1. Bridge Building History & Bridge Types

2. History Essential in the development and exploration of North America Allowed pioneers & explorers to move goods and services from one area to another in shorter periods of time ◦Without bridges they would have to wait for flooded rivers to recede/dry up or go miles out of their way ◦Crossing river beds was often dangerous  Wheels were skinny  Sank into river beds losing lives and goods

3. History Early bridges occurred naturally (were fallen logs, not good for movement of goods) Earliest known man-made bridge was a primitive rope bridge ◦Pre-cursor to suspension bridges

4. Bridge Types Rope Bridges Stone Arch Bridges Steel Arch Bridges Suspension Bridges Truss Bridges Cantilever Bridges

5. Rope Bridges Rope bridges (China) still used today ◦Strengths (cheap, relatively easy to build, move goods w/ pack animals) ◦Weaknesses (susceptible to high winds, not big enough to move vehicles)

6. Stone Arch Bridge Stone arch bridges ◦Strongest and most durable ◦Stones are in compression ◦Key Stone! Expensive (stones and cost of labour)

7. Steel Arch Bridge Steel arch bridges ◦Capable of covering great spans ◦Often combined with other bridge components (trusses, cables, etc.) ◦Arch in compression (cables in tension, trusses in both)

8. Suspension Bridges Suspension bridges ◦Can span the longest ◦Extremely efficient (material wise) ◦Use cables under tension to support bridge deck

9. George Washington Bridge  George Washington Bridge ◦ 2 cables – 3 feet in diameter, 1 mile long ◦ Each cable has 26,000 strands; together is 107,000 miles (4x around the earth) ◦ Can support 80,000 tons

10. Truss Bridge Truss bridge – distribute the load ◦Wood  Easy to build  Capable of carrying heavy loads (rigid & strong) ◦Steel  Not as good for long spans  Can be quickly assembled or pre-fabricated  Can support great loads  Used typically for railway bridges

11. Cantilever Bridge Cantilever bridge ◦Type of truss bridge ◦Built towards centre from each bank and joined with a middle section ◦Most challenging is setting centre section in place