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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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NBS by taking a weighted average (two parts outer layer plus one part inner layer divided by three) agree well with the FHWA specimens which extended through the full thickness. The data of NBS and U. S. Steel on the outer layers agree quite well with the results of the Battelle specimens from this layer for yield strength, but the Battelle specimens show somewhat lower tensile strength. The data for steel taken from eyebar No. 330 shows no significant difference with respect to the data for other bars. The values for all bars tested, when weighted averages are taken to add properties for inner and outer layers, fall within the specification requirement as to ultimate strength (105,000 psi), and the elastic limit value of 75,000 psi was satisfied. 5. It is difficult to compare the data on fatigue characteristics of this material obtained by the Battelle laboratories in their crack growth studies with either that obtained by FHWA in tension tests to failure of full thickness specimens or to those obtained by Professor Starkey on small rotating beam specimens. The latter two sets of data may be compared with each other more readily by reinspection of Figure 26 (FHWA) and Figure 31a (Starkey). The FHWA tests in general, covered a lower range of stress (closer to that which existed in the structure) with a maximum range of 66,000 psi and a minimum range of 42,000 psi. Starkey's specimens used full reversals of stress varying from 80,000 psi to 57,000 psi, so that there is actually no overlap with the FHWA work. At 60,000 psi stress range, the FHWA curve is displaced considerably to the left (toward shorter life), indicating a life of 160,000 cycles in comparison to the 240,000 cycles indicated by Starkey's data for a full alternating stress of 60,000 psi. This is probably due to the fact that Starkey's specimens were polished, whereas the FHWA specimens had the natural exterior surface of the eyebar on two faces. These natural surfaces contained corrosion pits and surface imperfections, so that displacement toward shorter life in a manner similar to Starkey's fretting specimens was to be expected (See Figure 31b). Below a stress range of 60,000 psi, Starkey assumed that an endurance limit existed for this material, since he obtained an extreme life of nearly five million cycles for one polished specimen at a range of 57,000 psi. The FHWA data and Starkey's data for pitted specimens do not exhibit such a tendency. If Starkey's data for the upper part of his stress range were extended in a straight line down to an alternating stress of 43,000 psi, the indicated life would be about 1,600,000 cycles. The FHWA specimens for a range of stress of 43,000 psi, indicate a life of about 1,400,000 cycles with some possibility of an endurance limit just below this level. A comparison of the fatigue crack growth rates obtained by Battelle with the FHWA fatigue data is difficult for the following reasons:
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