The big idea: Every object that holds a shape against a load is a structure — a bridge, a chair, a bicycle, a bone, a leaf.
Three questions to analyse one
- What load does it carry?
- What path does that load take to the ground?
- What stops it collapsing?
Three ways of carrying a load. Step through and notice that natural and human-made examples appear in every one.
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| Natural structure | The principle | Where a designer uses it |
|---|---|---|
| Honeycomb | Hexagonal cells give huge stiffness for almost no material, because the walls are loaded in their own plane | Aircraft floor panels, doors, bicycle wheels, packaging |
| Bone | Dense on the outside where bending stress is highest, spongy in the middle where it is nearly zero | Tubes rather than bars; ribbed mouldings; the I-beam |
| Eggshell | A thin curved shell carries load in compression through its surface and needs no internal support | Hard hats, domes, car monocoques, kettle bodies |
| Tree trunk | A tapered column, thickest at the root where the bending moment from wind is largest | Lamp posts, masts, cantilever brackets, table legs |
| Spider web | Pure tension throughout — no member is ever pushed, so nothing can buckle | Cable roofs, suspension bridges, bicycle spokes, tents |
Why the comparison is worth making: Natural structures have been tested by selection for a very long time, under real loads, with a hard limit on material.
So when a natural structure and a human-made one solve the same problem the same way, that is evidence the solution is efficient — not a coincidence worth admiring.
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Four questions, in order
What loads does it carry?
Its own weight, whatever is put on it, and whatever the environment adds — wind, snow, a person leaning, a vehicle stopping.
Where does each load go?
Follow it from where it is applied, through every member, to the ground. Any member the path does not use is carrying nothing.
Is each member pushed or pulled?
Compression members must be short or fat or they buckle. Tension members can be thin, and a cable is the extreme case.
What stops it moving?
Triangulation, a fixed joint, a wide base, a heavy foot, a fixing into a wall. Something must resist rotation as well as sliding.
The question that reveals most: Which members are doing nothing?
A member that carries no load is mass, cost and a joint that can fail, for no return. Finding one in an existing product is usually the fastest improvement available.
How this is tested — analysing and interpreting human-made and natural structures. It comes up two ways:
Paper 1 — multiple choice
- Identify the load path through a drawn structure.
- Match a natural structure to the principle it demonstrates.
Paper 2 — analysing a product
- Analyse a named structure: its loads, its load path and what stabilises it.
- Explain what a designer can take from a natural structure.
The trap: Describing what a structure looks like. An analysis follows the LOAD — where it enters, which members carry it, and how it reaches the ground.
Analyse a domestic step-ladder as a structure, and identify one principle it shares with a natural structure.
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