Download - Extended Project
THE FARNBOROUGH EXTENDED PROJECT 2010
ADVANCED LEVEL
AUTHOR DECLARATION
Title of the Extended Project:
What are the differences and similarities between Cable Stayed and
Suspension Bridges and where are they best suited?
Word count: 4,514
Submission date: 28.10.2010
I affirm that this Project is offered for assessment as my original and unaided work, except in so far as any advice/and or assistance from any other named person in preparing it, and any quotation used from written sources are duly and appropriately acknowledged. I agree that my submission may be referred to the JISC Plagiarism Service in order to fully authenticate my work.
Name: David Bedford
Candidate number: 91113
Supervisor: Jane Gostling
Project Leader: Simon Reigh, Faculty Director (Business, Information & Global Studies)
The Sixth Form College Farnborough, Prospect Avenue, Farnborough, Hampshire, GU14 8JX Tel: 01252 688200
What are the differences and similarities between
Cable Stayed and Suspension Bridges and where
are they best suited?
Acknowledgments
I would like to extend my thanks to Neale Lawson and to his extensive
library. I also would especially like to thank Jane, my supervisor. But most
of all: the internet and its many search engines.
Abstract
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This is a study of cable stayed and suspension bridges and where they are
best suited. I find that suspension bridges initially have the role of
spanning gaps, but prove to be inefficient in cost and build time but prove
to be affective of spanning huge gaps as they are the only type of bridge
that can do that.
I find that cable stayed bridges are more cost effective and a lot faster to
build than suspension bridges and are now taking the place of suspension
bridges where 50 years ago a cable stayed bridge would not have even
been an option.
I conclude that suspension bridges will not be as popular as they were and
that cable stayed bridges will be built more often but the suspension may
still be the only option when huge spans are necessary.
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What are the differences and similarities between Cable Stayed
and Suspension Bridges and where are they best suited?
When a bridge is commissioned many different bridge types and designs
can be submitted, this can lead to a difficult decision as to which is the
best suited for the place and budget. When it comes to bridging long
spans or wide rivers there is no competition for suspension or cable
stayed bridges. However these are relatively new bridges and in the past
these same gaps were
spanned with many piers
examples of the old a new
is visible in many places
such as the fourth estuary,
where you have the Fourth
Railway Bridge, a
cantilever bridge, and also
the Fourth Road Bridge, a suspension bridge.
Suspension bridges were first used thousands of years ago in Asia, South
America and Africa. They consisted of vines tied to trees across a valley;
they held strong twigs or wooden planks which were used as a walkway.
They were very important as they enabled people to cross rivers and
valleys much faster than would have otherwise been possible. However
these are not the type of suspension bridges we imagine today, bridges
made of steel and concrete, with supporting towers and huge lengths of
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cable. The first modern suspension bridge was built in 1801 by James
Findly, it was an iron chain bridge, however there is no more information
on this bridge as it served near as much no purpose other than as an
experiment. He built one after in 1808, this has more documentation. It
consisted of two spans; the longest of them was just over 60m or 200
feet. Part of it broke when a herd of cattle were driven over it and it fell
down later in heavy snow fall in 1816. It was not a great start but it drove
a rapid development in suspension bridges.
The first success came in 1810 with the Essex-Merrimac Bridge, built by
Finley and a carpenter called Carr, this had a span of 240 feet, the chains
broke in 1827 but were replaced and this bridge had a service of 99 years
before it was dismantled and replaced by a wire suspension bridge much
along the same lines. The first suspension bridge in the UK was the Union
Bridge, it spans the river tweed connecting England and Scotland. It was a
record breaker at the time with a span of 137 meters. It is still standing
today and serving its purpose of as a single lane road, it is the oldest
bridge in the world that
is still being used; it
dramatically cut journeys
by 11 miles. It is supported by 6 iron chains, 3 on each side, in 1902 wires
were added to support the roadway even further.
