Experimental and numerical investigation on the ultimate strength of multiple-ring-stiffened tube-gusset X-Joints under biaxial compressions.

• Multiple-ring-stiffened tube-gusset joints are investigated for their static strength. • Experimental studies of 13 specimens are conducted with numerical verification. • Influencing factor study by FE analysis helps reveal vital mechanical mechanisms. • Strength equations for multiple-ring-stiffened tube-gusset joints are proposed. Multiple-ring-stiffened (MRS) tube-gusset (TG) X-Joints have been widely adopted in steel tubular transmission towers for their excellent structural performances. However, no specific design guidance is available yet to determine the ultimate strengths of the joints. Therefore, experimental and numerical investigations are carried out to address this issue. Firstly, a total of thirteen specimens including unstiffened, triple-, and quinary-ring-stiffened joints are tested under static brace loads. Then, finite element models are established, and they are verified against the experimental data. Afterward, the numerical models are used for influencing factor analysis on the geometric configurations. Among the considered joint geometrics, the height of the ring has the most prominent influence on the joint strength, while the influence of the spacing of the rings is negligible. The joint with 160-mm-high ring stiffeners has a strength enhancement of 1600% in comparison with the unstiffened one. It is also concluded that the ultimate strength of the MRS TG X-Joint could be regarded as the strength of the unstiffened joint plus that of the rings, of which the latter accounts for 85% − 95%. This major contribution from the rings means that the failure mechanism of the joint is closely related to them, and that is the formation of plastic hinges at vortexes from bending action. According to this, an analytical model is proposed for the strength of the ring, and thus the formula. Furthermore, the equation for the strength of MRS TG X-Joint is given as the superposition of the formulae for the rings and the unstiffened joint. The accuracy of the equations is confirmed by the results of 455 numerical cases. This study therefore supplements the method to calculate the ultimate strength of MRS TG X-Joint. [ABSTRACT FROM AUTHOR]