How do structures resist forces, and how can they be made stronger?
The forces of tension, compression, bending, shear and torsion, how structures resist them, and ways to reinforce and stiffen a structure such as triangulation, webbing and folding.
A focused answer to the WJEC GCSE Design and Technology content on structures, covering the forces of tension, compression, bending, shear and torsion, how structures resist them, and ways to reinforce and stiffen a structure such as triangulation, webbing, lamination and folding.
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What this topic is asking
WJEC's content includes structures and the forces that act on them. You need to name the five forces, explain how structures resist them, and describe ways to make a structure stronger or stiffer. This is core knowledge for Unit 1 across all three routes, and it overlaps with mechanical devices and material properties.
The five forces
How structures resist forces
Reinforcing and stiffening a structure
Why a triangle is special
A rectangle made of four members joined at the corners can be pushed sideways into a parallelogram, because the joints can pivot. A triangle cannot change shape unless one of its sides changes length, so it stays rigid under load. This is why adding a single diagonal to a square frame, splitting it into two triangles, transforms a floppy frame into a rigid one.
Try this
Q1. Name the five forces that act on structures. [5 marks]
- Cue. Tension, compression, bending, shear, torsion.
Q2. State one way to stop a square frame being pushed out of shape. [1 mark]
- Cue. Add a diagonal member (triangulation).
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC-style4 marksName the forces acting on a shelf bracket and explain how the bracket is designed to resist them.Show worked answer →
A four mark application question. A loaded shelf puts the bracket under bending: the top edge is in tension (being stretched) and the lower part nearest the wall is in compression (being squashed), with a turning effect trying to pull the fixing out (2 marks for naming the forces correctly). The bracket resists them by being made of a strong, stiff material (such as steel), often with a diagonal strut (triangulation) between the wall and the shelf to carry the load in compression and stop the bracket bending (2 marks). Markers reward correct forces plus a design feature. A common error is to call the whole bracket simply "under pressure".
WJEC-style3 marksExplain how triangulation makes a structure stronger, with an example.Show worked answer →
A three mark Explain question. A rectangular frame can be pushed out of shape into a parallelogram because the joints can move (1 mark). Adding a diagonal member splits the rectangle into triangles, and a triangle cannot be deformed without changing the length of a side, so it holds its shape under load (1 mark). An example is a roof truss, bridge or shelf bracket that uses triangulation to stay rigid (1 mark). A weaker answer says triangles are strong without explaining that they keep their shape, which is the key point.
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