Spanning the Bay

In 1956 the American Society of Civil Engineering selected seven engineering wonders of the modern world. It named the San Francisco-Oakland Bay Bridge as one of these wonders.

Built between May 1933 and its opening on November 12, 1936, the Bay Bridge's design combined three different types of bridge-building technology over the five miles it covers between San Francisco and Oakland: a suspension span, a cantilevered span, and a tunnel. At the time of its completion the bridge was the longest steel structure on the globe. It also featured the deepest bridge pier ever built, and the world's largest bore tunnel.

This exhibit celebrates the construction of this engineering marvel, via the photograph collections of the California State Archives. It also highlights the people who built the bridge, a workforce of more than 8,000 who accomplished what many thought was impossible -- spanning the Bay to provide a critical link between two of California's largest cities.

In the late 1920s, the shortest way to get from Oakland to San Francisco was via ferry. In 1928 alone, ferries carried over 46 million passengers between the two cities. As Californians embraced the automobile, however, demand increased for a more direct means to cross the Bay.

In 1931, the State Legislature charged the California Toll Bridge Authority and the state's Department of Public Works with designing, acquiring land for, and building a crossing across the San Francisco Bay. In 1933, the Legislature provided the funding needed for acquisition and construction of such a bridge.

Construction of the San Francisco-Oakland Bay Bridge began in May 1933, with a formal groundbreaking ceremony conducted in July of that year. This photograph, taken about a year later, already shows tendrils of construction extending from Oakland (at the foot of the mountains in the background) toward Yerba Buena Island in the center of the Bay.

The design and construction of the Bay Bridge was one of the great engineering challenges of the twentieth century. The bridge needed to span more than five miles (four of which are over water) from Oakland to San Francisco, and be able to withstand turbulent tides, strong winds with a high salt content, and potentially devastating earthquakes.

To meet these challenges, the Toll Bridge Authority and the Department of Public Works appointed Charles H. Purcell as the project's Chief Engineer, Charles Andrew as Bridge Engineer, and Glenn Woodruff as Engineer of Design. The final design consisted of two suspension bridges on the San Francisco side of Yerba Buena Island, a tunnel through the island, and a series of truss and cantilever spans on the eastern portion of the bridge between the island and Oakland's shoreline.

These photographs show some of the stages in constructing a series of twenty-two support piers for the eastern span of the bridge. Pier E-3, near Yerba Buena Island, had the distinction of being the deepest bridge pier ever built up to that time, at a depth of 242 feet below water level.

The eastern span is the longest segment of the Bay Bridge, crossing a distance of almost four miles between Yerba Buena Island and the Oakland Toll Plaza. This was also the most complex portion of the bridge, in terms of the variety of construction types used.

The twenty-two piers of the eastern span supported, from east to west: ten plate girder spans, a long, fourteen-section continuous deck truss causeway, five medium through truss sections, and a cantilevered section supported by two towers. These photographs show the progress made on the cantilevered portion, near Yerba Buena Island, by early 1936.

This photograph shows the completed eastern span of the Bay Bridge, looking northeast from Yerba Buena Island. In one of the many innovations that the bridge's engineers had to develop during construction, the central portion of the cantilevered section (in the middle of the photo) was not raised into place from the water, as was typical at the time. Treacherous currents made such a process dangerous and unpredictable. Instead, the central section was built out from the ends of the cantilevered portions. Hydraulic jacks placed the very last section, a maneuver made tricky by winds and tidal flows incessantly shifting the superstructure.

The eastern span was completed six months ahead of the western, suspension portion of the bridge, with crews paving the bridge decks by April 1936.

The eastern span was eventually replaced after a section of the upper deck collapsed onto the lower deck during the 1989 Loma Prieta earthquake. The new east span, a suspension bridge with only one deck, opened to traffic in 2013.

Bridge engineers took advantage of the natural geography of San Francisco Bay in their planning for the Bay Bridge. They incorporated Yerba Buena Island into the construction, a small island positioned between San Francisco and Oakland. A 1,700-foot-long tunnel through this island connects the eastern and western spans of the Bay Bridge.

Workers began excavating the tunnel in sequential steps in early 1934. Temporary railroad tracks, built to move excavation debris, can be seen in the top-most photograph. The excavated material was transported via a disposal chute to a work-site north of Yerba Buena Island, where the U.S. Army Corps of Engineers was starting the long process of filling in shoals to create Treasure Island, future site of the Golden Gate International Exposition.

