|Bridge Across the Golden Gate|
The Golden Gate Bridge was the longest suspension bridge in the world when it was completed. in 1937. (Copyright Lee Krystek, 2011)
They said it couldn’t be built.
The strait that connects the Pacific Ocean with the San Francisco Bay is one of the most unforgiving stretches of water in the world. It is 6,700 ft (2,042 m) wide and in the center 500 ft (150 m) deep. Because of the tides moving in and out of the bay the water is subject to strong, swirling currents. Sometimes as the air is forced between the high hills on either side (which is called the “gate”), heavy, gusting winds result that can move as fast as 75 miles per hour. When the wind drops, the area is also often shrouded in heavy fog with near zero visibility. In 1916, because of these factors, San Francisco’s city engineer, Michael M. O’Shaughnessy, estimated that a bridge to span the strait would cost $100 million to construct, an incredible amount of money for that period of time.
Boca del Puerto de San Francisco
Seven Quick Facts
|-Length: 8,981 feet or (2,737 m)|
|-Height: Towers 746 ft (227 m) above the water. Deck 260ft (76 m)|
|-Finished: May 27, 1937|
|-Cost: $35 Million|
|-Location: Entrance to San Francisco Bay, California.|
|-Made of: Concrete base with steel structure in an Art Deco design.|
|-Other: To maintain Its unique International Orange color requires 10,000 gallons of paint a year.|
It took a long time for European explorers to even realize that the gate existed. Captains Juan Rodriguez Cabrillo and Francis Drake, who sailed along the coast in the 16th century missed the entrance to the bay completely, probably because it was covered in fog. It wasn’t until 1769 that Sgt. José Francisco Ortega, who was leading an exploration party by land up the coast, found the strait and reported to his superiors that it prevented him from traveling any further north. In 1775 Juan de Ayala with his ship the San Carlos actually entered the bay and landed on Angel Island, which is named in his honor. Less than a decade later the Spanish established a Fort and a mission on the southern hill of the gate and gave it the name Boca del Puerto de San Francisco with meant “Mouth of the Port of San Francisco.”
That name stuck until the 1840’s when John C. Frémont, an American explorer, military man and later politician, referred to the area in his memoirs as the “Chrysopylae”, or “Golden Gate” because it reminded him of the “Golden Horn” near Istanbul. This more picturesque term quickly replaced the older one, especially after the discovery of gold in California in 1848.
With its fine harbor, San Francisco quickly became a major city in the 19th century. Because of its location out on a peninsula, with the Pacific Ocean to the west and the San Francisco Bay to the East, it became dependent to ferry service to move goods and people to and from the other bayside communities. As the city entered the 20th century people began to recognize that the lack of bridges into the city was slowing its growth. Though there had been talk about building a bridge across the gate for many years, in 1916 a proposal for a bridge written by editor James Wilkins in the newspaper the San Francisco Bulletin got everyone’s attention and prompted O’Shaughnessy to make his estimate.
The gate to the bay in the late 19th century before the bridge was built.
The Challenge to Design the Bridge
O’Shaughnessy decided to reach out to other bridge engineers to see if they could come up with a way to bring the cost of such a structure within reason. Joseph Strauss was one those that responded. Though Strauss’s actual experience was limited to smaller drawbridges, as an engineering student he had designed a 55-mile (89 km) long railroad bridge across the Bering Strait between Russian and the United States. The Golden Gate was a challenge to his liking and he proposed a cantilever bridge with a suspended span in the very center that he thought could be built for $17 million.
No money was available for a bridge though until 1923, however, when the Golden Gate Bridge and Highway District Act was put into place giving the nearby counties the right to organize, borrow money, issue bonds, construct a bridge and collect tolls from it. Then in 1928 the Golden Gate Bridge and Highway District was formed to actually finance and erect the bridge and things started moving forward quickly.
The agency selected Strauss as chief engineer and hired a number of consulting engineers including Leon S. Moisseiff who had worked on the design of the Manhattan Bridge over the East River in New York and the Ben Franklin Bridge over the Delaware River in Philadelphia. Another important engineer involved was Charles Ellis, a former professor of structural and bridge engineering at the University of Illinois.
Moisseiff and Ellis reviewed Strauss’s original design and though they deemed it workable, recommended a full suspension bridge instead for engineering and atheistic reasons. It is fortunate they did. Strauss’s cantilever bridge was sturdy but didn’t have the sweeping lines that are so appreciated in the bridge today. After reviewing their observations, Strauss agreed that advances in the science of metals in the previous decade made a simple suspension bridge more practical and by 1929 the new design was set. In August of 1930 a permit was finally obtained from the War Department who had been opposing the bridge, fearing it might prove a navigation hazard to their ships. Construction began on January 5th 1933.
