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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.
“Cooper”1 page
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established that the stress level at which this was a critical size flaw was just about equal to the yield strength for this material, and a combination of stress analysis, model tests at FHWA, and full scale eyebar tests at Lehigh University showed that such levels probably existed at this location at the time of collapse. The fracture of a full scale eye at Battelle at 32 degrees Fahrenheit established that a cleavage fracture with no ductile zone could be produced in this material with slow "static" loading rates. 3. The questions of what initiated the crack in this eyebar and what mechanism was dominant in its growth to critical size are not completely resolved. There is general agreement among members of the working group that the crack initiated in a small corrosion pit on the pinhole surface. Whether or not this pit formation was accelerated by mechanical fretting is uncertain. Although Professor Starkey found evidence of fretting on some pins and at some points on the hole surfaces of eyebar No. 330, a positive identification of fretting debris with the crack in the plane of fracture was not possible due to the exposure of the fracture before laboratory examination. The most favorable conditions for the development of fretting action were at the same location as the most favorable location for the development of either stress-corrosion or corrosion-fatigue; namely, at the point on the hole surface on a plane through the center of the hole normal to the axis of the bar, referred to as the "90 degree" position. This was favorable for fretting action because at this point the greatest relative displacement of eyebar hole and pin surface took place due to elastic strains, combined with a reasonably high bearing pressure. It was also favorable for stress corrosion because of the geometry of the hole, which provided a tapered capillary space at this point which could collect and concentrate contaminants dissolved in rain water. It is believed that fretting was a factor in the initiation of these pits. The mechanism of growth of the pits to cracks of critical size was first thought to have been clearly identified as a stress-corrosion action on a basis of the early NBS work reported in February 1969 (Reference 17), although Professor Starkey had suggested corrosion fatigue in his report of February 28, 1969 (Reference 29), possibly associated with further fretting action. Subsequent work at Battelle supported the assumption of stress-corrosion, but the U. S. Steel laboratory found evidence of transgranular fracture, indicating that corrosion fatigue may have been involved. To resolve these questions, a task group was appointed by the Chairman to open a fresh crack in a piece taken from eyebar C9-C11 (south bar of north chain) without the use of cutting oils to avoid the possibility of contamination. The laboratory work of that task group, which included representatives of NBS, U. S. Steel, Battelle, and Modjeski
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