| Steel moment-resisting frames (MRF) consisting of welded-flange-bolted-web beam-to-column connections were widely used as lateral load resisting system of choice in regions of high seismic risk, because of their good performance under seismic load and facilely fabrication. But this opinion was changed after 1994 Northridge Earthquake and 1995 Hyogoken-Nanbu Earthquake, because beam-to-column connections experienced a great deal of brittle fracture, which indicated that cognitions on the damage mechanism of this type of joints were rather inadequate and the current seismic design specification were not ultimately reasonable. In order to avoid similar damage in the future, analyses of response of welded-bolted beam-to-column connections and their modified style joints are not only signification from the theoretical aspect, but also important in practice.The finite element model is established considering geometrical nonlinear, material nonlinear and contact, then the response of beam-to-column cover-plate (CP) connection under both monotonic and cyclic load is simulated with the use of ABAQUS. The accuracy of FEM is verified after comparing the results of both finite element analyses and the existent experimental analyses.Based on the prevailing size at present steel frame, the normative model named BASE is designed with the use of PKPM software. Then 8 series models (29 in total) are created by varying parameters of beam-to-column connection base on the model BASE. The major factors influencing the behavior of beam-to-column connection such as web thickness of panel zone, thickness and width of column flange, beam depth, thickness of beam flange, length and thickness of cover-plate and axial force of column, are analyzed systemically by a parametric computation subjected to both monotonic andcyclic load at the tip of the beam.By summarizing and analyzing the results of FEM computation deeply, the main conclusions are achieved as follows:(1) The development of plasticity and the location of plastic hinge are got by finite element analysis with monotonic load. The rigidity and the elastic ultimate bearing capacity of connections with cover-plate are discussed. The laws of the stress distribution on beam flange and web are revealed and the microscopic reason why the plastic hinge moved to the tail end of cover-plate is explained.(2) The performance of beam-to-column cover-plate connection under seismic load is obtained disciplinarily by the analysis of each connection model's hysteretic behavior, elastic ultimate bearing capacity subjected to cyclic load. Then some design criteria are given for this type of connection.In conclusion, the finite element model and the program adopted in this paper can well simulate the beam-to-column cover-plate connections under both monotonic and cyclic load. The analysis in this paper is rather systematic and has high precision, the conclusions achieved in this paper can be very useful for the further studies.
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