Lesson Notes By Weeks and Term v5 - Grade 7
Structures: types of structures and simple frame structures – Week 2 focus
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Structures: types of structures and simple frame structures – Week 2 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Technology
Class: Grade 7
Term: 1st Term
Week: 2
Theme: General lesson support
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This week, we delve deeper into the fascinating world of structures. Structures are all around us, from the houses we live in to the bridges we cross and the furniture we use. Understanding how structures are designed and built is crucial for technologists and anyone interested in creating stable and useful things. Here in South Africa, with our diverse landscapes and growing infrastructure needs, understanding structures is more important than ever. Whether we are designing a new classroom in a rural school, a bridge across a river, or even just a strong table, we need to know how different types of structures work and how to build them safely and efficiently.
What is a Structure? A structure is anything that is built or constructed. Its purpose is to support a load (something it carries) and resist forces that try to change its shape or break it.
Types of Structures: There are four main types of structures: Solid Structures: These structures are made almost entirely of solid material. They rely on the strength of the material itself to hold their shape and withstand forces. Examples include brick walls, dams, and mountains.
Example in South Africa:* The Great Zimbabwe ruins are essentially solid structures.
Advantages:* Strong and durable.
Disadvantages:* Can be very heavy and use a lot of material.
Frame Structures: These structures are made of separate parts (members) that are joined together to form a framework. The framework distributes the load across the entire structure. Examples include buildings with steel or wooden frames, bridges, and bicycles.
Example in South Africa:* The Nelson Mandela Bridge in Johannesburg is a frame structure.
Advantages:* Strong for their weight, use less material than solid structures.
Disadvantages:* Require careful design and construction.
Shell Structures: These structures use a thin, curved outer surface to provide strength and rigidity. They rely on their shape to distribute the load. Examples include eggshells, domes, and car bodies.
Example in South Africa:* The Moses Mabhida Stadium in Durban has a distinctive arch, a shell structure element.
Advantages:* Strong for their weight, can cover large areas without internal supports.
Disadvantages:* Complex to design and build.
Membrane Structures: These structures are thin, flexible sheets that are held in place by tension. They rely on their shape and the tension in the material to resist forces. Examples include tents, inflatable structures, and parachutes.
Example in South Africa:* Temporary shelters or tents used at festivals and events.
Advantages:* Lightweight, easy to transport and set up.
Disadvantages:* Can be easily damaged, require constant tension.
Frame Structures in Detail: Frame structures consist of individual components connected to form a stable network.
The most common components are: Beams: Horizontal structural members that resist bending forces. They support loads applied along their length.
Example:* The horizontal part of a table or a bridge deck.
Columns: Vertical structural members that resist compressive forces (pushing forces). They support loads from above.
Example:* The legs of a table or the pillars supporting a bridge.
Struts: Bracing members that resist compressive forces and provide support to other members. They are often angled.
Example:* Diagonal supports in a bridge or roof truss.
Ties: Tension members that resist tensile forces (pulling forces). They are often cables or ropes.
Example:* Cables in a suspension bridge.
Forces Acting on Structures: Structures are subjected to various forces. Understanding these forces is crucial for designing safe and stable structures.
Tension: A pulling force that stretches a material.
Compression: A pushing force that squeezes a material.
Shear: A force that causes one part of a material to slide past another part.
Bending: A force that causes a material to curve.
Torsion: A twisting force.
Example: A simple Goalpost (Frame Structure) A goalpost is a simple frame structure. The vertical posts are columns that resist compression. The horizontal bar is a beam that resists bending. If there are angled supports, they are struts that help to distribute the load and prevent the beam from bending too much. The stability of the goalpost depends on how well these components are connected and how strong they are. Guided Practice (With Solutions)
Question 1: Identify the type of structure represented by a corrugated iron sheet used for roofing. Explain your reasoning.
Solution: This is a shell structure. Corrugated iron sheets are thin and curved. The corrugations (the ridges and grooves) give the sheet increased strength and stiffness, allowing it to support a load (like rain or snow) without bending or collapsing. The curved shape helps distribute the load across the entire sheet.
Question 2: A bridge is made of steel beams connected by bolts. What type of structure is this? Name two components you would expect to see in its construction.
Solution: This is a frame structure. It is made of separate components (steel beams) joined together to form a framework. We would expect to see beams (horizontal members that support the road surface) and columns (vertical members that support the beams).
Question 3: Sketch a simple frame structure that could be used as a bus shelter. Label at least three components.
Solution: ``` Roof (Beam) / \ / \ /-------\ / \ / \ /-------------\ | Column | Column | | | | Ground ``` Labels: Roof (Beam), Columns, Ground. The roof acts as a beam supported by the two columns. Independent Practice (Questions Only) Name the four main types of structures.