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Bridges

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by

Andrew Martin

on 23 April 2014

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Transcript of Bridges

New River Gorge bridge
Types of Bridges
*Suspension
*Truss(Cantilever)
*Beam
*Arch
*Draw
Bridges
The Basics
Suspension Bridges
Can span 2,000 to 29,000 feet. Way longer than any other type of bridge! Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.
Bridges are used to cross many things such as rivers, ravines, and valleys. There are different kinds of bridges to. Different bridges need to be built differently.
The Golden Gate Bridge
Location: San Francisco and Sausalito, California, USA
Completion Date: 1937
Cost: $27 million
Length: 8,981 ft or 2737.4m
Purpose: Roadway
Materials: Steel, concrete
Engineer: Joseph B. Strauss
Firth of Forth
Truss (Cantilever) Bridges
The Truss bridge consists of an assembly of triangles. Every bar in a Truss bridge experiences some kind of pushing or pulling. They can be 500-9,000 ft. long.
Arch bridges
Bibliography
http://www.pbs.org/wgbh/buildingbig/bridge/index.html
Beam Bridges
Have a kind of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers. This is why beam bridges rarely span more than 250 feet.
Arch bridges have great natural strength. Romans built arches out of stone thousands of years ago. Most arch bridges are made of steel and concrete today. They also span up to 800 feet on average without modern engineering. With modern engineering, its average is 1,000 feet.
Location: Cape Charles and Virginia Beach, Virginia, USA
Completion Date: 1964
Cost: $200 million
Length:79,200ft or 24140.16m
Type: Beam, tunnel
Purpose: Roadway
Materials: Steel, concrete
Engineer: Sverdrup & Parcel
Chesapeake Bay Bridge-Tunnel
Vital Statistics:
Location: South Queensferry and North Queensferry, Scotland
Completion Date: 1890
Cost: $15 million
Length: 8,276 ft or 2,522.53m
Type: Cantilever
Purpose: Railway
Materials: Steel
Longest Single Span: 350 feet (center span)
Engineer(s): Benjamin Baker, John Fowler
Draw Bridges
Draw bridges are used when there are large boats coming through. They were once used in castles to keep intruders out because the bridge could be drawn up to block the entrance. Modern day draw bridges can get up to 333 ft.
Charles Berry Bridge
Location: Lorain, Ohio
Completion Date: 1930's
Cost: $1,741,499.60
Length: 1,052ft or 320.65m
Purpose: Roadway
Materials:Concrete and Steel
Engineer: ODOT(Ohio Department of Transportation)

http://www.loraincounty.us/Department/Cares-Berry-Bascule-Bridge.aspx
http://www.dot.oh.us/districts/DO3/Documents/Charles

The Process of Building a Suspension Bridge
Firstly the anchors that are going to support the cables must be set into the ground. They are normally made of concrete and need to be set into the ground and need to be set into solid ground for these support a big portion of the deck. The next part of the process is to construct the foundations for the towers. If the towers are to be constructed in water the water needs to dammed and pumped out. This is not the only problem though, as wherever the towers are going to be, the foundations need to be on solid ground as it is the towers are under compression and transfer the applied loads into the ground. The third step is to erect the towers. This is a key stage as suspension bridges are renowned for spanning long distance and the higher the towers are, the longer the bridge will be able to span.
www.academia.edu
Building a Suspension Bridge Continued
Next the main cables need to be stretched between the two anchor points and over the two towers. At the top of the two towers sit two saddles. These are joints that the cable can run freely over and they allow for slight movement in the bridge. If this movement was not allowed for then when the bridge moved the load would no longer run down the towers and there would be a risk of the bridge collapsing. The two main cables are made from twisted steel cable and the size of them will depend on factors such as the load of the bridge needs to take and the span of the bridge. Following this a truss system is attached to the main cable. These are put in place to stiffen the cable and make sure that in the wind the cable doesn't move. Smaller cables are then attached which are known as suspenders. These are joined to the trusses and are the cables that run from the main cable down to the support deck. The final part is the process of fixing the deck to the vertical cables and applying the finish to the deck.
Quick Facts
Building a Suspension Bridge Continued
When this has been completed the load path should be as follows. The load on the deck firstly goes into the deck. From the deck, the load will travel into the main cable. The load in the cable will then travel to the top of the two towers, through the saddle and down the towers into the ground. So as you can see the construction process of building a suspension bridge is is the reverse of the load path. In principal the stages are straight forward but later you will see some risk and construction problems involved in the construction of suspension bridges.
Have you ever seen gaps in a bridge and wondered why they are there ? Well they are there for a reason without them the bridge is more likely to collapse. They are made for changes in temperature Because when bridges,roads, metal etc. get hot they expand. But how ever when they get cold they contract.
The Construction of A Draw Bridge
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