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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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18,500 psi. for a stiffening truss composed of the same material. The actual computed maximum stress for the Florianopolis bridge was 14,500 psi. when the deflection theory was used to correct the computations performed by the linear elastic assumption. This comparison is, however, meaningless without consideration of the live loads which were used in the design. The designers of the Point Pleasant Bridge used a live load of 14,000 pounds/linear ft. of bridge plus a 42,000 lb. concentrated load for stiffening trusses, towers, and cables. This is in excess of the 640 lbs./ft./lane for a modern H20 loading on two lanes (as the structure was actually used), and no reduction was taken for the improbability of obtaining such loads over the long loaded lengths required for maximum chain loads or maximum stiffening truss bending moments. Steinman used a live load of 2200 pounds/linear ft. for two lanes of highway loading plus one lane of light railway loading down the center lane of the structure. A reduction of this live load was used for the design of the chains (1850 lbs./linear ft.) in view of the improbability of obtaining maximum loads over the full length of the structure. While the selection of the design stress for the stiffening trusses for the Point Pleasant Bridge appears to be somewhat high, it should be noted that the consideration of the deflection theory reduces actual stresses by approximately 16 percent below those indicated by the linear analysis on which the design was actually based. Moreover, yielding of the stiffening truss in a suspension bridge does not produce a collapse, since the truss is not required for equilibrium. Such yielding would lead to large deflections so that the cable could distort to provide a new stable equilibrium. This condition, could not, of course, be tolerated except in emergency conditions, for repetitions of such events would quickly lead to serious damage. There is no evidence to indicate that the failure of the Point Pleasant Bridge initiated in the stiffening trusses. 3. The problem of stress concentration was well recognized at the time of the design of the Point Pleasant Bridge. Both theoretical and experimental solutions for typical cases in machine design and structural engineering were available. The classic solution for the stresses at the edge of a circular hole in an infinitely wide plate subjected to uniaxial tension was known to give stress concentration factors approaching 3. There was, however, a general assumption that such effects could be ignored except when highly brittle materials were used or in cases where fatigue might occur. Castings of such materials as iron were provided with generous fillets, and machine parts subjected to repetitive loads were designed for conservative unit stress and detailed to avoid sharp discontinuities where possible. The structural engineering profession of that era assumed that these effects, which were present around every rivet hole and every abrupt change of section, could be ignored if:
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