Full-Scale Testing of Shear Keys for Adjacent Box Girder Bridges

Adjacent precast, prestressed box girder bridges are widely used in the United States, but the shear keys between the girders tend to crack and leak. Three different shear key configurations were studied, i.e., a current detail where [he shear key is approximately 10 in. (250 mm) from the top of the girder and grouted with non-shrink grout, this same detail grouted with epoxy rather than nonshrink grout, and a proposed mid-depth keyway grouted with non-shrink grout. The tests were conducted on a full-scale, four-beam assembly which represented part of a bridge. The results showed that the currently used shear key defail cracks due to thermal stresses generated as the beams deflect upward and downward due to daily heating and cooling. The mid-depth shear key is less susceptible to these stresses and was found to be more resistant to cracking. The epoxied shear keys did not crack. Loading did not appear to cause new cracking, but rather seemed to propagate existing thermal cracks.