عنوان مقاله [English]
Tubular structures are made of hollow steel members with circular cross-sections and connecting them is one of the major challenges in their design. So far, some techniques to improve the performance of tubular connections have been proposed. Most of these methods (e.g., internal ring, doubler plate) can only be used for structures during the design, but there are only a few techniques (e.g., external ring, FRP) which can be applied during both fabrication and service. This paper investigates the ultimate strength of circular hollow section (CHS) X-connections stiffened with external ring subjected to axially compressive load. The SOLID186 in ANSYS was used to establish the finite element (FE) models. In these models, both geometric and material non-linearity were considered. Moreover, the welds joining the chord and brace members were modeled. The validation of the FE model with several experimental data indicated that the proposed FE model can accurately predict the static behavior of the ring-stiffened X-joints under compression. In the next step, 117 FE models were created and analyzed to evaluate the effect of the connection geometry and external ring size on the static capacity through a parametric study. Results indicated that the outer ring can considerably increase the initial stiffness. Moreover, the ultimate strength of the ring-reinforced X-joints under brace compression can be up to 367% to that of the strength of the corresponding unreinforced joint. Despite these significant differences between the ultimate strength of un-stiffened and ring-stiffened X-connections under compressive load, the investigations on this type of stiffened joints have been limited to only three X-joint tests. Also, no design equation is available to determine the ultimate strength of X-connections stiffened with the external ring. Hence, the parametric study was followed by the nonlinear regression analysis to propose a theoretical equation for the static design of X-connection stiffened with the outer ring in compressive load.