| In conventional steel frame analysis, the behavior of beam-to-column connections is treated as either pinned or rigid joints entirely. Pinned joints means no moment could be transferred from beam to column, and rigid joints means included angle between beam and column holds the line, from unchanged frame without loads to transfigured frame with loads. These idealized assumptions predigest the analysis and design of steel frame consumedly, but they could induce insecurity or conservative design for in practice engineering joints having semi-rigid characteristic. The dissertation focuses on the study of tip and bottom angle steel linking light steel frames with stomach plank angles.The dissertation imitates the semi-rigid of beam-column joints firstly, the method is based on 3-parameter exponential model, it gets the nonlinear M-θ relationship by the individual joint angle steel load-carrying analysis and calculate to get initial connection stiffness and ultimate moment-carrying capacity of joints, and attains to the purpose of imitating beam-column joint linking semi-rigid. When analyzing the steel frames ultimate load-carrying capacity, the dissertation uses geometric stiffness matrix to think over the frame geometric nonlinear, and thinks over the effect of joints semi-rigid, and introduces the modified plastic hinge model into the second-order inelastic analysis of the structure, and gives the method of how to switch the stiffness matrix after appearing plastic hinge and how to control internal force under the yielding surface. The dissertation uses arc length-method solve the nonlinear equation group.At the end, the dissertation develop a program to solve the ultimate load-carrying capacity of frames, which can be used to calculate the maximum strength of the multistory steel structures accurately.
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