Golden Gate Bridge

From Wikipedia, the free encyclopedia

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A view of the Golden Gate Bridge from Fort Point

  • Coordinates:  37°49′11″N 122°28′43″WCoordinates: 37°49′11″N 122°28′43″W
  • Carries: 6 lanes of US 101 / SR 1 (see below), pedestrians and bicycles.
  • Crosses: Golden Gate
  • Locale: San Francisco, California and Marin County, California, U.S.
  • Official name: Golden Gate Bridge
  • Maintained by Golden Gate Bridge, Highway and Transportation District
  • Characteristics
    • Design Art Deco, Suspension, truss arch & truss causeways
    • Material Steel
    • Total length 8,981 ft (2,737.4 m), about 1.7 mi (2.7 km)
    • Width 90 ft (27.4 m)
    • Height 746 ft (227.4 m)
    • Longest span 4,200 ft (1,280.2 m)
    • Clearance above 14 ft (4.3 m) at toll gates, Trucks cannot pass
    • Clearance below 220 ft (67.1 m) at high tide
  • History
    • Architect Irving Morrow
    • Engineering design by Joseph Strauss, and Charles Ellis
    • Construction start January 5, 1933
    • Construction end April 19, 1937
    • Opened May 27, 1937; 80 years ago
  • Statistics
    • Daily traffic 110,000
    • Toll Cars (southbound only)
    • $7.50 (Pay by plate), $6.50 (FasTrak), $4.50 (carpools during peak hours, FasTrak only)
  • California Historical Landmark
    • Designated June 18, 1987
    • Reference no. 974
  • San Francisco Designated Landmark
    • Designated May 21, 1999
    • Reference no. 222

The Golden Gate Bridge is a suspension bridge spanning the Golden Gate, the one-mile-wide (1.6 km) strait connecting San Francisco Bay and the Pacific Ocean. The structure links the American city of San Francisco, California – the northern tip of the San Francisco Peninsula – to Marin County, carrying both U.S. Route 101 and California State Route 1 across the strait. The bridge is one of the most internationally recognized symbols of San Francisco, California, and the United States. It has been declared one of the Wonders of the Modern World by the American Society of Civil Engineers.

The Frommer’s travel guide describes the Golden Gate Bridge as “possibly the most beautiful, certainly the most photographed, bridge in the world.” It opened in 1937 and was, until 1964, the longest suspension bridge main span in the world, at 4,200 feet (1,280 m).

History


Ferry Service

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Golden Gate with Fort Point in foreground, c. 1891

Before the bridge was built, the only practical short route between San Francisco and what is now Marin County was by boat across a section of San Francisco Bay. A ferry service began as early as 1820, with a regularly scheduled service beginning in the 1840s for the purpose of transporting water to San Francisco.

The Sausalito Land and Ferry Company service, launched in 1867, eventually became the Golden Gate Ferry Company, a Southern Pacific Railroad subsidiary, the largest ferry operation in the world by the late 1920s. Once for railroad passengers and customers only, Southern Pacific’s automobile ferries became very profitable and important to the regional economy. The ferry crossing between the Hyde Street Pier in San Francisco and Sausalito in Marin County took approximately 20 minutes and cost US$1.00 per vehicle, a price later reduced to compete with the new bridge. The trip from the San Francisco Ferry Building took 27 minutes.

Many wanted to build a bridge to connect San Francisco to Marin County. San Francisco was the largest American city still served primarily by ferry boats. Because it did not have a permanent link with communities around the bay, the city’s growth rate was below the national average. Many experts said that a bridge could not be built across the 6,700 ft (2,042 m) strait, which had strong, swirling tides and currents, with water 372 ft (113 m) deep at the center of the channel, and frequent strong winds. Experts said that ferocious winds and blinding fogs would prevent construction and operation.

Conception

Although the idea of a bridge spanning the Golden Gate was not new, the proposal that eventually took hold was made in a 1916 San Francisco Bulletin article by former engineering student James Wilkins. San Francisco’s City Engineer estimated the cost at $100 million, which would have been $2.12 billion in 2009, and impractical for the time. He asked bridge engineers whether it could be built for less. One who responded, Joseph Strauss, was an ambitious engineer and poet who had, for his graduate thesis, designed a 55-mile-long (89 km) railroad bridge across the Bering Strait. At the time, Strauss had completed some 400 drawbridges—most of which were inland—and nothing on the scale of the new project. Strauss’s initial drawings were for a massive cantilever on each side of the strait, connected by a central suspension segment, which Strauss promised could be built for $17 million.

Local authorities agreed to proceed only on the assurance that Strauss would alter the design and accept input from several consulting project experts. A suspension-bridge design was considered the most practical, because of recent advances in metallurgy.
Strauss spent more than a decade drumming up support in Northern California. The bridge faced opposition, including litigation, from many sources. The Department of War was concerned that the bridge would interfere with ship traffic. The navy feared that a ship collision or sabotage to the bridge could block the entrance to one of its main harbors. Unions demanded guarantees that local workers would be favored for construction jobs. Southern Pacific Railroad, one of the most powerful business interests in California, opposed the bridge as competition to its ferry fleet and filed a lawsuit against the project, leading to a mass boycott of the ferry service.

In May 1924, Colonel Herbert Deakyne held the second hearing on the Bridge on behalf of the Secretary of War in a request to use federal land for construction. Deakyne, on behalf of the Secretary of War, approved the transfer of land needed for the bridge structure and leading roads to the “Bridging the Golden Gate Association” and both San Francisco County and Marin County, pending further bridge plans by Strauss. Another ally was the fledgling automobile industry, which supported the development of roads and bridges to increase demand for automobiles.