Each of the towers stands 746 feet (227m) above the water. (Copyright Lee Krystek, 2011)
Making the Longest Suspension Bridge in the World
The first steps in building the bridge were to construct the anchorages on either side to tie down the bridge’s two main cables. This required a huge amount of concrete and plants were built on both the north and south sides of the gate to meet the need. The anchorages took three years to finish and were completed in 1936.
At the same time the two towers, the highest ever built for a suspension bridge, were started. The north one was located on shore which made construction easier, but the south tower was in the water over a thousand feet from the southern bank. To create an artificial island to put the tower on construction crews lowered concrete “fenders” 30 feet long down to the sea bed. The fenders enclosed an area about the size of a football field which was then pumped out and filled with concrete. The steel tower was then constructed on top of that. Once the towers and anchorages were in position, then work on the main cables could start.
Unlike other designs a suspension bridge’s strength rests on its cables. In the case of the Golden Gate Bridge the main cables are 36 inches in diameter and contain 27,572 individual galvanized steel wires. The cables are anchored in concrete at either end and run 7,650 ft (2,332 m) over the top of the two towers. The weight of the roadbed and all the traffic on it is transmitted up to the main cables by 250 pairs of vertical suspender cables. The load on the main cables is then transmitted to the towers (61,500 tons or 56,000,000 kg for each tower) as a downward force.
Moisseiff came up with the idea of allowing the roadbed to flex a bit in the breeze and transmitting the forces caused by the wind through the cables to the towers . This made the deck lighter and thinner then on pervious suspension bridge designs. This saved time and money and also made the bridge more ascetically pleasing. Moisseiff later applied an even more extreme version of this idea to the Tacoma Narrows Bridge which he designed a few years later. Unfortunately, in that case he made the roadbed too flexible and only a few months after it opened in 1940, the bridge deck started oscillating wildly in a forty mile-per hour wind, and after a few hours collapsed.
The bridge’s two main suspension cables are three feet across. (Photo by Tewy licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.)
Near the end of construction on the Golden Gate a terrible accident happened. Strauss had designed a safely netting that was suspended under the bridge to catch members of the construction crew who lost their balance. Because the bridge’s deck was so high, around 250 feet, someone falling off the bridge would not only be at risk for drowning in the water, but would also hit the surface at a speed of over 75 miles per hour. Such an impact, even into water, is often fatal by itself unless the victim hits the surface at just the right angle.
The net Strauss had created saved a number of lives during construction, but on Feb. 17, 1937, a 5-ton work platform fell from the bridge into the net along with 10 workers. The safety device, under the strain, slowly gave way and the workers, entangled in the net, drowned.
One of the last jobs was to paint the bridge. Architect Irving Morrow, who was responsible for the bridge’s art deco appearance (a style that emphasizes bold lines and symmetry), decided to keep the International Orange color was originally meant only to be a sealant for the steel. The Golden Gate Bridge has displayed that unique color ever since. It complements the surrounding hills and also enhances the bridges visibility in fog.
The span of steel was completed at a cost of $35 million and opened to pedestrians on May 27, 1937. An estimated 200,000 people walked, ran or roller-skated across it and the next day President Franklin D. Roosevelt remotely used a telegraph to officially open it to vehicles.
When it was opened, at a length of 1.7 miles and with a central span of 4,200 ft, it was the longest suspension bridge in the world. Though several bridges have surpassed its record over the years, it remains perhaps the most beautiful bridge in the world, matched perfectly with its majestic surroundings.
In 1994 the American Society of Civil Engineers named the bridge one of the Seven Wonders of the Modern World. (Copyright Lee Krystek, 2011)
Though Strauss is often remembered at the designer of the bridge, much of the credit should really go to Ellis. The thousands of calculations necessary to design the bridge were in large part made by him in an era before computers. For reasons that are still unclear he was fired part way through the project by Strauss. Despite this Ellis, obsessed with the finishing the bridge, continued working on his own time filling some ten books with the needed calculations, done by hand, to finish the construction.
Unfortunately the notoriety of the bridge has an unpleasant side effect. It draws an inordinate number of depressed people to it who commit suicide by jumping off the span. Despite efforts to address this by putting suicide hotline telephones on the bridge and increasing security, it is estimated that more than 30 people perish this way per year. Because the bridge is often shrouded in fog and the strong currents may wash bodies out to sea, many of the deaths go unnoticed.
The Golden Gate Bridge has become beloved symbol of the City of San Francisco and thousands of tourists come to see the bridge that couldn’t be built each day. In 1994 the American Society of Civil Engineers named it as one of the seven wonders of the modern world.