Science 7: Unit D – Structures and Forces Topic 2: Describing Structures

Describing Structures  There are a number of important factors you must use when describing or designing structures. Some factors are more important than others for different structures, but they all apply. At this level we’ll consider six different factors:  1. Function: What is the purpose of the structure? Does it have more than one function? This is the most important design factor. Eg. a grocery store must be designed to be large to store many products in it.

2. Safety  2. Safety: the structure must be built so that it’s safe for people to use and stable enough for people to enter.  Eg. a bridge must be designed to support the weight of itself and the many cars on it.  Margin of Safety – designing a structure to handle loads heavier than it will deal with in actual use.

3. Cost  3. Cost: the amount of money it will take to design, building, and maintain the structure. Most businesses today building new structures want it built well, but also as cheap as possible. Governments, and organizations place cost as lower end factor.

4. Aesthetics  4. Aesthetics: How attractive the structure looks. This is an very important factor when designing monument or artistic structures. Aesthetic buildings are also good at attracting tourists and making a city look better.

5. Materials  5. Materials: When describing a structure you can talk about what materials make it up. The better quality, stronger materials usually end up costing more.  Eg. the Ark of the Covenant was supposedly made of solid gold.

Strengthening Materials  There are some ways we can strengthen weaker materials:  A. Laminated/Layer Materials: Layers of different materials (eg. tetra pak) are pressed and glued together, combining the properties of the materials together. The layers are called laminations.  B. Composite Materials: A material is strengthened by reinforcing it with another material. (eg. concrete rebar).  C. Woven or Knit Materials: Spinning, twisting, looping, or knotting fibres together give material more strength.

6. Joints  6. Joints: are how the parts of a structure are connected together. There are two main types:  A. Mobile Joints – are joints that allow movement. Examples include door hinges, shoulder joints, etc.  B. Rigid Joints – do not allow any movement at all. Two metal beams welded together represent a rigid joint. Your skull is three bone plates sealed together.

Types of Joints  Fasteners: joints which involve something drilled, hammered, etc. through two or more structure parts connecting them together. Examples include nails, staples, bolts, etc. Unfortunately, the holes made in the structure, by the fastener, actually weaken the overall structure.  Interlocking Shapes: pieces fit or snap together like jigsaw or lego pieces. Eg. dental filling.  Ties: pieces tied together. Eg. stitching, tying laces.  Adhesives: Sticky substances fasten things together. Chemical bonds strengthen the structure’s joints.  Melting/Welding: pieces of metal or plastic are melted together.

7. Environmental Impact  7. Environmental Impact: How the building and using of the structure affects the environment. This factor is becoming more and more important as the environment becomes a more important issue.