Quinnipiac River Bridge Cracking

A large crack was discovered in November l973 in a fascia girder of the suspended span of the Quinnipiac River Bridge near New Haven, Conn. Crack propagation was found to occur in different stages. Fatigue cracks were found to originate at lack of fusion areas in horizontal stiffener splices. After the crack penetrated the web thickness it resulted in brittle fracture of the web. Rapid crack growth was arrested in the flange. On basis of evidence available, brittle fracture occurred at temperatures between 10° F (-12° C) and -10° F (-23° C). Crack instability developed when the stress intensity at the crack tip reached the material fracture toughness. The fracture toughness was estimated from J-integral measurements and from Charpy V-notch test data. An increase in fracture toughness would not have appreciably affected the behavior of the girder. Random truck loading would have continued to grow the web crack in a stable manner until a critical crack length was eventually reached.