The Silver Bridge Upon Completion
This view is from Point Pleasant, looking west to Ohio. The railroad truss, just to the north, still stands.
Photo by US Federal Highway Administration
BH Photo #148929
On December 15, 1967 at approximately 4:50 PM, while packed with cars during rush hour, the Silver Bridge that crossed the Ohio River between Point Pleasant, West Virginia and Kanauga, Ohio, collapsed. 46 people perished in the collapse, two bodies were never found.
The 1928 bridge, which took its name from the aluminum paint that covered it, used a modified eyebar chain design that was relatively new at the time of its construction. Although eyebar chain bridges had been built around the world since the early 19th century, the Silver Bridge used a modified design without the extra redundancy of earlier eyebar chain bridges. After the collapse, another eyebar chain bridge of similar design, upriver at St. Marys, was immediately closed. The St. Marys bridge was demolished in 1971.
During the failure analysis, it was found that Eyebar #330, closer to the Ohio side of the Silver Bridge, had developed a tiny stress crack, perhaps even during manufacture. When the crack reached 0.1" in depth, it went critical and failed soon after. Because all components of the bridge were balanced together, the failure of that one component caused all the others to fail. Witnesses reported that the bridge collapse took about one minute.
"The Mothman Prophesies" add to the mystique of the area, and to the bridge collapse. Legend has it that the mysterious "Mothman" fortold the collapse of the bridge.
According to the NTSB, there were three major contributors to the failure of the bridge:
"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."
At the time of its construction, the typical automobile was light and small. A Model T Ford weighed 1,500 pounds but by 1967, family cars were twice the size and weighed two or three times the weight of a typical contemporary automobile. Bumper-to-bumper traffic jams, unheard of in 1928, were common in 1967. The bridge carried far more weight and traffic, on a daily basis, than designers in 1927 could ever have imagined. (Note that the replacement bridge carries over 25,000 vehicles per day.)
As a result of the Silver Bridge disaster, the NBIS, National Bridge Inspection Standard, was created. NBIS mandates that all bridges in the United States, longer than 20 feet, must be inspected every two years.
Construction of a replacement bridge for this important crossing began almost immediately, because the nearest crossing was the Pomeroy-Mason Bridge about 14 miles upriver. The replacement, the Silver Memorial Bridge opened exactly two years later, on December 15, 1969.
There is a great deal of information about the collapse of the Silver Bridge and even the Mothman Prophecies are available. The Point Pleasant River Museum has displays and pages about the bridge. The Silver Bridge appears on Nicolas Janberg's Structurae Database with even more links to Silver Bridge information. The West Virginia Historical Society also published an article about the collapse, The Collapse of The Silver Bridge, in 2001.
Even though the tragedy of the Silver Bridge collapse resulted in infrastructure awareness and the creation of the NBIS, the fact is, bridge inspections are mostly visual. Tiny stress fractures are not always in a visible location. The same type of failure was missed in an NBIS inspection in 2000, on an approach span of the Daniel Webster Hoan Bridge in Milwaukee, where the span failure did not result in total collapse, nor loss of life. Tragically, a similar undetected flaw resulted in the 2007 catastrophic failure of the Mississippi River/I-35 Bridge in Minneapolis.
In the future, new bridges promise to be "smart structures" with electronic monitoring to detect changes in a bridge, indicating potential problems, before they become problems of catastrophic size. (Some bridges are already being so monitored, but not many.)
So-called "smart structures" are all in the future. For now, we must remember the victims of bridge tragedies and count on the visual NBIS to keep our infrastructure in place.
Author's Note: Portions of this article first appeared in the News section here, on December 15, 2008, in a "This day in history..." feature.