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LONG-SPANBRIDGES
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Long-span bridges have always held a fascination for structural engineers and
indeed, for the general public with the longest bridges of each type generally
categorised by their worldwide rating. When a new record is set, as seems to happen
on a regular basis, the latest title-holder is accorded great publicity and guaranteed
an audience around the world.
But as our supplement makes clear, the biggest challenges in long-span bridge engineering
are not necessarily the record-breaking structures. These may be challenging when they
are under construction particularly if they are being built in regions which experience
extreme weather conditions but often they employ tried and tested design approaches and
construction technologies, with the longer spans generally driven by topography or other
project-specific criteria.
The skills of engineers and architects working on any long-span bridges can often be testedmore thoroughly when it comes to designing them for highly-seismic locations, using unusual
combinations such as those with multiple cable-supported spans in series, or being tasked with
creating aesthetically-pleasing structures at this kind of scale.
In this special supplement we kick off with an overview of long-span bridges in China, where
many of the worlds longest spans can currently be found; canvass opinion on the hot-topics in
long-span bridges around the world, and report on some of the ongoing, planned and recently-
completed long-span crossings. It is by no means exhaustive, that would be impossible in a
publication of this size, but I hope it will give readers a flavour of some of the challenges the
industry is facing today
Editor Helena Russell
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Deputy editorJos Mara Snchez de MuniinT+44 1935 37 [email protected]
Advertisement sales managerLisa BentleyT+44 20 7973 4698 F+44 20 7233 [email protected]
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Bridge design & engineering
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Circulation manager Maggie SpillaneDesigner Lisa ArcangeliProduction Gareth ToogoodManaging director Graham Bond
ContributorsLisa Russell, Man-Chung Tang
Bridge design & engineeringis published quarterly and is available onsubscription at the rate of UK105/162/US$218 per year, which includesfour issues of Bd&eand eight issues of Bridge updatenewsletter.Subscription payment can only be accepted in the currency of thecountry in which a company is registered. If not registered in the UK, theEU or the US, payment should be made in US dollars.
Bridge design & engineering(ISSN No: 1359-7493, USPS No: 003-140) ispublished quarterly by Hemming Group and distributed in the USA byby SPP, 17B S Middlesex Ave, Monroe NJ 08831. Periodicals postage paidat New Brunswick, NJ. POSTMASTER: send address changes to Bridgedesign & engineering, 17B S Middlesex Ave, Monroe NJ 08831.
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Printed by Latimer TrendISSN 1359-7493Published by Hemming Information Services(a division of Hemming Group Limited)Hemming Group Ltd 2016
Helena RussellEditor
Contents
Editors comment
04 THE LONG GAME: Half of the worlds top twenty longest-span suspensionbridges are in China, as are six out of nine of the longest spans of other types of
bridges. Man-Chung Tang reports on recent progress in the current internationa
hot-spot for long-span bridges
14 EXTREME LENGTHS: Some of our longest-span bridges have been aroundfor several decades now, and to a large extent the technologies and engineering
know-how of these structures are tried and tested. Lisa Russell explores the
influences on long-span bridge design today, and the challenges of our ageing
structures.
34 SUBSCRIBE: Get your own copy of Bridge design & engineeringevery quarter.
43 SPONSORED COMPANY PROFILES: Our commercial partners highlighttheir expertise and recent projects in the asset management sector.
43 INDEX OF FEATURED COMPANIES
LONG-SPAN BRIDGES
LONG-SPAN BRIDGES SUPPLEMENT 2016 www.bridgeweb.com 0
Cover image: Rendering of Hlogaland Bridge which isunder construction in Norway(Dissing & Weitling)
Bridge design & engineering group
@bdebridgeweb
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LONG-SPAN BRIDGES
The long game
Half of the worlds top twenty longest-spansuspension bridges are in China, as are six out
of nine of the longest spans of other types ofbridges. Man-Chung Tangreports on recentprogress in a hot-spot for long-span bridges
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LONG-SPAN BRIDGES
Over the last 30 years, China
has built a huge network of
highways of about 4,000,000km
of regular highways and more
than 75,000km of expressways. A
comparison of Chinas expressway system
to the US Interstate bears discussion. The
US began to build the Interstate system in
1956 while China did not start until 1987.Being the strongest economy in the world
at that time, the US interstate system took
off very quickly. By contrast, China was a
very poor country in 1987 and the countrys
network of expressways was slower to
develop. But eventually, it overtook the
US and now has the greatest length of
expressways of any country in the world.
The expansion of Chinas highway system
is not the only reason so many bridges are
needed; its cities are also developing and
need increased river-crossing capacity. It
is somewhat sobering to consider that in
1985, there were only three bridges over
the entire 6,300km length of the Yangtze
River one in Chongqing, one in Nanjing
and one in Wuhan.
Today, there are more than a hundred.
In addition to those major bridges, a large
number of crossings have also been built
over other rivers and valleys, and many of
these are long span bridges.
How is long-span defined? Among the
Bridge type Name Span (m) Country Yearcompleted
Suspension Akashi-Kaikyo 1991 Japan 1998
Xihoumen 1650 China 2009
Great Belt East 1624 Denmark 1998
Cable-stayed Russky 1104 Russia 2012
Sutong 1088 China 2008
Stonecutters 1018 China 2009
Arch Chaotianmen 552 China 2009
Lupu 550 China 2003
Bosideng 530 China 2012
Girder Shibanpo 330 China 2006
Stolmasundet 301 Norway 1998
Costa e Silva 300 Brazil 1974
four categories of bridges in the world
girder bridges, cable-stayed bridges, arch
bridges and suspension bridges the
definition of long span depends on the
type of structure. A 300m span might be
very long in a girder bridge, but it would
be considered very short if it were a
suspension bridge.
The table below lists the three longestspans in the world in the four categories
of bridges; of these 12, seven of them are
in China, and of the 20 longest suspension
bridges, which are also the 20 longest
spans of all bridges either completed or
under construction, ten of them are in
China. There is no doubt this bridge boom is
an exciting time for bridge lovers.
In terms of bridge technology, China is a
latecomer, but it has been a rapid learner.
The countrys first real long-span bridge,
the 423m-span cable-stayed Nanpu Bridge
in Shanghai, was opened to traffic in 1992,
while most of the longest spans in Europe
and North America were completed many
years previously. Real long-span suspension
bridges flourished in the 1930s in the USA
while segmental girder bridges and cable-
stayed bridges began in the early 1950s
in Germany. So bridge building is neither
a modern technology nor considered a
high-tech venture. Building a conventional
long-span bridge today even the worlds
longest span is only contingent on cost,
as the technology for building bridges
is already mature. In many ways it is the
speciality bridge that hold more interest,
though they may not be the longest spans
in the world, or even in China.
Girder bridges
Of all bridge types, the girder bridge is the
most common. But the Shibanpo Bridge in
Chongqing, which is a 330m-span hybrid
structure, currently holds the world record
for span length. It is located next to an
existing girder bridge which was completedin 1981 and because of the proximity of
the two bridges, it was natural to design
the new structure as a girder bridge for
aesthetic reasons.
