Fluidization analysis of hardness and toughness of beam-column spring sequence
July 02 13:18:13, 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, z). The cantilever beam is constrained along the z-axis. Solid185 elements are used to simulate the beam and end plate, while Solid92 elements represent the bolts. Contact elements Contac174 and Targe170 are employed to model the contact between the end plate, column, and bolt, taking friction into account. The maximum friction coefficient is 0.141. Prestress is applied using the Prests179 element with a value of 155 kN.
The finite element model is meshed with refined cells at critical nodes to capture local behavior accurately. This study focuses on the influence of the joint’s geometry on its performance, without considering welds or residual stresses. The analysis uses displacement-controlled loading, with the load applied vertically at the beam end. An incremental loading approach combined with the improved Newton-Raphson method is used for solving the nonlinear problem.
The results include key parameters such as yield load (Py), ultimate load (Pu), and initial stiffness (Rin). According to the data, the initial stiffness line and 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, marking the yield point. The limit state occurs when plastic deformation develops at the beam end, leading to buckling of the end plate and bolt yielding. The mid-rotation angle is calculated as the ratio of beam end displacement to beam length.
Comparing specimens TS2 and TS3, which differ only in column flange thickness, it is evident that increasing the column flange thickness enhances both the bearing capacity and initial stiffness. Similarly, comparing TS6 with TS5 and TS7 with TS3, it is clear that reducing the bolt spacing on either side of the beam flange increases initial stiffness and load capacity. A thinner end plate leads to less deformation, but the bolts have a more significant impact on its deformation. Increasing the column web thickness also improves joint performance, albeit to a lesser extent than increasing the flange thickness.
TS3 vs. TS4 shows that increasing the end plate thickness significantly improves initial stiffness and load capacity. However, simply increasing the end plate height has minimal effect. Reducing the bolt pitch also improves performance, though not as effectively as reducing the bolt spacing near the beam flange. The inner bolt on the upper flange experiences the highest stress, validating the T-joint assumption used in some countries. The traditional assumption of infinite end plate stiffness is unsafe, as shown by the stress concentration observed in the model.
Although weld effects are not included in the model, high stress between the end plate and beam suggests that proper weld design and quality control are essential. In conclusion, the study analyzed nine specimens under monotonic loading, revealing that smaller bolt spacing, thicker column flanges, webs, and end plates improve joint performance, but reduce ductility. Design should prioritize strong joints and weak beams to ensure seismic resistance. Stress concentrations at the end plate-beam and web-end plate interfaces require careful welding and structural measures to prevent early failure.