# A Study on the Seismic Performance of Steel H-Column and T-Beam-Bolted Joints
## 5 Conclusions  
In this paper, a comparative analysis is conducted on the differences in failure modes, hysteretic curves, skeleton curves, initial stiffness, ductility, bearing capacity, and energy consumption of space joints under different T-shaped stiffness, column wall thicknesses, axial compression ratios, and bolt preloading. Previous studies on beam-column joints mainly focused on planar joints, and the research on spatial joints under two-way loads was relatively insufficient. This study fills this gap by establishing a finite-element model of column joints in the space of single-bolt-connected T-shaped parts and comprehensively analyzes the influence of various parameters on the seismic performance of spatial joints, providing a more comprehensive theoretical basis for the seismic design of steel-frame structures. Through parameter optimization (such as T-part 1 web \(\geq\) 18 mm, column wall \(\geq\) 12 mm), this study solves the problem that the seismic performance of space nodes is worse than that of plane nodes, pointed out by [PERSON] et al. [4]. Compared with the cold-formed steel pipe joint proposed by [PERSON] et al. (2021) [3], the ductility coefficient of this joint is increased by 20%-30% under the same coaxial pressure ratio (Figure 20, Table 3). The stiffness calculation formulas of each component are derived and analyzed based on the component method, and the following conclusions are drawn:  
1. For T-parts in unilateral bolted space joints, there are three failure modes: plastic-hinge failure of the beam flange; joint brittle failure caused by column wall-buckling failure; and joint brittle failure caused by T-part fracture. When the thickness of the column wall is extremely small, the bolt holes and their edges will yield due to stress concentration, and the column wall will buckle. Moreover, the buckling phenomenon becomes more pronounced as the displacement increases, eventually leading to the buckling failure of the column wall. When the web thickness of T-part 1 is thin, the first row of bolt holes on the web of T-part 1 is pulled off. To fully exploit the performance of the single-bolted space joints of T-parts, the stiffness of the joint domain can be enhanced by increasing the thickness of the web or column wall of the T-parts. 2. The stiffness of T-part 1 exerts a significant influence on the joint. By increasing the thickness of the web plate of T-part 1, the bearing capacity and stiffness of the space joint can be enhanced. To prevent the brittle failure of joints resulting from the web fracture of T-part 1, achieve the ideal failure mode of forming a plastic hinge on the beam flange, and optimize the steel usage, it is recommended that the web thickness of T-part 1 should not be less than 18 mm. Specifically, compared with the BASE nodes, when the web thickness increases from 16 mm to 18 mm, the yield load and bearing capacity of the space node increase by approximately 12% and 16%, respectively, (see Figure 13). 3. The thickness variations in the web and flange of T-part 2 have a negligible impact on the seismic resistance of the joint. Whether the stiffness of T-part 2 decreases or increases, the yield load, bearing capacity, initial stiffness, and ductility of the joints do not exhibit significant changes. When the web thickness of T-part 2 increased from 6 mm to 14 mm, the yield load increased by only 0.8% (from 372.5 kN to 375.5 kN), and the peak load increased by 1.1% (from 435.2 kN to 439.9 kN) (Table 5, Figure 17). The stiffness varies by less than 6%, and the ductility coefficient (\(\Delta_{\text{u}}/\Delta_{\text{y}}\) = 2.7-2.8) is almost unchanged (Table 3). 4. When the thickness of the column wall is overly thin, the column wall is prone to buckling failure. As the wall thickness increases, the bearing capacity and stiffness of the joint increase. Additionally, the increase in wall thickness alleviates the deformation of the column wall to a certain degree.