The span arrangement of the old
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bridge has two main spans of 156m and
174m, and the original intention was to align
the piers of the new bridge with those of
the old bridge. However the Waterways
Authority was concerned that the 174m-long
main span of the old bridge was already
very tight for modern river traffic and
the presence of the new piers would have
created a tunnel effect for ship navigation.
Thus, the authority insisted that the pier
between the two spans be deleted, creating
a 330m-long main span. To date, the longest
all-concrete box girder bridge is the 301m
span Stolmasunde Bridge in Norway, which
was completed in 1998, while the longest
all-steel girder bridge is the 300m span
Costa e Silva Bridge in Brazil, completed in
1974.
For the Shibanpo Bridge, with its
330m-long main span, a concrete structure
would have been too heavy and the long-
term deflection would have been difficult
to control, especially at the middle portion
of the bridge. A steel bridge on the other
hand would have required very thick plates
and would have been too difficult and too
expensive to fabricate, especially the girder
portion over the piers.
To avoid these problems, TY Lin
International designed a prestressed
concrete girder bridge with a 130m-long
steel box at the mid span. The concrete
portion of the bridge was built segmentally
using form travellers a large number of
concrete segmental bridges had already
been built in China, so this was rather
routine.
The steel box girder was fabricated
in Wuhan, which is about 1,000km
downstream of the bridge site. To facilitate
its transportation, the steel box was
designed to act as a barge as well. After
closing the two ends it was launched like a
ship onto the Yangtze River and towed to
the site where it was lifted and connected
to the two cantilevers. The lifting operation
was completed within the permitted 12-hour
window and the bridge was opened to
traffic in 2006.
Arch spans
The worlds three longest span arch
bridges are all in China; the 552m span
Chaotianmen Bridge which crosses the
Yangtze River in Chongqing; the 550m span
Lupu Bridge crossing the Huangpu River
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With a 116-year
history of completing
the worlds most
challenging projectsbehind us, were fully
focused on the future.
Because it will always
be legendary.
LEGENDARY
CONSTRUCTION
The Queensferry Crossing, Edinburgh, Scotla
Photo Credit: Transport Scotla
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LONG-SPAN BRIDGES
in Shanghai and the 530m-span Bosideng
Bridge over the Yangtze River in Luzhou.
The Chaotianmen Bridge is a truss arch,
the arch ribs of the Lupu Bridge have box
shape cross-sections and the arch ribs of
the Bosideng Bridge are concrete-filled
steel tubes. The design and construction
of first two bridges was fairly conventional
with the Chaotianmen Bridge constructedas a pair of cantilevers and the arch ribs of
the Lupu Bridge built using highlines and
temporary cable stays.
China has built more than 400 arch
bridges using concrete filled steel tubes, as
this type of construction is very economical
in China and many steel fabricators have
acquired the equipment needed to produce
the spirally-welded steel tubes used for
this type of arch bridge. Erection is mainly
done using highlines and most of these arch
spans are relatively moderate in length.
But the Bosideng Bridge in Luzhou,
Sichun, which opened to traffic last year,
has a span of 530m, with the steel portion
of the arch measuring 518m. The arches
typically consist of a group of steel tubes
braced against each other by smaller
steel tubes. The main tubes are filled
with concrete after the arch has been
constructed. To ensure that the tubes were
completely filled with concrete, the vacuum
pumping method was successfully applied
to the Bosideng Bridge for the first time.
Currently, the worlds longest concrete
arch span is the Wanxian Bridge in
Chongqing a 420m span bridge which
crosses the Yangtze River in Wanxian and
was opened to traffic in 1997. The arch rib
is shaped like a catenary and is 16m wide
and 7m deep with a rectangular triple-cell
box concrete section. An arch truss madeof steel tubes was first erected with the
help of temporary cable stays. This steel
arch was designed to be embedded in the
concrete section and was used as a form
support for theconcrete arch, which was
cast segmentally from both abutments
toward the span centre. The concrete deck
is 23m wide and 140m above the normal
water level of the Yangtze River, and it
consists of precast T-beams resting on
vertical spandrel columns.
Cable-stayed bridges
The first major cable-stayed bridge to be
built in China was the Nanpu Bridge over
the Huangpu River in Shanghai, which
opened to traffic in December 1991. Its
main span of 423m was the longest in
China at the time of its completion. The
same team of engineers and contractors
went on to design and build another cable-
stayed bridge, the Yangpu Bridge, also over
the Huangpu River in Shanghai. It took
them just 29 months to design and build
this second bridge which had a span of
602m and was the worlds longest cable-
stayed bridge when it opened to traffic in
September 1993. This bridge opened 16
months before the 856m span Normandy
Bridge, even though it began construction
later.
It is interesting to note that these bridgeswere all designed and built by the Chinese
themselves with only DRC Consultants,
which merged with TY Lin International in
1995, as a special consultant to the owner,
the designer and the contractor.
China currently has the worlds second
longest cable-stayed bridge, the Sutong
Bridge in Jiangsu Province, not far from
Shanghai. It crosses the Yangtze River near
Suzhou. The main bridge has a main span of
1,088m with side spans of 300m and 100m
and a roadway width of 30.5m. It was the
worlds longest cable-stayed bridge when it
opened to traffic in 1997.
Suspension bridges
As previously noted, half of the 20 longest
span suspension bridges in the world
today are in China. Considering that China
only built its first long-span suspension
bridge, the 888m span Humen Bridge in
Guangdong Province 17 years ago, the pace
of construction has been remarkable.
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Since that time, China has built many
long-span suspension bridges. The worlds
second longest suspension bridge, the
1,650m span Xihoumen Bridge in Zhoushan
was opened to traffic in December 2009.
Almost all long-span suspension bridges
have a steel box girder with an orthotropic
deck and have been produced exclusively
in China by Chinese fabricators. Likewise,
the wires for the main cables are also
manufactured in China and both air
spinning and prefabricated strands have
been used for the installation of the main
cables in those suspension bridges. Because
of the plans to continue building many
more long-span bridges, the industry was
willing to invest in new equipment and
learn new technologies. At the current
time, China probably has the most modern
steel fabrication facilities in the world; the
steel components of the new San Francisco
Oakland Bay Bridge in California, USA,
including the girder, the tower and the
cables were all fabricated in China.
Worth mentioning are a few smaller
suspension bridges in mountainous areas:
the 1,176m span Aijai Bridge in Hunan,
completed in 2012; the 1,088m span
Balinghe Bridge in Guizhou, completed in
2009, and the 1,196m span Longjiang Bridge
in Yunnan, which will open to traffic in 2016.
In these cases, because transportation
through mountainous terrain can be
difficult, a long-span bridge across the
entire valley is sometimes the best solution.
As well as the challenge of supply of
materials, the construction of a suspension
bridge over such a mountainous area poses
two major difficulties; erection of the lead
strand for the catwalk and erection of the
main girder. Unlike construction of a bridge
over water where the lead strand can be
carried by a barge from one tower to the
other, the same solution is not possible in
the mountains where it would be caught
by trees and rocks along the way. For theLongjiang Bridge, the lead cable was carried
from one end of the bridge to the other
end by a drone; in Xihoumen Bridge by an
airship, and in Siduhe Bridge by a rocket
which was provided by the military.
