Bridge Building History & Bridge Types
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
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
Bridge Types Rope Bridges Stone Arch Bridges Steel Arch Bridges Suspension Bridges Truss Bridges Cantilever Bridges
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)
Stone Arch Bridge Stone arch bridges ◦Strongest and most durable ◦Stones are in compression ◦Key Stone! Expensive (stones and cost of labour)
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)
Suspension Bridges Suspension bridges ◦Can span the longest ◦Extremely efficient (material wise) ◦Use cables under tension to support bridge deck
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
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
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