Building the impossible: Golden Gate Bridge - Alex Gendler

In the mid-1930s, two familiar spires towered above the morning fog. Stretching 227 meters into the sky, these 22,000-ton towers would help support California’s Golden Gate Bridge. But since they were currently in Pennsylvania, they first had to be dismantled, packaged, and shipped piece by piece over 4,500 kilometers away. Moving the bridge’s towers across a continent was just one of the challenges facing Charles Ellis and Joseph Strauss, the project's lead engineers. Even before construction began, the pair faced all kinds of opposition. The military feared the bridge would make the important harbor an even more vulnerable target. Ferry companies claimed the bridge would steal their business, and residents wanted to preserve the area's natural scenery. Worse still, many engineers thought the project was impossible. The Golden Gate Strait was home to 96-kilometer-per-hour winds, swirling tides, an endless blanket of fog, and the earthquake-prone San Andreas fault. But Strauss was convinced the bridge could be built; and that it would provide San Francisco’s commuters more reliable passage to the city. He was, however, a bit out of his depth. Strauss’s initial plans to span the strait used a cantilever bridge. This kind of bridge consists of a single beam anchored at one end and extended horizontally like a diving board. Since these bridges can only extend so far before collapsing under their own weight, Strauss’s design used two cantilevers, linked by a structure in the middle. But Ellis and his colleague Leon Moisseif convinced Strauss to pursue a different approach: the suspension bridge. Where a cantilever bridge is supported from one end a suspension bridge suspends its deck from cables strung across the gap. The result is a more flexible structure that’s resilient to winds and shifting loads. This kind of design had long been used for small rope bridges. And in the 1930s, advanced steel manufacturing could create cables of bundled wire to act as strong steel rope for large-scale construction. At the time, the Golden Gate Bridge was the longest and tallest suspension bridge ever attempted, and its design was only possible due to these innovations. But cables and towers of this size could only be built at large steelworks on the country’s east coast. While the recently completed Panama Canal made it possible to ship these components to California, reassembling the towers on site didn’t go quite as smoothly. It was relatively easy to find a stable, shallow foundation for the north tower. But building the south tower essentially required erecting a ten-story building underwater. Since the strait’s depth prevented them drilling or digging the foundations, bombs were dropped on the ocean floor, creating openings for pouring concrete. A seawall was built to protect the site from powerful currents, and workers operated in 20-minute shifts between tides. The towers had so many compartments that each worker carried a set of plans to prevent getting lost. And at one point, an earthquake rocked the south tower nearly 5 meters in each direction. Strauss took worker safety very seriously, requiring hard hats at all times and stretching a safety net below the towers. But not even these precautions could prevent an entire scaffolding platform from falling in 1937, carrying ten workers to their deaths. Once the towers were complete, workers spun the cables in place, hung suspenders at 50-foot intervals, and laid down the concrete roadway. The bridge was finished, but there was still one more task ahead: painting it. After production, the steel had been coated with a reddish paint primer it maintained throughout construction. But the Navy had been pushing hard to paint the bridge a tactical black and yellow. Consulting architect Irving Morrow actually thought the primer itself paired nicely with the strait’s natural backdrop— and he wasn’t alone. Citing numerous letters from locals, Morrow’s 30-page pitch to paint the bridge “international orange” beat out the Navy’s plans. And today, this iconic color still complements the strait’s blue water, green hills, and rolling fog.

Channel: TED-Ed

Views: 743,567

Keywords: golden gate bridge, golden gate, golden gate strait, san andreas fault, charles ellis, joseph strauss, suspension bridge, cantilever bridge, california, bridge engineering, panama canal, seawall, irving morrow, architecture, international orange, san francisco, engineering, bridge design, golden gate fog, golden gate spire, construction, history, education, animation, alex gendler, anton bogaty, TED-Ed, TED Ed, Teded, Ted Education

Id: EPd2w5d_qAk

Length: 5min 27sec (327 seconds)

Published: Tue Feb 22 2022