The girders of most suspension bridges
are erected by raising the segments from
a barge, but again this is not possible if
the terrain underneath the bridge is not
accessible. So, a new method was developed
for the Aijai Bridge. Firstly, a temporary rail
system was attached to the suspenders at
the girder level once the main cables and
all suspenders were in place. The segments
were then pulled along this rail system one
by one from the work platform at the tower
to their final position, until the entire girder
was completed.
China has built a large number of self-
anchored suspension bridges, although
most of them have spans at the shorter
end of the spectrum. They are suitable for
sites with poor soil conditions which are
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LONG-SPAN BRIDGES
not good for building anchors. However,
the Pingsheng Bridge in Foshan, which was
completed in 2006, has a main span of
350m, and was the longest self-anchored
span in the world until 2013, when the new
east span of the San Francisco Oakland
Bay Bridge with its 385m-long main span
was opened to traffic. A year later, this was
overtaken by another Chinese bridge, the
420m span Huanghe Bridge in Zhengzhou,
Henan. Nevertheless, the Pingsheng Bridge
and San Francisco Oakland Bay Bridge
spans have only single towers, while the
Huanghe Bridge has two.
This record is set to be broken again in
the near future, as a record-breaking self-
anchored suspension bridge designed by
TY Lin International and Smedi is currently
under construction the Ergongyan Bridge
in Chongqing. This bridge is being built
next to an existing suspension bridge with
a 600m span, and for aesthetic reasons,
the new suspension bridge will also have
a 600m span. The ideal solution would
have been to build the new structure as
a traditional suspension bridge. However,
the soil conditions at the site were not
reliable enough to be able to securely
anchor the main cables, hence the client
decided to build a self-anchored suspension
bridge even though the main span will be
rather long. The towers are now underconstruction and the girder will be erected
using temporary stay cables. Once the
girder is in place, the main cables will be
installed and the load of the girder will be
transferred to the suspenders, after which
the stay cables will be removed.
Partially cable-supported girder bridges
A further development on the extradosed
bridge concept has recently been developed
in China for medium-span bridges; the
partially cable-supported girder bridge.
The process involves first designing the
structure as a girder bridge, which does not
have sufficient capacity to carry all of the
loads; this is supplemented by the forces
from the cables. Cables can be provided as
a suspension system, a stay-cable system
or from an arch rib. The system ensures
that the capacity of the girder and the cable
system are both fully exploited. It may look
similar to an extradosed bridge, but the
basic premise of an extradosed bridge is
that it is a girder bridge with post-tensioning
tendons raised above the deck to gain more
eccentricity. The cables are designed as
prestressing tendons with higher allowable
stresses, and they must have a relatively
flat inclination and the bridge towers
must be relatively short. A partially cable-
supported girder bridge does not have these
restrictions and the cables are designed as
stay cables.
The difference between a cable-stayed
bridge and a partially cable-supported girder
bridge is the function of the girder and
the cable system. In a traditional cable-
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stayed bridge, the cables are designed to
carry all the loads from the girder and the
capacity of the girder is only there to resist
local bending moments and axial forces.
Therefore the girder of a cable-stayed
bridge can be made very flexible, often with
a span to girder depth ratio of more than
150 or even 300, as in case of the ALRT
Skytrain Bridge in Vancouver, Canada. As
a rule of thumb, the span to girder depth
ratio for a girder bridge is around 20. For
many medium span bridges, the span to
depth ratio is often in the range of 25 to 45;
the girder itself can carry a large proportion
of the loads so the cable system is only to
carry the load that the girder is not able
to carry. Thus the required capacity of the
cables and the towers is much less than
that in a traditional cable-stayed bridge.
In the case of the Sanho Bridge, for
example, the cables carry only 50% of the
total load. This means a saving of 50%
of the cables and tower compared to a
conventional cable-stayed bridge.
The first partially cable-supported girder
bridge was the Sanho Bridge in Shengyang,
China, which was completed in 2008 and
has two spans of 100m.
The longest partially cable-supported
girder bridge is the Dongshuimen Bridge
in the city of Chongqing which was opened
to traffic in 2014. It has a 445m-long
main span and the girder is 13m deep
to accommodate transit trains on the
lower deck. It is located at the tip of the
peninsular where the Jialing River meets
the Yangtze River. The client wanted a
bridge that was prominent and beautiful
to serve as a landmark, but the design had
to minimise any obstruction of the view
of the city. The design of this partially
cable-supported girder bridge, takes full
advantage of the carrying capacity of such
a deep girder with its span to girder depth
ratio of 34, so fewer cables were required,
which makes the bridge even more
transparent. It has a sister bridge on the
other side of the peninsular, the Qianximen
Bridge, which was also designed as a
partially cable-supported girder bridge.
Over the last 30 years, China has built
many new bridges and with its population of
1.4 billion and its boom in construction, this
trend looks set to continue.
Man-Chung Tang is chairman of the board
of TY Lin International
LONG MULTIPLICATION
In recent years, many multi-span cable-
supported bridges have been designed and
built in China, including the Taizhou Bridge,
the worlds largest multi-span suspension
bridge (see page 15)and the Jiashao Bridge
(right), which is the largest multi-span cable-
stayed bridge.
Jiashao Bridge crosses Hangzhou Bay in
Zhejiang Province and is a six-tower cable-
stayed bridge which has five main spans each
428m long, and side spans of 200m. It is the
largest multi-span cable-stayed bridge in the
world and has a deck width of 55.6m.Compared to a traditional cable-stayed
bridge, the multi-tower version has a lower
vertical stiffness under live load, and hence
this needs to be improved by increasing the
size of the tower, increasing the stiffness of the
deck or adding auxiliary cables; none of these
options was practicable for the Jiashao Bridge
so alternatives had to be developed.
An x-shaped bracket was designed to
support the deck in plan at the towers and a
rigid hinge in the middle of the bridge releases
the temperature-induced load and longitudinal
displacement, hence reducing its impact on the
towers, while constraining rotation, deformation
and shearing displacement of the bridge deck.
One of the other major challenges for the
Jiashao Bridge was design of a maintenance
gantry for the twin box-girder deck; a traditional
system could not be used due to the obstruction
caused by the brackets at the towers, and the
rigid hinge at the centre of the main span. By
design of a special gantry, the number of units
required was reduced from 20 to just four.
China Foto Press/Getty Images
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Cable stayed bridge, Marchetti viaduct, Ivrea (Italy)
YOUR CHALLENGES,
OUR SOLUTIONS.
tensainternational.com
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Four decades on from the advent of
the aerodynamic box girder bridge
deck on the Severn Bridge in the
UK, the impact of wind loading is still
one of the most critical factors in the
design of long-span bridges. But more recent
influences such as new procurement routes,
and the introduction of high-strength materials
also have an impact on the process.
Wind effects continue to be the governing
factor in the structural design of long-span
bridges, and more advanced testing rigs
and advanced computational methods are
being used nowadays to better mitigate the
aerodynamic instabilities, agrees Ender
Ozkan, a technical expert at Rowan Williams
Davies & Irwin. Another area of interest for
aerodynamic performance is the retrofit of
existing long-span bridges. Bronx Whitestone
Some of our longest-span bridges have been around for several decades now, and to alarge extent the technologies and engineering know-how of these structures are tried andtested. Lisa Russellexplores the influences on long-span bridge design today, and thechallenges of our ageing structures
Bridge is a good example where engineers
took advantage of the retrofitting to improve
the aerodynamic performance and breathe
new life into an ageing structure.
