Bridges

Reasons the Tacoma Narrows fell

1)the bridge's deck-stiffening truss was insufficient for the span and 2) the wind that day was at just the right speed and hit the bridge at just the right angle to set off the deadly vibration.

cast iron

A brittle alloy with high carbon content; iron that has been melted, then poured into a form and cooled; can be made into any shape desired

shear

A force that causes parts of a material to slide past one another in opposite directions

girder

A large beam, usually steel or concrete

tuned mass dampener

A mechanical counterweight designed to reduce the effects of motion, such as subduing a bridge deck's tendency to vibrate

cantilever

A projecting structure supported only at one end, like a shelf bracket or a driving board

mechanical equilibrium

A state wherein no physical changes occur; a state of steadiness

caisson disease

An affliction developed by people moving in and out of caissons quickly; also called the bends and decompression sickness

steel

An alloy of iron and carbon that is hard, strong, and malleable

geotechnical engineer

An engineer who evaluates and stabilizes foundations for buildings, roads, and other structures

structural engineer

An engineer who investigates the behavior and design of all kinds of structures, including dams, domes, tunnels, bridges, and skyscrapers, to make sure they are safe and sound for human use

wrought iron

An iron alloy that is less brittle than cast iron

The Bosporus Bridge

At the time in 1973, this was the only bridge that linked two continents (Asia and Europe); shuttles traffic on an eight-lane deck. Each direction has three lanes for vehicles, plus one emergency lane and one sidewalk. Pedestrians were allowed to access the bridge until 1977; in 2005, Venus Williams and Ïpek Senoglu played a tennis match on the bridge

reinforced concrete

Concrete with steel bars or mesh embedded in it for increased strength into tension

Gateshead Millenium Bridge

In this bascule bridge, one or two pieces of the bridge deck, known as leaves, swing up to provide clearance for boat traffic passing underneath; spanned the Tyne River; The bridge has a pair of steel arches. In its "down" position, one arch forms the deck of the pedestrian and cycle path. The other arch sits at a 90-degree angle to the first, with cables strung between the two to provide support for the deck. When the bridge needs to move to its "up" position, eight electric motors tilt both arches as a single, rigid structure. As one arch lowers, the other rises to act as a counterbalance.

continuous span beam bridge

Simple bridge made by linking one beam bridge to another; some of the longest bridges in the world are continuous span beam bridges

DeNeveu Creek Bridge

Since steel rebar can corrode when exposed to the elements, rebar is usually coated with epoxy to shield the steel from corrosive chemicals. But this bridge (in Wisconsin) is the first to use a reinforcing matrix made from a fiber-reinforced polymer. Since it's nonmetallic, the polymer material won't corrode

tensile strength

The ability of a material to withstand tension

torsion

The rotational or twisting force that bridges face

first condition for equilibrium

The sum of all forces is zero

second condition for equilibrium

The sum of all torques is zero

cables

These structures, running between the bridge's two anchorages, receive most of the tension on a suspension bridge. They're literally stretched from the weight of the bridge and its traffic.

St. Anthony Falls Bridge

This bridge opened in 2008, after a steel deck truss bridge carrying motorists in and out of Minneapolis collapsed into the Mississippi River in 2007; has 323 sensors constantly monitoring and collecting data that can be analyzed to determine stress points or trouble spots; the concrete is also cleaning the air (because it contains an agent that, in the presence of light, breaks down air pollutants, including carbon monoxide, nitrogen oxide and benzene).

aqueduct

a bridge that conveys water over an obstacle, such as a ravine or valley.

arch bridge

a curved structure that converts the downward force of its own weight, and of any weight pressing down on top of it, into an outward force along its sides and base

resonance

a fatal force to a bridge that is a vibration caused by an extended force that is in harmony with the natural vibration of the original thing. These vibrations travel through a bridge in waves.

tension

a force that acts to expand or lengthen the object it's acting on; one of the two primary forces a bridge has to contend with

compression

a force that acts to shorten the object it's acting on; one of the two primary forces a bridge has to contend with

