Behavior of bolted circular flange connections subject to tensile loading

Abstract

This paper presents the tensile behavior of bolted circular flange connections that represent typical connectivity of leg members in a steel guyed lattice communication tower. A total of twelve specimens have been tested to failure under increasing monotonic tension. Each test specimen consists of a pair of circular flange plates (Φ178 mm), where each plate is welded to a solid circular bar. The flanges are bolted back-to-back using two high-strength bolts located 180o apart. The focus of the experiment includes the development of gaps between the upper and lower flanges connected with ASTM A325 bolts (Φ16 mm), increase in bolt forces, and prying action. The development of gaps between the flanges is significantly influenced by the size of leg members. The increase in the bolt force at failure is approximately 40%, relative to the initial preload of 110 kN. The maximum prying force is observed at the preload level and the prying force decreases gradually as the flanges are further loaded, indicating a complete separation of the upper and lower flanges. The widely used T-stub design equations conservatively predict the behavior of bolted circular flange connections. The proposed predictive equations agree well with the test data, especially near the failure of the bolts.