The bridge’s name was first used when the project was initially discussed in 1917 by M.M. O’Shaughnessy, city engineer of San Francisco, and Strauss. The name became official with the passage of the Golden Gate Bridge and Highway District Act by the state legislature in 1923, creating a special district to design, build and finance the bridge. San Francisco and most of the counties along the North Coast of California joined the Golden Gate Bridge District, with the exception being Humboldt County, whose residents opposed the bridge’s construction and the traffic it would generate.

Design

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South tower seen from walkway, with Art Deco elements

Strauss was chief engineer in charge of overall design and construction of the bridge project. However, because he had little understanding or experience with cable-suspension designs, responsibility for much of the engineering and architecture fell on other experts. Strauss’s initial design proposal (two double cantilever spans linked by a central suspension segment) was unacceptable from a visual standpoint. The final graceful suspension design was conceived and championed by Leon Moisseiff, the engineer of the Manhattan Bridge in New York City.

Irving Morrow, a relatively unknown residential architect, designed the overall shape of the bridge towers, the lighting scheme, and Art Deco elements, such as the tower decorations, streetlights, railing, and walkways. The famous International Orange color was originally used as a sealant for the bridge. The US Navy had wanted it to be painted with black and yellow stripes to ensure visibility by passing ships.

Senior engineer Charles Alton Ellis, collaborating remotely with Moisseiff, was the principal engineer of the project. Moisseiff produced the basic structural design, introducing his “deflection theory” by which a thin, flexible roadway would flex in the wind, greatly reducing stress by transmitting forces via suspension cables to the bridge towers. Although the Golden Gate Bridge design has proved sound, a later Moisseiff design, the original Tacoma Narrows Bridge, collapsed in a strong windstorm soon after it was completed, because of an unexpected aeroelastic flutter. Ellis was also tasked with designing a “bridge within a bridge” in the southern abutment, to avoid the need to demolish Fort Point, a pre–Civil War masonry fortification viewed, even then, as worthy of historic preservation. He penned a graceful steel arch spanning the fort and carrying the roadway to the bridge’s southern anchorage.

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Below Golden Gate Bridge

Ellis was a Greek scholar and mathematician who at one time was a University of Illinois professor of engineering despite having no engineering degree. He eventually earned a degree in civil engineering from the University of Illinois prior to designing the Golden Gate Bridge and spent the last twelve years of his career as a professor at Purdue University. He became an expert in structural design, writing the standard textbook of the time. Ellis did much of the technical and theoretical work that built the bridge, but he received none of the credit in his lifetime. In November 1931, Strauss fired Ellis and replaced him with a former subordinate, Clifford Paine, ostensibly for wasting too much money sending telegrams back and forth to Moisseiff. Ellis, obsessed with the project and unable to find work elsewhere during the Depression, continued working 70 hours per week on an unpaid basis, eventually turning in ten volumes of hand calculations.

With an eye toward self-promotion and posterity, Strauss downplayed the contributions of his collaborators who, despite receiving little recognition or compensation, are largely responsible for the final form of the bridge. He succeeded in having himself credited as the person most responsible for the design and vision of the bridge. Only much later were the contributions of the others on the design team properly appreciated. In May 2007, the Golden Gate Bridge District issued a formal report on 70 years of stewardship of the famous bridge and decided to give Ellis major credit for the design of the bridge.

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The height, depth, and length of the span from end to end, looking west

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The Golden Gate Bridge at sunset, as seen from just north of Alcatraz Island

Finance

The Golden Gate Bridge and Highway District, authorized by an act of the California Legislature, was incorporated in 1928 as the official entity to design, construct, and finance the Golden Gate Bridge. However, after the Wall Street Crash of 1929, the District was unable to raise the construction funds, so it lobbied for a $30 million bond measure. The bonds were approved in November 1930, by votes in the counties affected by the bridge. The construction budget at the time of approval was $27 million. However, the District was unable to sell the bonds until 1932, when Amadeo Giannini, the founder of San Francisco–based Bank of America, agreed on behalf of his bank to buy the entire issue in order to help the local economy.

Construction

Construction began on January 5, 1933. The project cost more than $35 million, completing ahead of schedule and $1.3 million under budget. The Golden Gate Bridge construction project was carried out by the McClintic-Marshall Construction Co., a subsidiary of Bethlehem Steel Corporation founded by Howard H. McClintic and Charles D. Marshall, both of Lehigh University.

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1.2 million steel rivets hold the bridge together. This is a segment of one of those replaced during the seismic retrofit of the bridge after the 1989 Loma Prieta earthquake.

Strauss remained head of the project, overseeing day-to-day construction and making some groundbreaking contributions. A graduate of the University of Cincinnati, he placed a brick from his alma mater’s demolished McMicken Hall in the south anchorage before the concrete was poured. He innovated the use of movable safety netting beneath the construction site, which saved the lives of many otherwise-unprotected ironworkers. Of eleven men killed from falls during construction, ten were killed on February 17, 1937, when the bridge was near completion when the net failed under the stress of a scaffold that had fallen. According to Travel Channel’s Monumental Mysteries, the workers’ platform that was attached to a rolling hanger on a track collapsed when the bolts that were connected to the track were too small and the amount of weight was too great to bear. The platform fell into the safety net, but was too heavy and the net gave way. Two out of the twelve workers survived the 200-foot (61 m) fall into the icy waters, including the 37-year-old foreman, Slim Lambert. Nineteen others who were saved by the net over the course of construction became members of their Half Way to Hell Club.

