Faculty Of Civil Engineering
Written By : Hussein Hasan
Supervised By : Prof. Eng. Mouaid Soubh
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Bridge ) .
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
Worlds 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
Structural Types Of 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
Disadvantages: they have a limited span and do not allow large boats or vehicles to pass
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.
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.
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.
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
Disadvantages: complex structures and can be difficult to maintain.
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
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
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.
The technique of cable spinning for suspension bridges was invented by the
French engineer Louis Vicat, a contemporary of Roebling. Vicats 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 fathers 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,
Dsseldorf, 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.