The this report, this could be for several reasons;

 

The bridge consists of two
bridge towers tied together at the upper level by two horizontal walkways,
designed to withstand the horizontal tension forces exerted by the suspended
sections of the bridge on the landward sides of the towers. The vertical
components of the forces in the suspended sections and the vertical reactions
of the two walkways are carried by the two robust towers. The bascule pivots
and operating machinery are housed in the base of each tower.

Tower Bridge – Bascule

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However, there are other bridge
designs that are still being used and there are still some very iconic bridges
around the world which were constructed with different designs.

·        
Quicker to construct

·        
Easier to construct

·        
Reliability

·        
Cost

Most of the bridges in the
world are constructed with the designs mentioned above in this report, this
could be for several reasons;

Other Bridge Designs

 

The mono design uses a
single cable from its towers and is one of the lesser-used examples of the
class.
In the harp or parallel design, the cables are
nearly parallel so that the height of their attachment to the tower is
proportional to the distance from the tower to their mounting on the deck.
In the fan design, the
cables all connect to or pass over the top of the towers. The fan design
is structurally superior with a minimum moment applied to the towers, but,
for practical reasons, the modified fan (also called the semi-fan) is
preferred, especially where many cables are necessary. In the modified fan
arrangement, the cables terminate near to the top of the tower but are
spaced from each other sufficiently to allow better termination, improved
environmental protection, and good access to individual cables for
maintenance.
In the star design,
another relatively rare design, the cables are spaced apart on the tower,
like the harp design, but connect to one point or several closely spaced
points on the deck

There are four major classes of
rigging on cable-stayed bridges: mono,
harp, fan, and star.

Cable-stayed bridges have been known
since the 16th century and used widely since the 19th. Early examples often
combined features from both the cable-stayed and suspension designs, including
the famous Brooklyn Bridge. The design fell from favor through the 20th century
as larger gaps were bridged using pure suspension designs, and shorter ones
using various systems built of reinforced concrete. It once again rose to
prominence in the later 20th century when the combination of new materials,
larger construction machinery, and the need to replace older bridges all
lowered the relative price of these designs.

A cable-stayed bridge has a single tower, sometimes more than one, from
these towers cables support the bridge deck. A standout feature are the cables
which run directly from the tower to the deck, normally forming a fan or harp-like
pattern or a series of straight lines that run parallel. They have some
similarities to the suspension bridge, where the cables that support the deck
are suspended vertically from the main cable, anchored at both ends of the
bridge and running between the towers. The cable-stayed bridge is optimal for
spans longer than cantilever bridges and shorter than suspension bridges. This
is the range where cantilever bridges would rapidly grow heavier if the span
were lengthened, while suspension bridge cabling would not be more economical
if the span were shortened.

2,6        Cable Stayed Bridges

 

One of the worlds most famous bridges
and most photographed bridge is The Golden
Gate Bridge which is a suspension bridge spanning the Golden Gate on the
West Coast of the United States of America. This bridge is one-mile-wide and connects
San Francisco Bay to Marin County

Suspension bridges are generally constructed
to link land that is separated by a large body of water, they allow for people
to commute and travel, saving time in the process. Roads and footpaths can be
placed on the deck of the bridge at the same time.

The cables used to suspend the deck
must be anchored at each end of the bridge, these main cables transform any
load applied to the bridge through a tension in the cables. The main cables don’t
stop at the supporting pillars. They continue beyond the pillars to deck-level
supports, and then onto connections with anchors in the ground which prevents
the cables from becoming too slack or loose. The deck or roadway is supported
by vertical suspender rods and/or cables which are called hangers. Depending on
the location of the bride, the towers may sit on a canyon or valley edge where
the road may proceed directly to the main span, if this is not the case then
the bridge will usually have two smaller spans which run between either pair of
pillars and the connecting road which may be supported by suspender cables.

Suspension Bridges get that name from
the cables suspended between towers, and also the vertical suspender cables that take the weight
of the deck below, upon which pedestrians and also traffic cross. This sort of
arrangement allows for the deck to be level or in some cases to arc upwards
towards the middle pf the bridge deck for additional clearance.

The suspension bridge is a type of bridge in which the load-bearing
portion (the deck) is suspended underneath cables on vertical suspenders. Like many
of the modern bridge designs one of the first examples of this bridge design was
built in the early 19th century during the industrial revolution.

2,5        Suspension
Bridge

 

                The Forth Bridge pictured above boasts three double
cantilevers and is a World Heritage site       situated
in Scotland. The bridge serves its purpose as a railway bridge which connects
two   villages, North and South
Queensferry                       

 

 

                This image was taken from

           

The cantilever bridge became a popular
bridge to construct due to their being a high demand for bridges that could
span longer distances. The main use for these bridges in to allow transport to
pass over such as trains and cars. Shortening travel time and distance.

