Research on the Influence of Bolt Preload on the Distribution of Hole-Wall Bearing and Friction in Transmission Tower Joints

Currently， Chinese transmission line design specifications provide clear guidelines for the bearing capacity calculation of bolted connections， but the relevant formulas do not account for the influence of bolt preload. Meanwhile， construction acceptance standards indirectly specify the preload magnitude by defining tightening torque values. Although both academia and the engineering community widely recognize the contribution of preload to joint performance， debate persists over the recommended preload values in the specifications， primarily due to the lack of systematic research on the frictional behavior at rough contact interfaces in bolted joints. This paper focuses on a typical angle steel joint as the research object， analyzing the influence of interface friction on its load-bearing performance. Through a well-designed research program and finite element simulations， the dynamic evolution of the load-transfer mechanism in the joint is revealed： initially， the load is primarily supported by interface friction； as bolt slippage occurs， the load-transfer mechanism gradually shifts to being dominated by the bearing action between the bolt shank and the hole wall. The results demonstrate that the ultimate bearing capacity of the joint is provided jointly by the bearing capacity of the bolt hole wall and the friction at the contact surface， with friction accounting for approximately 20% of the total bearing capacity. This study systematically elucidates the complementary relationship between the friction and the hole-wall bearing force， providing an important theoretical foundation for improving the design theory and performance evaluation of bolted connections.