Wire suspended bridges started later than its chain counterparts, they
quickly overtook the chain bridges as they were more reliable and less
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likely to suddenly break as it is more apparent when wires break as it is a
slow process and is easily observable. When James Findly's bridge
collapsed in 1808 it was temporarily replaced by a wire bridge. The first
permanent wire suspended bridge came in 1823 and had two spans of
40m, but they have really come of age since. The first suspension bridge
to use steel cables was constructed in New York by John Roebling who
died before its construction so his son, Washington Roebling and his wife
saw it through, it connected Brooklyn and Manhattan, the Brooklyn Bridge.
It was 50% bigger than anything that had been done before. It is one of
the few bridges of this time to still be standing as none of them were
tested against the wind before being built. Roebling built a truss system
that was 6 times stronger than he thought it needed to be and that's why
it is still standing today. It was thought that the bridge would not be
strong enough as nothing on this scale had ever been attempted before
so an extra 250 cables were added diagonally – much like a cable stayed
bridge, these were later found to be unnecessary, rather than be used
elsewhere they left them because of their distinctive beauty.
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The Akashi-Kaikyō
Bridge, also called
Pearl Bridge, is
longest suspension
bridge with a span
just shy of 2km (1,991
metres), it was
finished in 1998 and
overtook the Humber Bridge which has a span of 1,410 meters, it took 12
years to build and was built after a series of deaths from the ferry crossing
which happened in quick succession. During construction an earthquake
hit when only the towers had been built. They had moved as a result, this
meant that an extra 1 meter had to be constructed, harder than it sounds!
It has been built to withstand winds of 286 km/h (178mph) and
earthquakes measuring 8.5 on the Richter scale. The steel cables contain
300,000 km of wire and are 1.12 meters thick. It is a truly amazing feet
and a real testimony to modern engineering.
Cable stayed bridges can be traced back to 1784 when a German, Carl
Emanuel Löscher designed a timber bridge. They were not used or
developed as the French engineer Navier inducted a study in the 19th
century which showed that suspension bridges should be used rather than
cable stayed bridges as the process of balancing the load could not have
been done as easily as modern technology now allows. German engineers
headed up the design of cable stayed bridges after the Second World War
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when they were challenged to find new and different ways of crossing the
Rhine to replace many of the old existent bridges and the ones that had
been destroyed during the war. Dischinger proposed a type of suspension
bridge that incorporated cable
stayed bridges. He conducted a
study into this, it lead to no bridges
but proved to be a major step
forward to creating the first ones. It
was not until the late 1950's when
Dischinger designed the first truly
cable stayed bridge. The Strömsund Bridge built in 1955 had a main span
of 183m and two side spans of 75m. Spans of this size really only became
possible after improvements were made through structural analysis. Cable
stayed bridges had been attempted before this but this is considered the
first by many. A further three bridges were built over the Rhine.
The first cable stayed bridges used very little cable but this created
substantial erection costs as supports would been needed to hold the
deck as wires were put in place. More cables were added generally as this
proved more economically viable. They were really only given their break
when suspension bridges started failing due to wind causing oscillations
and eventually failure. The most famous of which is the Tacoma Narrows
Bridge, nicknamed Galloping Gertie, which collapsed only 4 months after
it was completed in 1940.
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The Sutong Bridge in
China has the longest
span of any cable stayed
bridge. At 1,088 meters
it is not as vast as the
longest suspension
bridges but is certainly
catching up. It was awarded the 2010 outstanding civil engineering
achievement award by the American Society of Civil Engineers. As well as
being the longest suspension bridge in the world it also has records for
the largest foundation ever attempted and the 577 meter long cable stays
were the longest ever manufactured. The total length of the bridge is
8,206 meters; it took 4 years to built and cost £1.1 billion. It reduces the
time to get from Shanghai to Nantong form a four hour ferry crossing to a
1 hour drive.
