Built in 1937 and still the ninth longest suspension bridge in the world, the Golden Gate Bridge across San Francisco Bay remains in fine shape despite its age - Andrew Bardin Williams writes The Golden Gate Bridge turned 75 years old on May 27 and continues to play a key role in the transportation, engineering, construction and ITS communities. The structure has played an important historical role, an engineering success that boosted the economy of the region. And it also led the way as the first major pub
A team of painters continuously touch up the paintwork of the structure (Image courtesy of www.goldengate.org)
Built in 1937 and still the ninth longest suspension bridge in the world, the Golden Gate Bridge across San Francisco Bay remains in fine shape despite its age - Andrew Bardin Williams writes
The Golden Gate Bridge turned 75 years old on May 27 and continues to play a key role in the transportation, engineering, construction and ITS communities. The structure has played an important historical role, an engineering success that boosted the economy of the region.And it also led the way as the first major public private partnership in transportation and as the pioneer of reversible flow traffic lanes.
A huge celebration was held for this landmark structure’s landmark anniversary, including a massive firework display.
Showers of sparks cascaded off the deck of the Golden Gate Bridge and disappeared into the dark waters of the bay, sending up columns of steam reminiscent of the fog that often obscures the steel towers of what is arguably the world’s most recognisable bridge. Hundreds of thousands of spectators came to view the spectacle, ringed around San Francisco Bay from Crissy Fields, the Marina and Lincoln Park to the Marin headlands, Berkeley and the Oakland Hills.
The longest suspension bridge in the world when it was built, the Golden Gate Bridge may be 75 years old but is carrying its age well. When it opened, the span connected a region that had just been ravaged by a mighty earthquake, linked San Francisco with the Redwood Empire in the north and created a vital transportation route that cut days off travel from the Mexican to Canadian borders. The economic impact throughout its 75 year history is immeasurable.
The success of the bridge sparked a slew of public-private partnerships that constructed great public works across the country from the Hoover Dam in Arizona to the Federal Highway System, showing the world that building infrastructure creates jobs, encourages growth and is capable of bringing the world out of a global depression.
In the years since, the
However, the bridge was almost never built. Engineering, economic, political and geological roadblocks almost sidelined the project before it got started. But built it was, combining utility and function with aesthetics.
The vision to build a bridge across the Golden Gate had been around since the Gold Rush, but it was not until the advent of the automobile that people seriously considered the engineering involved. According to Kevin Starr, the former state library for California, ferry traffic from San Francisco to the recreation areas north of the city increased 700% from 1910-1920. By the middle of the 1920s, 3,000 vehicles/day crossed the Bay with up to a three hour wait to board and load. Labor Day 1930 saw 68,000 vehicles cross the Bay, bringing traffic to a standstill while creating congestion that stretched for 24km.
At the same time, the region was booming. Not since the Gold Rush had the area seen so much growth as communities blossomed in the North Bay, East Bay and the Peninsula.
Lumber from the Redwood Empire north of the city was in desperate need, but it often took days to transport lumber around San Francisco Bay. It was evident that a bridge would have to be built across the 1/6km-wide Golden Gate. It was just a matter of how to engineer such an undertaking and who was the right team to manage the project. Nothing of this magnitude had been attempted before anywhere.
City engineer Michael O’Shaughnessy and businessman/engineer/promoter Joseph Strauss stepped into the void, drawing up preliminary designs in 1921 to bridge the strait. Originally a mixed-type design consisting of two fix-frame cantilevered structures joined by a suspension span, the plans were widely discredited due to aesthetic concerns, but the engineering played out and officials were convinced the strait could be spanned.
Soon after, O’Shaughnessy and Strauss joined forces with Chamber of Commerce organisations and other business interests in neighboring counties and founded the Golden Gate Bridge and Highway District—one of the first public-private partnership initiatives to result in a transportation project. Federal funds were unavailable due to the San Francisco-Oakland Bay Bridge under construction a short distance away, so the Strauss-O’Shaughnessy plans called for a bridge to be funded through civic bonds that would be paid back with toll revenues. Another San Francisco institution, Bank of America, agreed to cover the bonds, its president at the time citing the need for banking to serve as a source of social development. After years of legal and political challenges, the bridge was finally authorised, and the Golden Gate Bridge and Highway District was born in 1928.
Recognising they were in over their head, Strauss hired a team comprising the top engineers in the world. They would have to build a strong bridge that would be the longest in the world up to that point over a body of water with strong tides and frigid temperatures. Gusts of wind over 160km/h had been recorded, and heavy, steel-corroding fog often enveloped the strait. If that was not enough, the bridge would be constructed less than 3.2km from the San Andreas Fault that had just let loose a 7.9 magnitude quake less than 25 years prior. In addition, the bridge was not to tarnish some of the most pristine coastline on the Pacific West Coast.
Of the dozens of engineers on staff, Charles Ellis, Leon Moisseiff and Othmar Ammann took the lead in developing the design for a 1.28km suspension span with a vertical clearance of 67m that would eventually be approved by the bridge authority (the site was deemed of major strategic military value, so the War Department also had final say on any designs and construction of a bridge).