But the definition of a long span is
often the subject of discussion within the
engineering community, as Aecom vice
president Barry Colford pointed out in his
keynote at last years European Bridge
Conference in Edinburgh, Scotland.
In terms of numbers there are around 220
cable-supported bridges throughout the
world with spans greater than 300m; the
majority are either suspension bridges or
cable-stayed bridges and there is almost an
equal split in numbers of each of these two
main types.
As might be expected, it is economics
at the construction stage that is driving
the long-span bridge market and at spans
between 150m and 1,000m, cable-stayed
bridges now appear to be the preferred
option for most clients and engineers,
said Colford in his paper. Even in the USA,
where the development and use of cable-
stayed bridges has lagged behind Europe,
the cable-stayed form seems to be gaining
in popularity. Whether the industry wants
to continue to push the envelope out and
build cable-stayed bridges of 1,200m span
or more remains to be seen. Both forms of
cable-supported bridge have advantages and
disadvantages, he says. Recent problems
with corrosion of main cables may have
dented confidence in suspension bridges,
but Colford believes that the success of
dehumidification retrofit projects could
reverse this.
Spanning the future
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LONG-SPAN BRIDGES
Chacao Channel Bridge is a flagship
project for Latin America - though onethat is still some way from coming to
fruition. It will be the regions the first multi-
suspension bridge with spans longer than
1,000m; the three-tower crossing will have
main spans of 1,155m and 1,055m.
At present, the client Chiles Ministry of
Public Works is in the process of reviewing
the final design. Construction is due to start
soon and the target is for the bridge to come
into operation in 2020.
The project has had a long gestation and
has been talked about for decades as part ofthe plan for a road to link the whole of the
American contintent, from Alaska to south of
Chile.
A scheme to build the bridge under a public-
private partnership was cancelled in 2006,
mainly for financial reasons. The project was
then re-evaluated during 2011-2012 from both
economic and technical standpoints. The
decision was taken to use traditional funding to
build the bridge for a maximum cost of US$740
CHACAO CHANNEL BRIDGE, CHILE
New forms
Chinas Taizhou Bridge, which opened in
2012, was first three-tower, two-main span
continuous suspension bridge system. The
structural behaviour of this type of system is
different from that of a conventional two-towersuspension bridge system, says Robin Sham;
cable slip at the saddles must be prevented
under all loading conditions, which leads to
conflicting demands at the central tower. A
flexible tower would help prevent cable slip but
would be ineffective in the control of girder
deflection; while a stiff central tower would
make it hard to prevent cable slip, although
it would improves deflection control of the
girder. The main reason for adopting the
three-tower form is that it enables very large
distances to be crossed, with only the minimal
number of bridge supports, Sham says. Oneof the challenges at Taizhou was that the
superstructure construction for a three-tower
suspension bridge system is much more
complicated than that for a two-tower system,
particularly in the main cable erection, main
girder erection and bridge geometry control.
Another different form of cable-supported
bridge is currently reaching completion in
Turkey. The final deck segment was raised
into place in early March of a hybrid cable-
stayed suspension bridge that is being built
north of Istanbul over the Bosphorus Straits;
a concept developed by Michel Virlogeux andT Engineering. The Third Bosphorus Bridge
officially called the Yavuz Sultan Selim Bridge
is being built by a joint venture of Astaldi and
IC Ictas and has 1,408m main span far longer
than the world record for a traditional cable-
stayed bridge, the 1,104m-span Russky Bridge.
The new bridges A-shaped towers stand a
million, including associated work such as
access roads.
The government signed a contract with
a joint venture of OAS, Hyundai, Systra and
Aas-Jakobsen in February 2014. Chile is one ofthe countries most affected by earthquakes,
making the project particularly challenging.
Not only is the bridge in a highly seismic
region, but also there are strong winds,
high tides and fast currents to address all
significant issues for construction. Both cable-
stayed and suspension bridge options were
studied before concluding that a suspension
bridge would offer many advantages, including
in terms of seismic behaviour.
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LOOKING AFTER OLDER BRIDGES
Many of todays challenging issues for bridge engineers come
from looking after old structures. In the years to come, Cowis
Tina Vejrum expects to see more projects to replace decks on
existing suspension bridges, following Canadas original lead with the
Lions Gate Bridge and now the ongoing Macdonald Bridge project.
I think there is a new market there with interesting challenges, she
says. A number of such bridges are reaching the end of their service
life, she says. Fortunately on a suspension bridge we can replace the
deck its a lot easier than for a cable-stayed bridge. Limiting closure
times is a key issue, as too is maintaining the aerodynamic stability in
the interim phase where the bridge is not fully connected and has two
different cross sections.
Another issue is deterioration of the main cables of suspension
bridges. Following successful use elsewhere, dehumidification is
being discussed for a number of US bridges including the George
Washington, Anthony Wayne and Benjamin Franklin. And in February,
the Delaware River & Bay Authority awarded American Bridge a
US$33.6 million contract to install a dehumidification system for the
main suspension cables on both structures of the Delaware Memorial
Bridge.
Dehumidification on main cables has passed the tipping point
in the USA, believes Aecoms Barry Colford. What has convinced
owners (and me) are the results from acoustic monitoring of the
UK bridges following application of dehumidification. These are
of course confidential and sensitive but owners are likely to be
aware of them through the International Cable Supported BridgeOperators Association, he says. It not only the results from acoustic
monitoring that have increased confidence in the effectiveness
of dehumidification. The results of internal inspections post
dehumidification have been very encouraging, Colford adds.
Hydrogen embrittlement needs moisture to generate hydrogen ions
and of course corrosion needs moisture and oxygen. If we can stop
moisture from getting into cables then we can potentially stop both of
these things happening, he says. The whole ethos is to make sure that
the service life of the cables matches the service life of the bridge. I
do think that dehumidification is the only way that we can be given
some assurance that this will happen. We now know that painting initself doesnt stop moisture getting into cables. We also know that
oiling doesnt appear to work either.
Aecom has been working on the dehumidification of the two
Chesapeake Bay Bridges and the scheme is now up and running. The
cables have dried out really well, says Colford.
Novel solutions involving complex surgery can also be required
when long-span crossings age, but some of the issues may not become
apparent until work begins. A recent project at the Humber Bridge has
highlighted the need for the client, designer and contractor to work
closely together to address any unexpected challenges on site. It has
also demonstrated some of the potential difficulties of using the new
higher-strength steels.
The Humber Bridge opened in 1981 and its 1,410m-long suspended
main span held the world record until 1997. The ends of the deck
boxes at the towers and anchorages were supported by pairs of steel
A-frames to allow free longitudinal movement of the deck boxes undertraffic and other effects, and providing horizontal restraint under wind
loading.
Routine inspections had raised concerns over a lack of articulation
and wear, so a scheme was designed by Arup for the Humber Bridge
Board, to replace the 3.8m-high A-frames with vertical pendels and
wind-shoes (Bd&e issue no 73). Owners of similar long-span bridges
are likely to have to contend with similar issues in the coming years,
says Spencer Group deputy managing director Richard Burgess.
His firm won the contract and completed the work in 2015, without
needing to close the bridge.