The bottom photograph shows the construction of the viaduct carrying the eastern span to the tunnel entrance. The cantilevered portion of the bridge can be seen in the background.

This photograph, taken within the eastern portal of the tunnel, facing Oakland, clearly illustrates the double-decker nature of the Bay Bridge. As originally designed, two-way traffic ran on the top deck, while trucks and interurban trolleys utilized the bottom deck. In the late 1950s and early 1960s, the trolley tracks were removed, and automobile traffic redirected so that the upper deck carried west-bound traffic, and the lower deck the east-bound vehicles.

The far left and bottom right photographs depict the vertical walls and arched roof of the Yerba Buena tunnel prior to construction of the upper deck. The horseshoe-shaped tunnel is composed of vertical walls 76 feet apart at the widest point, topped by an arched ceiling 58 feet high (at the crest of the arch). At the time of its construction, this was the largest bore tunnel in the world.

Once excavation was complete and the arched ceiling lined with three feet of concrete, work crews poured the two road decks and lined the inner surface of the tunnel with tile. The top right photograph shows the western portal of the completed tunnel, on the San Francisco side of the island, a week after the bridge opened to the public.

The western span of the San Francisco-Oakland Bay Bridge is the most visually striking portion of the structure, featuring two suspension bridges connected in the middle by a central pier.

This design was necessitated by the 1.8-mile distance between Yerba Buena Island and San Francisco's shoreline. Such a distance was too long for a single suspension span, so engineers had to devise a method to anchor not one, but two suspension bridges over the Bay. Their solution, perhaps the most innovative aspect of the Bay Bridge, was the construction of a massive center anchorage between Yerba Buena Island and San Francisco. The anchorage, seen in the upper right-hand photograph, was the equivalent of a 40-story building covering an entire city block. Some sense of the scale can be determined by noting the ferry in the left-hand corner of the picture.

Construction was further complicated by the depth of the water, reaching one hundred feet in places. Project engineers therefore had to develop an innovative new method for constructing the piers upon which the bridge would stand. Daniel Moran conceived of a system that involved sinking caissons (water-tight chambers) made up of a series of domed cylinders to form the foundation for each pier. His technique allowed the piers to sink through up to 170 feet of mud to the bedrock beneath the Bay. Once on bedrock, crews could begin construction of the massive towers on top of the piers.

After crews completed the supporting piers and central anchorage, work could begin on the superstructure of the western span of the Bay Bridge. This work consisted of three major steps: building the towers and central anchorage, spinning suspension cables from San Francisco and Yerba Buena Island, and suspending stiffening trusses and the bridge deck from the support cables.

The towers on the western span range in height from 414 to 458 feet above their base plates on the piers. The central anchorage rose to a height of 300 feet. These towers included almost 35 thousand tons of steel and more than 505,000 rivets. Much of this construction was completed by June 1935, when the process of spinning the cables was started.

The process of spinning the suspension cables involved carrying wire from one tower to the next, anchored at the tops of the towers by cast steel "saddles." The cables themselves consisted of thirty-seven strands of wire, each strand in turn made up of 472 round steel wires. The strands were bound together and compacted to form a cylinder of cables 28.75 inches in diameter.

Once the suspension cables were spun and in place, work began on hanging the stiffening trusses that subsequently supported the roadway deck (a section of which is clearly seen in the top photograph). Workers used wire cables or "ropes" 2.25 inches in diameter to hold the trusses in place. Altogether, approximately forty-three miles of such wire was incorporated into this segment of the bridge.

Altogether, construction of the San Francisco-Oakland Bay Bridge took a little over three years. Astonishingly, at least in terms of modern construction projects, the work was completed six months ahead of schedule, and under budget. Financed primarily through the sale of bonds and borrowing against the states' Gas Tax Fund (to be paid back by tolls), the bridge cost an estimated $77,200,000 to build.

Major construction projects also exacted a high price in human lives. At the time the Bay Bridge was built, the recognized “rule of thumb” predicted one death for every million dollars spent on construction. The fact that there were relatively few major disasters reduced, but did not prevent, accidents. Sadly, twenty-eight men lost their lives during the construction process. To this day, their work still stands.

