1. What is the key purpose of a roof?

2. Why are there so many different styles of roof?

3. Tensile and Compression Force
Tension
The rope is under tension as the two people pull on it. This stretching puts the rope under tension.
Compression
Weightlifters find that their body is compressed by the weights they are holding above their head.

4. Basic structural elements
All structures have forces acting on them. The part of the structure that has a tensile force acting on it is called a TIE. The part that has a compressive force acting on it is called a STRUT.

5. Roof design
The roof beams are under pressure from the weight of the tiles on the roof (compressive force). The ceiling beam is being stretched (tensile force).

6. Tension or compression?
Identify which members are in tension or compression

7. Tension or compression?
Identify which members are in tension or compression

8. Tension or compression?
Identify which members are in tension or compression

9. Tension or compression?
Identify which members are in tension or compression