1. GRADE 7
TOPIC
STRUCTURES

2. STRUCTURES
A structure can be defined as any form of construction that support the load.
The purposes of structures are to:
1. Contain
2. Protect
3. Span
4. Support
Classification of structures
1. Natural structures
2. Man made structures
Types of structures
1. Shell – Usually made of one part and contains the load .
2. Frame – Usually made from different parts combined together and supports the load .
3. Solid structure – A non hollow one part structure
Some structures such as skull and rib cage can serve as both frame and shell.
As a shell the skull protects and contains the brain and as a frame, the skull holds the nose, ears and the head skin.
As a shell, the rib cage contains the heart, liver and lungs and as a frame it supports the breast, chest and the skin.

3. STIFFENING OF STRUCTURES
Stiffening refers to processing of materials to make them suitable for use in structures.
Methods of stiffening are:
Tubing – hollow construction of a single plate or sheet.
It can be made in different shapes:
- Round
- Triangle
- Square
- Rectangle

4. STIFFENING OF STRUCTURES
Folding - repeated rolling of a sheet or plate to make it rigid.
An example of folding is the making of paper dowels.

5. STIFFENING OF STRUCTURES
Corrugation – Repeated bending of a sheet to make it rigid.
Common examples of corrugation are:
- Corrugated zinc sheet used on house roofs.
- Hard card boxes usually used to contain.

6. STRNGTHNING OF STRUCTURES
Some of the methods used to strengthen structures are:
Triangulation
Cross bracing

7. METHODS USED TO MAKE THE STRUCTURE STABLE
Wider on the base and
narrower at the top.
Made as low as possible.
The top is lighter in mass than the
base

8. ACTIVITIES
Individual groups should make a table using different methods of stiffening as well as strengthening. The height, the length as well as the breath of the table should be the same and equal to 150 mm. The table top to be made of corrugated paper attached to two sheets of paper on either side. The method of strengthening the table should be triangulation on one side and cross bracing on the other side. NB. The groups should differ with the type of the table legs to be used.

9. ACTIVITY cont....... GROUP 1 GROUP 2 GROUP 3 GROUP 4
Square tubing should be used with a flat two ply of paper for triangulation and cross bracing.
GROUP 2
Rectangular tubing should be used with a flat two ply of paper for triangulation and cross bracing.
GROUP 3
Round tubing should be used with a flat two ply of paper for triangulation and cross bracing.
GROUP 4
Triangular tubing should be used with a flat two ply of paper for triangulation and cross bracing.
(The whole activity to take only 30 minutes)