Characterization of slip resistance of high strength bolted connections with zinc-based metallized faying surfaces

Bolted connections are designed as slip-critical if they would be subjected to fatigue or significant load reversal, typical in steel girder bridges. In this type of connection, slip of any magnitude must be prevented to eliminate intolerable geometric changes and consequent stability problems. The surface condition of the connected steel components, also known as the faying surface, controls the level of the slip resistance. Design provisions for slip-critical bolted connections in contemporary standards, such as the Canadian Highway Bridge Design Code CAN/CSA S6-06 and the American Institute of Steel Construction (AISC) Specifications, specify desired conditions for faying surfaces and associated slip coefficients for design purposes. Currently, these standards do not address faying surface conditions that are metallized, although steel bridge elements are widely metallized to provide long-term protection against wear and corrosion. Steel bridge fabricators are thus compelled to mask off all faying surfaces before applying the protective coating on the structural elements. This practice is highly labor-intensive, costly and time consuming. In this paper, the resistance of slip-critical bolted joints with zinc-based metallized faying surfaces is characterized in the light of the North American design standards. The mean slip coefficients obtained from short-duration compression and tension test regimes for different connection parameters revealed much greater slip resistance than the typical uncoated blast-cleaned Class B faying surface.