High-strength steel, grade S690 had been specified to reduce
the element sizes in the limited space available. But we found that
we couldnt meet the weld strength requirements with that steel,
says Burgess. When we dropped down a grade we got a far more
compliant material it was more weldable and still met the strength
requirements for the bridge, he says.
As a result, engineers believe caution is needed over the use of such
steel in bridges, where demanding fracture toughness requirements
may be coupled with the heightened risk of hydrogen embrittlement.
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LONG-SPAN BRIDGES SUPPLEMENT 2016 www.bridgeweb.com
record-breaking 322m-tall and its 59m width
will accommodate an eight-lane motorway
and two railway lines (Bd&e issue no 80)
It is an innovative structure, not only
because of its hybrid design but also because
the cables are the biggest ever installed on a
bridge, explains Erik Mellier, technical director
of Freyssinet, which designed and installed the
cables. Another notable feature is the use of
1,960MPa strand. It is the first time that we
are using such a high-strength strand, he says.
We have celebrated the biggest stay cable
ever installed in terms of length and size, says
Mellier. The longest of the cables are 597m
long, and have 151 strands. Compact cables are
being used, to reduce the drag.
The company has taken advantage of its
earlier work at Russky Island. It was a good
thing to have done before, because we could
take all the experience we had accumulated
there and adapt it to this project, says Mellier.
The initial challenges were in the design
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of the system, which had to be upgraded
compared to the standard. We carried out a
quite significant testing campaign, with fatigue
tests both in Germany and Chicago, says
Mellier. In addition, the bridge is quite flexible
and so there were issues during the design
stage about deformations and fatigue of the
cables. A special test was carried out, looking
at the behaviour of the cable under highdeflections.
Looks matter
Every long-span bridge is the result of
countless decisions - but some of those
decisions naturally have a far more profound
impact than others. The choice of procurement
method is one of the most fundamental,
affecting everything from the type of bridge
to how much influence the contractor and the
eventual maintenance team will have on what
it is made from and how it is built.
Procurement choices can also govern
the degree of receptiveness to innovative
approaches, whether involving the use of the
latest high-strength materials or by looking
for better ways of addressing issues such as
vulnerabilities.
But on all too many projects, price turns
out to be the only thing that matters in the
end, says Poul Ove Jensen, bridges director at
Dissing & Weitling. He is surprised that there
is so little focus on the appearance of major
bridges, particularly as they have an enormous
impact on the visual environment, much more
than buildings.
It is also surprising because clients seem
fully aware of the power of bridges as symbols;
in any project brief these days there is a clause
saying that the bridge must be a landmark, a
signature structure or an icon. Therefore its
very disappointing that at the end of the daythey just take the cheapest one, he says.
The client isnt even necessarily saving much
- if any - money. As far as were concerned,
there is no real relationship between cost and
lets call it beauty, he says. There is no reason
why a cheap bridge cant be a beautiful bridge.
There are many great bridges being built
around the world - but also quite a few
mediocre and some outright ugly ones, he
feels. The reason for this is not lack of talented
bridge designers, but often that clients are
not prepared to do what it takes, or dont
understand what it takes, to achieve the
intended result. The procurement method is
often the problem, Jensen feels.
The decline in the traditional approach
of completing design before construction
tenders are invited has been accompanied by
a corresponding increase in formats where the
contractors team is given responsibility for
much of the design. In design and construct
tenders, the bidders often see no reason to
make an effort because they assume only the
price matters - and all too often they are right,
he says. But in fact we can usually save them
money, he adds. For instance, this might come
from input such as reducing the concrete
quantities for the bridge.
Our main problem as architects is that
architecture is still considered an add-on to
bridge design, says Jensen. Yet in working with
engineers, no-one can see where the architects
work stops and the engineers begins; it doesnt
matter who came up with which idea we
always work as a team, he adds.
Balancing different demands in procurement
causes much debate, including the extent
to which you prescribe details, while leaving
sufficient opportunity for achieving value.
Client-based designs with construction-only
contracts do still happen, particularly in
some regions such as the Middle East. These
days, markets such as the USA or Europe
tend to go down the design and build route,
or public-private partnerships, says Stuart
Withycombe, who is CH2Ms director of major
crossings. How far you take the definition
drawings determines how much room you
leave for choice in terms of design, he adds.
If you want to be fairly protective of what
your output looks like then I think there is
justification for provision of a high level of
definition. But in other areas, maybe less so.
As well as appearance, the choice of
procurement method naturally has aconsiderable effect on who pockets any
savings that arise from value engineering. In
design-bid-build, savings arising from changes
that are accepted by the client may be shared
50:50 between client and contractor. But in
design-build, the contractor will simply seek to
put in the lowest price possible; all the savings
from the innovations therefore go to the
owner. At the same time, the concern is that
the owner may not get exactly what it wanted,
adds Marwan Nader, senior vice president at
TY Lin International.
However the use of definition designs is
starting to open up a new option for clients
in this regard, enabling them to lock-in the
appearance they want from the start. The new
Champlain Bridge in Montreal, Canada also
known as the New Bridge for the St Lawrence
is a current illustration. We ended up with a
definition design that was mandatory for the
bidders, explains Jensen. The Oresund Bridge,
which opened in 2000, was an early example
of this process, which is still only rarely used.
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Some see such an approach as beneficial,
others less so, feeling that it does not really
engage the creativity and resourcefulness of
the private sector. There can also be situations
where the ambitions of the architect ambitions
and the engineer dont really converge.
In Montreal, client Infrastructure Canada
was determined that the new bridge should
meet local expectations of a landmark bridge.
However, the project has an exceptionally
tight time schedule, particularly because
of the urgent need to replace the existing
bridge, which is in poor condition. A design
competition would have delayed the 2018
target completion. Use of the mandatory
definition design was a good solution, Jensenbelieves; it would have been impossible
to describe the architectural treatment,
proportions and so on sufficiently well in
words. The owner effectively had a guarantee
that it would get what was envisaged.
The public-private partnership agreement
with the government of Canada was won
by Signature on the Saint Lawrence Group,
which includes designer TY Lin International.
The aggressive schedule could never have
been achieved under a design-bid-build
environment, according to Nader. What the
client is getting is the best of both worlds, he
says. The project can meet the schedule, and
will be the bridge that was envisioned.
The Mersey Gateway in the UK (see page 42)
took an intermediate approach, partly using
the planning process to provide that definition,
says Withycombe, with some rules for what the
structure would look like. That took a high-
level view that nevertheless was very careful in
terms of how it defined visual quality, he says.
Were getting better as designers in
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terms of making things look better but its
not just how it looks its making sure it
works better as well, says Withycombe.
Aspects such as durability and choice of
materials are important. Its important to
fix the requirements so that you dont rule
out contractors coming along with their
most creative and best ideas for how to
build it. Contractors bring important areas of
innovation to the project.
This influence also extends to maintenance:
concession projects run for perhaps 30 or 35
years and clearly the structure needs to be in
a certain condition when handed back to the
client. This means designing for a particular
measure of performance 30 years from now,or risking expensive repairs before handover.
There have been changes in our world
because of the advent of PPP. says Mike
Cegelis, senior vice president at American
Bridge. There is a much greater focus on
the operational and maintenance costs of
components of the bridge than there was in
former times.
