Bridges Cable Stayed-14 Pages

8/14/2019 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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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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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

Bridges Cable Stayed-14 Pages

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