Engineering Challenges on the Golden Gate Bridge Term Paper

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Figure 1. Golden Gate Bridge's Safety Net

Source: http://www.zingarate.com/network/san-francisco/files/2012/11/safett_net.jpg

The safety net was an essential risk management feature for the bridge project because the bridge needed to be 220 feet tall to accommodate commercial and naval vessels and falls from this height would certainly be fatal (Design and Construction 4). Unfortunately, this turned out to be the case during the final phases of construction. Despite this expensive security precaution, a catwalk collapsed on February 17, 1937, plunging 22 workers 220 feet into the bay below, killing ten of them (one man was saved when his leg became entangled in the safety net) (Stansen 5).

Project Duration

Construction began on January 5, 1933 and was completed on May 27, 1937 (Design and Construction 1).

Obstacles and Barriers

The first major obstacle encountered by the design engineers was the fact that the Golden Gate bay is more than one mile wide and more than 300 feet deep (Fireman and Kale 10). In this regard, the WGBH Educational Foundation emphasizes that, "The idea of a bridge linking the city with its neighboring counties was appealing, but the mile-wide gap between San Francisco and Marin presented huge challenges" (Golden Gate 3). Some of the more significant obstacles associated with this site included wind and water. For instance, historians emphasize that, "At the mouth of the Gate, the oncoming force of the Pacific Ocean creates turbulent waves and ripping currents. The location is plagued by gale-force winds and dense fogs" (Golden Gate 3).

In addition, the Golden Gate Bridge project represented an unprecedented attempt to construct a suspension bridge support using a tower situation in open ocean (Standen 3). This engineering barrier was overcome by an ambitious plan by Strauss to have workers initially construct a huge protection fender to prevent damage by from shipping (Underwater Construction 3). The fender, with 40-foot-thick concrete walls, enclosed about two-and-a-half acres of ground on the bay floor and was capable of being dried by pumping the water out, making a working space for bridge workers to build the concrete tower foundation inside (Underwater Construction 4).

With no Occupational Safety and Health Administration at work during this period in America's history, it is not surprising that the work in the fender was exceedingly treacherous. In this regard, the WGBH Educational Foundation emphasizes that, "Work inside the fender was the riskiest. At any moment, its walls could collapse from contact with a stray ship lost in the fog, or from the intense pressure exerted by the currents" (Underwater Construction 5). One diver that worked in the fender described his experiences thusly: "We were down damn near 50 feet, and every time you go down 29 feet you double your atmospheric pressure. Well, that's strong enough it can hold you smack against a wall, and you can't move" (Underwater Construction 5). Following the divers' completion of work on the fender, water was reintroduced into the fender to provide additional strength against the bay's strong current (Underwater Construction 4).

Working in the fender was grueling, but the conditions above the water were also arduous. According to Standen, "Divers faced powerful currents as they helped anchor the massive concrete bridge support onto the ocean floor. And up on the towers, workers stuffed newspapers in their jackets to keep warm" (3). Notwithstanding the ever-present dangers involved in working on the bridge itself above water, the conditions below water were truly extreme. The historians at the WGBH Educational Foundation reports that, "Divers were crucial to the plan. They guided beams, panels, blasting tubes and 40-ton steel forms into position and secured them, striving all the while to avoid being swept away in the current" (Underwater Construction 2).

Even today, these engineering barriers would be difficult to overcome, but the labor-intensive approaches used during the 1930s were effective but primitive -- and dangerous by comparison. In this regard, the WGBH Educational Foundation also notes that, "Workers shot timed black powder bombs deep into bedrock through the blasting tubes, often with such power that dozens of fish would be thrown out of the water and onto the south shore" (Underwater Construction 3). The bridge's project management team, though, persevered with the vital assistance of the underwater crews that dived up to 90 feet deep to clear debris from the black powder bombs and smooth the floor of the bay with underwater hoses that shot water out at

500 pounds of hydraulic pressure (Underwater Construction 4). Moreover, visibility at those depths in the bay was extremely limited and divers were required to work in virtually blind conditions in cumbersome diving suits amid heavy underwater currents (Underwater Construction 4).