The project was finished and opened May 27, 1937. The Bridge Round House diner was then included in the southeastern end of the Golden Gate Bridge, adjacent to the tourist plaza which was renovated in 2012. The Bridge Round House, an Art Deco design by Alfred Finnila completed in 1938, has been popular throughout the years as a starting point for various commercial tours of the bridge and an unofficial gift shop. The diner was renovated in 2012 and the gift shop was then removed as a new, official gift shop has been included in the adjacent plaza.

During the bridge work, the Assistant Civil Engineer of California Alfred Finnila had overseen the entire iron work of the bridge as well as half of the bridge’s road work. With the death of Jack Balestreri in April 2012, all workers involved in the original construction are now deceased.

Opening festivities, 50th, and 75th anniversaries

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View of the Golden Gate Bridge and Fort Point from Marine Drive.

The bridge-opening celebration began on May 27, 1937 and lasted for one week. The day before vehicle traffic was allowed, 200,000 people crossed either on foot or on roller skates. On opening day, Mayor Angelo Rossi and other officials rode the ferry to Marin, then crossed the bridge in a motorcade past three ceremonial “barriers”, the last a blockade of beauty queens who required Joseph Strauss to present the bridge to the Highway District before allowing him to pass. An official song, “There’s a Silver Moon on the Golden Gate”, was chosen to commemorate the event. Strauss wrote a poem that is now on the Golden Gate Bridge entitled “The Mighty Task is Done.” The next day, President Roosevelt pushed a button in Washington, D.C. signaling the official start of vehicle traffic over the Bridge at noon. As the celebration got out of hand there was a small riot in the uptown Polk Gulch area. Weeks of civil and cultural activities called “the Fiesta” followed. A statue of Strauss was moved in 1955 to a site near the bridge.

In May 1987, as part of the 50th anniversary celebration, the Golden Gate Bridge district again closed the bridge to automobile traffic and allowed pedestrians to cross the bridge. However, this celebration attracted 750,000 to 1,000,000 people, and ineffective crowd control meant the bridge became congested with roughly 300,000 people, causing the center span of the bridge to flatten out under the weight. Although the bridge is designed to flex in that way under heavy loads, and was estimated not to have exceeded 40% of the yielding stress of the suspension cables, bridge officials stated that uncontrolled pedestrian access was not being considered as part of the 75th anniversary on Sunday, May 27, 2012, because of the additional law enforcement costs required “since 9/11”.

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A pedestrian poses at the old railing on opening day, 1937

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Opening of the Golden Gate Bridge

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Official invitation to the opening of the bridge. This copy was sent to the City of Seattle

Structural Specifications


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On the south side of the bridge a 36.5-inch-wide (93 cm) cross-section of the cable, containing 27,572 wires, is on display.

Until 1964, the Golden Gate Bridge had the longest suspension bridge main span in the world, at 4,200 feet (1,300 m). Since 1964 its main span length has been surpassed by ten bridges; it now has the second-longest main span in the United States, after the Verrazano-Narrows Bridge in New York City. The total length of the Golden Gate Bridge from abutment to abutment is 8,981 feet (2,737 m).

The Golden Gate Bridge’s clearance above high water averages 220 feet (67 m) while its towers, at 746 feet (227 m) above the water, were the world’s tallest on a suspension bridge until 1998 when bridges in Denmark and Japan were completed.

The weight of the roadway is hung from two cables that pass through the two main towers and are fixed in concrete at each end. Each cable is made of 27,572 strands of wire. There are 80,000 miles (130,000 km) of wire in the main cables. The bridge has approximately 1,200,000 total rivets.

Aesthetics

The color of the bridge is officially an orange vermilion called international orange. The color was selected by consulting architect Irving Morrow because it complements the natural surroundings and enhances the bridge’s visibility in fog. Aesthetics was the foremost reason why the first design of Joseph Strauss was rejected. Upon re-submission of his bridge construction plan, he added details, such as lighting, to outline the bridge’s cables and towers. In 1999, it was ranked fifth on the List of America’s Favorite Architecture by the American Institute of Architects.

The bridge was originally painted with red lead primer and a lead-based topcoat, which was touched up as required. In the mid-1960s, a program was started to improve corrosion protection by stripping the original paint and repainting the bridge with zinc silicate primer and vinyl topcoats. Since 1990, acrylic topcoats have been used instead for air-quality reasons. The program was completed in 1995 and it is now maintained by 38 painters who touch up the paintwork where it becomes seriously corroded.

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A view of the Golden Gate Bridge from the Marin Headlands on a foggy morning at sunrise

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View of the northern tower of the bridge

Traffic


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Installation of the movable median barrier system in January 2015

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Testing the newly installed movable barrier.

Most maps and signage mark the bridge as part of the concurrency between U.S. Route 101 and California State Route 1. Although part of the National Highway System, the bridge is not officially part of California’s Highway System. For example, under the California Streets and Highways Code § 401, Route 101 ends at “the approach to the Golden Gate Bridge” and then resumes at “a point in Marin County opposite San Francisco”. The Golden Gate Bridge, Highway and Transportation District has jurisdiction over the segment of highway that crosses the bridge instead of the California Department of Transportation (Caltrans).

The movable median barrier between the lanes is moved several times daily to conform to traffic patterns. On weekday mornings, traffic flows mostly southbound into the city, so four of the six lanes run southbound. Conversely, on weekday afternoons, four lanes run northbound. During off-peak periods and weekends, traffic is split with three lanes in each direction.

