Damascus University

Faculty Of Civil Engineering

Structural Engineering

Suspension Bridges

VS

Cable-Stayed Bridges

Written By : Hussein Hasan

Supervised By : Prof. Eng. Mouaid Soubh

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Abstract وانجسىز املدعىمت برنكىابم , ونكه انجسىز املعهاقت مر بني اقرزوتاملمه هري اندزاست هى انهدفإن

وانجسىز انجرئزٌت بداٌت تم استعساض أوىاع انجسىز بحسب انجمهت اإلوشرئٍت وهً انجسىز

إىل محىز ثم اوتاقهىر وانجسىز انظفسٌت اناقىسٍتانجسىز و (ذاث انجىائز انشبكٍتانجمرنىوٍت )

مٍزاث انتحسي عه شدودة برنكىابم ووانجسىز املوهى انشسح انىايف عه انجسىز املعهاقت دزاستىر

)حتى اَن ( سس يف انعرنموكمثرل عه انجسىز املعهاقت قمىر بدزاست أهم ج ,ىهر كم م ومسروئ

وكرنك األمس برنىسبت نهجسىز يف انٍربرن (Akashi Kaikyo) وهى جسسٌصىف مه هرا انىىع

Russkyاملدعىمت برنكىابم واملثرل هىر انجسس األطىل يف انعرنم مه هرا انىىع وهى جسس )

Bridgeيف زوسٍر ) .

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Contents

I Structural Types Of Bridges 4

Beam Bridges 4

Truss Bridges 5

Arch Bridges 6

Suspension Bridges 7

Cantilever Bridges 8

Cable-stayed bridges 9

II Suspension Bridges 10

World’s Longest-Span Suspension Bridges 12

Advantages and Disadvantages of Suspension Bridge 13

Example : Akashi Kaikyo Bridge 14

III Cable-Stayed Bridges 15

Construction Of Cable-Stayed Bridges 17

Example : Russky Bridge 18

((Resources)) 19

4

Structural Types Of Bridges

Beam Bridges

Beam bridges are the oldest and simplest bridge design consisting of vertical piers and

horizontal beams - e.g. just a simple plank or stone slab. They are suitable only for short spans

but can used for larger crossings by adding additional piers.

Forces: As the bridge is loaded, by traffic for example, the beam bends which causes the top

surface to be compressed and the bottom surface to be stretched or put in tension.

Advantages: they are easy to build and inexpensive relative to other bridge types so are very

common.

Disadvantages: they have a limited span and do not allow large boats or vehicles to pass

underneath.

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Truss Bridges

Truss Bridges are structures built up by jointing together lengths of material to form an open

framework - based mainly on triangles because of their rigidity. They are very strong and can

support heavy loads.

Forces: As with a Beam Bridge the top of a loaded truss is placed in compression and bottom

in tension. These forces are shared among the angled members.

Advantages: They are very strong and make efficient use of materials

Disadvantages: They are more complex to construct and need a high level of maintenance.

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Arch Bridges

Arch bridges were built by the Romans and have been in use ever since. They are often

chosen for their strength and appearance.

Forces: the compressive forces created by the load are transferred down through the arch and

resisted by the supports, or abutments, at its base. Abutment support prevents the arch

spreading under load.

Advantages: they are very strong and can be built from a wide range of materials

Disadvantages: limited spans unless multiple arches (or viaducts) are used and

uneconomical use of materials.

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Suspension Bridges

Suspension bridges main elements are a pair of main suspension cables stretching over two

towers and attached at each end to an anchor buried deep in the ground. Smaller vertical

suspender cables are attached to the main cables to support the deck below.

Forces: any load applied to the bridge is transformed into a tension in the main cables which

have to be firmly anchored to resist it.

Advantages: strong and can span long distances such as across rivers

Disadvantages: expensive and complex to build.

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Cantilever Bridges

Cantilever bridges are based on structures that project horizontally into space, supported at

only one end - like a spring board.

Forces: if two cantilevers project out from a central pier the forces are balanced.

Advantages: more easily constructed at difficult crossings by virtue of using little or no false

work.

Disadvantages: complex structures and can be difficult to maintain.

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Cable-Stayed Bridges

Cable-stayed bridges may appear to be similar to suspension bridges, but in fact they are

quite different in principle and in their construction. There are two major classes of cable-

stayed bridges: Fan type, which are the most efficient, and Harp or parallel type, which allow

more space for the fixings.

