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Introduction As I go up 19th Avenue, off to the distance suddenly I see the rise of a huge orange tower unveiling itself by the nearby cypress trees. It is a tower, which bears half of its weight over the gateway that leads us to the rest of the world. It is the Golden Gate Bridge. The breadth and promise that the Statue of Liberty suggests for the eastern half of America is the statement that the Golden Gate Bridge implies for the west. To many Asians who have immigrated here via the pacific, such as my father, this wondrous structure symbolizes freedom and hope. As a bridge itself, it is fascinating to think of the power it has by bringing two things that were once separate together. Hope in a literal sense is what this great structure provides. Bridges and cities go together, in large part because so many of our greatest cities were founded where they are precisely because of the proximity to water. (Petroski, "Engineers of Dreams" 3) The Golden Gate Bridge networks a great city across a treacherous body of water to a multitude of cities. The daily hustle and bustle of commerce and trade, which many lives depend on and flourish, happen because of this connection. For us to understand and appreciate this event, I will discuss the History, Politics, Economics, Criteria for a bridge, Building overview of the Golden Gate Bridge, Cabling, Suspension bridge technical data, Parabolic Formulas, and Applied Physics. In conclusion, I will bring you back to the Golden Gate Bridge today. History The unimaginable becomes functional and tangible. As early as 1872 there was talk about "bridging the gate" by a railroad owner, Charles Crocker who proposed a train to be built where the Golden Gate now triumphs. City officials thought this would just be too risky and others thought it would be impossible. However, with continued push for development of "marvelous Marin", the means of ferryboat for the sole commute was no longer adequate. James Wilkins, raised in San Rafael and a graduate of Berkeley with a degree in engineering was one who could no longer tolerate the delayed time it took a ferryboat to cross the bay, when an automobile could transport a man 20 miles in a half an hour. Although he studied engineering, James Wilkins took employment with the San Francisco Bulletin and in 1916 began an editorial campaign to bridge the gate. He was also one of the few who realized the development of Marin was very dependent of its relationship to San Francisco. Soon Wilkins was able to attract the interest of San Francisco City engineer M.M. O'Shaughnessy. O'Shaughnessy being a civic authority, would be key in promoting such a span. Throughout the depression and WWI O'Shaughnessy continued to believe in and support the idea. As a practicing engineer himself he assessed many different opinions from other engineers. Most were naysayers. The opinion was that the cost would be astronomical with estimates as high as $100,000,000. Until finally O'Shaughnessy met with Joseph Baermann Strauss also an engineer, who by this time was responsible for building 400 bridges on nearly every continent. Strauss evaluated Wilkins' ideas for O'Shaughnessy and proposed the initial project for $17 million. In the process other estimates figured were between $25million and $30million. The project ultimately cost $35million. Finally, on December 4, 1928, the Golden Gate Bridge and Highway District. were formed to oversee and manage the building and funding of the Golden Gate Bridge. At last, on May 27, 1937 the Golden Gate Bridge officially opened. Politics Strauss, possessing a Wagnerian character with the stubbornness of a mule, always shot from the hip. This did very little for the diplomacy needed dealing with the politics of this tremendous project. Fortunately, his genius ability led him to chameleon into a politician himself. "It took two decades and two hundred million words to convince people that the bridge was feasible"The super span the world would soon come to know was first met with great resistance by the War department, Counties north of San Francisco, and Southern Pacific Railroad. Approval from the War Department was crucial to the construction of any kind since it had jurisdiction over the harbor. The concern was over any building that might interrupt shipping traffic or affect military logistics, since it owned the land on either side of the narrows of the Gate, including the Presidio and Fort Baker in Marin. Secondly there was a major concern for reasons of defense. Would the bridge be a hindrance to navigation during a bomb attack? Strauss made his case and was able to win over the War department with a speech conveying a tone of conviction. "San Francisco has often done the impossible. Now it only remains for her to connect up with the contiguous territory to make her the great city she is destined to be. Ways of transportation are essential to a city's welfare; it means the decline or growth