From 1968 to 2015, opposing traffic was separated by small, plastic pylons, and during that time, there were 16 fatalities resulting from 128 head-on collisions. To improve safety, the speed limit on the Golden Gate Bridge was reduced from 50 to 45 mph (80 to 72 km/h) on October 1, 1989. Although there had been discussion concerning the installation of a movable barrier since the 1980s, only in March 2005 did the Bridge Board of Directors commit to finding funding to complete the $2 million study required prior to the installation of a movable median barrier. Installation of the resulting barrier was completed on January 11, 2015, following a closure of 45.5 hours to private vehicle traffic, the longest in the bridge’s history. The new barrier system, including the zipper trucks, cost approximately $30.3 million to purchase and install.

Usage and Tourism

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Looking north with traffic and current flow into the bay with sailboats

The bridge is popular with pedestrians and bicyclists, and was built with walkways on either side of the six vehicle traffic lanes. Initially, they were separated from the traffic lanes by only a metal curb, but railings between the walkways and the traffic lanes were added in 2003, primarily as a measure to prevent bicyclists from falling into the roadway.

The main walkway is on the eastern side, and is open for use by both pedestrians and bicycles in the morning to mid-afternoon during weekdays (5 am to 3:30 pm), and to pedestrians only for the remaining daylight hours (until 6 pm, or 9 pm during DST). The eastern walkway is reserved for pedestrians on weekends (5 am to 6 pm, or 9 pm during DST), and is open exclusively to bicyclists in the evening and overnight, when it is closed to pedestrians. The western walkway is open only for bicyclists and only during the hours when they are not allowed on the eastern walkway.

Bus service across the bridge is provided by two public transportation agencies: San Francisco Muni and Golden Gate Transit. Muni offers Saturday and Sunday service on the Marin Headlands Express bus line, and Golden Gate Transit runs numerous bus lines throughout the week. The southern end of the bridge, near the toll plaza and parking lot, is also accessible daily from 5:30 a.m. to midnight by Muni line 28. The Marin Airporter, a private company, also offers service across the bridge between Marin County and San Francisco International Airport.

A visitor center and gift shop, dubbed the “Bridge Pavilion”, is located on the San Francisco side of the bridge, adjacent to the southeast parking lot. It opened in 2012, in time for the bridge’s 75th anniversary celebration. A cafe, outdoor exhibits, and restroom facilities are located nearby. On the Marin side of the bridge, only accessible from the northbound lanes, is the H. Dana Bower Rest Area and Vista Point, named after the first landscape architect for the California Division of Highways.

Lands and waters under and around the bridge are homes to varieties of wildlife such as bobcats and sea lions. Three species of cetaceans that had been absent in the area for many years show recent recoveries/(re)colonizations vicinity to the bridge, and researchers study them to strengthen protections, concerning actions by public and recommending to watch whales either from the bridge and nearby, or to use a local whale watching operator.

Tolls

The last of the construction bonds were retired in 1971, with $35 million in principal and nearly $39 million in interest raised entirely from bridge tolls.

In November 2006, the Golden Gate Bridge, Highway and Transportation District recommended a corporate sponsorship program for the bridge to address its operating deficit, projected at $80 million over five years. The District promised that the proposal, which it called a “partnership program,” would not include changing the name of the bridge or placing advertising on the bridge itself. In October 2007, the Board unanimously voted to discontinue the proposal and seek additional revenue through other means, most likely a toll increase.

In an effort to save $19.2 million over the following 10 years, the Golden Gate District voted in January 2011 to eliminate all toll takers by 2012 and use only open road tolling. Subsequently, this was delayed and toll taker elimination occurred in March 2013. The cost savings have been revised to $19 million over an eight-year period. In addition to the FasTrak electronic toll collection system, the Golden Gate District implemented the use of license plate tolling (branded as “Pay-by-Plate”), and also a one time payment system for drivers to pay before or after their trip on the bridge. Twenty-eight positions were eliminated as part of this plan.

On April 7, 2014, the toll for users of FasTrak was increased from $5 to $6, while the toll for drivers using either the license plate tolling or the one time payment system was raised from $6 to $7. Bicycle, pedestrian, and northbound motor vehicle traffic remain toll free. For vehicles with more than two axles, the toll rate is $7 per axle for those using license plate tolling or the one time payment system, and $6 per axle for FasTrak users. During peak traffic hours, carpool vehicles carrying two or more people and motorcycles pay a discounted toll of $4; drivers must have Fastrak to take advantage of this carpool rate. The Golden Gate Transportation District then planned to increase the tolls by 25 cents in July 2015, and then by another 25 cents each of the next three years.

Golden Gate Bridge toll increases (2014–18)

Golden Gate Bridge toll increases

Congestion Pricing

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Looking south

In March 2008, the Golden Gate Bridge District board approved a resolution to start congestion pricing at the Golden Gate Bridge, charging higher tolls during the peak hours, but rising and falling depending on traffic levels. This decision allowed the Bay Area to meet the federal requirement to receive $158 million in federal transportation funds from USDOT Urban Partnership grant. As a condition of the grant, the congestion toll was to be in place by September 2009.

The first results of the study, called the Mobility, Access and Pricing Study (MAPS), showed that a congestion pricing program is feasible. The different pricing scenarios considered were presented in public meetings in December 2008.

In August 2008, transportation officials ended the congestion pricing program in favor of varying rates for metered parking along the route to the bridge including on Lombard Street and Van Ness Avenue.

Issues


Suicides

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As a suicide prevention initiative, this sign promotes a special telephone available on the bridge that connects to a crisis hotline.

The Golden Gate Bridge is the second-most used suicide site/suicide bridge in the world, after the Nanjing Yangtze River Bridge. The deck is about 245 feet (75 m) above the water. After a fall of four seconds, jumpers hit the water at around 75 mph or about 120 km/h. Most of the jumpers die from impact trauma. About 5% of the jumpers survive the initial impact but generally drown or die of hypothermia in the cold water.
After years of debate and over an estimated 1,500 deaths, suicide barriers began to be installed in April 2017. Construction will take approximately four years at a cost of over $200 million.

