Fluidization analysis of hardness and toughness of beam-column spring sequence
July 02 13:55:00, 2025
The model exhibits structural and force symmetry, so only half of the structure is built using symmetry. The top of the column is constrained in the x and y directions, while the bottom plate is fixed in all three directions (x, y, and z). The cantilever beam is constrained in the z-direction. Solid185 elements are used to simulate the beam and end plate, while Solid92 elements represent the bolts in the solid model. Contact elements Contac174 and Targe170 are employed to simulate all contact surfaces between the end plate, column, and bolt, taking into account friction. The maximum friction coefficient is 0.141. Prestress is applied using the Prests179 element, with a prestress value of 155 kN.
The finite element model is meshed with refined cells at critical nodes to capture local behavior accurately. In this study, the influence of the joint’s prominent structure on its performance is analyzed, while welds and residual stresses are not considered. Displacement-controlled loading is used, with the load applied vertically at the beam end. The solution is obtained through an incremental loading method combined with the improved Newton-Raphson iteration technique.
The finite element results are summarized, where Py represents the yield load, Pu is the ultimate load, and Rin indicates the initial stiffness. According to the data, the initial stiffness line and the tangential stiffness in the M-φ curve degrade to 1/10 of the initial stiffness. The tangential stiffness line intersects the M-φ curve perpendicularly at the φ-axis. The yield load corresponds to the load at the yield point, and the ultimate state is defined by plastic development at the beam end, end plate buckling, and bolt yielding. The mid-rotation angle is calculated as the ratio of beam end displacement to beam length.
The TS2 and TS3 specimens differ only in the thickness of the column flange. From the results, it is clear that increasing the column flange thickness enhances both the bearing capacity and initial stiffness of the joint. Comparing TS6 with TS5 and TS7 with TS3 shows that reducing the bolt spacing on both sides of the beam flange increases the initial stiffness and load-carrying capacity. A smaller end plate thickness leads to less deformation, but the bolt's influence on deformation is significant. Comparing TS1 and TS4 reveals that increasing the column web thickness also improves the joint’s strength and stiffness to some extent. TS3 versus TS4 demonstrates that increasing the end plate thickness significantly boosts the initial stiffness and load capacity.
Results from TS5, TS1, TS8, and TS3 indicate that simply increasing the end plate height has limited impact on joint stiffness and capacity. Comparing TS3 and TS9 shows that reducing the bolt pitch can improve the joint’s strength and rigidity, although not as effectively as reducing the bolt spacing near the beam flanges. It is evident from the calculations that the inner-side bolts on the upper flange of the beam are the most stressed, supporting the validity of the T-joint assumption used in the UK and other countries. The traditional assumption of infinite end plate stiffness is unsafe, as the triangle algorithm (assuming the outermost bolt is most stressed) may lead to overestimation. Although welding effects are not included in the model, the high stress levels observed between the end plate and beam suggest that proper weld design and quality control are essential for the joint.
In conclusion, nine model specimens were analyzed under monotonic loading to investigate the effects of end plate thickness and height, column flange and web dimensions, and bolt spacing on joint performance. Key findings include: (1) Smaller bolt spacing on both sides of the beam flange increases joint strength and stiffness, so bolts should be placed close to the flange and web, while leaving space for construction. (2) Increasing the thickness of the column flange, web, and end plate improves joint strength and stiffness but reduces deformation capacity. Design should follow the principle of weak beam and strong joint to ensure seismic resistance. (3) Stress concentration is significant at the connection between the end plate and beam, especially in the compression zone. Proper weld design and structural measures are necessary to prevent early failure.