Key Stage 2 design and technology · Technical knowledge

KS2 strengthening and reinforcing structures: a guide for parents

In Key Stage 2 design and technology, children apply what they know about making structures stronger, stiffer and more stable to more complex structures, such as bridges, towers, shelters and frames. They also choose from a wider range of materials and components according to their properties and how they look. The key idea is that shape and construction matter at least as much as how much material you use.

Strengthening and reinforcing structures, explained

In Key Stage 1 children explore how simple structures can be made stronger, stiffer and more stable. In Key Stage 2 the structures are larger and more demanding, and the curriculum asks pupils to apply their understanding of how to strengthen, stiffen and reinforce them. Strong means resisting breaking. Stiff means resisting bending. A structure may need to be one, the other or both, and children learn to say which they need, and why, for a given job.

Children meet two main kinds of structure. Frame structures are built from a skeleton of struts, like a bicycle frame, a climbing frame or an electricity pylon. Shell structures are hollow surfaces that carry the load themselves, like an egg, a cycle helmet or a cardboard box. Complex structures often combine the two, such as a bridge with a deck, supports and cross-bracing. Children also learn that structures face forces: a load pushing down, parts being squashed (compression), parts being pulled (tension) and beams bending.

The main techniques are surprisingly simple. A triangle cannot change shape unless one of its sides changes length, whereas a square or rectangle made with pinned corners can easily collapse sideways, so diagonal braces and triangles are used to make frames rigid. Corner pieces called gussets strengthen joints. Folding or corrugating a sheet of paper or card makes it far stiffer without any extra material, and so does rolling it into a tube. Gluing several layers together (laminating) also makes card stiffer and stronger. A beam that is deeper from top to bottom resists bending much better than a flat one of the same weight. Joints are usually the weakest point, so teachers show children how to overlap pieces and reinforce corners rather than relying on a blob of glue.

The second objective is choosing a wider range of materials and components according to their functional properties and aesthetic qualities. Functional properties include strength, stiffness, hardness, durability and being waterproof. Aesthetic qualities include colour, texture and finish. Construction materials such as wood, card, plastics and dowel are common, but the objective also covers textiles and ingredients, so some schools apply it to a fabric shelter or tent, or to a structure made with food. Which materials a class uses is the school’s choice, but children are expected to give a reason for their choice rather than picking what looks nicest.

Design and technology classes treat structures as a cycle: research, design, build a prototype, test it, then improve it. The testing needs to be fair, which means the same size of material, the same gap to span and the same way of adding a load each time. Children measure how much a structure carries, or how far it bends, and compare designs. They often find that their first idea fails in an interesting place, and the next version is better because of it.

Words your child will hear

Frame structure: A structure built from a skeleton of connected bars or struts, such as a pylon.
Shell structure: A hollow structure whose outer surface carries the load, such as an egg or a box.
Load: The weight or force a structure has to carry.
Brace: A diagonal piece that stops a frame from folding sideways. Triangles are the basic shape of bracing.
Reinforce: To make a weak point stronger by adding material, a support or a different shape.
Compression: A squashing force that pushes parts of a structure together.
Tension: A pulling force that stretches parts of a structure.

What the National Curriculum says

The programme of study for Key Stage 2 says:

When designing and making, pupils should be taught to apply their understanding of how to strengthen, stiffen and reinforce more complex structures
When designing and making, pupils should be taught to select from and use a wider range of materials and components, including construction materials, textiles and ingredients, according to their functional properties and aesthetic qualities

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

Try it: making a paper bridge stiffer

Two piles of books stand 20 cm apart. You have identical sheets of A4 paper. Which shape will make the stiffest bridge from a single sheet?

Plan a fair test. Use the same size of paper, the same 20 cm gap, the same overlap on each side (about 2 cm) and the same load. Add identical coins one at a time to a small paper cup in the middle of the bridge, and record how many it carries before it sags badly or collapses. Lay the paper with its long side across the gap. Change only the shape of the paper.
Test the flat sheet. This is the control. It is very likely to sag almost at once, because a thin flat sheet resists bending very badly. Record the result and the number of coins.
Test a folded sheet. Fold the paper into a concertina along its length, with folds about 1.5 cm wide, and lay it across the gap. Each fold works like a small beam, and the sheet is much harder to bend. Record the number of coins.
Test a tube and a triangular tube. Roll a sheet into a long tube, then fold another into a long triangular tube, and fasten each join with a little tape. A tube spreads the paper out away from its middle, which makes it much harder to bend. Record both.
Compare and reinforce. Put the results side by side. Then add a reinforcement, such as sticking card gussets or a second folded layer, retest the best shape and see whether it carries more.

Exact numbers depend on the paper and the coins, so each child’s results will differ, but the flat sheet will carry the least and the folded and rolled shapes will carry far more, even though every sheet weighs the same. The conclusion: with exactly the same amount of material, changing the shape makes a structure much stiffer, which is why stiffened shapes are used in cardboard boxes, drinks cans and bridges.

Common mistakes and how to help

Believing that more material always makes a structure stronger

Everyday experience says that thick things are strong and thin things are weak, so the response to a weak design is to add more.

What helps: Use the same-sheet test above. When the same sheet of paper becomes far stiffer just by being folded, children see that shape counts.

Using “strong” and “stiff” to mean the same thing

In everyday language both mean “hard to damage”. In design they are different properties.

What helps: Give examples: a plastic ruler bends a long way without breaking, so it is fairly strong but not very stiff. A stick of dry spaghetti hardly bends at all, so it is stiff, but it snaps easily, so it is not strong. Ask which property the structure needs.

Thinking that a square or rectangular frame is rigid

Squares look sturdy and are easy to draw, but with pinned or loosely glued corners they fold into a diamond when pushed sideways.

What helps: Make a square from four strips of card and paper fasteners, push it, then add a diagonal strip. The wobble disappears. This is why you see triangles in pylons and roof trusses.

Relying on lots of glue to hold joints together

A big blob of glue feels reassuring, but wet glue slides, takes a long time to set and gives a joint that is bulky and weak.

What helps: Use a larger overlap, a small amount of glue, a gusset in the corner and enough drying time. Test the joints before testing the whole structure.

How to help at home

Run the paper bridge test. Span a gap between two piles of books with a sheet of paper and see how many coins it carries when flat, folded, and rolled. Check your results together and explain why they differ.
Wobble test a frame. Make a square from four straws or card strips joined with paper fasteners, push it sideways, then add one diagonal and push again. Children enjoy seeing a wobbly shape lock rigid.
Find the stronger direction. Cut two strips of corrugated cardboard, one with the ridges running along its length and one across. Bend each and feel which resists more. Scissors are fine; leave knives to adults.
Spot structures on a walk. Look for frames and shells, and for triangles in gates, pylons, roofs, bridges and bike frames. Stay on pavements and paths. Ask which parts are being squashed and which are being pulled.
Choose a material and say why. If your child is making a shelter, a den or a model, ask why they picked the material, using words like stiff, light, waterproof or flexible. A reason that mentions a property is what teachers want to hear.

Builds on

Key Stage 1: Strong, stiff, stable structures
Key Stage 1: Levers and sliders
Key Stage 1: Wheels and axles

Leads on to

Key Stage 3: Properties of materials
Key Stage 3: Beams, frames and forces
Key Stage 3: Gears, levers and mechanisms
Key Stage 3: Electronic circuits and systems
Key Stage 3: Sensors, actuators and microcontrollers