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Engineering the Design
In 1921, engineer Joseph B. Strauss submitted a design for a bridge that would cross the Golden Gate Strait -- a hybrid bridge with a suspension span supported at each end by cantilever trusses. By 1929, consulting engineers Leon S. Moisseiff and O.H. Ammann had persuaded Strauss to accept the more graceful all-suspension bridge design that we see today.
Strauss assigned engineer Charles A. Ellis to work in collaboration with Moisseiff to perform the calculations needed to complete the design, which was complex and challenging work done without modern computers. The most common "calculator" that structural engineers used in that era was a slide rule, and drafting was done with pencil and paper on drawing boards.
The engineers relied on recent advances in suspension bridge design theory. They verified those calculations with tests on a steel tower model of 1:56 scale (56 times smaller than one of the actual towers). The tests confirmed that the tower calculations were sound.
The geology of the south tower location was investigated before construction could begin. The south tower was planned for construction over 1,100 feet (335 meters) offshore on serpentine rock. Consulting geologist Andrew C. Lawson oversaw a load test performed by placing weight equivalent to a fully loaded railroad boxcar on an area of serpentine rock only 20 inches (508 millimeters) square. The rock was more than strong enough. |