There are two main types of
cable stayed bridges – radial
(fan) and parallel (harp). This
represents the arrangement of
the cables. In a radial cable
stayed bridge all the cables
come from a single point on the
tower to several points on the road, the advantage to this is that it can
create a near vertical force on the tower due to the smaller angles
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between the cables and the tower. A parallel cable stayed bridge the
cables come from different points on the tower and the deck, and all the
cables are parallel to each other. This can mean that large horizontal
forces from the deck are transferred on to the towers which can cause a
lot of stress. This is overcome by having a split in the concrete or
structure allowing for movement.
Bridges have to be able to support two loads: its own weight which is
called a dead weight and also the weight of the things crossing it, the live
load. Bridges do this through tension and compression. Tension is where a
material is stretched, in metals it causes atoms to slip over each other
stretching the metal. In other materials it causes them to snap and sheer.
Compression occurs when a material is squished causing a metal to
buckle and deform and non-metals to crush. All bridges manage these
forces in different ways. Hanging bridges, suspension and cable stayed,
deal with these in the same way. The tension is in the wires, as they are
being pulled by the road deck to where they are attached either to an
anchorage point, in the case of suspension bridges, or onto the
tower/opposite road deck, in the case of cable stayed bridges. The tension
in the wires in turn exerts compression on the towers which they are
attached to or resting on, this compression is the dissipated into the
foundations bellow the bridge. There is also compression and tension on
the road deck, the road deck wants to bend, the wires are required to
reduce and support the bending preventing disaster. As the deck bends
with the ends pointing towards the ground there is tension at the top and
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compression on the underside. A successful bridge manages these forces
well enabling it to both carry the dead weight and the live weight.
Suspension bridges can be anchored in two ways, the cables need
anchoring so as to keep tension in the cables, keeping the bridge from
falling down. They can either be self-anchoring or use like most have
separate anchorage points. Self anchoring bridges have their cables
attached to the end of the road deck this limits the length of the span as it
would put large amounts of stress on the road deck, the longest of this
type has a span of 300m. The proven method is creating a separate
anchorage point. This usually consists of the cables embedded in large
amounts of concrete, the wires are spread in the concrete foundations so
the there is not too much force at any point acting on the foundations.
This can be costly due to the vast amount of materials needed, take the
Humber Bridge for example: it uses 490,000 tonnes of concrete. This all
has to be laid in one sitting so cracks do not form. During the construction
of the anchorage points for the Humber Bridge 1000m ³ of concrete was
laid per day.
This is an advantage of cable stayed bridges in that they do not need
anchorage points as the weight is balanced out on each side meaning that
one side is supporting other and that same side is supporting the other
side -which is supporting it. This is also a technique used in buildings;
Wembley stadium wanted an uninterrupted viewing area this meant there
could no pillars supporting the roof. They decided to build a huge arch
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that would not only be a landmark but also support the roof. The roof was
tied to the arch using the same cables that would be used on a cable
stayed bridge. The brilliant thing is that the arch needed no supports
either as it was held in place by the weight of the roof. This is a great cost
cutter as fewer materials are needed.
A suspension bridge deck is held by the suspending cable, its distinctive
curve is called a cantenary. This usually refers to a curve of an object
under its own weight such as in a chain held at two points. But in a
suspension bridge the weight of the cable is usually negligible, the curve
is created by the uniform distribution of the weight against the length of
the cable. The curve can be represented by an equation. If you call the
length between the towers L and the weight is uniform then the total load
can be expressed by wL w being mg(mass x gravity). The “sag” of the
curve is s and the cable pulls on the tower with a total force or tension T.
The vertical component can be represented by V
and the horizontal by H. If we consider the total
forces in the x axis then T=H at the lowest point as
H is a tangent to the curve at that point. If V
equals the weight of the cable as weight acts in vertical component, then
the dy/dx (gradient) of the cantenary is WV/H. When integrated this then
gives y=(w/2H)x² which is a parabola x² with parameter w/2H. We can find
out the value of H by using the tension at certain points on the curve and
using trigonometry to work out the horizontal component. The total forces
of the horizontal component must equal 0 otherwise the bridge would
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collapse. This gives the remainder Hs=(wL/2)(L/4). At the bottom of the
curve there are no vertical components so (wL/2)(L/2) =Hs+(wL/2)(L/4).
