By
Paul Nerrad
Many of the most famous bridges in the world are suspension
bridges. The Golden Gate Bridge in San Francisco being one of them.
Since the early 19th century this type of bridge has been in existence.
The defining feature is that a suspension bridge has the deck hung below
suspension cables on suspenders that are vertical. The history of
suspension bridges dates back to early drawings found in 1595 in the
book Machinae Novae by Fauso Veranzio a Croatian engineer.
In 1801 in Pennsylvania the first suspension bridge was constructed by James Finley. This type of bridge is known as a chain bridge. In England the Dryburgh Abbey Bridge was constructed in the same fashion in 1817 with a 137 meter span, the Union Bridge was built in 1820 and the Manai Suspension Bridge in 1826. The Clifton Suspension Bridge was completed in 1864 with a 214 meter central span and is one of the longest of this type of bridge.
The wire cable suspension bridge, the Footbridge at Falls of Schuylkill, was built in 1816 following the collapse of the chain suspension bridge built by James Finley. It spanned 124 meters and has a 0.45 wide deck. The first large wire cable bridge in the United States was the Wire Bridge in Philadelphia, Pennsylvania designed by Charles Ellet, Jr. And completed in 1842 with a span of 109 meters.
The structural forces of a suspension bridge are compression in the pillars with the tension in the cables. All the force is vertically downward and is stabilized by the cables. Towers suspend the cables which hold up the deck and the weight is transferred by the cables to the towers and then to the ground.
The advantages of a suspension bridge over any other type of bridge is that it can be made of materials such as wood and wire rope. Spans can be longer than in other type of bridge and less material is required to build them. A waterway can remain unobstructed as construction can be done from above. They are better able to withstand an earthquake. Conversely they are stiffer in high winds.
An underspanned suspension bridge is where the main cable hangs under the deck and is anchored to the ground. The deck is less stable and very few bridges have been built in this manner. An example is the Pont des Bergues designed by Guillaume Henri Dufour in 1834.
In older bridges the main suspension cable was often made from linked or chain bars. In modern bridges cables are made from strands of wire giving it greater reliability. If one strand in a hundred breaks it poses less of a threat than one link or one chain which would close the entire bridge. Wire strands are easier to lift from mid-air when constructing rather than lifting heavy chains or links.
Most modern suspension bridges have an open truss structure supporting the roadbed. The Tacoma Narrows Bridge collapsed in 1940 due to its use of plate girders. However with newly developed technology plate structures are being reintroduced as they do not have the danger of vortex shedding found in the Tacoma Narrows Bridge. There are three types of forces on all bridges; the dead load, the dynamic load and the live load. The dead load is the weight of the bridge. Gravity can force a bridge to collapse. A dynamic load refers to environmental conditions such as weather, earthquakes and gusts of wind. Live loads are the traffic that moves across the bridge and the changes in temperatures.
In 1801 in Pennsylvania the first suspension bridge was constructed by James Finley. This type of bridge is known as a chain bridge. In England the Dryburgh Abbey Bridge was constructed in the same fashion in 1817 with a 137 meter span, the Union Bridge was built in 1820 and the Manai Suspension Bridge in 1826. The Clifton Suspension Bridge was completed in 1864 with a 214 meter central span and is one of the longest of this type of bridge.
The wire cable suspension bridge, the Footbridge at Falls of Schuylkill, was built in 1816 following the collapse of the chain suspension bridge built by James Finley. It spanned 124 meters and has a 0.45 wide deck. The first large wire cable bridge in the United States was the Wire Bridge in Philadelphia, Pennsylvania designed by Charles Ellet, Jr. And completed in 1842 with a span of 109 meters.
The structural forces of a suspension bridge are compression in the pillars with the tension in the cables. All the force is vertically downward and is stabilized by the cables. Towers suspend the cables which hold up the deck and the weight is transferred by the cables to the towers and then to the ground.
The advantages of a suspension bridge over any other type of bridge is that it can be made of materials such as wood and wire rope. Spans can be longer than in other type of bridge and less material is required to build them. A waterway can remain unobstructed as construction can be done from above. They are better able to withstand an earthquake. Conversely they are stiffer in high winds.
An underspanned suspension bridge is where the main cable hangs under the deck and is anchored to the ground. The deck is less stable and very few bridges have been built in this manner. An example is the Pont des Bergues designed by Guillaume Henri Dufour in 1834.
In older bridges the main suspension cable was often made from linked or chain bars. In modern bridges cables are made from strands of wire giving it greater reliability. If one strand in a hundred breaks it poses less of a threat than one link or one chain which would close the entire bridge. Wire strands are easier to lift from mid-air when constructing rather than lifting heavy chains or links.
Most modern suspension bridges have an open truss structure supporting the roadbed. The Tacoma Narrows Bridge collapsed in 1940 due to its use of plate girders. However with newly developed technology plate structures are being reintroduced as they do not have the danger of vortex shedding found in the Tacoma Narrows Bridge. There are three types of forces on all bridges; the dead load, the dynamic load and the live load. The dead load is the weight of the bridge. Gravity can force a bridge to collapse. A dynamic load refers to environmental conditions such as weather, earthquakes and gusts of wind. Live loads are the traffic that moves across the bridge and the changes in temperatures.
This article was prepared by Paul Nerrad on behalf of Crafty Design www.logcabintoys.com. Crafty Design is located in Surrey, British Columbia, Canada and specializes in Canyon Suspension Bridge Kits.
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