Bridge BuildingHistory & 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 BridgesStone Arch BridgesSteel Arch BridgesSuspension BridgesTruss BridgesCantilever 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