Mechanical Behavior of a Novel Reconnectable Bolt-Sphere Joint

Abstract

A novel reconnectable bolt-sphere joint (RBJ) is proposed for spatial grid structures to address the challenge of replacing damaged high-strength bolts. The failure modes and mechanisms of RBJs are investigated through uniaxial tensile tests on 24 RBJ specimens and four standard high-strength bolt (HSB) specimens. A parametric analysis is then conducted to evaluate the effects of installation torque, leg length, slot length, leg thickness, expansion end inclination angle, and number of legs on tensile behavior. For RBJ-II configurations (M16/M20 specifications), optimal dimensional parameters and installation torque values are recommended. Theoretical models for contact stiffness, elastic stiffness, strengthening stiffness, and ultimate capacity are established. Finally, the bending behavior of RBJs is evaluated. The results indicated that RBJs exhibit three primary failure modes under tension: pullout failure, shear failure of the expansion bolt cylinder (EBC), and bolt shank fracture. The load-displacement response is characterized by four distinct stages: initial, elastic, strengthening, and failure. The tensile bearing capacity is found to meet Chinese specifications. RBJ-II demonstrated superior tensile bearing capacity and stiffness compared with RBJ-I. The EBC thickness and installation torque are identified as critical parameters, and the torque coefficient K d is determined as 0.41. The theoretical stiffness and ultimate capacity showed good agreement with experimental and finite-element results, accurately reflecting the mechanical behavior of the RBJ during tension. Compared with joints with conventional HSBs, finite-element analysis (FEA) predicted that RBJ-II achieves an increase of 20% or more in ultimate bending moment, suggesting superior flexural per‍formance.