The Golden Gate was a tough place to build a bridge. The bridge's planners were required to explore factors in an array of scientific fields, including geology, meteorology, seismology, and hydrography. The location's weather, earthquake potential, water currents, wind patterns, and other elements added up to a challenging environment.
By a Fault Line
California's ominous San Andreas Fault slashes from north to south through the Bay area, passing the Golden Gate a short distance out to sea. How would a bridge across the Golden Gate fare in an earthquake? Charles Ellis sounded a confident note in a 1929 lecture to the National Academy of Sciences:
"If I knew that there was to be an earthquake in San Francisco tomorrow and I couldn't get into an airplane and had to remain in the city, I think I should get a piece of clothesline about 1,000 or 2,000 feet long, and a hammock, and I would string it from the tops of two of the tallest redwoods I could find, get into the hammock and feel reasonably safe. If this bridge were built at that time, I would tie me to the center of it, and while watching the sun sink into China across the Pacific, I would feel content with the thought that in case of an earthquake, I had chosen the safest spot in which to be."
Fog-Bound and Cold
Although Ellis had faith in his bridge, he never had to stand on it all day enduring bad weather, as did the project's workers. Signaller Harold McClain recalled, "I'd never been so cold in my life... A guy brought me an overcoat, and I put it on... Eventually, I worked standing in half a barrel." In summer, the Golden Gate was often shrouded in the chilly, gloomy fog that surged through the strait, the largest and lowest of the gaps in the coastal range. The wildly unpredictable intermingling of cold ocean water and moist air teamed with strong winds and could cause air temperatures to drop as many as 30 degrees in a few hours.
Working conditions weren't any better underwater. Over the course of six hours, twice a day, the San Francisco Bay empties one-sixth of its volume into the ocean. The tidal action generates an average flow of 2.3 million cubic feet of water per second (about 3-1/2 times the volume of water the Mississippi River dumps into the Gulf of Mexico). Water currents at the Golden Gate range from 4-1/2 to 7-1/2 knots. When workers had to dive as deep as 90 feet below the surface, the combination of tumultuous tides and currents restricted underwater working time to four twenty-minute periods per day. One construction manager, Jack Graham, stated that it was like trying to build a bridge in the middle of a river.
Exposed to the Elements
Workers began spinning the bridge's cables in November 1935. Exposed out in the middle of the strait, moving carefully on slender catwalks vulnerable to the wind, some said that the construction conditions were the worst they had ever experienced. "You'd wonder what the hell you were doing out there," recalled George Albin. "Fog, cold, wind in your face." Gusting winds and rain caused days of work delays.
When the bridge was finished in 1937, no one fully knew how it would perform in the most extreme conditions. Working with bridge theorist Leon Moisseiff, Charles Ellis had anticipated every possible force on the bridge, and designed accordingly. Yet some things -- the effects of wind on such a long and narrow span, for instance -- could not be predicted. Anemometers and accelerometers were placed to record wind velocities, wind angles, and span movement. Only time would tell how the bridge would do.
Tested by Extremes
On February 9, 1938, the bridge passed its first test. Strong storm winds deflected the bridge off center by as much as eight to ten feet, and caused the roadbed to undulate. In 1941, a 60-mile-per-hour wind made the towers and roadway bend nearly five feet. These events were within the designed tolerances, however, so they did not trigger any retrofitting.
December 1951 brought another test, a severe storm that set the structure to rippling again. This time, bridge officials responded by investing $3.5 million in steel girders to stiffen and add support to the roadway. It was one of only two major modifications made to the bridge in its first six decades. The other was the replacement of corroded suspender ropes in 1970. Considering the harsh environment in which it stands, the bridge has performed admirably.
My American Experience
From the Empire State Buiding to the carvings on Mount Rushmore, the Golden Gate Bridge, and the Space Needle, the U.S. has dozens of impressive, important, and iconic structures. Which ones have you been to? Which has had the biggest impact?