Abstract
The purpose of this study was to conduct slip coefficient testing of bolted connections made from ASTM A709 Grade 50CR steel to determine how they fit into the current AASHTO LRFD Bridge Design Specifications surface condition classifications. At this time, Grade 50CR steel is not included in these classifications because it was not being used for bridges when the existing surface condition classifications were developed. The slip coefficient tests in this study were conducted according to the Research Council of Structural Connections. Some test specimens were made up entirely of Grade 50CR steel, while others were dissimilar metal connections, consisting of Grade 50CR steel and either weathering or galvanized steel. Dissimilar metal connections were included in the testing because their use is anticipated in which a bridge girder would be constructed using both Grade 50CR steel and other ASTM A709 bridge steels. Results showed that unblasted Grade 50CR steel has a slip coefficient value of at least 0.30, meeting the current AASHTO Class A surface condition for unblasted steel. Blast-cleaned Grade 50CR steel from either steel shot or garnet media has a slip coefficient value of 0.50, meeting the current AASHTO Class B surface condition for blast-cleaned steel. When dissimilar metal connections are made with Grade 50CR steel, the design slip coefficient value of the connection can be taken as equal to the smaller of the two slip coefficient values being joined.
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