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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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actual level of stress in certain critical members in the system. These studies were reported in Section III and are documented in Reference 16. Secondary stresses due to bending moments introduced in elements by joint rigidity were checked at the connection of the chain bent post to the chain bent girder, at the lower end of a typical vertical truss member, in gusset plate U7N, and in the eyebar head at joint C11. The stresses associated with the measured strains at these locations due to joint rigidity are not believed to have a significant influence on the safety of the structure, since they were well within the 10-15 percent of primary stress which is assumed in setting the allowable stress levels for primary stress. Significant dynamic bending stresses were found in the hanger system, but these were also a small fraction of the total dead load plus live load stress for which the hangers were designed. The eyebar chains also showed significant dynamic strain effects for a rapidly moving test vehicle as compared to the strains produced by the same vehicle moving at a slow crawl speed. These results, however, are for a single moving vehicle. With a large number of vehicles on the span, the ratio of resultant dynamic effects to the static live load stress would decrease, since it would not be likely that all of the dynamic vehicle effects would be in phase. 2. A second possibility with respect to dynamic stresses exists in the occasional excitation of the structure by wind. Prior to the public hearing of May 1968, computations were performed to determine the natural mode shapes and frequencies of the Point Pleasant Bridge. These were checked experimentally by mechanical excitation of the St. Marys Bridge and were found to be in reasonable agreement with the computations. The energy absorption capabilities of the structure while undergoing oscillations were also determined experimentally for each mode, and were found to be somewhat higher than usual for a suspension bridge of this span length. This was probably due to friction generated in the pin joints of the chain, which did show some movements when moving loads were in the center span. On a basis of this evidence, Mr. Vincent expressed his expert opinion at the hearings to the effect that aeroelastic excitation of the Point Pleasant Bridge for the condition existing at the site at the time of collapse was highly improbable. It was noted that the wind velocity at the time was only about six miles per hour and that the wind was blowing parallel to the longitudinal axis of the structure. This did not preclude, however, the possibility that winds blowing transverse to the axis of the structure at various times during its history could have excited oscillations which might have contributed to a reduction of the life expectancy by producing cyclic loadings in the eyebar chain.
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