Cantilever
bridges are bridges built using cantilevers, cantilevers are the
structures that project horizontally into space, with only one end supported.
the cantilevers may be simple steel beams whereas the larger cantilever bridges
which are designed to handle road or rail traffic use a truss structure built
from structural steel, or box girders which are made from prestressed concrete.
The steel truss cantilever bridge was a huge engineering breakthrough when it
was first constructed, as it can span distances of over 460 metres and can be
simply constructed at difficult crossings as there was very little falsework
needed.

2.4        Cantilever Bridge

 

 

 

 

 

 

This is a bridge whose load-bearing
superstructure is composed of something called a truss, a structure composed of
connected elements which often form triangular units. The connected elements
that tend to be straight may be stressed from tension or compression. In terms
of modern bridges, truss bridges have been around for a long time and once the
industrial revolution came about, materials like wood and iron were being used
to make structures. Before the industrial revolution bridges where commonly
only constructed making stone but iron and wood allowed architects to design
stronger and more reliable structures. Truss bridges have always been known for
their basic designs and are economical to construct due to the efficient use of
materials.

2.3        Truss

 

Under
load, the top surface of the beams is pushed down or compressed at the same
time, the bottom edge is stretched or placed under tension.

These
bridges are the simplest form of bridge. Early examples of a beam bridge were
constructed using just a log that was placed across a stream, however, todays
examples are made using large steel girders and can be constructed in different
ways.

Stiffness is the key to the construction of a beam bridge as it needs to resist
twisting and bending under load.
In its most basic form, a beam bridge consists of a straight horizontal beam
that is supported by piers at each end. The weight of the beam pushes straight
down on the piers.

2.2        Beam

 

Rather
than pushing directly down, an arch bridges load is carried outward along the
curve of the arch to the supports at each end. This results in the transfer of
weight to the supports at either end. These supports, called the abutments have
a sole purpose to carry the load and keep the ends of the bridge from
collapsing or spreading out.

This
type of bridge is one of the oldest types of bridges and they have been around
for centuries. Arch bridges are known for their great natural strength and were
originally constructed using stone or brick, but todays arch bridges are built
using reinforced concrete or steel thus allowing arch bridges to be longer with
lower spans due to the newer materials being stronger and more durable.

2.1        Arch

 

There are 7 different types of
bridges, Arch, Beam, Truss, Cantilever, Suspension and Cable-stayed.

 

 

 

 

This corbel arch bridge was built out of cyclopean
stones and was built with the sole purpose of being able to allow chariots to
pass over the small valley. The
structure is 22 metres long, 5.60 metres wide at the base and 4 metres high. Making
it a relatively small bridge in comparison to some of the Goliath Size bridges
we see today. The width of the roadway atop is about 2.50 metres and was just
wide enough to allow chariots to pass over. This being the main mode of transport
at the time when the bridge was constructed. This bridge shows just how long a
bridge can last and it also shows us that bridges have been important to humans
for centuries.

Having done some research into
the types of bridges I have found that there are 7 main bridge types. All
varying in shape, structure, size and all of them built to serve different
purposes in different situations. These bridge types are the most commonly used
and are still constructed all around the world using different materials.
Bridges that you see and use almost every day are designed by very skilled
architects and built with precision and accuracy by only the best engineers.
The time, money and work that goes into making a bridge is unprecedented. From
architects to engineers, the design and construction of a bridge can take
months, years and in some cases decades but that is nothing in comparison to
how long these bridges are designed to last. One of the oldest bridges that
exists and is still in use is The Arkadiko Bridge also known as
The Kazarma Bridge which can be
dated back to somewhere between 1300 and 1190 BC in the Greek Bronze Age.

 

3.    
The
different types of bridge

 

A bridge is a structure built to span
obstacles allowing for space underneath for roads, valleys or stretches of
water to allow passage over the obstacle underneath. There are several designs
that each serve a specific purpose and are built with different situations in
mind. Bridges are designed around certain variables, whether it be the terrain on
which the bridge is being built, the location of the bridges anchor(s), what
material is being used to build the bridge, and the overall funding of the
bridge.

 

2.    
What
is a bridge

 

 

The aim of this report is to write
comprehensively about bridges, the different types of bridges and the purpose
of all the different types of bridges. Bridges are designed with certain
purposes in mind, from one extreme to the other. From carrying heavy loads to
carrying lighter loads. Other bridges are built to allow ships and/or other
vehicles to pass under them. This will be explained within the report.

 

1.    
My
introduction into my report on Bridges