1. Science 7 – Unit D: Structures and Forces Topic 6: Designing with Forces

2. How to Design Stable Structures  Structures must deal with loads (structural strength) and external forces (structural stability). Designers/engineers must recognize, analyze, and deal with the types of loads and external forces that their structures will deal with. Remember external forces cause internal stresses.  They can deal with these external forces in one of three ways:

3. I. Spread the Load  Distribute the load throughout the structure so that no single part is carrying most of the load.  Domes are good examples of this strategy.

4. II. Use Angled Components  Engineers may use angled components so that forces are directed along them and are used to hold pieces together rather then pulling them apart.  Triangular structural components are a good example of this strategy.

5. III. Shape the Parts to Deal With the External Force.  Engineers shape the parts to stand up to the specific type of force they are likely to experience.  Eg. The Vasco Da Gama Bridge, the longest bridge in Europe is curved to better deal with tsunamis and earthquakes.

6. How To Support Heavy Loads  Different Structural Components can be used to help support heavy loads.  Arches, braces, cantilevers, large columns, flying buttresses and triangular corrugations give added structural strength to a structure.  Eg. A double cantilever bridge uses the cantilever component to support the loads of the vehicles on it.

7. You need to use the right materials to deal with specific internal forces.  Certain materials such as concrete are very good at resisting compression, but not at resisting tension.  Others such as most metals can handle tension a lot better than compression.  Finally, certain materials can handle a number of different forces such as steel.

8. Friction can be a good thing too!  Friction is a force that resists movement. Friction is very important in structures. Unless you’re talking about mobile joints, you want a lot of friction in your structures.  Nails, screws, bolts, glue, staples, mortar etc. are all types of rigid joints that use friction to help hold structural components together.