Forces: As traffic pushes down on the roadway, the cables, to which the roadway is attached,

transfer the load to the towers, putting them in compression. Tension is constantly acting on

the cables, which are stretched because they are attached to the roadway.

Advantages: good for medium spans, greater stiffness than the suspension bridge, can be

constructed by cantilevering out from the tower, horizontal forces balance so large ground

anchorages are not required.

Disadvantages: typically more expensive than other types of bridge, except suspension

bridges .

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Suspension Bridges

Suspension bridge, bridge with overhead cables supporting its roadway. One of

the oldest of engineering forms, suspension bridges were constructed by

primitive peoples using vines for cables and mounting the roadway directly on the

cables. A much stronger type was introduced in India about the 4th century AD

that used cables of plaited bamboo and later of iron chain, with the roadway

suspended.

In modern times, the suspension bridge provided an economical solution to the

problem of long spans over navigable streams or at other sites where it is difficult

to found piers in the stream. British, French, American, and other engineers of

the late 18th and early 19th centuries encountered serious problems of stability

and strength against wind forces and heavy loads; failures resulted from storms,

heavy snows, and droves of cattle. Credit for solving the problem belongs

principally to John Augustus Roebling, a German-born American engineer who

added a web truss to either side of his roadways and produced a structure so

rigid that he successfully bridged the Niagara Gorge at Niagara Falls, New York,

the Ohio River at Cincinnati, and, finally, in his masterpiece, the East River

between Brooklyn and Manhattan at New York City.

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The technique of cable spinning for suspension bridges was invented by the

French engineer Louis Vicat, a contemporary of Roebling. Vicat’s method

employed a traveling wheel to carry the continuous cable strand from the

anchorage on one side up over the tower, down on a predetermined sag

(catenary) to the midpoint of the bridge, up and over the tower on the farther side

to the farther anchorage, where a crew received the wheel, anchored the strand,

and returned the wheel, laying a fresh strand. From these successive parallel

strands a cable was built up.

Another major development in the modern suspension bridge was the pneumatic

caisson, which permitted pier foundation at great depths. It was used initially by

French, British, and American engineers, including Washington Roebling, who

completed his father’s Brooklyn Bridge.

For a time in the 1930s, American engineers experimented with a narrow solid

girder in place of the web truss to stiffen the roadway, but the failure of the

Tacoma Narrows Bridge in 1940 under aerodynamic forces instigated a return to

the web truss. Later, aerodynamically stable box girders replaced the web truss.

By the late 1980s, three suspension bridges (the Golden Gate, in San Francisco,

the Verrazano-Narrows, in New York City, and the Humber Bridge, near Hull,

England) had main-span lengths of more than 4,000 feet (1,200 meters). Modern

steel alloys are considered capable of much greater spans. Though suspension

bridges can be made strong enough to support freight trains, they have nearly all

been designed for automobile traffic.

A cable-braced bridge was developed by German engineers at Cologne,

Düsseldorf, and elsewhere in the 1950s and ’60s; in this form a single tower at

the midpoint supports the roadway by means of a number of cables. Another

development of the 1960s, aimed at reducing time of construction, was cable

fabricated in the shop.

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Advantages and Disadvantages of Suspension Bridge

Economic Advantage The area spanned by a suspension bridge is very long in proportion to the amount of materials required to construct bridges.

Height Advantage Built over waterways, suspension bridges can be built high, allowing the passage of tall ships unhindered by the bridge. The Golden Gate bridge has a clearance of 220 feet over the waters of San Francisco Bay at high tide.

Construction Advantage During construction, temporary central supports do not need to be built, and access to the construction is not required from beneath. This means busy roadways and waterways do not need to be disrupted.

Flexibility Advantages/Disadvantages Suspension bridges are flexible, which is an advantage until conditions become severe. Instability in extremely turbulent conditions or during strong earthquakes may require temporary closure. In 1940, high winds caused the Tacoma Narrows bridge, near Seattle, Washington, to collapse.

Foundation Disadvantages When built in soft ground, suspension bridges require extensive and expensive foundation work to combat the effects of the heavy load on foundation towers.

Heavy Loads Flexibility also becomes a disadvantage when heavy, concentrated loads are involved. Suspension bridges are not generally used for regional rail crossings that carry maximum weight loads, which adds dangerous stress to the structure.

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Akashi Kaikyo Bridge

Akashi Kaikyo Bridge is the world’s

largest suspension bridge with a main

span of 1,991 meters . The bridge spans

the Akashi Strait , between Kobe and

Awaji - shima in Japan. Akashi Strait is a

known fishing spot and there are about

1,300 boats spacewalks strait daily.

