Silver Bridge Collapse

At  5:00 PM on December 15, 1967, 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.”

The Ohio approach to the Bridge After Collapse.

    The Old Silver Bridge next to the  Norfolk Southern Rail Bridge(To the lift still Intact).

Above -Wreckage of the Silver Bridge

Above- Rescue personnel  trying to save People in the Ohio River

Above- personnel pulling a car out of the Ohio River

Above- What is lift of the Ohio Side Span

Above- Most of the  Ohio Side Span crashed on to land

Above- Coast Gard Examining the Center Span

Above- Another look and the Ohio approach to the Bridge

Above- Side view of the Ohio Approach.

The bridge failure was found to be due to a defect in a single link, eyebar 330. It was situated 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 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 now only held together by three eyebars, and another slipped off the pin at the centre 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 reckoned that it only took about a minute for the whole bridge to disappear.

HIGHWAY ACCIDENT REPORT
Adopted: December 16, 1970
COLLAPSE OF U. S. 35 HIGHWAY BRIDGE
POINT PLEASANT, WEST VIRGINIA
DECEMBER 15, 1967

SYNOPSIS
The U. S. 35 Highway Bridge connecting Point Pleasant, West Virginia, with Kanauga, Ohio, collapsed at approximately 5 p.m. (EST) December 15, 1967. Forty-six persons died in the accident, nine were injured, and 31 of the 37 vehicles on the bridge fell with the bridge. Twenty-four vehicles fell into the Ohio River and seven fell on the Ohio shore. There were no pedestrians on the bridge at the time of collapse.

The initial failure in the bridge structure was a cleavage fracture in the lower limb of the eye of eyebar 330 (north bar, north chain, Ohio side span) at joint C13N, the first eyebar chain joint west of the Ohio tower of the bridge. The cleavage fracture was followed by a ductile fracture in the upper limb of the eye of eyebar 330 at joint C13N, separating eyebar 330 from the chain. Immediately following the separation of eyebar 330 from joint C13N, the sister eyebar 33 slipped from the C13N joint pin, resulting in the separation of the north chain at that location. The collapse of the bridge began in the Ohio side span, moving eastward toward the West Virginia shore, with the result that within a period of about 1 minute, the 700-foot center span, the two 380-foot side spans, and the towers had collapsed.

The Safety Board finds that the cause of the bridge collapse was the cleavage fracture in the lower limb of the eye of eyebar 330 at joint C13N of the north eyebar suspension chain in the Ohio side span. The fracture was caused by the development of a critical size flaw over the 40-year life of the structure as the result of the joint action of stress corrosion and corrosion fatigue.

Contributing causes are:

1. 1. In 1927, when the bridge was designed, the phenomena of stress corrosion and corrosion fatigue were not known to occur in the classes of bridge material used under conditions of exposure normally encountered in rural areas.
2. The location of the flaw was inaccessible to visual inspection.
3. The flaw could not have been detected by any inspection method known in the state of the art today without disassembly of the eyebar joint.

RECOMMENDATIONS

The Safety Board recommends that:

1. The Secretary of Transportation expand existing research programs or institute new research programs to:

a. Identify bridge building materials susceptible to slow flaw growth by any of the suspected mechanisms;
b. Determine critical flaw size under various stress levels in bridge building materials;
c. Develop inspection equipment capable of detecting critical or near critical flaws in standing bridge structures;
d. Devise analytical procedures to identify critical locations in bridge structures which require detailed inspection;
e. Develop standards which incorporate appropriate safeguards in the design and fabrication of future bridges to ensure protection against failures of material such as occurred in the Point Pleasant Bridge;
f. Develop standards for the qualification of materials for future bridge structures, using the information disclosed in this investigation;
g. Devise techniques for repair, protection, or salvage of bridges damaged by internal flaws; and
h. Expand the knowledge of loading history and life expectancy of bridges.

2. The Secretary of Transportation explore the alternatives for action to assure mandatory application of the bridge safety requirements of the 1968 Federal-Aid-Highway Act to all highway bridges in the United States, since the majority of older bridges in the country are not in the Federal-Aid-Highway System and these bridges are most susceptible to extensive repair or replacement; including such alternative courses of action as urging the adoption by the States of mandatory standards, or the enactment of Federal legislation applicable to all highway bridges.

3. The Secretary of Transportation consider the advisability of proposing a program of Federal aid to ensure the adequate repair of all bridges not in the Federal-Aid-System.

"Inspection prior to construction would not have been able to notice the miniature 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

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 three other bridges built to a similar design, one upstream at St Mary's and a longer bridge at Florianopolis,  Brazil. They were both closed immediately, and the St Mary's bridge demolished. The Brazlian bridge remains, but is closed to traffic. It was built to a higher safety factor. Modern non-destructive testing  methods allow some of the older bridges to remain in service where they are located on lightly traveled roads, while most heavily used bridges of this type have been replaced with modern bridges of various types, and as an extra benefit containing additional lanes.

The new bridge that replaced the Silver Bridge was named the Silver Memorial Bridge.