Critical to the construction of the Bay Bridge was the ability to secure the underpinnings of the bridge. Master Diver William Reed held the job of underwater inspector. Reed made inspection dives of up to 240 feet with equipment that he designed. Because he worked at such depths, Reed had no light to aid his inspection. He used his hands and fingers instead as a guide. These skills were developed during his twenty-one years of underwater inspection experience.

Reed's duties were hazardous. During one particularly dangerous dive, he straightened a leaning caisson by igniting a dynamite charge to clear an underwater obstruction. On another dive Reed was forced to cut his lifeline, which had become entangled on a cable at the bottom of the Bay. Because of the depths of the dives, Reed was always subject to the "bends" and after every dive was rushed to the on-site decompression chamber.

Because Reed’s job was so hazardous he was paid the substantial salary of $15,000 per year, plus one dollar per foot per dive, a great deal of money during the height of the Great Depression. This equates to approximately $250,000 in today’s dollars.

Unfortunately, most of the individuals within these construction photographs are unidentified. Bridge Engineer Charles E. Andrew (photograph on far right) is one of the few that is named in the collection. Employed by the state, Andrew worked closely with Chief Engineer Charles H. Purcell throughout the construction of the Bay Bridge.

The other two photographs show workers hand-wrapping the south cable of the western span of the bridge (to prevent the cables from being damaged by environmental factors like wind and other harsh weather conditions), and another worker receiving rivets for the construction work. Hot steel rivets were used for much of the construction -- over 500,000 rivets were used in the towers of the west span alone. These rivets were replaced by high-strength tension control nuts and bolts during a later retrofit of the western span, as it was found that the steel rivets were subject to failure by shearing under certain conditions.

Constructing a bridge requires work under a wide range of conditions. The San Francisco-Oakland Bay Bridge was built by men who dealt with wind, rain, and fog at lofty heights hundreds of feet above the ground, cramped and dark tunnels deep under the earth, and even the rough currents and cold waters of the Bay itself. In the top photograph, a construction crew is working on the east cantilever arm of the eastern span (note the safety line extending from the man in the middle of the picture). The bottom photograph shows conditions in the tunnel for the north anchorage.

Most of the construction workers hailed from California, and many of the remainder came from the Pacific Northwestern states of Washington, Oregon, and Idaho. Some of the job specifications gave preference to ex-servicemen, particularly those with dependents. Sadly, little evidence remains regarding the daily lives of these workers, or their life histories.

On any given day, up to four thousand people were employed in the construction work. Most of these worked for one of several different construction contractors, including Columbia Steel Company (a subsidiary of the U.S. Steel Corporation); Transbay Construction Company; Bridge Builders, Inc.; Healy-Tibbets; and Clinton Construction. Dozens of state employees worked on the bridge as well.

These two photographs highlight the work crews that constructed the tunnel through Yerba Buena Island. The top photograph shows workers installing supports for the top arch of the tunnel. In the center of the bottom photograph, a worker places the last tile in the ceiling of the eastern entrance to the tunnel, while the rest of the work crew poses for the camera.

The construction crews of the Bay Bridge often worked at dizzying heights, evidenced by this photograph of workmen on the central portion of the cantilevered section of the eastern span. In fact, six men died while working on the superstructure of the eastern span, more people than on any other major element of the bridge's construction.

The Reconstruction Finance Corporation (RFC), a federal entity designed to provide states and local government entities with financial assistance for employment-generating public works projects, loaned funds to California in order to finance the Bay Bridge's construction. The conditions imposed by the RFC through this loan specified, among other things, that construction crews could only work thirty hours per week (usually in five six-hour shifts). Wages, established by the contracting firms themselves, ranged from $26.67 per day (for the underwater divers, due to the particularly hazardous nature of that work) to a low of $5.00 per day for general laborers.

The "saddle" referred to in the top-most photograph is a device at the top of each tower of a suspension bridge that carries the main suspension cables. These saddles, made of cast iron and each weighing approximately 46 tons, allowed the cables to safely flex in response to shifts in load due to construction or regular traffic on the bridge deck. At the time the saddles were built, they were considered to be the largest single-piece cast iron components ever used in bridge construction.

In the lower photograph, a worker seals the surface of the viaducts on Yerba Buena Island.