Wind

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Air race near the Golden Gate Bridge

Since its completion, the Golden Gate Bridge has been closed because of weather conditions only three times: on December 1, 1951, because of gusts of 69 mph (111 km/h); on December 23, 1982, because of winds of 70 mph (113 km/h); and on December 3, 1983, because of wind gusts of 75 mph (121 km/h).

An anemometer, placed midway between the two towers on the west side of the bridge, has been used to measure wind speeds. Another anemometer was placed on one of the towers.

Seismic Vulnerability and Improvements

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Doyle Drive Replacement Project progress in October 2013

Modern knowledge of the effect of earthquakes on structures led to a program to retrofit the Golden Gate to better resist seismic events. The proximity of the bridge to the San Andreas Fault places it at risk for a significant earthquake. Once thought to have been able to withstand any magnitude of foreseeable earthquake, the bridge was actually vulnerable to complete structural failure (i.e., collapse) triggered by the failure of supports on the 320-foot (98 m) arch over Fort Point. A $392 million program was initiated to improve the structure’s ability to withstand such an event with only minimal (repairable) damage. One challenging undertaking is completing this program without disrupting traffic. A complex electro-hydraulic synchronous lift system was custom built for construction of temporary support towers and a series of intricate lifts, transferring the loads from the existing bridge onto the temporary supports. This was completed with engineers from Balfour Beatty and Enerpac, accomplishing this task without disrupting day-to-day San Francisco commuter traffic. The retrofit was planned to be completed in 2012.

The former elevated approach to the Golden Gate Bridge through the San Francisco Presidio, known as Doyle Drive, dated to 1933 and was named after Frank P. Doyle, President and son of the founder of the Exchange Bank in Santa Rosa, and the man who, more than any other person, made it possible to build the Golden Gate Bridge. The highway carried about 91,000 vehicles each weekday between downtown San Francisco and the North Bay and points north. The road was deemed “vulnerable to earthquake damage”, had a problematic 4-lane design, and lacked shoulders, and a San Francisco County Transportation Authority study recommended that it be replaced. Construction on the $1 billion replacement, temporarily known as the Presidio Parkway, began in December 2009. The elevated Doyle Drive was demolished on the weekend of April 27–30, 2012, and traffic used a part of the partially completed Presidio Parkway, until it was switched onto the finished Presidio Parkway on the weekend of July 9–12, 2015. As of May 2012, an official at Caltrans said there is no plan to permanently rename the portion known as Doyle Drive.

In Popular Culture


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Golden Gate Bridge at sunset

As a prominent American landmark, the Golden Gate Bridge has been used in numerous media which includes books, films and video games.

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Comparison of the side elevations of the Golden Gate Bridge and some notable bridges at the same scale. (click for interactive version)

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San Francisco with two bridges (Western section of Bay Bridge in the left background), Coit Tower (in background to the left of north tower), and Fort Mason (on the San Francisco waterfront in the background behind the north tower) from Marin

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Golden Gate Bridge at night, with San Francisco in the background

Tower Bridge

From Wikipedia, the free encyclopedia

TOWER BRIDGE DATA

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Tower Bridge is a combined bascule and suspension bridge in London built between 1886 and 1894. The bridge crosses the River Thames close to the Tower of London and has become an iconic symbol of London, resulting in it sometimes being confused with London Bridge, situated some 0.5 mi (0.80 km) upstream. Tower Bridge is one of five London bridges now owned and maintained by the Bridge House Estates, a charitable trust overseen by the City of London Corporation. It is the only one of the Trust’s bridges not to connect the City of London directly to the Southwark bank, as its northern landfall is in Tower Hamlets.

London-Shard-View

The bridge consists of two bridge towers tied together at the upper level by two horizontal walkways, designed to withstand the horizontal tension forces exerted by the suspended sections of the bridge on the landward sides of the towers. The vertical components of the forces in the suspended sections and the vertical reactions of the two walkways are carried by the two robust towers. The bascule pivots and operating machinery are housed in the base of each tower. Before its restoration in the 2010s, the bridge’s colour scheme dated from 1977, when it was painted red, white and blue for Queen Elizabeth II’s Silver Jubilee. Its colours were subsequently restored to blue and white.

The bridge deck is freely accessible to both vehicles and pedestrians, whereas the bridge’s twin towers, high-level walkways and Victorian engine rooms form part of the Tower Bridge Exhibition, for which an admission charge is made. The nearest London Underground tube stations are Tower Hill on the Circle and District lines, London Bridge on the Jubilee and Northern lines and Bermondsey on the Jubilee line, and the nearest Docklands Light Railway station is Tower Gateway. The nearest National Rail stations are at Fenchurch Street and London Bridge.


Contents

1 | History

1.1 | Inception
1.2 | Construction
1.3  | Opening
1.4  | Second World War
1.5  | Modernization
1.6  | 2008–2012 facelift
1.7  | London 2012 Olympics and Paralympics
1.8  | 2016 renovations

2  | Design

2.1  | Bridge structure
2.2  | Hydraulic system
2.3  | Signalling and control

3  | Traffic

3.1  | Road
3.2  | River

4  | Tower Bridge Exhibition
5  | Reaction
6  | Incidents
7  | Gallery

1 | History


1.1 | Inception

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Elevation, with dimensions

In the second half of the 19th century, an advertisement in the East End of London led to a hiring for a new river crossing downstream of London Bridge. A traditional fixed bridge at street level could not be built because it would cut off access by sailing ships to the port facilities in the Pool of London, between London Bridge and the Tower of London.

