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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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more pronounced. The degree of reaction, however, was no greater than that found on other corrosion products found on steel exposed in rural atmospheres where hydrogen sulfide is not believed to have been present, indicating that the positive reaction noted may have been the result of manganese sulfide originally in the steel.
The scanning electron examination of the fracture surfaces of zones B and C showed that these were fractures of ductile-dimple type, whereas zone D was flat cleavage. Apparently the original crack (zone A) was extended through the transition zone (zone C) as a ductile fracture during the slow bending load until it reached critical size, resulting in the fast cleavage fracture of the remainder, except for zone B. This zone had a more favorable microstructure. The existence of the ductile zone C raised questions as to whether the lack of such a zone in the critical fracture in eyebar No. 330 indicated that this fracture might have been caused by forces other than a static load alone. This led to a decision to attempt to fracture a full scale eye containing a crack at $ 32^{\circ} \mathrm{F} $ at Battelle, as described above.
Further examinations of typical cracks were made. An attempt to examine one in Battelle specimens BTL-15, where work at that laboratory had indicated a crack existed, failed because no crack could be found. A mounted sample from the NBS laboratory which had been cut from eyebar No. 330 along a plane perpendicular to the fracture was carefully examined to check the nature of the propagation of secondary cracks roughly parallel to the primary crack of the fracture itself. These cracks were found to be relatively straight and unbranched, transgranular, relatively blunt at the tip, and filled with corrosion product. All of them started at pits on the original pinhole surface. A photomicrograph of the tip of one of these cracks which was about 0.01" from the fracture and which penetrated about 0.03" is given in Figure 25a. The different appearance of the branch cracks emanating from the primary fracture is shown in Figure 25b. Even those cracks showed some corrosion, most likely due to environmental exposure after collapse of the structure.
The author of the report expressed the opinion that the cracks starting at the pinhole surface showed evidence more characteristic of corrosion fatigue than of stress-corrosion, due to the fact that they conform to the behavior typical of the former type of propagation; namely, initiation of the cracks at pits or trenches in the surface, transgranular propagation, and relative absence of branching. This observation was at variance with the opinions expressed by both the NBS and Eattelle laboratories, and resulted in a meeting of the special task group which is discussed in Analysis.
## 4. Laboratory Tests at Structures Laboratory, Fairbank Highway Research Station, Federal Highway Administration
Two types of laboratory studies were conducted by the Structures and Applied Mechanics Division, Office of Research, Federal Highway Document, cited by the archive. The PDF is mirrored here; the original link is above. The text was read from the page images by GLM-OCR; expect the odd misread word. 202 pages are in the text index: search them above, or from the library's search.