Study on failure mechanism of bolted spherical joints considering buckling of members

Bolted spherical joints are frequently utilized in spatial truss structures. An investigation into joint fractures during the 2013 Lushan earthquake revealed notable findings. Remarkably, the member connected to the fractured bolt exhibited signs of buckling, suggesting that tension forces did not cause the bolt failure. This failure mode significantly deviates from expectations based on design principles and warrants a thorough examination of its fracture mechanism. Full-scale experiments were conducted on nine distinct bolted spherical steel tube composite members, focusing on their performance under earthquake conditions. As the member's buckling intensified, the bolt's angle increased, subjecting it to a bending moment. Cracks gradually appear until they break; it represents a newly identified failure mode of bolts in the bolted spherical joints. Furthermore, the test result indicated that as bolt thickness increased, lower ductility in the composite component decreased. A parametric analysis of the influence of bolt ball joint points on the buckling capacity of composite members was conducted, proposing a failure formula for the bolts in these joints that account for the member's buckling effect. The theoretical model explains that the larger the bolt diameter corresponds, the smaller the failure angles, making it easier for bolts to fracture. The relevant theories presented in this paper could enhance the design foundation for practical engineering projects.