of a city. I believe this bridge will bring an era of unprecedented prosperity. It will be, in my opinion, the greatest feat of construction ever developed." To answer the next concern regarding an enemy attack, "If the enemy got so close as to be able to bomb the bridge, there would be very little left of the city." One December 20th, 1924, Secretary of War John Weeks withdrew its opposition to the bridge provided that certain conditions were met. The district had to be responsible for all costs incurred with the building, moving, and replacing of property of the defensive and other military facilities damaged by construction. As well as to carry the entire expense of the construction and maintenance of the approaches to the bridge. Humbolt, Lake, and Mendocino and even Napa Counties reneged on their support for the structure, while San Francisco, Marin, Sonoma, and Del Norte stayed with it. During the political bickering of these northern counties, it seemed that not all could agree on the safety or the cost of the bridge. After Judge C.J. Luttrell, conducted six months of hearings from 5 counties with another 7 months spent analyzing the arguments of both sides, it was ruled in favor of the bridge district. "The cost of construction will not be prohibitive as compared with the revenues reasonably to be expected from the operation of the bridge. The project is feasible both from the standpoint of an engineering and a financial undertaking". During the Industrial era of America, Southern Pacific Railroad became a very powerful entity. The ferryboat industry transported more than 40 million passengers across the bay in all directions. Obviously, it was part of that railroad's great monopoly. Southern Pacific Railroad was accused of conspiring to block the building of the bridge. This was another court battle to be won. In 1932, the courts ruled in favor of the bridge. Economics The early twenties, was a bull market spend-free era but its time had come and gone. By the early thirties the Great depression was felt by everyone in America. This was considered poor timing and even impossible by many to fund such a large scale operation. But contrary to the high unemployment, the depression created worked as an advantage for the bridge builders. Their public supporters were to accept $35 million in bonded indebtedness. Since 14 million people were out of a work, the bond issue meant employment. So, to continue the funding process, the bonds issued were to finance the construction of the bridge. Then toll revenue generated from traffic would balance the bond value within 40 years. Also a profit of $90,000,000 was the expected net. Theoretically, this was ideal. However, two issues came up, the cost estimate and the district's projection of traffic. Crossfire took place again over who would be ultimately liable. After all the struggle and debate had ended, the depression had worsened and the bond strategy was a lost cause. Surprisingly, Amadeus P. Giannini, an Italian immigrant, surfaced. A. P. Giannini founded The Bank of Italy, which later became the Bank of America, that helped finance San Francisco after the 1906 earthquake. A builder himself, he believed in the American dream and took the $35 million in bonds. Criteria for a Bridge To further my knowledge of this structure I have listed criteria for a bridge with some additional information. Length of span required: The distance to be bridged determines the parameters of the bridge. It should be noted that length of span has been the primary limiting factor in bridge building. For example the George Washington Bridge, when built in 1931 was 50 percent longer than any suspension bridge ever built. The 3,500 feet of water it crosses could only have been spanned by a suspension bridge. Continuous span or arch bridges could only have been constructed with a frequency of foundations that would have ended river navigation. Load the bridge must bear: The bridge load is divided into two quantities: live and dead load. The dead load is the actual weight of materials used to construct the bridge. The Golden Gate Bridge's dead load is described in pounds per lineal foot as follows: cables, suspender and accessories 6,670, stiffening trusses 3,330, floor system, curbs and railings 3,830, bracing 600, concrete paving 6470, conduits and misc. 400. The total dead load as built is 21,300 pounds per lineal foot. Added dead load or (live load) is the weight of traffic that the bridge is being designed to carry. Dynamic Load/Wind Load: a load caused by wind that gives rise to vertical motion, creating vibrations in any direction. For example, the Golden Gate Bridge's wind pressures used in design were 30 pounds per square foot on the cables and suspended structure, and 50 pounds per square foot on the towers. Terrain to be bridged: Terrain also affects the engineer's choice of design. A single span or arch might bridge a short deep ravine, anchored at each end. This simplifies the construction, as