research paper

The Tacoma Narrows Collapse

March, 2017

Imagine yourself driving through the third longest bridge with your beloved Golden Retriever on a hot sunny day. However, you suddenly feel the bridge kneeling towards the right and left. Seeing everyone in front of you vacating their cars and running away from the bridge before it collapses. Most likely, you would do the same even maybe 3 times faster before it’s too late. But sadly, when it’s too late and the bridge has collapsed you will eventually realize that you have left your beloved dog behind. The First Tacoma Narrows Bridge was being completed and designed in the state of Washington, Tacoma. The Tacoma Narrows bridge was constructed by Leon Moisseiff to be the third longest bridge and the most flexible bridge ever constructed. The construction of this bridge took 10 years. Construction began from the 1930’s to July 1, 1940.

Unfortunately, The Tacoma Narrows Bridge collapsed within the same year it was accessible for the public. The cause of the collapse was from a high random windstorm. The collapse of the bridge was recorded on film by Barney Elliott, the footage of the film is still used today for students majoring in engineering all over the globe. Minutes before the collapse people witnessed an unusual reaction in the bridge. The bridge was waving in a really strange way. Because, the bridge was built to be the most flexible bridge ever built. The Tacoma Narrows bridge might be today one of the greatest engineer failure disasters due to the collapse within the same year it was built in. There are important lessons that engineers can determine from studying the design and the collapse of the bridge to be able to avoid a terrible disaster like this from happening again in the future.

On November 7, 1940 high winds at the speed of 42 mph (64 km/h) buffeted the place and the bridge was moving considerably. At about 11 Am the first failure approached, when a part of concrete fell of the bridge. Minutes after, a 600 foot part of the bride went loose. At this time, the bridge kept moving back and forth in a weirdly way. According to (Tacoma Narrows Bridge collapses, 2009), “At one time, the elevation of the sidewalk on one side of the bridge was 28 feet above that of the sidewalk on the other side.”. In other words, all of a sudden the altitude of one side of the bridge was 28 feet higher than the sidewalk on the other side. Regardless of the strong carpent steel used in the making of the bridge, it showed no match in force while defending against the windstorm which finally led to the collapse.

After the Tacoma Narrows bridge collapsed, many people were unsure of what they have witnessed. The wildy toss left many questions behind, only engineers can answer them. Many engineers have studied the bridge collapse from the video footage (Elliott,2009) and have came to an instinct. Before they came to an instinct a huge and long argument about the causes of the collapse between those who worked on the bridge and others who might have an insight on why the bridge collapsed. There were many different sayings on why a random windstorm caused such a disaster to a national bridge in front of the eyes of the public. But after years of hard work and delicate studies on the footage of the collapse engineers and architecture came into a settlement about the mysterious reason that led to the collapse of the bridge.

The Tacoma Narrows Bridge, the third longest suspension bridge in the world. The main cause of the collapse lies on a part of the bridge and the type stiffening floor and girders. The bridge suspensions were too weak to hold itself from a random high windstorm. The blame of the collapse is mostly placed on the twisting made by the aerodynamic forces. Aerodynamic forces haven’t been seriously taken in the design of any bridge. because, The Tacoma Narrows bridge fundamental weakness was from its great flexibility. According to (first investigations-partial answers to why) “The deck was too shallow at 8 feet (a 1/350 ratio with the center span). The spans were too long compared with the length of the centre span. The cables were anchored at too great a distance from the side spans. The width of the deck was extremely narrow compared with its centre span length, an unprecedented ratio of 1 to 72.” While the bridge was moving vertically and in torsion it acted like aerofoil, creating drag and lift. Another cause

The failure of the Tacoma Narrows Bridge has ended Moisseiff's career. According to (Lessons From the Failure of a Great Machine)” it abruptly ended an entire generation of bridge engineering theory and practice, and the trend in designing increasingly flexible, light, and slender suspension spans.”. In other words, they have failed to do their jobs in constructing a bridge that meets its requirements to be safe for the public to use. The Tacoma Narrows Bridge was narrow compared with other suspension bridges previously built and very long. According to (Franklin Miller, Jr. (1963)) :The original design called for stiffening the suspended structure with trusses. However, funds were not available, and a cheaper stiffening was adopted using 8-foot tall girders running the length of the bridge on each side.”. In other words, the bridge original design was perfect but, there was no enough money and they had to choose the only 8-foot tall griders which are not stiff enough to resist such a windstorm.

Aerodynamic forces haven’t been taken seriously in the design of The Tacoma Narrows Bridge. By that time most bridges have been only designed to stand normal conditions. However, a lesson was learnt and engineers designing any bridge must consider aerodynamic effects and dynamic actions. dynamic models, elastic models and studies of resonance, aerodynamic, wind tunnels and damping must be in the design of any bridge. In the case of harmonic oscillations, the bridge was not structured to be very rigid. However, Civil engineers and architects can now increase the natural frequencies of the bridge to be able to stand greater windstorm wave frequency of very high winds. In addition (the physics teacher) states that most new bridges are much more rigid than the Tacoma Narrows Bridge.

Conclution

References

Tacoma Narrows Bridge collapses. (2009). Retrieved March 15, 2017, from http://www.history.com/this-day-in-history/tacoma-narrows-bridge-collapses

Fuller, R. G. (2000). Twin Views of the Tacoma Narrows Bridge Collapse. College Park, MD: AAPT, One Physics Ellipse.