Engineering the Design

In 1921, engineer Joseph B. Strauss submitted a design for a bridge across the Golden Gate Strait as a hybrid structure 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 design seen today. Strauss assigned engineer Charles A. Ellis to collaborate with Moisseiff on the calculations needed to complete the complex design, work done without modern computers, using slide rules and pencil-and-paper drafting on drawing boards. The engineers relied on recent advances in suspension bridge design theory and verified their calculations with tests on a 1:56 scale steel tower model, which confirmed that the tower calculations were sound. Before construction could begin, the geology of the south tower site was investigated, since the tower was planned more than 1,100 feet offshore on serpentine rock. Consulting geologist Andrew C. Lawson oversaw a load test that placed weight equivalent to a fully loaded railroad boxcar on a 20-inch-by-20-inch square area of serpentine rock, and the rock proved more than strong enough.

San Francisco, California · United States