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Introduction to Bridges

Loads on Bridges, and Types of Bridges

Ayesha Tarar

on 27 September 2012

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Transcript of Introduction to Bridges

What is a bridge?
Why are bridges important to us? Introduction to Bridges A structure that spans and provides passage over a gap or barrier. Bridge: Why are bridges important to us? weight distribution throughout a structure
loads caused by wind, earthquakes, and gravity
i.e. affect how weight is distributed throughout a structure What is a load? Load: A pressing force that squeezes a material together Compression Force: Tension There are two major forces that act on a bridge at all times Any action that tends to maintain or alter the position of a structure. The force that expands or lengthens the bridge Beam Bridge
Truss Bridge
Arch Bridge
Suspension Bridge
Swing Bridge
Lifting Bridge
Cable-Stayed Bridge Types of Bridges: A beam bridge is flat across and supported at the ends. Beam Bridge The weight of the beam pushes straight down on the piers.

The farther apart its piers, the weaker the beam becomes.

This is why beam bridges rarely span more than 250 feet. Beam Bridges Truss design is used to strengthen beam bridges

Consists of an assembly of triangles as their main element

Commonly made from a series of straight steel bars Truss Bridge Beam bridges are categorized by the design, location and composition of the trusses used.

These are a few common types: Beam Bridges: Arch bridge is one of the oldest form of bridge.

Developed by the Ancient Romans

Thousands of years ago, built out of stone Arch Bridge: Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet. Arch Bridge Span great distances and support enormous weights.

Two towers above the bridge’s surface that carries the cables the hold the bridge up.

Built with:
steel cables
concrete anchorages
steel towers
steel trusses The suspension bridge The arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end.

The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart. Forces on Arch Bridge can span 2,000 to 7,000 feet - way farther than any other type of bridge!

Most suspension bridges have a truss system beneath the roadway to resist bending and twisting. Suspension Bridge: In all suspension bridges, the roadway hangs from massive steel cables, which are draped over two towers and secured into solid concrete blocks, called anchorages, on both ends of the bridge. Forces on the Suspension Bridge: Modern Suspension Bridges http://www.pbs.org/wgbh/buildingbig/bridge/index.html The cars push down on the roadway, but because the roadway is suspended, the cables transfer the load into compression in the two towers. The two towers support most of the bridge's weight. World's Largest Suspension Bridges: No. Bridge Span (m) Country year
1 Akashi-Kaikyo 1991 Japan 1998
2 Great Belt East 1624 Denmark 1998
3 Runyang South 1490 China 2005
4 Humber 1410 UK 1981
5 Jiangyin 1385 China 1999
6 Tsing Ma 1377 China 1997
7 Verrazano-Narrows 1298 USA 1964
8 Golden Gate 1280 USA 1937
9 Höga Kusten 1210 Sweden 1997
10 Mackinac 1158 USA 1957 Swing Bridge: A swing bridge is a movable bridge that allows traffic to cross in its closed position and when a water vessel needs to pass the bridge, road traffic is stopped (usually by traffic signals and barriers), and then motors rotate the bridge approximately 90 degrees horizontally about its pivot point. Lifting Bridge: A vertical-lift bridge or lift bridge is a type of movable bridge in which a span rises vertically while remaining parallel with the deck. Cable-Stayed Bridge A cable-stayed bridge is a bridge that consists of one or more columns (normally referred to as towers or pylons), with cables supporting the bridge deck.

Compared to other bridge types, the cable-stayed is optimal for spans longer than typically seen in cantilever bridges, and shorter than those typically requiring a suspension bridge
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