Characterization of slip resistance for metallized-galvanized faying surfaces in slip-critical joints

Exposed structural steel surfaces, particularly in steel girder bridge construction, require coating protection from harsh environmental conditions to preserve structural integrity and provide longevity. Consequently, galvanization and metallization have evolved as effective long-term protection. Practical situations exist where galvanized secondary structural members are joined to primary elements that are metallized in a slip-critical connection. Design provisions for bolted connections in contemporary standards, such as the Canadian Highway Bridge Design Code CAN/CSA S6-06, do not specify slip coefficient for slip-resistant connections with galvanized-metallized faying surfaces (i.e. one connected face metallized and the other face galvanized). Bridge fabricators are thus compelled to mask off connection faying surfaces before applying the protective coatings on structural members. This practice is time-consuming, expensive, and exposes the connection to corrosion before assembling. In this investigation, the resistance of slip-critical joints having metallized-galvanized faying surfaces is characterized in view of the Canadian steel bridge design standard. The mean slip coefficient is determined from compression test regime and for varying parameters of coating thickness, surface conditions, and bolt preload.