Monday, August 4, 2008
Golden Gate Bridge
When it opened to traffic in May 1937, San Francisco’s Golden Gate Bridge boasted the longest single clear span in the world, a claim held true for twenty-seven years. The center span, at 4,200 feet (1,285 meters), was three times longer than the Brooklyn Bridge and 700 feet (214 meters) longer than the recently completed George Washington Bridge in New York. Including the two side spans of 1,125 feet (344 meters) and the 90-foot-wide (27.5-meter) road approaches, its total length was 8,981 feet (2,746 meters). Its towers were the tallest, its main cables the thickest and longest, its submarine foundations the largest ever built. Moreover, the foundation piers of the Golden Gate Bridge were built in the surging currents of the sea and its superstructure was erected across a canyon through which the wind howled at speeds up to 60 mph (96 kph). And all this was achieved without government funding in the midst of a deep economic depression. Against all the odds, the Golden Gate Bridge was a brilliant answer to a whole cluster of “insoluble” problems.
On 5 August 1775 Lieutenant Don Juan Manuel Ayala of the Spanish navy sailed the San Carlos from the Pacific Ocean into San Francisco Bay through the 3-mile-long by 1-mile-wide (4.8-by-1.6-kilometer) strait now known as the Golden Gate (one Captain John Fremont of the U.S. Army Topographical Engineers named it some 60 years later after Turkey’s Golden Horn).
There is a compelling myth that the San Francisco eccentric Joshua Norton, self-styled “Norton the First, Emperor of the United States and Protector of Mexico,” decreed in 1869 that a bridge be built across the Golden Gate. The story may have become confused with his pronouncement of March 1872 ordering a bridge across the Bay between Oakland Point and Goat Island, an idea he probably gleaned from well-publicized current transportation debates. In fact, the possibility of spanning the Golden Gate was first raised in 1872 by the railroad owner Charles Crocker, who naturally wanted to build a railroad bridge. But little more was heard of the matter until July 1916.
James Wilkins, editor of the San Francisco Call Bulletin, began a campaign that provoked City Engineer Michael O’Shaughnessy to seek, nationwide, the opinion of engineers on the project. Most said a bridge could not be built; the objections raised included the width of the strait, persistent foggy conditions, high winds and ocean currents, and not least, the high cost: some forecast $100 million. However, the experienced Chicago bridge builder Joseph Baermann Strauss (1870–1938) believed that a bridge was feasible and that it could be built for under $30 million. In June 1921 he proffered a preliminary design for a railroad trestle with a cost estimated at $27 million. Then he energetically tried to convince local politicians that he was right. Although urban growth and traffic congestion led to an urgent need to cross the Golden Gate, all available state and federal finance had then been diverted to other projects.
In 1922 O’Shaughnessy, Strauss, and Edward Rainey, secretary to San Francisco’s mayor James Rolph Jr., proposed the formation of a special bridge district comprising the twenty-one affected counties to oversee financing, design, and construction of the bridge. The California State legislature passed the Golden Gate Bridge and Highway District Act in May 1923. In December 1924 the War Department authorized San Francisco and Marin Counties to construct a bridge. Despite opposition from vested interests, the Golden Gate Bridge and Highway District was immediately formed to realize the project.
Eleven engineering firms submitted proposals, and Strauss, assisted by Clifford Paine, was selected as chief engineer in August 1929. Consulting engineers Othmar Amman and Leon Moisseiff, both of New York, and Professor Charles Derleth Jr. of the University of California were appointed. The consulting architects were the husband-wife team of Irving and Gertrude Morrow. Strauss, who had never designed a suspension bridge, first proposed an inelegant cantilever-cum-suspension structure, but Moisseiff, convinced that a simple suspension bridge was possible (although such a span had never been attempted), helped refine the design that was eventually built. The architects did their part, too, designing handrails and light poles, tapering the tower portals, and designing lighting, all to emphasize the bridge’s simple beauty. And, setting aside the conventional paint colors used on bridges, they selected the distinctive “international airways orange” for which the Golden Gate Bridge is famous. That, Irving Morrow believed, would look better in the spectacular landscape and would be more visible in the sea mists for which the Bay Area is noted.
In August 1930 the War Department approved a 4,200-foot (1,285-meter) main span, 220 feet (67 meters) above the sea. Although the United States was sunk in the Great Depression, a $35 million bond issue to finance the bridge received overwhelming popular support. Contracts worth $23.8 million were let in November 1932, and construction started the following January. Over the next four years it proceeded in the face of many natural problems—rapid sea currents, frequent fogs, and high winds—and technical ones, especially the construction of earthquake-resistant piers in 100 feet of open water. The latter was solved by building elliptical concrete fenders, 300 feet long and 155 wide (92 by 48 meters), within which the 148,000-ton (134,500-tonne) concrete piers could be poured; rising 15 feet (4.6 meters) above high-water mark, the fenders also protect the piers from the onslaught of the sea. The piers and the approach trestles were completed by December 1934 and the 121-foot-wide (37-meter), 750-foot-high (230-meter) towers were standing a little over six months later. The steel sections for the towers, fabricated in Bethlehem, Pennsylvania, were sent via East Coast seaports through the Panama Canal to McClintic-Marshall’s yards in Alameda. Then they were carried by lighters to the site, lifted by cranes, and erected by teams of riggers.
Catwalks spanned the Golden Gate by July 1935, and John A. Roebling and Sons of New Jersey began spinning the two main cables from the San Francisco and Marin anchorages four months later. Each galvanized steel cable is 36.375 inches (920 millimeters) in diameter, comprising 61 strands of 452 wires. They were completed by March 1936, and the roadway steel was placed from June through November, allowing construction of the flexible in situ concrete road deck, finished by April 1937. The bridge was opened to pedestrian traffic on 27 May 1937 and to vehicles at noon the following day. It had been achieved ahead of schedule and under budget. An estimated 200,000 people walked over it on the first day, and a weeklong Golden Gate Bridge Fiesta celebrated the event with fireworks, parades, and other entertainment.