Golden Gate Bridge Builders


Construction

The delays that arose ultimately were probably fortuitous, as the decade of the 1920’s saw many innovations, discoveries and inventions that arrived just in time to make the bridge possible to finish on schedule, under budget, and with a miraculous safety record for the times.

The Anchorages - A suspension bridge works by suspending the massive weight of the horizontal roadbed from huge cables draped over two rigid towers planted in the bedrock. The ends of the two cables, one on each side of the roadbed, are anchored by massive weights that are themselves planted in the earth. First, they started digging where they could on dry land, making giant holes in which to pour thousands of tons of concrete to hold down the ends of the main cables. They poured the concrete over a complex web of reinforcing bars and long steel beams with eye hooks sticking out at the correct angle, just slightly elevated above horizontal, to which the thousands of individual cables would be attached.

The Towers - Each rigid tower would be made of a “honeycomb” of hollow steel compartments put together like children’s blocks and held together by over 600,000 rivets. Rather than a complex grid of structural cross-members beneath the roadbed (think of a railroad trestle across a smaller valley), all of the weight of the roadbed would be transmitted by the cables to the two towers, which therefore had to be extremely strong and rigid. Even so, the winds would move them back and forth by up to 12 feet side to side at the top!

The Piers - Each tower would stand upon a “pier” of concrete attached to the earth. For the north tower, it involved “merely” digging and blasting a hole on the southernmost point of Marin County, and pumping the water out during construction. The pier was then constructed to create a flat footing for the tower, 64 feet above sea level.

The South Pier - The south tower was a different story altogether, accounting for at least one extra year of construction time alone. It’s pier would have to be connected to a shelf of bedrock 110 feet below sea level, and rise above the water a height equal to the north pier, with strong tides and currents making every step more difficult than we can imagine. This involved much strenuous and dangerous diving, digging and dynamite, overcoming a combination of depths and water pressure, air and sea currents, storms and shipping mishaps unprecedented in human history. They would have to shelter the workers and equipment from the rough seas by building a large concrete caisson, in this case a tube with the rough size and shape of the track around a football field, 110 feet deep and thick enough to hold back the waves and enormous water pressure at the bottom. Then they could pump out the water and build the pier up to the same height as the north one, 64 feet above the waves.

Bad Luck - This brought on the darkest hours of the entire project, as nature and shipping mishaps nearly crippled it more than once. A 1200 ft (400 meter) dock was built from the Presidio out over the water to allow trucks to haul equipment, concrete and other materials. With ships running into the dock and storms carrying away parts of the incomplete structure, it took 2 years to finish just the footing for the south tower, 8 months after the entire north tower was finished. Once above the water, tower construction was relatively straightforward, “just” riveting thousands of similarly sized “cells” of nearly 1-inch sheet steel. There are over 23 miles of ladders allowing workers to climb a vertical maze to the tops of the towers. There were many stories of workers being ”lost” and spending the night in the darkness alone.

Cabling - When both towers were finally finished, the complicated process of cabling began in earnest. Roebling and Sons, fresh from finishing the George Washington Bridge in New York, opened a West Coast branch to build this project. Two huge saddles, shaped somewhat like riding saddles were placed atop each tower. They hold the enormous weight of the suspended structure as the cables made their sharpest turns over the top. Steel was drawn into cables in forges at both ends, and wound onto spools like sewing thread, each spool about 1.7 miles long. Temporary cables were strung above the planned routes of the real ones. Each cable, less than a quarter of an inch in diameter, was attached to an eyelet anchored in concrete at one end, and then the spool was attached to a carriage which then made the trip across the Golden Gate, guided by the temporary ones, and then attached to the other side. There were 26000 trips made on each side of the roadbed, and cables were squeezed into bunches averaging about 400 each, 61 bundles on each side, for a total of 80,000 miles of cable. Each main cable is over 36 inches in diameter, and is covered in a steel sheath to protect it from the elements.

The Roadbed - Once the cabling was done, the suspenders were draped over the main cables and reconstructed frames were pulled into place in a carefully scripted order to make sure that the cables would not be loaded asymmetrically. That meant starting at each tower and moving away in both directions toward the shores and the center. Once the basic framework was finished in December of 1936, then the forms could be built and concrete poured in a similar pattern.

The Accident - For four years of construction, the project beat the actuarial odds with only one death, approximately 30 less than predicted. The roadbed consisted of steel grid work, with concrete poured over it. As always, the concrete had to be contained by plywood “forms” that give it shape and keep it from running down into the sea before setting. All the concrete had been poured and had set, and the forms that held the concrete while it was poured were being removed. This involved a sort of upside down railroad car - suspended from above by wheels that sat on the girders above, and hung down below the roadbed allowing men to pull the plywood and other waste material off and toss into the net for disposal. The “stripper“ tragically broke loose and tore through the safety net - 10 men were tangled up and fell with it into the bay in February of 1937.

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