There is increased interest in health checks
for the bridge, particularly as the cost of
instrumentation falls. It is very fashionable to
equip all your bridges with all kinds of sensors,
says VSL International group technical
officer Max Meyer. But there is no point in
collecting extensive data unless it can be used,
he stresses. Adding value involves helping
clients to come up with a system that gives
meaning to the data and enables maintenance
interventions to be well planned.
Checking for vulnerabilities
Risks such as accidents and the potential
of terrorism have a significant impact
for the long-span bridges that are often
critical infrastracture links and the choice of
procurement method can also affect how such
risks are addressed.
At the advent of privately-funded bridges,
financial backers were mostly concerned with
the seismic risk. Earthquakes had certainly
been considered before then, but it had not
been such an overriding issue, says TY Lin
International senior vice president David
Goodyear. The same is now becoming true for
vulnerability assessments, he says.
Someone financing a project for several
decades needs to weigh up risks and revenue
implications, not just of terrorism but of all
kinds of major incidents - perhaps a tanker
catching fire. My personal belief is that
there is a lot of good thinking generated by
having private financing step in front of public
financing, because with private financing there
seems to be more ownership of the funding
stream, says Goodyear.
Blast protection is increasingly a key issue
for long-span bridges, though this tends not
to be widely discussed in public for fear of
raising awareness about vulnerabilities. At the
same time, increased attention is being paid
to the issue of fire protection both in service
and during construction. Various incidents
have made owners more concerned about
the potential consequences of fire affecting
a main suspension cable, hangers or staycables. In one instance a few years ago, a truck
caught fire by the low point of a main cable of
new Little Belt Bridge in Denmark and direct
lightning strikes of bridges such as the Rion
Antirion Bridge in Greece, which damaged
a cable and a similar incident in Korea have
raised this as an issue. Cable and hanger
suppliers are developing systems to provide
some fire protection.
We are beginning to see a requirement in
design, reveals Tina Vejrum, vice president
of international bridges at Cowi. Replacing
hangers or stay cables is one thing, but would
be a different matter if the main cable of a
suspension bridge was affected, she says.
Meyer is aware of five or six cases of
fire damaging cables on ong-span bridges,
including a recent one at a bridge in China
where fire broke out when welding was taking
place inside a tower. Nine cables were lost,
snapping one after the other; luckily the sites
tower cranes were able to drop water into the
tower from above to put the fire out.
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The Post-Tensioning Institute has
acknowledged the risk of fire and has
formulated test requirements. Details of
fire resistance qualification testing were
among the significant additions and updates
introduced in its 2012 edition. If you want to
supply a system you need to be able to pass
this test, says Meyer.
One of the key questions to address on a
project is what level of protection is really
necessary. Once the bridge is in service,
tankers pose a particular risk and Meyer
suggests that a rule of thumb might be to
take the protection to double the height of the
vehicles that will be crossing the bridge.
It is not only heat that poses a risk: cold and
in particular the build-up of ice are potentially
damaging. High-profile cases such as Canadas
Port Mann Bridge have highlighted the
dangers and cable companies are developing
prevention or removal technologies.
The devastating tsunami of 2004 highlighted
a further risk that major bridges can be
exposed to. Awareness of disaster prevention
was heightened in the aftermath, points out
Aecom director Robin Sham, the companys
global leader of long-span bridges. This has
fed into projects such as the Second Penang
Bridge, where a study of the likelihood of a
tsunami event and the resulting soil liquefaction
phenomena was carried out. The bridge,
which opened in 2014, consists of precastsegmental concrete marine viaducts and a
475m-long cable-stayed bridge. The study
sought to determine the risks and magnitudes
of tsunami-generated waves on the bridge, says
Sham. A simulation was then calibrated with
records to allow a predicted wave height to be
accommodated in the bridge design.
Advanced materials
There is correlation between advances in
materials and increases in maximum span
length over time, says Nader. But such
increases have now tapered off, he feels. In
my opinion, we are now on the cusp of starting
to look at ultra-light high-strength concrete
and what that will bring to the equation. It is a
major factor when spanning longer distances.
I dont think at this point that somebody is
going to dream up structural systems that give
us the ability to go longer - its going to have to
be through the materials, he says. Ultra-high-
strength steel, fibres and ultra-light high-
strength concrete will all play their parts.
A difficulty with high-strength materials
arises in relation to codes and standards, says
Vejrum. At the moment we cant go higher
than the grades we are using. For instance,
manufacturers can produce 2,200MPa steel
but this is far outside codes that only allow
values of perhaps 1,860MPa or 1,960MPa.
There is a similar situation for high-strength
concrete; it all boils down to who takes
responsibility. Without the backing of codes,
its difficult to get the materials introduced as
standard on projects, she says; consultants
wouldnt take the responsibility if the client
doesnt want to.
Perhaps it is more likely in the meantime
that such materials find a home on PPP
projects where the contractor is responsible
for subsequent of maintenance. This could
be a likely way forward, says Vejrum, as the
contractor will benefit from a saving on initial
costs and would deal with any subsequent
issues. However, agreement would also be
needed with the independent checkers about
going outside the codes.
Introducing innovations is certainly
becoming more difficult, feels Mellier, partly
for reasons to do with issues like CE marking
and norms. I believe that most clients are
increasingly reluctant to be the first, he says.
You really need large projects, such as the
Third Bosphorus Bridge, in order to move
forward. The technology can then be used onsmaller projects, as clients are less reluctant
once someone else has demonstrated that
it works. They can also take confidence from
the fact that the larger schemes are closely
examined by top consultants.
Advanced materials like high-strength
steel are not necessarily straightforward to
use. Issues can arise when using this kind of
material under high tension in bridges exposed
to chlorides and water. For example American
Bridge has had to deal with high-profile failures
of a small proportion of the tension rods on
the self-anchored suspension span built as part
of the new East Span of the San Francisco-
Oakland Bay Bridge. There have also been
some rod issues on other projects.
Such materials are now part of the bridge-
building world, says Cegelis, and they solve a
lot of other issues in an economical manner.
But we are now highly dependent on the
success of this material. It has obviously
been proven in a test environment that it can
meet the stresses that are imposed on it but
the question is whether it can withstand the
environmental attack.
Samples of any new material tested in the
lab are checked over by the manufacturer
in tremendous detail, points out Cegelis. But
fabrication of these one-off test pieces is not
the same as for general production and normal
handling on site in the real world.
Such elements may have their benefits but
American Bridge has certainly become quite
wary about them. Cegelis observes that the
company asks a lot more questions about jobsthat will use them. However, he regards the
issues as part of a natural process - inherent
problems have to be overcome whenever
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technology advances.
Meyer too is seeing a move to go for higher
strength steel than the current 1,860MPa:
there are fabricators who want to push this to
something like 2,200MPa. The steel is harder
to produce - and more expensive - but for the
big bridges, wind is more of a controlling factor
and there is definite interest in keeping the
diameters of cables down, he says. However,
the product would need to be economical,
which may not be possible if the volume is not
there.
Patenting ideas
The long-span bridge engineering fraternityhas traditionally been very open with regard
to sharing details of innovations developed for
projects. Deciding what to patent is difficult.
We are patenting technology but we are
being quite careful about it, says Matt Carter,
Americas long-span bridge leader at Arup.
