Field Evaluation of Fatigue Cracking in Diaphragm-Girder Connections

Abstract

Many multigirder steel bridges built before 1985 are experiencing distortion-induced fatigue cracking at diaphragm-girder connections. In bridges in Birmingham, Ala. fatigue cracks in the welds and base metal in hundreds of diaphragm-girder connections have been discovered. In addition, one repair scheme, a bolted-angle retrofit, has not performed satisfactorily because of fatigue cracking in the connection angle. Field tests at six bridge sites in the Birmingham, Ala. area were conducted to evaluate the potential for further cracking at previously uncracked connections, the appropriateness of continuing a drilled hole repair of girder web cracks, and the performance of a proposed new bolted-angle retrofit. Primarily, surface strain measurements resulting from traffic and calibration trucks crossing the bridge were recorded to evaluate the performance of the connections. Results indicate cracking will continue at welded diaphragm-girder connections, hole-drilling crack tips is not a reliable fix of web cracking, and the proposed new bolted-angle retrofit is an improvement of the original bolted connection.