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- Failed bridges: case studies, causes and consequences by witold kowalczyk - Issuu
- Lessons From 10 of the Worst Engineering Disasters in US History
Introduction This memo is a failure analysis report on the Tacoma Narrows bridge. The bridge collapsed on November 7th, just over four months after it was opened to the public on July 1st, Green, The only casualties good word?? Research Papers words 2 pages. It is important for this device to be able to perform its purpose without failure as it will be dealing with people life and therefor the highest amount of safety is needed.
Though, everything must eventually fail, in some way e. Research Papers words 5.
It collapsed on November 7, just months after its opening on July 1, It was designed by Leon Moisseiff and at its time it was the third largest suspension bridge in the world with a center span of over half a mile long. The bridge was very narrow and sleek giving it a look of grace, but this design made it very flexible in the wind. Nicknamed the "Galloping Gertie," because of its undulating behavior, the Tacoma Narrows Bridge drew the attention of motorists seeking a cheap thrill Research Papers words 6. Legendary in its time, the Tacoma Narrows Bridge held many records and drew tourists from around the world in its short life.
However, the famous bridge is not known for its creative engineering or speedy construction, unfortunately the bridge was destined to fail Research Papers words 7. As stated, more than half of all small businesses fail within the first four years. There are many factors. Another factor could be making wrong business decisions that lead to loss of profits and force them into bankruptcy Research Papers words 2.
Major cities such as San Francisco, and Manhattan both have a suspension bridge. Due to the fact that suspension bridges are not completely supported throughout the length of the bridge, past bridges were unsafe.
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Research Papers words 3 pages. Probably the leading reason is that the manufacturer failed to research the consumer needs, wants, and preferences enough in detail to establish what is truly needed by the consumer Kerin, All new products need to be able to meet the needs of the targeted consumers. Three key points stood out:. The side spans were too long, compared with the length of the center 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 center span length, an unprecedented ratio of 1 to The pivotal event in the bridge's collapse , said the Board, was the change from vertical waves to the destructive twisting, torsional motion.
This event was associated with the slippage of the cable band on the north cable at mid-span. Normally, the main cables are of equal length where the mid-span cable band attaches them to the deck. When the band slipped, the north cable became separated into two segments of unequal length. The imbalance translated quickly to the thin, flexible plate girders, which twisted easily.
Once the unbalanced motion began, progressive failure followed. The investigation Board's most significant finding was simple and obvious: the engineering community must study and better understand aerodynamics in designing long suspension bridges. Meanwhile, Professor F. Farquharson continued wind tunnel tests. He concluded that the "cumulative effected of undampened rhythmic forces" had produced "intense resonant oscillation.
Leon Moisseiff , who was contacted immediately after the failure, said he was "completely at a loss to explain the collapse. Moisseiff's design, while pushing beyond the boundaries of engineering practice, fully met the requirements of accepted theory at the time. At the time the Narrows Bridge failed , the small community of suspension bridge engineers believed that lighter and narrower bridges were theoretically and functionally sound. In general, leading suspension bridge designers like David Steinman, Othmar Amman, and Leon Moisseiff determined the direction of the profession.
Very few people were designing these huge civil works projects. The great bridges were extremely expensive. They presented immensely complicated problems of engineering and construction. The work was sharply limited by government regulation, various social concerns, and constant public scrutiny.
A handful of talented engineers became pre-eminent. But, they had what has been called a "blind spot. That "blind spot" was the root of the problem. According to bridge historian David P. Billington, at that time among suspension bridge engineers, "there seemed to be almost no recognition that wind created vertical movement at all. The best suspension bridge designers in the s believed that earlier failures had occurred because of heavy traffic loading and poor workmanship. Wind was not particularly important.
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Engineers viewed stiffening trusses as important for preventing sideways movement lateral, or horizontal deflection of the cables and the roadway. Such motion resulted from traffic loads and temperature changes, but had almost nothing to do with the wind. This trend ran in virtual ignorance of the lessons of earlier times. Early suspension bridge failures resulted from light spans with very flexible decks that were vulnerable to wind aerodynamic forces. In the late 19th century engineers moved toward very stiff and heavy suspension bridges.
John Roebling consciously designed the Brooklyn Bridge so that it would be stable against the stresses of wind. In the early 20th century, however, says David P. Billington, Roebling's "historical perspective seemed to have been replaced by a visual preference unrelated to structural engineering. Just four months after Galloping Gertie failed , a professor of civil engineering at Columbia University, J. Finch, published an article in Engineering News-Record that summarized over a century of suspension bridge failures.
In the article, titled "Wind Failures of Suspension Bridges or Evolution and Decay of the Stiffening Truss," Finch reminded engineers of some important history, as he reviewed the record of spans that had suffered from aerodynamic instability.
Finch declared, "These long-forgotten difficulties with early suspension bridges, clearly show that while to modern engineers, the gyrations of the Tacoma bridge constituted something entirely new and strange, they were not new--they had simply been forgotten. An entire generation of suspension bridge designer-engineers forgot the lessons of the 19th century.
Failed bridges: case studies, causes and consequences by witold kowalczyk - Issuu
The last major suspension bridge failure had happened five decades earlier, when the Niagara-Clifton Bridge fell in And, in the s, aerodynamic forces were not well understood at all. As experience with leading-edge suspension bridge designs gave engineers new knowledge, they had failed to relate it to aerodynamics and the dynamic effects of wind forces. The collapse of Galloping Gertie on November 7, revealed the limitations of the "deflection theory.
The failure of the Tacoma Narrows Bridge effectively ended Moisseiff's career.
Lessons From 10 of the Worst Engineering Disasters in US History
More importantly, it abruptly ended an entire generation of bridge engineering theory and practice, and the trend in designing increasingly flexible, light, and slender suspension spans. Othmar Amman said of the collapse of the Narrows Bridge, "Regrettable as the Tacoma Narrows Bridge failure and other recent experiences are, they have given us invaluable information and have brought us closer to the safe and economical design of suspension bridges against wind action.
Amman, The end of the s witnessed the construction of two of the greatest suspension bridges in the world, built by two of the 20th century's greatest bridge engineers.
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Both of these monumental spans directly benefited from the legacies of the failed and the successful Tacoma Narrows Bridges. Over the course of the last 60 years since Galloping Gertie failed, bridge engineers have created suspension bridges that are aerodynamically streamlined, or stiffened against torsional motion, or both. Now, wind tunnel testing for aerodynamic effects on bridges is commonplace.
In fact, the United States government requires that all bridges built with federal funds must first have their preliminary design subjected to wind tunnel analysis using a 3-dimensional model. Failure of the Tacoma Narrows Bridge revealed for the first time limitations of the Deflection Theory. Since the Tacoma disaster, aerodynamic stability analysis has come to supplement the theory, but not replace it.