Bridges

Where and why do we use bridges (over rivers, valleys; for road, rail and foot transport)? What are they made of (originally fallen trees wood, stone, hemp and bamboo; nowadays concrete, steel)? What types of bridge are there (arches, suspension, cantilever, box girder)? The semi-circular arch was perfected by the Romans; the box girder, strong hollow blocks, was first used by Robert Stephenson over the Menai Straits in Wales.

Famous landmarks

Are there any bridges locally? Why are they needed? What would happen if they were closed? Do you know of any famous bridge landmarks (Sydney Harbour, Golden Gate, San Francisco; Tower Bridge, London; Ironbridge Shropshire)?

Concrete

What is concrete and why is it so widely used (tough, fireproof material made of sand, gravel, cement and water)? Pre-stressed concrete contains steel cable. Where is concrete used (roads, buildings, as well as bridges)?

Build your own

Make a simple bridge (for example, a ruler between two tables). Try a more complicated one (suspension bridge with string and straws; arch bridge with wooden blocks; cantilever bridge with spans between several pillars). Where do the major pressures come on your bridges?

Ted Wragg is professor of education at the University of Exeter