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Different structures have different functions or purposes. The individual parts of any structure need to be selected, arranged and fixed together carefully to make sure the structure carries out its function.

There are two main types of structures.

• A frame structure is a made from different parts joined together to make them stable and strong. Frame structures can be as simple as a garden fence or something much more complex such as a skyscraper.

• A shell structure has a thin curved outer layer and is hollow. These structures often are used to hold or protect something. They usually have only a small number of joins or no joins at all.

Find out more about shell structures and frame structures in this video.

A fence

A fence is a simple frame structure as it only has a few parts. Its function is to create a boundary without needing any extra support to stay upright.

A fence is strong and stable due to the vertical posts that are fixed into the ground. Burying these posts further into the ground makes the fence more stable. If they are placed too far apart they will create a weak fence.

Horizontal rails or panels are attached to the vertical fence posts. Nails or screws are added to create joints.

A suspension bridge

Frame structures can be used to make a suspension bridge. It's function is to cross large areas of land or water, carry heavy vehicles and remain standing in difficult environments.

Suspension bridges often have two or more towers and a deck, where the road is placed. This hangs from strong wires called cables. A force called tension is used by the structure. This means the bridge is pulled tight so the weight on the bridge is spread as the cables pull and tighten.

A skyscraper

A skyscraper is a complex frame structure. It is a very tall building with many stories, or floors. Its function is to provide a large amount of space to work or live in, while only taking up a small area on the ground.

Before the 19th century, tall buildings would have been made with brick or stone walls. The heavy weight of each floor made it impossible to build very tall buildings.

In the 19th century, steel, which is much lighter and stronger, made the building of modern skyscrapers possible. It is now used to construct extremely tall buildings.

See if you can identify the parts of a frame structure.

A bicycle helmet

A bicycle helmet is a simple shell structure. The function of a bicycle helmet is to help protect a cyclist’s head.

The thin curved outer layer of the helmet is usually made from plastic, because it is hard and strong.

Plastic is also light, easy to shape and cheap, making it a good choice of material to construct a helmet from.

An aeroplane's body

The tube that forms the main body of an aeroplane is an example of a shell structure.

The tube is filled with seats, equipment and the pilot's cockpit. Its function is to remain strong and protect whatever the plane is carrying.

The outer shells of most aeroplanes are made from a metal called aluminium. This metal is strong, lightweight and is resistant to rust.

Find out about some famous frame and shell structures in this activity.

Test your knowledge of frame and shell structures in this quiz.