— David Wagner 2009/09/01 11:50

A direct route was needed across the Ohio River between Columbus, Ohio, and Charleston, West Virginia. In 1926, Congress granted consent for the Gallia County Ohio River Bridge Company to build a bridge across the Ohio at Point Pleasant, West Virginia. By 1928, the Silver Bridge, so called because of its coating of aluminum paint, was complete and open to traffic.

To build the bridge cheaply, American Bridge Company elected to construct an alternative to the suspension bridge designed by J. E. Greiner Company. Instead of a parallel-wire-cable design, they built a bridge suspended by a giant chain made of eyebars, long steel bars widened at the ends and pinned together much like a giant bicycle chain with extra-long links. Although this design was believed to be adequate at the time, later analysis showed this unusual alternative had lower safety factors than the original design for both the ultimate and yield strengths of the steel used to construct the bridge. In addition, due to elongation of the eye to make construction easier, every pinned chain link joint was especially vulnerable to corrosion. This location inside the joint was inaccessible to visual inspection, and corrosion there could not be detected without disassembly by any means known when the bridge failed. There was also no structural redundancy to the suspension system, so a single link failure was likely to result in the failure of the entire structure, as it eventually did.[3]

It served its purpose for almost forty years, until December 15, 1967, before failing under normal load without warning during rush hour and breaking apart in about a minute.

A small manufacturing flaw in the one of the links of the northern chain, in the lower limb of the outer eye of eyebar 330 at joint C13N, grew larger over time. Stress corrosion and corrosion fatigue combined to cause a brittle fracture of the lower limb when the flaw reached critical size. This failure was immediately followed by ductile fracture of the upper limb and the pin holding the eyebars together fell out.[2] With the northern chain separated, the remaining structure was insufficient to withstand the load, and the whole bridge, including both approaches and the center span, was in the river in about sixty seconds.

Thirty-one of the thirty-seven vehicles on the bridge fell into the river or onto the shore, killing forty-six and injuring nine.[1] The consequences were so shocking that congress and the president acted swiftly to enact broad legislation intended to prevent bridge failures across the U.S.

Following the recommendations of the National Transportation Safety Board, the federal government responded with a number of laws and executive orders to determine the cause of failure and to prevent future failures. The most comprehensive of these was the institution of the National Bridge Inspection Standards (NBIS) requiring all bridges in the U.S. to be systematically inspected. Supporting legislation also included the funding of engineering research resulting in a better understanding of fracture mechanics, safer bridge design criteria, and the development of new testing and inspection methods.[3]

In fairly short order, the mandatory inspections showed that many bridges in the U.S. had dangerous flaws, and it is likely that dozens or even hundreds of bridge failures were prevented by the standards put in place as a result of the Point Pleasant bridge failure.[3]

The total failure of the Point Pleasant bridge would have been prevented had it been built according to the standards that were soon adopted. Although structural redundancy, the use of more ductile materials, and better safety factors can result in a suitably safe bridge, the eyebolt chain design is inherently flawed by the difficulty of adequately inspecting critical link joints. Only one similar bridge still stands, the Hercilio Luz Bridge in Florianopolis, Brazil, and it has been relegated to pedestrian use only.[3]

1. Collapse of U.S. 35 Highway Bridge Point Pleasant, West Virginia December 15, 1967, NTSB Highway Accident Report 71-01, National Transportation Safety Board, 1971. http://www.ntsb.gov/publictn/1971/HAR7101.htm accessed 2009-09-01.
2. Point Pleasant Bridge Collapse, National Bureau of Standards Technical News Bulletin Vol. 55, No. 8, pp.196-197. August 1971, http://museum.nist.gov/exhibits/silverbridge/PointPleasantBridge.pdf accessed 2009-09-01.
3. The Silver Bridge Collapse Recounted, Abba G. Lichtenstein, Journal of Performance of Constructed Facilities, Vol. 7, No. 4, November, 1993. ASCE, ISSN 0887-3828/93/0004-0249, http://www.asce.org/inside/PDF_response/Lichtenstein.pdf accessed 2009-09-01.