THE HISTORY OF BRIDGES
THE HISTORY
OF BRIDGES
TRANSPORTATION
IN
AMERICA
Why Do We Need Bridges?
To get from one place to another over
an obstacle.
COVERED WAGONS
In the 1850s, covered wagons heading West had to cross streams or rivers. Without adequate bridges in place, the pioneers would sometimes travel many miles out of the way to find a safe place to cross a river.
CROSSING A RIVER
Consider how long it would take to cross a river today if bridges were not included in the road systems.
DELIVERING GOODS
Consider how the movement of people, goods, and services would be affected without highways, which include bridges.
The entire American economy as we know it would be stifled.
EARLY BRIDGES
The earliest bridges consisted mainly of logs that had fallen or were placed across rivers.
While inexpensive, they were less than reliable. Moving heavy loads across them was often impossible.
LOG BRIDGE 1920
FOOT BRIDGE
Some bridges are made to withstand foot travel and small animals
(This is a famous foot bridge in Lucerne, Switzerland. It bends across a river)
BEAM BRIDGE
Consists of a horizontal beam supported at each end by piers
Flat across
Supported at the two ends
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.
TRUSS BRIDGE
Consists of an assembly of triangles. Truss bridges are commonly made from a series of straight, steel bars.
ARCH BRIDGE
Has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet.
A simple bridge reaching across a river in an arching shape
SUSPENSION BRIDGE
Can span 2,000 to 7,000 feet -- way farther than any other type of bridge! Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.
VOCABULARY
Aqueduct - A bridge or channel for conveying water, often over long distances
Cable - The staying or suspending bridge element; in modern suspension bridges, the main supporting cable is hung from towers, and formed from steel wire bound in strands.
VOCABULARY
Deckthe deck is the surface that all the traffic goes across on.
Span - a span is a beam that is supported by two or more support structures.
Famous Bridges
Hoover Dam Bypass
Navajo
Bridge
Essential Questions To Cover
Why Do We Need Bridges?
How Did People Travel Without Bridges?
What were early bridges probably made from – what materials were utilized?
What are the 5 main types of bridges?
