Silver Bridge (US 35) [Demolished]
The Silver Bridge carried U.S. Route 35 between Gallipolis, Ohio and Point Pleasant, West Virginia spanning the Ohio River. Planning for a new span between the two respective cities began with an act of Congress in 1926. The proposed alignment was approved by the Army Corps of Engineers and the Assistant Secretary of War in March 1927.(3) Construction began on May 1, and was completed on May 19, 1928 by the Gallia County Ohio River Bridge Company, later known as the American Bridge Company and the General Corporation.The two-lane eye-bar suspension bridge, measuring 2,235 ft. in length, including approaches, was designed to meet a "H-15" load demand. The name, "Silver Bridge," was derived from the fact that it was the first aluminum painted bridge in the region.(3) The span was designed with "high tension" eye-bar chains, a unique anchorage system, and "rocker" towers, and was the first eye-bar suspension bridge in the United States.
The bridge's eye-bars were linked together in pairs like a chain. A huge pin passed through the eye and linked each piece to the next. Each chain link consisted of a pair of 2" x 12" bars and was connected by an 11" pin. The length of each chain varied depending upon its location on the bridge. Some questions were raised when this design idea was brought forward. What if the two eye-bars did not share the four million pound load of the bridge equally? Would the eye- bars fail under the overloaded stress? The designers thought they had an answer.
The answer come in the type of material used for the eye-bars. The American Bridge Company developed a new heat-treated carbon steel to use on the construction of the Silver Bridge. This new steel would allow the individual members of the bridge to handle more stress. Along with the two eye-bars sharing the load, the steel could easily handle the four million pound load. The newly treated chain steel eye-bars had an ultimate strength of 105,000 pounds per square inch (psi) with an elastic limit of 75,000 psi along with a maximum working stress of 50,000 psi. The eye-bars embedded into the unique anchorage were also heat treated for an ultimate strength of 75,000 psi, an elastic limit of 50,000 psi and a maximum unit stress of 30 psi.
-"The Collapse of the Silver Bridge"
The answer come in the type of material used for the eye-bars. The American Bridge Company developed a new heat-treated carbon steel to use on the construction of the Silver Bridge. This new steel would allow the individual members of the bridge to handle more stress. Along with the two eye-bars sharing the load, the steel could easily handle the four million pound load. The newly treated chain steel eye-bars had an ultimate strength of 105,000 pounds per square inch (psi) with an elastic limit of 75,000 psi along with a maximum working stress of 50,000 psi. The eye-bars embedded into the unique anchorage were also heat treated for an ultimate strength of 75,000 psi, an elastic limit of 50,000 psi and a maximum unit stress of 30 psi.
-"The Collapse of the Silver Bridge"
The anchorage for the Silver Bridge had to be uniquely designed, as bedrock was not found at a depth considered to be practical. An unusual anchorage, constructed of reinforced concrete 200 feet long and 34 feet wide filled with soil and reinforced concrete, was supported on 405 16 inch octagonal reinforced concrete piles in which the cable pull is resisted by the weight of the anchorage and by sharing the halves of the piles.
Another unique design technique used on the Silver Bridge was the 'Rocker' towers. The innovative towers, which had a height of 130 feet, 10 1/4 inches, allowed the bridge to move due to shifting loads and changes in the chain lengths due to temperature variations. This was done by placing a curved fitting next to a flat one at the bottom of the piers. The rocker was then fitted with dowel rods to keep the structure from shifting horizontally. With this type of connection, the piers were not fixed to the bases.
-"The Collapse of the Silver Bridge"
-"The Collapse of the Silver Bridge"
The Silver Bridge opened as a tolled facility and was operated by the West Virginia-Ohio Bridge Corporation. On December 26, 1941, the state of West Virginia purchased the span for $1,040,000 and it included a $70,000 contract for bridge repairs and engineering services. The bridge became toll-free on December 3l, 1951.
The bridge underwent a thorough inspection just prior to the transition from toll to non-toll facility. On December 21, 1951, Bridge Engineer L. L. Jemison, suggested the following to H. K. Griffith, West Virginia State Maintenance Engineer:
1. Repairing the bridge seat of the upstream side of the Ohio Abutment.
2. Cutting Ventilator openings in all of the four anchor chambers and making frames for same.
3. Encasing the anchor bars inside of the anchor chambers with concrete.
4. Restoring the disintegrated concrete of the piers, anchorages and retaining walls.
5. Waterproofing the roadway of the anchorages and the approaches and surfacing same with asphaltic concrete.
6. Cleaning and painting steel work where necessary.
7. Revising the Ohio approach to provide better returns.
8. Extending the sidewalk along the Ohio approach.
9. Removing the Toll House.
10.Revising the lighting control system.
