Research on Mechanical Behavior of Doubler Plate-Reinforced CHS-to-SHS T-Joints Under Brace Axial Compression

To address the engineering issues of local plastic buckling of the chord wall and low ultimate capacity in unreinforced T-joints with square chord and circular brace (CHS-to-SHS) under brace axial compression, this paper proposes a doubler plate-reinforced CHS-to-SHS T-joint configuration. The mechanical behavior of the-reinforced joints is investigated based on a refined finite element (FE) model calibrated against experimental data. An extensive parametric analysis is conducted using FE method to investigate the key factors influencing the failure mode, ultimate capacity, and reinforcement efficiency of doubler plate-reinforced CHS-to-SHS T-joints, including the non-dimensional geometric parameters of the doubler plate (α2, β2, τ2), and the ratio between the brace diameter and chord width (β). The results indicate that the doubler plate thickness has the most significant effect on capacity enhancement, while the width has a limited influence. The ultimate capacity exhibits an initial increase followed by a plateau with increasing doubler plate length, with the optimal length ratio α2 equal to 1.2. A decreasing trend in the strength ratio is observed with an increase in β. The highest strength ratio of 3.29 is obtained at β = 0.445, and this value declines markedly to 1.4 when β increases to 0.795. However, β ≤ 0.445 tends to induce brace axial yielding, whereas β ≥ 0.795 is prone to cause chord bending failure—both cases constituting over-strengthening. Based on the systematic parametric results, a capacity calculation formula for doubler plate-reinforced CHS-to-SHS T-joints is established and demonstrated to show good agreement with the FE results, providing theoretical basis and design recommendations for the engineering design of doubler plate-reinforced CHS-to-SHS T-joints