the eye of the
Fig. 3. Bridge types. (a) Acosta Bridge (girder); (b) Old San Francisco-Oakland Bay
beholder.” Although beauty is very subjective, it has value. As an
Bridge (truss); (c) Crooked River Bridge (arch); (d) Talmadge Memorial Bridge analogy, most people do not simply wear the cheapest clothing;
(cable-stayed); (e) Golden Gate Bridge (suspension). in addition to considering cost, people choose clothing because

Fig. 4. The ABCs of structures.

Table 1
Longest bridge spans in the world for each bridge type.

Bridge type Name Span (m) Country Year of

completion
Girder Shibanpo Yangtze River Bridge 330 China 2006
Stolmasundet Bridge 301 Norway 1998
Presidente Costa e Silva Bridge 300 Brazil 1974
Arch Chaotianmen Yangtze Bridge 552 China 2009
Lupu Bridge 550 China 2003
New River Gorge Bridge 518 USA 1977
Suspension Akashi Kaikyō Bridge 1991 Japan 1998
Xihoumen Bridge 1650 China 2009
Great Belt East Bridge 1624 Denmark 1998
Cable-stayed Russky Bridge 1104 Russia 2012
Sutong Yangtze River Bridge 1088 China 2008
Stonecutters Bridge 1018 China 2009
 M.-C. Tang / Engineering 4 (2018) 267–276 271

they want to look good, or at least appropriate. We decorate our unknowingly. An attractive building in a nice neighbourhood can
homes because making them more beautiful enhances our love demand a higher rent. Consequently, aesthetic considerations have
of life. We travel to places simply to enjoy looking at the beauty always been important in the design of the exterior and interior of
of the scenery and surroundings there. There is no doubt that peo- commercial buildings.
ple are always willing to pay for aesthetics, whether knowingly or Since most bridges are paid for by tax dollars, they are indirectly
paid for by taxpayers or citizens. Consequently, it is the responsi-
bility of the bridge engineer to understand what the taxpayers
would do if they were to design the bridge. Considering that most
taxpayers are willing to pay for aesthetics in their daily life, there is
no reason why engineers should impose on taxpayers the cheapest
bridge possible. Besides, the inclusion of aesthetics does not always
cost money. Paying more attention to details can bring about a sig-
nificant improvement in the appearance of a structure.
A visit to Paris may include visits to the Eiffel Tower, the Louvre
and its famous paintings and sculptures, the Arc de Triumph, the
Pont Alexandre III, and other beautiful structures (Fig. 7). Some
of these structures have little or no functional value, such as the
Arc de Triumph. However, tourists and locals remember and love
them because they are beautiful; one need not be a bridge engineer
to notice that the bridges across the Seine River are beautiful struc-
tures that are designed with thoughtful attention to aesthetics. It
would be unthinkable for all of the bridges over the Seine River
to be built in the cheapest way possible. The resulting Paris would
not be the Paris we know today!
Fig. 5. Milestone maximum spans of various bridge forms. Obviously, it is difficult to estimate the value of beauty or a
landmark; however, in 2012, the Monza and Brianza Chamber of
Commerce of Italy made an effort to do just that. They evaluated
the most well-known landmarks of the world, and concluded that
the Eiffel Tower was worth about 544 billion USD to the French
economy. Considering that the French GDP was 3380 billion USD
in 2012, the economic value of the Eiffel Tower was estimated to
be as high as 16% of the French GDP in 2012—an enormous value!

8. Bridge aesthetics

A successful bridge design must be natural, simple, original, and

harmonious with its surroundings (Fig. 8). A bridge is usually a
large and very visible structure within its environs. It should look
natural and fit well into the landscape. It should also be simple
and not look superficial. A structure looks more natural if it can
convey an understandable impression to the public about how it
Fig. 6. Duisburg-Neuenkamp Bridge. works.

Fig. 7. Typical memories of Paris focus on the aesthetics of structures and other artwork, including the bridges across the Seine River.
272 M.-C. Tang / Engineering 4 (2018) 267–276

Fig. 8. A successful bridge design must be natural, simple, original, and harmonious with its surroundings.

