Two full-size AASHTO prestressed concrete girders, one Type III and one Type V, were tested for fatigue resistance. Both girders were impaired by transverse cracks in their top flanges near the midspan and the cracks extended well into the web of each girder. Each girder was subjected to one million cycles of service load and 2,500 cycles of intermittent overload as if the girder were made composite with a cast-in-place bridge deck. The overload was equivalent to 75% of the ultimate capacity of the composite girder. Prior to the fatigue test, each girder was tested beyond its cracking load to create flexural cracks in its tension flange. After the fatigue loadings, the girders were tested to failure to determine their ultimate load capacities.
Analytical studies were also conducted to model the behavior of the girders by using two separate computer programs, one called Cracked Beam and the other Response 2000. The former was developed by using Microsoft Excel and the latter was acquired from the University of Toronto in Canada.
The test results demonstrated that the fatigue loadings had virtually no effect on the girder behavior. The girders showed no degradation in stiffness or strength after 1,000,000 cycles of fatigue loading. Both girders showed considerable ductility, and their ultimate loads and maximum deflections exceeded predicted values.
