- 126 -
VI. CAUSE
The Safety Board finds that the cause of the bridge collapse was the cleavage fracture in the lower limb of the eye of eyebar 330 at joint C13N of the north eyebar suspension chain in the Ohio side span. The fracture was caused by the development of a critical size flaw over the 40-year life of the structure as the result of the joint action of stress corrosion and corrosion fatigue.
Contributing causes are:
1. In 1927, when the bridge was designed, the phenomena of stress corrosion and corrosion fatigue were not known to occur in the classes of bridge material used under conditions of exposure normally encountered in rural areas.
2. The location of the flaw was inaccessible to visual inspection.
3. The flaw could not have been detected by any inspection method known in the state of the art today without disassembly of the eyebar joint.