Bridges and Forces
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
