Failed Bridges
The engineer, Theodore Cooper (1839-1919), wrote paper on American Railroad bridges concerning the load trains carried and discussing bridge failure. He called for" calculation of stresses material testing, and for inspection, but added that a bridge's stability was more reliant on engineers instinct than 'merely upon a theory of stresses". 41 Some estimates say that as many as 25% of bridges collapsed at the end of the 19 th century. Although there is no documentation for this statement, it shows how many bridges were failing at this time. "Many collapses were attributable to causes other than structural inadequacies, including train derailment, fires, flooding". 42 Whatever the correct number may be, it appears to be no coincidence that with the increased load of the railroads more bridges did falter. Bridge failures may be caused by flawed designs, material failure, or environmental forces. As Professor Gehner said in seminar, "The reason for failures is often in the details". Prior to construction of a failed bridge students will be given the list of bridges below and categorize them. The information below should serve as a guide.
A wonderful story about the failure of a bridge concerns The Starimost Bridge, built from 1557 to 1566. Emperor Suleyman the Magnificent had the Ottoman architect, Mimar Hajrudin, build a stone bridge across the Neretva's, "ice cold, emerald green highland river." 43 It was to replace a wooden bridge. The first attempt failed when the scaffolding was removed. After the second attempt, Hajrudin ran away from the village for fear of being beheaded if his bridge failed a second time. He hid in a cemetery, crying, and dug his own grave. Luckily, the bridge held. He was handsomely paid. It was nicknamed the "Stone Crescent". The bridge lasted until November 1993 during the Bosnia Civil War, when it was destroyed. The first attempt to build the bridge was a structural failure. The second bridge which stood, also "failed" not through any design problems but because of environmental failure due to war.
The Dee Bridge in England was the longest metal bridge of it's time. This collapse occurred because engineer, Robert Stephenson, increased the span length miscalculating the load, and thus killing 5 in 1847. This is also an example of a design failure.
The Ashtabula Bridge in Ohio was the worst railroad disaster to date. This bridge was a Howe truss made out of wrought iron. During a blizzard on December 29, 1876 the two locomotive train with eleven cars derailed. The first locomotive made it across, but the other one along with the cars fell. This collapse was blamed on the joints and the wrought iron material failing. This accident is an example of structural failure and material failure. Two of the bridge designers ultimately committed suicide.
Thomas Bouch was knighted when his Tay Bridge was completed. His achievement collapsed on Dec. 28,1879 during a storm. He based his design on old data. He miscalculated the force of the wind. This failure would be caused by environmental forces, wind, but the primary reason was a design inadequacy. The Tay Bridge in Scotland collapsed killing 75 people.
The Quebec Bridge was completed on August 29, 1907 in Canada. It crossed the St. Lawrence River. Engineer, Theodore Cooper, expanded the arms of the cantilevers from 1600 to 1800 ft. causing the southern one to bend. A telegram halting work to investigate this bending was never heeded. It collapsed killing 75 workers. Its replacement collapsed in 1916 killing 11 people. This bridge was a design failure.
Tacoma Narrows Bridge, "Galloping Gertie" was completed in 1940. Its existence lasted only about four months when vibrations caused by 42m/hr winds caused her to fall. Its failure was due to its design. The sides were solid not allowing the wind to travel through it. The sides acted as a barrier. Its deck alone was too thin, caused it to twist uncontrollably. It was replaced with a deeper bridge with truss sides. There are video images of this phenomenon which are truly amazing to watch.
The Ludendorff Bridge at Remagen, Germany was built during World War I for German troops and goods. This truss arch had two towers at either end in which guns and other goods were stored. Hitler ordered it destroyed when the Allies appeared on the other side. Germans planned to blow it up, but when detonated, it didn't blow. Allies captured bridge and within days 25,000 Allied troops crossed into Germany. On March 17, 1945 the bridge collapsed due to damages incurred during multiple attempts to blow it up.
The San Francisco-Oakland Bridge was completed in 1936. It had two spans, 230 ft. each. On October 1989, the Loma Prieta earthquake measuring 7.1 on the Richter scale occurred, lasting 20 seconds. Sixty-two people were killed when the bridge collapsed. The bolts gave way on the upper truss deck section causing it to fall onto the lower deck. This bridge collapse was due to the environmental force of the earthquake and material issues.
Built in 1967, the I-35W Minneapolis Bridge, a steel truss arch, collapsed on August 1, 2007 during rush hour. This eight lane bridge fell into the Mississippi River killing thirteen people, and injuring approximately one hundred people. As of July, 2008, the NTSB has not determined the cause of the collapse. An error in design may have been a factor. Noted for black ice forming on the bridge, concerns have been raised that potassium acetate might have played a role in the collapse.
The Sunshine Skyway Bridge crossing Tampa Bay was comprised of two steel trusses
bridges built in 1954 and 1971. It was struck by the ship, Summit Venture, in May 1980. The ship knocked out a 1300 ft. section of the bridge, killing 35 people. The new bridge has concrete barriers to protect it against ships. The new version is painted yellow, and was completed in 1987. It is the worlds longest cable stay bridge. It has concrete spans with cables in the middle of the roadway. It rises 190 ft. above the water to allow for water traffic.
Some bridge failures have been a result of increasing the span or load overestimating the material's strength. Underestimating environmental factors such as wind, water, or corrosion has accounted for other disasters. Outside influences, such as ship traffic and war, have also been the cause of some failures. What will be the cause of bridge failures in the future?
"According to the U.S. Department of Transportation ("DOT"), one of every eight bridges in the nation is structurally deficient. Of the 597,340 bridges in the United States, 154,101 bridges are deficient, including 73,784 structurally deficient bridges, and 80,317 functionally obsolete bridges." 44 Structurally deficient means that the bridge is in poor condition or can not handle the traffic. It might need repair or weight restrictions. If a bridge is functionally obsolete, it does not meet traffic standards. It may not have enough clearance, or the lanes may be too narrow. "Washington D.C. has the countries least safe bridges with 63% of the district's 245 bridges being either structurally deficient or functionally obsolete". 45 According to an ABC News article, 13% of U.S. bridges have the same structural defect rating as the Minneapolis Bridge that collapsed in 2007. 46 The federal government requires bridge inspection once every two years. This inspection comprises of inspection of the substructure (underwater), the superstructure (above water), and the deck or roadway. Each state with the help of the federal government is responsible for maintaining bridges. The problem will be a daunting task in the future. Interstate highways were built in the 1960's, including their bridges. With bridges at least forty years old, the problem of replacement or repairs becomes apparent. "According to DOT, more than $65 billion could be invested immediately in a cost-beneficial way, by all level of government, to replace or otherwise address existing bridge deficiencies". 47 With the current economy, it is a real challenge. The primary means of inspection has been visual observation. As a means to detect problems, it has not been found that reliable. Ultra-sound, x-ray, and impact echo technologies are a few of the resources available. Hopefully, as states improve bridge inspection, and data is collected, funds will be found.
Today the biggest challenge the United States faces is not the fear of a poorly designed bridge, but one that is deficient, old. With computer technology and the resources available, the design of a new bridge should be a safe one. What we have to fear is the old ones. Bridges are a beautiful landmark, but they also connect communities, and make our economy thrive. The challenge is to keep them safe from failure. Hopefully, our country will not have to learn from our mistakes.
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