To work out the tension we can substitute x=L/2 back into y=(w/2H)x²
then s=wL²/8H and the equation is x²=(L²/4s)y. Knowing that L and s give
the shape of the curve and then the tension of any point of the curve can
be expressed as T=(wL/2)[(L/4s)² + (2x/L)²]^½.
In a cable stayed bridge the tension can be worked out as if it were a
triangle. It would be a right angled triangle therefore the simple laws of
trigonometry can be applied. To work out the tension you could express
the total load again as wL, this is held by two towers but they do support
the span load together so it is wL/2 for each tower. The weight only acts in
the vertical direction so the cables have to support this weight this means
the smaller the angle of the cable against the tower then the lower the
tension. By expressing this angle as θ then Tension=w/cosθ, as θ
increases cosθ decreases. In a cable stayed bridge, as in a suspension
bridge, the horizontal forces cancel out however in a suspension bridge
they are only acting on the towers, in a cable stayed bridge they are
acting on the towers and deck. This means that the deck is under
compression in the horizontal direction and has to be strengthened to
withstand Tsinθ. This is usually done by using steel box girders or
concrete. This is one of the main reasons why cable stayed bridges will
not be as long as suspension bridges as the towers would have to increase
considerably or the deck would have to be able to resist higher
compressive forces without gaining to much weight, where as in a
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suspension bridge they just have to make the anchorage points larger to
withstand the higher tension forces.
Another factor that engineers have to take into account with cable stayed
bridges is that the tension is going to change as the day goes on due to
expansion and contraction. This could lead to disaster as the towers could
shear as could the deck as it is lifted or dropped. They have allowed for
this by using an inverted Y which allows for bending even in concrete
structures. This means that taller towers could be built as expansion and
contraction be accounted for.
Britain still had one more Estuary to cross in the 1970's, the last big span
was needed over the Humber river, a bridge had be thought of for over
100 years and in 1935 after the completion of the Golden Gate bridge a
proposition was put forward Sir Ralf Freeman. It needed to be a single
span due to fierce opposition from the people who used it, Freeman
realised that a bridge would only be built if it was a single span. The
government only made feasibility study for the bridge in 1969. They
proposed due to the maximum traffic at the time that it was only feasible
to create a two lane highway across the river. In 1971, Freeman Fox &
Partners who had been waiting for the contract since 1927 finely got given
75% of the money to build the bridge. It was to be the longest single
spanned suspension in the world, yet it was produced very economically
using the latest bridge technology. The road deck was made using steel
box girders which Freeman Fox had used on the Severn Bridge and
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concrete towers which were less expensive than steel and could be built
faster and easier keeping costs low. It was built using the latest methods
such a wind testing, it had to withstand base winds of just under 100mph
and the top of the towers had to stand up to over 150mph. Various
models were crated and tested and they showed that it was feasible. It
was unknown territory for many as never had a bridge been built on this
scale with a low budget.
They met problems when looking at how they were going to make strong
foundations, the geology was different on the opposite sides of the river.
On the north side foundations would be relatively easy to build as the
chalk created a solid base. However on the south side the chalk had be
eroded from the glacial river before, all that was left was a clay that when
it contacted water it created a slurry, not ideal. As well as poor
foundations it was also being built 500m from the shore which adds extra
problems. The solutions was to build a hollow caisson to go 16m below
the surface, which is about 4 giraffes, 8m of which is bellow the
Kimmarage clay. As it was sunk it hit some high pressured water which
burst into the structure washing some lubricant away, this meant that an
extra 3,000 tonnes had to be
added to sink the tower, this
also caused costly time wise,
however on the north tower
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they regained that time from the experience that they had gained from
the south tower.