An artist specialising in Art Deco was hired to meld the bridge with its surrounding landscape and turn the span into a work of art.
Final plans for an-all suspension bridge with steel towers rising from two piers were finalised in 1930, and voters in six member counties approved US$35 million in bonds to finance the construction which began in earnest in January 1933.
Construction of the bridge was largely a local affair. According to Starr, the project was under the supervision of a localised bridge and highway district, set in motion by local authorities and financed by a syndicate headed up by a San Francisco-based bank.
In addition, $7.5 million in construction contracts were given to local companies and the two major suppliers, Bethlehem Steel and Roebling Company, were required to either fabricate or store the materials in the area. In addition, several thousand Northern Californians worked to put the bridge together, spinning cables, installing rivets and pouring concrete.
The anchorage, pier and approach spans were built on the northern Marin County side of the bridge, but the southern pier was designed to sit more than 305m off shore in the middle of the strait. The towers rise 164m above the water, taller than the Washington Monument and many New York skyscrapers at the time.
A saddle sat on top of each tower where the 2.332km long cables would rest. Spun on site—due to the massive weight of the finished cables—each cable consisted of 128,744km of spliced wire that is 5mm in diameter. More than 250 pairs of vertical steel ropes connect the wires to the suspended roadway.
Concrete was poured in sections to allow the roadway to constrict and contract with the weather conditions without cracking and was then paved over with asphalt to meet the highway standards set by the state department of transportation.
As difficult as he was to work with, Strauss made sure to manage the safest construction site in history. At the time, one death/$1million dollars in construction costs was the norm, and Strauss wanted to set a safety record.
Workers who set foot on the site were required to wear a new hard hat that was based on a miners’ helmet and was developed specifically for the project. Iron and steel workers were encouraged to wear special respirator helmets to protect them from noxious fumes, and glare-free goggles were given out as well.
The greatest safety measure, however, was a new $130,000 net that sat below the roadway as it was being built—another first for bridge construction. Over four years of construction, 19 workers were saved by the net—dubbing themselves the Halfway to Hell Club. Strauss also provided free hand and face cream to workers to protect them from wind and offered them sauerkraut juice every Monday morning to help with hangovers. He also had dieticians on hand to recommend diets that helped with dizziness and vertigo.
With construction winding down, the $35 million project saw only one death—the strong safety record universally attributed to the innovative measures set down by Strauss. However, an accident that occurred just three months before the bridge opened to traffic killed nine additional workers—one of the only black marks during the four-year project.
The Golden Gate Bridge opened May 27, 1937 when more than 200,000 pedestrians crowded the roadway before vehicle traffic opened the next day. It was an instant financial, transportation, economic and engineering success, and maybe a little too successful. By the middle of the 1960s, crossings increased 700% and the bridge topped out at 25 million vehicle crossings annually.
For the next decade, traffic congestion on the bridge was terrible. It often took hours to cross from Marin to San Francisco during the morning commute, but the bridge had simply tapped out and could not handle any more traffic.
According to Mary Currie, the current Public Affairs Director for the District, the GGBHTD looked to add capacity in other ways. A new bridge a few hundred metres into the Bay was considered, as was building a lower deck to the existing span. Some advocated for a tunnel under the strait or the expansion of the city’s mass transit system.
“The entire Bay Area exploded with traffic congestion in the 60s,” Currie said. “A new way of reducing that stress was needed without simply building more infrastructure. The District needed to be smarter about traffic management.”
Dale Luehring, the general manager of the bridge at the time, sought new, innovative solutions to the congestion problem. A reversible lane system that could shift the roadway’s middle lanes for either northbound or southbound dependent on traffic flow was implemented in 1963, and one-way toll collection was started in 1968. Both were firsts in the world for a bridge and served to improve traffic flow, easing congestion and shortening travel times. Thousands of bridge authorities around the world use similar traffic management strategies to reduce congestion today.
Several years later, Luehring was able to secure the authorisation of the GGBHTD as a multi-modal mass transportation agency, allowing the District to add bus lines and ferry service. Today, 30% of all trips across the Golden Gate are on a bus or ferry, taking nearly 13,000 vehicles/day off the span.
The mass transit systems rely on no federal funds for operation and are subsidised by bridge tolls. High Occupancy Vehicle lanes, vanpools and carshare services were added in the 1970s, and electronic toll collection was added in the 1990s.
Next year, the GGBHTD will migrate to an exclusive, and highly sophisticated, ETC system with motorists having the option to pre-pay, pay by mail or register online.
Other traffic management and safety measures on the bridge include a 72km/h speed limit, a double fine zone, LIDAR technology for speed enforcement, a designated Safety Awareness Zone and a moveable median barrier on the span and the approaches.
The result of these traffic management innovations throughout the bridge’s history is that congestion peaked in the 1960s despite the Bay Area nearly doubling in population since then. Now more than 40 million vehicles cross the Golden Gate Bridge annually with very little traffic impact on the bridge and its approaches.