Uniqueness is an important factor in any piece of art. Likewise, devoted an extraordinary amount of time to aesthetics 3000 years
each bridge should be unique in and of itself. Each structure has ago. Their buildings were very meticulously designed and con-
its own requirements and distinct surroundings. Each bridge structed, and the Parthenon has been recognized by many as the
design should be based on its own particular conditions. There- most perfect building in history. Careful investigation of the
fore, each bridge should be original and have its own style, Parthenon has indicated that every detail was meticulously
characteristics, and design. Like a painting, only an original bridge attended to in order to compensate for the perception of the
is valuable. human eye. For example, all the horizontal lines of the Parthenon
Being harmonious with its surroundings does not necessarily are curved upward to make them look horizontal. The spacing
mean that the bridge must only blend well with its environment. between columns is not the same, in such a way that it appears
It also means that the structure should be configured such that it the same to the human eye. The diameter of the columns is also
‘‘fits” well in its position. This may often mean that the bridge very specifically not uniform, in order to make it look uniform.
stands out from its surroundings, if doing so is more appropriate. These technical details were given particular attention, even
A bridge is viewed from many different angles, so looking good though they were based on common sense rather than on rules.
from only one viewpoint is not sufficient. Many scholars have tried to establish rules for structural
beauty, but none have succeeded. For example, the ‘‘golden sec-
9. What are bridge aesthetics? tion” concept, which is supposed to prescribe the proportion of
the best-looking rectangle, has been studied and promoted by var-
A bridge is mainly comprised of girders, piers, towers, and per- ious architects for years. However, even today, after centuries of
haps cables. The girders are relatively horizontal, and the piers and study and debate, no one can really say whether a rectangle with
towers are generally vertical. A bridge typically has two abut- a proportion of the two sides of U (U = 1.61803) definitely looks
ments, one at each end. These are all the elements to be dealt with. better than a square, under any circumstances.
Common sense recognizes the following: In general, aesthetics is about proportion, balance, and har-
 The soffit should camber upward to avoid a sagging appearance. mony. The Italian Renaissance architect Alberti defined beauty as
A haunch girder should have a smooth curvature. ‘‘a harmony of all the parts.” When we look at an object, we do
 Catenary, circular, and parabolic arch shapes each have different not go through any logical derivation to determine whether it is
characters. beautiful or not; our reaction is a more spontaneous one. Although
 The bridge alignment is usually straight. Curvature in a bridge human perception often changes with time, real beauty transcends
always introduces some form of intrigue; however, curves must time and style. A beautiful bridge can be dramatic and daring, but
be handled with care. Curvature can create completely different it can also be graceful and poetic. The basic idea of bridge design is
impressions when looked at from different viewpoints. to inspire an emotional response from viewers, and even a kind of
 For box girders, sloping webs look lighter; however, this may surprise. How we achieve this is can be called an art.
create complex and messy lines when the bridge is in a curve. Nature endorses simplicity; many of the important rules of nat-
 Symmetry looks more robust and traditional, but asymmetry ure are simple. Even the most important equations of nature in
offers a more intriguing appearance. physics are extremely simple, such as F = m
a, or E = m
c2. The
 Viewers may be located on the bridge, under the bridge, or look- human mind, which has historically been immersed in nature most
ing at the bridge from any angle of its surroundings. Glorifying of the time, is accustomed to simplicity. It has been repeatedly pro-
one view from a specific location and neglecting the other views ven that the simplest configuration is usually the best-looking
is not desirable. solution. It has been stated that in order to arrive at the most beau-
 Piers should express the flow of the load path. Textures can be tiful structure, the best method is to try to take away any compo-
used to reduce a monotonous appearance. nent that can be taken away, in a process of simplification.
 Long cantilever slabs over box girders cast a shadow, which Obviously, this requires experience and a good understanding of
makes the girders look more slender. structure and aesthetics.
Of course, the factors listed above are just commonsense obser- We teach our children to walk properly, talk properly, and move
vations, not rules. Most engineers are accustomed to following properly. A person with a good posture automatically emits a cer-
rules; however, even though not everyone agrees, most people tain charisma—clothing style and accessories are secondary. Good
have concluded that there are no rules for aesthetics. The Greeks posture costs nothing; once a person is well-trained in manners
 M.-C. Tang / Engineering 4 (2018) 267–276 273