Chesapeake Bay Bridge Tunnel

a series of bridges and tunnels that spans 17 miles of brackish water separating Cape Charles and Virginia Beach, Virginia; most is above water supported by 5000 piers. To allow ships to pass, two 1-mile long tunnels carry traffic beneath the bay's primary navigation channels. Man-made islands, each approximately 5 acres in size, are located at each end of the two tunnels and act as transition points between the tunnels and bridges.

beam bridge

a simple type of bridge, composed of horizontal beams supported by vertical posts

caisson

a watertight, dry chamber in which people can work underwater

truss

adds rigidity to the existing beam, greatly increasing its ability to dissipate the compression and tension (forces spread through this structure)

deck truss

almost all suspension bridges feature this supporting truss system beneath the bridge deck; it helps to stiffen the deck and reduce the tendency of the roadway to sway and ripple.

girder bridge

another name for a beam bridge

average span by bridge type (lowest to greatest)

beam, arch, suspension

BATS: Key structural components in bridge construction

beams, arches, trusses and suspensions.

truss

can be added to an existing beam to increase rigidity (greatly increasing its ability to dissipate the compression and tension forces)

abutments

components of the bridge that directly take on pressure

Incan empire

in the 1500s, it was discovered that this civilization was building 150 foot long bridges entirely out of grass.

Tacoma Narrows Bridge

most noteworthy example of resonance in 1940, destroyed this structure in Washington. The structure was designed to withstand winds up to 120 miles per hour and collapsed in a 40-mile per hour wind.

Octavio Frias de Oliveira Bridge

one of the most unique bridges in the world; this cable-stayed bridge spans the Pinheiros River, which bisects the western side of Sao Paulo, Brazil; its design features two curved decks that cross each other through an X-shaped supporting tower.

dampeners

structures designed within a bridge that disrupt resonance waves

Golden Gate Bridge

suspension bridge stretching 8,981-ft (2,737-meter) over the treacherous waters of the San Francisco Bay.

towers

suspension bridge's cables transfer the bulk of the compression to these structures which then dissipate the compression directly into the earth where the cables are buried.

Millau Viaduct

tallest vehicular bridge in the world; the tallest tower of this cable-stay bridge is higher than the Eiffel tower; drivers who can get over their fear of heights can shave 4 hours off their trip driving this way

span

the distance between two bridge supports

height

the factor that controls the distance that the beam can span

dead load

the weight of the bridge structure including columns, beams, nuts and bolts

live load

the weight of the people moving on or in a structure including people, cars, trains

Oresund Fixed Link bridge

the world's longest cable-stayed bridge for both road and railway Its towers are 669 feet high and provide a navigational clearance of 187 feet under the main span. The bridge features two levels, with the railway running along the lower deck and the roadway on the upper.

ways that cable-stayed bridges differ from suspension bridges

they don't require anchorages; they do not need two towers. (Instead, the cables run from the roadway up to a single tower that alone bears the weight)

Hangzhou Bridge

this cable stayed bridge opened in 2008; China's longest bridge; 22 miles long across the Qiantang River at the Yangtze River Delta on the East China Sea; carrying six lanes of traffic in both directions. Commuters pay $12 toll to cross

shape

this factor gives an arch bridge its strength

weather

this force is responsible for most bridge failures

Akashi Kaikyo Bridge

this longest spanning suspension bridge opened in 1998; spans 2.4 miles across the Akashi Strait, with a central section stretching almost half of that length. Its towers soar 928 feet above the water, and its cables carry tensile forces of 132,000 tons; it weathered a 7.2-magnitude earthquake during construction.

thermal load

when a structure changes shape with temperature

buckling

when compression is too much, and the bridge cannot endure it, this occurs

snapping

when tension surpasses an object's ability to handle the lengthening force

soil settlement

when the soil beneath a structure settles unevenly

through truss

where the truss work is above the roadway

deck truss

where the truss work is below the roadway