Corrosion Characteristics and Tensile Performance of Bolted Spherical Joints in Aggressive Environments

Bolted spherical joints (BSJs) are widely used in spatial grid structures owing to their clear force transmission paths and ease of on-site assembly. This study investigates the corrosion behavior and tensile performance of BSJs fabricated with #45 carbon steel joint spheres and 40Cr high-strength bolts (grade 10.9S) under chloride exposure under varying bolt screwing depths. Accelerated salt spray corrosion tests were conducted across different exposure cycles (20, 40, 60, and 80 cycles) and at screwing depths ranging from 0.8 d to 1.2 d, followed by uniaxial tensile testing. Results revealed that chloride-induced pitting corrosion was more pronounced on bolts than on joint spheres, with four distinct types of microscopic corrosion morphologies identified. Inadequate screwing depth (<1.0 d) led to pull-out failure, while greater depths (≥1.0 d) generally resulted in bolt fracture. Chloride exposure significantly reduced the ultimate tensile capacity of BSJs. For bolts with λ < 1.0, post-corrosion tensile strength dropped below the specification threshold, indicating a critical safety concern.