World Library  
Flag as Inappropriate
Email this Article

Silver Bridge

Article Id: WHEBN0023804840
Reproduction Date:

Title: Silver Bridge  
Author: World Heritage Encyclopedia
Language: English
Subject: Mothman, Suspension bridge, Rust, The Mothman Prophecies, Crevice corrosion
Collection: 1967 in Ohio, 1967 in West Virginia, Bridge Disasters Caused by Engineering Error, Bridge Disasters Caused by Maintenance Error, Bridge Disasters in the United States, Bridges Completed in 1928, Bridges Over the Ohio River, Buildings and Structures in Gallia County, Ohio, Buildings and Structures in Mason County, West Virginia, Former Bridges in the United States, Road Bridges in Ohio, Road Bridges in West Virginia, Suspension Bridges in the United States, Transport Disasters in 1967, Transportation Disasters in Ohio, Transportation Disasters in West Virginia, Transportation in Mason County, West Virginia
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Silver Bridge

Silver Bridge
The Silver Bridge upon completion in 1928
Crosses Ohio River
Locale Point Pleasant, Mason County, West Virginia, United States
Kanauga, Gallia County, Ohio, United States
Material Steel
Total length 681.2 m
Longest span 213.5 m
Design life 39 years
Constructed by American Bridge Company
Opened 1928
Followed by Silver Memorial Bridge
Collapsed December 15, 1967
Coordinates
References: [1]
The collapsed Silver Bridge, as seen from the Ohio side

The Silver Bridge was an eyebar-chain suspension bridge built in 1928 and named for the color of its aluminum paint. The bridge connected Point Pleasant, West Virginia, and Gallipolis, Ohio, over the Ohio River.

On December 15, 1967, the Silver Bridge collapsed while it was full of rush-hour traffic, resulting in the deaths of 46 people. Two of the victims were never found. Investigation of the wreckage pointed to the cause of the collapse being the failure of a single eyebar in a suspension chain, due to a small defect 0.1 inch (2.5 mm) deep. Analysis showed that the bridge was carrying much heavier loads than it had originally been designed for and had been poorly maintained.

The collapsed bridge was replaced by the Silver Memorial Bridge, which was completed in 1969.

Contents

  • History of eyebar-chain bridge construction 1
  • Silver Bridge structure 2
    • Low redundancy, high strength 2.1
    • Rocker towers 2.2
  • Design loads 3
  • Wreckage analysis 4
  • Aftermath 5
  • Legacy 6
  • In popular culture 7
  • References 8
    • Notes 8.1
    • Further reading 8.2
  • External links 9

History of eyebar-chain bridge construction

At the time of the Silver Bridge construction, eyebar bridges had been built for about 100 years. Such bridges had usually been constructed from redundant bar links, using rows of four to six bars, sometimes using several such chains in parallel. An example can be seen in the Clifton Suspension Bridge, designed by Isambard Kingdom Brunel. The chain eyebars are redundant in two dimensions. This is an early suspension bridge still in service. Other bridges of similar design include the earlier road bridge over the Menai Strait built by Thomas Telford in 1826; the Széchenyi Chain Bridge in Budapest, built in 1839–1849, destroyed in the closing days of World War II by retreating Germans in 1945, and rebuilt identically by 1949, with redundant chains and hangers; and the Three Sisters, suspension bridges of similar design in Pittsburgh.

Silver Bridge structure

Low redundancy, high strength

The eyebars in the Silver Bridge were not redundant, as links were composed of only two bars each, of high-strength steel (more than twice the tensile strength of common mild steel), rather than a thick stack of thinner bars of modest material strength "combed" together, as is usual for redundancy. With only two bars, the failure of one could impose excessive loading on the second, causing total failure — which would be unlikely if more bars were used. While a low-redundancy chain can be engineered to the design requirements, the safety is completely dependent upon correct, high-quality manufacturing, assembly, and maintenance.

In comparison, the Brooklyn Bridge, with wire-cable suspension, was designed with an excess strength factor of ten, which proved fortunate, owing to a contractor's substitution of wire weaker than that specified. This was discovered before completion and additional strands were placed in the bundles (though its overall strength was still reduced to a factor of six). Wire cables have extremely high levels of redundancy, with the failure of a single wire strand almost unnoticeable.

Rocker towers

The towers were "rocker" towers, which allow the bridge to respond to various live loads by a slight tipping of the supporting towers, which were parted at the deck level, rather than passing the suspension chain over a lubricated or tipping saddle, or by stressing the towers in bending. The towers required the chain on both sides for their support; failure of any one link on either side, in any of the three chain spans, would result in the complete failure of the entire bridge.

