Types of bridge
Building your own bridges from lolly sticks
You do not have to use lolly sticks and glue.
- The simplest of all bridges.
- A plank across a stream is a beam bridge.
- Advantages: Simple and cheap
- Disadvantages: Cannot span wide areas.
A modern beam bridge is often made out of reinforced concrete
A load on the bridge squashes the top of the of the bridge deck (compression and tries to stretch the lower part (tension)
The deck can be made lighter and stronger by changing the shape of the beams.
The deck can be supported by piers to help it take more load but this is more expensive if the piers have to be long.
Find out which shape of beam supports the most load
Make different shapes of beam from a piece of A4 paper and support the paper bridge on two piles of books.
Place coins (or anything else of similar size) on the paper bridge until the bridge collapses and record what load mad it collapse.
Keeping it a fair test
- Same size paper for each beam (eg half a sheet A4)
- Same size gap for each beam
- Same distribution on load
The deck will support larger loads if it is supported by an arch
The truss bridge uses a metal (or wood) framework (the ‘trusses) to help support the deck.
West Point Bridge Designer is a program you can download and run on your computer. It lets you design and test a truss bridge.
Download: West Point Bridge Designer 2016 (Windows)
Note that the bridge will not be allowed unless all the Trusses form triangles.
The deck is supported by flexible cables
Can span much larger distances.
Looks attractive and elegant.
- Disadvantages: Costs more to build.