Engineering in Bridge Building

ENGINEERING IN BRIDGE BUILDING

Great Structures

The 1930s witnessed the construction and completion of some of the most famous bridges in the United States. Some incorporated novel experimental approaches, as in the case of the Rogue River Bridge in Gold Beach, Oregon. This structure, comprising seven 230-foot two-rib arch spans, employed pre-compression techniques developed in France earlier in the century and was completed in 1931. Other projects not only proved to be engineering challenges but captured public attention. Ideas about extending a new bridge from Manhattan directly into New Jersey over the Hudson River had been proposed since the 1890s but were bogged down in bureaucratic and political issues, ranging from concerns about hindering river traffic to engineering disagreements. Such disagreements still occur despite the successful completion and use of the George Washington Bridge. Thirty-five hundred feet long with a wire-cable suspension system, it was begun in 1927 and completed four years later under the supervision of Othmar H. Ammann, a Swiss-born engineer.

The California Challenge

In San Francisco plans for extending a massive bridge to Oakland had been proposed since the 1850s. Repeatedly these ideas were deemed utopian in view of the huge dimensions of the proposed project. Nevertheless, demands for construction became increasingly pressing. By 1928 about thirty private construction proposals existed, but California decided to build one bridge with public funds following the example of the George Washington Bridge. With the help of President Herbert Hoover, California established the Transbay Bridge (San Francisco/Oakland Bay Bridge) Project in September 1929. Following the submission of tentative layouts in the summer of 1930, the California legislature appropriated more funds the following year for further studies. The U.S. War Department, which controlled the mouth of the bay, revised the plans to allow easier water navigation below, and a construction permit was obtained on 19 January 1932. The next challenge was to solve the distance problem. While a suspended bridge was the preferred design, it was unclear where it could actually be suspended over a two-mile length over water. The final decision called for two suspended bridges placed back to back, with an overall length of 8,100 feet (43,500 feet including the approaches), which would make the project the largest suspended bridge in the world. Groundbreaking took place on 9 July 1933, Despite the national economic crisis, financing was solved with the issuing of bonds by the Reconstruction Finance Commission. The final cost of construction was $79.5 million. The bridge opened on 12 November 1936,

The Golden Gate

Plans for building a bridge over the Golden Gate had flourished during World War I, but it was not until the 1920s that projects were seriously developed and permissions granted. The Golden Gate Bridge Company, established in 1928, appointed Joseph Strauss as chief engineer in August 1929. Following multiple ground surveys and test borings, ground was broken on 5 January 1933. Not only did construction face the challenge of strong sea tides that required the construction of a fender-shaped seawall, but the question of whether the tower foundation could withstand an earth-quake caused serious concern and still remains an issue, Despite such problems, the Golden Gate Bridge opened on 1 October 1937. The construction stands as a master-piece of modern American bridge design and engineering,

THE DEVELOPMENT OF FM RADIO

The use of amplitude modulation (AM) for early radio broadcasts made them subject to interference. Among the inventors who worked toward remedying this situation, Edwin H. Armstrong stands out as one of the developers of frequency modulation (FM). He filed four patents for frequency modulation between 1930 and 1933 for the purpose of creating a new kind of broadcasting system. In 1934, with the assistance of RCA, Armstrong conducted FM tests from the top of the Empire State Building in New York. In 1935 he publicly demonstrated his discovery to radio engineers in New York. RCA nevertheless felt there was too much at stake in the development of FM and dropped all support. Armstrong then went to work for competitors Zenith and General Electric. World War II interrupted further development of FM-band radio, although it was abundantly used by the military. The beginnings of FM commercial radio did not come until the 1950s and truly expanded only in the late 1960s.

Source:

Erik Barnouw, A History of Broadcasting in the United States, 3 volumes (New York: Oxford University Press, 1966-1970).

Sources:

David Nye, American Technological Sublime (Cambridge, Mass.: MIT Press,' 1994);

Daniel L. Schodek, Landmarks in American Civil Engineering (Cambridge, Mass.; MIT Press, 1987).