Today, the Golden Gate Bridge is maintained by 200 employees who work together to accomplish the critical day-to-day maintenance and safe roadway operations. Bridge operations personnel are responsible for public safety, security, toll collections, managing the flow of traffic and emergency response. The bridge captain (formerly known as the toll caption) oversees 24/7 operations that include toll collections, security and roadway service.
An urban myth, the Golden Gate Bridge does not get painted end to end in perpetuity. Rather, painting crews inspect critical bridge components and make touch-ups as needed, protecting the bridge’s steel components from the high salt content in the air. The distinct gold color is actually International Orange and was inspired by the original primer color. Black, grey and a yellow and black striped pattern were also considered, but the orange hue of the primer seen during construction seemed to perfectly meld into the surrounding landscape and accentuate the bridge’s art deco architecture. The original lead-based paint was replaced in the 1960s with an inorganic zinc silicate primer and acrylic emulsion topcoat.
In addition to constant maintenance, the Golden Gate Bridge has undergone several major retrofits aimed at improving stability and increasing capacity. Incredibly, the bridge suffered no major damage after the 1989 7.1 earthquake that killed 68 people, injured 3,700, rattled nerves and caused $6 billion in damage throughout the region, including the collapse of the upper deck of the nearby Bay Bridge. A three-phase Seismic Retrofit Design and Construction Project was implemented shortly afterward, enabling the bridge to now withstand an 8.3 magnitude earthquake. The retrofit cost $661 million and was funded by increasing tolls and grants. Meanwhile, the recent construction of the southern approach was funded with stimulus dollars.
An earlier retrofit finished in 1951 reinforced and stiffened the roadway with 250 steel struts which were able to increase the torsional rigidity of the bridge by a factor of 35. The suspender ropes were replaced in the 1970s and the concrete roadway deck was replaced with steel in the 1980s to reduce weight and increase load capacity from 5,952.8k-8,628.6kg/linear metre. This was a good thing too as more than 300,000 pedestrians swarmed the bridge on the 50th anniversary in 1989. With 14 million kg of humanity on its deck, the span visibly flattened out and started to sway. Luckily, no one panicked, and the bridge was cleared in a few hours.
A key factor in the continuing success of the Golden Gate Bridge is the extent to which it was over-engineered right from the start. This is an unintentional benefit of the limitations of the engineering science of the period in which it was designed. When it was built, no-one could have predicted the either massive explosion in vehicle numbers, or the far heavier trucks now using the roads. In the 1930s (and before), engineers typically designed structures with high factors of safety to ensure their longevity, which is why many other major structures from the same era, such as the Sydney Harbour Bridge in Australia, have lasted equally well.
Technology made huge steps forward during WWII, with the result that engineers were able to design structures more precisely to the loads they were expected to carry. Factors of safety were lowered because engineers no longer had to be so conservative in their designs. But this has had the result that many well-built structures designed and erected in the 1950s, 60s and 70s have actually fared less well under massively increased traffic volumes and heavier trucks than earlier structures. The Golden Gate Bridge or the Sydney Harbour Bridge, with their far more conservative factors of safety and over-engineering, have coped with load increases their designers could not have envisaged.
Despite its age, the bridge has lasted extremely well and shows the quality of engineering in its original construction. It has coped with huge increases in traffic volume, heavier vehicles, the corrosive seawater environment and the massive seismic shocks from earthquakes. A big point of pride among its maintenance workers is that the bridge never been completely closed to traffic due to maintenance. Although the bridge was been shut down due to weather three times (three hours was the longest period), for visiting dignitaries (president Franklin Delano Roosevelt and French president Charles de Gaulle) and for the 50th and 75th anniversary celebrations. All work, including major retrofits, is done in piecemeal as traffic continues over the span. Compare that to the Bay Bridge, which has been completely closed the past two Labor Days for construction of the new eastern span.
All Images supplied courtesy of Golden Gate National Parks Conservancy
KEY FACTS
DIMENSIONS:
Total length of Bridge including approaches from abutment to abutment:1.7 miles = 8,981 ft = 2,737m
Length of suspension span including main span and side spans: 1.2miles = 6,450ft = 1,966m
Width of roadway between curbs: 62 ft = 19m
Clearance above mean high water: 220 ft = 67m
WEIGHT:
Total weight of each anchorage: 60,000 tons = 54,400,000 kg
Original combined weight of Bridge, anchorages, and approaches: 894,400 tons = 811,500,000 kg
Total weight of Bridge, anchorages, and approaches (1986): 887,000 tons = 804, 700, 00 kg
CABLES
Length of one main cable: 7,650 ft = 2,332m
Total length of galvanized steel wire used in both main cables: 80,000 mi = 129, 000 km
Number of galvanized steel wires in one main cable that are 0.192 inches in diameter. 27,572
Number of bundles or strands of galvanized steel wire in one main cable: 61
Average number of galvanized steel wires in each of the 61 bundles: 452
Weight of both mainc ables, suspender cables and accessories: 24,500 tons = 22,200,000 kg key facts courtest of %$Linker:
