Numerical investigation of ultimate bearing capacity of circular and square concrete-filled double steel tubular T-joints

The punching shear problem in composite T-joints with doubler plates has been evaluated in various design codes of practice. However, code provisions do not address the behavior of concrete-filled double steel tubular T-joints filled with concrete, in which concrete contributes to a portion of the shear force to resist punching. The present study presents a finite element modeling analysis to investigate the ultimate load-bearing capacity of circular and square concrete-filled double steel tubular T-joints. A set of 24 double-skin concentric tubular joint specimens were modeled in ABAQUS. A subsequent parametric study was carried out to examine the influence of infill concrete compressive strength, steel tube cross section shape, and section width-to-thickness ratio. Accordingly, stress evolution pattern, buckling mode, stress-strain response, and load-displacement curve of the entire T-joints were investigated. Based on the results obtained, it was revealed that recession in the flange of the primary component, as well as the heaving of the primary component web, are the main reasons for the higher stress levels. It was also seen that when the compressive strength of the infill concrete is 45 MPa, the maximum stress level in circular concrete-filled double steel tubular joint is 2.6 x 102 MPa, while that in the square joint is 2.566 x 102 MPa. The corresponding values for concrete with a compressive strength of 30 MPa are 2.58 x 102 MPa and 0.455 x 102 MPa, respectively. It was also observed that when the width-to-thickness ratio is increased from 20 to 33.33 in circular T-joints, the ultimate load-bearing capacity is reduced by 15%.