Structures and Forces

1. Structures and Forces Unit D http://www.pbs.org/wgbh/buildingbig/educator/act_index.html

2. Learning Outcomes • Recognize and classify structural forms and materials. • Interpret and evaluate variation in the design structures that share a common function.

3. Every object that provides support is a structure!

4. Structural Strength: Refers to a structure’s capacity to hold itself up, as well as any weight added to it.

5. Structural Stability: Refers to a structure’s ability to maintain its position even when it is acted on by a force.

6. Structures have definite size and shape, which serve a definite purpose or function • Every part of the structure must resist forces(stresses such as pushes or pulls) • Forces can potentially damage its shape or size.

7. 3 basic structural forms: • Solid/Mass Structure • Frame Structure • Shell Structure

9. Natural Structures • Not made by people • Occur naturally in the environment

10. Manufactured Structures • Built by people • Many are modeled after natural structures

11. Solid/Mass Structures • Can be made by, piling up or forming similar materials into a particular shape or design. • It is held in place by its own weight, losing small parts often has little effect on the overall strength of the structure

12. Formed from a solid piece (or solid combination of pieces) of some strong material. • Solid structure has little or no space inside and relies on its own mass to resist the forces that act on it. • Usually stronger than either frame or shell structures.

13. Natural Mass Structures

14. Manufactured Mass Structures

15. Is this a solid/mass structure?

16. A Layered Look • Mass structures are not always solid, but are layered and have hollowed out areas for specific functions

17. A Layered Look • Sandbag Wall Structures are mass structures that are layered. They prevent flooding and have 4 key elements to avoid failure: • Must be heavy enough to stay in place • Must not be too heavy to compact the earth unevenly below it • Must be thick enough so it cannot be pushed out of place • Must be anchored firmly

18. Frame Structures • Have skeleton of strong materials, which is filled and covered with other materials, supporting the overall structure • Most of the inside part of the structure is empty space.

19. Frame Structures • Load-Bearing Walls: these are walls that support the load of the building

20. Frame Structures • Partition Walls: these are the walls that divide up the space in a building

21. Frame Structures • Most common construction choice because: • Easy to design • Easy to build • Inexpensive to manufacture

22. Frame Structures • Can be arranged in 2 dimensions (door/fence). • 3 dimensions (music stand/house). • Lighter than solid/mass structures • Use less material

23. Golf Ball Bridge • We will complete next week IF things go well

24. Shell Structures • Keep their shape and support loads, even without a frame, or solid mass material inside • Use a thin, carefully shaped, outer layer of material, to provide their strength and rigidity • Spreads forces throughout whole structure (every part of structure supports only a small part of the load)

25. Shell Structures

26. Shell Structures • Flexible Structures:are also shell structures but are more flexible rather than rigid

27. Shell Structures • They are completely empty so they make great containers • Their thin outside layer means they use very little materials

28. Shell Structures • Problems • A tiny weakness or imperfection on the covering can cause the whole structure to fail • When shell is created from hot or moist materials, uneven cooling can cause some parts to weaken other parts from pushing or pulling on nearby sections • Flat materials are hard to form into rounded shell shape • Assembly of flexible materials is very precise, so that seams are strong where the pieces are joined

29. Check & Reflect • Page 268, #s 1-4

30. Mix and Match • Football Helmets • Shell structure (to protect head) • Frame structure attached in front (to protect the face)

31. Mix and Match • Hydro-electric Dams • Mass structures with frame structure inside to house generators

32. Mix and Match • Airplanes • Frame structure • ‘skin’ that acts like a shell (giving it added strength to resist stresses and making it light weight and flexible)

33. Mix and Match • Domed Buildings • Combines shell and frame construction

34. Mix and Match • Warehouses • Often built with columns to support the roof (frame) and concrete blocks (mass structure) which stay in place because of their weight

35. Topic 1 Review • Page 268, Check & Reflect #s 1, 2, 3, & 4

36. Name the 3 main structural forms?

37. Remember that structures do not always fit into one form and can be combination structures. • The 3 main structures are: shell, frame, and solid (mass).

38. What is this example a combination of?

39. An umbrella is a combination of a shell and a frame. • And this?

40. The balloon is an example of a shell, and the basket is an example of a shell and a frame!

41. How can you tell if a wall is a load bearing wall? • Link

42. For the 3 structural forms, provide examples from the natural environment, and the human-made environment. • Try not to use examples that have been mentioned in the text.

44. Large human-built solid structures are often made from brick, concrete, mud, or stone. • Why do you think these materials are used to construct solid structures?

45. Brick, concrete, mud, stone • Solid structures need to be made of materials that can support large loads. • The mass of these materials allows them to resist the forces acting on them more effectively than materials that have little mass.

46. Why is it an advantage that bird’s winds are hollow and not solid? Or a supporting skeleton outside the body?

47. The advantage of a bird’s wing bones, and the outer skeleton of invertebrates such as sea stars and lobsters, is that both types of structures provide strength without adding much weight. • “Exoskeletons” also provide outer protection and support.

48. Topic 2- Describing Structures • Most structures have several functions: • Supporting (its own weight) • Containing (substances) • Transporting • Sheltering • Lifting • Fastening • Separating • Communicating • Breaking • Holding

49. Aesthetics • The study of beauty in nature • Best structural designs ‘look good’ or are ‘aesthetically pleasing’ • Aesthetics are accomplished by shape, texture, colour, type of material, and simplicity of the repeated pattern in a design.

50. Safety • All structures are designed and built within an acceptable margin of safety • Usually, structures are designed with a built-in large margin of safety YouTube - Construction and Building Inspectors