EVALUATION AND TESTING OF A FRACTURE CRITICAL BRIDGE

The 1-40 bridges over the Rio Grande in Albuquerque, New Mexico were d ue to be razed in the fall of 1993 due to geometry and traffic safety considerations, thus providing a unique opportunity for testing them. These medium span steel bridges represent a common design in the US an d are classified by AASHTO as nonredundant 'fracture critical' two gir der steel bridges (fracture critical classification means that failure of a primary member would probably cause collapse of the bridge). The subject bridge, built in 1963, is a 1275 foot (600m) bridge, and cons ists of three medium span continuous units with spa ns of 131'-163'-13 1' each. The bridge was field tested to determine the impact of a near full depth girder fracture on the redistribution of loads, the load c apacity, and the potential for collapse. Four levels of damage were in troduced in the middle span of the north plate girder by making variou s cuts in the web and the flange of the girder. The final cut resulted in a six foot deep crack in the 10 ft deep girder, extending from the bottom flange to the floor beam to girder connection. Data was taken under dead load and under a static live load consisting of an 82000 lb truck. The after fracture response and the load redistribution in the fractured bridge were evaluated. The contribution of the different me mbers to the redundancy of the structure was assessed.