1. Bridge Structures

2. Bridges
Bridges are designed to withstand force from loads such as people and vehicles
When a force pushes down on a structure, the structure is under compression
Depending on the design, forces can also pull down on parts of a structure causing tension. For example, wires on a suspension bridge are under tension

3. Things that help strengthen and stabilize the structure of bridges are:
1. triangulation (trusses): used for horizontal bracing of a bridge. Triangles are organized in shapes called trusses which adds strength to a bridge.

4. 2. struts: bars that give support or strength to a structure through compression

5. 3. beams: long pieces of wood, concrete or teal that support a roadway of a bridge

6. 3. girders: horizontal iron or steal beams that support a load and have an I shape

7. 4. ties: join two structural members together through tension

8. 5. cables: flexible steel rope that support the roadway of suspension bridges

9. 5. cables: flexible steel rope that support the roadway of suspension bridges

10. Constructing Bridges
When you construct your bridge, forces will be acting upon your structure
Loads place bridge components under compression and tension as seen in the diagrams from previous slides
These are internal forces
Compression is the pushing force that squeezes the top of the bridge
Tension is the pulling or stretching force because the bridge beams bend under a load.
External forces that may act upon a bridge include wind or earthquake tremors.

11. Factors that affect design choices:
Materials: must suit design and function of structures. Designers must take forces and materials into account (What materials will help support mass of cars and people? What materials are strong? Flexible?
Time: limited by time. Missing a deadline is inconvenient for buyers. So, you have to build structures in a specific amount of time.
Cost: the price it will take to build structures and the price it will cost people in the community
Visual appeal: interesting, attractive and alluring for people to look at

12. Consolidation Turn to page 37 of the Force Factor
We will discuss questions in the black print on the page as a class
Pay close attention the pictures of bridges on the page as well
How where they designed? What materials did they use? What is supporting their structure?