The steel box girders had proved very successful; they were part of the
longest bridge in the world outside the USA and on the Severn Bridge.
They wanted to stretch what they had done before by almost 50%. It is a
hollow box which has been built from a stiffened plate. The sections are
22m by 4.5m they are a trapezium shape giving them their extra strength.
They are shaped to also use the wind to relieve the deck of weight which
also adds to saving costs as they are shaped much like an aeroplane wing
providing lift. The structure also allows access from the inside which
makes it allot easier to build and fabricate and ensures a strong weld. It
took 124 box’s to complete the road deck each box weighs 120 tonnes,
which means the total weight is 14,880 tonnes. The total length of the
cable that supports this could go two times round the world! It was
completed in 1981 and was the longest single spanned suspension bridge
for 16 years, testament to its engineering.
The Tarn Valley in Southern France became a huge stepping stone when
the A75 was being built in 1975 and it was not until 1994 that they
decided a bridge a few miles down from Millau was the solution to the
huge valley. Then in 1996 the bridge was chosen, it was drawn up by Lord
Foster and headed by the French construction company Ponts et
Chaussées. It was chosen because of its aesthetic integration and just
pure beauty. In 1998 the government granted a 75 year period for the
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construction and management of the viaduct. On the 14 December 2001
the fist brick was laid and construction started making headway. The
Millau Viaduct was such a huge task that is called in the most advanced
technology and wide range of specialists ever on one building site.
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In was done in six stages which were: Raising the piers; launching the
deck; the junction; installing the pylons; the cable stays and laying the
road surface. The piers needed to have huge foundations which would
keep them upright. They are known as Moroccan Wells and are 5 metres
wide and 15 metres deep. There is also a foundation slab above this which
is 5 metres tall and required 2,100m³ concrete to be continually poured.
After this the piers began to rise at 4 metres every 3 days, work had
started on March 2002 and ended in December 2003. The deck is made of
173 central box beams and weighs 36,000 tonnes. As the bridge has a
slight curve each section is unique making production even harder. 96%
of the work on the deck was done at ground level which reduced risk and
cost. 150 people worked for 20 months to complete this section. Rather
than raising the deck to
the tallest bridge in the
world they slid each
section out. Giant
supports were used
between each pier to
help carry the load.
Hydraulic rams were
used to do this, they lifted the deck up each time and slid it forward
before repeating the process again 60cm at a time. At a speed of 9m per
hour they eventually meet on the 28th May 2004. As the launching
operation took place the piers were being put in place, they were
transported over the bridge, where they were partially stayed so the deck
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did not take a nose dive. Each pylon is 700 tonnes and 90 metres high.
Each pylon then carries and is supported by 11 pairs of cable stays in total
weighing 1,500 tonnes. The longest cables have a tension of 1,200 tonnes
and were installed in the protective sheathe cable by cable by a shuttle
were they would be pulled to the right tension. The deck was then
surfaced using a special formula that could cope with the contractions of
the bridge but meet motorway standards. It is 6cm to 7cm thick and is
without blemish to maximise longevity and the need for re-surfacing. It
added 9,500 tones to the bridge and was laid continually so minimise
imperfections, this meant there was a constant stream of 25 Lorries to
supply the two finishers. It was then heat sealed at 400ºC so the steel
deck bellow would not corrode. The bridge has been a great success and
is a modern marvel.
