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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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(a) The Battelle surface flaw specimens were so constructed that the initial flaw was on the side cut from the interior of the eyebar, where the structure is pearlitic and softer than the surface martensite, whereas the FHWA cracks initiated in the surface material. (b) No crack growth rates were measured in the FHWA tests. B. Actual Stress Levels in Various Components of the Structure as Compared to Primary Stress Analysis The stress analysis conducted by the designers of the Point Pleasant Bridge, as was customary in that era, was a linear elastic analysis for primary stresses only. The term "linear elastic" implies that all members were assumed to function in such a way that deformation is directly proportional to load. This condition is satisfied if all members remain within the elastic limit and if the deformations in the structure under load do not make significant changes in the equations of equilibrium. The first of these conditions is almost exactly satisfied, except for very minor localized deformations in the joints. The second condition is not satisfied in flexible suspension bridges due to the fact that small vertical displacements change the moment arm of the large forces in the eyebar chain to produce non-linear effects. The term "analysis for primary stresses only" implies that all joints in the truss as well as the real pin connections in the chain, are free to rotate as load is applied, thus producing only tension or compression in the members of the chain and stiffening truss system. This assumption is commonly made in the analysis of trussed structures even today, although it is well known that the rigidity of the actual joints in the trusses and the friction in the pin connections of the eyebar chain prevent free rotation of the ends of the connecting elements, introducing bending stresses in addition to the primary tension or compression. Finally, the original stress analysis included a 30 percent allowance in members of the floor system for dynamic stresses due to moving vehicles, but it assumed that the loadings used in the design of the stiffening trusses and chains were adequate to include any dynamic effects which might be present in these elements. A number of studies were conducted in order to assess the significance of several refinements in the stress analysis as follows: 1. The field studies of the essentially identical bridge at St. Marys, West Virginia, were used to obtain information which, together with analytical studies, would permit an assessment of the
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