BridgeBridgess

There are three major types of bridges:

arch bridge

suspension bridge

beam bridge

The biggest difference between the three bridge types is the distances they can cross in a single span

(distance between two bridge supports).

up to 7,000 feet

beam bridgebeam bridge

span distances

up to 200 feet

arch bridgearch bridge up to 800 - 1000 feet

suspension suspension bridgebridge

STRESS…STRESS…is a push or pull (a force) that acts on a structure.

There are 4 kinds of stress…

ShearShear

The beam bridgeThe beam bridge

consists of a horizontal beam

The weight on the beam pushes straight down on the beam and the piers (compression force). This makes the beam bend (tension force). The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 200 feet.

supported at each end by piers.piers.

The compressioncompression and tensiontension forces on this bridge are spread across the bars of the trusses.trusses. This reduces the stress on the beam and piers, and enables truss bridges to span farther than plain beam bridges.

The truss bridgeThe truss bridgeis a beam bridge reinforced with triangular supports called

trusses.

Truss Bridge ForcesTruss Bridge Forces

The compressioncompression force is directed down along the curve of the arch to the supports at each end.

Arch Bridge ForcesArch Bridge Forces

CompressionCompression is the only force acting on arch bridges.

The supports, called abutmentsabutments or buttressesbuttresses, push back on the arch and prevent the ends of the arch from spreading apart. This prevents the arch from collapsing.

Arch bridges can be made from many different materials…

stonestone

cast iron or steelcast iron or steel

concreteconcrete

brickbrick

In all suspension bridges, the roadway hangs from massive steel cablessteel cables, which are draped over two towerstowers and secured into solid concrete blocks, called anchoragesanchorages, on both ends of the bridge. The cars push down on the roadway (compression), but because the roadway is suspended, the cables transfer the load (weight) into compression in the two towers. The two towers support most of the bridge's weight.

Suspension Bridge Forces

Lynn Canyon Park suspension bridge, Vancouver

The Akashi-Kaikyo Bridge in Japan is currently the longest bridge in the world, being some four kilometers in total length with a centre span of 1990 meters.

Low-techLow-tech High-techHigh-tech

The cable-stayed bridge, like the suspension bridge, supports the roadway with massive steelsteel cablescables, but in a different way. The cables run directly from the roadway up to a tower, forming a unique "A" shape.

Cable-Stayed Bridges

Sunshine Skyway BridgeSunshine Skyway BridgeSt. Petersburg, Florida and Bradenton, Florida

Cable-stayed bridges, like the Sunshine Skyway in Florida, require less cable and can be built much faster than suspension bridges. Cable-stayed bridges are becoming the most popular bridges for medium-length spansmedium-length spans (between 500 and 3,000 feet).

The Leonard P. Zakim Bunker Hill Leonard P. Zakim Bunker Hill BridgeBridge, part of The Big Dig Project in Boston, is the widest cable-stayed bridge in the world (183 feet wide).

  

The distribution of forces in a cantilever bridge is shown in this demonstration using chairs, poles, counterweights, and humans.

Cantilever Cantilever BridgesBridges

Quebec Bridge

Firth of Forth Bridge, Scotland

A cantilever bridge is a bridge built using cantilevers: structures that project horizontally into space, supported on only one end.

Cantilever bridges link

Which type of stress is acting on the Tacoma Narrows Bridge, shown below?

TorsionTorsion, from high winds, tore this bridge apart in 45 minutes on November 7, 1940. Click on the link below to see a video of the bridge just before it collapsed.

The Tacoma Narrows Bridge Disaster, November 1940

Now that you’ve become an expert on bridges, take the Bridge Challenge. Just

click on the link below.

Bridge Challenge

Great Bridge Great Bridge WebsitesWebsites

Building Big: Bridges

Making the Modern World: Bridge Design

DLT Bridges

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