In terms of making an economically viable bridge then large spans are
more costly than multi-span counterparts. This is because of the increase
of expensive materials needed, hard and time consuming construction
techniques and engineering ability as well as other things. By breaking
records you have either found a really effective technique or more likely it
is a demonstration of a countries wealth. In some cases is it necessary like
at the Golden Gate Bridge when a single span was needed as the military
required it. This is why we are currently seeing more cable stayed bridges
as they are cheaper to build and take less time. Suspension bridges are
the most expensive because of the technicality of the, build, construction
and materials needed. Studies into how long it is possible to build the
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different types of bridges have been made. The American Society of Civil
Engineers suggests a suspension bridge could reach a single span of
7,000m; the limiting factor would be the stress in the main cable. This is
double the amount a single span of a cable stayed bridge could stretch to,
3,500m. The limiting factor of a cable stayed bridge would be girder as
compression forces would be too high. This really stresses how much it
would cost to build bridges with such large spans, as the longest
suspension bridge is 1,991m, 5,009m away from what is possible with
steel and concrete. And the longest span for a cable stayed so far is
1,088m; 2,412m away from what is possible. But these bridges are far
ahead of other types, arch bridges have a maximum span of 1,600m, and
truss bridges have no perceivable limit as long as the girder is deep
enough, however the financial limit would be a small 550m.
So why would you build a suspension bridge a not a cable stayed bridge or
the other way round, where are engineers today placing these bridges
and why did they use that type? Suspension bridges can span much
longer distance than that of a cable stayed; this would be used when a
busy shipping channel cannot be interrupted. Even if a multi-span cable
stayed bridge could give the height and spans for all large ships to pass
under, if one were to cash in to the towers foundations the result would be
disastrous; loss of lives, money and the connection that the bridge
provided in the first place. The amount of material is less than any other
bridge over long distances; this could leave to cost reduction and is more
environmentally friendly. During construction access is only needed to
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place the temporary cables so the waterway can remain open, reducing
financial strain on other companies also using the water way. They can
withstand large earthquakes due to less materials and their flexibility.
However they fair terribly in wind due to their flexibility and aerodynamic
properties, to stop this decks need stiffening and aerodynamic profiling.
Also thanks to its low deck stiffness it makes the suspension bridge
unsuitable for rail use and other high concentrated live loads.
Cable stayed bridges excel in places when the suspension bridge fails, it
has a much higher deck stiffness so can handle rail traffic as well as other
concentrated live loads. It can be constructed by pushing out the decks
using the cables as both the temporary and permanent supports. This
technique was used during the construction of the Millau as no materials
could be raised as the bridge was so high up, the largest tower was taller
that the Eiffel Tower a near impossible task that could not have been
feasibly spanned by a suspension bridge. The horizontal forces balance so
no large anchorage system is needed. They can also cover a larger
distance than suspension bridges as they can have multi-span structures,
where as a suspension bridge has a limit of two spans, however this itself
is incredibly hard to construct and anchor down. There is only one
suspension bridge which has three spans and that is technically two
suspension bridges joined together as there is a central anchorage point,
the San Francisco Oakland Bay Bridge. In all they both have there
advantages and disadvantages. I believe that cable stayed bridges will
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replace many of the original suspension bridges, like the Second Severn
Crossing or the proposed replacement for the Forth Road bridge.
Evaluation
When I decided to do an Extended Project I did not know what I wanted to
do it on. I knew it would be something to do with engineering, In the end I
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choose to do something with bridges so I started my research. I had
previously watched a program on the building of the Millau bridge, this
lead me to many other interesting articles on cable stayed bridges, so I
knew I was going to include that. It also highlighted that the general
public did not know the difference between cable stayed bridges and
suspension bridges. I decided that I would highlight the differences
between the two and also the similarities.
I knew my Granddad was also interested in engineering, I gave him a call
and he sent down a couple of books which I found interesting and also so
articles which help build my background knowledge, which I have found
very useful. I also took out a few books from the library some were not so
useful but one was particularly useful and gave the general gist of how
they worked and were built. Often when I was writing I did not quite have
a grasp of the topic so I would have to do some more research, so I knew
what I was writing was correct and could be justified. This took time and I
lost the fluidity that I was writing with so I had to leave it for a bit and then
come back. If I were to do it again I would have a more thorough plan and
therefore greater background knowledge. This would improve the fluidity
of the essay and make it easier to read.
