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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.
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b. Only primary stresses in the members of the eyebar chain and the stiffening stresses were considered. Secondary effects because rigidity of the joints in the truss induced bending in the members as the structure changed shape due to various patterns of traffic loading were not taken into account. Other secondary effects due to transverse bending of the floor beams, distortion of the chain bent post frame, and possible effects in the eyebar heads if they did not rotate freely on the pins were also ignored. c. The dynamic stresses introduced in the floor system by moving traffic were estimated by simple percentage increases in live load stress, which was the common practice at the time of the design of the structure. No allowance for dynamic effects was included in the analysis of eyebar chain, towers or stiffening truss. There were therefore questions with respect to the actual levels of dynamic stress which were appropriate for this structure and the possible significance of uncomputed secondary stresses. These questions were studied during the experimental work conducted on the St. Marys Bridge during the Spring of 1968 and the subsequent interpretation of the data obtained from these experiments. The questions associated with the superstructure defect branch of the logic tree had been only partially resolved at the time of the interim report (refer to Figure 3). Fortunately, positive evidence from the salvage operation showed that both towers fell toward the West Virginia shore. This permitted elimination of the possibility of a failure in the eyebar chains in either the central span or the West Virginia side span. It was clear that if a chain failure were responsible, it would have to be in the Ohio side span, since a break in the central span would have caused each tower to fall toward its respective end of the structure. Correspondingly, a break in the West Virginia side span would have caused both towers to fall toward Ohio. The only failure in the eyebar chain within the Ohio side span was the separation of the joint at C13N. As noted above, the mechanism of this joint separation had not been adequately explored. The possibility that there had been initial failures elsewhere in the truss or in the hanger system was responsible for much of the effort since the issue of the interim report. The possibility of failure in the towers was quickly eliminated by the fact that the north leg of the Ohio tower was in a single piece and was free from major distortions or plate buckling failures. The inspection of the pins in the pedestal shoes showed clearly that no tower leg had slipped off its pedestal at its base. The general nature of the failures in the tower bracing connections gave no indication that any of these failures had occurred prior to the general collapse.
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