Building BridgesBuilding Bridges

Physics of Bridge Building

• Three basic types– Span: simplest form – beam supported on vertical

supports. Also truss bridge, cantilever bridge– Arch: compression forces push outwards

horizontally against the supports– Suspension: main cables anchored to towers,

suspender cables support roadway. Cables are in tension.

A bridge in New South Wales, Australiaexample of truss system (rigid triangular

framework)

Forth Rail Bridge example of cantilever bridge

Clachan Bridge, Isle of Seil“The Bridge over the Atlantic”

example of stone arch bridge

Pont Du Gard Roman Aqueducttriple arch bridge

Corrieshalloch GorgeSuspension Bridge

Golden Gate Bridge San Fransiscoexample of suspension bridge

Akashi Kaikyo Bridge Japan(Longest single span in the world)

3-span 2-hinged truss-stiffened suspension bridge

Oresund Bridge, linking Sweden and Denmark

Lake Pontchartrain CausewayNew Orleans, LA

Some Physics Considerations• Choice of material

– Strength:

in tension, compression, bending, torsion

• Shape of framework – (why triangular?)

• Testing the design – use of models– Physical scale models– Computer models

Tacoma Narrows Bridge

Tacoma Narrows Bridge

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

Tacoma Narrows Bridge

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

Tacoma Narrows Bridge

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

Millenium Bridge, River Thames, London

Millenium Bridge, River Thames, London

The Bridge Competition

• You are a team of bridge designers working for the internationally known bridge building company ………………………………………….(choose a name for your company)

• Your task is to design and build a single span bridge to the specifications given on the sheet, using the materials provided.

• The bridges will be judged on three categories

– Technical Merit– Artistic Impression

– Weight

Technical specifications

>90cm

>10cm

<30°

Coke can (full)

Makes bridge bend by less than 2cm at the centre

Single-track car deck (made from card)