This set of photographs illustrates some of the steel elements that went into building the Bay Bridge. The photograph on the upper left shows a welder working on an expansion dam on the western span. Temperature changes, settling, and other factors cause concrete to expand and contract, which can in turn cause cracking. Expansion dams, or expansion joints, allow concrete to expand and contract without threatening the integrity of the structure as a whole.

The photograph on the upper right shows bundles of reinforcing steel, while the bottom photograph illustrates the scale of the cables used in the western span. These cables, from which the bridge deck is suspended, are composed of thirty-seven strands. Each of these strands are in turn composed of 472 steel wires bound together.

Over 152,000 tons of structural steel, 18,500 tons of cable wire, 30,000 tons of reinforcing steel, and a million cubic yards of concrete went into constructing the bridge. The steel elements amounted to one-eighth of the total steel production in the United States for the years during which the bridge was built.

Thousands of feet of steel wire were woven into strands to form the main cables on the western span of the San Francisco-Oakland Bay Bridge. The photograph on the far left shows a worker winding protective seizing around such a strand in preparation for it being strung on the bridge.

The photograph in the center shows a work crew compacting and wrapping the southern main cable (made up of thirty-seven strands like that in the first photograph) at the Yerba Buena anchorage. Steel cables also formed the basis of catwalks used by workers during the construction process. In the photograph on the far right, workers are beginning the process of building such a catwalk.

Many of the men who worked on the bridge were unprepared for the conditions in which they would work. Years later, one of the workers, Arthur Elliot recalled:

It was the depth of the Depression and there were many young men out there on the catwalk glad to have a job of any sort. They came out in suit coats and light sweaters to face the cold winds and the fog, wrapping themselves in burlap sacks or bits of canvas they might find to try to keep warm.

The top photograph, set against the backdrop of downtown San Francisco, shows men constructing one of the catwalks referred to by Elliot, which provided necessary platforms for work on the two suspension bridges that make up the western span.

In the bottom left photograph, men are working on the I-beams that make up part of the eastern span of the bridge, while the bottom right photograph provides a detailed look at the saddle carrying the south cable over the center anchorage of the western span.

These dramatic photographs show men working on the catwalks or footbridges connecting the towers of the western span, before the main suspension cables were strung. The ten-foot-wide catwalks, suspended hundreds of feet in the air, consisted of a mesh floor supported by wire ropes. The ferries present at the bottom of each photograph provide a sense of scale.

Alfred Zamper, an experienced steelworker, later described the severe acrophobia (fear of heights) that gripped many of the men working hundreds of feet above the Bay:

People freeze up there. They hang on -- they won't fall, but it would take three or four of us to break 'em loose. We'd put a line on 'em and let 'em down. They were mostly inexperienced men -- they think they can do it but they can't. They say, "Don't look down." I never avoided looking down -- it didn't bother me. I could look right down in the water and see big fish down there. You have to have a little bit of fear -- not too much -- way back here, in the back of your head. You can't daydream -- or you'll take chances.

The San Francisco-Oakland Bay Bridge opened to traffic on November 12, 1936. On hand for the celebration were former President Herbert Hoover, Governor Frank Merriam, and Chief Engineer Charles H. Purcell. Governor Merriam cut a symbolic chain with an acetylene torch and said, “This Bridge is not the product of a day.” Later in the proceedings, President Franklin D. Roosevelt activated a golden key in Washington D.C, which operated green signal lights, signaling traffic to proceed across both sides of the bridge. The dream of connecting Oakland and San Francisco had been realized.

Today, the San Francisco-Oakland Bay Bridge looks a bit different than the structure completed in 1936. The rail lines on the lower deck have been removed to allow automobile traffic instead. A metering system was installed on the bridge to manage the ever-increasing amount of traffic between San Francisco and Oakland.

The bridge has undergone extensive seismic retrofitting, and, most significantly, the eastern span has been replaced. A section of the eastern span's upper deck collapsed during the 1989 Loma Prieta earthquake. The section was repaired, but ultimately engineers decided to replace the entire eastern span. The new eastern span, completed in 2013, is a self-anchored suspension bridge with viaducts at each end, consisting of a single deck that carries ten lanes of traffic going both directions. At a width of over 258 feet, the new eastern span is, as of this writing, the widest bridge on earth.

Today, the Bay Bridge carries over 102 billion vehicles between San Francisco and Oakland each year. In the process of spanning the Bay, California created a crucial transportation link that stands as an engineering marvel and a testament to human ingenuity and perseverance.