Anti-Slip Experimental Research on Aluminum-Based Metalized Faying Surfaces of Q690 High Strength Steel with Different Bolt Hole Types

The application of high strength steels (HSS) in building structures can effectively reduce the consumption of structural steel and erection cost, lower the carbon footprints of building structures, and promote the high-quality development of the construction industry. As one of the most commonly used connection types in steel structures, the slip critical connection transfers the load through the friction forces between the faying surfaces of the connected plates, and is characterized by high rigidity and excellent performances against fatigue and vibrational loadings. So the slip critical connection is commonly used in bridges. In real projects, HSS slip critical connection faces the corrosion problems and low assembly accuracy in site construction. These problems can be solved by thermal spay of aluminum on connecting surfaces and hole reaming. Therefore, the anti-slip performance of HSS slip critical connections after thermal spay of aluminum and reaming has a crucial influence on the shear capacity of the connections. To investigate the anti-slip performance of aluminum-based metalized faying surfaces with high strength bolts of Q690 HSS with different bolt hole types, standard tests and pretension loss tests were carried out. Specimen surfaces were prepared by grit blasting and thermal spray of aluminum after grit blasting. Four bolt hole types were considered for metalized faying surface specimens, including standard holes, oversized holes, long slotted holes perpendicular and parallel to the loading direction, while only the standard hole was considered in the grit blasted group. When the specimens reached the slip load, failure occurred and significant slip was observed. The failure mode of the anti-slip specimens after grit blasting was the surface abrasion around bolt holes, while the failure modes of the anti-slip specimens after thermal spray of aluminum were the abrasion and peeling of coating around bolt holes. Test results indicated that the recommended values of anti-slip coefficient for Q690 HSS grit blasted and metalized faying surfaces connections were 0.50 and 0.60, respectively, and metalized faying surfaces specimens showed excellent slip resistant performance with high resistance and stable behavior; the loss of pretension at 100 h of metalized faying surfaces connections varied from 1.9% to 2.9%; the mean shape factors of Q690 HSS aluminum-based metalized surfaces connections with oversized holes, long slotted holes perpendicular and parallel to the loading direction were 0.98, 0.89 and 0.82, and the minimum shape factors were 0.93, 0.83 and 0.77, respectively, all higher than the specified values in current codes, and designs based on codes specified values got conservative results.