Bibliography
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Belard, A. (2005). the a75 autoroute (clermont-ferrand to béziers). Retrieved from ABelard.org: http://www.abelard.org/france//motorway-aires10.phpBenckett, D. (1984). Stephensons' Brittain. David and Charles Ltd.Bernado, S. D. (1990). Motion Based Design Of Cable Stayed Bridges. Rome: University of Rome.Blockley, D. (2010). Bridges. Bristol: OUP.Bridge Pros. (n.d.). Cable Stayed Bridge. Retrieved from BridgePros.com: http://bridgepros.com/learning_center/cable-stayed.htmBrown, D. J. (1998). Bridges: Three Thousand Years of Defying Nature [Paperback]. London: Mitchell Beazley; New edition edition (1 Sep 1998).Calvert, J. B. (2002). Parabola. Retrieved from MySite.du.eu: http://mysite.du.edu/~jcalvert/math/parabola.htmHumber Bridge Board. (2008). Engineering the Humber Bridge. Retrieved from HumberBridge.org: http://www.humberbridge.co.uk/media/Engineering_The_Humber_Bridge_e-book.pdfHumber Bridge Board. (2005). Technical Information. Retrieved from HumberBridge.co.uk: http://www.humberbridge.co.uk/explore_the_bridge/engineering/technical_information.phpLe Viaduc de Millau. (2007). History. Retrieved from LeViaducdeMillau.com: http://www.leviaducdemillau.com/english/divers/construction-histoire.htmlLocke, D. (2001). Cable Stayed Bridges. Retrieved from Brantacan.co.uk: http://www.brantacan.co.uk/cable_stayed.htmParabolas in Suspension Bridges! Oh, my! (n.d.). Retrieved from Carondelete.ca.us: http://www.carondelet.pvt.k12.ca.us/Family/Math/03210/page4.htmQingzhong, Y. (2007). Challenges of the Sutong Bridge. Retrieved from transportation.org: http://downloads.transportation.org/InternationalDay/You.pdfRyan, V. (2005). The Millau Bridge. Retrieved from TechonlogyStudent.com: http://www.technologystudent.com/struct1/millau1.htmRyan, V. (2002). The Normandy Bridge (Cable Stayed). Retrieved from TechnologyStudent.com: http://www.technologystudent.com/struct1/norman1.htmSayenga, D. (2008). James Finley. Retrieved from StructureMag.org: http://www.structuremag.org/article.aspx?articleID=804Tang, D. M.-C. (2010). The Story of World-Record Spans. Civil Engineering , 56-63.WGBH Science Unit. (1999). Super Bridge. Retrieved from PBS: http://www.pbs.org/wgbh/nova/bridge/Wikipedia. (2010). Millau Viaduct. Retrieved from Wikipedia.org: http://en.wikipedia.org/wiki/Millau_bridgeWikipedia. (2010). Suspension Bridge. Retrieved from Wikipedia.org: http://en.wikipedia.org/wiki/Suspension_bridge
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Wikipedia. (2010). Sutong Bridge. Retrieved from Wikipedia.org: http://en.wikipedia.org/wiki/Sutong_BridgeWikipedia. (2010). Union Bridge. Retrieved from Wikipedia.org: http://en.wikipedia.org/wiki/Union_Bridge_(Tweed)
(Qingzhong, 2007) (Ryan, The Millau Bridge, 2005) (Ryan, The NormandyBridge (Cable Stayed), 2002) (Wikipedia, 2010) (Wikipedia, 2010) (Bernado,1990; Benckett, 1984; Beckett, 1980) (Locke, 2001) (BBR, 2005) (Belard,2005) (Le Viaduc de Millau, 2007) (Humber Bridge Board, 2005) (Humber
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Bridge Board, 2008) (Parabolas in Suspension Bridges! Oh, my!) (Sayenga,2008) (Wikipedia, 2010) (Wikipedia, 2010) (Bridge Pros) (Calvert, 2002)(Blockley, 2010) (WGBH Science Unit, 1999; Brown, 1998) (Tang, 2010)
David Bedford