Childrens Illustrated Encyclopedia

82

Bridges

Arch bridge

A curved arch firmly

fixed to the banks

supports the bridge.

Arches are very

strong structures.

rAising the deck

Long lengths of cable, called

hangers, are fixed to the

suspending cables. the deck of

the bridge is made in sections

elsewhere. the sections are taken

to the bridge, lifted into position,

and attached to the hangers.

trAveL on LAnd is easier, safer, and

more direct with bridges. Motor vehicles

and trains can speed over lakes, rivers,

and deep valleys. bridges raise busy

roads over others so that the roads do

not meet. Major roads and railroads

enter cities on long bridges sometimes

called viaducts. Footbridges allow people

to cross roads, rivers, and railroads safely.

the first bridges were made by placing

tree trunks across rivers, and laying flat

stones on rocks in shallow streams. Later,

people made rope bridges by weaving

plants together and built stone bridges

with strong arches. similar kinds

of bridges are built today with

concrete and other strong, modern

materials instead of natural

materials. steel beams and cables

are used as supports. the world’s

longest bridge is the danyang–

kunshan grand bridge in china.

it is 102 miles (165 km) long.

the Longest spAns

the Akashi-kaikyo bridge in

Japan, has the longest single

span of any bridge. the

central span is 6,532 ft

(1,991 m) long. the bridge

was completed in 1997. the

humber bridge in england

(left) has the seventh-longest

single span, at 4,626 ft (1,410 m).

Aqueducts

bridges that carry water

are called aqueducts. the

aqueduct may be part of a

canal, or it may bring

a water supply to a town or

city. the romans built

many aqueducts with high

stone arches, several of

which survive today.

suspension bridge

A pair of long steel cables fixed

to high towers suspends the

roadway. suspension bridges

can span the longest distances

because they are lightweight.

cAntiLever bridge

each half of the bridge

is balanced on a support

in the river. Where the two

halves meet, there may be

a short central span.

cAbLe-stAyed bridge

sets of straight steel cables

attached to towers hold up the

bridge from above.

kinds oF bridges

there are various ways of building bridges

to span rivers and other barriers. Most

bridges rest on solid supports. pontoon

bridges, which are found on some lakes,

float on the surface of the water.

buiLding A suspension bridge

the supports and ends of the bridge are built

first, firmly fixed in the ground or the riverbed

and banks. the deck of the bridge carrying the

road or railroad is then built out from the ends

and supports or lifted

on to them.

suspending the cAbLes

the towers of a suspension bridge

are built first. steel ropes are then

placed over the towers. A machine

moves along the ropes, spinning

long lengths of wire into strong

steel cables.

beAM bridge

several columns in the riverbed or the

ground support the bridge

from beneath. sometimes

the bridge is made

of a hollow girder

through which cars

and trains can run.

Find out more

Architecture

ports and waterways

bAscuLe bridge

sections of the bridge tilt like a

drawbridge, allowing ships into port.

tAcoMA bridge disAster

the tacoma narrows bridge in

Washington, united states, failed

in 1940. the wind made the bridge

twist back and forth until the deck

gave way. nobody was hurt.

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