Golden Gate Bridge

The Golden Gate Bridge is a suspension bridge spanning the Golden Gate strait, the mile-wide, three-mile-long channel between San Francisco Bay and the Pacific Ocean. The structure links the U.S. city of San Francisco, on the northern tip of the San Francisco Peninsula, to Marin County, bridging 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 Frommers travel guide considers the Golden Gate Bridge "possibly the most beautiful, certainly the most photographed, bridge in the world". It opened in 1937 and had, until 1964, the longest suspension bridge main span in the world, at 4,200 feet (1,300 m).

Specifications

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. 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.

Structure

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.

Traffic

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 median markers between the lanes are moved 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, or three and two lanes with one buffer lane.

Traffic is separated by small, plastic pylons, and from 1971 through 2007, there were 16 fatalities from head-on collisions. To improve safety, the speed limit on the Golden Gate Bridge was reduced from 55 to 45 mph (89 to 72 km/h) on October 1, 1983. Although there has been discussion concerning the installation of amovable 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. The movable barrier is set to be installed in either late October or early November 2014, during which the bridge will be closed completely for 52 hours, starting on a Friday night. This is the longest closure in the history of the bridge.

Design

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' 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 New York’s Manhattan Bridge designer Leon Moisseiff.

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.

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.

Construction

Construction began on January 5, 1933. The project cost more than $35 million, completing ahead of schedule and 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.

The project was finished by April 1937, $1.3 million under budget. 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. 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 steelworkers. Of eleven men killed from falls during construction, ten were killed (when the bridge was near completion) when the net failed under the stress of a scaffold that had fallen. Nineteen others who were saved by the net over the course of construction became proud members of their Half Way to Hell Club. 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.

Seismic Retrofit

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 (reparable) 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.

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