Bridges Cable Stayed-14 Pages
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Transcript of Bridges Cable Stayed-14 Pages
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Cable-Stayed Bridges
What They Are All AboutCarmen, Sean, Keisha, Ivan
Period 5
Clark Bridge, Alton, ILFigg Engineering Group
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What is a Cable-St ayed
Br idge?
A cable-stayed bridge, one of the most
modern bridges, consists of a continuousstrong beam (girder) with one or morepillars or towers in the middle
Cables stretch diagonally between thesepillars or towers and the beam These cables support the beam
The cables are anchored in the towerrather than at the end
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Tw o Major Classes of Cable-
St ayed Br idges
Different based onhow the cables areattached to the pillars
parallel attachment
design cables are made nearly
parallel by having theheight of attachment on
the pillar be similar tothe distance from thepillar along the roadway
These distances areequal
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Tw o Major Classes of Cable-
St ayed Br idges
Different based onhow the cables areattached to the pillars
Radial attachmentdesign:
the cables all connectto or pass over the top
of the pillar.
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Bui ld ing A Cable-St ayed
Br idge
Many things to think about mathematically:
Horizontal distance from tower to point of attachment
Height of point of attachment above bridge level
Stretched length of cable
Angle between cable and tower
Experiments to consider:
Cable needs to be tested to see how its stretch varies
with the angle to the vertical an experiment to determine how much a length of cable
stretches when it supports a mass
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Bui ld ing A Cable-St ayed
Br idge
The tower of the bridge forms the vertical side of
the right triangle The distance between the points of attachment of
preceding cables on the tower should be equal
Likewise, the points of attachment of the cables onthe beam of the span should be equidistant.
You can calculate the length of the remaining
cables after the first cable has been installed byapplying the proportionality concept or thePythagorean theorem
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Bui ld ing A Cable-St ayed
Br idge
When building a cable-stayed bridge, to
figure out how long the cables need to be,engineers either use scale drawings orPythagoras and trigonometry to find therequired length of cable for each sectionand the angle between the cable and the
vertical
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Tension and Com press ion
Impor tan t !
Tension
Compression
The tower is
responsible for absorbingand dealing withcompression forces
Tension occurs alongthe cable lines
This works because a movingload is not applied evenly acrossthe bridge, and as it moves oneset or the other of the diagonalswill find itself in tension
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Let s Look a t ShapesTriangles are one of the
shapes used by the attachmentof the cables and the beam
this shape is used because ofits ability to transfer the tensionas the moving load goes acrossthe bridge
In this bridge, the distanceof the cable up the toweris equal to the distance
from the tower toconnection point on thebeam and is a 90 degreeangle
A rectangle is
attached at theconvergencepoint of thebeam and towerfor stability
Triangulated bracing between thecables reduces the amplitude ofoscillations
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Visions of Cable-Stayed Bridges
credit to http://brantacan.co.ukand to
Derek Locke.
Maumee River Bridge,Toledo, OH
Figg Engineering Group
Jackfield Bridge inCoalbrookdale
Cable
StayedBridge,Kiev,
Ukraine
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Visions of Cable-Stayed Bridges
The Sunshine Skyway Bridge over Tampa, FLWinner of 17 design awards
Figg Engineering Group
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Let s Look a t Com binat ions o f
Side Lengt hs
1 1/4
1 1/4
1 3/4
1 1/2
1 1
The red triangle has two sidesof 1 and one side of 1 1/2. Ifyou use what we learned about
triangles,
a + b > c; 1+1 > 1 1/2.
The yellow triangleyellow triangle has two
sides of 1 1/4 and one side of 13/4. So, 1 1/4 + 1 1/4 > 1 3/4
Both triangles are very close toan equilateral triangle with all
sides being equal. This is thestrongest triangle.
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St reng t hs of Cable -St ayed Br i dges
Uses a single support only
Well-balanced Cables can be fabricated separately
Horizontal loads are contained within the structure Ideal for use when the river banks are fragile
For example if the banks are alluvial mud
The cables disperse a load across more area easily Cables from nodes on tower to road is variant of a triangle
Greater inherent rigidity of the triangulated cable-
stayed bridges
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Mat h - Helping Me Unders t and
My World
Civil engineers need to use a combination of
geometric shapes to build the strongeststructures Extremely important for engineers to carry out
the technical calculations necessary to plan a
bridge project If the specifications are not correct, the bridge couldcollapse
For medium length spans between 500 and
2,800 feet, cable-stayed is fast becoming thebridge of choice Modern looking geometric shapes (eye pleasing as
well as necessary for strength)
Cost effective