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This is the final highway accident report (NTSB-HAR-71-1) from the National Transportation Safety Board, adopted in December 1970. It covers the collapse of the U.S. 35 bridge between Point Pleasant, West Virginia, and Kanauga, Ohio, on December 15, 1967, which killed 46 people. The Board found that the cause was a cleavage fracture in eyebar 330 at joint C13N. That fracture grew from a flaw produced over 40 years by stress corrosion and corrosion fatigue, in a spot that could not be seen or found by inspection.
“The Advance”2 pages
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carried out by a linear elastic procedure involving the consideration of the elastic energy within the system. As noted in a previous section of this report, this original analysis has now been thoroughly checked by two independent groups and has been found accurate with a few very minor deviations. There is no record to establish whether the designers reexamined these results to consider the effects of distortion by applying the so-called "deflection theory" to the analysis. For suspension bridges, however, the more exact deflection theory will indicate lower stresses in the stiffening truss than will the linear elastic theory, so that the use of linear theory tended to increase rather than decrease the factor of safety in the structure. A simple check of one loading case at one point in the center of the main span indicates that the more refined analysis would have reduced the stiffening truss chord stress by approximately 16 percent. Both the second and third considerations make it feasible to raise the allowable design stresses above those commonly used for short span structures. This practice was and is common for stiffening trusses and main supporting elements of suspension bridges. The designers of the eyebar chain alternate for the Point Pleasant Bridge selected an allowable stress for the eyebar chain of 50,000 psi. This was approved by the consultants. This material was to be manufactured so as to produce a minimum clastic limit of 75,000 pounds/sq. in. This provides a nominal factor of safety on the elastic limit of 1.50. Such a factor of safety appeared reasonable, in the judgment of the designers, in view of the fact that approximately 75 percent of the stress in the eyebar chain elements was due to the weight of the structure which could be quite precisely calculated. It is interesting to compare this factor of safety for the main supporting chain with those of other bridges designed during the same era. In the design of the Florianopolis bridge in Brazil, D. B. Steinman used an allowable stress of 46,500 psi. for an eyebar chain composed of essentially identical material. This would yield a factor of safety on the elastic limit of 1.61. The Florianopolis bridge, however, was designed to carry both highway and rail loadings, resulting in the dead load stress being a slightly lower fraction of the total stress in the chain (approximately 70 percent). The typical factor of safety used in the design of wire cable bridges at the same period was from 1.6 to 1.7 based on the yield strength. Similar increases in the allowable stresses in the stiffening truss over and above those common in short span bridges were customary for long span structures. In the design of the Point Pleasant Bridge an allowable stress of 24,000 pounds/sq. in. in tension was used in a material (A7-24 carbon structural steel) for which the stipulated minimum yield point was 30,000 psi. This corresponds to a safety factor of 1.25 on the yield point. Steinman in the design of the Florianopolis bridge used a basic allowable stress of
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