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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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showed that high strain rates in the presence of a mild notch could produce brittle fracture at temperatures of about 0 degrees Fahrenheit, as compared to -230 degrees Fahrenheit for the same specimen configuration with slow loading rates. In spite of this, the material showed reasonable resistance at slow load rates in the presence of a sharp crack at room temperature, as evidenced by the ductile fracture in the surface-flawed specimen tested at Battelle in an attempt to obtain the critical stress intensity factor. A repeat test of the same type at 0 degrees Fahrenheit showed essentially the same result.
3. Chemical analyses were conducted on samples of the eyebar steel by both the National Bureau of Standards and the U. S. Steel laboratories. A summary of the results is presented in Table 5. It will be seen that these results are in excellent agreement. The carbon content was appropriate to "1060 carbon steel," and the control of sulfur and phosphorous was adequate. The analysis of the C13 end of eyebar No. 330 shows no significant differences compared to other specimens, or compared to mill tests on sample eyebars made in 1927.
4. The tests to determine mechanical properties of the eyebar steel were extensive due to the fact that metallurgical examination showed that there was a considerable variation in structure between the surface and the interior of the eyebar. This material was heat treated by heating to $ 850^{\circ}-900^{\circ} \mathrm{C} $ , quenching in water, and then heating at $ 600^{\circ}-650^{\circ} \mathrm{C} $ for 2 hours. The nature of the heat treatment process produced these variations due to the difference in cooling rates and hardenability of the steel during quenching. The outer material cooled most rapidly and formed martensite, which became mixed with slack quenched products as the depth increased, and changed to primarily pearlite and ferrite in the interior. These observations were made by NBS, U. S. Steel, and the Battelle laboratories. These laboratories also noted that the outer layer of martensite was decarburized near the surface of the bar, usually for a depth of about 0.1 to 0.2 inches, but to less depth in the pinhole surfaces where material had been removed by machining. Some spheroidization of the carbides was noted by both NBS and Battelle. Many checks of hardness were made to maintain a careful control of the specimens used for mechanical tests, and care was taken to separate the specimens taken from the different layers. In the specimen plan established for checking the properties of the eyebar steel, arrangements were made to ship adjacent specimens to different laboratories in order to permit reliable comparisons (see Figure 5a through 5c).
A comparison of the principal mechanical properties as found by the various laboratories is given in Table 6. For the results of NBS and U. S. Steel laboratories, where the properties of the outer layers were measured separately from those of the inner layers, there is excellent agreement. It will also be noted that the estimated effective values of yield and tensile strength for the entire bar computed by Document, cited by the archive. The PDF is mirrored here; the original link is under it. The text was read from the page images by an OCR model; expect the odd misread word. 202 pages are in the text index: search them above, or from the library's search.