bridge 2.
 
 
 This is the oldest and simplest of the four types of bridges. Originally people used a long piece of stone or tree trunk to cross small streams. Its possible that bridges made of stone slabs found in south west England are the oldest in the world. We don’t know exactly when they were built but they are still standing.
As eight is !laced on theAs eight is !laced on the
beam the com!ressionbeam the com!ression
force shortens the u!!erforce shortens the u!!er
!art. This tension causes!art. This tension causes
the loer !art tothe loer !art to
lengthen. The beamlengthen. The beam
bends and if the !ressurebends and if the !ressure
is too great it ill break.is too great it ill break.
weight weight 
 
 
"an# of the beam bridges that #ou see above roads are"an# of the beam bridges that #ou see above roads are
made of steel or concrete to make sure that the# aremade of steel or concrete to make sure that the# are
strong enough to hold the eight. The si$e of the beam%strong enough to hold the eight. The si$e of the beam%
and es!eciall# its height% controls the s!an of the bridge.and es!eciall# its height% controls the s!an of the bridge.
&ts !ossible to !ut more eight on the beam b#&ts !ossible to !ut more eight on the beam b#
increasing its thickness or height. A frameork or truss isincreasing its thickness or height. A frameork or truss is
used to build high bridges and this structure s!reads theused to build high bridges and this structure s!reads the
tension and the com!ression.tension and the com!ression.
 
 
 
 
 
Cantilever Bridges
Cantileer bridges are made from beams supported on one side only. ! cantileer bridge is a form of beam bridge.
 Two cantileers with a short Two cantileers with a short
beam between them are oftenbeam between them are often
used.used.
 
 
The raila# bridge over the river )orth in *cotland. An e+am!le of
a cantilever bridge.
 
 
This t#!e of bridge as invented b# the ,omans. The# realised that a edge sha!ed stone called voussoirs could carr# heav# loads if built in the sha!e of an arch
-ocking stone
 A wooden framework has to be built to support the stones A wooden framework has to be built to support the stones
while building the arch bridge. After putting the lockingwhile building the arch bridge. After putting the locking
 stone in place the wooden frame is removed and the arch stone in place the wooden frame is removed and the arch
 should stand by itself. should stand by itself.
 
 
 
 
 
 
 
 
 
ging bridges
of alesof ales  Two of the most famous Two of the most famous
hanging bridges in thehanging bridges in the
world are in Wales.world are in Wales. 
 
Severn BridgeSevern Bridge
'anging bridges to carry roads depend'anging bridges to carry roads depend
on tight strong steel cables. $trongon tight strong steel cables. $trong
winds can be dangerous for a hangingwinds can be dangerous for a hanging
bridge and they must be carefullybridge and they must be carefully
designed to cope with stormydesigned to cope with stormy
conditions.conditions.