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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.
“The Advance”2 pages
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(a) The loadings to be applied were essentially static. (b) Appropriate reductions of allowable stress were made when large ranges of stress due to repetitive loading were involved, especially when reversal of stress was involved. The first assumption was based upon the experimental evidence from tests of such items as riveted joints, where local overstress and yielding resulted in redistribution of stress and had little effect on the ultimate load. The whole theory of design of riveted connections depended upon this concept. A similar concept applied to the design of eyebars, where static tests also showed that a properly proportional head could develop the strength of the shank of the eyebar in spite of the stress concentrations at early stages of loading. The "appropriate reductions of allowable stress" for elements subjected to repetitive loadings were determined either by experience or by laboratory tests, which showed that most structural metals then in use exhibited an "endurance limit" stress level, below which it was immune to fatigue failure. These general assumptions are still in use today for such structures as bridges and buildings of ordinary structural steels. Somewhat more refined techniques are used in the design of pressure vessels, or structures of high strength alloys or nonferrous metals. Relatively little was known of the stress-corrosion-cracking mechanism with respect to the common structural steels used in bridges of that era, or the role of hydrogen-stress cracking or corrosion-fatigue for these materials. Such fatigue mechanisms were beginning to be understood in the high alloy steels and nonferrous metals, but even here the quantitative data was limited. References 36 and 37 give some indication of the status of knowledge in the early 1930's, some five years after the design of the Point Pleasant Bridge. The state of knowledge at that time with respect to stress-corrosion of mild steels is reflected in References 38 and 39, which deal mostly with the benefits of deoxidation or "killing" of steel to inhibit intergranular stress-corrosion. Even today there is little data available for many of the steels which have been used in bridge building over the past fifty years or are in common use at the present time to make reliable quantitative crack growth predictions, where such growth is due to either stress-corrosion cracking or corrosion fatigue. Nor are there reliable data as to what constitutes critical crack size for brittle fracture. Since many of the materials in question possess considerable ductility, it is even doubtful that the discipline of linear fracture mechanics will be adequate for the determination of such critical crack sizes, and new advances to extend these concepts will be required before sufficient insight will be obtained to interpret flaws in these materials.
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