S1 Technology
Structures
Experiences and Outcomes
TCH 3-01a
‘From my studies of technologies in the world around me, I can begin to understand the relationship between key scientific principles and technological developments.’
St. Maurice’s High School

Bridges
Bridges provide a useful means of crossing river valleys, estuaries, gorges, roads, railways and even seas. Most bridges are fixed but some can be raised or swung round to allow tall traffic, such as ships to pass safely underneath.
Engineers take great pride in the bridges they build and very often the bridge takes on national significance, for example the Fourth Rail Bridge.
The first bridges built by primitive people consisted simply of a tree trunk thrown across a stream.
Since then more and more elaborate bridges have been built to span wider gaps.
With all bridges, the problem for engineers is to design structures which won’t sag or crack under the weight they have to carry.
Task 1
Using a piece of A5 paper, construct a bridge which will support a weight over a span of 150mm.
Describe how well your bridge worked.
Now let’s look at how engineers have solved the problem of spanning a large gap.
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Types of Bridges
There are six basic types of bridge
1.
The Beam Bridge. Sometimes called the Girder Bridge.
2.
The Arch Bridge
3.
The Suspension Bridge
4.
The Cantilever Bridge
5.
The Cable-Stayed Bridge
6.
The Truss Bridge
Beam Bridge
This is the simplest type of bridge. Rigid beams or girders made from wood, iron, steel or steelreinforced concrete are laid across the gap to be spanned. The downward force of the bridge’s weight is supported by the ground. If the gap is too wide to be spanned by a single beam then piers are built at intervals to support several beams laid end to end.
Task 2
Using a piece of A5 card and some glue construct a Beam bridge. You should find it is much stronger than the paper one you made.
How did it perform?
Arch Bridge
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In an Arch bridge the weight is supported and spread to the sides by an arch. This arch pushes onto the ground at each end of the bridge. The arch can be made of either brick, stone, concrete, wood, iron or steel.
Ponte Saint Angelo
Task 3
Using the stones and the wooden scaffolding, construct an Arch Bridge.
Suspension Bridge
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Very large spans are often crossed by Suspension Bridges. In this type of bridge the deck is suspended from steel cables which hang between tall towers. To take the strain, the ends of these cables are anchored in the banks. Old suspension bridges sometimes have chains rather than cables.
One of the most famous suspension bridges is the Golden Gate Bridge between San Francisco and
Mar County.
San Francisco Bridge
Task 4
Build a simple Suspension Bridge.
Cantilever Bridge
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In cantilever bridge construction, long rigid sections are used as in a beam bridge. But instead of being attached to the river bank it is attached to cantilevers.
Quebec Bridge
Task 5
Using the apparatus make a cantilever.
Cable Stayed
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A Cable-Stayed bridge is a bridge that consists of one or more towers with cables supporting the deck.
Vidyasagar Setu, India
The Truss Bridge
A truss bridge is a bridge composed of connected pieces of metal. Truss bridges are one of the oldest types of modern bridges. A truss bridge is economical to construct owing to its efficient use of materials.
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Assessment
1.
Report on Thomas Telford
2.
Building of paper and card bridges
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3.
Investigating different types of bridges
4.
Quiz on bridges
5.
Building of Roman Arch. Pupils work in groups of four for this exercise.
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