1.2 Reinforcing structures

Technology

Grade 8

Structures

Module 3

Reinforcing structures

Activity 1

How do we reinforce structures?

• Rectangular objects are not necessarily sturdy. A rectangle can convert to a rhombus quite easily when force is exerted on it. The triangle is the figure that provides the greatest degree of stability. Consider the framework of a bicycle. Are there any triangles?

Assignment 1

• Take four 150 mm long cardboard strips. Form them into triangles, joining the ends together with split pins. Apply some pressure to your structure to test its strength. Now strengthen it by inserting supports.

• This type of support or reinforcement is known as triangular trussing. It is particularly noticeable in bridges, cranes and roofs.

Assignment 2

1. The bookcase illustrated below needs reinforcement. Indicate where you would place a support/supports to strengthen the shelf.

1. The legs of a trestle that supports a tabletop are held in place by means of a length of rope. Will this structure be able to withstand forces of stress or compression? Explain your answer and suggest a solution for the problem.

Assessment

Memorandum

ACTIVITY 1

Assignment 1

• Square : A triangle provides the strongest reinforcement; a single diagonal beam in one direction will be stronger than any other kind of reinforcement.
• Triangle : Which of the beams in the illustrated structure bears the most weight? Do all the beams bear equal weight? Let the learners decide. How could this be tested? Remove beams in turn and check whether the structure is weakened.
• Learners could also use pipe cleaners to represent a bicycle frame. Let the learners name further examples and allow class discussion.

Assignment 2

1. Which factors determine the strength of the strut? The thickness of the strut, the joins and the distance between the joins and the ends.Encourage the learners to list examples in common practice and discuss this.
2. The forces of both stress and compression. Force from above causes vertical compression (right down) and stress on the rope (horizontal) to keep the legs from shifting. If the force is not applied from above but from the side, one of the legs will be able to move. It can be rectified by replacing the rope with a solid bar.
3. Which factors determine the strength of the strut? The thickness of the strut, the joins and the distance between the joins and the ends.Encourage the learners to list examples in common practice and discuss this.
4. The forces of both stress and compression. Force from above causes vertical compression (right down) and stress on the rope (horizontal) to keep the legs from shifting. If the force is not applied from above but from the side, one of the legs will be able to move. It can be rectified by replacing the rope with a solid bar.