Design loads

At the time of the bridge construction, a typical family automobile was the Ford Model T, with a weight of about 1,500 lb (680 kg). The maximum permitted truck gross weight was about 20,000 lb (9,072 kg). By contrast, at the time of the collapse, a typical family automobile weighed about 4,000 lb (1,814 kg) and the large truck limit was 60,000 lb (27,216 kg) or more. Bumper-to-bumper traffic jams on the bridge were also much more common, occurring several times a day, five days each week, thus causing more stress to the bridge elements.

Wreckage analysis

The bridge failure was due to a defect in a single link, eye-bar 330, on the north of the Ohio subsidiary chain, the first link below the top of the Ohio tower. A small crack was formed through fretting wear at the bearing, and grew through internal corrosion, a problem known as stress corrosion cracking. The crack was only about 0.1 inches (2.5 mm) deep when it went critical, and it broke in a brittle fashion. Growth of the crack was probably exacerbated by residual stress in the eyebar created during manufacture.

When the lower side of the eyebar failed, all the load was transferred to the other side of the eyebar, which then failed by ductile overload. The joint was then held together only by three eyebars, and another slipped off the pin at the center of the bearing, so the chain was completely severed. Collapse of the entire structure was inevitable since all parts of a suspension bridge are in equilibrium with one another. Witnesses afterward estimated that it took only about a minute for the whole bridge to fall.

The damage to the link would have been difficult to see during inspection of the bridge:

Inspection prior to construction would not have been able to notice the tiny crack. ... the only way to detect the fracture would have been to disassemble the eye-bar. The technology used for inspection at the time was not capable of detecting such cracks.[2]

Aftermath

The collapse focused much needed attention on the condition of older bridges, leading to intensified inspection protocols and numerous eventual replacements. There were only two bridges built to a similar design, one upstream at St. Marys, West Virginia, and the notably longer Hercilio Luz Bridge at Florianópolis, Brazil. The St. Marys bridge was immediately closed to traffic and the bridge was demolished by the state in 1971. A small truss bridge was kept to allow access to an island in the river. The Hercilio Luz Bridge remained in active service until 1991 and still stands at Florianópolis due to being built to a higher safety factor than the West Virginia bridge. Modern non-destructive testing methods allow some of the older bridges to remain in service where they are located on lightly traveled roads. Most heavily used bridges of this type have been replaced with modern bridges of various types.

The collapse inspired legislation to ensure that older bridges were regularly inspected and maintained. Aging infrastructure is still a problem in the United States. In 1983 the Mianus River Bridge in Greenwich, Connecticut, collapsed, causing the deaths of three drivers. In early September 2009, the failure of an eyebar in the San Francisco–Oakland Bay Bridge was discovered during a scheduled closure, resulting in an emergency repair to reinforce the failed member.

A scale model of the original Silver Bridge can be seen at the Point Pleasant River Museum. An archive of literature about the bridge is kept there for public inspection. On the lower ground floor, the museum displays an eyebar assembly from the original bridge.

A memorial was installed in Point Pleasant to commemorate the 46 bridge collapse victims.

Legacy

Reviewing the collapse and subsequent investigation in his 2012 book To Forgive Design, engineering historian [3]

He does not fault the bridge's designers, who were ignorant of many of these hazards. Instead he points to the future. "If there is anything positive about the Silver Bridge failure", he concludes, "it is that its legacy should be to remind engineers to proceed always with the utmost caution, ever mindful of the possible existence of [3]

In popular culture

References

Notes

  1. ^ "Silver Bridge". Retrieved August 26, 2013. 
  2. ^ "Silver Bridge disaster", West Virginia Culture.
  3. ^ a b  
  4. ^ Gail Arlene De Vos (June 30, 2012), What Happens Next?: Contemporary Urban Legends and Popular Culture, ABC-CLIO, pp. 89ff,  

Further reading

  • Seim, Charles (May 2008). "Why Bridges Have Failed Throughout History". Civil Engineering 78 (5): 64–71, 84–87. 
  • The Lost Souls of Bell Valley

External links

  • (vol. xv, no. 4, Oct. 2001)West Virginia Historical Society Quarterly"The Collapse of the Silver Bridge," by Chris LeRose in
  • Silver Bridge at Structurae
  • West Virginia Division of Culture and History "On This Day", section-- provides a link to the official WVa state's disaster video the next day, archive 1.6 mb wmv file having good quality, no sound http://www.wvculture.org/history/av/silverbridge256.wmv
  • Bridge collapse video to show sequence of events
  • Case study of bridge collapse
  • Video concerning collapse includes comparison of Silver Bridge and earlier chain bar suspension bridges using lower strength materials.
  • "The Collapse of the Silver Bridge: National Bureau of Standards Determines Cause". National Institute of Standards and Technology Virtual Museum.
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.