We are not going down the line of patenting
everything in sight.
One idea on which Arup does have a patent,
jointly with GS Engineering, involves earth-
anchored cable-stayed bridges. The system
enables thinner steel plates to be used for
very long spans. We felt there were good
arguments for cable-stayed bridges up to the
1,400m kind of range, and we felt that the
technology that really works well at that range
was to build partially earth-anchored cable-
stayed bridges, says Carter.
But publishing rather than patenting was
the choice for an innovative idea that was
developed at the time of bidding for the Izmit
Bay Bridge (see page 30), which Arup didnt
win. The concept involves a way of seismically
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LONG-SPAN BRIDGES
TYPE TALK
What counts as a long span naturally depends on the type of the bridge. Acrow Bridge
recently supplied two bridges to a flood-damaged area in the Himalayas. The bridges were
customised with modular components to address local conditions and had clear spans of
60m and 80m. Such bridges can be operational in days, with minimal construction machinery and
using unskilled labour, says Acrow Bridge president Bill Killeen. In remote areas such as this, building
a modular steel bridge on site is often the best option, since constructing a conventional bridge of a
long length in-situ is most likely not feasible due to challenging topography, he says. Substandard
road conditions also make it difficult to transport heavy highway construction equipment or materials
to site. In contrast, the components for the Acrow structures were shipped in standard ocean
containers, which were then loaded onto compact trucks with a length of 6.5m.
isolating the anchorage of a suspension
bridge. Arup toyed with trying to keep the
technique as secret as possible though the
information had been included in the bid or
patenting it. But at Arup were not trying to
patent too much construction technology,
says Carter. We are a relatively patent-free
industry. We dont want to be a market leader
in taking us to a place where engineering
consultants are suing each other for patent
infringements. Instead, the decision was
taken to publish. He regards it as very positive
that the sector promotes a collaborative
environment, where people want to discuss
and share the work theyve done.
Technology
As bridge engineers design ever longer spans,
they typically depend on highly sophisticated
analysis models to use in the process. Vanja
Samec, global director bridges at Bentley
Systems, points to the issues involved for large
prestressed concrete and composite bridges
built using the incremental launching or free
cantilevering methods. The challenge is to
model accurately the erection process, while
considering different construction stages,
time-dependent behaviour, and the required
pre-cambering in order to achieve the design
shape once construction has been finished,
she says.
However, different challenges face engineers
when designing ultra-long-span bridges, such
as stay cable or suspension bridges with
high pylons and slender steel or concrete
decks. Here the challenges are mainly related
to optimising the stressing sequence of
the cables to the geometrically non-linear
behaviour of the structure, and to dynamic
problems such as wind-induced vibrations
and seismic events. It is natural that wind-
load effects would be greater on longer span
lengths of cable-supported bridges, she says.
These phenomena include vortex shedding
and the lock-in, across-wind galloping and wake
galloping, torsional divergence, flutter, and
wind buffeting.
Another area of IT development is in 3D
printing. Its going to change our industry in
a very big way, predicts Nader. Being able to
go from the computer to printing the bridge
would bypass a major part of the contracting
process. It may not happen within our lifetimes,
but could happen someday.
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www.acrow.com
+1.973.244.0080
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For over 60 years, Acrow has been creating and restoring transportation lifelines under extreme
circumstances. In the spectacular foothills of the Himalayas, pilgrims make the annual trek to a Temple at
3,700 meters. Damaging floods cut off the route to the temple. Acrow supplied a clear span modular bridge
with components customized for local conditions. Installed in a matter of days, with minimal construction
machinery and unskilled labor, locals are able to make the pilgrimage again.
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LONG-SPAN BRIDGES
HLOGALAND BRIDGE, NORWAY
Anew suspension bridge with
distinctive A-shaped towers and an
unusual cable arrangement is taking
shape over the Rombak Fjord near Narvik in
northern Norway.
Hlogaland Bridges 1,145m main span will
make it one of the longest in Europe, though
it is certainly not among the widest of the
worlds major suspension bridges as the
main spans steel box girder deck measures
just 18.6m across. It is also notable for its
A-shaped towers, the form of which has
governed the unconventional arrangementof the cables and hangers. As a result, the
bridge will be the longest in the world with
a spatial cable system: its main cables will
follow an oval shape in the horizontal plane
and the hangers will be slightly inclined in
the vertical plane.
Client for the scheme is the northern
region of the Norwegian Public Roads
Administration, Statens Vegvesen. The
bridge is typical of Norways crossings of
deep and wide fjords, in that traffic levels are
relatively low and so it will carry just a single
traffic lane in each direction, as well as a3.5m-wide walkway.
The towers have been designed very much
with aesthetics in mind. What we always
try to do is to take advantage of the special
conditions at the site and in this case it was
natural for us to choose an A-shaped tower,
says architect Poul Ove Jensen, bridges
director at Dissing & Weitling. The choice
suited the requirement for an attractive
structure, but decisions arent taken for
aesthetic reasons alone, he stresses. Design
should take account of a sites specific
requirements, rather than trying to invent
some dramatic forms, which often lead tovery contrived results. In this case a long
span bridge with an extremely narrow deck
it was quite a logical concept.
It is not a solution that would work
everywhere. For a conventional suspension
bridge, it would be difficult to have A-shaped
towers because of the very wide deck, says
Assad Jamal, chief project manager for
international bridges at Cowi.
At the start of design, members of the
team went to visit the site. By the end
of the week, we had the concept, recalls
Jensen. An H-shaped tower didnt look very
good, given the tall height and narrow width
needed; and a central tower between traffic
lanes was out of the question with the two-
lane road. The design team quite quickly
came to the conclusion that the A-shape was
right.
Two separate contractors are building the
bridge, with Sichuan Road & Bridge Group
responsible for the steelwork deck
Norways low trafficvolumes and localtopography have
led to creation of astunningly slender
structure
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28 www.bridgeweb.com LONG-SPAN BRIDGES SUPPLEMENT 2016
LONG-SPAN BRIDGES
and cables and NCC for the concrete.
By March 2016, construction of both of the
concrete towers had been completed, and
the catwalk installation, which will take aboutthree months, had just begun. Installation of
the prefabricated main cable is due to start
at the end of July.
The tower design has dictated the layout
of the rest of the structure, in particular the
unusual spatial arrangement of the cables
and hangers. The two main cables meet at
saddles on a narrow support on the top of
the towers, splaying out at the centre of the
bridge. As a result of this alignment of the
main cable, the bridges hangers are slightly
inclined. In terms of stability of the bridge
subjected to traffic load, this has minor butbeneficial effect in regards of wind stability,
says Jamal though it did mean that
additional load cases had to be considered.
Having the A-shaped towers poses extra
challenges for installation of the cable
system; a special construction sequence
is needed to obtain the correct shape,
beginning by allowing the two main cables to
hang vertically during air spinning. Initially,
there will be a single common catwalk
between the two main-span cables.
The next step will be to displace the main
cables horizontally using an hydraulic strutsystem to create the oval shape, with struts
at 16m centres. The struts need to span
approximately 16m at the centre of the main
span, and they need to be able to telescope
outwards by using a hydraulic system,
explains Jamal.
The hangers can then be installed and the
deck erected, before the struts are removed.
