Building 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, Australia
example 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 Aqueduct
triple arch bridge
Corrieshalloch Gorge
Suspension Bridge
Golden Gate Bridge San Fransisco
example of suspension bridge
Akashi Kaikyo Bridge Japan
(Longest single span in the world)
3-span 2hinged trussstiffened
suspension
bridge
Oresund Bridge,
linking Sweden
and Denmark
Lake Pontchartrain Causeway
New 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.
Tacoma Narrows Bridge
QuickTime™ and a
decompressor
are needed to see this picture.
Tacoma Narrows Bridge
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
Single-track
car deck (made
from card)
Coke can (full)
Makes bridge
bend by less than
2cm at the centre
<30°
>10cm
>90cm