Semi-rigid Connection Of Steel Frame Finite Element Analysis And The Second Order Approximation Calculation

The conventional studies of steel frame are performed using the assumption that connections are either fully rigid or ideally pinned, these idealized assumptions simplify the analysis and design of steel frame consumedly, but they could not reflect the actual work conditions of structures. In recent decades, the results have proved out that all connections of the beam-column are semi-rigid in nature, and its performance is between fully rigid and ideally hinged. The assumption of Semi-rigid connections, will not only change the internal force distribution between the beam and column, but also increase the sway of the framework, thereby increase the second-order effect of the framework. Around this theme, this paper mainly discusses and studies the following aspects.Firstly, the paper introduces the present findings of semi-rigid connections and the aspects need to improve, the beam-column connection's design and calculates methods on the criterion of domestic and foreign steel structure, the classification of steel structure's connected nodes, as well as the mathematical model of the semi-rigid connections. Then we describe the basic theory and research methods of the analysis of semi-rigid connections.Secondly, based on the previous studies, we deduce beam and column element stiffness matrix of steel frame in the condition of taking the semi-rigid connections,material plastic and axial force effect into account and give the building process of balance-equation in the semi-rigid steel frame . We use the software ansys to analysis a six-floor framework with the same span, where we use the beam element to simulate beam and column, use spring element to simulate the semi-rigidity of the beam-column connection. By comparing the results of semi-rigid steel frame with steel frame , Some meaningful conclusions are obtained, such as the redistribution of internal force and the increasing of second-order effect of steel frame.Thirdly, The calculation formulas of the end moments, the rotation rigidity and the transmission coefficient were derived by modifying the stiffness of beam and column ,which is based on the rigid theoretical analysis. An approximate calculation method for the internal forces of the semi-rigid jointed steel frame was given on the condition of the vertical force. Modifying the stifihess of column, an approximate calculation method for the internal forces and sway of the semi-rigid jointed steel frame were given on the condition of the level force. Besides, the paper list the design and calculation methods in the criterion of steel structure of the United States and China by taking the second-order effect(P-δ,P-△) into account, and point out the deficiency of the criterion. Finally, comparing the approximate result of an example with the result of rigid connection and the result of finite element analysis, the approximate calculation result meet the desire of precision and can be used for practical project.Fourthly, some prospects have been given out for the research of semi-rigid steel frame in the future.