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Silver Bridge Collapse

Page history last edited by Steve Escher 15 years, 2 months ago


Silver Bridge Collapse




          photo credits: Harvey Eugene Smith/AP, left; Corbis, right. Accessed from the Time photo gallery here.




Contributing Causes


Several causes contributed to the dramatic failure.  In the eyebar where the collapse initiated, there was a design flaw causing very high tensile stress.  At the time of construction, stress corrosion and corrosion fatigue were not well understood.  In addition, the location of the flaw was not accessible by visual inspection, and the flaw was undetectable with any method used at that time without disassembling the joint itself.  Disassembling the joint was impossible once the bridge had been completed.





After the bridge collapsed, governmental agencies hurried to action to prevent future collapses and placate the public.  President Lynden Johnson immediately created a task force on bridge safety.  The task force conducted a national survey on bridge safety that analyzed the standards and procedures used to keep other bridges safe.  The tak force also developed recommendations to keep the public safe.  In 1968 Congress passed National Bridge Inspection Standards (NBIS). New inspections initiated in response to the failure found cracking in steel plate girders on other bridges.


From the Federal Highway Administration (FHWA), about the NBIS:


The NBIS sets the national standards for the proper safety inspection and evaluation of all highway bridges in accordance with 23 U.S.C. 151.  The FHWA bridge inspection program regulations were developed as a result of the Federal-Aid Highway Act of 1968 (sec. 26, Public Law 90-495, 82 Stat. 815, at 829) that required the Secretary of Transportation to establish national bridge inspection standards (NBIS). The primary purpose of the NBIS is to locate and evaluate existing bridge deficiencies to ensure the safety of the traveling public.


The 1968 Federal-Aid Highway Act directed the States to maintain an inventory of Federal-aid highway system bridges. The Federal-Aid Highway Act of 1970 (sec. 204, Public Law 91-605, 84 Stat. 1713, at 1741) limited the NBIS to bridges on the Federal-aid highway system. After the Surface Transportation Assistance Act of 1978 (STAA) (sec. 124, Public Law 95-599, 92 Stat. 2689, at 2702) was passed, NBIS requirements were extended to bridges greater than 20 feet on all public roads. The Surface Transportation and Uniform Relocation Assistance Act of 1987 (STURRA) (sec.125, Public Law 100-17, 101 Stat. 132, at 166) expanded bridge inspection programs to include special inspection procedures for fracture critical members and underwater inspection. (1)


For more information, visit: 





1.  Federal Highway Administration, 2005 Questions and Answers on National Bridge Inspection Standards.  Retrieved May 1, 2008.


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