Architectural Importance of the Golden Gate Bridge

Architectural Importance of the Golden Gate Bridge
Institution
Date
Part 1
Golden Gate Bridge served as the principal component of the only highway connecting San Francisco with the countries to its north. It is considered as one of the western civilization’s greatest achievements. The bridge is a unique architectural structure consisting of a 1280 m main span and two 343 m side spans. These spans suspend from two continuous 924 mm diameter steel wire cables spaced at 27.4 m. Cables supported on steel towers, and then anchored in concrete anchorage blocks. More than one million tons of concrete was used to build the anchorages. The towers consist of two thin steel beams that are braced together with struts. The 210m towers consist of tall, thin steel beams braced with struts. Above the roadway, the beams are braced by trussed portal struts. Below the roadway, they are braced by double diagonal struts. Cast steel saddles at the top of the shafts secured the cables to the shaft. In addition, a weak connection between the steel tower and the reinforced concrete was provided to resist wind loads during construction. Shear plates welded to a 127mm thick base plate were riveted to the tower plates.
The tower shafts were modeled using two and three-node 3-dimensional elastic beam elements with shear deformations. The tower struts were modeled using beam elements with shear area equivalent to the actual laced members. The tower struts connections were modeled using rigid constraints of dimensions similar to that of the joints. The gusset plates connecting the individual strut members were also modeled using their corresponding section properties. The tower plinth was modeled using membrane elements with a simple elastic-plastic material. Towers fixed about the longitudinal axis of the bridge enabled the rotation, and the membrane elements were connected to the reinforced concrete piers with gap elements to allow for uplifts.
Steel dowels embedded in the pier restrained sliding of the base plates. The suspended structure consists of two 7.6 m deep stiffening trusses spaced at 27.4 m. The stiffening trusses are connected with top and bottom lateral bracing systems. The orthographic deck and the sidewalks are carried by floor beams that are spaced at 7.6 m. Fandel (2006) say, “The north pier, which supports the tower, was built quickly on a bedrock ledge 6m below the water. But on the southern San Francisco side, Joseph Strauss (Project Engineer) had to build his pier in the open ocean, 30m below the surface. He built an enormous watertight cofferdam and pumped in hundreds of ton of concrete. By 1935, the towers were complete, and cable-spinning began”1. Still, Steel frame and steel cables played a critical role in the construction of the Golden Gate Bridge. “The fabricated steel used in the construction of the Golden Gate Bridge was manufactured by Bethlehem Steel in plants, in Trenton, New Jersey, and Sparrow Point. The shipment of the steel was timed to coincide with the construction of the bridge. Cable spinning began in October 1935. To create the cables, Roebling developed a method called parallel wire construction. The innovative technique enabled a cable of any length and thickness to be formed by binding together thin wires. The plan promised engineers the freedom to build a bridge of infinite length”2.
Understandably, the Golden Gate Bridge is constructed under suspended construction, also known as the Principle of the Long-Span Suspension Bridge. It involves hanging bridge segments or elements. MacDonald, Donald, and Ira Nadel (2013) states, “the suspension bridge is always suspended by hangers, each attached to the main cable, which in turn is anchored into the ground at its ends. The deck provides some stiffness to the system so that concentrated loads on the floor are spread to several hangers. Suspension bridge has a thin deck that carries bending only”3. Meaning: that the static design of this kind of bridge is straightforward since there is no compression. Another concept that put into consideration is the lateral wind loading. In the construction of the Golden Gate Bridge, an equation engineers developed the equation below to prove the cable deformed into a parabola, and the horizontal component force in the cable was a constant value.
Figure 1


The figure above indicates one of the two weight blocks that counterbalance the cable supports. Overhead crane provides massive stiffening. Murray (2003) suggests, “these structures are concrete shells loaded with material heavy enough to resist three times the anticipated strain. Under them are eye-bars that reach deeply into concrete anchorage for a relentless grip on the southern shore. Forward from the anchorage and the weight blocks is the cable housing. It shelters the cable strands from sun and rain when they spread fan-wide from the pylons, each to its eye-bar. The pier, made up of 147,600 tons of concrete, was built in 37m of open water. It was achieved by the concrete fender that in itself is a marvel of construction; it is 108m long and 56m wide at the center line of the bridge. The fender consists of 152,800 tons of concrete. It was built to assist in the construction of the pier and to protect it from the sweep of ocean currents. Sea water comes in through surge-holds to the space between the pier and fender to counter-balance pressure on the fender”4.
The Golden Gate Bridge presents a decent impression of balance between its mass and voids, and between light and shadow. Still, it’s geometric balance between depths and spans, lengths and spans are also excellent. Esthetic refinement of the bridge makes it more unique than other bridges in the world. The two columns across the width of the bridge floor prevent the oblique angles of view from creating an opaque barrier on the bridge. Orange Vermilion blends well with the span’s natural setting as it is a warm color consistent with the span’s natural setting. It is a warm color consistent with the warm colors of the land masses in the setting as distinct from the cool colors of the sky and sea. It also provides enhanced visibility in the fog for passing ships.
Figure 2: Golden Gate Bridge


