The extended end-plate connections provide excellent performance in resisting seismic loads in high-risk areas. Most scholars’ experiments and finite element studies on this type of joint are focused on the method of applying displacement loads on the beam tip, while the method of applying displacement on the column side has not been the subject of further study. However, the load transmission mechanism of this type of connection is not completely consistent in actual engineering, as the design concept of “strong column weak beam” does not apply to all joints. Therefore, in this paper, the lateral displacement of the applied column is used to simulate the seismic horizontal force to study the mechanical properties of the connection joints of the “weak column and strong beam” under the limit state of earthquake action. Based on the two internal columns (IC-EP1/2) and two edge columns (EC-EP1/2), the failure modes, strength, stiffness, moment–rotation curve, skeleton curve, ductility, and energy dissipation of this type of connection were studied. Experiment results indicated that this type of connection features semi-rigid and partial strength joints. The connection rotation angle of all specimens in the test exceeds 0.05 rad, which suggests it is an ideal seismic joints. Besides, the relationship between the thickness of the end-plate and the diameter of the bolt has a greater impact on the failure mode of the joint. The finite element (FE) analysis models were established for the above connection. The numerical model was validated against experimental results and showed acceptable consistency.

As the square steel tube in the tension zone is always the weakest part of moment-resisting joints, modified blind bolts (Hollo-Bolts) and a locally strengthened steel tube in the panel zone were adopted to enhance the joint performance. Cyclic loading tests were carried out on eight anchored blind-bolted extended end-plate joints between square concrete-filled steel tube (CFST) columns and steel beams. The test parameters included the end-plate thickness, steel tube wall thickness, beam section size, local strengthening connection method, blind bolt anchorage method, and stiffeners. The failure mode, hysteretic behavior, stiffness, strength, ductility, strength degradation, stiffness degradation, and energy dissipation capacity of the joints were studied and analyzed. The test results showed that the application of anchored blind bolts and a locally strengthened steel tube can fully utilize the bolt strength and significantly improve the joint performance, especially in terms of strength and strength degradation. The test observations revealed three typical failure modes for the joints, and the failure mode depended on the weakest component. In addition, the local reinforcement of C-channel and change in the anchorage method had a limited effect on the initial stiffness. Greater end-plate thickness and the use of stiffeners significantly increased the joint stiffness and decreased the rate of stiffness degradation. The use of stiffeners also significantly enhanced the ductility and energy dissipation by moving plastic hinge outward from the joints. Finally, finite element analysis (FEA) models were developed and validated against the experimental results, and the stress distribution and force transfer pattern were investigated.

Summary Due to recent advances in computational power, high efficiency and high precision semi‐rigid calculation methods of steel connections are necessary. In this paper, four connection experiments were designed to study the mechanical behavior of the top and seat angle connections. In the experiment, a monotonic load was applied at the end of the beam to study its moment–rotation characteristics. In addition, this paper proposed a second derivative method to determine the yield point, the starting point of the plastic strengthening stage, and the initial rotational stiffness of the connections according to the moment–rotation curve. Loading test experiments (EX) results and finite element analysis (FEA) results showed that the compression side angle stiffener has little effect on the initial rotational stiffness. Nevertheless, it can delay the top and seat angle connection in entering the elastoplastic stage and the starting point of the plastic strengthening stage. The results also showed that the tension side angle stiffener could significantly increase the initial rotational stiffness, but makes the angle connection enter the yield stage earlier. When the connection's top and seat angles have no stiffener, the elastoplastic deformation range on the curve is smaller. Finally, based on the theory of Plates and Shells, this paper proposed the calculation method for the deformation stiffness of the key components and the initial rotational stiffness of the connection. Results from the theoretical calculation method showed high calculation accuracy and high calculation efficiency, as compared with the EX and the FEA results.

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The bolted angle connections which are simple, fast, cost-effective, high quality, and no site welding have been recognized as their excellent performance. The moment-rotation behavior of both major and minor axis should be both taken into considering, however, the lack of research on minor axis limits the more comprehensive application. Five monotonic tests were carried out to investigate the influence under different parameters, and a new type connection were considered and detailed. Refined finite element models were built to validate the experimental results and to do several parametric analyses on initial rotational stiffness and plastic moment resistance, including of a presence of stiffened seat angle, angle thickness, and prying force. Furthermore, a new simplified plate method was proposed for calculating stiffness of stiffened angle and web in bending. The stiffened angle gives a significant increase at the moment-resisting capacity and the initial stiffness, the ultimate rotation of all tested specimens was beyond 0.067rad. The initial stiffness and plastic moment resistance of the joints were also controlled by the column web. The presence of the stiffener in the compression zone has the none effect on initial stiffness. The numerical analysis has captured the failure reason for weld and more attention should be paid to welding of stiffener in engineering design and practice. Adding stiffener at the top-and-seat angle joint can reduce the prying force of bolt, but it still cannot be ignored. The theoretical results were in good agreement with the experimental data and finite element results; therefore, it can be used to guide the design and selection of joints.