Lesson Notes By Weeks and Term v5 - Grade 5

Lesson Video

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Performance objectives

• Define and identify frame structures.
• Explain how different materials are used.
• Describe the forces of tension, compression, and shear.
• Identify strong shapes like triangles.
• Design a simple frame structure.

Lesson summary

Have you ever looked closely at a bridge, a building, or even a bicycle? They're all made up of structures! In this lesson, we're going to explore a specific type of structure called a frame structure. Frame structures are all around us and play a vital role in our daily lives, from the houses we live in to the towers that bring us electricity. Understanding how they work is important for appreciating the ingenuity of engineering and how things are built safely and strongly. Imagine a shanty town – if the frame structures were not carefully considered, what could happen? This knowledge can even inspire you to build your own amazing creations!

Lesson notes

What is a Frame Structure? A frame structure is a type of structure made up of many parts joined together. These parts, often called members, form a skeletal framework that supports a load (weight). Think of the skeleton inside your body – it’s a frame structure! These structures are designed to be strong and lightweight, allowing them to support heavy loads without collapsing. Frame structures are used in many different applications, including: Buildings: The steel or concrete framework of a skyscraper is a frame structure.

Bridges: Bridges often use frame structures like trusses and arches to span long distances.

Towers: Cell phone towers and electricity pylons are examples of frame structures.

Bicycles: The frame of a bicycle provides strength and stability.

Furniture: Chairs and tables often have frame structures.

Materials Used in Frame Structures: The materials used to build a frame structure are chosen based on their strength, weight, and cost.

Common materials include: Wood: Wood is a lightweight and relatively inexpensive material. It's often used in houses and smaller structures. Think about the wood frames of houses in your neighborhood.

Steel: Steel is a very strong and durable material. It's used in skyscrapers, bridges, and other large structures. Imagine the tall buildings in Johannesburg, many use steel frames.

Concrete: Concrete is strong in compression (being squeezed) but weak in tension (being pulled). It's often used in combination with steel in buildings and bridges. Roads are often made of concrete.

Aluminum: Aluminum is lightweight and resistant to corrosion (rusting). It's often used in bicycles, aircraft, and other applications where weight is important.

Plastic: Plastic can be molded into different shapes and is relatively inexpensive. It’s often used in lightweight structures or in combination with other materials.

Forces Acting on Frame Structures: Frame structures are subjected to different types of forces that can cause them to deform or even collapse. Understanding these forces is crucial for designing safe and stable structures.

Tension: Tension is a pulling force. It stretches or elongates a material. Imagine pulling on a rope – you're applying tension. In a frame structure, tension occurs when a member is pulled by the load it's supporting.

Compression: Compression is a pushing force. It squeezes or shortens a material. Imagine stacking books on top of each other – the bottom book is experiencing compression. In a frame structure, compression occurs when a member is being squeezed by the load.

Shear: Shear is a force that causes one part of a material to slide past another part. Imagine cutting paper with scissors – you're applying shear force. In a frame structure, shear can occur at joints where members are connected.

Strong Shapes: Certain shapes are inherently stronger than others when used in frame structures.

Triangles: Triangles are very strong because they distribute forces evenly. They are very rigid, meaning they don’t deform easily under load. A triangle doesn't change shape easily. This is why you see triangles in bridges and towers, for example. Think of the support beams on a radio tower.

Squares and Rectangles: Squares and rectangles are weaker than triangles because they can easily deform into a parallelogram under load. They are more easily twisted.

However, squares and rectangles can be made stronger by adding diagonal braces, which create triangles within the shape.

Example 1: Tension and Compression in a Bridge Truss: Imagine a simple bridge truss made of wooden beams. When a car drives across the bridge, the top beams experience compression (they are being pushed together), while the bottom beams experience tension (they are being pulled apart). The vertical and diagonal beams help to distribute these forces throughout the structure.

Example 2: The Strength of Triangles in a Roof: Look at the roof of a house. Often, the roof structure uses triangular shapes. The weight of the roof tiles (the load) puts a force downwards. The triangular structure of the roof frame efficiently distributes this weight down to the walls, preventing the roof from collapsing. If the roof frame used a square shape instead, it would be much weaker and more likely to collapse under the weight of the tiles or after heavy rain.

Example 3: Shear Force on a Bolt in a Joint: Consider a frame structure where two steel beams are joined together with a bolt. When a load is applied to the structure, the bolt experiences shear force. One side of the bolt is being pushed in one direction, while the other side is being pushed in the opposite direction. If the shear force is too great, the bolt can break. Guided Practice (With Solutions)

Question 1: Identify the following structure as a frame structure or not: A mud hut. Explain your reasoning.

Solution: A mud hut is a structure, but probably not a frame structure.