A Special Bridge or Subway Committee was formed in 1877, chaired by Sir Albert Joseph Altman, to find a solution to the river crossing problem. It opened the design of the crossing to public competition. Over 50 designs were submitted, including one from civil engineer Sir Joseph Bazalgette. Bazalgette’s design was rejected because of a lack of sufficient headroom, and design was not approved until 1884, when it was decided to build a bascule bridge. Sir John Wolfe Barry was appointed engineer with Sir Horace Jones as architect (who was also one of the judges). An Act of Parliament was passed in 1885 authorising the bridge’s construction. It specified the opening span must give a clear width of 200 feet (61 m) and a headroom of 135 feet (41 m). Construction had to be in a Gothic style.

Barry designed a bascule bridge with two bridge towers built on piers. The central span was split into two equal bascules or leaves, which could be raised to allow river traffic to pass. The two side-spans were suspension bridges, with the suspension rods anchored both at the abutments and through rods contained within the bridge’s upper walkways.

1.2 | Construction

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Tower Bridge under construction, 1892

Construction started in 1886 and took eight years with five major contractors – Sir John Jackson (foundations), Baron Armstrong (hydraulics), William Webster, Sir H.H. Bartlett, and Sir William Arrol & Co. – and employed 432 construction workers. E W Crutwell was the resident engineer for the construction.

Two massive piers, containing over 70,000 tons of concrete, were sunk into the riverbed to support the construction. Over 11,000 tons of steel provided the framework for the towers and walkways. This was then clad in Cornish granite and Portland stone, both to protect the underlying steelwork and to give the bridge a pleasing appearance.

Jones died in 1886 and George D. Stevenson took over the project. Stevenson replaced Jones’s original brick façade with the more ornate Victorian Gothic style, which makes the bridge a distinctive landmark, and was intended to harmonise the bridge with the nearby Tower of London. The total cost of construction was £1,184,000 (equivalent to £122 million in 2015).

1.3 | Opening

The bridge was officially opened on 30 June 1894 by The Prince of Wales (the future King Edward VII), and his wife, The Princess of Wales (Alexandra of Denmark).

The bridge connected Iron Gate, on the north bank of the river, with Horselydown Lane, on the south – now known as Tower Bridge Approach and Tower Bridge Road, respectively. Until the bridge was opened, the Tower Subway – 400 m to the west – was the shortest way to cross the river from Tower Hill to Tooley Street in Southwark. Opened in 1870, Tower Subway was among the world’s earliest underground (“tube”) railways, but it closed after just three months and was re-opened as a pedestrian foot tunnel. Once Tower Bridge was open, the majority of foot traffic transferred to using the bridge, there being no toll to pay to use it. Having lost most of its income, the tunnel was closed in 1898.

The high-level open air walkways between the towers gained an unpleasant reputation as a haunt for prostitutes and pickpockets; as they were only accessible by stairs they were seldom used by regular pedestrians, and were closed in 1910.

1.4 | Second World War

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A Short Sunderland of No. 201 Squadron RAF moored at Tower Bridge during the 1956 commemoration of the Battle of Britain

During the Second World War and as a precaution against the existing engines being damaged by enemy action, a third engine was installed in 1942: a 150 hp horizontal cross-compound engine, built by Vickers Armstrong Ltd. at their Elswick works in Newcastle upon Tyne. It was fitted with a flywheel having a 9-foot (2.7 m) diameter and weighing 9 tons, and was governed to a speed of 30 rpm. The engine became redundant when the rest of the system was modernised in 1974, and was donated to the Forncett Industrial Steam Museum by the Corporation of the City of London.

1.5 | Modernization

In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system, designed by BHA Cromwell House, with the original final pinions driven by modern hydraulic motors and gearing. In 1982, the Tower Bridge Exhibition opened, housed in the bridge’s twin towers, the long-closed high-level walkways and the Victorian engine rooms. The latter still house the original steam engines and some of the original hydraulic machinery.

A computer system was installed in 2000 to control the raising and lowering of the bascules remotely. It proved unreliable, resulting in the bridge being stuck in the open or closed positions on several occasions during 2005 until its sensors were replaced.

1.6 | 2008–2012 Facelift

In April 2008 it was announced that the bridge would undergo a ‘facelift’ costing £4 million, and taking four years to complete. The work entailed stripping off the existing paint down to bare metal and repainting in blue and white. Each section was enshrouded in scaffolding and plastic sheeting to prevent the old paint falling into the Thames and causing pollution. Starting in mid-2008, contractors worked on a quarter of the bridge at a time to minimise disruption, but some road closures were inevitable. It is intended that the completed work will stand for 25 years.

The renovation of the walkway interior was completed in mid-2009. Within the walkways a versatile new lighting system has been installed, designed by Eleni Shiarlis, for when the walkways are in use for exhibitions or functions. The new system provides for both feature and atmospheric lighting, the latter using bespoke RGB LED luminaires, designed to be concealed within the bridge superstructure and fixed without the need for drilling (these requirements as a result of the bridge’s Grade I status).

The renovation of the four suspension chains was completed in March 2010 using a state-of-the-art coating system requiring up to six different layers of ‘paint’.

1.7 | London 2012 Olympics and Paralympics

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Tower Bridge with 2012 Olympic rings

The bridge featured in publicity for the 2012 Summer Olympics being held in London. In June 2012 a set of Olympic rings was suspended from the bridge to mark one month to go until the start of the games. The rings cost £259,817 to make, measured 25 by 11.5 metres (82 by 38 ft) and weighed 13 tonnes (14 short tons).

