Bridges and Forces

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torsion

1940's, Tacoma Narrows Bridge twisted and collapsed from high wind and it's narrow design

Upward Force

= bridge supports

torsion

= twist

Downward Force

= weight and gravity

Brooklyn Bridge

Longest bridge from 1853-1903, 1,596 feet

Danyang-Kunshan Grand Bridge

Longest bridge in the world, 102.4 miles

Silverbridge collapse 1967

Micro crack in bridge, 31 cars fell, 46 perished, laws enacted to require bridge inspections

bridge

a structure built to span a valley, road, railroad track, river or any other physical obstacle.

Stabilized the Tacoma Narrows Bridge

added trusses (cross bending) so wind could pass through

types of bridges

beam, arch, suspension, truss

bending

bottom is pushed together and the top edge is pulled apart

Connecting beam bridges

can be spanned by connecting a series of simple beam bridges into what is known as a continuous span.

bridge painters

clean and coat every part of steel to help prevent rusting, also watch closely for anything that may seem wrong

Arch bridges

compression allows bridge to carry great loads, simple to build (stone), spans short distances

Suspension bridge

expensive construction costs, uses towers and cable

Roman bridge engineering

first to use arch, first discovered natural cement called pozzolana

Sunshine Skyway, Tampa Bay 1980

freighter crashed into bridge, 35 killed, replaced by cable stay

Roller Joints

give columns and beams the freedom to expand and contract as the temperature changes

Bridge Engineer

goal: to design the strongest, safest, most long lasting and economical bridge possible

Deep Piles

heavy concrete pillars to support a structure from soft, unstable soil movement

Lake Pontcharrtain Bridge

longest continuous span bridge, almost 24 miles

pozzolana

natural cement made from water, lime, sand and volcanic rock

single beam spans

rarely more than 250 feet

Beam bridge

simplest form of bridge, cheap to build, spans relatively short distances

Sheer Walls

solid walls to reinforce concrete that resist horizontal movement

triangels

strongest type bridge

abutments

supports to prevent ends of bridges coming apart from the compression of the arch

Bridge forces

the balance between the downward and upward forces allows a bridge to stand and carry weight

Vibrations from loads

thicker beams are used making them less likely to bend

bridge purpose

to allow easy passage over an obstacle

keystone

towers support most of the weight with compression. Also tension forces acting on cables in suspension bridges

Truss bridge

triangle shapes, economical to construct, span enormous distances

Cable stay bridge

type of suspension bridge but more economical to build, can span enormous distances, elegant looking

Inca bridge engineering

used rope (suspension) bridges

arch

very strong bridge

dead load

weight of the bridge itself (beams, nuts, bolts...)

live load

weight of the traffic, cars, pedestrians

bending

weight pushing straight down

tension

when material is being pulled or stretched

sheer

when one part of material slides past another

compression

when weight pushes on a material (squeezes it together)

square/rectangle

will shift to the side, collapse flat under heavy load

first bridges

wooden logs or planks then eventually stone


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