Unit d: Structure and forces

1. Unit d: Structure and forces

2. Introduction • Structures can be found in both natural and human-constructed environments • We will investigate the different materials used in all structures • We will test the materials under various loads and forces • We will explore construction methods used in the past and present and how technology has played a part

3. Section 1: Structures are found in natural and human-made environments

4. 1.1 Classifying Structural Forms • Every object that provides support is a structure.Structures may be made up of many things in different sizes. • Think of some structures are Lethbridge

5. Writing on Stone • Lethbridge Bridge • Coulees • Birds of Prey • Head Smashed Inn Buffalo Jump

6. Vocabulary All structures around you will vary in strengths and stability • Structural Strength: refers to a structure`s capacity to hold itself up as well as any added weight • Structural Stability: structure`s ability to maintain its position even when it is being acted on by a force

7. Vocabulary First thing people notice about a structure is its shape or form. There are three basic forms: • Solid Structures: is formed from a solid piece (or solid combination of pieces) of some strong material; Solid structures have little or no space inside and relies on its own mass to resist the forces that act on it. These structures are usually stronger than the other two and harder to move. (ex. Brick wall, hockey puck, water damn)

8. Frame Structures: is made up of a rigid arrangement of parts, or structural components, fastened together. The strength of a frame depends on the way the components are put together. You need all components in order for the frame to be strong. They are lighter due to the fact they are made up of less materials. (ex. Skeleton, made up of bone, ligaments and joints) • Shell Structures: have a solid outer surface which may be rounded and flat in shape and a hollow inner area.

9. Lesson Activity Open your text books to page 265 • “Take the Pop Bridge Challenge” Small Group Discussion • Have the students get into groups of no more than four and brainstorm a list of natural and human-made examples of structural forms.

10. 1.2 The Function of Structures When people are designing structures they also must take into consideration the function of the design. Who is going to be using it and what is the purpose? • Cement Benches • EnmaxSeats

11. The Function of Structures Con’t Many structures are designed to serve more than one function. • Come up with some example: • A train and plan – provides movement and shelter (Moves people or cargo or both) • When you know all the functions of the structure are to be, then you can better design the structure

12. The Function of Structures Con’t • Function and Effective Design: Have the students think about a paint brush and a Paint Roller. • Common Function, Different Design: Some structures, although they look very different from one another in their design, actually share a common function. • All roofs serve the same purpose, they provide a top covering for a building and protect the contents inside • Do all roofs need to be built the same way to be equally effective?

13. The Function of Structures Con’t • Aesthetics: refers to the pleasing appearance or effect that an object has because of its design. (not all structures are aesthetically pleasing)

15. Lesson Activities Look at page 273, answer the following questions 1. How else are they similar besides design? 2. How are they different?

16. Problem Solving Activity Look at page 271

17. 1.3 Human – Built Structure Around the World Structures are so varied do to climate, culture, tradition, technology and economics. The Human Home: • Homes around the world were built for shelter and protection but also to be portable (think of a teepee) • All homes share 2 essential characteristics: • They are all basically stable • They all provide shelter for the people who live in them

18. Tents offer desert dwellers protection from the sun, wind, and cool night temps Provided a home and protection from invasion In tropical climate, houses must be kept cool and dry

19. Floating Homes Igloos Stone Mountain Huts

20. Section Two: External and internal forces act on structures • 2.1 Measuring Forces • 2.2 External Forces Acting on Structures • 2.3 Internal Forces within Structures • 2.4 Designing Structures to Resist Forces and Maintain Stability

21. 2.2 External Forces Acting on Structures • An external force is a force that is applied on a structure by something else. (Think about when you walk into the wind, that is an external force, also think of gravity as an external force) • Mass: is the amount of matter in an object. The more mass an object has, the greater the gravitational force.

22. The Centre of Gravity: Gravity is having an effect on the stability of your body. The location of the centre of gravity of a structure determines the structures stability. The main method of increasing a structure’s stability is to increase the width of its base relative to its height.

23. Symmetry is a balanced arrangement of mass that occurs on opposite sides of a line or plane or around a centre or axis. The force of gravity on either side of the centre point of the ruler it is same. If you were to move your finger outside of the centre then the gravity would be higher on that side and you would have no centre of gravity. For a symmetrical structure to be stable, its mass must be distributed equally around the centre of the structure’s base.

24. Load: When designers are making their plans they have to consider all impacts the structure will occur. The weight of the load the structure will have to hold on top of the structure itself and also natural elements if the structure is outside (think of a book shelve, a hammock, bunk beds, a bridge, roads in hot climates and cold) • Static and Dynamic Loads: A load is an external force on a structure. A load can be a weight; there are two different types of loads that can affect structures: (Static and Dynamic)

25. Static Load: The weight of the structure and non-moving load it supports. These forces stay in place for a long people of time, (not moving or changing) (also called dead load) • Dynamic Load: is an external force that moves or changes with time. This loads can change very quickly and can be also consider a live load.

28. Researching Bridges • Read pages 290 – 291 and make study notes for the following four bridges. • Beam Bridge • Truss Bridge • Suspension Bridge • Arch Bridge

29. Pond Discussion/Activity • In your groups you will go through each pond station and discuss the question at each station. • You will get 5-7 minutes for each question • You will have to have a different recorder for each station (someone you writes down the answer) • That will be handed in at the end of class

30. 2.3 Internal Forces within Structures Internal forces are forces that act within a structure. Internal forces can be classified by the direction in which they act within an object. • There are three internal forces

31. Compression: : is a force that acts to squeeze an object or push parts within an object together. (Solid structures can usually resist the force of compression because of the strong materials they are made of)

32. Tension: is a force that acts to stretch and pull apart something. It can cause lengthening and possibly snapping of a component.

33. Shear: is a force that acts to push parts that are in contact with each other in opposite directions. • Structures with parts that must resist shear include doors, airplanes, and scissors

34. 2.4 Designing Structures to Resist Forces and Maintain Stability

35. Structural Components • Arches: can support a large load because the force of the load is carried down through the arch to the foundation. This spreads out the load • Beams: Common components in a range of structures. • Simple Beams: is a flat structure that is supported at each end, you cannot place to much in the middle or it cause the cause to bend which is something that you do not want

36. I-Beam: gives it strength, they have less mass than solid beams • Girders: (box beams) are long beams in the shape of hollow rectangular prisms. • Columns: is a solid structure that can stand by itself. They are used as support beams • Truss: is a framework of beams joined together, they usually form interlocking triangles. • Cantilever: is a beam that is supported only at one end

37. Structural Stress, Fatigue or Failure • Structural Stress: is caused by external and internal forces in a combination • Structural Fatigue: Repeated abnormal use of the structural then it was intended, all when a structural can no longer stand up to the forces acting on it.