The Collapse of the Tacoma Narrows Bridge - Essay Example

Ethics issues History and Background The Tacoma Narrows Bridge was created between Kitsap and Peninsula and the Tacoma City in Washington State. The development of the bridge drew a lot of interest that began in the early 1880s. Initially, the railroad had proposed the construction of a trestle bridge for the railroad traffic carriage. However, these initial efforts did not achieve any significant results mainly due to the coming of the automobile. This promoted the building of a bridge that was capable of handling the automobile traffic. The development of financing interests for the project began in the 1920s by governments and businesses. The first design for the project was developed by Joseph Strauss and David Steinman who presented a suspended bridge. Due to suspicions that Steinman was not capable of raising sufficient money for the project, the chamber of commerce in Tacoma resorted to terminating its contract in the year 1931. Fresh interests however developed in 1937 with the creation of the Washington State Toll Bridge Authority by Washington State. Using the revenue from the tolls of the bridge, the authority conducted a practicability study. In the end it became clear that the design and construction of the bridge was not possible through the toll revenue finances alone. Another interested body in the building of the bridge was the United States military. The military required a route to directly link the Bremerton’s Puget Sound Naval Shipyard to Army’s McChord Field and Fort Lewis on the side of Tacoma. The Puget Sound Naval Shipyard was on the Pierce County of the Narrows (Board of Engineers Appointed to Report on the Failure of the Tacoma Narrows Bridge, Othmar Hermann Ammann 143). It was also in the interest of the federal agencies to create more job opportunities amidst the Great Depression. This set up the political and economic forces that later on contributed to the collapse of the Tacoma Narrows Bridge. This meant a lot of upheavals in the development of the bridge. All these were occasioned by the low revenue projection toll. Under engineer Clark Eldridge’s direction, the Washington Department of Highways began the preparation of a suspended bridge. This took high gear especially with the promises of funds from the government. Deep truss girders that were 25 feet supported the roadway to stiffen it. Therefore, the Eldridge design was submitted to the Federal Public Works Administration (PWA) by the Authority. The requested fee was $ 11 million. This prompted Leon Moisseiff, a renowned New York to submit a proposal to the Reconstruction Finance Corporation (RFC) and PWA for the design of $8 million Bridge. As compared to other initial projects, this implied a huge and significant savings. The costs saved came as a result of the 25-feet deep roadway through the replacement done by Moisseiff. These supported the truss girders with that had a depth of 8-feet. This design was not only slender and elegant but also reduced the bridge’s stiffness (Cronn-mills 11). The bridge’s cost savings and the reputation of Moisseff together slender and beauty of the design led to awarding of the contract to Moisseff and the engineering firm that was associated with him. The engineering firm was called the Moran & Proctor. Apparently, this engineering firm was favored instead of Washington Department of Highways and Eldridge. By the month of June 1938, PWA had permitted $6 million for the project. The remaining cost was paid with proceeds from the toll revenue. By the end of the project, a total of $6.4 million had been spent on it. It took 19 months to complete the project that began in September 1938. Characterized by the major span of 2800 feet, this became the third highest bridge on suspension. In July 1940, the bridge was opened. However, it collapsed in November of the same year (Scott 273). Sequence of Events The Moiseiff design began with the theoretical underpinning that was published in a 1933 paper with the help of Fred Liehard. The Moisseiff theory proposed the bridge stiffening through plate girders that were eight foot deep. This was in contrast of the Washington Department of Highways’ 25 deep feet tussle. It was partly because of this change that the estimated cost of the project reduced. The bridge was initially designed to handle light projects with two opposing lanes and 39 feet width. Compared to its length, this was narrower. The girders provided the depth upon the roadway section of the bridge. The narrower and shallower girders use later cost the bridge its life. The thin roadways that supported the girders meant that the bridge was not sufficient enough and was therefore moved easily by wind. This movement of the bridge became its defining features. Even with weak amount of wind, the bridge would rise and fall at intervals of diverse intervals. Apparently, the workers who had participated in the construction of the bridge had experienced these flexibilities and consequently christened the bridge the ‘Galloping Gertie”. Even at the opening of the bridge, the movements were felt by members of the public (Akesson 193). In response to the oscillations observed during the bridge’s construction, proposals started coming up in favor of the reduction of the bridge’s motion. In that regard, several implementations were made on the bridge including the attachment of cables that were tied down on the girder before being anchored on a concrete weighing 50 ton located on the shore. Additionally, the addition of the inclined cable pair helped in holding the cables connected to the dock of the bridge at the span in the middle. Until the collapse of the bridge, these cables remained intact. The other form of implementation included the installation of hydraulic buffers for equipping the structure. Installed between the floor system and the buffer, these buffers helped in damping the main span’s longitudinal motion. However, the sand blasting of the bridge damaged the unit seals and thereby nullifying the effectiveness of the dampers from the hydraulic buffers (Nieto and Mosquera 106). Professor Fredrick Burt Farquharson who was teaching engineering at the University of Washington was then hired to perform tests wind tunnel and subsequently come up with solutions that could help in the reductions of the bridge’s oscillations. Consequently, the professor built bridge model of 1: 200 scales and a deck model of 1:20 scale. Five days before the collapse of the bridge, the professor recommended that holes be drilled along the deck and in the lateral girders to allow for free flow of air. Apparently, the first recommendation seemed irreversible and as a result was not favored. The blowing winds at the Narrows at 42 miles per hour were the initial factors that contributed to the disintegration of the bridge. At around 10 am on November 7, 1940, severe oscillations began at the bridge in a torsional mode. As a result, traffic was removed from the bridge. After one hour ten minutes, the center span of the bridge collapsed. Although a small dog died in the accident, no human death or injuries were recorded. The aftermath of the collapse of the bridge After the collapse of the bridge, the Federal Works Agency formed a commission to investigate the circumstances that led to its collapse. From its findings, the collapsed could have been occasioned by three things including random velocity fluctuations, formation of eddy currents and vibrations that were self induced. It narrowed down the cause to the cause to self induced vibrations. The initial design of the bridge opened lattice beam trusses that supported the roadbed. Works cited Akesson, Bjorn. Understanding Bridge Collapses. London ; New York: Taylor & Francis Group, 2008. Board of Engineers Appointed to Report on the Failure of the Tacoma Narrows Bridge, Othmar Hermann Ammann. The Failure of the Tacoma Narrows Bridge: A Report to the Honorable John M. Carmody, Administrator, Federal Works Agency, Washington, D.C. Board of Engineers: Othmar H. Ammann, Theodore Von Karman [and] Glenn B. Woodruff. [Pasadena? Calif.] : United States. Federal Works Agency, 2006. Cronn-mills, Kirstin. Collapse!: The Science of Structural Engineering Failures. Mankoto, MN : Capstone, 2009. Nieto, Felix and A Mosquera. Bridge Aeroelasticity: Sensitivity Analysis and Optimum Design. Southampton: WIT Press, 2011. Scott, Richard. In the wake of Tacoma: suspension bridges and the quest for aerodynamic stability. Reston, VA: ASCE Publications, 2001. Read More