Strength of Shapes — Part II!

The Challenge: Using only 3 sheets of A4 paper, create a bridge strong enough to hold up a tin of beans!

3 min readJun 2, 2020


You will need:

· Something to place your bridge onto — books are good!

· 3 sheets of A4 paper

· Tin of beans, or similar.

1) Place your books so that there is a gap of 20cm between them;

2) Create your bridge using only the paper — sticky tape not allowed!

3) Place your bridge onto the supports (books);

4) Put your tin on the bridge;

But, a couple of other things:

5) No props are allowed underneath the bridge!


6) The whole of the tin must be above the gap between the books!

We’d love to see your attempts — good luck!!

How we did it

In short, we used the strength of triangles!!

First, we placed the sheets of paper on top of each other:

We then folded them back and forth to make peaks and troughs — these are called “corrugations”. You can see them in the photo below and you’ll notice they form triangular shapes:

We then placed our bridge between the supports and placed the tin on top. It worked — all thanks to triangles!

Why are triangles so strong?

Well, to put it simply, when a force — in our case the weight of the tin — is applied to the point of a triangle, rather than bend, the triangle keeps its shape. And by creating lots of little triangles, we can apply quite a lot of force onto materials that we tend to think are quite weak — such as paper!

Try the challenge again and see whether making more corrugations can hold more weight. But please don’t stack things too high!!

Did you know?

Because of their strength, triangles are used by engineers a lot — particularly when building bridges. Can you see the triangular shapes in the photographs of the bridges below?



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