bridges by doug knight

7/28/2019 Bridges by Doug Knight

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. Introduction to Bridges

By Doug Knight

This introduction discusses bridge types and real-world considerations forbuilding bridges

Why have a bridge

To get across a gap - often water-filled

May also carry water - called an aquaduct

How can we get across the gap

Ford or swim

Get wet

Current may be too strong

Cold water

Stepping stones

Cannot use for wheeled traffic

Slippery

Deep water

Ferry

Floating bridge

Not carry heavy traffic

Must be tended

Cut down a tree

Two logs tied together

One log rolls


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Limited span

Need a tree


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So we build a bridge

Rope Bridge

How do you get the rope across

Maintenance

Not too stable

Beam

Solid pillar on both ends

Truss

Uses strength and rigidity of triangles

Cantilever

Anchor one end, and rest the other on beam with a bit hangingout

Cantilever with suspended span


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Suspension

Need real solid anchor for the cable

May flap in the wind

Portable bridges - pontoon bridges

What materials are used in bridge construction?

Wood

Quick

Deteriorates quickly

Burns

Stone

More durable

But span is limited

Iron

Strong

Expensive

Upkeep is difficult (rust)

Concrete

Usually with steel rods inside it - rebar

Road surface

Asphalt


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What does an engineer have to consider inbuilding a bridge

Length of the crossing

Weight the bridge must carry - vehicle weight plus its own

Ice loads

Ship collision loads

Water eroding the support piers - erosion

Seismic effects - earthquake - applies even here

Height of the bridge - do ships have to go underneath?CONFEDERATION BRIDGE VG

Strength of the land it will sit on - PEACE RIVER BRIDGE VG

Weatherconditions HARTLAND BRIDGE VG

Wind affect - TACOMA NARROWS BRIDGE VG

Environmental effects - what will the bridge do to the environment?

How long must it last?

Funding


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What if we have to put a support in the middle ofthe river?

Supports must be on bedrock

Use a cofferdam and pump out the water - good for shallow water

Large metal cylinder (caisson) and gradually dig it into the river bed -pressure becomes a problem, because the pressure inside thecylinder must be high enough to keep the water out - nitrogennarcosis - the bends - Brooklyn Bridge

Dredge the silt and place pre-assembled pieces in place from afloating barge - Confederation Bridge

Expansion Joint

Allows the bridge to expand with differences in temperature

One end fixed - the other slides

Cable stretches - bridge moves up and down


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Famous Canadian Bridges

Quebec Bridge - longest cantilever RR bridge in the world

Confederation Bridge - longest bridge in the world over an ice-

covered waterway

Sault Ste Marie Bridge - railway swing bridge

Hartland NB - longest covered bridge

Peace River Bridge - suspension bridge - fell down

http://www.abcdpittsburgh.org/webshots.htm

http://www.swishweb.com/Science_and_Technology/Bridges/

www.confederationbridge.com

www. ufacademy.com/webmania/bridges

www.buildingtechnology.com/bcba/bridges/basics.htm
http://www.buildingtechnology.com/bcba/bridges/basics.htmhttp://www.buildingtechnology.com/bcba/bridges/basics.htm


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Simple Beam Bridge

Truss - Uses strength and rigidity of triangles


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Cantilever Span

Anchor one end, and rest the other on beam with

a bit hanging out

Cantilever with suspended span in the middle


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Suspension Bridge


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Peace River Bridge

Built in 1942, the foundations of the Peace River Bridge at Taylor, BC, wereunknowingly built on unstable soil. Ground water eroded away the banks,and despite regular maintenance the bridge collapsed in October 1957.

Peace River Bridge after collapse


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Tacoma Narrows Bridge (Washington, USA)

Wind 1, Bridge 0

The wind rushing down the gorge started the bridge swaying and twisting.

Eventually the bridge collapsed.


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The Longest Covered Bridge in the World

Hartland, New Brunswick


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Cantilever Bridges

The Longest Cantilever Road Bridge in the World The Firth Bridge

The Longest Cantilever Railroad Bridge in the World Quebec Bridge


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The Longest Bridge over an Ice-coveredWaterway

The Confederation Bridge linking NewBrunswick and Prince Edward Island


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The Sioux Narrows Bridge

An Example of a Truss Bridge


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Aquaduct A Bridge That Carries Water


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Pontoon Bridge

bridges by doug knight

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