Behaviour Of Semi-Rigid Beam-to-Column Minor Axis Connections In Steel Frames

Advanced analysis is structure system-based analysis/design method that can overcome the difficulties of using member-based design approaches. The main nonlinear behavior of steel frame structures can be considered in advanced analysis. Since the power of personal computers and engineering workstations are rapidly improving, it is feasible to use advanced analysis techniques in design office. In recent years, the refined plastic-hinge method can be employed to analysis and design planar steel frames, while the advanced analysis of space frames need to be developed.Moment-rotation behavior of beam-to-column minor axis connections should be considered in space frame analysis. Since connections are integral part of steel frames and their behavior affects overall frame performance, and the semi-rigid connections influence the moment distribution in beams and columns as well as the drift (P-â–³effect) of the frame, nonlinear response of connections should be incorporated in advanced analysis of steel buildings. As part of the research project Advanced Analysis Theory of Steel Structure in Three Dimension Space, moment behavior of semi-rigid minor axis connections were researched in this paper.Moment-rotation relationship of semi-rigid beam-to-column minor axis connections was researched through experimental tests, theoretical analysis and finite element analysis in this study. The connections studied herein were top-and-seat angle connection, including minor axis web connection and two type new connections designed according to the force-displacement character of minor axis joints. Nine big-scale specimens under monotonic loading were tested. All tests employed similar beam and column sizes, test apparatus, instrumentation and test procedures. All tested connections showed some moment capacity and very good rotation capacity.Based on classical theory of mechanics, analytical procedure was developed to predict initial stiffness, plastic stiffness and plastic ultimate moment capacity of top-and-seat angle minor axis connections. Three parameter power model and exponent model were employed to describe the moment-rotation curves of studied connections, and the parameters used in both models come from theoretical calculation according to analytical models developed in the paper. The predicted moment-rotation curves were found to compare favorably with experimentally determined connection behavior.Nonlinear FEM analysis was also performed. Models employed in the analysis involving geometric large deformation, materials nonlinear and contact-friction of faying face. Von mises yield criterion with the associative flow rule was selected in the analysis, and solid elements were used for all connection components and beam/column members. Main factors which affect connections behavior were researched in the FEM analysis parametrically. Location of the rotation center and contact frication state of connection components were another objective of this study. FEM analysis fit well with test results.The main results of this study includes:1) The stiffness and moment capacity of minor axis connected joints are related to displacement and failure mode of connection components.2) The stiffness and moment capacity of minor axis angle connection depend on the stiffness and plastic strength of connection components. Components with smaller stiffness have greater affect on overall stiffness of the connection, and the plastic moment capacity of the connection depends on the component with smallest plastic mechanical capacity.3) The FEM parametric analysis suggests that angel thickness, beam depth, bolts location, thickness of column web or thickness of T-stub flange of new type angle connection affect the stiffness and strength of angle connection more significant than other factors. The most effective parameter on the behavior of angle connection is angel thickness.4) As one of the typical semi-rigid connection, top-and-seat angle minor axis connection demonstrates good rotation capacity, some moment capacity and excellent plastic strengthening potentiality.5) The contact-friction state of top-and-seat angle minor axis connection is stable, and the slide between connection components doesn't reduce the ultimate moment capacity. The slide effects can be neglected in engineering design.6) It seems that three-plastic-hinge model agree well to the real plastic deformation of top angle than two-plastic-hinge model, and it is more rational to calculate the stiffness and plastic moment according to three-plastic-hinge model.