| The conventional analysis and design 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 order to estimate or predict the behavior of steel frame correctly, in the Code for design of steel structures(GB50017-2003), the semi-rigid connections are referred to, but are not specified how to use it in design. At the same time, there are no provisions about second-order analysis of plane steel frames with semi-rigid connections. Semi-rigid connection effects not only internal force and displacement of structure, but also stability and dynamic characteristics. According to these problems, some suggestions are proposed in present study, but they are not comprehensive when it comes to how to take consideration of the effect of semi-rigid connection on structure performance during process of structural design. Aimed at the point, the characteristics of semi-rigid steel frame are discussed and studied as following three aspects:Firstly, the present findings of semi-rigid connections, the method for design of beam-to-column connections in the codes from China and other countries, and the characters about semi-rigid connections, the simulated method of the M-θ_r relation curve of semi-rigid connections, were briefly introduced in the paper. The contents and methods of design and calculating about extended-end-plate beam-to-column connections in our country and other countries were discussed. As the following, the methods of calculating and design about steel frame with semi-rigid connections, were briefly addressed too.Secondly, based on the current nonlinear analysis and calculation methods of the research on steel frames with semi-rigid connections,taking the structure as a whole considering semi-rigid connection flexibility, material nonlinear and geometric nonlinear, three new types of members are adopted herein: plane steel beam-column member considering geometric nonlinear and material nonlinear; beam member with semi-rigid connections considering semi-rigid beam-column connection flexibility and material nonlinear; beam-column member with semi-rigid column base considering column base's flexibility, geometric nonlinear and materialnonlinear. With the principle of functional minimum potential energy, the nonlinear element stiffness matrixes are derived. To do global analysis about steel frames with semi-rigid connections, not to divide it into many parts and study one by one, so it could reflect actual work capability of steel frame system more exactly.Thirdly, using finite element method, a steel frame with semi-rigid connections is analyzed. The effect of different rotational stiffness on internal force, deformation, stability and period of steel frame is discussed. According to comparison between rigid steel frame and semi-rigid steel frame, some conclusion and corresponding design suggestions are put forward.Finally, conclusions are put forward and some prospects have been given about the research of semi-rigid steel frame.
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