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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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loadings imposed are subject to errors arising from several sources. One can calculate with great precision that portion of the load which is produced by the weight of the structure itself (probably within one to two percent error), but the loads imposed by external loads of traffic and the environment cannot be determined with the same precision. There is obvious difficulty in estimating what types of heavy vehicles we will be moving on our highways in the year 2010, which is the same 40 year projection into the future that was faced by the designers of the Point Pleasant Bridge in 1927. Besides the difficulty of projecting the loads likely to be produced by individual vehicles in the future, there is a problem of what combinations of these heavy vehicles are likely to occur on the structure where the influence of more than one vehicle is involved in the stress computations. For example, the maximum stress in the eyebar chain due to traffic was produced when both lanes of the structure were loaded over the full length of the suspended portion of the structure. It is highly improbable that this full length would be occupied entirely by vehicles of the maximum weight for which individual local elements of the deck were designed. It is even more improbable that this event could occur simultaneously with a temperature condition producing maximum stress and with maximum stresses due to a wind blowing at right angles to the structure. The designer, therefore, must use careful judgment in deciding which influences should be assumed to occur simultaneously and must make appropriate reductions in the factor of safety for highly improbable conditions. One further matter is involved in the establishment of the actual factor of safety; namely, the precision with which the stress analysis is conducted. The greater the refinement of the stress analysis and the accuracy of estimating such factors as dynamic effects of moving loads, the lower need be the nominal factor of safety to achieve a given level of improbability of failure. Systematic procedures by which all of these factors had been incorporated into highway bridge design practice were fairly well established by 1926. A nationally recognized design specification appeared in 1923, when the first edition of such a specification was issued by the American Association of State Highway Officials. A similar specification for railroad bridges had been issued in 1910 by the American Railway Engineering Association. The basic procedure consists essentially of four elements: (a) An allowable working stress for basic tension members is stipulated, usually in terms of a percentage of the elastic limit stress for the material to be used (more recently in terms of the
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