Three Bridge Types

shrubflattenUrban and Civil

Nov 25, 2013 (3 years and 4 months ago)

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Characteristics of
Three Bridge Types

Important Terms:

Squeezing (
Compression
)

Compression is a force that squeezes a
material together. When a material is in
compression, it tends to become shorter.

See a
demonstration
of these forces!

Stretching (
Tension
)

Tension is a force that stretches a
material apart. When a material is in
tension, it tends to become longer.

1. Truss Bridges


Consist
of vertical, lower horizontal &

diagonal
members






Typically composed of triangular


units that are connected at joints



The

truss


is usually a triangular
unit.

Characteristics of
Truss Bridges


It creates a very rigid structure & one
that transfers the load from a single
point to a much wider area


Truss bridges are usually made from
a series of straight, steel bars.


Forces Acting on
Truss Bridges

The larger the

height is compared

to the span, the

g
reater its strength

Every bar in this bridge experiences
either a pushing or pulling force.

The bars rarely bend.

Pros & Cons of

Truss Bridges



Economical to construct



Spans longer distances than
beam bridges



Ability to support weight relies on
the strength of the joints




2. Beam Bridges



Also known as a

girder



bridge



Simplest type of bridge




Made up of a horizontal beam
supported at each end by piers.

Characteristics of
Beam Bridges


The weight of the beam pushes
straight down on the piers.


The farther apart its piers, the weaker
the beam becomes.


These bridges rarely span more than
250 feet.

Under load, the beam's top surface is
pushed down or
compressed

while the
bottom edge is stretched or placed
under
tension


When something pushes down on
the beam the beam bends. Its top
edge is pushed together, and its
bottom edge is pulled apart.

Pros & Cons of

Beam Bridges



Needs
to resist twisting and


bending under
load




Simple design: Less expensive
and


requires little
maintenance




Only
suitable for short spans

(
about


thirty to six hundred feet)


3. Suspension Bridges



Cables are hooked on vertical


suspenders that support the


load




These bridges can span 2,000 to 7,000
feet
--

much farther than any other
type of bridge!

Characteristics of
Suspension Bridges


Most suspension bridges have a truss
system beneath the roadway to resist
bending and twisting.

“Cable
-
stayed” suspension


In all suspension bridges, the roadway
hangs from massive steel cables, which are
draped over two towers and secured into
solid concrete blocks, called
anchorages
, on
both ends of the bridge.


Cars push down on the roadway, but
because the roadway is suspended, the
cables transfer the load into
compression

in
the two towers. The two towers support
most of the bridge's weight.


Early suspension bridges

did not account for wind

Pros & Cons of

Suspension Bridges



Allows for longer spans than other bridge types




Requires stable ground for the

anchorages


at


either end




May withstand earthquakes better than other


bridge types




Aesthetically more beautiful than other two


types of bridge




Lots of
bridge photos
on the quiz link