The building of the bridge began in 1988

and in 1998 the bridge finished. During

construction vari 1995 there was one

earthquake in Kobe area. When shifted

the foundations of the towers so that the

main span was increased by 0.8 m

Akashi Kaikyo Bridge is designed to

withstand earthquakes of up to 8.5 on

the Richter scale and speed of 80

meters per second. The main cable has

a diameter of 1122 mm and consists of

36,830 small wires of 5.23 mm in

diameter. The main cable has a dry air system to protect the main cable from

corrosion. The system provides dry air into the cables so that the humidity inside

the cables remain constant. Akashi Kaikyo Bridge is lighting with 1737 lamps,

lamps that are on the main cable changing colors. Next to the bridge is a

wonderful bridge museum.

Akashi Kaikyo Bridge

Design Suspension bridge

Total length 3,911 metres ( 2.430 mi)

Height 282.8 metres (928 ft) (pylons)

Longest span 1,991 metres (1.237 mi)

Clearance below 65.72 metres (215.6 ft)

Designer Satoshi Kashima

Construction begin 1988

Construction end 1998

Opened April 5, 1998

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Cable-Stayed Bridges

A typical cable stayed bridge is a continuous girder with one or more towers

erected above piers in the middle of the span. From these towers, cables stretch

down diagonally (usually to both sides) and support the girder.

Steel cables are extremely strong but very flexible. Cables are very economical

as they allow a slender and lighter structure which is still able to span great

distances. Though only a few cables are strong enough to support the entire

bridge, their flexibility makes them weak to a force we rarely consider: the wind.

For longer span cable-stayed bridges, careful studies must be made to

guarantee the stability of the cables and the bridge in the wind.

The lighter weight of the bridge, though a disadvantage in a heavy

wind, is an advantage during an earthquake. However, should

uneven settling of the foundations occur during an earthquake or over

time, the cable-stayed bridge can suffer damage so care must be

taken in planning the foundations. The modern yet simple

appearance of the cable-stayed bridge makes it an attractive and

distinct landmark.

The unique properties of cables, and the structure as a whole, make the design

of the bridge a very complex task. For longer spans where winds and

temperatures must be considered, the calculations are extremely complex and

would be virtually impossible without the aid of computers and computer

analysis. The fabrication of cable stay bridges is also relatively difficult. The cable

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routing and attachments for the girders and towers are complex structures

requiring precision fabrication.

There are no distinct classifications for

cable-stayed bridges. However, they can

distinguished by the number of spans,

number of towers, girder type, number of

cables, etc. There are many variations in

the number and type of towers, as well as the number and arrangement of

cables. Typical towers used are single, double, portal, or even A-shaped towers.

Cable arrangements also vary greatly. Some typical varieties are mono, harp,

fan, and star arrangements . In some cases,

only the cables on one side of the tower are

attached to the girder, the other side being

anchored to a foundation or other

counterweight.

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Construction Of Cable-Stayed Bridges

Construction of cable-stayed bridges usually follows the cantilever method. After

the tower is built, one cable and a section of the deck are constructed in each

direction. Each section of the deck is pre-stressed before continuing. The

process is repeated until the deck sections meet in the middle, where they are

connected. The ends are anchored at the abutments.

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Russky Bridge

The Russky Bridge (Russian:

Русский мост – Russian Bridge) is a

bridge built across the Eastern

Bosphorus strait, to serve the Asia-

Pacific Economic Cooperation

conference that took place in

Vladivostok in 2012. The bridge

connects the mainland part of the city

(Nazimov peninsula) with Russky

Island, where the main activities of

the summit took place. The bridge

was completed in July 2012 and

opened by Russian Prime Minister

Dmitry Medvedev. On September 3,

2012, the bridge was officially given

its name.

Russky Bridge

Design Cable-Stayed bridge

Total length 3,100 meters (10,200 ft)

Height 320.9 meters (1,053 ft)

Width 29.5 meters (97 ft)

Longest span 1,104 meters (3,622 ft)

Clearance below 70 m

Opened July 2012

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Resources

http://www.britannica.com/technology/bridge-engineering

http://www.historyofbridges.com/facts-about-bridges/types-of-bridges/

https://en.wikipedia.org/wiki/Bridge

https://en.wikipedia.org/wiki/Akashi_Kaiky%C5%8D_Bridge

https://en.wikipedia.org/wiki/Russky_Bridge

http://www.dtonline.org/vle/mod/lesson/view.php?id=276

http://pghbridges.com/basics.htm