Silver Bridge

The Silver Bridge was an eyebar-chain suspension bridge that spanned the Ohio River, connecting Point Pleasant, West Virginia, and Gallipolis, Ohio. Its name came from its shiny aluminum paint.

The bridge was built in 1928 and collapsed in 1967 during rush hour traffic, resulting in the death of 46 people and increased safety inspections and regulations of bridges across the country.

The bridge was replaced by the Silver Memorial Bridge in Hendeson, West Virginia, just south of Point Pleasant two years later.

History
Constructed by the American Bridge Company, the two-lane bridge opened on May 30, 1928 as the Hoover Bridge, but it took on the name, Silver Bridge, due to its shiny aluminum paint. Aluminum was rarer then and harder to say, so the name "Silver Bridge" stuck. It comprised a 1,750-ft. span of U.S. Route 35. It was described as an "engineering marvel" at the time.

Structure
Bridges have been using the eye-bar-chain suspension for over 100 years before the Silver Bridge, but used rows of four to six bars, sometimes with the chains in parallel.

The eye-bars in the Silver Bridge were not redundant and links only had two bars each, made of high-strength steel (more than twice the tensile strength of common mild steel). This allowed the builders to use only two bars instead of a thick stack of thinner bars of modest material strength "combed" together that was usually used for redundancy. However, this two-bar design made a failure of one cause a total failure.

The bridge also had "rocker" towers that allowed the bridge to respond to various live loads by a slight tipping of the supporting towers, which were parted at deck level. This design required the chain on both sides for support, so the failure of one would result in a total failure.

At the time of construction, the bridge was designed for Ford Model T (about 1,500 lbs.) and 10-ton (20,000 lbs.) truck traffic. By the time of its collapse, the typical family automobile weighed about 2 tons (4,000 lbs.) and the large truck limit was 30 tons (60,000 lbs.) or more. Traffic jams on the bridge became more common as well, causing more stress to the bridge.

A scale model of the bridge can be seen at the Point Pleasant River Museum as well as a display of an eye-bar assembly from the original bridge.

Collapse
At around 5 p.m. Dec. 15, 1967, the Silver Bridge was packed with bumper-to-bumper traffic during rush hour. Eye-bar 330 on the first link on the north side of the Ohio subsidiary chain failed when a 2.5 mm crack formed through fretting wear at the bearing grew from corrosion and broke in a brittle fashion. The transferred load caused a chain-reaction of overloading and breaking other areas of support resulting in a total failure since all parts of a suspension bridge are in equilibrium with one another. The location of the crack would have hidden it during the inspections of the bridge.

There was an estimated 75 vehicles on the bridge when it collapsed and 46 people died in the incident. Two victims were never recovered.

At the time of the collapse, the bridge carried over 9,000 cars per day. Private ferry companies helped the local communities as the area built a replacement. The collapse focused attention of the condition of older and similar bridges. This led to intensified inspection protocols and replacements. The Silver Bridge was replaced by the Silver Memorial Bridge in Henderson, West Virginia, just south of the original bridge site in 1969.