Part 2
Among several innovations in the 20th century, Golden Gate Bridge is one of remarkable achievement based on the engineering concepts.
“Our world of today…revolves completely around things that at one time could not be done because they were supposedly beyond the limits of human endeavor. Do not be afraid to dream”5.
The impressive design began in the 19th century under the leadership of Joseph Strauss. The San Francisco’s wonder is a suspension bridge with two pillars, each located at the either ends of the water. The deck of Golden Gate Bridge is suspended from the cables connected to the shafts towers, which are ballasted to the ground. This feature is esthetic pleasing compared to the conventional bridges in the sense that it spans from 2000-7000 feet. This range is far much wider than the low bridges, given that its construction occurred over water mass. In additional, the above attribute was significant to allow passage of large ships, hence opening up the traffic in America.
“In every aspect of its design, a suspension bridge challenges the traditional assumptions of bridge design, but in ways that require an understanding and appreciation, an informed view, of the principles being challenged” 6.
The complex Golden Gate Bridge design was essential in order to create a link between San Francisco Bay and the Pacific Ocean. It presented a challenging project to American and the rest of the world, hence numerous criticisms during the groundbreaking stage. However, the construction team remained optimistic about the success of the project, which eventually turned real. The importance of the San Francisco’s Golden Gate Bridge is evident through evaluation of its construction history, political and social responses, legislation, innovations, financial and structural integrity.
Golden Gate Bridge was an important and a symbolic undertaking based on the time of the undertaking. The idea was first authorized in 1869 by then the United States Emperor, Joshua. However, City Engineer M.M. O’Shaughnessy staged a serious consideration of the Joshua’s idea. Conducting soundings at the behest of the state legislature in 1920, the United States Coast, and Geodetic Survey declared the project unfeasible due to inadequate bedrock and unstable currents. While early estimates were in the range of $100 million, the San Francisco Supervisors held a reasonable cost to be $25 million. It seemed that the bridging the Golden Gate would be prohibitively difficult and costly. O’Shaughnessy wondered how he would turn the bridge idea into reality. The answer to the technical and financial problems of bridging the Golden Gate seemed to appear in the person of Joseph B. Strauss. In 1919, O’Shaughnessy contacted a number of prominent engineers in America to submit plans and bids for the Golden Gate Bridge project. Strauss demonstrated the most interest in the project. Strauss was an experienced bridge builder who had won some recognition for an innovation in bascule bridge design. He worked with O’Shaughnessy previously in planning a ride for the Panama-Pacific International Exposition, and constructed a small cantilever bridge for San Francisco. Strauss graduated with bachelor’s degree from the University of Cincinnati, but never received any advanced training as an engineer. Instead, he gained practical knowledge of the field in an iron foundry that specialized in bridge materials, a series of jobs with engineering companies and the Chicago Department of Sanitary Engineering, and finally as the head of his own bridge building firm.
The idea of building a bridge across the Golden Gate inspired eminent interest in Strauss. In his enthusiasm, Strauss discounted the warnings of other engineers and the discouraging results of 1920 soundings, quickly developing plans for cantilever-suspension hybrid bridge. Strauss awkward design caused O’Shaughnessy considerable apprehension. O’Shaughnessy remarked that:
“Strauss design had a greater resemblance to an inverted rat trap than to a bridge and lowered considerably my estimate of (his) capacity for designing a large bridge”7.
This project required the perusal and verification by the U.S legislative body of the construction works. Frank Coombs drafted a bill that would oversee the implementation and construction of the Golden Gate Bridge in order to ease traffic challenge in the San Francisco.
The bill aimed at “transforming the transportation districts from a pure toll-taking activity to a smug transit agency so impregnable that it has spurned all attempts to reform it”8.
The agency originated with the 1923 California Bridge and Highway District Act, specifically intended to allow for the public financing, construction and administration of a bridge across the Golden Gate; in 1969 legislation authorized it to take on mass transportation. With a new name and a new purpose, its officials took over a failing private bus system and began the revival of ferry service in the Golden Gate Corridor.
In 1924, the Francisco Counties requested for a building permit from the War Department. In December 1924, the constructors received the government permit, with the construction work beginning on January 5, 1933. The legislation delegated the building capacity “under the aegis of the HYPERLINK "...