Tacoma Bridge Narrow Collapse Ethical Issue
Unfortunately, the bridge only lasted for four months and “on 7th November 1940, it collapsed. The incident did not claim any human life, only one dog died,” (Irvine 3-8). The failure of Tacoma Narrows Bridge was a wakeup call for engineers to come up with the best approaches to construct better bridges. In handling this report, I will discuss all the unfolding events that led to the failure of the bridge, ethical aspects, lessons learnt and eventually the recommendations. Problems To determine why the Tacoma Narrows Bridge lasted for only four months before collapsing and killing a dog; a combination of various factors i. At that time, the engineering theoretical framework was a major concern, currently, the use of technology has led to multiple options.
Theoretical concepts and discussion The deflection theory was set up in the construction of the Tacoma Narrows Bridge for the first time. The theory entails the use of cables which are static in nature. For instance, each span in a cable may be from E and also F is supported by a girder. According to this model, the pylon centrally supports the girder. On the other hand, the main cables were designed in a unique manner to link two piers constructed thus connecting east and also the west side of the river. The connection was specifically designed to dispense the load through the two piers and the cables to deeply support anchorage on both sides of the river irrespective of the tension.
The rigid connection can be ranked as high innovative skills from engineers and they deployed rolling saddles that are ideally meant for the top application of suspension bridge towers which permits the cable to easily move over. The suspension bridge characteristics such as its ability to withstand vibration pressure under different dynamic conditions i. e. 72 (Fuller et al 1-5). Through the investigation, it can also be stated that the impact of “traffic, aerodynamic stability, earthquake resistant, soil structure, the vibration characteristics and the natural frequency” are very crucial in the process of designing a similar project. The Tacoma Narrows Bridge was a complex structure which researchers have established that it is challenging to determine the vibrations characteristics (Fuller et al 1-5).
However, the technology revolution across the world is now a reality and the engineering industry is not spared. Computers through various software, provide a better alternative for analyzing complex structures. For example, according to (Bleich et al 8-10) he focused on the “torsional vibration and also free vertical vibrations. ” The study is instrumental in calculating the lowest modes that are of great complexity and also redundancy linked to suspension bridges. Other researchers who have played a vital role in establishing the vertical and also lateral vibration include of (Yamada and Goto 23-32). The study was aimed to link lateral and vertical vibration to the tower-pier system that comprised the suspended three-span bridge through a lumped mass model structured and interconnected with spring elements.
According to the researchers, they anticipated harmonic excitations and instead applied it differently. The forces of the suspension bridge which are under “moving load in most cases excite the bridge, as well as the vertical seismic acceleration, have a resonance effect that is as a result of a moving load. ” The moving loads usually thrill the bridge that is always in a higher mode and affects long-span bridges. The dynamic analysis affects moving vehicles especially on railway, slab, cable, girder and suspended bridges. The natural frequencies from the bridge, moving path, vehicle velocity, relative positions specifically on the bridge, vehicle properties, vehicle and surface roughness are some of the dynamics that affect a moving vehicle along the bridge. Long suspension bridges during the early erection phase are more complex and problematic as compared to the final stages.
The Bridge was considered as standard despite exceeding the ratios depth, length and width. It was, later on, revealed that engineers did not focus on aerodynamic forces, despite the location is prone to strong winds. During those days, most of the engineers did not consider “aerodynamic forces as a threat to suspension bridges” (Irvine 3-8). All the efforts of Leon Moisseiff were thwarted “on 7th November 1940 when high winds rocked the area and eventually swayed the bridge. The first incident struck at 11 am and the concrete from the bridge dropped. Conclusion The unique and one of the third highest bridge by then was opened to the public in 1940. The region was prone to strong winds and during the construction, engineer Leon Moisseiff did not consider it as a threat.
The bridge was constructed to be one of the most flexible projects. However, critics claimed that Tacoma Narrows Bridge was not proportional i. e. This type of theory uses a pylon that supports the girder. The principle suggests that the structure looks more of a suspended continuous beam. Various studies have been launched on why Tacoma Narrows Bridge collapsed. The suspension and also vibration characteristics are some of the issues that early researchers such as Bleich et al. , 1950 based on. The two were very shallow and not effective enough to withstand strong winds. The winds failed to pass through since solid metals could not allow the girders to work effectively. Dynamic analysis is very instrumental in constructing suspended bridges just like the Tacoma one.
It has a strong effect on slab, cable, railway and also suspended bridges. The natural frequencies that emanate from the bridge, vehicle velocity, moving path and rough surfaces are the main dynamics that piles more pressure on suspended bridges. The bridge can be excited due to vertical seismic acceleration which comprises the resonance effect. Ethical issues Engineers have derived a lot from the collapse of the third suspension bridge that was launched in 1940 but only lasted for several months before collapsing. Construction of suspension bridges comprises of much theoretical analysis deployed during the construction. For instance, during the construction of Tacoma Narrows Bridge, most of the engineers did not have adequate information about different designs that would fit the construction of such a project.
The engineer in charge deployed 8 feet solid girders. The use of steel beam plates proved to be ineffective since the wind could not pass. The failure of the Tacoma Narrows Bridge can be attributed to lack of knowledge on the best design to use for the suspension bridge. In summary, it was just a matter of trial and error. Recommendations 1. Experienced engineers should be contracted and make maximum use of appropriate theories. " Journal of sound and vibration 216. Bleich, Friedrich. The mathematical theory of vibration in suspension bridges. Department of commerce, Bureau of public roads, 1950. Larsen, Allan, and Klaus H. https://www. engineering. uiowa. edu/sites/www. engineering. Accessed 19 Sept. Larsen, Allan, and Klaus H. Ostenfeld. "Bridge engineering and aerodynamics. " Aerodynamics of Large Bridges.
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