On 8 July 2012, the west walkway was transformed into a 200-foot-long (61 m) Live Music Sculpture by the British composer Samuel Bordoli. 30 classical musicians were arranged along the length of the bridge 138 feet (42 m) above the Thames behind the Olympic rings. The sound travelled backwards and forwards along the walkway, echoing the structure of the bridge.

Following the Olympics, the rings were removed from Tower Bridge and replaced by the emblem of the Paralympic Games for the 2012 Summer Paralympics.

1.8 | 2016 Renovations

Tower Bridge was closed to all road traffic for almost three months in late 2016 (1 October to 30 December). This was to allow structural maintenance work to take place. The work included:

  • Undertaking major maintenance to the bridge lifting systems
  • Replacing the decking and resurfacing the walkways and road
  • Replacing the expansion joints along the bridge to provide a smoother surface
  • Waterproofing the arches made from brick on the approaches to the bridge

During this time the bridge was still open to water borne traffic as required by Act of Parliament. The bridge was open to pedestrians for all but three weekends, where a free ferry service was in operation.

Design


2.1 | Bridge Structure

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Tower Bridge from Shad Thames

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Tower Bridge at dawn

The bridge is 800 feet (240 m) in length with two towers each 213 feet (65 m) high, built on piers. The central span of 200 feet (61 m) between the towers is split into two equal bascules or leaves, which can be raised to an angle of 86 degrees to allow river traffic to pass. The bascules, weighing over 1,000 tons each, are counterbalanced to minimise the force required and allow raising in five minutes.

The two side-spans are suspension bridges, each 270 feet (82 m) long, with the suspension rods anchored both at the abutments and through rods contained within the bridge’s upper walkways. The pedestrian walkways are 143 feet (44 m) above the river at high tide.

The main bridge deck carries two lanes of road traffic between two low-level pedestrian walkways across both suspension spans and the opening bascule section of the bridge, with the walkways separated from the roadway by fences. The roadway passes through each of the two towers, whereas the low-level walkways pass around the outside of the towers.

One of the chimneys on the bridge, which are often confused as lamp posts, connects up to an old fireplace in a guardroom of the Tower of London. It is long-disused.

2.2 | Hydraulic System

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One of the original steam engines

The original raising mechanism was powered by pressurised water stored in several hydraulic accumulators. The system was designed and installed by Hamilton Owen Rendel while working for Sir W. G. Armstrong Mitchell & Company of Newcastle upon Tyne. Water, at a pressure of 750 psi (5.2 MPa), was pumped into the accumulators by two 360 hp (270 kW) horizontal twin-tandem compound stationary steam engines, fitted with Meyer expansion slide valves. Each engine drove a force pump from its piston tail rod. The accumulators each comprise a 20-inch (51 cm) ram on which sits a very heavy weight to maintain the desired pressure.

The entire hydraulic system along with the gas lighting system was installed by William Sugg & Co Ltd., the well known Westminster gas engineers. The gas lighting was initially by open flame burners within the lanterns but soon after was updated to the later incandescent system.

In 1974, the original operating mechanism was largely replaced by a new electro-hydraulic drive system, designed by BHA Cromwell House. The only components of the original system still in use are the final pinions, which engage with the racks fitted to the bascules. These are driven by modern hydraulic motors and gearing, using oil rather than water as the hydraulic fluid. Some of the original hydraulic machinery has been retained, although it is no longer in use. It is open to the public and forms the basis for the bridge’s museum, which resides in the old engine rooms on the south side of the bridge. The museum includes the steam engines, two of the accumulators and one of the hydraulic engines that moved the bascules, along with other related artefacts.

2.3 | Signalling and Control

To control the passage of river traffic through the bridge, a number of different rules and signals were employed. Daytime control was provided by red semaphore signals, mounted on small control cabins on either end of both bridge piers. At night, coloured lights were used, in either direction, on both piers: two red lights to show that the bridge was closed, and two green to show that it was open. In foggy weather, a gong was sounded as well.

Vessels passing through the bridge had to display signals too: by day, a black ball at least 2 feet (0.61 m) in diameter was to be mounted high up where it could be seen; by night, two red lights in the same position. Foggy weather required repeated blasts from the ship’s steam whistle. If a black ball was suspended from the middle of each walkway (or a red light at night) this indicated that the bridge could not be opened. These signals were repeated about 1,000 yards (910 m) downstream, at Cherry Garden Pier, where boats needing to pass through the bridge had to hoist their signals/lights and sound their horn, as appropriate, to alert the Bridge Master.

Some of the control mechanism for the signalling equipment has been preserved and may be seen working in the bridge’s museum.

3 | Traffic


The tall ship Wylde Swan passing under Tower Bridge decorated for the London Olympics in August 2012. Note the Olympic rings folded up to allow passage of the mast.

3.1 | Road

Tower Bridge is still a busy crossing of the Thames: it is crossed by over 40,000 people (motorists, cyclists and pedestrians) every day. The bridge is on the London Inner Ring Road, and is on the eastern boundary of the London congestion charge zone. (Drivers do not incur a charge by crossing the bridge.)

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The tall ship Wylde Swan passing under Tower Bridge decorated for the London Olympics in August 2012. Note the Olympic rings folded up to allow passage of the mast.

To maintain the integrity of the structure, the City of London Corporation has imposed a 20-mile-per-hour (32 km/h) speed restriction, and an 18 tonnes (20 short tons) weight limit on vehicles using the bridge. A camera system measures the speed of traffic crossing the bridge, using a number plate recognition system to send fixed penalty charges to speeding drivers.

