Background: AISC prequalifies several rigid connections that provide acceptable seismic performance for steel moment-resisting frames. In conventional design practice, the connection type is often not explicitly considered in numerical modeling, and different rigid connections are commonly modeled in a similar manner. However, the actual behavior of each connection can result in significant differences in lateral stiffness, energy dissipation, and ductility. This study investigates the effects of three rigid connection types, namely welded unreinforced flange–bolted web (WUF-W), welded flange plate (WFP), and bolted flange plate (BFP) connections, on the lateral stiffness of steel moment-resisting frames through a combined experimental and numerical approach.
Methods: Three full-scale steel moment frames with a span of 2.8 m and a height of 1.8 m were constructed. Beam and column sections were equivalent to IPE270 and IPB180, respectively, and the strong-column–weak-beam criterion was satisfied. The specimens were subjected to the ATC-24 cyclic loading protocol under displacement control. The yield displacement was 20 mm, and loading continued to a maximum displacement of 100 mm. Numerical modeling was performed using Abaqus with C3D8R elements, combined isotropic–kinematic hardening, and the von Mises yield criterion. Welds were modeled using tie constraints, while bolts were modeled as solid elements with prestressing. The numerical results were validated against the experimental data. Initial, post-yield, and secant stiffness, cumulative plastic energy, and damping were extracted from the hysteresis curves.
Results: The results showed that the use of top and bottom flange plates in the WFP connection, compared with the WUF-W connection, increased the initial stiffness by 83% and the ultimate strength by 89%, while reducing ductility by 9% and damping by 17%. The BFP connection exhibited intermediate behavior, with an initial stiffness of 0.46 ton/mm and an ultimate strength of 21.5 ton. In the WUF-W connection, plastic hinging occurred in the panel zone, whereas in the WFP and BFP connections, plastic deformation shifted toward the adjacent column. The comparison of the numerical and experimental results showed good agreement, with differences ranging from 6% to 12%.
Conclusion: The selection of connection type should be based on the design priorities. For seismic applications, the WUF-W connection is recommended because of its higher ductility and damping and its beam-hinging behavior. For higher stiffness and strength, the WFP connection is more suitable. The BFP connection is recommended when repairability and balanced structural behavior are prioritized.