Structures · Grade 3
A structure is anything that holds its shape and supports a load, from a bridge or a tower to an egg or a bird’s nest. Engineers make structures strong, stable and light by choosing the right shape as well as the right material.
Key facts
- Frame structures are skeletons of parts joined together (pylons, bicycle frames, roof trusses). Shell structures are hollow outer layers (eggs, cans, helmets). Solid structures are built up from solid material (walls, dams).
- Compression squashes, tension stretches and torsion twists. A strut is a part in compression; a tie is a part in tension.
- A triangle is rigid: it cannot change shape unless a side bends or breaks. A square frame can be pushed into a slanted shape.
- Adding a diagonal strut turns a square into triangles (triangulation). Gussets (corner plates) make joints stronger.
- Folding (corrugating), rolling into tubes and making arches all make thin materials much stronger.
- A structure is stable when it has a wide base and its heavy parts are low down.