Bridges
There are basically 5 different
types of bridges:
• Beam bridge
• Truss bridge
• Arch bridge
• Suspension bridge
• Cable-stayed bridge
An engineer would choose the correct bridge based on how
far it must span from one support to the next.
Engineers must take many variables into consideration.
Each bridge deals differently with tension and compression.
•If part of the bridge cannot stand the compression it will
buckle.
•If part of the bridge cannot stand the tension it will snap.
Bridges
The four main factors are used in
describing a bridge. By combining these
terms one may give a general description of
most bridge types:
span (simple, continuous, cantilever),
material (stone, concrete, metal, etc.),
placement of the travel surface in
relation to the structure (deck, pony,
through),
form (beam, arch, truss, etc.).
Beam Bridges
The beam bridge...
consists of a horizontal beam supported at each end by piers. The
weight of the beam pushes straight down on the piers.
The farther apart its piers, the weaker the beam becomes. This is
why beam bridges rarely span more than 250 feet.(76,2m)
When something pushes down on the beam, the beam bends. Its
top edge is pushed together, and its bottom edge is pulled apart.
beam bridges are usually metal or reinforced concrete.
Forces acting on a Beam Bridge
Beam Bridges
Typical Spans 10m-200m
Worlds Longest Span
700m (Ponte Costa in
Silva, Brazil)
Truss Bridges
(Most Popular Type of Beam Bridge)
The truss bridge...
consists of an assembly of triangles.
Truss bridges are commonly made from a series of straight, steel
bars.
Rigid arms extend from both sides of two piers, creating a triangle.
Diagonal steel tubes, projecting from the top and bottom of each
pier, hold the arms in place. The arms that project toward the
middle are only supported on one side, like really strong diving
boards. These "diving boards," called cantilever arms, support a
third, central span.
Truss Bridges
Dump Road Bridge , Minnesota
Typical Spans 40m-500m
Worlds Longest Span
863m (Pont de Quebec)
Sellwood Bridge, Oregon
Arch bridges
Second oldest bridge type
next to beam bridges.
Well suited to be made out
of stone.
Best suited for crossing
rivers and valleys, because
they don’t require piers in
the center.
Known for their beauty
Both ends of the bridge are
fixed, and do not allow any
horizontal movement.
The Natchez Trace Bridge, Tennessee
Forces acting on an Arch Bridge

The arch is squeezed together, and this squeezing force is carried outward
along the curve to the supports at each end. The supports, called abutments,
Natchez Trace Bridge, Tennessee
push back on the arch and prevent the ends ofThethe
arch from spreading
apart.
Arch Bridges
Arch bridge is one of the most popular types of bridges,
which came into use over 3000 years ago and remained
in height of popularity until industrial revolution and
invention of advanced materials enabled architect to
create other 118 modern bridge designs.
The greatest bridge builders of antiquity were the ancient
Romans. The Romans built arch bridges and aqueducts
that could stand in conditions that would damage or
destroy earlier designs.
Arch Bridges
Due to no horizontal movement the ground that the
bridge is built on has to be very solid and stable.
Typical spans 40m-150m
Worlds longest span 924m (New River George Bridge,
US
Suspension Bridges
Humber Bridge, England
Golden Gate Bridge, California
Suspension Bridges
use steel cables to
support weight. Steel
wire is very strong
and can support large
tensile forces. A
single 0.1” thick wire
can support more
than half a ton without
breaking!
Akashi Kaikyo Bridge, Japan
Suspension Bridges
A typical suspension bridge is a continuous girder with one or
more tower erected above piers in the middle of the span.
At both ends the cables the cables have large anchors or counter
weights, to hold the ends of the cable.
Typical spans 70m – 1000+ m
Worlds longest span 3911m (Akashi Kaikyo Bridge, Japan)
Forces acting on Suspension Bridges

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. The 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.
Cable-Stayed Bridges
Cable-stayed bridges differ
from suspensions bridges in
the way that the cables are
connected to the towers.
In cable-stayed bridges, the
cables are attached to the
towers, which bear the load
alone.
Cable-Stayed Bridges
The cables of a
suspension bridges ride
freely across the
towers, transmitting the
load to the anchorages
at either end.
Cable-Stayed Bridges
Cable-stayed bridges are distinguished by the number of
spans, number of towers, girder type, number of cables and
the arrangement of their cables.
Typical towers include:
Single
Double
Portal
Typical cable arrangements include:
Mono
Fan
Harp
Star
A-shaped
The Cable Stayed Bridge
A typical cable stayed bridge is a continuous
girder with one or more tower erected above
piers in the middle of the span.
 From these towers, cables stretch down
diagonally (usually to both sides) and support
the girder.
 Steel cables are extremely strong but very
flexible.

Cable Stayed Bridge Cont.
Cables are very economical as they allow a
slender and lighter structure which is still able
to span great distances.
 Typical spans 110m - 480m
 World’s Longest span 1,480m (Tatara Bridge,
Japan)
