Technical Description

by Russell Mohammed

By: Russell Mohammed

Suspension Bridges:
The History of Suspension Bridges

Across the world, there are a great number of bridges that have been built in order for individuals to get from point A to point B. However, most people are not aware of the different bridges that have been made in today’s society. For example, one of the oldest bridges made by man is the suspension bridge. One of the most famous suspension bridges is the Golden Gate Bridge in San francisco that was completed in 1937.

(Figure 1)

What is a Suspension Bridge?
Suspension bridges are known to be one of the oldest bridges made by man that provide a solution for long span distances across a stream of water. A suspension bridge is a bridge where the main deck is supported by vertical cables that are suspended by larger cables, holding up the two towers. Suspension bridges get their name, due to the fact that the roadway is suspended by two tall towers. Before cables, designers often used iron chains to support the structure.The first iron chain suspension bridge on U.S soil was in 1801, made at Jacobs Creek in Westmoreland County, Pennsylvania.
(Figure 2)

How Are Suspension Bridges Designed?
In order for a suspension bridge to be built, engineers often design a cable support system where most of the weight is supported by the two towers. The main supporting cables have smaller cables called suspenders that run vertically from the bridge deck. The suspenders create arcs between the towers and the anchorage because of the deck’s compression force being transferred to the towers. With the forces of work being balanced on both side of the towers, the bridge deck pulls inward on the towers. As the deck is pulling on the towers, the main support cables are anchored on each end into solid rock or massive concrete blocks underground. Furthermore, the anchorage pulls outward on the towers with an equal force creating balance, and centering the weight of the bridge. This unique design allows suspension bridges to span to distances as great as 7,000 feet or more.
(Figure 3)
The Golden Gate Bridge:
One of the longest and well known suspension bridges in the world is the Golden Gate Bridge. It spans almost two miles across the Golden Gate where the San Francisco Bay meets with the Pacific Ocean. The idea of the bridge began in 1869 by Charles Crocker who made a proposal to the board of supervisors in 1872. However, the idea didn’t follow through because the cost for the bridge would of been too high. Then, in 1917 Joseph Strauss got involved with the bridge and met Michael O’Shaughnessey the City Engineer. In 1919, O’ Shaughnessy obtained permission by the board of supervisors to undergo more studies of the bridge. O’Shaughnessy results stated, the bridge would cost 100 million dollars to build. With the help of Joseph Strauss, he started designing ideas and coming up with a pure suspension bridge that will range between 25-35 million dollars. Eventually by May 1923, the state legislature passed the Golden Gate Bridge and Highway District Act of California. While most of the obstacles were being cleared for the bridge, the Great Depression of 1929 begun, limiting financial options. However, in 1932, San Francisco’s Bank of America agreed to buy the entire project in order to help the economy. Finally, on January 5th, 1933 construction commenced and on May 27th, 1937 The Golden Gate Bridge officially opened. It had a distance of 8,981 feet, with the towers having a height of 500 feet and two main cables to support the towers.
(Figure 4)
Conclusion:
In conclusion, suspension bridges are vital to our society because they broaden our horizons. They have been the oldest bridges made by man that led to the ideas of different forms of bridges. They’re of great convenience, allowing millions of people to complete tasks that would have otherwise proven difficult without. Suspension bridges contributes to everyone differently. For example, providing safe transport of goods from one location to another, more job opportunities for people living outside of that area, and even save passage for those who would like to visit their loved ones. With each bridge we’re opening doors to new opportunities, and new experiences whether it’s personal or professional reasons they are beneficial to us all.
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