and attitude, it comes naturally. A similar premise applies to bridge

design and, in fact, to any kind of art. If we disregard the skill of the
artist or the designer, the actual cost of a good painting versus a
bad one is basically the same and comprises the costs of the can-
vas, paint, brushes, and so forth. In the same way, the difference
in the basic cost of a beautiful bridge versus that of a mediocre
bridge may be very little. In reality, a well-designed, attractive
bridge is usually more economical because it is more natural and
simple; it follows the intentions of nature.
We should treat bridge design as an art. However, a bridge is
not just a function of art: The basic purpose of a bridge is still to
carry traffic. A sculpture may be created simply because it looks
attractive, but a bridge is never built for the same reason. It is obvi-
ous that there are three distinct differences between bridge design
and other art forms. First, a bad painting or other artwork will just Fig. 9. Aesthetic lighting gives vibrancy to bridges at night.
end up gathering dust in a basement somewhere, whereas a bridge,
once complete, will be prominently displayed in the public eye for
hundreds of years. The community cannot escape being affected by accommodated in the structure. Some lighting elements may
it. Second, the fruits of success are rewarded to the painter or other appear unattractive in the daytime if they are not properly located.
artist, whereas in our present system, there is little incentive for a
bridge engineer to spend additional effort to strive for the best- 12. Who designs the bridge—the engineer or the architect?
looking bridge form—his/her fee will probably be the same regard-
less. Finally, most other artists work more or less alone, whereas an A bridge is not a sculpture; in addition to having a pleasing
engineer works in a group and must deal with many related par- design, a bridge must be safe, functional, and economical. These
ties, including economists and politicians, who may elect to impose matters are best dealt with by engineers. It is a bad idea to leave
their own ideas on the bridge design and designer. the aesthetics of a bridge to architects alone; architects cannot
Making the effort to search for the best-looking bridge alterna- conceptualize a complete bridge because they do not have suffi-
tive requires time and effort. However, once this practice becomes cient training in structural engineering to perform this task. It is
routine in design, the additional effort is not significant. Despite also a bad idea, albeit one that is practiced by many engineers, to
the abovementioned factors, it is still the responsibility of the ask an architect to beautify a bridge after the engineer has finished
bridge engineer to pay attention to aesthetics. An unattractive the structural design. At that point, all an architect can do is add
bridge is a kind of pollution to the community—one that will decorations, which may not always be appropriate.
remain present for a very long time. Aesthetics are not an addition to a bridge, but are an integral
part of the bridge design. Both structural configuration and aes-
thetics must be considered together during the conceptual stage
10. Decorations of bridge design. To achieve such a task, the bridge engineer must
have a good understanding of structural theory and bridge aesthet-
Decoration is like cosmetics: True beauty does not need ics. Unfortunately, most engineering schools do not teach aesthet-
makeup. The most successful bridge is one that fully expresses ics. A bridge engineer must learn aesthetics, whether inside or
itself through its structural form. The touching up of small details, outside of his/her educational training. As a rule, the engineer must
such as adding covers to hide cable anchorages, is not decoration; be the prime designer of a bridge. He/she must conceptualize the
installing statues or flowerpots is. bridge to satisfy all structural and functional requirements with
A bridge is a large structure. In most cases, the magnitude and due consideration for aesthetics. As a compromise, he/she can also
form of the bridge itself are so powerful that decoration only work together with an architect during the conceptual stage of the
makes the bridge look less impressive. However, if a bridge is built design.
to symbolize certain events or a relationship, like the Pont Alexan-
dre III in Paris, which was built to celebrate the friendship between
the Russian Empire and France, decoration can convey certain 13. Innovation
meanings and impressions.
In general, city bridges tend to be more suitable for decorations, As discussed earlier, each bridge should be treated as a unique
which can create more harmony with the bridge’s surroundings. design. It is acceptable to borrow recognized concepts from exist-
City bridges tend to be smaller in size as well. A bridge in a natural ing bridges; however, each concept must be applied in a unique
setting should be more natural and simple; decoration is usually way. It is unacceptable to copy another bridge design. To make
not desirable. an analogy, although many great artists have painted roses, each
artist painted roses in his/her own way. Therefore, each original
painting of roses is unique. In contrast, a copy of a painting has lit-
11. Aesthetic lighting tle value because it lacks the creative spirit of art. Originality and
uniqueness together form innovation; however, innovation also
Aesthetic lighting is an art in itself: It not only makes bridges means something new and perhaps nontraditional. New and non-
visible, but also gives them vibrancy at night. However, it is impor- traditional designs are often met with resistance.
tant to differentiate between illumination and aesthetic lighting. Although an artist creates a sculpture or a painting basically by
Illumination simply makes a bridge visible; aesthetic lighting himself/herself, the building of a bridge involves many parties: the
makes use of the interaction between light and the structure to owner, the managing agent, various engineers, the contractor, and
create special effects and impressions (Fig. 9). others. The engineer may not always be the master of the project.
It is important for aesthetic lighting to be considered early on in As the saying goes, ‘‘The donkey was the product of a committee
the design so that all the physical facets of lighting can be properly that intended to create the most beautiful horse.”
274 M.-C. Tang / Engineering 4 (2018) 267–276

