Experimental and numerical study on the ultimate bearing capacity of a K-type tube-gusset plate joint of a steel transmission tower

The ultimate bearing capacity of K-type tube-gusset plate joints was experimentally investigated in the engineering context of ultrahigh voltage (UHV) steel tube transmission towers. Three K-joint specimens were fabricated: ZK30, ZK50 and PK30, where the eccentricity e of the ZK and PK specimens was 0 and D/4, respectively. The branch and main load ratios λ are 29.41% and 50% for ZK30 and ZK50, respectively, and 29.41% for PK30. The experimental results show that increasing λ has a negative effect on the bearing capacity of the main tube. Compared with ZK30, ZK50 has 17% lower main tube axial force and 33% higher branch tube axial force when the specimen was failed. In contrast, the negative eccentricity is beneficial to the bearing capacity of the main tube. Compared with ZK30, PK30 has the same main tube axial force and 6.7% higher branch tube axial force when the specimen was failed. Local buckling occurs in both ZK30 and ZK50, while overall failure occurs in the PK specimen. The finite element model (FEM) in the ABAQUS platform with initial geometric defects was verified by the experimental results. The stress distribution, failure mode and ultimate bearing capacity of the FEM show agreement with the experimental results. The simplified FEM was employed to analyze the bending capacity of K-joints with different diameters of the main tube, different thicknesses of the main tube and different lengths of the gusset plate. The results show that for the K-joints analyzed in this paper, the bending bearing capacity only decreased by 16.41% as the diameter of the main pipe increased by 50.25%, increased by 48.99% as the length of the node plate increased by 37.50%, and increased by 145.33% as the wall of the main pipe increased by 71.43%. The formula for calculating the bending capacity of the K-type tube-gusset plate joint was fitted. Compared with the existing specifications, calculation results with the fitting formula are more similar to those of the FEM.