The Golden Gate Bridge

Updated February 21, 2017 | Factmonster Staff

Golden Gate Bridge Opens
May 27, 1937
by Marcus McGraw

Golden Gate Bridge
Source: Wide World Photos
Even with views of the Pacific Ocean on one side and vistas of the city of San Francisco on the other, these days the most important place to look while on the Golden Gate Bridge is straight down. The long drop serves as a reminder to those on the bridge that they are vulnerable to earthquakes.

Today seismic engineers are hurrying to design a retrofit of the bridge to ensure that it is secure when an earthquake hits. The millions of people that travel on the bridge each month, the 200 foot drop and the nearby San Andreas and Hayward faults together have sparked a race against time to complete the task. While the Golden Gate bridge has fared well during previous tremors, engineers believe its 1930s design literally won't stand up when a major quake hits the area.

In 1937 the Golden Gate Bridge first opened to vehicle traffic providing a major artery between Marin County and San Francisco. Now pictures of the city before the bridge was built seem incomplete. With its 746 foot international orange towers, its sweeping cables and its position on the foot of the ocean, the Golden Gate Bridge is both a major roadway for daily commuters and a popular tourist attraction.

Since the Golden Gate opened, nearly 1.5 billion people have crossed the 1.7 mile stretch. During its first 30 years of operation vehicle traffic jumped 750 percent, sparking the creation of both bus and ferry operations, which are subsidized by today's three dollar toll for southbound drivers.

While engineers did find a way to secure the bridge's towers in the heavy ocean currents, accommodating earthquakes was not part of their original design.

The nearby Oakland-San Francisco Bay Bridge, also built in the 1930s, provides an example of what occurs when tremors and old bridge designs mix. That bridge was hit hard by an earthquake in 1989, forcing the upper deck of the bridge to fall and killing several people traveling below.

San Francisco

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It took four years to build the Golden Gate Bridge, but today's seismic engineers estimate it could take less than sixty seconds to destroy if an earthquake's epicenter hits near the bridge. Even a weaker earthquake could cause unrecoverable damage that would close the bridge.

The integrity of the bridge is now intact, but seismic engineers believe a $175 million retrofit is required to prevent a disaster. To design the retrofit supercomputers are being used to simulate an earthquake's effect on each part of the bridge. The retrofit will take approximately five years to complete and although its cost is significant, it represents only about one-tenth of the eventual $1.4 billion replacement cost of the Golden Gate Bridge.

The retrofit will help reduce the amount of violent action caused by ground motion. To achieve this, several areas will be strengthened to secure the bridge when tremors arrive. The main work will occur on the structural steel, the approach viaducts, as well the concrete piers, pylons and anchorage housings. And the main cable saddles that run to the tops of the towers will be reinforced. The steel tower shafts and the struts that connect them will be overhauled. After work is complete, engineers hope that no matter how hard the bridge is hit, it will be able to remain open to emergency vehicles and that vehicle traffic will return within a month.

For now, everything remains the same on the Golden Gate. Vehicles rush to the city and tourists walk along the railings admiring the great view. So if you're one of the lucky ones to visit the landmark, remember where to look and when to get off.

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