Stiffness and ultimate strength of multi-ring-stiffened tube-gusset X-joints with dual-function stiffeners.

• The intermediate stiffener plate failed due to local buckling under compressive loading when the joint reached its ultimate state. • The bolted connection regions constrained the local deformation of the ring-stiffener plates. • The larger the initial defect amplitude of a stiffener plate, the more significant its local buckling and the faster its stiffness decreased. • Theoretical results for ultimate bearing capacities of joints slightly higher than experimental results, max diff <10%. Tube-gusset (TG) joints that use stiffener plates as connecting plates for the crossarm chord are the main method for joining chords to tower bodies of transmission steel pipe towers. These joints experience the highest compression loads of the entire transmission tower structure. This study presents experimental research, numerical simulations, and theoretical analysis on the TG joint with a five-ring stiffener, where the middle stiffener plate serves as a connecting plate (referred to as C-Stiffener). This study elucidates the failure mechanism and mechanical characteristics of the C-Stiffener, identifies the key factors influencing its local buckling under compression, and proposes a stiffness calculation method for this type of stiffener plate. A calculation approach for the ultimate bearing capacity of the C-Stiffener is established by utilising its stiffness-deformation curve and a calculation method for the ultimate bearing capacity of the five-ring-stiffened TG joint under axial compression loading is proposed. The findings of this study can provide guidance for the meticulous design of joints between the crossarms and bodies of steel pipe transmission towers, thereby ensuring the safety and stability of transmission lines. [ABSTRACT FROM AUTHOR]