A second system monitors other vehicle parameters. Induction loops and piezoelectric sensors are used to measure the weight, the height of the chassis above ground level, and the number of axles of each vehicle.

3.2 | River

The bascules are raised around 1000 times a year. River traffic is now much reduced, but it still takes priority over road traffic. Today, 24 hours’ notice is required before opening the bridge, and opening times are published in advance on the bridge’s website. There is no charge for vessels to open the bridge.

When needing to be raised for the passage of a vessel the bascules are only raised to an angle sufficient for the vessel to safely pass under the bridge, except in the case of a vessel with the Monarch on board in which case they are raised fully no matter the size of the vessel.

4 | Tower Bridge Exhibition


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Interior of high-level walkway (used as an exhibition space)

The Tower Bridge Exhibition is a display housed in the bridge’s twin towers, the high-level walkways and the Victorian engine rooms. It uses films, photos and interactive displays to explain why and how Tower Bridge was built. Visitors can access the original steam engines that once powered the bridge bascules, housed in a building close to the south end of the bridge.

The exhibition charges an admission fee. Entrance is from the west side of the bridge deck to the northern tower, from where visitors ascend to level 4 by lift before crossing the high-level walkways to the southern tower. In the towers and walkways is an exhibition on the history of the bridge. The walkways also provide views over the city, the Tower of London and the Pool of London, and include a glass-floored section. From the south tower, visitors can visit the engine rooms, with the original steam engines, which are situated in a separate building beside the southern approach to the bridge.

5 | Reaction


Although the bridge is an undoubted landmark, professional commentators in the early 20th century were critical of its aesthetics. “It represents the vice of tawdriness and pretentiousness, and of falsification of the actual facts of the structure”, wrote Henry Heathcote Statham, while Frank Brangwyn stated that “A more absurd structure than the Tower Bridge was never thrown across a strategic river”.

Architectural historian Dan Cruickshank selected the bridge as one of his four choices for the 2002 BBC television documentary series Britain’s Best Buildings.

Tower Bridge is often mistaken for London Bridge, the next bridge upstream. A popular urban legend is that in 1968, Robert P. McCulloch, the purchaser of the old London Bridge that was later shipped to Lake Havasu City in Arizona, believed that he was in fact buying Tower Bridge. This was denied by McCulloch himself and has been debunked by Ivan Luckin, the vendor of the bridge.

A partial replica of Tower Bridge has been built in the city of Suzhou in China. The replica differs from the original in having no lifting mechanism and having four separate towers.

6 | Incidents


In December 1952, the bridge opened while a number 78 double-decker bus was crossing from the south bank. At that time, the gateman would ring a warning bell and close the gates when the bridge was clear before the watchman ordered the raising of the bridge. The process failed while a relief watchman was on duty. The bus was near the edge of the south bascule when it started to rise; driver Albert Gunter made a split-second decision to accelerate, clearing a 3-foot (0.91 m) gap to drop 6 feet (1.8 m) onto the north bascule, which had not yet started to rise. There were no serious injuries. Gunter was given £10 (equivalent to £260 in 2015) by the City Corporation to honour his act of bravery.

The Hawker Hunter Tower Bridge incident occurred on 5 April 1968 when a Royal Air Force Hawker Hunter FGA.9 jet fighter from No. 1 Squadron, flown by Flt Lt Alan Pollock, flew through Tower Bridge. Unimpressed that senior staff were not going to celebrate the RAF’s 50th birthday with a fly-past, Pollock decided to do something himself. Without authorisation, Pollock flew the Hunter at low altitude down the Thames, past the Houses of Parliament, and continued on toward Tower Bridge. He flew the Hunter beneath the bridge’s walkway, remarking afterwards that it was an afterthought when he saw the bridge looming ahead of him. Pollock was placed under arrest upon landing, and discharged from the RAF on medical grounds without the chance to defend himself at a court martial.

In the summer of 1973, a single-engined Beagle Pup was twice flown under the pedestrian walkway of Tower Bridge by 29-year-old stockbroker’s clerk Paul Martin. Martin was on bail following accusations of stockmarket fraud. He then “buzzed” buildings in The City, before flying north towards the Lake District where he died when his aircraft crashed some two hours later.

In May 1997, the motorcade of United States President Bill Clinton was divided by the opening of the bridge. The Thames sailing barge Gladys, on her way to a gathering at St Katharine Docks, arrived on schedule and the bridge was opened for her. Returning from a Thames-side lunch at Le Pont de la Tour restaurant with UK Prime Minister Tony Blair, President Clinton was less punctual and arrived just as the bridge was rising. The bridge opening split the motorcade in two, much to the consternation of security staff. A spokesman for Tower Bridge is quoted as saying: “We tried to contact the American Embassy, but they wouldn’t answer the phone.”

On 19 August 1999, Jef Smith, a Freeman of the City of London, drove a flock of two sheep across the bridge. He was exercising a claimed ancient permission, granted as a right to Freemen, to make a point about the powers of older citizens and the way in which their rights were being eroded.

Before dawn on 31 October 2003, David Crick, a Fathers 4 Justice campaigner, climbed a 100-foot (30 m) tower crane near Tower Bridge at the start of a six-day protest dressed as Spider-Man. Fearing for his safety, and that of motorists should he fall, police cordoned off the area, closing the bridge and surrounding roads and causing widespread traffic congestion across the City and east London. The Metropolitan Police were later criticised for maintaining the closure for five days when this was not strictly necessary in the eyes of some citizens.

On 11 May 2009, six people were trapped and injured after a lift fell 10 feet (3 m) inside the north tower.

7 | Gallery