1. Describing Structures
Topic 3

2. Designing Structures
Designers need to consider 4 main parts for a successful structure:
Function
Aesthetics
Safety
Cost
Materials &Environmental Impact

3. Function What does a structure do?
Contain, transport, shelter, support, lift, fasten, separate, communicate, break, hold
Loads are forces (weight) a structure resists
Live loads change
Cars on a bridge, snow on a roof
Dead loads stay the same
the weight of the structure

4. Function
How does the function of each of these structures differ?

5. FUNction – Rube Goldberg
This Too Shall Pass
List as many functions as you can see in this video!

6. Aesthetics
Aesthetics is the study of beauty in art and nature – does it look good?
‘Beauty is in the eye of the beholder’

7. Safety Safety very important to designers
Better safe than sorry is the basis of a margin of safety.
Extra strength in case of failure - Many roofs in Canada have a margin of safety for snow load!
Cost is sometimes challenging to balance with safety

8. Safety Not all safety concerns can be foreseen! Tacoma Narrows Bridge
The designers did not take into account the effect the wind in the area would have on the design

9. Safety
Forth Rail Bridge
Safety vs. Cost

10. Safety - Earthquakes

11. Cost – Choosing Materials
The properties of a material must serve the purpose of a structure.
Would you set sail in a concrete canoe?

12. Materials – Composites
Composites combine multiple materials
They bring together strengths of materials and balance weaknesses
Rebar tensile strength
Concrete Compression Strength
Concrete and steel are able to resist opposite types of strength.
What are some other composite materials?

13. Materials – Layered Layers of a material are called laminations
Often, layers will be put together in a particular way to balance weaknesses
Think of napkins!
Juice boxes
Coolers, fridges, walls
Windshields
What are some other layered structures?

14. Materials – Woven & Knit
Woven or knit materials are made up of linked threads which distribute forces through the whole structure
They offer flexibility and can be layered
Cotton clothing, rugs, netting, screens

15. Materials – Flexibility
Pressed or melted substances can also offer flexibility
Plastic wrap, aluminum foil, felt, paper
Flexible materials are great for structures that need to be folded, rolled or molded
If they are lightweight it can make transport, storing, and use more convenient
Tents, parachutes, clothing

16. Think about it!
What allows these hard structures to be bendy?

17. Material Choice Consider:
Cost
Appearance
Environmental Impact
Energy efficiency
How would these be considered in choosing materials to build a house?

18. Materials

19. Design – Joints
Materials often need to be connected, joints are typically weak points
Mobile joints – allow movement
Door hinges, elbows, bike chains
Rigid joints – are locked in place
Dovetail joints, rivets, nails, welds
Can you think of other examples?

20. Design – Joints Fasteners Interlocking shapes Ties Adhesives
Nails, staples, bolts, screws, rivets, dowels
Interlocking shapes
Folded seams, dovetails, puzzles, Lego, zippers
Ties
Thread, string, rope: shoes, drawstrings,
Adhesives
Thermosetting (hot glue guns), solvent based (crazy glue), epoxies - stronger bond = stronger chemicals
Melted bonds
Welds, soldering

21. Forces, Loads & Stresses
Topic 4

22. Forces
External forces are stresses that act on a structure from outside
Weight of a car, wind blowing, snow; live loads
They cause internal forces – stresses within the materials of the structure
Internal stresses can change the shape or size of a structure this is called deformation.
Deformations can be repairable or cause a structure to fail

23. External Forces – Loads
A dead load is a permanent force, acting on a structure.
This includes the weight of the structure itself.
A live load is a changing, or non-permanent force acting on a structure.
This includes the force of the wind ,the weight of objects on a structure
Impact forces (collisions with the structure) are another type of live load.

24. Internal Forces – Tension
Tension forces stretch a material by pulling its ends apart
Tensile strength measures the largest tension force the material can resist before failing.

25. Internal Forces – Compression
Compression forces crush a material by squeezing it together.
Compressive strength measures the largest compression force the material can resist before it loses its shape or fails.

26. Internal Forces – Shear
Shear forces bend or tear a material by pressing different parts in opposite directions at the same time.
Shear strength measures the largest shear force the material can resist before it rips or fails

27. Internal Forces – Torsion
Torsion forces twist a material by turning the ends in opposite directions.
Torsion strength measures the largest torsion force the material can withstand and still spring back into its original shape.

28. Internal Forces – Bending
A bending force is a combination of tension and compression

29. Internal Forces

30. Forces on Structures What forces are present in a swing set?
How can the design of a swing set resist these forces?
Page 324

31. Resisting Stresses
The strength of a material is often determined at the level of particles
Steel has high tensile strength – it has strong forces pulling the particles together
Graphite has low sheer strength – the particles are arranged in layers with weak bonds between layers – used for writing
Rubber has high torsion strength – each particle is attracted in all directions and can return to its place easily
See page 314

32. FORCES LAB
You will be in small groups and will rotate through stations to test the different types of forces.
Lab write ups must be completed in your booklet and handed in!