Final report on I79 tied arch cracking - neville island bridge, December 1984 82p

Cracks were detected in the daiphragm to tie girder web welds of the I79 Neville Island Bridge in July 1983. These cracks were observed at the top and bottom ends of the transverse welds between the diaphragm and the outside plate at floor beams. Samples removed from these cracked regions showed that all of these cracks developed from lack of fusion in the welded connections. Cyclic stresses developed in the diaphragms normal to these welds resulted in fatique crack growth. Strain measurement under randum truck traffic demonstrated that the web gap at all four box corners were subjected to large distortion induced stresses. Removal of the loading bar at a typical joint verified that crack growth had occurred. Connecting the diaphragm to the top and bottom tie girder flanges prevented distortion in the outside tie girder web. However, it did not reduce the distortion induced cyclic stresses at the bottom inside connection. It was found necessary to provide a positive bolted splice between the floor beam flange and the tie girder flange.