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Golden Gate Bridge | Article

Leon Moisseiff

Latvian native Leon Moisseiff arrived in the United States in 1891, at age 19. Five years later, after receiving a civil engineering degree, Moisseiff became an American citizen. He was so happy about living in America that he named one of his daughters Liberty. In the years to come, his adopted country would be good to him; Moisseiff would join the New York City Bridge Department and become one of America's best-known bridge designers and theorists.

Leon Moisseiff, San Francisco Public Library

Bridge Advisor
In 1925, engineer Joseph Strauss was busy hawking his idea for a bridge to unite San Francisco and its northern neighbor, Marin County. He was also searching for credentialed engineers to lend their names to his project. Through the well-known engineer and textbook author Charles Ellis, Strauss recruited Moisseiff, designer of New York City's Manhattan Bridge. He asked Moisseiff to serve on a board of consultants to the Golden Gate Bridge. Moisseiff, who by that time had become a heavyweight in bridge design theory, publicly loaned support to Strauss' plans.

Withheld Design Judgment
Moisseiff might not have loved glad-handing, but he did display tact. When asked to give his overall judgment of Strauss' plans, he simply mused on the estimated cost, which he deemed was "about correct and may be exceeded by not more than $2,000,000."

A Brilliant Collaboration
Moisseiff worked in tandem with Charles Ellis on the engineering of the Golden Gate Bridge. Moisseiff especially contributed to the force calculations related to wind impact on the bridge. From his New York office, he traded telegrams with Ellis in Chicago, going over an endless string of engineering questions.

Flexible Design
Together, Moisseiff and Ellis explored a practical application of Moisseiff's deflection theory of suspension bridges. They made their bridge design flexible enough to withstand the gales that often blew through the Golden Gate. The bridge would be lighter, longer, and narrower than any of its predecessors -- for example, the solid, rigid Brooklyn Bridge. "Moisseiff believed that up to half the stress caused by winds could be absorbed in a suspension bridge by the bridge cables and suspender ropes, and transmitted to the bridge towers and abutments," author John Van Der Zee said. "So if a bridge were designed all to bend and sway with the winds, the suspended structure -- the roadbed -- would act as a counterweight and restore the bridge to equilibrium."

Beloved Monument
As Ellis and Moisseiff solved the problems associated with the suspension bridge design, Strauss came around to the idea of building a suspension bridge instead of the hybrid cantilever-suspension bridge he'd originally conceived. The suspension bridge would use less steel and be faster to build. Persuaded by these cost and time considerations, Strauss soon endorsed the suspension plan whole-heartedly. The bridge that resulted from Ellis and Moisseiff's technical labors and Irving Morrow's design contributions would become a beloved San Francisco monument.

A Step Too Far
Leon Moisseiff's career culminated in 1940, with a bridge spanning the Tacoma Narrows in the state of Washington. The third-longest suspension bridge at the time pushed Moisseiff's deflection theory to another level — an unsafe level. Nicknamed "Galloping Gertie," the span moved alarmingly in the wind. Just a few months after the bridge opened, it literally twisted itself apart in 42 mile-per-hour winds, although it had been rated able to withstand winds up to three times as strong.

Final Years
The Tacoma Narrows bridge collapse was a true disaster, but it did have a silver lining. It motivated the engineering community to do extensive testing and research to make suspension bridges safer. For Moisseiff, it meant the end of his career. He died three years later of a heart attack.

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