BSI Education

Bridges and tunnels

Background notes

Structures are all around us and students should be encouraged to identify and recognise the different families of structures that exist. The development of this skill can be practised in product analysis exercises such as the examination of plastic bottles or packaging. For example, the bumps on the base of a 2 litre bottle form a structure that holds the bottle’s shape whilst acting as a strong base on which the bottle can be supported. The structure of an egg carton or the base of a plastic biscuit holder are other examples of where structures are seen. Students need to be reminded that structures are not simply bridges, climbing frames or metal skeletons on which other objects are formed. The principles are often taught in this way but by encouraging discussion and observation, students will develop their knowledge and understanding of the topic further.

Bridges and tunnels

Suggested time: approx 4 hours

Starter – help students to identify five man-made structures and five natural structures. Define a structure as something that ‘has evolved in nature or that has been man-made and resists loads or forces’. Ask students to investigate structures and draw conclusions about their design from teacher-led discussion. For example, exploration of human skeleton, leaf, feather, egg shell, static and dynamic loads. Further exploration of structures could include the framework of a typical house roof, car frame, climbing frame, classroom chair or sports equipment in the school gym. Encourage students to identify where loads and forces are present and whether they are static or dynamic.

Teaching sequence

Activity 1 – discuss with students the basic principles of a structure. For example, a brick wall standing in the wind has force acting on it which would cause it to fall over without support. A beam sticking out from the wall at 90° would be both in tension on top (stretch) and compression below (pushing). This can be demonstrated using a piece of sponge with cuts along its width at either side. Explain to students that a thin beam positioned with its wide edge vertical will be very strong. A ruler shows this idea well and also demonstrates the relative weakness if positioned horizontally. Ask students to identify where this may be practised in the workshop, for example sunken roof, beams and joints across the ceiling.

Activity 2 – help students to identify tension force and compressive force in a number of situations, for example on a picture frame support wire, lamp shade, set of shelves, chair leg, rope bridge, ladder. Ensure students are familiar with frame structures and spend time revisiting the theories for struts and ties, and compressive and tension forces.

Discuss triangulation and the different types of trussed bridges, for example warren girder, pratt truss, howe truss, lattice girder and bowstring and provide students with an explanation of arches and their strength in compression, i.e. key stone. Remind students that tunnels are structures and not holes in the earth and that the outside of the walls create strength. This will prepare students for the following activity.

Activity 3 – in this activity, students can design their own structure, making reference to BSI information to assess its safety, stability and security. Explain to students that their structure is to be a bridge that spans a gap of approximately 380mm (between two desks) and the bridge structure needs to support increasing weights up to a maximum value (alternatively the weights could be added until destruction of the bridge). Remind students that some Standards require testing to destruction.

If possible, students can make use of a 2D designtools programme to a draw a profile of their structure. The profile can then be printed off and material cut accurately from thin balsa wood or kits. Students should design their structure profile on an A3 sheet. The profile then needs to be printed off and used to lay on appropriate materials that have been cut to size. Finally, students can produce two profiles and link them together to make a complete structure.

Students can produce a prototype of their structures in a choice of materials, depending on school resources, for example paper tube kits, Meccano, Lego, spaghetti, cut timber.

Finally, students can design and carry out a test of their structures that replicate Standards procedures (use the links below to help form an appropriate test).

Extension

  • Using a sheet of newspaper and sticky tape, construct a small structure to protect an egg from the impact of a fall from approximately 35cm. This can be varied with a light bulb, or through the use of card or paper, depending on how the structure will be tested.
  • A small group of students could design a trebuchet that can fire a small weight the longest distance using only elastic bands as the power supply.
  • Invite an engineer or architect to class to discuss Standards with which they have had to comply relating to structures they have built.

Homework

  • Ask students to investigate the life and works of a famous architect, for example Gustave Eiffel, Mies van der Rohe, Norman Foster, and devise their own class book of records. This can be used as a wall chart display.
  • Explore the following constructions and complete investigations on the bridges and tunnels from around the world:
    • Millau Viaduct, Norman Foster, France
    • Millennium Bridge, Foster and Partners, UK
    • Clifton Suspension Bridge, Isambard Kingdom Brunel, UK
    • Golden Gate Bridge, Joseph B. Strauss, US
    • Brooklyn Bridge, Washington Roebling, US
    • Eurotunnel