The saddles are at the top of the towers,
and the shape of the towers means that the
saddles are very close together. As they are
so close together, there is an influence on
how the loads are distributed between theside span and the main span cables: where
a conventional suspension bridge tower
will twist for uneven main cable loading
in the main span, this is not the case for
Hlogaland Bridge. The towers do not twist,
which means that the loads of the back span
cables are shared evenly.
The ratio of span length to tower height
above deck for the bridge is 1:9; the ratio of
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LONG-SPAN BRIDGES
LONG-SPAN BRIDGE SUPPLEMENT 2016 www.bridgeweb.com
main span length to the distance between
the cables is 90, while typical values for
suspension bridges are in the range 55-
60, explains Jamal. This combination of
a slender bridge with a long main span
posed considerable design challenges in
order to fulfil the requirement of ensuring
aerodynamic stability at 63m/s at bridge
deck level. The aerodynamic stability was
verified through numerical analyses and
wind tunnel tests; this showed a critical wind
speed of 68m/s.
The bridges box section deck is arranged
with a slope of 15.8 of the lower inclined
side plates relative to the horizontal bottom
plate, says Jamal. Wind tunnel tests carried
out in smooth flow proved that there will beno vortex-induced vibrations, thus saving the
potential costs of installing and maintaining
any mitigation measures.
Each tower is topped with a towerhouse; a naturally-ventilated structure
designed to enclose them the cable saddles
and give extra protection. They will also
be an architectural feature; their internallighting will be the only strictly non-
functional feature on the bridge, admits
Jensen.
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30 www.bridgeweb.com LONG-SPAN BRIDGES SUPPLEMENT 2016
LONG-SPAN BRIDGES
Anew bridge with one of the worlds
longest suspension spans is nearing
completion in Turkey. Izmit Bay Bridge,
which has a 1,550m main span, is being built
by IHI Infrastructure Systems and Itochu.
The team was given notice to proceed in
September 2011 and the bridge is set to open
in May this year a very short period for such
a major crossing.
The project had been on track for
completion in the first quarter of this year, but
suffered a setback last year when the catwalk
collapsed in March just as the contractor was
preparing to start erecting the main cable.
Luckily bad weather had halted work that
day and no-one was injured; the catwalk was
completely reconstructed and ready for use
by August.
The bridge is in a region that is seismically
very active and where a major earthquake
occurred on the North Anatolian fault in 1999.
Seismic issues have placed considerable
additional demands on the design.
Deck erection began at the start of this
year with the erection of three 51.2m-long
segments at each of the towers. A floating
crane was used for installation of the initial
segments at locations including the towers
and the ends of the side spans, with the
remaining deck segments positioned by a
lifting device mounted on the main cable.
Detailed design of the bridge has been
carried out by Cowi, with Dissing & Weitling
as the project architect. CH2M performed
the independent design check. Steel has
been used both for the main towers and the
One of two major bridges currently being built in Turkey isa long-span suspension bridge which forms part of a new420km-long motorway in the north of the country
IZMIT BAY BRIDGE, TURKEY
deck of the new bridge. The 235m-tall towers
have two legs and two cross beams; and the
legs measure 7m by 8m in cross section at
the base. The suspended deck is a single,
orthotropic box girder that is 30m wide and
4.75m deep and has a 2.8m-wide inspection
walkway attached to each leg.
The main cables on the main span have
been formed from 110 prefabricated parallel
wire strands each made of 127, 5.91mm-
diameter cable wires with a breaking strength
of 1,760MPa. The main cable on the side
spans has two extra strands of the same
size. Hanger ropes are of parallel wire strand,typically formed of 133, 7mm-diameter wires
with a breaking strength of 1,760MPa. They
are connected to a cable clamp at the top and
hanger anchorage at the bottom.
The side spans flanking the 1,550m main
span are each 625m long, giving a total
suspended deck length of 2.8km, which is
continuous between the two side-span piers.
A key design change was made early in
the project following ground investigations
by Fugro that showed a potential fault at the
planned location to the south anchorage. This
led to the anchorage being moved 138m to a
safe zone, reducing the main span from theoriginally planned 1,688m.
The structure is a central part of the
420km-long Orhangazi-Izmir motorway
project, which is being developed by Nomayg,
a consortium of six companies. The bridge will
carry the new link across the Sea of Marmara
at the Bay of Izmit in northern Turkey.
Read our full feature about Izmit Bay Bridge in
Bd&e issue no 83
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Project scope:38 nos. MAURER MSM
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the foundation.
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33 www.bridgeweb.com LONG-SPAN BRIDGES SUPPLEMENT 2016
QUEENSFERRY CROSSING, UK
A
landmark cable-stayed crossing
is in its final year of construction
alongside two other famous bridgesover the Firth of Forth near Edinburgh in
Scotland. Design and construction of the
new Queensferry Crossing began almost five
years ago and the bridge is on track to be
completed by spring 2017.
The new bridge will take the record for
the worlds longest three-tower cable-stayed
bridge and it will also be the UKs tallest
bridge. Queensferry Crossing will itself
provide reasons enough for people to visit
the area when it opens next year - but it also
stands alongside one of Europes longest
suspension spans, the Forth Road Bridge,
and close to the historic Forth Bridge, which
carries railway traffic.
Forth Crossing Bridge Constructors,
a joint venture of Hochtief Solutions,
American Bridge International, Dragados
and Morrison Construction, is responsible
for designing and building the cable-
stayed bridge which will create a new link
between South Queensferry and North
Queensferry when it opens.
Including the north and south approach
viaducts, the bridge has a total of 14 spans,three concrete single-leg towers which
are on the centre-line of the transverse
cross-section, two planes of stay cables
anchored along the centre of the structure
and a composite steel and concrete deck
superstructure.
The three bridge towers reached
full height at the end of 2015, marking
a key milestone for the project team.
The reinforced concrete towers start at
bedrock nearly 40m below the water. The
middle tower is a height of 210m, while
the flanking towers are each 207m tall.
The towers are roughly rectangular in
cross-section, with the east and west sides
curved and the north and south sides
(where cable anchorages are located)
inclined. They were built in 4m sections
using climbing formwork, with a total of
54 lifts per tower. Each of the 54 tower
lifts had a slightly different profile, as the
hollow structure tapers from 16m by 14m
at the base to just 5m by 7.5m the top.
The towers are integrated onto structural
foundations through heavy verticalreinforcement and embedded into the
massive 25,000m3concrete bases formed
by using 1,219t steel caissons sunk to the
Forths seabed (Bd&e issue no 70).
The focal point of the visible bridge is the
cable-stayed section which makes up just
over 2km of the total 2,638m of the main
crossing, including the twin main spans of
650m supported by the three main towers.
The bridge has a multi-cell steel box girder
design with a composite reinforced and post-
tensioned concrete deck; a parallel strand
system is used to anchor the deck girders to
the towers.
Deck construction began with the erection
of temporary falsework at each tower to
accept four starter segments. The starter
segments contain more steel and concrete,
making them heavier, and so were erected
on the temporary falsework in order to allow
the concrete decks to be cast in situ. For the
rest of the units the typical segments
LONG-SPAN BRIDGES
The worlds longest three-tower cable-stayed bridge is reaching completion in Scotland
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+44 (0)20 7973 6694
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