Bridges - Needham.k12.ma.us

frizzflowerUrban and Civil

Nov 29, 2013 (3 years and 9 months ago)

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Bridges
Bridges


There are three major types of bridges:
arch bridge

suspension
bridge

beam bridge


The biggest
difference
between the three bridge types
is the

distances they can cross in a single
span

(distance between two bridge supports).

up to 7,000 feet
beam bridge
beam bridge
span

distances
up to 200 feet
arch bridge
arch bridge
up to 800 - 1000 feet
suspension
suspension
bridge
bridge


STRESS…
STRESS…
is a
push
or
pull

(
a force
)
that acts on a structure.
There are 4 kinds of stress…

Shear
Shear


The beam bridge
The beam bridge
consists of a horizontal

beam

The weight on the beam
pushes straight down
on the
beam and the piers (
compression

force). This makes
the beam
bend
(
tension

force). The farther apart its
piers, the weaker the beam becomes. This is why beam
bridges rarely
span
more than 200 feet.
supported at each end by

piers.
piers.


The
compression
compression

and
tension
tension


forces on this bridge are spread
across the bars of the
trusses.
trusses.

This reduces the stress on the
beam

and
piers
, and enables
truss bridges to span farther
than plain beam bridges.

The truss bridge
The truss bridge
is a beam bridge reinforced with

triangular supports

called

trusses
.
Truss Bridge Forces
Truss Bridge Forces


The
compression
compression
force is directed down along the curve
of the arch to
the supports at each end.
Arch Bridge Forces
Arch Bridge Forces
Compression
Compression

is the only force acting on arch bridges.
The supports, called
abutments
abutments
or
buttresses
buttresses
, push
back on the arch and prevent the ends of the arch from
spreading apart. This prevents the arch from collapsing.


Arch bridges can be made from many different materials…
stone
stone


cast iron or steel
cast iron or steel


concrete
concrete


brick
brick


In all suspension bridges, the roadway hangs from massive
steel cables
steel cables
, which are draped over two
towers
towers
and
secured into solid
concrete
blocks, called
anchorages
anchorages
, on
both ends of the bridge. The cars push down on the
roadway
(compression)
,
but because the roadway is
suspended, the cables transfer the
load
(weight)
into
compression
in the two towers. The two towers support
most of the bridge's weight.
Suspension Bridge Forces


Lynn Canyon Park suspension
bridge, Vancouver

The Akashi-Kaikyo Bridge in Japan is currently the
longest bridge in the world, being some four kilometers
in total length with a centre span of 1990 meters.
Low-tech
Low-tech
High-tech
High-tech


The cable-stayed bridge, like the suspension bridge,
supports the roadway with massive
steel
steel


cables
cables
, but
in a different way. The cables run directly from the
roadway up to a
tower
, forming a unique "A" shape.
Cable-Stayed Bridges


Sunshine Skyway Bridge
Sunshine Skyway Bridge
St. Petersburg, Florida and Bradenton, Florida
Cable-stayed bridges, like the
Sunshine Skyway in Florida,
require less cable and can be
built much faster than
suspension bridges. Cable-
stayed bridges are becoming
the most popular bridges for
medium-length spans
medium-length spans

(between 500 and 3,000 feet).
The
Leonard P. Zakim Bunker Hill Bridge
Leonard P. Zakim Bunker Hill Bridge
, part
of The Big Dig Project in Boston, is the widest
cable-stayed bridge in the world (183 feet wide).


 
 
The distribution of forces in a cantilever bridge is
shown in this demonstration using chairs, poles,
counterweights, and humans.
Cantilever
Cantilever
Bridges
Bridges
Quebec Bridge
Firth of Forth Bridge, Scotland
A
cantilever bridge

is a bridge built using
cantilevers:
structures that
project horizontally
into space, supported
on only one end.
Cantilever bridges

link


Which type of stress is acting on the Tacoma Narrows
Bridge, shown below?
Torsion
Torsion
, from high winds, tore this bridge apart in 45
minutes on November 7, 1940. Click on the link below to
see a video of the bridge just before it collapsed.
The Tacoma Narrows Bridge Disaster, November 1940


Now that you’ve become an
expert on bridges, take the
Bridge Challenge. Just click
on the link below.
Bridge Challenge


Great Bridge Websites
Great Bridge Websites
Building Big: Bridges
Building Big: Bridges
Making the Modern World: Bridge Design
Making the Modern World: Bridge Design
DLT Bridges
DLT Bridges
Richman Galleries
Richman Galleries