Laboratory Tests of Bolted Diaphragm-Girder Connections

Many multigirder steel bridges built before 1985 are experiencing distortion-induced fatigue cracking at diaphragm-girder connections. Fatigue cracks in the welds and base metal in hundreds of diaphragm-girder connections in bridges in the Birmingham, Ala. area have been discovered. Many of the welded connections have been replaced with angles bolted to the diaphragm and girder web. The replacement angles have not performed satisfactorily due to fatigue cracking in the connection angle. Laboratory tests of three existing and one proposed replacement angle were conducted to determine the fatigue limit for the replacement angles and the most appropriate replacement angle to use on future repairs. Primarily, surface strain measurements and vertical girder deflections due to fatigue loading were recorded during fatigue tests of the laboratory model to evaluate the performance of the connections. Results indicate that the appropriate bending stress fatigue limit is 165 MPa and the proposed new replacement angle should be used for future repairs.