4.2.7 Strong and stable

Inquire

In this topic, you will explore how structures can be built to distribute force so that they are strong and stable. You will look at structures that have been built throughout history, and see how humanity has learnt to manage force in more sophisticated ways. Finally, you will explore what the structures of the future could look like!

Here are some images of some famous structures. Can you name them?

With a partner, for each image:

observe the form of the structure. What does it consist of?

analyse the function of the structure. How does it stay strong and stable, do you think?

ask a question. What does it make you wonder?

 Throughout history and across cultures, humans have refined the ways in which they build structures. The structures in the images above are all relatively massive, but compare to the image below of a Mongolian yurt .

Yurts (in Mongolian, "Gher") have been used by Mongolian nomads for centuries to the present day. They are lightweight and portable - they can be taken apart and rebuilt wherever the nomads travel. The yurt is strong enough to withstand the fierce winds of the Mongolian plains, and warm enough to keep its occupants warm in the freezing winter.

All these structures use particular forms to distribute and manage force. We can analyse the structures in terms of some fundamental structural forms that are found around the world.

Act

Read and watch the demonstrations about the different structural shapes and how they distribute force in different ways. Identify the forces in the structures.

You can find explainers hidden at the end of this activity.

1. Simple beam cantilever

A beam is any straight, rigid piece of a structure that crosses over a gap.

A cantilever is a beam that is only supported at one end.

Watch what happens when we apply load to the cantilever.

Describe the way the cantilever deforms under load.

Suggest the way the forces are distributed in this structure.

2. Arch

An arch is a curved structure that can support load.

Notice that the ends of the arch need to be fixed into the ground or pushed against a 'foot' (called an abutment).

Watch what happens when we construct an arch from wooden blocks.

Describe the way the arch deforms under load.

Suggest the way the forces are distributed in the arch.

3. Suspension bridge

Triangular structures operate in some ways like an arch, but they are usually built from rigid materials that can sustain both tension and compression.

Watch what happens to the suspension bridge when load is applied.

Describe the way the bridge deforms under load.

Suggest the way that the shapes in the structure distribute force.

Challenge and extend

Tensegrity structures seem to work like magic. The Kurilpa bridge in Brisbane, Australia is an example of a full-scale tensegrity structure. The bridge seems to support itself with no pillars in the central section:

Watch this video from Steve Mould Science about making a tensegrity table.

Describe the way the table uses tension forces to give the appearance of 'floating.'

... and here is a tensegrity structure I built at home! Try it for yourself! I used lollipop sticks, nylon thread and a hot glue gun.