foundations and piers do not need to be built. One aspect of the effect of terrain on bridge design concerns the navigation requirements of the water to be spanned. Waterways vital to river traffic cannot be bottled up by a mass of foundation work. Longevity of bridge: We tend to think that bridges are built to last forever. But this is not always the case. Engineers did not build many early military bridges. In Asia, suspension bridges were made with vines and were not expected to last. Remember the scene in Indiana Jones? Available economic resources: The availability of both labor and money has always affected bridge design. Many bridges are financed by bonds that are repaid by the tolls charged. Unfortunately, once a bridge was paid for, tolls were often discontinued. Many bridges are closed due to the fact that money is never levied for their maintenance. Available materials and state of technology at the time of construction: Although length, load and longevity are all factor that become intertwined in decisions concerning bridge construction, the availability of materials has dominated consideration of how to build a bridge through all ages. Until the industrial age, wood and masonry were the primary building materials. Then, within a short period of time cast iron, wrought iron, concrete, steel, reinforced concrete, allow and silicon steel, and prestressed concrete. Now that we have some fundamental information in what it takes to build a bridge, lets check out the results! Here's an overview of the building of the Golden Gate Bridge. Cabling Suspension Technical Data While doing my research on this bridge, I constantly came upon the name "Roebling". I then, briefly read that John A. Roebling an immigrant from Germany, studied suspension bridges at the University of Berlin. Eventually becoming an engineer he later came to the United States and settled as a farmer in Pennsylvania. In the early days, the process of transporting up hill was still done using rope made from hemp as cabling. John Roebling's desire to transport uphill faster and more productively brought on the idea of wire cabling. John Roebling's contribution to the fabrication and development of wire cabling has impacted industry all throughout America's industrial era and presently into the information age era. Roebling's engineering participation and contributions brought us the Brooklyn Bridge, the George Washington Bridge the San Francisco Golden Gate Bridge as well as others. The quality engineering and refinement of Roebling cabling as of today is unsurpassed. Suspension Technical Data and Parabolic Formulas To further our knowledge on design and various types of bridge cabling, the following will provide more on suspension technical data. Now for an in-depth break down on how a bridge is constructed in terms of mathematics, Parabolic Formulas, reference: equations (1-14) are presented for determining cabling and suspender lengths and cable tensions. Applied Physics "The first wire that is strung across from anchorage to anchorage is known as the guide wire. This wire serves as a guide for the balance of the wires, and is carefully adjusted to the proper sag. The sag is the vertical distance, at mid-span, from a horizontal line projected across the tower tops from the centers of the saddles. The amount of sag determines the amount of tension, or pole, in the wire, which is worked out according to a mathematical formula. To "spot" this guide wire, a transit was mounted on the hillside, in a line of site taken at the point of proper sag. If the wire sags too much, the sag is reduced by pulling in on the ends of the wires at the anchorages; if too little, the wire is slacked off. Here is a technical diagram to provide us with a more practical understanding." The Golden Gate Bridge Today Even as a second generation American I still get the feeling of being awestruck when approaching the San Francisco Golden Gate Bridge. Perhaps not for the same reason my father did, but just the mere power, strength, and stability the structure represents. In May of 24th 1987, I "did the bridge walk" to honor the bridge's 50th anniversary. The gridlock produced from the masses of people ascending the bridge caused it to flatten out. I admit, I did feel threatened about this. I have learned that an average of 50 pounds per square foot is ample when applied throughout the structure of the bridge. Of course this applies to the "live load", the weight of the traffic, the bridge is designed to carry (referring to cars, and other moving vehicles) that have distributed weight. The suspending superspan covering more than 4200 feet continues to carry the load of people and transport daily. We in return have given it respect through its daily maintenance to keep her strong and resilient for future generations to come. Please join me with a walk through the San Francisco Golden Gate Bridge. Bibliography Books: Cassidy, Stephen. Spanning The Gate.Links: Photo Sampler Two, Online. |