Research on the Behavior of Steel Frame Beam-to-column Extended-end-plate Connections DUAN Qi cheng,LI Wei xiong (Department of Architecture Engineering,Hunan Building Materials College,Hengyang 421008,China)Based on the simplified mechanical model of steel frame beam to column extended end plate connections, a nonlinear mathematic model to predict the M θ r relations was proposed by use of the known sizes of the connections in this paper. The major parameters of the model were the initial rotational stiffness and the bearing capacity. After the mechanical analysis about the initial deformation and the bearing capacity of the connections, formulas of calculating the initial rotational stiffness and the bearing capacity were proposed. Compared with the test results, the methods to calculate the initial rotational stiffness and to calculate the bearing capacity were testified to be true at the end of this paper.extended end plate connections; relationship of moment and rotation; initial rotational stiffness; bearing capacity