11.Miscellaneous steelwork: Repair Railing, Clean out holes at bottom of tower verticals, Furnishing and installing gutters under expansion devices, Making and installing bird screens,
12. Restoring concrete around anchor bars removed for inspection.
1. Repairing the bridge seat of the upstream side of the Ohio Abutment.
2. Cutting Ventilator openings in all of the four anchor chambers and making frames for same.
3. Encasing the anchor bars inside of the anchor chambers with concrete.
4. Restoring the disintegrated concrete of the piers, anchorages and retaining walls.
5. Waterproofing the roadway of the anchorages and the approaches and surfacing same with asphaltic concrete.
6. Cleaning and painting steel work where necessary.
7. Revising the Ohio approach to provide better returns.
8. Extending the sidewalk along the Ohio approach.
9. Removing the Toll House.
10.Revising the lighting control system.
11.Miscellaneous steelwork: Repair Railing, Clean out holes at bottom of tower verticals, Furnishing and installing gutters under expansion devices, Making and installing bird screens,
12. Restoring concrete around anchor bars removed for inspection.
In addition to this, the bridge was inspected periodically on July 28, 1955, November 15, 1961, and on April 8 and 9, 1965. Some suggestions were made to the West Virginia Department of Highways for some bridge improvements but were not implemented due to a lack of funds. Each inspection, without the improvements, deemed the bridge to be structurally safe.
The Collapse of the Silver Bridge
The Silver Bridge collapsed on December 15, 1967 at 5 P.M. due to a deficiency on one of the eyebars."The answer was the unique eye-bar design made from the newly innovated heat treated-carbon steel. The old saying, "A chain is only as strong as its weakest link," turned out to be a fact in the failure of the Silver Bridge. The heat-treated carbon steel eye-bar broke, placing undue stress on the other members of the bridge. The remaining steel frame buckled and fell due to the newly concentrated stresses.
The cause of failure was attributed to a cleavage fracture in the lower limb of eye-bar 330 at joint C13N of the north eye-bar suspension chain in the Ohio side span." The fracture was caused from a minute crack formed during the casting of the steel eye-bar. Over the years, stress corrosion and corrosion fatigue allowed the crack to grow, causing the failure of the entire structure. At the time of construction, the steel used was not known for subduing to corrosion fatigue and stress corrosion. Inspection prior to construction would not have been able to notice the miniature crack. Over the life span of the bridge, 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.
Stress corrosion cracking is the formation of brittle cracks in a normally sound material through the simultaneous action of a tensile stress and a corrosive environment.(20) Combined with corrosion fatigue, which occurs as a result of the combined action of a cyclic stress and a corrosive environment, disaster was inevitable for the Silver Bridge. The two contributing factors, over the years continued to weaken the eye-bar and unfortunately the entire structure."
-"The Collapse of the Silver Bridge"
The cause of failure was attributed to a cleavage fracture in the lower limb of eye-bar 330 at joint C13N of the north eye-bar suspension chain in the Ohio side span." The fracture was caused from a minute crack formed during the casting of the steel eye-bar. Over the years, stress corrosion and corrosion fatigue allowed the crack to grow, causing the failure of the entire structure. At the time of construction, the steel used was not known for subduing to corrosion fatigue and stress corrosion. Inspection prior to construction would not have been able to notice the miniature crack. Over the life span of the bridge, 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.
Stress corrosion cracking is the formation of brittle cracks in a normally sound material through the simultaneous action of a tensile stress and a corrosive environment.(20) Combined with corrosion fatigue, which occurs as a result of the combined action of a cyclic stress and a corrosive environment, disaster was inevitable for the Silver Bridge. The two contributing factors, over the years continued to weaken the eye-bar and unfortunately the entire structure."
-"The Collapse of the Silver Bridge"
Another factor that went into the collapse was that the bridge simply could not handle the rigors of daily traffic. When the bridge was designed, a Model T-Ford (1,500 lbs.) was used as a design vehicle and the maximum weight by West Virginia law at the time was 20,000 pounds. By 1967, the average car weighed nearly 4,000 pounds and the maximum weight was 60,800 and up to 70,000 with special permits.(2)
Thirty-seven vehicles were crossing the bridge at the time of the collapse. Thirty-one vehicles fell into the river. As a result, nine were seriously injured and forty-six perished. Exactly two years later in 1969, the new Silver Memorial Bridge opened downstream of the original Silver Bridge.
Administrator Frank Turner comments on efforts to ensure the lessons learned prevent future tragedies: "Involved are complex secrets of the physical sciences not yet completely understood and thus not readily detectable. But within your government, dedicated men and women are seeking the answers to these and many other problems . . . . When we build upon tragedy . . . and find new solutions to increase safety for others, we then can perhaps find small consolation that such a loss has not been in vain. It is really this effort which we dedicate here today."
The St. Mary's Bridge, upstream of the Silver Bridge, had a similar design and was promptly closed for inspection.
Further reading
1. The Collapse of the Silver Bridge by the West Virginia Division of Culture
2. FHWA By Day
3. Silver Bridge at Structurae
4. Silver Memorial Bridge at Structurae
Sources
1. "FHWA By Day." Federal Highway Administration. 15 March 2004 Article.
2. LeRose, Chris. "The Collapse of the Silver Bridge." West Virginia Historical Society Oct. 2001. 16 March 2004 Article.
3. Bolte, Jason. Point Pleasant. Charleston: Arcadia, 2007. 93-108.
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