At 5:00 PM, the Silver Bridge collapsed claiming 46 lives and injuring 9. The Christmas rush applied an extra load to the 40 year old bridge causing a cleavage fracture in one of the "eyebars". This was followed by a ductile fracture near the pin. Unable to support the weight of the entire bridge, the south side chain also snapped. The structure only took about 1 minute to completely fall into the river below. An investigation, led by John Bennett, immediately followed the collapse of the Silver Bridge. The bridge was constructed of carbon steel, which tends to crack. Many cracks were found throughout the bridge among extensive corrosion. The failure resulted from stress corrosion and corrosion fatigue, two concepts which were not known in 1927. It was also found that the flaw could not have been detected, even by today's methods, unless the bridge was taken apart and tested.In addition to the investigation, the federal government mandated the National Bridge Inspection Standards (NBIS). The new standards required periodic inspection of all the nation's bridges.
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