Friction Coefficient of Slip Critical Bolted Joints with Inorganic Zinc-Rich Paint Focusing on Contact Surface Pressure

Recently, some researchers have reported that the friction coefficient is influenced by the contact surface pressure, and the Coulomb and Amontons’ law of friction undergoes breakdown. To develop and apply the bolt that introduces a higher bolt tension to the slip critical bolted joint with the inorganic zinc-rich paint, it is necessary to appropriately evaluate the dependence of the friction coefficient on the contact pressure. This study conducted the friction test, which has various contact surface pressures and application times of contact force, to explore the relationship between friction coefficient and contact surface pressure. The target of faying surface treatment is the inorganic zinc-rich paint coating and blast-cleaned surface, used in slip critical bolted joints of bridges. From obtained results, as the surface pressure increased, the friction coefficient of the inorganic zinc-rich paint case decreased. On the other hand, when the surface pressure varied, the friction coefficient of the blast-cleaned surface case was stable. Considering these slip properties of inorganic zinc-rich paint surfaces, a novel relationship between the friction coefficient and contact surface pressure was proposed. In addition, the theoretical slip strength of bolted joints was calculated using the friction coefficient formulas and the actual contact pressure distribution of the joints. In comparison with the theoretical and experimental slip strength, it was found that the theoretical slip strength calculated based on the proposed friction coefficient formulas depending on contact pressure was closer to the experimental value than that based on the constant friction coefficient and could estimate the tendency of the experimental results.