Behaviour and rehabilitation of distortion-induced fatigue cracks in bridge girders

In many multi-girder bridges distortion-induced fatigue cracking is prevalent in the web gap region of the diaphragm-to-girder connection. CN Railway made available girders from such a bridge, which had over 300 distortion-induced fatigue cracks, for laboratory testing.; Fatigue and fracture tests were performed to assess the behaviour of the fatigue cracks and to assess the effectiveness of rehabilitations. The combination of drilled stop holes and an angle bolted to the transverse stiffener and the tension flange was found to be an effective rehabilitation if performed once the fatigue cracks were detected.; In addition to the experimental program, a finite element analysis was performed to investigate the stresses in the web gap region. Results from the analysis showed that the designation of the web gap detail as a fatigue Category C' detail results in a conservative prediction of the fatigue life.