Under such circumstances, uniqueness can often be met with railings, the required minimum width of the deck is about 30 m.
resistance, whether from an owner who prefers to do exactly what The design speed for this city bridge is 60 km
h 1, and the live load
others have done before, or—and surprisingly often—from fellow is based on the Chinese city class A car loading [4].
engineers. Some engineers can be very conservative and tend to Both ends of the bridge connect to existing streets, so the deck
prefer repeating what has been done before. These resistances elevation of the bridge is fixed. The bridge also accommodates
are sometimes rational, and sometimes not. future sightseeing boats on the river. These two requirements
Some great designs were never built because of the resistance of restrict the maximum girder depth to 1.38 m at the centerline of
others. A group of engineering experts vetoed Thomas Telford’s the bridge. The cross slope further reduces this to 1.3 m at the edge
design of the London Bridge as unbuildable. Fortunately, the same of the traffic lanes.
design concept was used to build the beautiful Craigellachie Bridge Tianjin is very close to Tangshan, where a major earthquake in
in Scotland [3]. Similarly, when the Eiffel Tower was proposed, 1976 caused very extensive damage and fatalities. Consequently,
people denounced it as unbuildable and ugly. Today, 100 years the Dagu Bridge was designed for the highest seismic forces in
later, it has become the jewel of Paris and the pride of French con- China. Unfortunately, the upper layers of soil are very soft, which
struction and ingenuity. In fact, the public has been in love with eliminated all bridge types from consideration that required
the Eiffel Tower since its opening. anchorages for horizontal forces.
Philosophers and fine artists can live in an intellectual world
generations ahead of others. They do not have to seek approval, 14.1. The Dagu Bridge concept
and they own their ideas and concepts. An engineering project,
on the other hand, always includes an owner and a designer. Conceptual design is the most important step in the design of a
Although a bridge engineer designs the bridge, the bridge engineer bridge. A proper conceptual design solidifies the structural system,
does not own the bridge. The owner represents the public, and the aesthetics, cost, and functionality of the bridge. It should also come
public has a right to ask for what it wants. Thus, a bridge engineer with a construction method and solution for important details.
should never try to build a monument for himself/herself. A bridge Every bridge has certain restrictions. The conceptual design must
engineer is there to serve the public with his/her best effort. Still, properly consider and provide solutions for all these restrictions.
despite all these considerations, an engineer must not give up After it was determined that the Dagu Bridge was to be a tied
the responsibility to ensure that a bridge is beautiful, in addition arch bridge, the logic for the conceptual development that led to
to being safe, functional, and economical. the final configuration was suggested (Fig. 11), as outlined below:
 Due to the river’s navigational requirement, the arch must be
above the deck.
14. An example: Dagu Bridge, Tianjin
 The minimum deck width is about 30 m, and the girder depth is
restricted to 1.38 m at the centerline of the bridge, as shown in
The Dagu Bridge may be a good example of a bridge design pro-
Fig. 11(a).
ject (Fig. 10). This bridge, which is located at the center of the city
 The arch bridge should have two arch ribs, usually one on each
of Tianjin, is part of the Downtown Redevelopment Project that
side of the deck. These ribs should be over 32 m apart, as shown
revitalized the old city. One of the first goals of the Downtown
in Fig. 11(b).
Redevelopment Project was to have a signature structure that
 The girder is only 1.38 m deep; this is not sufficient to span a 32
could become a symbol of the city of Tianjin.
m wide deck transversely, so the arch ribs cannot be located
The width of the river at this location is 96 m. The bridge was
outside of the deck. As a solution, the two arches can be moved
designed to avoid having any piers in the river, with the resulting
to the edges of the six traffic lanes (they ended up about 24 m
design featuring a main span of 106 m. The bridge carries six lanes
apart, as shown in Fig. 11(c)).
of traffic and two pedestrian paths, one on each side of the bridge
 If the two arch ribs were not connected to each other, they
deck. The minimum width of each of the pedestrian paths is 3 m.
would have to be quite bulky in order to avoid lateral buckling.
Two of the traffic lanes are 3.75 m wide, and the other four lanes
This is aesthetically unpleasing and unacceptable; moreover,
are 3.5 m wide each. Along with the median divider, barriers, and
two vertical arch ribs would appear mundane.
 It is customary to tie the two arch ribs together with struts to
stabilize them so they can be more slender, as shown in
Fig. 11(d). However, this would look too messy because the
bridge span is relatively short and the arches are rather small.
This solution is also aesthetically unacceptable.
 To reduce the length of the braces, it is possible to incline the
arch ribs inward to form a basket-handle arch, as shown in
Fig. 11(e). However, for a relatively short, 106 m span, a
basket-handle configuration appears too flat and bulky.
 Instead of the conventional transverse braces, a three-
dimensional structural system employs two planes of hangers
tying each arch rib to the deck girder. The two planes of hangers
give support to the arch rib in both the vertical and transverse
directions. This stabilizes the arch against lateral buckling. Thus,
the ribs can be made very slender, as shown in Fig. 11(f).
 Now, with two planes of hangers stabilizing each arch rib, the
arch ribs can be tilted in any way desired. Here, they are tilted
outward. This offers a very open view looking from the deck.
 The surrounding landscape is very asymmetrical; therefore, the
height of one arch can be increased to make it more intriguing.
The taller arch is given a smaller inclination so that it does not
Fig. 10. Renderings of the Dagu Bridge in Tianjin. lean too far outward.
 M.-C. Tang / Engineering 4 (2018) 267–276 275

