Removal of Diaphragms from Three-Span Steel Girder Bridge

Many multigirder steel bridges built before 1985 are experiencing distortion-induced fatigue cracking at diaphragm-girder connections. A means of eliminating the cyclic stresses that cause those fatigue problems is to remove the interior diaphragms (diaphragms not at the girder supports). The effects of removing interior channel diaphragms from an existing three-span bridge with rolled steel girders are reported in this paper. The effects of removing the diaphragms are evaluated using field measurements of girder stresses and deflections made before and after the diaphragms were taken out. Results from tests with trucks of known weight indicate that removing the diaphragms results in increases up to 15% in the maximum bottom flange stresses at the most heavily loaded girder. Comparisons of measured and calculated stresses show that the conservatism of common design practice is not significantly reduced by removing diaphragms, and the effects of removing interior diaphragms are judged insignificant.