Study on ultimate bearing capacity of CHS X-joints strengthened with CFRP

In order to study the influence of carbon fiber reinforced plastic (CFRP) on the X-shaped circular steel tubular joints, the ABAQUS finite element software was redeveloped. The VGM model was compiled into the VUSDFLD subroutine by Fortran language. The finite element analysis of 90 joint models was carried out, and the effects of the ratio of the outer diameter of the branch to the main pipe β, the ratio of the diameter to the thickness of the main pipe γ, the ratio of the length of CFRP to the diameter of the main pipe L, and the number of CFRP layers n on the bearing capacity of the joints were studied. The results show that CFRP can reduce the stress concentration of the joint and improve the bearing capacity of the joint. The cracking of the joint will occur at the weld root where the inner side of the saddle point weld of the intersecting line intersects with the branch pipe. With increasing of the load, the crack develops from the weld saddle point along the intersecting line to the crown point. Parameters analysis of the joint show that with the increasing of γ, the ultimate bearing capacity of the joint decreases gradually, with the increasing of β, the ultimate bearing capacity of the joint increases gradually, with the increasing of n and L, the ultimate bearing capacity of the joint will increase. For the failure of the joint occured in the weld, the formula for the weld bearing capacity of the CFRP strengthened X-shaped circular steel tube intersecting joint was proposed. Compared with the finite element results, it can be found that the results of the formula fitted are unsafe when the wall thickness of the main pipe of the joint is small and the outer diameter of the branch pipe is large.