Fig. 11. Development of the Dagu Bridge concept.

14.2. Design of the Dagu Bridge 14.3. Aesthetic lighting

The owner metaphorized the development of the Hai River as a Three different sources of light illuminate the Dagu Bridge. The
‘‘golden dragon dance” because the Hai River runs diagonally first light source is the streetlights on the bridge and along the
across the entire city, a bit like a dragon’s sinuous tail. The config- riverbanks. The second light source is the spotlights on each hanger
uration of the Dagu Bridge symbolizes the sun with its large arch, at a level slightly below the bridge deck. Two spotlights are
the moon with its small arch, and the stars with the lights around installed at each hanger location in order to obtain a more uniform
the edges of the deck; all of these compliment the concept of the reflection on the arch ribs. These lights illuminate the arches and
dragon (Fig. 12). cables. The third light source is a set of lights under the edge plates
In this basic structural system, the arch ribs provide the vertical at the outer rim of the pedestrian paths. These lights reflect the
stiffness for the bridge; the deck provides the lateral stiffness, and water underneath and horizontally through the holes in the edge
the cables combine the two together into a compact system. The plates. The intensity of these three light sources is well coordinated
bridge itself is stable while supported on piles. and expresses the elegance of the structure at night (Fig. 13).
For a 106 m span, the rise of the arch ribs would usually be
about 20 m. To introduce some architectural surprise and intrigue,
the two arch ribs are of unequal heights, as mentioned earlier. The
small arch is 19 m high and the large arch is 39 m high. To create
further architectural interest, the pedestrian paths curve outward
to offer additional space for pedestrians to rest and enjoy their
surroundings.

Fig. 12. The large arch of the Dagu Bridge symbolizes the sun, the smaller arch Fig. 13. The Dagu Bridge. (Note: T.Y. Lin International provided the conceptual and
symbolizes the moon, and the lights around the edges of the deck symbolize the preliminary designs of the Dagu Bridge. Tianjin Urban Construction Design Institute
stars. provided the construction plans.)
276 M.-C. Tang / Engineering 4 (2018) 267–276

15. Summary the enjoyment of all of its citizens. This is the only world we
have.
By taking advantage of the flexibility of engineering and by uti-
lizing the three basic elements—the ABCs of structures—engineers References
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