Indeed, the bay's heavy currents introduced yet another project management barrier since it restricted the timeframes in which divers could work (Underwater Construction 5).

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Project managers addressed this barrier by allowing divers to remain submerged for just four 20-minute periods a day, but even this limited underwater exposure carried additional risks. Because of the construction team's tight schedule, the WGBH Educational Foundation reports that "Divers were often forced to surface before having sufficient time to decompress, increasing the likelihood that they would develop caisson disease, a nitrogen deficiency also known as 'the bends' (Underwater Construction 5). Because construction was taking place in the Depression-era United States, there was no shortage of willing men to accept these hazardous jobs because they paid well and regularly (Underwater Construction 6).

Despite the barriers and obstacles that were involved, the underwater work was completed successfully. Three members of the project's team, the chief diver, the pier job superintendent and a resident engineer descended to an inspection site, inspected the work on the foundation on December 3, 1934 and pronounced the work a success (Underwater Construction 6). Thereafter, a geologist also descended to the underwater site and "reported that the rock of the entire area is compact, strong serpentine remarkably free from seams... When struck with a hammer, it rings like steel" (Underwater Construction 6).

Another enormous construction obstacle faced by the Golden Gate Bridge builders concerned the physical transportation of the bridge's components (Design and Construction 3). To facilitate the construction process and improve worker safety, some of the larger components and building materials for the bridge were constructed off-site and transported through the recently completed Panama Canal from regions on the East Cost including New Jersey, Pennsylvania and Maryland (Design and Construction 3).

Beyond the foregoing obstacles and barriers, there were still other construction problems experienced due to the site's extreme environmental conditions (Design and Construction 4). For instance, the WGBH Educational Foundation points out that, "The dense fog proved to be dangerous, decreasing visibility in the mornings. Construction on such a large structure would be nearly impossible without full visibility" (Design and Construction 4). Besides the aforementioned strong currents in the bay, completed the bridge's foundations was exceedingly challenges due to high winds that became worse at higher elevations (Design and Construction 4). In fact, the bridge was not completely stabilized until the workers completed its construction, meaning that every day was a new adventure in dread (Design and Construction 4). Another obstacles involved in the bridge project was the need to complete the force calculations needed for the design manually since computers were not available, a process that required several months to complete (Design and Construction 3).

A final obstacle to the bridge's construction involved building the cables needed to span the bay. In this regard, the WGBH Educational Foundation reports that, "The 6,450-foot span would be the longest cable-spinning distance attempted to date. To spin the main suspension cables, Strauss hired Roebling & Sons, who shipped 80,000 miles of wire from New Jersey" (Golden Gate 5). Developing an innovative approach to spinning the cables in place, construction proceeded quickly on this part of the project (Golden Gate 5). As the historians at the WGBH Educational Foundation conclude, "The cable system is really the lifeline of a suspension bridge. That big cable, that looks so solid when we see it today, was spun in place from individual wires that are each about the size of a pencil" (Golden Gate 5).

Forecasting Effectiveness

The scope and location of the Golden Gate Bridge project meant that engineers had a great deal to consider in their forecasting. In this regard, Sumrall and Mott emphasize that, "Engineers, architects, and builders have many factors to consider when planning for construction, including the moral and ethical obligation to protect fellow human beings, cost, and how long the structure will last and what kind of stresses it can undergo" (45). Notwithstanding these forecasting challenges, on May 20, 1936, the last cable wire was laid, two months ahead of schedule (Golden Gate 5).

Conclusion

The research showed that planning for the Golden Gate Bridge begin in earnest in the 1920s and after a major modification, the plans called for what was then the world's longest suspension bridge. Funded by a taxpayer approved bond for $35 million that was purchased by….....

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